Publications
Book

1Peter J. Schreier and Louis L. Scharf
Statistical signal processing of complexvalued data
The theory of improper and noncircular signals
330 pages, Cambridge University Press, 2010.
Complexvalued random signals are embedded in the very fabric of science and engineering, yet the usual assumptions made about their statistical behavior are often a poor representation of the underlying physics. This book deals with improper and noncircular complex signals, which do not conform to classical assumptions, and it demonstrates how correct treatment of these signals can have significant payoffs. The book begins with detailed coverage of the fundamental theory and presents a variety of tools and algorithms for dealing with improper and noncircular signals. It provides a comprehensive account of the main applications, covering detection, estimation, and signal analysis of stationary, nonstationary, and cyclostationary processes. Providing a systematic development from the origin of complex signals to their probabilistic description makes the theory accessible to newcomers. This book is ideal for graduate students and researchers working with complex data in a range of research areas from communications to oceanography. [BibTeX]@book{SchreierScharf:2010:StatisticalSignalProcessingofComplex,
abstract = {Complexvalued random signals are embedded in the very fabric of science and engineering, yet the usual assumptions made about their statistical behavior are often a poor representation of the underlying physics. This book deals with improper and noncircular complex signals, which do not conform to classical assumptions, and it demonstrates how correct treatment of these signals can have significant payoffs. The book begins with detailed coverage of the fundamental theory and presents a variety of tools and algorithms for dealing with improper and noncircular signals. It provides a comprehensive account of the main applications, covering detection, estimation, and signal analysis of stationary, nonstationary, and cyclostationary processes. Providing a systematic development from the origin of complex signals to their probabilistic description makes the theory accessible to newcomers. This book is ideal for graduate students and researchers working with complex data in a range of research areas from communications to oceanography.},
title = {Statistical signal processing of complexvalued data: the theory of improper and noncircular signals},
author = {Schreier, Peter J. and Scharf, Louis L.},
year = {2010},
publisher = {{C}ambridge {U}niversity {P}ress},
}
Journal articles

2Determining the dimension of the improper signal subspace in complexvalued data
(Tanuj Hasija, Christian Lameiro and Peter J. Schreier)
IEEE Signal Process. Lett. 24, pp. 1606–1610, November 2017. [BibTeX]
@article{HasijaSPletter:2016aa,
abstract = {Abstract: A complexvalued signal is improper if it is correlated with its complex conjugate. The dimension of the improper signal subspace, i.e., the number of improper components in a complexvalued measurement, is an important parameter and is unknown in most of the applications. In this letter, we introduce two approaches to estimate this dimension: one based on an informationtheoretic criterion and the other based on hypothesis testing. We also present reducedrank versions of these approaches that work for scenarios where the number of observations is comparable to or even smaller than the dimension of the data. Unlike other techniques for determining model orders, our techniques also work in the presence of additive colored noise.},
title = {Determining the dimension of the improper signal subspace in complexvalued data},
author = {Hasija, Tanuj and Lameiro, Christian and Schreier, Peter J.},
month = {{N}ovember},
year = {2017},
journal = {IEEE Signal Process. Lett.},
pages = {1606–1610},
volume = {24},
}
[Abstract]
Abstract: A complexvalued signal is improper if it is correlated with its complex conjugate. The dimension of the improper signal subspace, i.e., the number of improper components in a complexvalued measurement, is an important parameter and is unknown in most of the applications. In this letter, we introduce two approaches to estimate this dimension: one based on an informationtheoretic criterion and the other based on hypothesis testing. We also present reducedrank versions of these approaches that work for scenarios where the number of observations is comparable to or even smaller than the dimension of the data. Unlike other techniques for determining model orders, our techniques also work in the presence of additive colored noise.3Rate region boundary of the SISO Zinterference channel with improper signaling
(Christian Lameiro, Ignacio Santamaría and Peter J. Schreier)
IEEE Trans. Comm., 2016, accepted for publication. [BibTeX]
@article{Lameiro:2016ac,
title = {Rate region boundary of the {SISO Z}interference channel with improper signaling},
author = {Lameiro, Christian and Santamar{\'i}a, Ignacio and Schreier, Peter J.},
year = {2016, accepted for publication},
journal = {{IEEE} {T}rans.\ {C}omm.},
}
[Abstract]4Spatial interference shaping for underlay MIMO cognitive networks
(Christian Lameiro, Wolfgang Utschick and Ignacio Santamaría)
Signal Process., 2016, accepted for publication. [BibTeX]
@article{Lameiro:2016ab,
title = {Spatial interference shaping for underlay {MIMO} cognitive networks},
author = {Lameiro, Christian and Utschick, Wolfgang and Santamar{\'i}a, Ignacio},
year = {2016, accepted for publication},
journal = {Signal Process.},
}
[Abstract]5A pessimistic approximation for the Fisher information measure
(Manuel S. Stein and Josef A. Nossek)
IEEE Trans. Signal Process., 2016, accepted for publication. [BibTeX]
@article{Stein:SPT:2016:1,
title = {A pessimistic approximation for the {F}isher information measure},
author = {Stein, Manuel S. and Nossek, Josef A.},
year = {2016, accepted for publication},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
}
[Abstract]6Fisher information bounds with applications in nonlinear learning, compression and inference
(Manuel S. Stein, Josef A. Nossek and Kurt Barbé)
submitted, 2016. [BibTeX]
@article{Stein:SPT:2016:2,
title = {Fisher information bounds with applications in nonlinear learning, compression and inference},
author = {Stein, Manuel S. and Nossek, Josef A. and Barb{\'e}, Kurt},
year = {2016},
journal = {submitted},
}
[Abstract]7Canonical correlation analysis of highdimensional data with very small sample support
(Yang Song, Peter J. Schreier, David Ramírez and Tanuj Hasija)
Signal Process. 128, pp. 449–458, November 2016. [BibTeX]
@article{Song:2016aa,
title = {Canonical correlation analysis of highdimensional data with very small sample support},
author = {Song, Yang and Schreier, Peter J. and Ram{\'i}rez, David and Hasija, Tanuj},
month = {{N}ovember},
year = {2016},
journal = {{S}ignal {P}rocess.},
pages = {449–458},
volume = {128},
}
[Abstract]8Samplepoor estimation of order and common signal subspace with application to fusion of medical imaging data
(Y. LevinSchwartz, Yang Song, Peter J. Schreier, V.D. Calhoun and Tülay Adali)
NeuroImage 134, pp. 486–493, July 2016. [BibTeX]
@article{LevinSchwartz:2016aa,
title = {Samplepoor estimation of order and common signal subspace with application to fusion of medical imaging data},
author = {LevinSchwartz, Y. and Song, Yang and Schreier, Peter J. and Calhoun, V.D. and Adali, T{\"u}lay},
month = {{J}uly},
year = {2016},
journal = {{N}euro{I}mage},
pages = {486–493},
volume = {134},
}
[Abstract]9Shrinkage of covariance matrices for linear signal estimation using crossvalidation
(Jun Tong, Peter J. Schreier, Qinghua Guo, S. Tong, Jiangtao Xi and Y. Yu)
IEEE Trans. Signal Process. 64 (11), pp. 2965–2975, June 2016. [BibTeX]
@article{Tong:2016aa,
title = {Shrinkage of covariance matrices for linear signal estimation using crossvalidation},
author = {Tong, Jun and Schreier, Peter J. and Guo, Qinghua and Tong, S. and Xi, Jiangtao and Yu, Y.},
month = {{J}une},
year = {2016},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {2965–2975},
volume = {64},
number = {11},
}
[Abstract]10A unified scheme to achieve the degreesoffreedom region of the MIMO interference channel with delayed channel state information
(Mohsen Rezaee, Peter J. Schreier, M. Guillaud and B. Clerckx)
IEEE Trans. Comm. 64 (3), pp. 1068–1082, March 2016. [BibTeX]
@article{Rezaee:2016aa,
title = {A unified scheme to achieve the degreesoffreedom region of the {MIMO} interference channel with delayed channel state information},
author = {Rezaee, Mohsen and Schreier, Peter J. and Guillaud, M. and Clerckx, B.},
month = {{M}arch},
year = {2016},
journal = {{IEEE} {T}rans.\ {C}omm.},
pages = {1068–1082},
volume = {64},
number = {3},
}
[Abstract]11Experimental evaluation of interference alignment for broadband WLAN systems
(C. Lameiro, Ó. González, J.A. GarcíaNaya, I. Santamaría and L. Castedo)
EURASIP Journal on Wireless Communications and Networking, 2015.
DOI:10.1186/s136380150409z.
[BibTeX]
@article{LameiroGonzalezGarciaNaya:2015:Experimentalevaluationofinterferencealignment,
abstract = {In this paper, we present an experimental study on the performance of spatial interference alignment (IA) in indoor wireless local area network scenarios that use orthogonal frequency division multiplexing (OFDM) according to the physicallayer specifications of the IEEE 802.11a standard. Experiments have been carried out using a wireless network testbed capable of implementing a 3user MIMO interference channel. We have implemented IA decoding schemes that can be designed according to distinct criteria (e.g., zeroforcing or MaxSINR). The measurement methodology has been validated considering practical issues like the number of OFDM training symbols used for channel estimation or feedback time. In case of asynchronous users, a timedomain IA decoding filter is also compared to its frequencydomain counterpart. We also evaluated the performance of IA from bit error ratio measurementbased results in comparison to different timedivision multiple access transmission schemes. The comparison includes single and multipleantenna systems transmitting over the dominant mode of the MIMO channel. Our results indicate that spatial IA is suitable for practical indoor scenarios in which wireless channels often exhibit relatively large coherence times.},
title = {Experimental evaluation of interference alignment for broadband {WLAN} systems},
author = {C. Lameiro and {\'O}. Gonz{\'a}lez and J.A. Garc{\'i}aNaya and I. Santamar{\'i}a and L. Castedo},
year = {2015},
journal = {EURASIP Journal on Wireless Communications and Networking},
doi = {10.1186/s136380150409z},
}
[Abstract]
In this paper, we present an experimental study on the performance of spatial interference alignment (IA) in indoor wireless local area network scenarios that use orthogonal frequency division multiplexing (OFDM) according to the physicallayer specifications of the IEEE 802.11a standard. Experiments have been carried out using a wireless network testbed capable of implementing a 3user MIMO interference channel. We have implemented IA decoding schemes that can be designed according to distinct criteria (e.g., zeroforcing or MaxSINR). The measurement methodology has been validated considering practical issues like the number of OFDM training symbols used for channel estimation or feedback time. In case of asynchronous users, a timedomain IA decoding filter is also compared to its frequencydomain counterpart. We also evaluated the performance of IA from bit error ratio measurementbased results in comparison to different timedivision multiple access transmission schemes. The comparison includes single and multipleantenna systems transmitting over the dominant mode of the MIMO channel. Our results indicate that spatial IA is suitable for practical indoor scenarios in which wireless channels often exhibit relatively large coherence times.12Asymptotic parameter tracking performance with measurement data of 1bit resolution
(Manuel Stein, Alexander Kürzl, Amine Mezghani and Josef A. Nossek)
IEEE Trans. Signal Process. 63 (22), pp. 6086–6095, November 2015.
DOI:10.1109/TSP.2015.2458778.
[BibTeX]
@article{Stein:SPT:2016,
title = {Asymptotic parameter tracking performance with measurement data of 1bit resolution},
author = {Stein, Manuel and K{\"u}rzl, Alexander and Mezghani, Amine and Nossek, Josef A.},
month = {{N}ovember},
year = {2015},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {6086–6095},
volume = {63},
number = {22},
doi = {10.1109/TSP.2015.2458778},
}
[Abstract]13Detection of multivariate cyclostationarity
(D. Ramírez, P. J. Schreier, J. Via, I. Santamaria and L. L. Scharf)
IEEE Trans. Signal Processing 63 (20), pp. 5395–5408, October 2015. [BibTeX]
@article{RamirezSchreierVia:2015:Detectionofmultivariatecyclostationarity,
title = {Detection of multivariate cyclostationarity},
author = {D. Ram{\'i}rez and P. J. Schreier and J. Via and I. Santamaria and L. L. Scharf},
month = {October},
year = {2015},
journal = {IEEE Trans. Signal Processing},
pages = {5395–5408},
volume = {63},
number = {20},
}
[Abstract]14Overdemodulation for highperformance receivers with lowresolution ADC
(Manuel Stein, Theiler Sebastian and Josef A. Nossek)
IEEE Wireless Comm. Lett. 4 (2), pp. 169–172, April 2015.
DOI:10.1109/LWC.2015.2388675.
[BibTeX]
@article{Stein:WCL:2015,
title = {Overdemodulation for highperformance receivers with lowresolution {ADC}},
author = {Stein, Manuel and Sebastian, Theiler and Nossek, Josef A.},
month = {{A}pril},
year = {2015},
journal = {{IEEE} {W}ireless {C}omm. {L}ett.},
pages = {169–172},
volume = {4},
number = {2},
doi = {10.1109/LWC.2015.2388675},
}
[Abstract]15Benefits of improper signaling for underlay cognitive radio
(Christian Lameiro, Ignacio Santamaría and Peter J. Schreier)
IEEE Wireless Comm. Lett. 4, pp. 22–25, February 2015.
DOI:10.1109/LWC.2014.2360179.
[BibTeX]
@article{LameiroSantamariaSchreier:2015:BenefitsofImproperSignalingforUnderlay,
abstract = {In this letter we study the potential benefits of improper signaling for a secondary user (SU) in underlay cognitive radio networks. We consider a basic yet illustrative scenario in which the primary user (PU) always transmit proper Gaussian signals and has a minimum rate constraint. After parameterizing the SU transmit signal in terms of its power and circularity coefficient (which measures the degree of impropriety), we prove that the SU improves its rate by transmitting improper signals only when the ratio of the squared modulus between the SUPU interference link and the SU direct link exceeds a given threshold. As a byproduct of this analysis, we obtain the optimal circularity coefficient that must be used by the SU depending on its power budget. Some simulation results show that the SU benefits from the transmission of improper signals especially when the PU is not highly loaded.},
title = {Benefits of improper signaling for underlay cognitive radio},
author = {Lameiro, Christian and Santamar{\'i}a, Ignacio and Schreier, Peter J.},
month = {{F}ebruary},
year = {2015},
journal = {IEEE Wireless Comm. Lett.},
pages = {22–25},
volume = {4},
doi = {10.1109/LWC.2014.2360179},
}
[Abstract]
In this letter we study the potential benefits of improper signaling for a secondary user (SU) in underlay cognitive radio networks. We consider a basic yet illustrative scenario in which the primary user (PU) always transmit proper Gaussian signals and has a minimum rate constraint. After parameterizing the SU transmit signal in terms of its power and circularity coefficient (which measures the degree of impropriety), we prove that the SU improves its rate by transmitting improper signals only when the ratio of the squared modulus between the SUPU interference link and the SU direct link exceeds a given threshold. As a byproduct of this analysis, we obtain the optimal circularity coefficient that must be used by the SU depending on its power budget. Some simulation results show that the SU benefits from the transmission of improper signals especially when the PU is not highly loaded.16A flag representation for finite collections of subspaces of mixed dimensions
(Bruce Draper, Michael Kirby, Justin Marks, Tim Marrinan and Chris Peterson)
Lin. Alg. Appl. 451, pp. 15–32, Elsevier, 2014.
DOI:10.1016/j.laa.2014.03.022.
[BibTeX]
@article{draperLAA,
title = {A flag representation for finite collections of subspaces of mixed dimensions},
author = {Draper, Bruce and Kirby, Michael and Marks, Justin and Marrinan, Tim and Peterson, Chris},
year = {2014},
journal = {{L}in.\ {A}lg.\ {A}ppl.},
pages = {15–32},
volume = {451},
doi = {10.1016/j.laa.2014.03.022},
publisher = {Elsevier},
}
[Abstract]17Multiantenna spectrum sensing by exploiting spatiotemporal correlation
(S. Ali, D. Ramírez, M. Jansson, G. SecoGranados and J. A. LópezSalcedo)
Eurasip J. Applied Signal Process. 160, 2014.
DOI:10.1186/168761802014160.
[BibTeX]
@article{AliRamirezJansson:2014:Multiantennaspectrumsensingbyexploiting,
abstract = {In this paper, we propose a novel mechanism for spectrum sensing that leads us to exploit the spatiotemporal correlation present in the received signal at a multiantenna receiver. For the proposed mechanism, we formulate the spectrum sensing scheme by adopting the generalized likelihood ratio test (GLRT). However, the GLRT degenerates in the case of limited sample support. To circumvent this problem, several extensions are proposed that bring robustness to the GLRT in the case of high dimensionality and small sample size. In order to achieve these sampleefficient detection schemes, we modify the GLRTbased detector by exploiting the covariance structure and factoring the large spatiotemporal covariance matrix into spatial and temporal covariance matrices. The performance of the proposed detectors is evaluated by means of numerical simulations, showing important advantages over existing detectors.},
title = {Multiantenna spectrum sensing by exploiting spatiotemporal correlation},
author = {S. Ali and D. Ram{\'i}rez and M. Jansson and G. SecoGranados and J. A. L{\'o}pezSalcedo},
year = {2014},
journal = {{E}urasip\ {J}.\ {A}pplied {S}ignal {P}rocess.},
volume = {160},
doi = {10.1186/168761802014160},
}
[Abstract]
In this paper, we propose a novel mechanism for spectrum sensing that leads us to exploit the spatiotemporal correlation present in the received signal at a multiantenna receiver. For the proposed mechanism, we formulate the spectrum sensing scheme by adopting the generalized likelihood ratio test (GLRT). However, the GLRT degenerates in the case of limited sample support. To circumvent this problem, several extensions are proposed that bring robustness to the GLRT in the case of high dimensionality and small sample size. In order to achieve these sampleefficient detection schemes, we modify the GLRTbased detector by exploiting the covariance structure and factoring the large spatiotemporal covariance matrix into spatial and temporal covariance matrices. The performance of the proposed detectors is evaluated by means of numerical simulations, showing important advantages over existing detectors.18Finding brain oscillations with power dependencies in neuroimaging data
(S. Dähne, V. V. Nikulin, D. Ramírez, P. J. Schreier, K.R. Müller and S. Haufe)
NeuroImage 96, pp. 334–348, 2014.
DOI:10.1016/j.neuroimage.2014.03.075.
[BibTeX]
@article{DahneNikulinRamirez:2014:Findingbrainoscillationswith,
abstract = {Phase synchronization among neuronal oscillations within the same frequency band has been hypothesized to be a major mechanism for communication between different brain areas. On the other hand, crossfrequency com munications are more flexible allowing interactions between oscillations with different frequencies. Among such crossfrequency interactions amplitudetoamplitude interactions are of a special interest as they show how the strength of spatial synchronization in different neuronal populations relates to each other during a given task. While, previously, amplitudetoamplitude correlations were studied primarily on the sensor level, we present a source separation approach using spatial filters which maximize the correlation between the envelopes of brain oscillations recorded with electro/magnetoencephalography (EEG/MEG) or intracranial multichannel re cordings. Our approach, which is called canonical source power correlation analysis (cSPoC), is thereby capable of extracting genuine brain oscillations solely based on their assumed coupling behavior even when the signalto noise ratio of the signals is low. In addition to using cSPoC for the analysis of crossfrequency interactions in the same subject, we show that it can also be utilized for studying amplitude dynamics of neuronal oscillations across subjects. We assess the performance of cSPoC in simulations as well as in three distinctively different analysis sce narios of real EEG data, each involving several subjects. In the simulations, cSPoC outperforms unsupervised stateoftheart approaches. In the analysis of real EEG recordings, we demonstrate excellent unsupervised dis covery of meaningful powertopower couplings, within as well as across subjects and frequency bands.},
title = {Finding brain oscillations with power dependencies in neuroimaging data},
author = {S. D{\"a}hne and V. V. Nikulin and D. Ram{\'i}rez and P. J. Schreier and K.R. M{\"u}ller and S. Haufe},
year = {2014},
journal = {NeuroImage},
pages = {334–348},
volume = {96},
doi = {10.1016/j.neuroimage.2014.03.075},
}
[Abstract]
Phase synchronization among neuronal oscillations within the same frequency band has been hypothesized to be a major mechanism for communication between different brain areas. On the other hand, crossfrequency com munications are more flexible allowing interactions between oscillations with different frequencies. Among such crossfrequency interactions amplitudetoamplitude interactions are of a special interest as they show how the strength of spatial synchronization in different neuronal populations relates to each other during a given task. While, previously, amplitudetoamplitude correlations were studied primarily on the sensor level, we present a source separation approach using spatial filters which maximize the correlation between the envelopes of brain oscillations recorded with electro/magnetoencephalography (EEG/MEG) or intracranial multichannel re cordings. Our approach, which is called canonical source power correlation analysis (cSPoC), is thereby capable of extracting genuine brain oscillations solely based on their assumed coupling behavior even when the signalto noise ratio of the signals is low. In addition to using cSPoC for the analysis of crossfrequency interactions in the same subject, we show that it can also be utilized for studying amplitude dynamics of neuronal oscillations across subjects. We assess the performance of cSPoC in simulations as well as in three distinctively different analysis sce narios of real EEG data, each involving several subjects. In the simulations, cSPoC outperforms unsupervised stateoftheart approaches. In the analysis of real EEG recordings, we demonstrate excellent unsupervised dis covery of meaningful powertopower couplings, within as well as across subjects and frequency bands.19A quadratically convergent method for interference alignment in MIMO interference channels
(Óscar González, Christian Lameiro and Ignacio Santamaría)
IEEE Signal Process. Lett. 21, pp. 1423–1427, November 2014.
DOI:10.1109/LSP.2014.2338132.
[BibTeX]
@article{GonzalezLameiroSantamaria:2014:AQuadraticallyConvergentMethodforInterference,
abstract = {Alternating minimization and steepest descent are commonly used strategies to obtain interference alignment (IA) solutions in the $K$user multipleinput multipleoutput (MIMO) interference channel (IC). Although these algorithms are shown to converge monotonically, they experience a poor convergence rate, requiring an enormous amount of iterations which substantially increases with the size of the scenario. To alleviate this drawback, in this letter we resort to the GaussNewton (GN) method, which is wellknown to experience quadratic convergence when the iterates are sufficiently close to the optimum. We discuss the convergence properties of the proposed GN algorithm and provide several numerical examples showing that it always converges to the optimum with quadratic rate, reducing dramatically the required computation time in comparison to other algorithms, hence paving a new way for the design of IA algorithms.},
title = {A quadratically convergent method for interference alignment in {MIMO} interference channels},
author = {Gonz{\'a}lez, {\'O}scar and Lameiro, Christian and Santamar{\'i}a, Ignacio},
month = {{N}ovember},
year = {2014},
journal = {IEEE Signal Process. Lett.},
pages = {1423–1427},
volume = {21},
doi = {10.1109/LSP.2014.2338132},
}
[Abstract]
Alternating minimization and steepest descent are commonly used strategies to obtain interference alignment (IA) solutions in the Kuser multipleinput multipleoutput (MIMO) interference channel (IC). Although these algorithms are shown to converge monotonically, they experience a poor convergence rate, requiring an enormous amount of iterations which substantially increases with the size of the scenario. To alleviate this drawback, in this letter we resort to the GaussNewton (GN) method, which is wellknown to experience quadratic convergence when the iterates are sufficiently close to the optimum. We discuss the convergence properties of the proposed GN algorithm and provide several numerical examples showing that it always converges to the optimum with quadratic rate, reducing dramatically the required computation time in comparison to other algorithms, hence paving a new way for the design of IA algorithms.20Detecting directionality in random fields using the monogenic signal
(S. C. Olhede, D. Ramírez and P. J. Schreier)
IEEE Trans. Inform. Theory 60 (10), pp. 6491–6510, October 2014.
DOI:10.1109/TIT.2014.2342734.
[BibTeX]
@article{OlhedeRamirezSchreier:2014:DetectingDirectionalityinRandomFields,
abstract = {Detecting and analyzing directional structures in images is important in many applications since onedimensional patterns often correspond to important features such as object contours or trajectories. Classifying a structure as directional or nondirectional requires a measure to quantify the degree of directionality and a threshold, which needs to be chosen based on the statistics of the image. In order to do this, we model the image as a random field. So far, little research has been performed on analyzing directionality in random fields. In this paper, we propose a measure to quantify the degree of directionality based on the random monogenic signal, which enables a unique decomposition of a 2D signal into local amplitude, local orientation, and local phase. We investigate the secondorder statistical properties of the monogenic signal for isotropic, anisotropic, and unidirectional random fields. We analyze our measure of directionality for finitesize sample images, and determine a threshold to distinguish between unidirectional and nonunidirectional random fields, which allows the automatic classification of images.},
title = {Detecting directionality in random fields using the monogenic signal},
author = {S. C. Olhede and D. Ram{\'i}rez and P. J. Schreier},
month = {{O}ctober},
year = {2014},
journal = {{IEEE} {T}rans.\ {I}nform.\ {T}heory},
pages = {6491–6510},
volume = {60},
number = {10},
doi = {10.1109/TIT.2014.2342734},
}
[Abstract]
Detecting and analyzing directional structures in images is important in many applications since onedimensional patterns often correspond to important features such as object contours or trajectories. Classifying a structure as directional or nondirectional requires a measure to quantify the degree of directionality and a threshold, which needs to be chosen based on the statistics of the image. In order to do this, we model the image as a random field. So far, little research has been performed on analyzing directionality in random fields. In this paper, we propose a measure to quantify the degree of directionality based on the random monogenic signal, which enables a unique decomposition of a 2D signal into local amplitude, local orientation, and local phase. We investigate the secondorder statistical properties of the monogenic signal for isotropic, anisotropic, and unidirectional random fields. We analyze our measure of directionality for finitesize sample images, and determine a threshold to distinguish between unidirectional and nonunidirectional random fields, which allows the automatic classification of images.21Optimization and estimation of complexvalued signals
(Tulay Adali and Peter J. Schreier)
IEEE Signal Processing Magazine 31 (5), pp. 112–128, September 2014.
DOI:10.1109/MSP.2013.2287951.
[BibTeX]
@article{AdaliSchreier:2014:Optimizationandestimationofcomplexvaluedsignals,
abstract = {Complexvalued signals occur in many areas of science and engineering and are thus of fundamental interest. When developing signal processing methods in the complex domain, there are two key issues: making use of the full statistical information and optimization. In this article, we review the necessary tools to address these two key issues and provide examples in filtering and blind source separation (BSS) that utilize these tools.},
title = {Optimization and estimation of complexvalued signals},
author = {Adali, Tulay and Schreier, Peter J.},
month = {{S}eptember},
year = {2014},
journal = {{IEEE} {S}ignal {P}rocessing {M}agazine},
pages = {112–128},
volume = {31},
number = {5},
doi = {10.1109/MSP.2013.2287951},
}
[Abstract]
Complexvalued signals occur in many areas of science and engineering and are thus of fundamental interest. When developing signal processing methods in the complex domain, there are two key issues: making use of the full statistical information and optimization. In this article, we review the necessary tools to address these two key issues and provide examples in filtering and blind source separation (BSS) that utilize these tools.22Informationpreserving transformations for signal parameter estimation
(Manuel Stein, Mario Castañeda, Amine Mezghani and Josef A. Nossek)
IEEE Signal Process. Lett. 21 (7), pp. 866–870, July 2014.
DOI:10.1109/LSP.2014.2315537.
[BibTeX]
@article{Stein:SPL:2014:02,
title = {Informationpreserving transformations for signal parameter estimation},
author = {Stein, Manuel and Casta{\~n}eda, Mario and Mezghani, Amine and Nossek, Josef A.},
month = {{J}uly},
year = {2014},
journal = {{IEEE} {S}ignal {P}rocess.\ {L}ett.},
pages = {866–870},
volume = {21},
number = {7},
doi = {10.1109/LSP.2014.2315537},
}
[Abstract]23A lower bound for the Fisher information measure
(Manuel Stein, Amine Mezghani and Josef A. Nossek)
IEEE Signal Process. Lett. 21 (7), pp. 796–799, July 2014.
DOI:10.1109/LSP.2014.2316008.
[BibTeX]
@article{Stein:SPL:2014:01,
title = {A lower bound for the {F}isher information measure},
author = {Stein, Manuel and Mezghani, Amine and Nossek, Josef A.},
month = {{J}uly},
year = {2014},
journal = {{IEEE} {S}ignal {P}rocess.\ {L}ett.},
pages = {796–799},
volume = {21},
number = {7},
doi = {10.1109/LSP.2014.2316008},
}
[Abstract]24A Bayesian approach for adaptive multiantenna sensing in cognitive radio networks
(J. MancoVásquez, M. LázaroGredilla, D. Ramírez, J. Vía and I. Santamaría)
Signal Process. 96, Part B, pp. 228–240, March 2014.
DOI:10.1016/j.sigpro.2013.10.005.
[BibTeX]
@article{MancoVasquezLazaroGredillaRamirez:2014:ABayesianapproachforadaptivemultiantenna,
abstract = {Recent work on multiantenna spectrum sensing in cognitive radio (CR) networks has been based on generalized likelihood ratio test (GLRT) detectors, which lack the ability to learn from past decisions and to adapt to the continuously changing environment. To overcome this limitation, in this paper we propose a Bayesian detector capable of learning in an efficient way the posterior distributions under both hypotheses. Our Bayesian model places priors directly on the spatial covariance matrices under both hypotheses, as well as on the probability of channel occupancy. Specifically, we use inversegamma and complex inverseWishart distributions as conjugate priors for the null and alternative hypotheses, respectively; and a binomial distribution as the prior for channel occupancy. At each sensing period, Bayesian inference is applied and the posterior for the channel occupancy is thresholded for detection. After a suitable approximation, the posteriors are employed as priors for the next sensing frame, which forms the basis of the proposed Bayesian learning procedure. The performance of the Bayesian detector is evaluated by simulations and by means of a CR testbed composed of universal radio peripheral (USRP) nodes. Both the simulations and experimental measurements show that the Bayesian detector outperforms the GLRT in a variety of scenarios.},
title = {A {B}ayesian approach for adaptive multiantenna sensing in cognitive radio networks},
author = {J. MancoV{\'a}squez and M. L{\'a}zaroGredilla and D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a},
month = {{M}arch},
year = {2014},
journal = {{S}ignal {P}rocess.},
pages = {228–240},
volume = {96, Part B},
doi = {10.1016/j.sigpro.2013.10.005},
}
[Abstract]
Recent work on multiantenna spectrum sensing in cognitive radio (CR) networks has been based on generalized likelihood ratio test (GLRT) detectors, which lack the ability to learn from past decisions and to adapt to the continuously changing environment. To overcome this limitation, in this paper we propose a Bayesian detector capable of learning in an efficient way the posterior distributions under both hypotheses. Our Bayesian model places priors directly on the spatial covariance matrices under both hypotheses, as well as on the probability of channel occupancy. Specifically, we use inversegamma and complex inverseWishart distributions as conjugate priors for the null and alternative hypotheses, respectively; and a binomial distribution as the prior for channel occupancy. At each sensing period, Bayesian inference is applied and the posterior for the channel occupancy is thresholded for detection. After a suitable approximation, the posteriors are employed as priors for the next sensing frame, which forms the basis of the proposed Bayesian learning procedure. The performance of the Bayesian detector is evaluated by simulations and by means of a CR testbed composed of universal radio peripheral (USRP) nodes. Both the simulations and experimental measurements show that the Bayesian detector outperforms the GLRT in a variety of scenarios.25Testing blind separability of complex Gaussian mixtures
(D. Ramírez, P. J. Schreier, J. Vía and I. Santamaría)
Signal Process. 95, pp. 49–57, February 2014.
DOI:10.1016/j.sigpro.2013.08.010.
[BibTeX]
@article{RamirezSchreierVia:2014:Testingblindseparabilityofcomplex,
abstract = {The separation of a complex mixture based solely on secondorder statistics can be achieved using the Strong Uncorrelating Transform (SUT) if and only if all sources have distinct circularity coefficients. However, in most problems we do not know the circularity coefficients, and they must be estimated from observed data. In this work, we propose a detector, based on the generalized likelihood ratio test (GLRT), to test the separability of a complex Gaussian mixture using the SUT. For the separable case (distinct circularity coefficients), the maximum likelihood (ML) estimates are straightforward. On the other hand, for the nonseparable case (at least one circularity coefficient has multiplicity greater than one), the ML estimates are much more difficult to obtain. To set the threshold, we exploit Wilks' theorem, which gives the asymptotic distribution of the GLRT under the null hypothesis. Finally, numerical simulations show the good performance of the proposed detector and the accuracy of Wilks' approximation.},
title = {Testing blind separability of complex {G}aussian mixtures},
author = {D. Ram{\'i}rez and P. J. Schreier and J. V{\'i}a and I. Santamar{\'i}a},
month = {{F}ebruary},
year = {2014},
journal = {{S}ignal {P}rocess.},
pages = {49–57},
volume = {95},
doi = {10.1016/j.sigpro.2013.08.010},
}
[Abstract]
The separation of a complex mixture based solely on secondorder statistics can be achieved using the Strong Uncorrelating Transform (SUT) if and only if all sources have distinct circularity coefficients. However, in most problems we do not know the circularity coefficients, and they must be estimated from observed data. In this work, we propose a detector, based on the generalized likelihood ratio test (GLRT), to test the separability of a complex Gaussian mixture using the SUT. For the separable case (distinct circularity coefficients), the maximum likelihood (ML) estimates are straightforward. On the other hand, for the nonseparable case (at least one circularity coefficient has multiplicity greater than one), the ML estimates are much more difficult to obtain. To set the threshold, we exploit Wilks' theorem, which gives the asymptotic distribution of the GLRT under the null hypothesis. Finally, numerical simulations show the good performance of the proposed detector and the accuracy of Wilks' approximation.26Neue Anwendungsgebiete für Computer Assisted Surgery (CAS)
(Peter J. Schreier)
ForschungsForum Paderborn 17, pp. 24–30, February 2014. [BibTeX]
@article{Schreier:2014:ForschungsForumPaderborn,
title = {Neue {A}nwendungsgebiete f{\"u}r {C}omputer {A}ssisted {S}urgery {(CAS)}},
author = {Schreier, Peter J.},
month = {{F}ebruary},
year = {2014},
journal = {{ForschungsForum} {Paderborn}},
pages = {24–30},
volume = {17},
}
[Abstract]27Optical coherence tomography assessment of vessel wall degradation in thoracic aortic aneurysms
(Eusebio Real, Alma Eguizabal, Alejandro Pontón, Marta Calvo Díez, José Fernando ValBernal, Marta Mayorga, José M. Revuelta, José M. LópezHiguera and Olga M. Conde)
J. Biomed. Opt. 18 (12), pp. 126003–126003, December 2013.
DOI:10.1117/1.JBO.18.12.126003.
[BibTeX]
@article{RealEguizabalPonton:2013:Opticalcoherencetomographyassessmentofvessel,
abstract = {Optical coherence tomography images of human thoracic aorta from aneurysms reveal elastin disorders and smooth muscle cell alterations when visualizing the media layer of the aortic wall. These disorders can be employed as indicators for wall degradation and, therefore, become a hallmark for diagnosis of risk of aneurysm under intraoperative conditions. Two approaches are followed to evaluate this risk: the analysis of the reflectivity decay along the penetration depth and the textural analysis of a twodimensional spatial distribution of the aortic wall backscattering. Both techniques require preprocessing stages for the identification of the air–sample interface and for the segmentation of the media layer. Results show that the alterations in the media layer of the aortic wall are better highlighted when the textural approach is considered and also agree with a semiquantitative histopathological grading that assesses the degree of wall degradation. The correlation of the cooccurrence matrix attains a sensitivity of 0.906 and specificity of 0.864 when aneurysm automatic diagnosis is evaluated with a receiver operating characteristic curve.},
title = {Optical coherence tomography assessment of vessel wall degradation in thoracic aortic aneurysms},
author = {Eusebio Real and Alma Eguizabal and Alejandro Pontón and Marta Calvo Díez and José Fernando ValBernal and Marta Mayorga and José M. Revuelta and José M. LópezHiguera and Olga M. Conde},
month = {{D}ecember},
year = {2013},
journal = {J. Biomed. Opt.},
pages = {126003–126003},
volume = {18},
number = {12},
doi = {10.1117/1.JBO.18.12.126003},
}
[Abstract]
Optical coherence tomography images of human thoracic aorta from aneurysms reveal elastin disorders and smooth muscle cell alterations when visualizing the media layer of the aortic wall. These disorders can be employed as indicators for wall degradation and, therefore, become a hallmark for diagnosis of risk of aneurysm under intraoperative conditions. Two approaches are followed to evaluate this risk: the analysis of the reflectivity decay along the penetration depth and the textural analysis of a twodimensional spatial distribution of the aortic wall backscattering. Both techniques require preprocessing stages for the identification of the air–sample interface and for the segmentation of the media layer. Results show that the alterations in the media layer of the aortic wall are better highlighted when the textural approach is considered and also agree with a semiquantitative histopathological grading that assesses the degree of wall degradation. The correlation of the cooccurrence matrix attains a sensitivity of 0.906 and specificity of 0.864 when aneurysm automatic diagnosis is evaluated with a receiver operating characteristic curve.28Convergent systems vs. incremental stability
(Björn S. Rüffer, Nathan van de Wouw and Markus Mueller)
Systems Control Lett. 62, pp. 277–285, 2013.
DOI:10.1016/j.sysconle.2012.11.015.
[BibTeX]
@article{rufferwouwmueller2013convergentsystemsvs.incrementalstability,
abstract = {Two similar stability notions are considered; one is the long established notion of convergent systems, the other is the younger notion of incremental stability. Both notions require that any two solutions of a system converge to each other. Yet these stability concepts are different, in the sense that none implies the other, as is shown in this paper using two examples. It is shown under what additional assumptions one property indeed implies the other. Furthermore, this paper contains necessary and sufficient characterizations of both properties in terms of Lyapunov functions.},
title = {Convergent systems vs. incremental stability},
author = {R{\"u}ffer, Bj{\"o}rn S. and van de Wouw, Nathan and Mueller, Markus},
year = {2013},
journal = {{S}ystems {C}ontrol {L}ett.},
pages = {277–285},
volume = {62},
doi = {10.1016/j.sysconle.2012.11.015},
}
[Abstract]
Two similar stability notions are considered; one is the long established notion of convergent systems, the other is the younger notion of incremental stability. Both notions require that any two solutions of a system converge to each other. Yet these stability concepts are different, in the sense that none implies the other, as is shown in this paper using two examples. It is shown under what additional assumptions one property indeed implies the other. Furthermore, this paper contains necessary and sufficient characterizations of both properties in terms of Lyapunov functions.29A unified framework for regularized linear estimation in communication systems
(Jun Tong and Peter J. Schreier)
Signal Process. 93 (9), pp. 2671–2686, September 2013.
DOI:10.1016/j.sigpro.2013.03.002.
[BibTeX]
@article{TongSchreier:2013:Aunifiedframework,
abstract = {Two concerns often arise simultaneously when applying linear estimation in communication systems: the computational complexity can be prohibitively high when the system size is large, and the performance may degrade dramatically when the presumed model is mismatched with the actual system. In this paper, we introduce a subspace expansion framework to jointly address these concerns, in which the observation is first projected onto a lowerdimensional subspace and then the solution of the projected problem is regularized. We discuss two projection methods based on eigensubspace and Krylov subspace expansions. We show that the Krylov subspace projection provides an economical solution to regularized linear estimation. We also compare different regularization methods, such as principal components and diagonal loading. We show that diagonal loading generally outperforms other alternatives and that Krylov subspace rank reduction can yield a regularization effect close to diagonal loading. Finally, we investigate the impact of preconditioning on the performance and complexity for mismatched modeling and propose a loaded preconditioner, which can reduce complexity as well as preserve the regularization effect. Under the proposed framework, various regularization schemes are studied and some guidelines for choosing the right scheme are provided.},
title = {A unified framework for regularized linear estimation in communication systems},
author = {Tong, Jun and Schreier, Peter J.},
month = {{S}eptember},
year = {2013},
journal = {{S}ignal {P}rocess.},
pages = {2671–2686},
volume = {93},
number = {9},
doi = {10.1016/j.sigpro.2013.03.002},
}
[Abstract]
Two concerns often arise simultaneously when applying linear estimation in communication systems: the computational complexity can be prohibitively high when the system size is large, and the performance may degrade dramatically when the presumed model is mismatched with the actual system. In this paper, we introduce a subspace expansion framework to jointly address these concerns, in which the observation is first projected onto a lowerdimensional subspace and then the solution of the projected problem is regularized. We discuss two projection methods based on eigensubspace and Krylov subspace expansions. We show that the Krylov subspace projection provides an economical solution to regularized linear estimation. We also compare different regularization methods, such as principal components and diagonal loading. We show that diagonal loading generally outperforms other alternatives and that Krylov subspace rank reduction can yield a regularization effect close to diagonal loading. Finally, we investigate the impact of preconditioning on the performance and complexity for mismatched modeling and propose a loaded preconditioner, which can reduce complexity as well as preserve the regularization effect. Under the proposed framework, various regularization schemes are studied and some guidelines for choosing the right scheme are provided.30Regularized preconditioning for Krylov Subspace Equalization of OFDM systems over doubly selective channels
(Jun Tong and Peter J. Schreier)
IEEE Wireless Comm. Lett. 2 (4), pp. 367–370, August 2013.
DOI:10.1109/WCL.2013.042313.130096.
[BibTeX]
@article{TongSchreier:2013:RegularizedPreconditioningforKrylovSubspace,
title = {Regularized preconditioning for {K}rylov Subspace Equalization of {OFDM} systems over doubly selective channels},
author = {Tong, Jun and Schreier, Peter J.},
month = {{A}ugust},
year = {2013},
journal = {{IEEE} {W}ireless {C}omm. {L}ett.},
pages = {367–370},
volume = {2},
number = {4},
doi = {10.1109/WCL.2013.042313.130096},
}
[Abstract]31Direct identification of breast cancer pathologies using blind separation of labelfree localized reflectance measurements
(Alma Eguizabal, Ashley M. Laughney, P. Beatriz GarciaAllende, Venkataramanan Krishnaswamy, Wendy A. Wells, Keith D. Paulsen, Brian W. Pogue, Jose M. LopezHiguera and Olga M. Conde)
Biomed. Opt. Express 4 (7), pp. 1104–1118, June 2013.
DOI:10.1364/BOE.4.001104.
[BibTeX]
@article{EguizabalLaughneyGarciaallende:2013:Directidentificationofbreastcancerpathologies,
abstract = {Breast tumors are blindly identified using Principal (PCA) and Independent Component Analysis (ICA) of localized reflectance measurements. No assumption of a particular theoretical model for the reflectance needs to be made, while the resulting features are proven to have discriminative power of breast pathologies. Normal, benign and malignant breast tissue types in lumpectomy specimens were imaged ex vivo and a surgeonguided calibration of the system is proposed to overcome the limitations of the blind analysis. A simple, fast and linear classifier has been proposed where no training information is required for the diagnosis. A set of 29 breast tissue specimens have been diagnosed with a sensitivity of 96% and specificity of 95% when discriminating benign from malignant pathologies. The proposed hybrid combination PCAICA enhanced diagnostic discrimination, providing tumor probability maps, and intermediate PCA parameters reflected tissue optical properties.},
title = {Direct identification of breast cancer pathologies using blind separation of labelfree localized reflectance measurements},
author = {Alma Eguizabal and Ashley M. Laughney and P. Beatriz GarciaAllende and Venkataramanan Krishnaswamy and Wendy A. Wells and Keith D. Paulsen and Brian W. Pogue and Jose M. LopezHiguera and Olga M. Conde},
month = {{J}une},
year = {2013},
journal = {Biomed. Opt. Express},
pages = {1104–1118},
volume = {4},
number = {7},
doi = {10.1364/BOE.4.001104},
}
[Abstract]
Breast tumors are blindly identified using Principal (PCA) and Independent Component Analysis (ICA) of localized reflectance measurements. No assumption of a particular theoretical model for the reflectance needs to be made, while the resulting features are proven to have discriminative power of breast pathologies. Normal, benign and malignant breast tissue types in lumpectomy specimens were imaged ex vivo and a surgeonguided calibration of the system is proposed to overcome the limitations of the blind analysis. A simple, fast and linear classifier has been proposed where no training information is required for the diagnosis. A set of 29 breast tissue specimens have been diagnosed with a sensitivity of 96% and specificity of 95% when discriminating benign from malignant pathologies. The proposed hybrid combination PCAICA enhanced diagnostic discrimination, providing tumor probability maps, and intermediate PCA parameters reflected tissue optical properties.32Robust stability of networks of iISS systems: Construction of sumtype Lyapunov functions
(Hiroshi Ito, ZhongPing Jiang, Sergey Dashkovskiy and Björn S. Rüffer)
IEEE Trans. Autom. Control 58 (5), pp. 1192–1207, May 2013.
DOI:10.1109/TAC.2012.2231552.
[BibTeX]
@article{itojiangdashkovskiyruffer2013robuststabilityofnetworksofiisssystems:constructionofsumtypelyapunovfunctions,
abstract = {This paper gives a solution to the problem of verifying stability of networks consisting of integral inputtostate stable (iISS) subsystems. The iISS smallgain theorem developed recently has been restricted to interconnections of two subsystems. For largescale systems, stability criteria relying only on gaintype information that were previously developed address only inputtostate stable (ISS) subsystems. To address the stability problem involving iISS subsystems interconnected in general structure, this paper shows how to construct Lyapunov functions of the network by means of a sum of nonlinearly rescaled individual Lyapunov functions of subsystems under an appropriate smallgain condition.},
title = {Robust stability of networks of {iISS} systems: Construction of sumtype {L}yapunov functions},
author = {Hiroshi Ito and ZhongPing Jiang and Sergey Dashkovskiy and Bj{\"o}rn S. R{\"u}ffer},
month = {{M}ay},
year = {2013},
journal = {{{IEEE}} {T}rans. {A}utom. {C}ontrol},
pages = {1192–1207},
volume = {58},
number = {5},
doi = {10.1109/TAC.2012.2231552},
}
[Abstract]
This paper gives a solution to the problem of verifying stability of networks consisting of integral inputtostate stable (iISS) subsystems. The iISS smallgain theorem developed recently has been restricted to interconnections of two subsystems. For largescale systems, stability criteria relying only on gaintype information that were previously developed address only inputtostate stable (ISS) subsystems. To address the stability problem involving iISS subsystems interconnected in general structure, this paper shows how to construct Lyapunov functions of the network by means of a sum of nonlinearly rescaled individual Lyapunov functions of subsystems under an appropriate smallgain condition.33Locally most powerful invariant tests for correlation and sphericity of Gaussian vectors
(D. Ramírez, J. Vía, I. Santamaría and L. L. Scharf)
IEEE Trans. Inform. Theory 59 (4), pp. 2128–2141, April 2013.
DOI:10.1109/TIT.2012.2232705.
[BibTeX]
@article{RamirezViaSantamaria:2013:LocallyMostPowerfulInvariant,
abstract = {In this paper we study the existence of locally most powerful invariant tests (LMPIT) for the problem of testing the covariance structure of a set of Gaussian random vectors. The LMPIT is the optimal test for the case of close hypotheses, among those satisfying the invariances of the problem, and in practical scenarios can provide better performance than the typically used generalized likelihood ratio test (GLRT). The derivation of the LMPIT usually requires one to find the maximal invariant statistic for the detection problem and then derive its distribution under both hypotheses, which in general is a rather involved procedure. As an alternative, Wijsman's theorem provides the ratio of the maximal invariant densities without even finding an explicit expression for the maximal invariant. We first consider the problem of testing whether a set of Ndimensional Gaussian random vectors are uncorrelated or not, and show that the LMPIT is given by the Frobenius norm of the sample coherence matrix. Second, we study the case in which the vectors under the null hypothesis are uncorrelated and identically distributed, that is, the sphericity test for Gaussian vectors, for which we show that the LMPIT is given by the Frobenius norm of a normalized version of the sample covariance matrix. Finally, some numerical examples illustrate the performance of the proposed tests, which provide better results than their GLRT counterparts.},
title = {Locally most powerful invariant tests for correlation and sphericity of {G}aussian vectors},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a and L. L. Scharf},
month = {{A}pril},
year = {2013},
journal = {{IEEE} {T}rans.\ {I}nform.\ {T}heory},
pages = {2128–2141},
volume = {59},
number = {4},
doi = {10.1109/TIT.2012.2232705},
}
[Abstract]
In this paper we study the existence of locally most powerful invariant tests (LMPIT) for the problem of testing the covariance structure of a set of Gaussian random vectors. The LMPIT is the optimal test for the case of close hypotheses, among those satisfying the invariances of the problem, and in practical scenarios can provide better performance than the typically used generalized likelihood ratio test (GLRT). The derivation of the LMPIT usually requires one to find the maximal invariant statistic for the detection problem and then derive its distribution under both hypotheses, which in general is a rather involved procedure. As an alternative, Wijsman's theorem provides the ratio of the maximal invariant densities without even finding an explicit expression for the maximal invariant. We first consider the problem of testing whether a set of Ndimensional Gaussian random vectors are uncorrelated or not, and show that the LMPIT is given by the Frobenius norm of the sample coherence matrix. Second, we study the case in which the vectors under the null hypothesis are uncorrelated and identically distributed, that is, the sphericity test for Gaussian vectors, for which we show that the LMPIT is given by the Frobenius norm of a normalized version of the sample covariance matrix. Finally, some numerical examples illustrate the performance of the proposed tests, which provide better results than their GLRT counterparts.34Amplifyandforward strategies in the twoway relay channel with analog TxRx beamforming
(Christian Lameiro, Javier Vía and Ignacio Santamaría)
IEEE Trans. Veh. Techn. 62, pp. 642–654, February 2013.
DOI:10.1109/TVT.2012.2226612.
[BibTeX]
@article{LameiroViaSantamaria:2013:AmplifyandForwardStrategiesintheTwoWayRelay,
abstract = {In this paper, we study the multipleinput multipleoutput twoway relay channel (MIMOTWRC) when the nodes and relay use analog beamforming. Following the amplifyandforward (AF) strategy, the problem consists of finding the transmit and receive beamformers of the nodes and relay (as well as the power allocated to each one) that achieve the boundary of the optimal rate region. To solve it, we first express the optimal node beamformers in terms of relay beamformers and then show that the optimal rate region can efficiently be characterized using convex optimization techniques. We also extend our study to the multiplerelay scenario when the source nodes are single antenna and propose a distributed algorithm to compute the relay beamforming matrices. The proposed algorithm consists of solving two different subproblems. First, each individual TWRC is optimized independently. Next, a distributed beamforming is applied to make the signals from the relays add up coherently at the source nodes. Numerical examples are provided to illustrate the performance of the proposed techniques and to compare the performance of analog beamforming architectures against conventional MIMO schemes that operate at the baseband.},
title = {Amplifyandforward strategies in the twoway relay channel with analog {TxRx} beamforming},
author = {Lameiro, Christian and V{\'i}a, Javier and Santamar{\'i}a, Ignacio},
month = {{F}ebruary},
year = {2013},
journal = {IEEE Trans. Veh. Techn.},
pages = {642–654},
volume = {62},
doi = {10.1109/TVT.2012.2226612},
}
[Abstract]
In this paper, we study the multipleinput multipleoutput twoway relay channel (MIMOTWRC) when the nodes and relay use analog beamforming. Following the amplifyandforward (AF) strategy, the problem consists of finding the transmit and receive beamformers of the nodes and relay (as well as the power allocated to each one) that achieve the boundary of the optimal rate region. To solve it, we first express the optimal node beamformers in terms of relay beamformers and then show that the optimal rate region can efficiently be characterized using convex optimization techniques. We also extend our study to the multiplerelay scenario when the source nodes are single antenna and propose a distributed algorithm to compute the relay beamforming matrices. The proposed algorithm consists of solving two different subproblems. First, each individual TWRC is optimized independently. Next, a distributed beamforming is applied to make the signals from the relays add up coherently at the source nodes. Numerical examples are provided to illustrate the performance of the proposed techniques and to compare the performance of analog beamforming architectures against conventional MIMO schemes that operate at the baseband.35On the instantaneous frequency of Gaussian stochastic processes
(Patrik Wahlberg and Peter J. Schreier)
Probab. Math. Statist. 32, pp. 69–92, 2012. [BibTeX]
@article{WahlbergSchreier:2012:OntheinstantaneousfrequencyofGaussi,
abstract = {We study the instantaneous frequency (IF) of continuoustime, complexvalued, zeromean, proper, meansquare differentiable, nonstationary Gaussian stochastic processes. We compute the probability density function for the IF for fixed time, which generalizes a result known for widesense stationary processes to nonstationary processes. For a fixed point in time, the IF has either zero or infinite variance. For harmonizable processes, we obtain as a consequence the result that the mean of the IF, for fixed time, is the normalized firstorder frequency moment of the Wigner spectrum.},
title = {On the instantaneous frequency of {Gaussian} stochastic processes},
author = {Wahlberg, Patrik and Schreier, Peter J.},
year = {2012},
journal = {{P}robab.\ {M}ath.\ {S}tatist.},
pages = {69–92},
volume = {32},
}
[Abstract]
We study the instantaneous frequency (IF) of continuoustime, complexvalued, zeromean, proper, meansquare differentiable, nonstationary Gaussian stochastic processes. We compute the probability density function for the IF for fixed time, which generalizes a result known for widesense stationary processes to nonstationary processes. For a fixed point in time, the IF has either zero or infinite variance. For harmonizable processes, we obtain as a consequence the result that the mean of the IF, for fixed time, is the normalized firstorder frequency moment of the Wigner spectrum.36Development and integration of xerogel polymeric absorbance microfilters into labonchip systems
(Ester CarregalRomero, Cesar FernandezSanchez, Alma Eguizabal, Stefanie Demming, Stephanus Büttgenbach and Andreu Llobera)
Opt. Express 20 (21), pp. 23700–23719, October 2012.
DOI:10.1364/OE.20.023700.
[BibTeX]
@article{CarregalromeroFernandessanchezEguizabal:2012:Developmentandintegrationofxerogelpolymeric,
abstract = {This work reports on the implementation of different absorption microfilters based on a dyedoped hybrid organicinorganic xerogel polymeric material synthesized by the solgel process. Microstructures containing eight different filter widths were fabricated in polydimethylsiloxane (PDMS), bonded to glass substrates and filled with the corresponding dye doped polymeric material by a soft lithography approach. The filtering capacity as a function of dye concentration and filter width was studied and revealed a linear dependence with both parameters, as expected according to the BeerLambert law. Zero passband transmittance values and relatively sharp stopband regions were achieved with all the filters, also showing rejection levels between ?6 dB and ?55 dB. Finally, such filters were monolithically integrated into a disposable fluorescencebased photonic labonachip (PhLoC) approach. Calibration curves carried out with a model fluorophore target analyte showed an over twofold increase in sensitivity and a thirtyfold decrease of the limit of detection (LOD) compared with the values recorded using the same PhLoC system but without the polymeric filter structure. The results presented herein clearly indicate the feasibility of these xerogelbased absorbance filtering structures for being applied as lowcost optical components that can be easily incorporated into disposable fluorescencebased photonic lab on a chip systems},
title = {Development and integration of xerogel polymeric absorbance microfilters into labonchip systems},
author = {Ester CarregalRomero and Cesar FernandezSanchez and Alma Eguizabal and Stefanie Demming and Stephanus B{\"u}ttgenbach and Andreu Llobera},
month = {{O}ctober},
year = {2012},
journal = {Opt. Express},
pages = {23700–23719},
volume = {20},
number = {21},
doi = {10.1364/OE.20.023700},
}
[Abstract]
This work reports on the implementation of different absorption microfilters based on a dyedoped hybrid organicinorganic xerogel polymeric material synthesized by the solgel process. Microstructures containing eight different filter widths were fabricated in polydimethylsiloxane (PDMS), bonded to glass substrates and filled with the corresponding dye doped polymeric material by a soft lithography approach. The filtering capacity as a function of dye concentration and filter width was studied and revealed a linear dependence with both parameters, as expected according to the BeerLambert law. Zero passband transmittance values and relatively sharp stopband regions were achieved with all the filters, also showing rejection levels between ?6 dB and ?55 dB. Finally, such filters were monolithically integrated into a disposable fluorescencebased photonic labonachip (PhLoC) approach. Calibration curves carried out with a model fluorophore target analyte showed an over twofold increase in sensitivity and a thirtyfold decrease of the limit of detection (LOD) compared with the values recorded using the same PhLoC system but without the polymeric filter structure. The results presented herein clearly indicate the feasibility of these xerogelbased absorbance filtering structures for being applied as lowcost optical components that can be easily incorporated into disposable fluorescencebased photonic lab on a chip systems37Linear precoding for MIMO systems with lowcomplexity receivers
(Jun Tong, Peter J. Schreier and Steven R. Weller)
IEEE Trans. Wireless Comm. 11 (8), pp. 2828–2837, August 2012.
DOI:10.1109/TWC.2012.070912.110877.
[BibTeX]
@article{TongSchreierWeller:2012:LinearprecodingforMIMOsystemswithl,
abstract = {This paper considers large multipleinput multipleoutput (MIMO) communication systems with linear precoding and linear minimum meansquared error (LMMSE) equalization based on the iterative conjugate gradient (CG) algorithm. Convergence of the CG algorithm is fast when the eigenvalues of the received signal's covariance matrix are clustered, suggesting that meansquared error and receiver complexity can be managed with judicious precoder design. In order to accelerate convergence of an iterative CG receiver, we incorporate constraints on two measures of eigenvalue clustering into the precoder design. Closedform solutions to the optimal precoders are derived using majorization theory and convex optimization techniques. We show that if there are constraints on receiver complexity, the proposed precoders can improve performance for large MIMO systems operating over slowly timevarying fading channels.},
title = {Linear precoding for {MIMO} systems with lowcomplexity receivers},
author = {Tong, Jun and Schreier, Peter J. and Weller, Steven R.},
month = {{A}ugust},
year = {2012},
journal = {{IEEE} {T}rans.\ {W}ireless {C}omm.},
pages = {2828–2837},
volume = {11},
number = {8},
doi = {10.1109/TWC.2012.070912.110877},
}
[Abstract]
This paper considers large multipleinput multipleoutput (MIMO) communication systems with linear precoding and linear minimum meansquared error (LMMSE) equalization based on the iterative conjugate gradient (CG) algorithm. Convergence of the CG algorithm is fast when the eigenvalues of the received signal's covariance matrix are clustered, suggesting that meansquared error and receiver complexity can be managed with judicious precoder design. In order to accelerate convergence of an iterative CG receiver, we incorporate constraints on two measures of eigenvalue clustering into the precoder design. Closedform solutions to the optimal precoders are derived using majorization theory and convex optimization techniques. We show that if there are constraints on receiver complexity, the proposed precoders can improve performance for large MIMO systems operating over slowly timevarying fading channels.38Variability of moisture in coarse woody debris from several ecologically important tree species of the temperate zone of Europe
(V. Pichler, M. Homolák, W. Skierucha, M. Pichlerová, D. Ramírez, J. Gregor and P. Jaloviar)
Ecohydrology 5 (4), pp. 424–434, July 2012.
DOI:10.1002/eco.235.
[BibTeX]
@article{PichlerHomolakSkierucha:2012:Variabilityofmoistureincoarsewoody,
abstract = {Deadwood moisture affects multiple functions of downed logs in forest ecosystems. They include provision of habitats for xylobionts, additional water stores and organic carbon stocks. In contrast to Northern American forests, little is known about moisture variability in downed logs of important tree species within the Temperate Zone of Europe. Therefore, our study aimed at elucidating this variability according to species, site and decay class (DC). Measurements were taken by TDR during two vegetation periods in eight Carpathian natural forests representing distinct site conditions, ranging from xerothermophilous to subalpine. Downed logs of \emph{Quercus} spp., \emph{Abies alba} Mill., \emph{Fagus sylvatica} L., and \emph{Picea abies} L., belonging to various DCs, were selected and instrumented with TDR probes. Species and DCspecific TDR calibration showed the importance of intrinsic wood porosity. The course of deadwood moisture consisted of drying during the early decay stage, except for \emph{A. alba} and \emph{F. sylvatica}, and an intense water reabsorption at later decay stages. Average moisture for all species and sites displayed seasonal trends, reflecting the occurrence of precipitation clusters and dry periods, as well as shortterm fluctuations. Crossspectral analysis revealed that both sapwood and heartwood participated in wetting and drying processes, but only after reaching an advanced stage of decay. New findings can be applied in interpreting, modelling and predicting deadwood water stores, habitat properties and respiration.},
title = {Variability of moisture in coarse woody debris from several ecologically important tree species of the temperate zone of {E}urope},
author = {V. Pichler and M. Homol{\'a}k and W. Skierucha and M. Pichlerov{\'a} and D. Ram{\'i}rez and J. Gregor and P. Jaloviar},
month = {{J}uly},
year = {2012},
journal = {{E}cohydrology},
pages = {424–434},
volume = {5},
number = {4},
doi = {10.1002/eco.235},
}
[Abstract]
Deadwood moisture affects multiple functions of downed logs in forest ecosystems. They include provision of habitats for xylobionts, additional water stores and organic carbon stocks. In contrast to Northern American forests, little is known about moisture variability in downed logs of important tree species within the Temperate Zone of Europe. Therefore, our study aimed at elucidating this variability according to species, site and decay class (DC). Measurements were taken by TDR during two vegetation periods in eight Carpathian natural forests representing distinct site conditions, ranging from xerothermophilous to subalpine. Downed logs of Quercus spp., Abies alba Mill., Fagus sylvatica L., and Picea abies L., belonging to various DCs, were selected and instrumented with TDR probes. Species and DCspecific TDR calibration showed the importance of intrinsic wood porosity. The course of deadwood moisture consisted of drying during the early decay stage, except for A. alba and F. sylvatica, and an intense water reabsorption at later decay stages. Average moisture for all species and sites displayed seasonal trends, reflecting the occurrence of precipitation clusters and dry periods, as well as shortterm fluctuations. Crossspectral analysis revealed that both sapwood and heartwood participated in wetting and drying processes, but only after reaching an advanced stage of decay. New findings can be applied in interpreting, modelling and predicting deadwood water stores, habitat properties and respiration.39Design and analysis of large MIMO systems with Krylov subspace receivers
(Jun Tong, Peter J. Schreier and Steven R. Weller)
IEEE Trans. Signal Process. 60 (5), pp. 2482–2493, May 2012.
DOI:10.1109/TSP.2012.2187287.
[BibTeX]
@article{TongSchreierWeller:2012:DesignandanalysisoflargeMIMOsystem,
abstract = {This paper studies large multipleinput multipleoutput (MIMO) communication systems with linear precoding and reducedrank Krylov subspace receivers. We design precoders and analyze their performance by exploiting largedimensional random matrix theory. We first devise lowcomplexity precoding schemes that can improve performance of lowrank Krylov subspace receivers in the regime of high signaltonoise ratio (SNR). We then introduce a potential theorybased method for analyzing the convergence behavior of the meansquared error (MSE) for various transmission schemes. This method can be applied to a broader range of problems compared to previous analytical tools. The analysis reveals that the MSE decreases super exponentially with the rank of the receiver. Numerical examples show that the proposed precoders can outperform conventional precoders when lowrank Krylov subspace receivers are used, and that the performance of such receivers can be accurately predicted.},
title = {Design and analysis of large {MIMO} systems with {Krylov} subspace receivers},
author = {Tong, Jun and Schreier, Peter J. and Weller, Steven R.},
month = {{M}ay},
year = {2012},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {2482–2493},
volume = {60},
number = {5},
doi = {10.1109/TSP.2012.2187287},
}
[Abstract]
This paper studies large multipleinput multipleoutput (MIMO) communication systems with linear precoding and reducedrank Krylov subspace receivers. We design precoders and analyze their performance by exploiting largedimensional random matrix theory. We first devise lowcomplexity precoding schemes that can improve performance of lowrank Krylov subspace receivers in the regime of high signaltonoise ratio (SNR). We then introduce a potential theorybased method for analyzing the convergence behavior of the meansquared error (MSE) for various transmission schemes. This method can be applied to a broader range of problems compared to previous analytical tools. The analysis reveals that the MSE decreases super exponentially with the rank of the receiver. Numerical examples show that the proposed precoders can outperform conventional precoders when lowrank Krylov subspace receivers are used, and that the performance of such receivers can be accurately predicted.40Stability verification for monotone systems using homotopy algorithms
(B. S. Rüffer and Fabian R. Wirth)
Numer. Algorithms 58 (4), pp. 529–543, 2011.
DOI:10.1007/s1107501194683.
[BibTeX]
@article{rufferwirth2011stabilityverificationformonotonesystemsusinghomotopyalgorithms,
abstract = {A monotone selfmapping of the nonnegative orthant induces a monotone discretetime dynamical system which evolves on the same orthant. If with respect to this system the origin is attractive then there must exist points whose image under the monotone map is strictly smaller than the original point, in the componentwise partial ordering. Here it is shown how such points can be found numerically, leading to a recipe to compute order intervals that are contained in the region of attraction and where the monotone map acts essentially as a contraction. An important application is the numerical verification of socalled generalized smallgain conditions that appear in the stability theory of largescale systems.},
title = {Stability verification for monotone systems using homotopy algorithms},
author = {R{\"u}ffer, B. S. and Wirth, Fabian R.},
year = {2011},
journal = {{N}umer. {A}lgorithms},
pages = {529–543},
volume = {58},
number = {4},
doi = {10.1007/s1107501194683},
}
[Abstract]
A monotone selfmapping of the nonnegative orthant induces a monotone discretetime dynamical system which evolves on the same orthant. If with respect to this system the origin is attractive then there must exist points whose image under the monotone map is strictly smaller than the original point, in the componentwise partial ordering. Here it is shown how such points can be found numerically, leading to a recipe to compute order intervals that are contained in the region of attraction and where the monotone map acts essentially as a contraction. An important application is the numerical verification of socalled generalized smallgain conditions that appear in the stability theory of largescale systems.41Locally stationary harmonizable complex improper stochastic processes
(Patrik Wahlberg and Peter J. Schreier)
J. Time Ser. Anal. 32 (1), pp. 33–46, Blackwell Publishing Ltd, 2011.
DOI:10.1111/j.14679892.2010.00682.x.
[BibTeX]
@article{WahlbergSchreier:2011:Locallystationaryharmonizablecomplex,
abstract = {This article concerns continuoustime secondorder complexvalued improper stochastic processes that are harmonizable and locally stationary in Silverman's sense. We study necessary and sufficient conditions for the property of local stationarity in the time and frequency domains. A sufficient condition by Silverman is generalized and extended to the improper case. We obtain a result on the absolute continuity of the complementary spectral measure with respect to the spectral measure, which is related to a spectral characterization of improper widesense stationary processes.},
title = {Locally stationary harmonizable complex improper stochastic processes},
author = {Wahlberg, Patrik and Schreier, Peter J.},
year = {2011},
journal = {{J}.\ {T}ime {S}er.\ {A}nal.},
pages = {33–46},
volume = {32},
number = {1},
doi = {10.1111/j.14679892.2010.00682.x},
publisher = {{B}lackwell {P}ublishing {Ltd}},
}
[Abstract]
This article concerns continuoustime secondorder complexvalued improper stochastic processes that are harmonizable and locally stationary in Silverman's sense. We study necessary and sufficient conditions for the property of local stationarity in the time and frequency domains. A sufficient condition by Silverman is generalized and extended to the improper case. We obtain a result on the absolute continuity of the complementary spectral measure with respect to the spectral measure, which is related to a spectral characterization of improper widesense stationary processes.42Complexvalued signal processing: the proper way to deal with impropriety
(Tülay Adali, Peter J. Schreier and Louis L. Scharf)
IEEE Trans. Signal Process. 59 (11), pp. 5101–5125, November 2011.
DOI:10.1109/TSP.2011.2162954.
[BibTeX]
@article{AdaliSchreierScharf:2011:ComplexValuedSignalProcessing:ThePr,
abstract = {Complexvalued signals occur in many areas of science and engineering and are thus of fundamental interest. In the past, it has often been assumed, usually implicitly, that complex random signals are proper or circular. A proper complex random variable is uncorrelated with its complex conjugate, and a circular complex random variable has a probability distribution that is invariant under rotation in the complex plane. While these assumptions are convenient because they simplify computations, there are many cases where proper and circular random signals are very poor models of the underlying physics. When taking impropriety and noncircularity into account, the right type of processing can provide significant performance gains. There are two key ingredients in the statistical signal processing of complexvalued data: 1) utilizing the complete statistical characterization of complexvalued random signals; and 2) the optimization of realvalued cost functions with respect to complex parameters. In this overview article, we review the necessary tools, among which are widely linear transformations, augmented statistical descriptions, and Wirtinger calculus. We also present some selected recent developments in the field of complexvalued signal processing, addressing the topics of model selection, filtering, and source separation.},
title = {Complexvalued signal processing: the proper way to deal with impropriety},
author = {Adali, T{\"u}lay and Schreier, Peter J. and Scharf, Louis L.},
month = {{N}ovember},
year = {2011},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {5101–5125},
volume = {59},
number = {11},
doi = {10.1109/TSP.2011.2162954},
}
[Abstract]
Complexvalued signals occur in many areas of science and engineering and are thus of fundamental interest. In the past, it has often been assumed, usually implicitly, that complex random signals are proper or circular. A proper complex random variable is uncorrelated with its complex conjugate, and a circular complex random variable has a probability distribution that is invariant under rotation in the complex plane. While these assumptions are convenient because they simplify computations, there are many cases where proper and circular random signals are very poor models of the underlying physics. When taking impropriety and noncircularity into account, the right type of processing can provide significant performance gains. There are two key ingredients in the statistical signal processing of complexvalued data: 1) utilizing the complete statistical characterization of complexvalued random signals; and 2) the optimization of realvalued cost functions with respect to complex parameters. In this overview article, we review the necessary tools, among which are widely linear transformations, augmented statistical descriptions, and Wirtinger calculus. We also present some selected recent developments in the field of complexvalued signal processing, addressing the topics of model selection, filtering, and source separation.43Detection of rankP signals in cognitive radio networks with uncalibrated multiple antennas
(D. Ramírez, G. VazquezVilar, R. LópezValcarce, J. Vía and I. Santamaría)
IEEE Trans. Signal Process. 59 (8), pp. 3764–3774, August 2011.
DOI:10.1109/TSP.2011.2146779.
[BibTeX]
@article{RamirezVazquezVilarLopezValcarce:2011:DetectionofrankPsignalsinCognitive,
abstract = {Spectrum sensing is a key component of the Cognitive Radio paradigm. Primary signals are typically detected with uncalibrated receivers at signaltonoise ratios (SNRs) well below decodability levels. Multiantenna detectors exploit spatial independence of receiver thermal noise to boost detection performance and robustness. We study the problem of detecting a Gaussian signal with rank$P$ unknown spatial covariance matrix in spatially uncorrelated Gaussian noise with unknown covariance using multiple antennas. The generalized likelihood ratio test (GLRT) is derived for two scenarios. In the first one, the noises at all antennas are assumed to have the same (unknown) variance, whereas in the second, a generic diagonal noise covariance matrix is allowed in order to accommodate calibration uncertainties in the different antenna frontends. In the latter case, the GLRT statistic must be obtained numerically, for which an efficient method is presented. Furthermore, for asymptotically low SNR, it is shown that the GLRT does admit a closed form, and the resulting detector performs well in practice. Extensions are presented in order to account for unknown temporal correlation in both signal and noise, as well as frequencyselective channels.},
title = {Detection of {rank$P$} signals in cognitive radio networks with uncalibrated multiple antennas},
author = {D. Ram{\'i}rez and G. VazquezVilar and R. L{\'o}pezValcarce and J. V{\'i}a and I. Santamar{\'i}a},
month = {{A}ugust},
year = {2011},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {3764–3774},
volume = {59},
number = {8},
doi = {10.1109/TSP.2011.2146779},
}
[Abstract]
Spectrum sensing is a key component of the Cognitive Radio paradigm. Primary signals are typically detected with uncalibrated receivers at signaltonoise ratios (SNRs) well below decodability levels. Multiantenna detectors exploit spatial independence of receiver thermal noise to boost detection performance and robustness. We study the problem of detecting a Gaussian signal with rankP unknown spatial covariance matrix in spatially uncorrelated Gaussian noise with unknown covariance using multiple antennas. The generalized likelihood ratio test (GLRT) is derived for two scenarios. In the first one, the noises at all antennas are assumed to have the same (unknown) variance, whereas in the second, a generic diagonal noise covariance matrix is allowed in order to accommodate calibration uncertainties in the different antenna frontends. In the latter case, the GLRT statistic must be obtained numerically, for which an efficient method is presented. Furthermore, for asymptotically low SNR, it is shown that the GLRT does admit a closed form, and the resulting detector performs well in practice. Extensions are presented in order to account for unknown temporal correlation in both signal and noise, as well as frequencyselective channels.44Frequencydomain methodology for measuring MIMO channels using a generic test bed
(J. Gutiérrez, Ó. González, J. Pérez, D. Ramírez, L. Vielva, J. Ibáñez and I. Santamaría)
IEEE Trans. Instrum. Meas. 60 (3), pp. 827–838, April 2011.
DOI:10.1109/TIM.2010.2082432.
[BibTeX]
@article{GutierrezGonzalezPerez:2011:FrequencyDomainMethodologyforMeasuringMIMO,
abstract = {A multipleinput multipleoutput (MIMO) frequencydomain channel measurement methodology is pre sented. This methodology can be implemented in any transmit/receive hardware consisting of radio frequency modules and baseband digital processing units. It involves the transmission and reception of frequency and phaseoptimized complex exponentials through antenna arrays, followed by an offline frequency estimation, which makes additional synchronization circuitry unnecesary. To test the feasibility of this method, a series of measurements is presented, employing a $4 \times 4$ dualband (2.4/5 GHz) MIMO test bed.},
title = {Frequencydomain methodology for measuring {MIMO} channels using a generic test bed},
author = {J. Guti{\'e}rrez and {\'O}. Gonz{\'a}lez and J. P{\'e}rez and D. Ram{\'i}rez and L. Vielva and J. Ib{\'a}{\~n}ez and I. Santamar{\'i}a},
month = {{A}pril},
year = {2011},
journal = {{IEEE} {T}rans. {I}nstrum. {M}eas.},
pages = {827–838},
volume = {60},
number = {3},
doi = {10.1109/TIM.2010.2082432},
}
[Abstract]
A multipleinput multipleoutput (MIMO) frequencydomain channel measurement methodology is pre sented. This methodology can be implemented in any transmit/receive hardware consisting of radio frequency modules and baseband digital processing units. It involves the transmission and reception of frequency and phaseoptimized complex exponentials through antenna arrays, followed by an offline frequency estimation, which makes additional synchronization circuitry unnecesary. To test the feasibility of this method, a series of measurements is presented, employing a 4 times 4 dualband (2.4/5 GHz) MIMO test bed.45Performance analysis of superposition coded modulation
(Jun Tong and Li Ping)
Physical Comm. 3 (3), pp. 147–155, 2010.
DOI:10.1016/j.phycom.2009.08.008.
[BibTeX]
@article{TongPing:2010:Performanceanalysisofsuperpositionco,
abstract = {This paper presents a comprehensive analysis of superposition coded modulation (SCM). Two types of SCM schemes, i.e., the singlecode SCM (SCSCM) and multicode SCM (MCSCM), are analyzed. The basic features of SCM are described, followed by the informationtheoretic analysis. Different encoding/decoding strategies are compared from the capacity point of view. A semianalytical evolution technique is proposed to track the convergence behavior of iterative decoding. Analytical errorrate analysis is then conducted to predict the asymptotic performance. Numerous examples demonstrate that the analysis tools discussed in this paper can provide reasonably accurate performance prediction for SCM schemes.},
title = {Performance analysis of superposition coded modulation},
author = {Tong, Jun and Ping, Li},
year = {2010},
journal = {{P}hysical {C}omm.},
pages = {147–155},
volume = {3},
number = {3},
doi = {10.1016/j.phycom.2009.08.008},
}
[Abstract]
This paper presents a comprehensive analysis of superposition coded modulation (SCM). Two types of SCM schemes, i.e., the singlecode SCM (SCSCM) and multicode SCM (MCSCM), are analyzed. The basic features of SCM are described, followed by the informationtheoretic analysis. Different encoding/decoding strategies are compared from the capacity point of view. A semianalytical evolution technique is proposed to track the convergence behavior of iterative decoding. Analytical errorrate analysis is then conducted to predict the asymptotic performance. Numerous examples demonstrate that the analysis tools discussed in this paper can provide reasonably accurate performance prediction for SCM schemes.46Detection of spatially correlated Gaussian time series
(D. Ramírez, J. Vía, I. Santamaría and L. L. Scharf)
IEEE Trans. Signal Process. 58 (10), pp. 5006–5015, October 2010.
DOI:10.1109/TSP.2010.2053360.
[BibTeX]
@article{RamirezViaSantamaria:2010:DetectionofSpatiallyCorrelatedGaussian,
abstract = {This work addresses the problem of deciding whether a set of realizations of a vectorvalued time series with unknown temporal correlation are spatially correlated or not. For wide sense stationary (WSS) Gaussian processes, this is a problem of deciding between two different power spectral density matrices, one of them diagonal. Specifically, we show that for arbitrary Gaussian processes (not necessarily WSS) the generalized likelihood ratio test (GLRT) is given by the quotient between the determinant of the sample spacetime covariance matrix and the determinant of its blockdiagonal version. Furthermore, for WSS processes, we present an asymptotic frequencydomain approximation of the GLRT which is given by a function of the Hadamard ratio (quotient between the determinant of a matrix and the product of the elements of the main diagonal) of the estimated power spectral density matrix. The Hadamard ratio is known to be the GLRT detector for vectorvalued random variables and, therefore, what this paper shows is how frequencydependent Hadamard ratios must be merged into a single test statistic when the vectorvalued random variable is replaced by a vectorvalued time series with temporal correlation. For bivariate time series, the derived frequency domain detector can be rewritten as a function of the wellknown magnitude squared coherence (MSC) spectrum, which suggests a straightforward extension of the MSC spectrum to the general case of multivariate time series. Finally, the performance of the proposed method is illustrated by means of simulations.},
title = {Detection of spatially correlated {G}aussian time series},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a and L. L. Scharf},
month = {{O}ctober},
year = {2010},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {5006–5015},
volume = {58},
number = {10},
doi = {10.1109/TSP.2010.2053360},
}
[Abstract]
This work addresses the problem of deciding whether a set of realizations of a vectorvalued time series with unknown temporal correlation are spatially correlated or not. For wide sense stationary (WSS) Gaussian processes, this is a problem of deciding between two different power spectral density matrices, one of them diagonal. Specifically, we show that for arbitrary Gaussian processes (not necessarily WSS) the generalized likelihood ratio test (GLRT) is given by the quotient between the determinant of the sample spacetime covariance matrix and the determinant of its blockdiagonal version. Furthermore, for WSS processes, we present an asymptotic frequencydomain approximation of the GLRT which is given by a function of the Hadamard ratio (quotient between the determinant of a matrix and the product of the elements of the main diagonal) of the estimated power spectral density matrix. The Hadamard ratio is known to be the GLRT detector for vectorvalued random variables and, therefore, what this paper shows is how frequencydependent Hadamard ratios must be merged into a single test statistic when the vectorvalued random variable is replaced by a vectorvalued time series with temporal correlation. For bivariate time series, the derived frequency domain detector can be rewritten as a function of the wellknown magnitude squared coherence (MSC) spectrum, which suggests a straightforward extension of the MSC spectrum to the general case of multivariate time series. Finally, the performance of the proposed method is illustrated by means of simulations.47Iterative soft compensation for OFDM systems with clipping and superposition coded modulation
(Jun Tong, Li Ping, Zhonghao Zhang and Vijay K. Bhargava)
IEEE Trans. Comm. 58 (10), pp. 2861–2870, October 2010.
DOI:10.1109/TCOMM.2010.083110.09296.
[BibTeX]
@article{TongPingZhang:2010:IterativesoftcompensationforOFDMsys,
abstract = {This paper deals with the clipping method used in orthogonal frequencydivision multiplexing (OFDM) systems to reduce the peaktoaverage power ratio (PAPR). An iterative soft compensation method is proposed to mitigate the clipping distortion, which can outperform conventional treatments. The impact of signaling schemes on the residual clipping noise power is studied via the symbol variance analysis. It is found that superposition coded modulation (SCM) can minimize the residual clipping noise power among all possible signaling schemes. This indicates that SCMbased OFDM systems are more robust to clipping effect than other alternatives when soft compensation is applied. It is also shown that a multicode SCM scheme can further reduce the clipping effect and its overall performance can be quickly evaluated using a semianalytical evolution method. Numerical examples are provided to verify the analysis.},
title = {Iterative soft compensation for {OFDM} systems with clipping and superposition coded modulation},
author = {Tong, Jun and Ping, Li and Zhang, Zhonghao and Bhargava, Vijay K.},
month = {{O}ctober},
year = {2010},
journal = {{IEEE} {T}rans.\ {C}omm.},
pages = {2861–2870},
volume = {58},
number = {10},
doi = {10.1109/TCOMM.2010.083110.09296},
}
[Abstract]
This paper deals with the clipping method used in orthogonal frequencydivision multiplexing (OFDM) systems to reduce the peaktoaverage power ratio (PAPR). An iterative soft compensation method is proposed to mitigate the clipping distortion, which can outperform conventional treatments. The impact of signaling schemes on the residual clipping noise power is studied via the symbol variance analysis. It is found that superposition coded modulation (SCM) can minimize the residual clipping noise power among all possible signaling schemes. This indicates that SCMbased OFDM systems are more robust to clipping effect than other alternatives when soft compensation is applied. It is also shown that a multicode SCM scheme can further reduce the clipping effect and its overall performance can be quickly evaluated using a semianalytical evolution method. Numerical examples are provided to verify the analysis.48Properness and widely linear processing of quaternion random vectors
(J. Vía, D. Ramírez and I. Santamaría)
IEEE Trans. Inform. Theory 56 (7), pp. 3502–3515, July 2010.
DOI:10.1109/TIT.2010.2048440.
[BibTeX]
@article{ViaRamirezSantamaria:2010:PropernessandWidelyLinearProcessing,
abstract = {In this paper, the secondorder circularity of quater nion random vectors is analyzed. Unlike the case of complex vectors, there exist three different kinds of quaternion properness, which are based on the vanishing of three different complemen tary covariance matrices. The different kinds of properness have direct implications on the Cayley–Dickson representation of the quaternion vector, and also on several wellknown multivariate statistical analysis methods. In particular, the quaternion exten sions of the partial least squares (PLS), multiple linear regression (MLR) and canonical correlation analysis (CCA) techniques are analyzed, showing that, in general, the optimal linear processing is \emph{fullwidely linear}. However, in the case of jointly $\mathbb{Q}$proper or $\mathbb{C}^{\eta}$proper vectors, the optimal processing reduces, respectively, to the \emph{conventional} or \emph{semiwidely linear} processing. Finally, a measure for the degree of improperness of a quaternion random vector is proposed, which is based on the Kullback–Leibler diver gence between two zeromean Gaussian distributions, one of them with the actual augmented covariance matrix, and the other with its closest proper version. This measure quantifies the entropy loss due to the improperness of the quaternion vector, and it admits an intuitive geometrical interpretation based on Kullback–Leibler projections onto sets of proper augmented covariance matrices.},
title = {Properness and widely linear processing of quaternion random vectors},
author = {J. V{\'i}a and D. Ram{\'i}rez and I. Santamar{\'i}a},
month = {{J}uly},
year = {2010},
journal = {{IEEE} {T}rans.\ {I}nform.\ {T}heory},
pages = {3502–3515},
volume = {56},
number = {7},
doi = {10.1109/TIT.2010.2048440},
}
[Abstract]
In this paper, the secondorder circularity of quater nion random vectors is analyzed. Unlike the case of complex vectors, there exist three different kinds of quaternion properness, which are based on the vanishing of three different complemen tary covariance matrices. The different kinds of properness have direct implications on the Cayley–Dickson representation of the quaternion vector, and also on several wellknown multivariate statistical analysis methods. In particular, the quaternion exten sions of the partial least squares (PLS), multiple linear regression (MLR) and canonical correlation analysis (CCA) techniques are analyzed, showing that, in general, the optimal linear processing is fullwidely linear. However, in the case of jointly mathbbQproper or mathbbC^etaproper vectors, the optimal processing reduces, respectively, to the conventional or semiwidely linear processing. Finally, a measure for the degree of improperness of a quaternion random vector is proposed, which is based on the Kullback–Leibler diver gence between two zeromean Gaussian distributions, one of them with the actual augmented covariance matrix, and the other with its closest proper version. This measure quantifies the entropy loss due to the improperness of the quaternion vector, and it admits an intuitive geometrical interpretation based on Kullback–Leibler projections onto sets of proper augmented covariance matrices.49On Wiener filtering of certain locally stationary stochastic processes
(Patrik Wahlberg and Peter J. Schreier)
Signal Process. 90 (3), pp. 885–890, March 2010.
DOI:10.1016/j.sigpro.2009.09.013.
[BibTeX]
@article{WahlbergSchreier:2010:OnWienerfilteringofcertainlocallys,
abstract = {We study linear minimum mean squared error filters for continuoustime secondorder stochastic processes that are locally stationary in Silverman's sense. We show that the optimal filter is rarely locally stationary even when the covariance functions have Gaussian shape. Using Mehler's formula we derive series expansions of the filter kernel for locally stationary covariances that are determined by Gaussians.},
title = {On {Wiener} filtering of certain locally stationary stochastic processes},
author = {Wahlberg, Patrik and Schreier, Peter J.},
month = {{M}arch},
year = {2010},
journal = {{S}ignal {P}rocess.},
pages = {885–890},
volume = {90},
number = {3},
doi = {10.1016/j.sigpro.2009.09.013},
}
[Abstract]
We study linear minimum mean squared error filters for continuoustime secondorder stochastic processes that are locally stationary in Silverman's sense. We show that the optimal filter is rarely locally stationary even when the covariance functions have Gaussian shape. Using Mehler's formula we derive series expansions of the filter kernel for locally stationary covariances that are determined by Gaussians.50Gabor discretization of the Weyl product for modulation spaces and filtering of nonstationary stochastic processes
(Patrik Wahlberg and Peter J. Schreier)
Appl. Comput. Harmon. Anal. 26 (1), pp. 97–120, 2009.
DOI:10.1016/j.acha.2008.02.005.
[BibTeX]
@article{WahlbergSchreier:2009:GabordiscretizationoftheWeylproduct,
abstract = {We discretize the Weyl product acting on symbols of modulation spaces, using a Gabor frame defined by a Gaussian function. With one factor fixed, the Weyl product is equivalent to a matrix multiplication on the Gabor coefficient level. If the fixed factor belongs to the weighted Sj{\"o}strand space M ω ∞ , 1 , then the matrix has polynomial or exponential offdiagonal decay, depending on the weight ω. Moreover, if its operator is invertible on L 2 , the inverse matrix has similar decay properties. The results are applied to the equation for the linear minimum mean square error filter for estimation of a nonstationary secondorder stochastic process from a noisy observation. The resulting formula for the Gabor coefficients of the Weyl symbol for the optimal filter may be interpreted as a time–frequency version of the filter for widesense stationary processes, known as the noncausal Wiener filter.},
title = {Gabor discretization of the {Weyl} product for modulation spaces and filtering of nonstationary stochastic processes},
author = {Wahlberg, Patrik and Schreier, Peter J.},
year = {2009},
journal = {{A}ppl.\ {C}omput.\ {H}armon.\ {A}nal.},
pages = {97–120},
volume = {26},
number = {1},
doi = {10.1016/j.acha.2008.02.005},
}
[Abstract]
We discretize the Weyl product acting on symbols of modulation spaces, using a Gabor frame defined by a Gaussian function. With one factor fixed, the Weyl product is equivalent to a matrix multiplication on the Gabor coefficient level. If the fixed factor belongs to the weighted Sj"ostrand space M ω ∞ , 1 , then the matrix has polynomial or exponential offdiagonal decay, depending on the weight ω. Moreover, if its operator is invertible on L 2 , the inverse matrix has similar decay properties. The results are applied to the equation for the linear minimum mean square error filter for estimation of a nonstationary secondorder stochastic process from a noisy observation. The resulting formula for the Gabor coefficients of the Weyl symbol for the optimal filter may be interpreted as a time–frequency version of the filter for widesense stationary processes, known as the noncausal Wiener filter.51Superposition coded modulation and iterative linear MMSE detection
(Li Ping, Jun Tong, Xiaojun Yuan and Qinghua Guo)
IEEE J. Select. Areas Comm. 27 (6), pp. 995–1004, August 2009.
DOI:10.1109/JSAC.2009.090817.
[BibTeX]
@article{PingTongYuan:2009:Superpositioncodedmodulationanditera,
abstract = {We study superposition coded modulation (SCM) with iterative linear minimummeansquareerror (LMMSE) detection. We show that SCM offers an attractive solution for highly complicated transmission environments with severe interference. We analyze the impact of signaling schemes on the performance of iterative LMMSE detection. We prove that among all possible signaling methods, SCM maximizes the output signaltonoise/ interference ratio (SNIR) in the LMMSE estimates during iterative detection. Numerical examples are used to demonstrate that SCM outperforms other signaling methods when iterative LMMSE detection is applied to multiuser/multiantenna/multipath channels.},
title = {Superposition coded modulation and iterative linear {MMSE} detection},
author = {Ping, Li and Tong, Jun and Yuan, Xiaojun and Guo, Qinghua},
month = {{A}ugust},
year = {2009},
journal = {{IEEE} {J}.\ {S}elect.\ {A}reas {C}omm.},
pages = {995–1004},
volume = {27},
number = {6},
doi = {10.1109/JSAC.2009.090817},
}
[Abstract]
We study superposition coded modulation (SCM) with iterative linear minimummeansquareerror (LMMSE) detection. We show that SCM offers an attractive solution for highly complicated transmission environments with severe interference. We analyze the impact of signaling schemes on the performance of iterative LMMSE detection. We prove that among all possible signaling methods, SCM maximizes the output signaltonoise/ interference ratio (SNIR) in the LMMSE estimates during iterative detection. Numerical examples are used to demonstrate that SCM outperforms other signaling methods when iterative LMMSE detection is applied to multiuser/multiantenna/multipath channels.52Superposition coded modulation with peakpower limitation
(Jun Tong, Li Ping and Xiao Ma)
IEEE Trans. Inform. Theory 55 (6), pp. 2562–2576, June 2009.
DOI:10.1109/TIT.2009.2018224.
[BibTeX]
@article{TongPingMa:2009:Superpositioncodedmodulationwithpeak,
abstract = {We apply clipping to superposition coded modulation (SCM) systems to reduce the peaktoaverage power ratio (PAPR) of the transmitted signal. The impact on performance is investigated by evaluating the mutual information driven by the induced peakpowerlimited input signals. It is shown that the rate loss is marginal for moderate clipping thresholds if optimal encoding/decoding is used. This fact is confirmed in examples where capacityapproaching component codes are used together with the maximum a posteriori probability (MAP) detection. In order to reduce the detection complexity of SCM with a large number of layers, we develop a suboptimal soft compensation (SC) method that is combined with softinput softoutput (SISO) decoding algorithms in an iterative manner. A variety of simulation results for additive white Gaussian noise (AWGN) and fading channels are presented. It is shown that with the proposed method, the effect of clipping can be efficiently compensated and a good tradeoff between PAPR and biterror rate (BER) can be achieved. Comparisons with other coded modulation schemes demonstrate that SCM offers significant advantages for highrate transmissions over fading channels.},
title = {Superposition coded modulation with peakpower limitation},
author = {Tong, Jun and Ping, Li and Ma, Xiao},
month = {{J}une},
year = {2009},
journal = {{IEEE} {T}rans.\ {I}nform.\ {T}heory},
pages = {2562–2576},
volume = {55},
number = {6},
doi = {10.1109/TIT.2009.2018224},
}
[Abstract]
We apply clipping to superposition coded modulation (SCM) systems to reduce the peaktoaverage power ratio (PAPR) of the transmitted signal. The impact on performance is investigated by evaluating the mutual information driven by the induced peakpowerlimited input signals. It is shown that the rate loss is marginal for moderate clipping thresholds if optimal encoding/decoding is used. This fact is confirmed in examples where capacityapproaching component codes are used together with the maximum a posteriori probability (MAP) detection. In order to reduce the detection complexity of SCM with a large number of layers, we develop a suboptimal soft compensation (SC) method that is combined with softinput softoutput (SISO) decoding algorithms in an iterative manner. A variety of simulation results for additive white Gaussian noise (AWGN) and fading channels are presented. It is shown that with the proposed method, the effect of clipping can be efficiently compensated and a good tradeoff between PAPR and biterror rate (BER) can be achieved. Comparisons with other coded modulation schemes demonstrate that SCM offers significant advantages for highrate transmissions over fading channels.53Bounds on the degree of impropriety of complex random vectors
(Peter J. Schreier)
IEEE Signal Process. Lett. 15, pp. 190–193, 2008.
DOI:10.1109/LSP.2007.913134.
[BibTeX]
@article{Schreier:2008:BoundsontheDegreeofImproprietyofC,
abstract = {A complex random vector is called improper if it is correlated with its complex conjugate. We introduce a measure for the degree of impropriety, which is a function of the canonical correlations between the vector and its complex conjugate (sometimes called the circularity spectrum). This measure is invariant under linear transformation, and it relates the entropy of an improper Gaussian random vector to its corresponding proper version. For vectors with given spectrum, we present upper and lower bounds on the attainable degree of impropriety, in terms of the eigenvalues of the augmented covariance matrix.},
title = {Bounds on the degree of impropriety of complex random vectors},
author = {Schreier, Peter J.},
year = {2008},
journal = {{IEEE} {S}ignal {P}rocess.\ {L}ett.},
pages = {190–193},
volume = {15},
doi = {10.1109/LSP.2007.913134},
}
[Abstract]
A complex random vector is called improper if it is correlated with its complex conjugate. We introduce a measure for the degree of impropriety, which is a function of the canonical correlations between the vector and its complex conjugate (sometimes called the circularity spectrum). This measure is invariant under linear transformation, and it relates the entropy of an improper Gaussian random vector to its corresponding proper version. For vectors with given spectrum, we present upper and lower bounds on the attainable degree of impropriety, in terms of the eigenvalues of the augmented covariance matrix.54Analysis and design of OFDMIDMA systems
(Jun Tong, Qinghua Guo and Li Ping)
European Trans. Comm. 19 (5), pp. 561–569, John Wiley & Sons, 2008.
DOI:10.1002/ett.1304.
[BibTeX]
@article{TongGuoPing:2008:AnalysisanddesignofOFDMIDMAsystems,
abstract = {This paper deals with the analysis and design of orthogonal frequencydivision multiplexing interleavedivision multipleaccess (OFDMIDMA). We begin with the analysis of the informationtheoretical advantages of nonorthogonal transmission schemes in fading multipleaccess channels. We then turn attention to practical design issues. A signaltonoise ratio (SNR) evolution technique is developed to predict the biterrorrate (BER) performance of OFDMIDMA. This technique is applied to system design and optimisation. Through proper power allocation, OFDMIDMA can achieve the multiuser gain (MUG) predicted by informationtheoretical analysis. It is also an attractive option in compensating for the clipping effect caused by peakpower limitation. Numerical examples show that OFDMIDMA can (i) alleviate the PAPR problem commonly suffered by OFDMbased schemes; (ii) deliver significant MUG compared with other orthogonal alternatives; (iii) provide robust communications in frequencyselective channels; and (iv) support high singleuser throughput. Copyright {\copyright} 2008 John Wiley & Sons, Ltd.},
title = {Analysis and design of {OFDMIDMA} systems},
author = {Tong, Jun and Guo, Qinghua and Ping, Li},
year = {2008},
journal = {{E}uropean {T}rans.\ {C}omm.},
pages = {561–569},
volume = {19},
number = {5},
doi = {10.1002/ett.1304},
publisher = {{J}ohn {W}iley \& {S}ons},
}
[Abstract]
This paper deals with the analysis and design of orthogonal frequencydivision multiplexing interleavedivision multipleaccess (OFDMIDMA). We begin with the analysis of the informationtheoretical advantages of nonorthogonal transmission schemes in fading multipleaccess channels. We then turn attention to practical design issues. A signaltonoise ratio (SNR) evolution technique is developed to predict the biterrorrate (BER) performance of OFDMIDMA. This technique is applied to system design and optimisation. Through proper power allocation, OFDMIDMA can achieve the multiuser gain (MUG) predicted by informationtheoretical analysis. It is also an attractive option in compensating for the clipping effect caused by peakpower limitation. Numerical examples show that OFDMIDMA can (i) alleviate the PAPR problem commonly suffered by OFDMbased schemes; (ii) deliver significant MUG compared with other orthogonal alternatives; (iii) provide robust communications in frequencyselective channels; and (iv) support high singleuser throughput. Copyright copyright 2008 John Wiley & Sons, Ltd.55A comparative study of STBC transmissions at 2.4 GHz over indoor channels using a 2 times 2 MIMO testbed
(D. Ramírez, I. Santamaría, J. Pérez, J. Vía, J. A. GarcíaNaya, T. M. FernándezCaramés, H. PérezIglesias, M. González López, L. Castedo and J. M. TorresRoyo)
Wireless Comm. and Mobile Computing 8 (9), pp. 1149–1164, November 2008.
DOI:10.1002/wcm.558.
[BibTeX]
@article{RamirezSantamariaPerez:2008:AcomparativestudyofSTBCtransmissions,
abstract = {In this paper we employ a $2 \times 2$ MultipleInput MultipleOutput (MIMO) hardware platform to evaluate, in realistic indoor scenarios, the performance of different spacetime block coded (STBC) transmissions at 2.4 GHz. In particular, we focus on the Alamouti orthogonal scheme considering two types of Channel State Information (CSI) estimation: a conventional pilotaided supervised technique and a recently proposed blind method based on Second Order Statistics (SOS). For comparison purposes, we also evaluate the performance of a Differential (noncoherent) STBC (DSTBC). DSTBC schemes have the advantage of not requiring CSI estimation but they incur in a 3 dB loss in performance. The hardware MIMO platform is based on highperformance signal acquisition and generation boards, each one equipped with a 1 GB memory module that allows the transmission of extremely large data frames. Upconversion to RF is performed by two RF vector signal generators whereas downconversion is carried out with two custom circuits designed from commercial components. All the baseband signal processing is implemented offline in Matlab, making the MIMO testbed very flexible and easily reconfigurable. Using this platform we compare the performance of the described methods in lineofsight (LOS) and nonlineofsight (NLOS) indoor scenarios.},
title = {A comparative study of {STBC} transmissions at 2.4 {GHz} over indoor channels using a $2 \times 2$ {MIMO} testbed},
author = {D. Ram{\'i}rez and I. Santamar{\'i}a and J. P{\'e}rez and J. V{\'i}a and J. A. Garc{\'i}aNaya and T. M. Fern{\'a}ndezCaram{\'e}s and H. P{\'e}rezIglesias and M. Gonz{\'a}lez L{\'o}pez and L. Castedo and J. M. TorresRoyo},
month = {{N}ovember},
year = {2008},
journal = {{W}ireless {C}omm.\ and {M}obile {C}omputing},
pages = {1149–1164},
volume = {8},
number = {9},
doi = {10.1002/wcm.558},
}
[Abstract]
In this paper we employ a 2 times 2 MultipleInput MultipleOutput (MIMO) hardware platform to evaluate, in realistic indoor scenarios, the performance of different spacetime block coded (STBC) transmissions at 2.4 GHz. In particular, we focus on the Alamouti orthogonal scheme considering two types of Channel State Information (CSI) estimation: a conventional pilotaided supervised technique and a recently proposed blind method based on Second Order Statistics (SOS). For comparison purposes, we also evaluate the performance of a Differential (noncoherent) STBC (DSTBC). DSTBC schemes have the advantage of not requiring CSI estimation but they incur in a 3 dB loss in performance. The hardware MIMO platform is based on highperformance signal acquisition and generation boards, each one equipped with a 1 GB memory module that allows the transmission of extremely large data frames. Upconversion to RF is performed by two RF vector signal generators whereas downconversion is carried out with two custom circuits designed from commercial components. All the baseband signal processing is implemented offline in Matlab, making the MIMO testbed very flexible and easily reconfigurable. Using this platform we compare the performance of the described methods in lineofsight (LOS) and nonlineofsight (NLOS) indoor scenarios.56Polarization ellipse analysis of nonstationary random signals
(Peter J. Schreier)
IEEE Trans. Signal Process. 56 (9), pp. 4330–4339, September 2008.
DOI:10.1109/TSP.2008.925961.
[BibTeX]
@article{Schreier:2008:PolarizationEllipseAnalysisofNonstat,
abstract = {We present a novel way of extending rotarycomponent and polarization analysis to nonstationary random signals. If a complex signal is resolved into counterclockwise and clockwise rotating phasors at one particular frequency only, it traces out an ellipse in the complex plane. Rotarycomponent analysis characterizes this ellipse in terms of its shape and orientation. Polarization analysis looks at the coherence between counterclockwise and clockwise rotating phasors and whether there is a preferred rotation direction of the ellipse (counterclockwise or clockwise). In the nonstationary case, we replace this ellipse with a timedependent local ellipse that, at a given time instant, gives the best local approximation of the signal from a given frequency component. This local ellipse is then analyzed in terms of its shape, orientation, and degree of polarization. A timefrequency coherence measures how well the local ellipse approximates the signal. The ellipse parameters and the timefrequency coherence can be expressed in terms of the Rihaczek timefrequency distribution. Under coordinate rotation, the ellipse shape, the degree of polarization, and the timefrequency coherence are invariant, and the ellipse orientation is covariant. The methods presented in this paper provide an alternative to ellipse decompositions based on wavelet ridge analysis.},
title = {Polarization ellipse analysis of nonstationary random signals},
author = {Schreier, Peter J.},
month = {{S}eptember},
year = {2008},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {4330–4339},
volume = {56},
number = {9},
doi = {10.1109/TSP.2008.925961},
}
[Abstract]
We present a novel way of extending rotarycomponent and polarization analysis to nonstationary random signals. If a complex signal is resolved into counterclockwise and clockwise rotating phasors at one particular frequency only, it traces out an ellipse in the complex plane. Rotarycomponent analysis characterizes this ellipse in terms of its shape and orientation. Polarization analysis looks at the coherence between counterclockwise and clockwise rotating phasors and whether there is a preferred rotation direction of the ellipse (counterclockwise or clockwise). In the nonstationary case, we replace this ellipse with a timedependent local ellipse that, at a given time instant, gives the best local approximation of the signal from a given frequency component. This local ellipse is then analyzed in terms of its shape, orientation, and degree of polarization. A timefrequency coherence measures how well the local ellipse approximates the signal. The ellipse parameters and the timefrequency coherence can be expressed in terms of the Rihaczek timefrequency distribution. Under coordinate rotation, the ellipse shape, the degree of polarization, and the timefrequency coherence are invariant, and the ellipse orientation is covariant. The methods presented in this paper provide an alternative to ellipse decompositions based on wavelet ridge analysis.57A unifying discussion of correlation analysis for complex random vectors
(Peter J. Schreier)
IEEE Trans. Signal Process. 56 (4), pp. 1327–1336, April 2008.
DOI:10.1109/TSP.2007.909054.
[BibTeX]
@article{Schreier:2008:AUnifyingDiscussionofCorrelationAna,
abstract = {The assessment of multivariate association between two complex random vectors is considered. A number of correlation coefficients based on three popular correlation analysis techniques, namely canonical correlation analysis, multivariate linear regression, and partial least squares, are reviewed and connected to performance measures in signal processing and communications, such as meansquared estimation error, mutual information, and signaltonoise ratio (SNR). For complex data, there are three types of correlation coefficients, which account for rotational, reflectional, and total (i.e., rotational and reflectional) dependencies between two random vectors. These three types are defined and analyzed for different correlation coefficients, and a numerical example is given. It is often required to compare two complex random vectors in a lowerdimensional subspace. For the large class of increasing, Schurconvex correlation coefficients, it is shown that the lowrank approximations of two random vectors maximizing a particular correlation coefficient are determined only by the constraints imposed on the correlation analysis technique. In this context, the correlation spread is defined as a normalized measure of how much of the overall correlation is contained in a lowdimensional subspace.},
title = {A unifying discussion of correlation analysis for complex random vectors},
author = {Schreier, Peter J.},
month = {{A}pril},
year = {2008},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {1327–1336},
volume = {56},
number = {4},
doi = {10.1109/TSP.2007.909054},
}
[Abstract]
The assessment of multivariate association between two complex random vectors is considered. A number of correlation coefficients based on three popular correlation analysis techniques, namely canonical correlation analysis, multivariate linear regression, and partial least squares, are reviewed and connected to performance measures in signal processing and communications, such as meansquared estimation error, mutual information, and signaltonoise ratio (SNR). For complex data, there are three types of correlation coefficients, which account for rotational, reflectional, and total (i.e., rotational and reflectional) dependencies between two random vectors. These three types are defined and analyzed for different correlation coefficients, and a numerical example is given. It is often required to compare two complex random vectors in a lowerdimensional subspace. For the large class of increasing, Schurconvex correlation coefficients, it is shown that the lowrank approximations of two random vectors maximizing a particular correlation coefficient are determined only by the constraints imposed on the correlation analysis technique. In this context, the correlation spread is defined as a normalized measure of how much of the overall correlation is contained in a lowdimensional subspace.58Spectral relations for multidimensional complex improper stationary and (almost) cyclostationary processes
(Patrik Wahlberg and Peter J. Schreier)
IEEE Trans. Inform. Theory 54 (4), pp. 1670–1682, April 2008.
DOI:10.1109/TIT.2008.917626.
[BibTeX]
@article{WahlbergSchreier:2008:SpectralRelationsforMultidimensional,
abstract = {We study continuoustime multidimensional wide sense stationary (WSS) and (almost) cyclostationary processes in the frequency domain. Under the assumption that the correlation function is uniformly continuous, we prove the existence of a unique sequence of spectral measures, which coincide with the restrictions to certain subdiagonals of the spectral measure in the strongly harmonizable case. Moreover, the offdiagonal measures are absolutely continuous with respect to the diagonal measure. As a consequence, for strongly harmonizable scalar improper almost cyclostationary processes, we obtain representation formulas for the components of the complementary spectral measure and the offdiagonal components of the spectral measure, in terms of the diagonal component of the spectral measure. We apply these results to analytic signals, which produces sufficient conditions for propriety for almost cyclostationary analytic signals.},
title = {Spectral relations for multidimensional complex improper stationary and (almost) cyclostationary processes},
author = {Wahlberg, Patrik and Schreier, Peter J.},
month = {{A}pril},
year = {2008},
journal = {{IEEE} {T}rans.\ {I}nform.\ {T}heory},
pages = {1670–1682},
volume = {54},
number = {4},
doi = {10.1109/TIT.2008.917626},
}
[Abstract]
We study continuoustime multidimensional wide sense stationary (WSS) and (almost) cyclostationary processes in the frequency domain. Under the assumption that the correlation function is uniformly continuous, we prove the existence of a unique sequence of spectral measures, which coincide with the restrictions to certain subdiagonals of the spectral measure in the strongly harmonizable case. Moreover, the offdiagonal measures are absolutely continuous with respect to the diagonal measure. As a consequence, for strongly harmonizable scalar improper almost cyclostationary processes, we obtain representation formulas for the components of the complementary spectral measure and the offdiagonal components of the spectral measure, in terms of the diagonal component of the spectral measure. We apply these results to analytic signals, which produces sufficient conditions for propriety for almost cyclostationary analytic signals.59The OFDMIDMA approach to wireless communication systems
(Li Ping, Qinghua Guo and Jun Tong)
IEEE Wireless Comm. 14 (3), pp. 18–24, June 2007.
DOI:10.1109/MWC.2007.386608.
[BibTeX]
@article{PingGuoTong:2007:TheOFDMIDMAapproachtowirelesscommu,
abstract = {This article outlines the basic principles of OFDMIDMA. Comparisons with other alternative technologies such as OFDMCDMA and OFDMA are provided. Some attractive features of OFMDIDMA are explained, including lowcost iterative multiuser detection, flexible rate adaptation, frequency diversity, and significant advantages regarding spectral and power efficiency.},
title = {The {OFDMIDMA} approach to wireless communication systems},
author = {Ping, Li and Guo, Qinghua and Tong, Jun},
month = {{J}une},
year = {2007},
journal = {{IEEE} {W}ireless {C}omm.},
pages = {18–24},
volume = {14},
number = {3},
doi = {10.1109/MWC.2007.386608},
}
[Abstract]
This article outlines the basic principles of OFDMIDMA. Comparisons with other alternative technologies such as OFDMCDMA and OFDMA are provided. Some attractive features of OFMDIDMA are explained, including lowcost iterative multiuser detection, flexible rate adaptation, frequency diversity, and significant advantages regarding spectral and power efficiency.60Causal Wiener filter banks for periodically correlated time series
(Mark S. Spurbeck and Peter J. Schreier)
Signal Process. 87 (6), pp. 1179–1187, Amsterdam, The Netherlands, Elsevier NorthHolland, Inc., June 2007.
DOI:10.1016/j.sigpro.2006.10.008.
[BibTeX]
@article{SpurbeckSchreier:2007:CausalWienerfilterbanksforperiodica,
abstract = {A causal filter bank implementation of the cyclic Wiener filter for periodically correlated (PC) time series is developed. By converting a PC time series into a vectorvalued widesense stationary (WSS) time series, the existing literature on factorization of spectral density matrices may be utilized. However, because PC analytic and equivalent baseband signals are generally complex improper, spectral factorization algorithms must be adapted to the improper case. Based on the factorization of the spectral density matrix for the equivalent WSS vector process, causal synthesis and whitening filters for PC time series can be built. These techniques are exploited to implement a causal cyclic Wiener filter as a multirate filter bank or an equivalent polyphase structure. This filter bank is shown to be an efficient equivalent implementation of a frequency shift (FRESH) filter. Therefore, the results derived in this paper also show how to build a causal FRESH cyclic Wiener filter.},
title = {Causal {Wiener} filter banks for periodically correlated time series},
address = {{A}msterdam, {T}he {N}etherlands},
author = {Spurbeck, Mark S. and Schreier, Peter J.},
month = {{J}une},
year = {2007},
journal = {{S}ignal {P}rocess.},
pages = {1179–1187},
volume = {87},
number = {6},
doi = {10.1016/j.sigpro.2006.10.008},
publisher = {{E}lsevier {N}orth{H}olland, {I}nc.},
}
[Abstract]
A causal filter bank implementation of the cyclic Wiener filter for periodically correlated (PC) time series is developed. By converting a PC time series into a vectorvalued widesense stationary (WSS) time series, the existing literature on factorization of spectral density matrices may be utilized. However, because PC analytic and equivalent baseband signals are generally complex improper, spectral factorization algorithms must be adapted to the improper case. Based on the factorization of the spectral density matrix for the equivalent WSS vector process, causal synthesis and whitening filters for PC time series can be built. These techniques are exploited to implement a causal cyclic Wiener filter as a multirate filter bank or an equivalent polyphase structure. This filter bank is shown to be an efficient equivalent implementation of a frequency shift (FRESH) filter. Therefore, the results derived in this paper also show how to build a causal FRESH cyclic Wiener filter.61Higherorder spectral analysis of complex signals
(Peter J. Schreier and Louis L. Scharf)
Signal Process. 86 (11), pp. 3321–3333, November 2006.
DOI:10.1016/j.sigpro.2006.02.027.
[BibTeX]
@article{SchreierScharf:2006:Higherorderspectralanalysisofcomple,
abstract = {Even though higherorder spectral analysis is by now a mature field, complex signals are still not routinely used, as they are in secondorder analysis. The reason is the complexity of the complex case: nth order moment functions of a complex signal can be defined in 2 n different ways, depending on the placement of complex conjugate operators. It is demonstrated that only a few of these different moments are required for a complete nth order description. Properties of nth order moments and spectra with different conjugation patterns are investigated. For the special case of analytic signals, it is shown how spectra with different conjugation patterns provide different information about the signal. Both energy and power signals and deterministic and stochastic signals are discussed. A major focus lies on extending results from continuoustime signals to their sampled versions. Such an extension is not straightforward due to a phenomenon called higherorder or dimensionreduction aliasing. It is demonstrated why spectra of sampled nonstationary signals may suffer from dimensionreduction aliasing unless they are sufficiently oversampled.},
title = {Higherorder spectral analysis of complex signals},
author = {Schreier, Peter J. and Scharf, Louis L.},
month = {{N}ovember},
year = {2006},
journal = {{S}ignal {P}rocess.},
pages = {3321–3333},
volume = {86},
number = {11},
doi = {10.1016/j.sigpro.2006.02.027},
}
[Abstract]
Even though higherorder spectral analysis is by now a mature field, complex signals are still not routinely used, as they are in secondorder analysis. The reason is the complexity of the complex case: nth order moment functions of a complex signal can be defined in 2 n different ways, depending on the placement of complex conjugate operators. It is demonstrated that only a few of these different moments are required for a complete nth order description. Properties of nth order moments and spectra with different conjugation patterns are investigated. For the special case of analytic signals, it is shown how spectra with different conjugation patterns provide different information about the signal. Both energy and power signals and deterministic and stochastic signals are discussed. A major focus lies on extending results from continuoustime signals to their sampled versions. Such an extension is not straightforward due to a phenomenon called higherorder or dimensionreduction aliasing. It is demonstrated why spectra of sampled nonstationary signals may suffer from dimensionreduction aliasing unless they are sufficiently oversampled.62A generalized likelihood ratio test for impropriety of complex signals
(Peter J. Schreier, Louis L. Scharf and Alfred Hanssen)
IEEE Signal Process. Lett. 13 (7), pp. 433–436, July 2006.
DOI:10.1109/LSP.2006.871858.
[BibTeX]
@article{SchreierScharfHanssen:2006:Ageneralizedlikelihoodratiotestfor,
abstract = {A complex random vector is called improper if it is correlated with its complex conjugate. We present a hypothesis test for impropriety based on a generalized likelihood ratio (GLR). This GLR is invariant to linear transformations on the data, including rotation and scaling, because propriety is preserved by linear transformations. More specifically, we show that the GLR is a function of the squared canonical correlations between the data and their complex conjugate. These canonical correlations make up a complete, or maximal, set of invariants for the Hermitian and complementary covariance matrices under linear, but not widely linear, transformation},
title = {A generalized likelihood ratio test for impropriety of complex signals},
author = {Schreier, Peter J. and Scharf, Louis L. and Hanssen, Alfred},
month = {{J}uly},
year = {2006},
journal = {{IEEE} {S}ignal {P}rocess.\ {L}ett.},
pages = {433–436},
volume = {13},
number = {7},
doi = {10.1109/LSP.2006.871858},
}
[Abstract]
A complex random vector is called improper if it is correlated with its complex conjugate. We present a hypothesis test for impropriety based on a generalized likelihood ratio (GLR). This GLR is invariant to linear transformations on the data, including rotation and scaling, because propriety is preserved by linear transformations. More specifically, we show that the GLR is a function of the squared canonical correlations between the data and their complex conjugate. These canonical correlations make up a complete, or maximal, set of invariants for the Hermitian and complementary covariance matrices under linear, but not widely linear, transformation63Regularised approach to detection of constant modulus signals in MIMO channels
(D. Ramírez and I. Santamaría)
Electr. Lett. 42 (3), pp. 184–186, February 2006.
DOI:10.1049/el:20063870.
[BibTeX]
@article{RamirezSantamaria:2006:Regularisedapproachtodetectionofconstant,
abstract = {A new suboptimal algorithm for detection of constant modulus signals in multipleinput multipleoutput (MIMO) channels is presented. The deviation of the solution from the desired constant modulus property is used as a penalty or regularization term in the conventional least squares cost function, and an iterative reweighted least squares (IRWLS) procedure is used to minimize the regularized functional.},
title = {Regularised approach to detection of constant modulus signals in {MIMO} channels},
author = {D. Ram{\'i}rez and I. Santamar{\'i}a},
month = {{F}ebruary},
year = {2006},
journal = {{E}lectr. {L}ett.},
pages = {184–186},
volume = {42},
number = {3},
doi = {10.1049/el:20063870},
}
[Abstract]
A new suboptimal algorithm for detection of constant modulus signals in multipleinput multipleoutput (MIMO) channels is presented. The deviation of the solution from the desired constant modulus property is used as a penalty or regularization term in the conventional least squares cost function, and an iterative reweighted least squares (IRWLS) procedure is used to minimize the regularized functional.64Analysis and optimization of CDMA systems with chiplevel interleavers
(Lihai Liu, Jun Tong and Li Ping)
IEEE J. Select. Areas Comm. 24 (1), pp. 141–150, January 2006.
DOI:10.1109/JSAC.2005.858896.
[BibTeX]
@article{LiuTongPing:2006:AnalysisandoptimizationofCDMAsystem,
abstract = {In this paper, we present an unequal power allocation technique to increase the throughput of codedivision multipleaccess (CDMA) systems with chiplevel interleavers. Performance is optimized, respectively, based on received and transmitted power allocation. Linear programming and power matching techniques are developed to provide solutions to systems with a very large number of users. Various numerical results are provided to demonstrate the efficiency of the proposed techniques and to examine the impact of system parameters, such as iteration number and interleaver length. We also show that with some very simple forward error correction codes, such as repetition codes or convolutional codes, the proposed scheme can achieve throughput reasonably close to that predicted by theoretical limit in multiple access channels.},
title = {Analysis and optimization of {CDMA} systems with chiplevel interleavers},
author = {Liu, Lihai and Tong, Jun and Ping, Li},
month = {{J}anuary},
year = {2006},
journal = {{IEEE} {J}.\ {S}elect.\ {A}reas {C}omm.},
pages = {141–150},
volume = {24},
number = {1},
doi = {10.1109/JSAC.2005.858896},
}
[Abstract]
In this paper, we present an unequal power allocation technique to increase the throughput of codedivision multipleaccess (CDMA) systems with chiplevel interleavers. Performance is optimized, respectively, based on received and transmitted power allocation. Linear programming and power matching techniques are developed to provide solutions to systems with a very large number of users. Various numerical results are provided to demonstrate the efficiency of the proposed techniques and to examine the impact of system parameters, such as iteration number and interleaver length. We also show that with some very simple forward error correction codes, such as repetition codes or convolutional codes, the proposed scheme can achieve throughput reasonably close to that predicted by theoretical limit in multiple access channels.65Canonical coordinates for transform coding of noisy sources
(Peter J. Schreier and Louis L. Scharf)
IEEE Trans. Signal Process. 54 (1), pp. 235–243, January 2006.
DOI:10.1109/TSP.2005.861085.
[BibTeX]
@article{SchreierScharf:2006:Canonicalcoordinatesfortransformcodi,
abstract = {Based on the additive white quantization noise model, linear transform coders are derived for Gaussian sources corrupted by noise. There are two alternative design objectives: minimizing the trace of the error correlation matrix and thus minimizing the meansquared error, or minimizing the determinant of the error correlation matrix and thus maximizing information rate. It is shown that a solution to both problems is to first transform the noisy observations into canonical coordinates, quantize and apply a Wiener filter in this coordinate system, and then transform the result back to the original coordinates. Canonical coordinates are uncorrelated, and quantization and Wiener filtering are applied to each component independently. The type of canonical coordinate system depends on the design objective: Quantization in halfcanonical coordinates minimizes the meansquared error and quantization in fullcanonical coordinates maximizes information rate. Finally, it is also demonstrated in this paper that majorization is the fundamental principle underlying proofs of optimal transform coding.},
title = {Canonical coordinates for transform coding of noisy sources},
author = {Schreier, Peter J. and Scharf, Louis L.},
month = {{J}anuary},
year = {2006},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {235–243},
volume = {54},
number = {1},
doi = {10.1109/TSP.2005.861085},
}
[Abstract]
Based on the additive white quantization noise model, linear transform coders are derived for Gaussian sources corrupted by noise. There are two alternative design objectives: minimizing the trace of the error correlation matrix and thus minimizing the meansquared error, or minimizing the determinant of the error correlation matrix and thus maximizing information rate. It is shown that a solution to both problems is to first transform the noisy observations into canonical coordinates, quantize and apply a Wiener filter in this coordinate system, and then transform the result back to the original coordinates. Canonical coordinates are uncorrelated, and quantization and Wiener filtering are applied to each component independently. The type of canonical coordinate system depends on the design objective: Quantization in halfcanonical coordinates minimizes the meansquared error and quantization in fullcanonical coordinates maximizes information rate. Finally, it is also demonstrated in this paper that majorization is the fundamental principle underlying proofs of optimal transform coding.66The Hilbert space geometry of the Rihaczek distribution for stochastic analytic signals
(Louis L. Scharf, Peter J. Schreier and Alfred Hanssen)
IEEE Signal Process. Lett. 12 (4), pp. 297–300, April 2005.
DOI:10.1109/LSP.2005.843772.
[BibTeX]
@article{SchreierScharfHanssen:2005:TheHilbertspacegeometryoftheRihacz,
abstract = {The Rihaczek distribution for stochastic signals is a time and frequencyshift covariant bilinear timefrequency distribution (TFD) based on the Crame acute;rLoe grave;ve spectral representation for a harmonizable process. It is a complex Hilbert space inner product (or cross correlation) between the time series and its infinitesimal stochastic Fourier generator. To this inner product, we may attach an illuminating geometry, wherein the cosine squared of the angle between the time series and its infinitesimal stochastic Fourier generator is given by the Rihaczek distribution. The Rihaczek distribution also determines a timevarying Wiener filter for estimating a time series from its infinitesimal stochastic Fourier generator and measures the resulting error covariance. We propose a factored kernel to construct estimators of the Rihaczek distribution that are contained in Cohen's class of bilinear TFDs.},
title = {The {Hilbert} space geometry of the {Rihaczek} distribution for stochastic analytic signals},
author = {Scharf, Louis L. and Schreier, Peter J. and Hanssen, Alfred},
month = {{A}pril},
year = {2005},
journal = {{IEEE} {S}ignal {P}rocess.\ {L}ett.},
pages = {297–300},
volume = {12},
number = {4},
doi = {10.1109/LSP.2005.843772},
}
[Abstract]
The Rihaczek distribution for stochastic signals is a time and frequencyshift covariant bilinear timefrequency distribution (TFD) based on the Crame acute;rLoe grave;ve spectral representation for a harmonizable process. It is a complex Hilbert space inner product (or cross correlation) between the time series and its infinitesimal stochastic Fourier generator. To this inner product, we may attach an illuminating geometry, wherein the cosine squared of the angle between the time series and its infinitesimal stochastic Fourier generator is given by the Rihaczek distribution. The Rihaczek distribution also determines a timevarying Wiener filter for estimating a time series from its infinitesimal stochastic Fourier generator and measures the resulting error covariance. We propose a factored kernel to construct estimators of the Rihaczek distribution that are contained in Cohen's class of bilinear TFDs.67Detection and estimation of improper complex random signals
(Peter J. Schreier, Louis L. Scharf and Clifford T. Mullis)
IEEE Trans. Inform. Theory 51 (1), pp. 306–312, January 2005.
DOI:10.1109/TIT.2004.839538.
[BibTeX]
@article{SchreierScharfMullis:2005:Detectionandestimationofimpropercom,
abstract = {Nonstationary complex random signals are in general improper (not circularly symmetric), which means that their complementary covariance is nonzero. Since the KarhunenLoeve (KL) expansion in its known form is only valid for proper processes, we derive the improper version of this expansion. It produces two sets of eigenvalues and improper observable coordinates. We then use the KL expansion to solve the problems of detection and estimation of improper complex random signals in additive white Gaussian noise. We derive a general result comparing the performance of conventional processing, which ignores complementary covariances, with processing that takes these into account. In particular, for the detection and estimation problems considered, we find that the performance gain, as measured by deflection and meansquared error (MSE), respectively, can be as large as a factor of 2. In a communications example, we show how this finding generalizes the result that coherent processing enjoys a 3dB gain over noncoherent processing.},
title = {Detection and estimation of improper complex random signals},
author = {Schreier, Peter J. and Scharf, Louis L. and Mullis, Clifford T.},
month = {{J}anuary},
year = {2005},
journal = {{IEEE} {T}rans.\ {I}nform.\ {T}heory},
pages = {306–312},
volume = {51},
number = {1},
doi = {10.1109/TIT.2004.839538},
}
[Abstract]
Nonstationary complex random signals are in general improper (not circularly symmetric), which means that their complementary covariance is nonzero. Since the KarhunenLoeve (KL) expansion in its known form is only valid for proper processes, we derive the improper version of this expansion. It produces two sets of eigenvalues and improper observable coordinates. We then use the KL expansion to solve the problems of detection and estimation of improper complex random signals in additive white Gaussian noise. We derive a general result comparing the performance of conventional processing, which ignores complementary covariances, with processing that takes these into account. In particular, for the detection and estimation problems considered, we find that the performance gain, as measured by deflection and meansquared error (MSE), respectively, can be as large as a factor of 2. In a communications example, we show how this finding generalizes the result that coherent processing enjoys a 3dB gain over noncoherent processing.68Stochastic timefrequency analysis using the analytic signal: why the complementary distribution matters
(Peter J. Schreier and Louis L. Scharf)
IEEE Trans. Signal Process. 51 (12), pp. 3071–3079, December 2003.
DOI:10.1109/TSP.2003.818911.
[BibTeX]
@article{SchreierScharf:2003:Stochastictimefrequencyanalysisusing,
abstract = {We challenge the perception that we live in a ``proper world'', where complex random signals can always be assumed to be proper (also called circularly symmetric). Rather, we stress the fact that the analytic signal constructed from a nonstationary real signal is, in general, improper, which means that its complementary correlation function is nonzero. We explore the consequences of this finding in the context of stochastic timefrequency analysis in Cohen's class. There, the analytic signal plays a prominent role because it reduces interference terms. However, the usual timefrequency representation (TFR) based on the analytic signal gives only an incomplete signal description. It must be augmented by a complementary TFR whose properties we develop in detail. We show why it is still advantageous to use the pair of standard and complementary TFRs of the analytic signal rather than the TFR of the corresponding real signal.},
title = {Stochastic timefrequency analysis using the analytic signal: why the complementary distribution matters},
author = {Schreier, Peter J. and Scharf, Louis L.},
month = {{D}ecember},
year = {2003},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {3071–3079},
volume = {51},
number = {12},
doi = {10.1109/TSP.2003.818911},
}
[Abstract]
We challenge the perception that we live in a ``proper world'', where complex random signals can always be assumed to be proper (also called circularly symmetric). Rather, we stress the fact that the analytic signal constructed from a nonstationary real signal is, in general, improper, which means that its complementary correlation function is nonzero. We explore the consequences of this finding in the context of stochastic timefrequency analysis in Cohen's class. There, the analytic signal plays a prominent role because it reduces interference terms. However, the usual timefrequency representation (TFR) based on the analytic signal gives only an incomplete signal description. It must be augmented by a complementary TFR whose properties we develop in detail. We show why it is still advantageous to use the pair of standard and complementary TFRs of the analytic signal rather than the TFR of the corresponding real signal.69Secondorder analysis of improper complex random vectors and processes
(Peter J. Schreier and Louis L. Scharf)
IEEE Trans. Signal Process. 51 (3), pp. 714–725, March 2003.
DOI:10.1109/TSP.2002.808085.
[BibTeX]
@article{SchreierScharf:2003:Secondorderanalysisofimpropercomple,
abstract = {We present a comprehensive treatment of the secondorder theory of complex random vectors and widesense stationary (WSS) signals. The main focus is on the improper case, in which the complementary covariance does not vanish. Accounting for the information present in the complementary covariance requires the use of widely linear transformations. Based on these, we present the eigenanalysis of complex vectors and apply it to the problem of rank reduction through principal components. We also investigate joint properties of two complex vectors by introducing canonical correlations, which paves the way for a discussion of the Wiener filter and its rankreduced version. We link the concepts of propriety and joint propriety to eigenanalysis and canonical correlation analysis, respectively. Our treatment is extended to WSS signals. In particular, we give a result on the asymptotic distribution of eigenvalues and examine the connection between WSS, proper, and analytic signals.},
title = {Secondorder analysis of improper complex random vectors and processes},
author = {Schreier, Peter J. and Scharf, Louis L.},
month = {{M}arch},
year = {2003},
journal = {{{IEEE}} {{T}}rans.\ {{S}}ignal\ {{P}}rocess.},
pages = {714–725},
volume = {51},
number = {3},
doi = {10.1109/TSP.2002.808085},
}
[Abstract]
We present a comprehensive treatment of the secondorder theory of complex random vectors and widesense stationary (WSS) signals. The main focus is on the improper case, in which the complementary covariance does not vanish. Accounting for the information present in the complementary covariance requires the use of widely linear transformations. Based on these, we present the eigenanalysis of complex vectors and apply it to the problem of rank reduction through principal components. We also investigate joint properties of two complex vectors by introducing canonical correlations, which paves the way for a discussion of the Wiener filter and its rankreduced version. We link the concepts of propriety and joint propriety to eigenanalysis and canonical correlation analysis, respectively. Our treatment is extended to WSS signals. In particular, we give a result on the asymptotic distribution of eigenvalues and examine the connection between WSS, proper, and analytic signals.
Conference articles

70A weighting strategy for active shape models
(Alma Eguizabal and Peter J. Schreier)
Proc. IEEE International Conference on Image Processing, Beijing, China, September 2017. [BibTeX]
@inproceedings{eguizabal2017weighting,
title = {A weighting strategy for active shape models},
address = {Beijing, China},
author = {Eguizabal, Alma and Schreier, Peter J.},
booktitle = {{P}roc. IEEE International Conference on Image Processing},
month = {{S}eptember},
year = {2017},
}
[Abstract]71Adaptive visual sort and summary of micrographic images of nanoparticles for forensic analysis
(Elizabeth Jurrus, Nathan Hodas, Nathan Baker, Tim Marrinan and Mark D Hoover)
Technologies for Homeland Security (HST), 2016 IEEE Symposium on, pp. 1–6, 2016.
DOI:10.1109/THS.2016.7568959.
[BibTeX]
@inproceedings{jurrusHST,
title = {Adaptive visual sort and summary of micrographic images of nanoparticles for forensic analysis},
author = {Jurrus, Elizabeth and Hodas, Nathan and Baker, Nathan and Marrinan, Tim and Hoover, Mark D},
booktitle = {Technologies for Homeland Security (HST), 2016 IEEE Symposium on},
year = {2016},
pages = {1–6},
doi = {10.1109/THS.2016.7568959},
}
[Abstract]72Flagbased detection of weak gas signatures in longwave infrared hyperspectral image sequences.
(Tim Marrinan, J. Ross Beveridge, Bruce Draper, Michael Kirby and Chris Peterson)
SPIE Defense, Security, and Sensing, 2016.
DOI:10.1117/12.2224117.
[BibTeX]
@inproceedings{marrinanSPIE,
title = {Flagbased detection of weak gas signatures in longwave infrared hyperspectral image sequences.},
author = {Marrinan, Tim and Beveridge, J. Ross and Draper, Bruce and Kirby, Michael and Peterson, Chris},
booktitle = {SPIE Defense, Security, and Sensing},
year = {2016},
doi = {10.1117/12.2224117},
}
[Abstract]73Bootstrapbased detection of the number of signals correlated across multiple data sets
(Tanuj Hasija, Yang Song, Peter J. Schreier and David Ramírez)
Proc. Asilomar Conf. Signals Syst. Computers, Pacific Grove, CA, USA, November 2016. [BibTeX]
@inproceedings{Hasija:2016ab,
title = {Bootstrapbased detection of the number of signals correlated across multiple data sets},
address = {Pacific Grove, CA, USA},
author = {Hasija, Tanuj and Song, Yang and Schreier, Peter J. and Ram{\'i}rez, David},
booktitle = {{P}roc.\ {A}silomar {C}onf.\ {S}ignals\ {S}yst. {C}omputers},
month = {{N}ovember},
year = {2016},
}
[Abstract]74Crossvalidation techniques for determining the number of correlated components between two data sets when the number of samples is very small
(Christian Lameiro and Peter J. Schreier)
Proc. Asilomar Conf. Signals Syst. Computers, Pacific Grove, CA, USA, November 2016. [BibTeX]
@inproceedings{Lameiro:2016aa,
title = {Crossvalidation techniques for determining the number of correlated components between two data sets when the number of samples is very small},
address = {Pacific Grove, CA, USA},
author = {Lameiro, Christian and Schreier, Peter J.},
booktitle = {{P}roc.\ {A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {November},
year = {2016},
}
[Abstract]75Determining the number of signals correlated across multiple data sets for small sample support
(Yang Song, Tanuj Hasija, Peter J. Schreier and David Ramírez)
Proc. Eur. Signal Process. Conf., Budapest, Hungary, September 2016. [BibTeX]
@inproceedings{Song:2016ab,
title = {Determining the number of signals correlated across multiple data sets for small sample support},
address = {Budapest, Hungary},
author = {Song, Yang and Hasija, Tanuj and Schreier, Peter J. and Ram{\'i}rez, David},
booktitle = {{P}roc.\ {E}ur.\ {S}ignal {P}rocess.\ {C}onf.},
month = {{S}eptember},
year = {2016},
}
[Abstract]76Detecting the dimension of the subspace correlated across multiple data sets in the sample poor regime
(Tanuj Hasija, Yang Song, Peter J. Schreier and David Ramírez)
Proc. IEEE Work. Stat. Signal Process., Palma de Mallorca, Spain, June 2016. [BibTeX]
@inproceedings{Hasija:2016aa,
title = {Detecting the dimension of the subspace correlated across multiple data sets in the sample poor regime},
address = {Palma de Mallorca, Spain},
author = {Hasija, Tanuj and Song, Yang and Schreier, Peter J. and Ram{\'i}rez, David},
booktitle = {{P}roc.\ {IEEE} {W}ork.\ {S}tat.\ {S}ignal {P}rocess.},
month = {{J}une},
year = {2016},
}
[Abstract]77Measurementdriven quality assessment of nonlinear systems by exponential replacement
(Manuel Stein, Josef A. Nossek and Kurt Barbé)
Proc. IEEE Int. Instrum. & Meas. Tech. Conf., Taipei, Taiwan, May 2016. [BibTeX]
@inproceedings{Stein:I2MTC:2016,
title = {Measurementdriven quality assessment of nonlinear systems by exponential replacement},
address = {Taipei, Taiwan},
author = {Stein, Manuel and Nossek, Josef A. and Barb{\'e}, Kurt},
booktitle = {{P}roc.\ {IEEE} {I}nt. Instrum. \& Meas. Tech.\ {C}onf.},
month = {{M}ay},
year = {2016},
}
[Abstract]78Detection of cyclostationarity in the presence of temporal or spatial structure with applications to cognitive radio
(Aaron Pries, David Ramírez and Peter J. Schreier)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 4249–4253, Shanghai, China, March 2016.
DOI:10.1109/ICASSP.2016.7472478.
[BibTeX]
@inproceedings{pries2016,
abstract = {One approach to spectrum sensing for cognitive radio is the detection of cyclostationarity. We extend an existing multiantenna detector for cyclostationarity proposed by Ram{\'i}rez et al. [1], which makes no assumptions about the noise beyond being (temporally) widesense stationary. In special cases, the noise could be uncorrelated among antennas, or it could be temporally white. The performance of a general detector can be improved by making use of a priori structural information. We do not, however, require knowledge of the exact values of the temporal or spatial noise covariances. We develop an asymptotic generalized likelihood ratio test and evaluate the performance by simulations.},
title = {Detection of cyclostationarity in the presence of temporal or spatial structure with applications to cognitive radio},
address = {Shanghai, China},
author = {Aaron Pries and David Ram{\'i}rez and Peter J. Schreier},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}arch},
year = {2016},
pages = {4249–4253},
doi = {10.1109/ICASSP.2016.7472478},
}
[Abstract]
One approach to spectrum sensing for cognitive radio is the detection of cyclostationarity. We extend an existing multiantenna detector for cyclostationarity proposed by Ramírez et al. [1], which makes no assumptions about the noise beyond being (temporally) widesense stationary. In special cases, the noise could be uncorrelated among antennas, or it could be temporally white. The performance of a general detector can be improved by making use of a priori structural information. We do not, however, require knowledge of the exact values of the temporal or spatial noise covariances. We develop an asymptotic generalized likelihood ratio test and evaluate the performance by simulations.79Maximally improper interference in underlay cognitive radio networks
(Christian Lameiro, I. Santamaría, W. Utschick and Peter J. Schreier)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Shanghai, China, March 2016. [BibTeX]
@inproceedings{Lameiro:2016aa,
title = {Maximally improper interference in underlay cognitive radio networks},
address = {Shanghai, China},
author = {Lameiro, Christian and Santamar{\'i}a, I. and Utschick, W. and Schreier, Peter J.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}arch},
year = {2016},
}
[Abstract]80DOA parameter estimation with 1bit quantization  Bounds, methods and the exponential replacement
(Manuel Stein, Kurt Barbé and Josef A. Nossek)
Proc. ITG Int. Work. Smart Ant., Munich, Germany, March 2016. [BibTeX]
@inproceedings{Stein:WSA:2016,
title = {{DOA} parameter estimation with 1bit quantization  {B}ounds, methods and the exponential replacement},
address = {Munich, Germany},
author = {Stein, Manuel and Barb{\'e}, Kurt and Nossek, Josef A.},
booktitle = {{P}roc.\ {ITG} {I}nt.\ {W}ork.\ Smart Ant.},
month = {{M}arch},
year = {2016},
}
[Abstract]81Choosing the diagonal loading factor for linear signal estimation using cross validation
(Jun Tong, Qinghua Guo, Jiangtao Xi, Y. Yu and Peter J. Schreier)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Shanghai, China, March 2016. [BibTeX]
@inproceedings{Tong:2016ab,
title = {Choosing the diagonal loading factor for linear signal estimation using cross validation},
address = {Shanghai, China},
author = {Tong, Jun and Guo, Qinghua and Xi, Jiangtao and Yu, Y. and Schreier, Peter J.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}arch},
year = {2016},
}
[Abstract]82Performance analysis for pilotbased 1bit channel estimation with unknown quantization threshold
(Manuel Stein, Shahar Bar, Josef A. Nossek and Joseph Tabrikian)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Shanghai, China, February 2016. [BibTeX]
@inproceedings{Stein:ICASSP:2016:01,
title = {Performance analysis for pilotbased $1$bit channel estimation with unknown quantization threshold},
address = {Shanghai, China},
author = {Stein, Manuel and Bar, Shahar and Nossek, Josef A. and Tabrikian, Joseph},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{F}ebruary},
year = {2016},
}
[Abstract]83Asymptotic performance analysis for 1bit Bayesian smoothing
(Lin Zhang, Manuel Stein and Josef A. Nossek)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Shanghai, China, February 2016. [BibTeX]
@inproceedings{Zhang:ICASSP:2016,
title = {Asymptotic performance analysis for $1$bit {B}ayesian smoothing},
address = {Shanghai, China},
author = {Zhang, Lin and Stein, Manuel and Nossek, Josef A.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{F}ebruary},
year = {2016},
}
[Abstract]84A simple DoFachievable scheme for the Gaussian interference channel with delayed CSIT
(M. Rezaee, P. J. Schreier, M. Guillaud and B. Clerckx)
Proc. IEEE Global Communications Convference: Communication Theory, San Diego, CA, December 2015. [BibTeX]
@inproceedings{RezaeeSchreierGuillaud:2015:AsimpleDoFachievableschemefortheGaussian,
title = {A simple {DoF}achievable scheme for the {Gaussian} interference channel with delayed {CSIT}},
address = {San Diego, CA},
author = {M. Rezaee and P. J. Schreier and M. Guillaud and B. Clerckx},
booktitle = {Proc. IEEE Global Communications Convference: Communication Theory},
month = {{D}ecember},
year = {2015},
}
[Abstract]85Flag manifolds for the characterization of geometric structure in large data sets
(Tim Marrinan, J. Ross Beveridge, Bruce Draper, Michael Kirby and Chris Peterson)
Numerical Mathematics and Advanced ApplicationsENUMATH 2013, pp. 457–465, Springer, 2015.
DOI:10.1007/9783319107059_45.
[BibTeX]
@inproceedings{marrinanENUMATH,
title = {Flag manifolds for the characterization of geometric structure in large data sets},
author = {Marrinan, Tim and Beveridge, J. Ross and Draper, Bruce and Kirby, Michael and Peterson, Chris},
booktitle = {Numerical Mathematics and Advanced ApplicationsENUMATH 2013},
year = {2015},
pages = {457–465},
doi = {10.1007/9783319107059_45},
publisher = {Springer},
}
[Abstract]86Signal parameter estimation performance under a sampling rate constraint
(Andreas Lenz, Manuel Stein and Josef A. Nossek)
Asilomar Conf. Signals Syst. Computers, Pacific Grove, USA, November 2015. [BibTeX]
@inproceedings{Lenz:ASILO:2015,
title = {Signal parameter estimation performance under a sampling rate constraint},
address = {Pacific Grove, USA},
author = {Lenz, Andreas and Stein, Manuel and Nossek, Josef A.},
booktitle = {{A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {{N}ovember},
year = {2015},
}
[Abstract]87An experimental evaluation of broadband spatial IA for uncoordinated MIMOOFDM systems
(Jacobo Fanjul, Christian Lameiro, Ignacio Santamaría, Jose A. GarcíaNaya and Luis Castedo)
Proc. IEEE Int. Conf. Digital Signal Process., Singapore, July 2015. [BibTeX]
@inproceedings{FanjulLameiroSantamaria:2015:AnExperimentalEvaluationofBroadbandSpatial,
abstract = {In this paper we present an experimental study on the performance of spatial Interference Alignment (IA) in broadband indoor wireless local area network scenarios that use Orthogonal Frequency Division Multiplexing (OFDM) according to the IEEE 802.11a physicallayer specifications. Experiments have been carried out using a wireless network testbed made up of six nodes equipped with MultipleInput MultipleOutput (MIMO) radio interfaces. This setup allows the implementation of a 3user MIMO interference channel. We have implemented different IA decoding schemes that operate either before or after the Fast Fourier Transform block. IA has been experimentally evaluated comparing both approaches to analyze its performance in synchronous and asynchronous transmissions. Our results indicate that spatial IA performs satisfactorily in practical broadband indoor scenarios in which wireless channels often exhibit relatively large coherence times.},
title = {An experimental evaluation of broadband spatial {IA} for uncoordinated {MIMOOFDM} systems},
address = {Singapore},
author = {Fanjul, Jacobo and Lameiro, Christian and Santamar{\'i}a, Ignacio and Garc{\'i}aNaya, Jose A. and Castedo, Luis},
booktitle = {Proc. IEEE Int. Conf. Digital Signal Process.},
month = {July},
year = {2015},
}
[Abstract]
In this paper we present an experimental study on the performance of spatial Interference Alignment (IA) in broadband indoor wireless local area network scenarios that use Orthogonal Frequency Division Multiplexing (OFDM) according to the IEEE 802.11a physicallayer specifications. Experiments have been carried out using a wireless network testbed made up of six nodes equipped with MultipleInput MultipleOutput (MIMO) radio interfaces. This setup allows the implementation of a 3user MIMO interference channel. We have implemented different IA decoding schemes that operate either before or after the Fast Fourier Transform block. IA has been experimentally evaluated comparing both approaches to analyze its performance in synchronous and asynchronous transmissions. Our results indicate that spatial IA performs satisfactorily in practical broadband indoor scenarios in which wireless channels often exhibit relatively large coherence times.88Analysis of maximally improper signalling schemes for underlay cognitive radio
(Christian Lameiro, Ignacio Santamaría and Peter J. Schreier)
Proc. IEEE Int. Conf. Comm., London, UK, June 2015. [BibTeX]
@inproceedings{LameiroSantamariaSchreier:2015:Analysisofmaximallyimpropersignalling,
abstract = {In this paper, the impact of improper Gaussian signaling is studied for an underlay cognitive radio (CR) scenario comprised of a primary user (PU), which has a rate constraint, and a secondary user (SU), both singleantenna. We first derive expressions for the achievable rate of the SU when it transmits proper and maximally improper Gaussian signals (assuming that the SU is solely limited by the CR constraint). These expressions depend on the channel gains to and from the SU through a single variable. Thereby, we observe that improper signaling is beneficial whenever the SU rate is below a threshold, which depends on the signaltonoise ratio (SNR) and rate requirement of the PU. Furthermore, we provide bounds on the achievable gain that also depend only on the PU parameters. Then, the achievable rate is studied from a statistical viewpoint by deriving its cumulative distribution function considering a constant received SNR at the PU. In addition, we specialize this expression for the Z interference channel, for which the expected achievable rate is also derived. Numerical examples illustrate our claims and show that the SU may significantly benefit from using improper signaling.},
title = {Analysis of maximally improper signalling schemes for underlay cognitive radio},
address = {London, UK},
author = {Lameiro, Christian and Santamar{\'i}a, Ignacio and Schreier, Peter J.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {C}omm.},
month = {{J}une},
year = {2015},
}
[Abstract]
In this paper, the impact of improper Gaussian signaling is studied for an underlay cognitive radio (CR) scenario comprised of a primary user (PU), which has a rate constraint, and a secondary user (SU), both singleantenna. We first derive expressions for the achievable rate of the SU when it transmits proper and maximally improper Gaussian signals (assuming that the SU is solely limited by the CR constraint). These expressions depend on the channel gains to and from the SU through a single variable. Thereby, we observe that improper signaling is beneficial whenever the SU rate is below a threshold, which depends on the signaltonoise ratio (SNR) and rate requirement of the PU. Furthermore, we provide bounds on the achievable gain that also depend only on the PU parameters. Then, the achievable rate is studied from a statistical viewpoint by deriving its cumulative distribution function considering a constant received SNR at the PU. In addition, we specialize this expression for the Z interference channel, for which the expected achievable rate is also derived. Numerical examples illustrate our claims and show that the SU may significantly benefit from using improper signaling.89An asymptotic LMPI test for cyclostationarity detection with application to cognitive radio (invited paper)
(D. Ramírez, P. J. Schreier, J. Vía, I. Santamaría and L. L. Scharf)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Brisbane, Australia, April 2015. [BibTeX]
@inproceedings{RamirezSchreierVia:2015:AnasymptoticLMPItestforcyclostationarity,
abstract = {We propose a new detector of primary users in cognitive radio networks. The main novelty of the proposed detector in comparison to most known detectors is that it is based on sound statistical principles for detecting cyclostationary signals. In particular, the proposed detector is (asymptotically) the locally most powerful invariant test, i.e. the best invariant detector for low signaltonoise ratios. The derivation is based on two main ideas: the relationship between a scalarvalued cyclostationary signal and a vectorvalued widesense stationary signal, and Wijsman's theorem. Moreover, using the spectral representation for the cyclostationary time series, the detector has an insightful interpretation, and implementation, as the broadband coherence between frequencies that are separated by multiples of the cycle frequency. Finally, simulations confirm that the proposed detector performs better than previous approaches.},
title = {An asymptotic {LMPI} test for cyclostationarity detection with application to cognitive radio (invited paper)},
address = {Brisbane, Australia},
author = {D. Ram{\'i}rez and P. J. Schreier and J. V{\'i}a and I. Santamar{\'i}a and L. L. Scharf},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{A}pril},
year = {2015},
}
[Abstract]
We propose a new detector of primary users in cognitive radio networks. The main novelty of the proposed detector in comparison to most known detectors is that it is based on sound statistical principles for detecting cyclostationary signals. In particular, the proposed detector is (asymptotically) the locally most powerful invariant test, i.e. the best invariant detector for low signaltonoise ratios. The derivation is based on two main ideas: the relationship between a scalarvalued cyclostationary signal and a vectorvalued widesense stationary signal, and Wijsman's theorem. Moreover, using the spectral representation for the cyclostationary time series, the detector has an insightful interpretation, and implementation, as the broadband coherence between frequencies that are separated by multiples of the cycle frequency. Finally, simulations confirm that the proposed detector performs better than previous approaches.90Modelorder selection for analyzing correlation between two data sets using CCA with PCA preprocessing
(N. Roseveare and P. J. Schreier)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Brisbane, Australia, April 2015. [BibTeX]
@inproceedings{RoseveareSchreier:2015:Modelorderselectionforanalyzingcorrelation,
title = {Modelorder selection for analyzing correlation between two data sets using {CCA} with {PCA} preprocessing},
address = {Brisbane, Australia},
author = {N. Roseveare and P. J. Schreier},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{A}pril},
year = {2015},
}
[Abstract]91Determining the number of correlated signals between two data sets using PCACCA when sample support is extremely small
(Y. Song, P. J. Schreier and N. Roseveare)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Brisbane, Australia, April 2015. [BibTeX]
@inproceedings{SongSchreierRoseveare:2015:Determiningthenumberofcorrelatedsignals,
title = {Determining the number of correlated signals between two data sets using {PCACCA} when sample support is extremely small},
address = {Brisbane, Australia},
author = {Y. Song and P. J. Schreier and N. Roseveare},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{A}pril},
year = {2015},
}
[Abstract]92Ranging with high accuracy and without ambiguities
(Sebastian Theiler, Manuel Stein and Josef A. Nossek)
Proc. IEEE Work. Pos. Nav. & Com., Dresden, Germany, March 2015. [BibTeX]
@inproceedings{Theiler:WPNC:2015,
title = {Ranging with high accuracy and without ambiguities},
address = {Dresden, Germany},
author = {Theiler, Sebastian and Stein, Manuel and Nossek, Josef A.},
booktitle = {{P}roc.\ {IEEE} {W}ork. {P}os.\ {N}av. \& {C}om.},
month = {{M}arch},
year = {2015},
}
[Abstract]93Inputtostate stability for discretetime monotone systems
(Björn S. Rüffer and Rudolf Sailer)
Proc. 21st Int. Symp. Mathematical Theory of Networks and Systems (MTNS), 2014. [BibTeX]
@inproceedings{ruffersailer2014inputtostatestabilityfordiscretetimemonotonesystems,
abstract = {It is well known that inputtostate stability admits an astonishing number of equivalent characterizations. Here it is shown that for monotone systems on $\Rnp$ there are some additional characterizations that are useful for network stability analysis. These characterizations include system theoretic properties, algebraic properties, as well as the problem of finding simultaneous bounds on solutions to a collection of inequalities.},
title = {Inputtostate stability for discretetime monotone systems},
author = {Bj{\"o}rn S. R{\"u}ffer and Rudolf Sailer},
booktitle = {Proc. 21st Int. Symp. Mathematical Theory of Networks and Systems (MTNS)},
year = {2014},
}
[Abstract]
It is well known that inputtostate stability admits an astonishing number of equivalent characterizations. Here it is shown that for monotone systems on Rnp there are some additional characterizations that are useful for network stability analysis. These characterizations include system theoretic properties, algebraic properties, as well as the problem of finding simultaneous bounds on solutions to a collection of inequalities.94Finding the subspace mean or median to fit your need
(Tim Marrinan, Bruce Draper, J. Ross Beveridge, Michael Kirby and Chris Peterson)
CVPR, pp. 1082–1089, 2014.
DOI:10.1109/CVPR.2014.142.
[BibTeX]
@inproceedings{marrinanCVPR,
title = {Finding the subspace mean or median to fit your need},
author = {Marrinan, Tim and Draper, Bruce and Beveridge, J. Ross and Kirby, Michael and Peterson, Chris},
booktitle = {CVPR},
year = {2014},
pages = {1082–1089},
doi = {10.1109/CVPR.2014.142},
}
[Abstract]95A regularized maximum likelihood estimator for the period of a cyclostationary process
(D. Ramírez, P. J. Schreier, J. Vía, I. Santamaría and L. L. Scharf)
Proc. Asilomar Conf. Signals Syst. Computers, Pacific Grove, USA, November 2014. [BibTeX]
@inproceedings{RamirezSchreierVia:2014:ARegularizedMaximumLikelihoodEstimator,
abstract = {We derive an estimator of the cycle period of a univariate cyclostationary process based on an information theoretic criterion. Transforming the univariate cyclostationary process into a vectorvalued widesense stationary process allows us to obtain the structure of the covariance matrix, which is blockToeplitz, and its block size depends on the unknown cycle period. Therefore, we sweep the block size and obtain the ML estimate of the covariance matrix, required for the information theoretic criterion. Since there are no closedform ML estimates of blockToeplitz matrices, we asymptotically approximate them as blockcirculant. Finally, some numerical examples show the good performance of the proposed estimator.},
title = {A regularized maximum likelihood estimator for the period of a cyclostationary process},
address = {Pacific Grove, USA},
author = {D. Ram{\'i}rez and P. J. Schreier and J. V{\'i}a and I. Santamar{\'i}a and L. L. Scharf},
booktitle = {{P}roc.\ {A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {{N}ovember},
year = {2014},
}
[Abstract]
We derive an estimator of the cycle period of a univariate cyclostationary process based on an information theoretic criterion. Transforming the univariate cyclostationary process into a vectorvalued widesense stationary process allows us to obtain the structure of the covariance matrix, which is blockToeplitz, and its block size depends on the unknown cycle period. Therefore, we sweep the block size and obtain the ML estimate of the covariance matrix, required for the information theoretic criterion. Since there are no closedform ML estimates of blockToeplitz matrices, we asymptotically approximate them as blockcirculant. Finally, some numerical examples show the good performance of the proposed estimator.96Interferencetemperature limit for cognitive radio networks with MIMO primary users
(Christian Lameiro, Wolfgang Utschick and Ignacio Santamaría)
Proc. Asilomar Conf. Signals Syst. Computers, Pacific Grove, CA, USA, November 2014.
DOI:10.1109/ACSSC.2014.7094625.
[BibTeX]
@inproceedings{LameiroUtschickSantamaria:2014:InterferenceTemperatureLimitforCognitiveRadio,
abstract = {This paper derives the interferencetemperature (IT) limit for a multiantenna primary user (PU) with a rate constraint. While in the case of a singleantenna PU there is a onetoone mapping between IT and achievable rate, this correspondence does not hold anymore when a multipleinput multipleoutput (MIMO) system is considered. In such cases, the spatial distribution of the interference must be taken into account, since it strongly affects the PU performance. To this end, we derive a closedform expression for the maximum IT that can be tolerated by identifying the worstcase interference covariance matrix, which results in a multilevel waterfilling problem.},
title = {Interferencetemperature limit for cognitive radio networks with {MIMO} primary users},
address = {Pacific Grove, CA, USA},
author = {Lameiro, Christian and Utschick, Wolfgang and Santamar{\'i}a, Ignacio},
booktitle = {{P}roc.\ {A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {{N}ovember},
year = {2014},
doi = {10.1109/ACSSC.2014.7094625},
}
[Abstract]
This paper derives the interferencetemperature (IT) limit for a multiantenna primary user (PU) with a rate constraint. While in the case of a singleantenna PU there is a onetoone mapping between IT and achievable rate, this correspondence does not hold anymore when a multipleinput multipleoutput (MIMO) system is considered. In such cases, the spatial distribution of the interference must be taken into account, since it strongly affects the PU performance. To this end, we derive a closedform expression for the maximum IT that can be tolerated by identifying the worstcase interference covariance matrix, which results in a multilevel waterfilling problem.97Optimizing spatial filters for the extraction of envelopecoupled neural oscillations
(S. Dähne, V. V. Nikulin, D. Ramírez, P. J. Schreier, K.R. Müller and S. Haufe)
Proc. Int. Work. Pattern Recognition In Neuroimaging, Tübingen, Germany, June 2014.
DOI:10.1109/PRNI.2014.6858514.
[BibTeX]
@inproceedings{DahneNikulinRamirez:2014:Optimizingspatialfiltersfortheextraction,
abstract = {Amplitudetoamplitude interactions between neural oscillations are of a special interest as they show how the strength of spatial synchronization in different neuronal populations relates to each other during a given task. While, previously, amplitudetoamplitude correlations were studied primarily on the sensor level, we present a source separation approach using spatial filters which maximize the correlation between the envelopes of brain oscillations recorded with electro/magnetencephalography (EEG/MEG) or intracranial multichannel recordings. Our approach, which is called canonical source power correlation analysis (cSPoC), is thereby capable of extracting genuine brain oscillations solely based on their assumed coupling behavior even when the signaltonoise ratio of the signals is low.},
title = {Optimizing spatial filters for the extraction of envelopecoupled neural oscillations},
address = {T{\"u}bingen, Germany},
author = {S. D{\"a}hne and V. V. Nikulin and D. Ram{\'i}rez and P. J. Schreier and K.R. M{\"u}ller and S. Haufe},
booktitle = {Proc.\ Int. Work. Pattern Recognition In Neuroimaging},
month = {{J}une},
year = {2014},
doi = {10.1109/PRNI.2014.6858514},
}
[Abstract]
Amplitudetoamplitude interactions between neural oscillations are of a special interest as they show how the strength of spatial synchronization in different neuronal populations relates to each other during a given task. While, previously, amplitudetoamplitude correlations were studied primarily on the sensor level, we present a source separation approach using spatial filters which maximize the correlation between the envelopes of brain oscillations recorded with electro/magnetencephalography (EEG/MEG) or intracranial multichannel recordings. Our approach, which is called canonical source power correlation analysis (cSPoC), is thereby capable of extracting genuine brain oscillations solely based on their assumed coupling behavior even when the signaltonoise ratio of the signals is low.98Regularized successive interference cancellation (sic) under mismatched modeling
(Jun Tong, Qinghua Guo, Peter J. Schreier and Jiangtao Xi)
Proc. IEEE Work. Stat. Signal Process., Gold Coast, Australia, June 2014.
DOI:10.1109/SSP.2014.6884642.
[BibTeX]
@inproceedings{TongGuoSchreier:2014:Regularizedsuccessiveinterferencecancellation,
abstract = {Successive interference cancellation (SIC) has been extensively applied to estimate transmit signals in communication systems. When the channel state information (CSI) and noise statistics are imperfectly estimated, the standard SIC estimators that ignore the model mismatch may perform poorly. This paper introduces regularized SIC estimation to provide robustness against the model mismatch. Suboptimal, lowcomplexity implementations using (sorted) QR decomposition and approximate choice of regularization parameters are also introduced. Simulation examples demonstrate that the regularized SIC estimators can significantly outperform the standard version.},
title = {Regularized successive interference cancellation (sic) under mismatched modeling},
address = {Gold Coast, Australia},
author = {Tong, Jun and Guo, Qinghua and Schreier, Peter J. and Xi, Jiangtao},
booktitle = {{P}roc.\ {IEEE} {W}ork.\ {S}tat.\ {S}ignal {P}rocess.},
month = {{J}une},
year = {2014},
doi = {10.1109/SSP.2014.6884642},
}
[Abstract]
Successive interference cancellation (SIC) has been extensively applied to estimate transmit signals in communication systems. When the channel state information (CSI) and noise statistics are imperfectly estimated, the standard SIC estimators that ignore the model mismatch may perform poorly. This paper introduces regularized SIC estimation to provide robustness against the model mismatch. Suboptimal, lowcomplexity implementations using (sorted) QR decomposition and approximate choice of regularization parameters are also introduced. Simulation examples demonstrate that the regularized SIC estimators can significantly outperform the standard version.99An asymptotic GLRT for the detection of cyclostationary signals
(D. Ramírez, L. L. Scharf, J. Vía, I. Santamaría and P. J. Schreier)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Florence, Italy, May 2014.
DOI:10.1109/ICASSP.2014.6854234.
[BibTeX]
@inproceedings{RamirezScharfVia:2014:AnasymptoticGLRTforthedetectionofcyclostationary,
abstract = {We derive the generalized likelihood ratio test (GLRT) for detecting cyclostationarity in scalarvalued time series. The main idea behind our approach is Gladyshev's relationship, which states that when the scalarvalued cyclostationary sig nal is blocked at the known cycle period it produces a vector valued widesense stationary process. This result amounts to saying that the covariance matrix of the vector obtained by stacking all observations of the time series is blockToeplitz if the signal is cyclostationary, and Toeplitz if the signal is wide sense stationary. The derivation of the GLRT requires the maximum likelihood estimates of Toeplitz and blockToeplitz matrices. This can be managed asymptotically (for large num berofsamples)exploitingSzego ̈'stheoremanditsgeneraliza tion for vectorvalued processes. Simulation results show the good performance of the proposed GLRT.},
title = {An asymptotic {GLRT} for the detection of cyclostationary signals},
address = {Florence, Italy},
author = {D. Ram{\'i}rez and L. L. Scharf and J. V{\'i}a and I. Santamar{\'i}a and P. J. Schreier},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2014},
doi = {10.1109/ICASSP.2014.6854234},
}
[Abstract]
We derive the generalized likelihood ratio test (GLRT) for detecting cyclostationarity in scalarvalued time series. The main idea behind our approach is Gladyshev's relationship, which states that when the scalarvalued cyclostationary sig nal is blocked at the known cycle period it produces a vector valued widesense stationary process. This result amounts to saying that the covariance matrix of the vector obtained by stacking all observations of the time series is blockToeplitz if the signal is cyclostationary, and Toeplitz if the signal is wide sense stationary. The derivation of the GLRT requires the maximum likelihood estimates of Toeplitz and blockToeplitz matrices. This can be managed asymptotically (for large num berofsamples)exploitingSzego ̈'stheoremanditsgeneraliza tion for vectorvalued processes. Simulation results show the good performance of the proposed GLRT.100Interference shaping constraints for underlay MIMO interference channels
(Christian Lameiro, Ignacio Santamaría and Wolfgang Utschick)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Florence, Italy, May 2014.
DOI:10.1109/ICASSP.2014.6855020.
[BibTeX]
@inproceedings{LameiroSantamariaUtschick:2014:InterferenceShapingConstraintsforUnderlay,
abstract = {In this paper, a cognitive radio (CR) scenario comprised of a secondary interference channel (IC) and a primary pointtopoint link (PPL) is studied, when the former interferes the latter. In order to satisfy a given rate requirement at the PPL, typical approaches impose an interference temperature constraint (IT). When the PPL transmits multiple streams, however, the spatial structure of the interference comes into play. In such cases, we show that spatial interference shaping constraints can provide higher sumrate performance to the IC while ensuring the required rate at the PPL. Then, we extend the interference leakage minimization algorithm (MinIL) to incorporate such constraints. An additional power control step is included in the optimization procedure to improve the sumrate when the interference alignment (IA) problem becomes infeasible due to the additional constraint. Numerical examples are provided to illustrate the effectiveness of the spatial shaping constraint in comparison to IT when the PPL transmits multiple data streams.},
title = {Interference shaping constraints for underlay {MIMO} interference channels},
address = {Florence, Italy},
author = {Lameiro, Christian and Santamar{\'i}a, Ignacio and Utschick, Wolfgang},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2014},
doi = {10.1109/ICASSP.2014.6855020},
}
[Abstract]
In this paper, a cognitive radio (CR) scenario comprised of a secondary interference channel (IC) and a primary pointtopoint link (PPL) is studied, when the former interferes the latter. In order to satisfy a given rate requirement at the PPL, typical approaches impose an interference temperature constraint (IT). When the PPL transmits multiple streams, however, the spatial structure of the interference comes into play. In such cases, we show that spatial interference shaping constraints can provide higher sumrate performance to the IC while ensuring the required rate at the PPL. Then, we extend the interference leakage minimization algorithm (MinIL) to incorporate such constraints. An additional power control step is included in the optimization procedure to improve the sumrate when the interference alignment (IA) problem becomes infeasible due to the additional constraint. Numerical examples are provided to illustrate the effectiveness of the spatial shaping constraint in comparison to IT when the PPL transmits multiple data streams.101Optimum analog receive filters for detection and inference under a sampling rate constraint
(Manuel Stein, Andreas Lenz, Amine Mezghani and Josef A. Nossek)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Florence, Italy, May 2014. [BibTeX]
@inproceedings{Stein:ICASSP:2014,
title = {Optimum analog receive filters for detection and inference under a sampling rate constraint},
address = {Florence, Italy},
author = {Stein, Manuel and Lenz, Andreas and Mezghani, Amine and Nossek, Josef A.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2014},
}
[Abstract]102Spatial shaping and precoding design for underlay MIMO interference channels
(Christian Lameiro, Wolfgang Utschick and Ignacio Santamaría)
Proc.Int. ITG Work. Smart Antennas, Erlangen, Germany, March 2014. [BibTeX]
@inproceedings{LameiroUtschickSantamaria:2014:SpatialShapingandPrecodingDesign,
abstract = {In this paper, we study coexistence issues between an underlay singlebeam interference channel (IC) and a primary pointtopoint link (PPL) that has a rate constraint. We derive spatial shaping constraints at the secondary transmitters and show that they generalize the socalled interference temperature (IT) when the PPL transmits multiple streams. We propose a successive convex approximation algorithm to compute the spatial shaping matrices that maximize the allowed transmit power of the IC while ensuring the rate constraint of the PPL. Then, we provide general interference leakage minimization (MinIL) and maximum signaltointerferenceplusnoise ratio (MaxSINR) algorithms that can incorporate both types of constraint. An additional power control step is included in the optimization procedure to further improve the sumrate of the IC. Different numerical examples are provided to illustrate the effectiveness of the proposed techniques and to compare the performance improvement when the IC is subject to spatial shaping constraints in comparison to IT.},
title = {Spatial shaping and precoding design for underlay {MIMO} interference channels},
address = {Erlangen, Germany},
author = {Lameiro, Christian and Utschick, Wolfgang and Santamar{\'i}a, Ignacio},
booktitle = {Proc.Int. ITG Work. Smart Antennas},
month = {{M}arch},
year = {2014},
}
[Abstract]
In this paper, we study coexistence issues between an underlay singlebeam interference channel (IC) and a primary pointtopoint link (PPL) that has a rate constraint. We derive spatial shaping constraints at the secondary transmitters and show that they generalize the socalled interference temperature (IT) when the PPL transmits multiple streams. We propose a successive convex approximation algorithm to compute the spatial shaping matrices that maximize the allowed transmit power of the IC while ensuring the rate constraint of the PPL. Then, we provide general interference leakage minimization (MinIL) and maximum signaltointerferenceplusnoise ratio (MaxSINR) algorithms that can incorporate both types of constraint. An additional power control step is included in the optimization procedure to further improve the sumrate of the IC. Different numerical examples are provided to illustrate the effectiveness of the proposed techniques and to compare the performance improvement when the IC is subject to spatial shaping constraints in comparison to IT.103Informationpreserving spatial filtering for directionofarrival estimation
(Manuel Stein, Mario Castañeda and Josef A. Nossek)
Proc. ITG Int. Work. Smart Ant., Erlangen, Germany, March 2014. [BibTeX]
@inproceedings{Stein:WSA:2014,
title = {Informationpreserving spatial filtering for directionofarrival estimation},
address = {Erlangen, Germany},
author = {Stein, Manuel and Casta{\~n}eda, Mario and Nossek, Josef A.},
booktitle = {{P}roc.\ {ITG} {I}nt.\ {W}ork.\ Smart Ant.},
month = {{M}arch},
year = {2014},
}
[Abstract]104Will the 1bit GNSS receiver prevail?
(Manuel Stein and Josef A. Nossek)
Proc. IEEE/ION Pos. Nav. Symp., Monterey, USA, March 2014. [BibTeX]
@inproceedings{Stein:PLANS:2014,
title = {Will the 1bit {GNSS} receiver prevail?},
address = {Monterey, USA},
author = {Stein, Manuel and Nossek, Josef A.},
booktitle = {{P}roc.\ {IEEE}{\/}{ION} {P}os. {N}av.\ Symp.},
month = {{M}arch},
year = {2014},
}
[Abstract]105Inputdependent stability analysis of systems with saturation in feedback
(Alexander Yu. Pogromsky, Alexey S. Matveev, Antoine Chaillet and Björn S. Rüffer)
Proc. 52nd IEEE Conf. Decis. Control, pp. 5903–5908, 2013. [BibTeX]
@inproceedings{pogromskymatveevchailletruffer2013inputdependentstabilityanalysisofsystemswithsaturationinfeedback,
abstract = {The paper deals with global stability analysis of linear control systems with saturation in feedback driven by an external input. Various new criteria based on nonquadratic Lyapunov functions are proposed, that unlike many previous results, offer better account for the role of the external excitation by providing inputdependent conditions for stability of solutions. For example, it is shown that even if the system fails to satisfy the incremental version of the circle criterion, the stability is guaranteed whenever the uniform root mean square value of the input signal is less than a computable threshold. The general theoretical results are illustrated in the case of the double integrator closed by a saturated linear feedback with an external excitation.},
title = {Inputdependent stability analysis of systems with saturation in feedback},
author = {Alexander {Yu.} Pogromsky and Alexey S. Matveev and Antoine Chaillet and Bj{\"o}rn S. R{\"u}ffer},
booktitle = {{P}roc. 52nd {IEEE} {C}onf. {D}ecis. {C}ontrol},
year = {2013},
pages = {5903–5908},
}
[Abstract]
The paper deals with global stability analysis of linear control systems with saturation in feedback driven by an external input. Various new criteria based on nonquadratic Lyapunov functions are proposed, that unlike many previous results, offer better account for the role of the external excitation by providing inputdependent conditions for stability of solutions. For example, it is shown that even if the system fails to satisfy the incremental version of the circle criterion, the stability is guaranteed whenever the uniform root mean square value of the input signal is less than a computable threshold. The general theoretical results are illustrated in the case of the double integrator closed by a saturated linear feedback with an external excitation.106Separable Lyapunov functions for monotone systems
(Anders Rantzer, Björn S. Rüffer and Gunther Dirr)
Proc. 52nd IEEE Conf. Decis. Control, pp. 4590–4594, 2013. [BibTeX]
@inproceedings{rantzerrufferdirr2013separablelyapunovfunctionsformonotonesystems,
abstract = {Separable Lyapunov functions play vital roles, for example, in stability analysis of largescale systems. A Lyapunov function is called maxseparable if it can be decomposed into a maximum of functions with onedimensional arguments. Similarly, it is called sumseparable if it is a sum of such functions. In this paper it is shown that for a monotone system on a compact state space, asymptotic stability implies existence of a maxseparable Lyapunov function. We also construct two systems on a noncompact state space, for which a maxseparable Lyapunov function does not exist. One of them has a sumseparable Lyapunov function. The other does not.},
title = {Separable {L}yapunov functions for monotone systems},
author = {Anders Rantzer and Bj{\"o}rn S. R{\"u}ffer and Gunther Dirr},
booktitle = {{P}roc. 52nd {IEEE} {C}onf. {D}ecis. {C}ontrol},
year = {2013},
pages = {4590–4594},
}
[Abstract]
Separable Lyapunov functions play vital roles, for example, in stability analysis of largescale systems. A Lyapunov function is called maxseparable if it can be decomposed into a maximum of functions with onedimensional arguments. Similarly, it is called sumseparable if it is a sum of such functions. In this paper it is shown that for a monotone system on a compact state space, asymptotic stability implies existence of a maxseparable Lyapunov function. We also construct two systems on a noncompact state space, for which a maxseparable Lyapunov function does not exist. One of them has a sumseparable Lyapunov function. The other does not.107A Razumikhin approach for the incremental stability of delayed nonlinear systems
(Antoine Chaillet, Alexander Yu. Pogromsky and Björn S. Rüffer)
Proc. 52nd IEEE Conf. Decis. Control, pp. 1596–1601, 2013. [BibTeX]
@inproceedings{chailletpogromskyruffer2013arazumikhinapproachfortheincrementalstabilityofdelayednonlinearsystems,
abstract = {This paper provides sufficient conditions for the incremental stability of timedelayed nonlinear systems. It relies on the RazumikhinLyapunov approach, which consists in invoking smallgain arguments by treating the delayed state as a feedback perturbation. The results are valid for multiple delays, as well as bounded timevarying delays. We provide conditions under which the limit solution of a timedelayed nonlinear system to a periodic (resp. constant) input is itself periodic and of the same period (resp. constant). As an illustration, a specific focus is given on a class of delayed Lur'e systems.},
title = {A {R}azumikhin approach for the incremental stability of delayed nonlinear systems},
author = {Antoine Chaillet and Alexander {Yu.} Pogromsky and Bj{\"o}rn S. R{\"u}ffer},
booktitle = {{P}roc. 52nd {IEEE} {C}onf. {D}ecis. {C}ontrol},
year = {2013},
pages = {1596–1601},
}
[Abstract]
This paper provides sufficient conditions for the incremental stability of timedelayed nonlinear systems. It relies on the RazumikhinLyapunov approach, which consists in invoking smallgain arguments by treating the delayed state as a feedback perturbation. The results are valid for multiple delays, as well as bounded timevarying delays. We provide conditions under which the limit solution of a timedelayed nonlinear system to a periodic (resp. constant) input is itself periodic and of the same period (resp. constant). As an illustration, a specific focus is given on a class of delayed Lur'e systems.108A twophase approach to stability of networks given in iISS framework: utilization of a matrixlike criterion
(Hiroshi Ito and Björn S. Rüffer)
Proc. IEEE American Contr. Conf., pp. 4838–4843, 2013. [BibTeX]
@inproceedings{itoruffer2013atwophaseapproachtostabilityofnetworksgiveniniissframework:utilizationofamatrixlikecriterion,
abstract = {This article is concerned with global asymptotic stability (GAS) of dynamical networks. The case when subsystems are integral inputtostate stable (iISS) has been recognized as notoriously difficult to deal with in the literature. In fact, the lack of energy dissipation for large input denies direct application of the smallgain argument for inputtostate stable (ISS) subsystems. Here for networks consisting of iISS subsystems it is demonstrated that a twophase approach allows us to make use of the ISS smallgain argument by separating a trajectory into a transient and a subsequent convergence. In contrast to the previous iISS results, the twophase approach immediately leads to a sufficient criterion for GAS of general nonlinear networks in a matrixlike form (order condition).},
title = {A twophase approach to stability of networks given in {iISS} framework: utilization of a matrixlike criterion},
author = {Ito, Hiroshi and R{\"u}ffer, Bj{\"o}rn S.},
booktitle = {{P}roc. {IEEE} {A}merican {C}ontr. {C}onf.},
year = {2013},
pages = {4838–4843},
}
[Abstract]
This article is concerned with global asymptotic stability (GAS) of dynamical networks. The case when subsystems are integral inputtostate stable (iISS) has been recognized as notoriously difficult to deal with in the literature. In fact, the lack of energy dissipation for large input denies direct application of the smallgain argument for inputtostate stable (ISS) subsystems. Here for networks consisting of iISS subsystems it is demonstrated that a twophase approach allows us to make use of the ISS smallgain argument by separating a trajectory into a transient and a subsequent convergence. In contrast to the previous iISS results, the twophase approach immediately leads to a sufficient criterion for GAS of general nonlinear networks in a matrixlike form (order condition).109Linear equalization in communications with mismatched modeling using Krylov subspace expansion
(Jun Tong and Peter J. Schreier)
Proc. IEEE Wireless Comm. Networking Conf. (WCNC), 2013. [BibTeX]
@inproceedings{TongSchreier:2013:Linearequalizationincomm,
title = {Linear equalization in communications with mismatched modeling using {K}rylov subspace expansion},
author = {Tong, Jun and Schreier, Peter J.},
booktitle = {Proc. IEEE Wireless Comm. Networking Conf. (WCNC)},
year = {2013},
}
[Abstract]110Joint spacetime interference mitigation for embedded multiantenna GNSS receivers
(Mario Castañeda, Manuel Stein, Felix Antreich, Emrah Tasdemir, Lothar Kurz, Tobias G. Noll and Josef A. Nossek)
ION GNSS+, Nashville, USA, September 2013. [BibTeX]
@inproceedings{Castaneda:ICASSP:2013,
title = {Joint spacetime interference mitigation for embedded multiantenna {GNSS} receivers},
address = {Nashville, USA},
author = {Casta{\~n}eda, Mario and Stein, Manuel and Antreich, Felix and Tasdemir, Emrah and Kurz, Lothar and Noll, Tobias G. and Nossek, Josef A.},
booktitle = {{ION} {G}NSS+},
month = {{S}eptember},
year = {2013},
}
[Abstract]111An interference alignment algorithm for structured channels
(Christian Lameiro, Óscar González and Ignacio Santamaría)
Proc. IEEE Work. Signal Process. Advances in Wireless Comm., Darmstadt, Germany, June 2013.
DOI:10.1109/SPAWC.2013.6612059.
[BibTeX]
@inproceedings{LameiroGonzalezSantamaria:2013:AnInterferenceAlignmentAlgorithmforStructured,
abstract = {In this paper we propose a new interference alignment (IA) algorithm specifically designed to work with structured channels (e.g., diagonal or blockdiagonal). Multipleinput multipleoutput (MIMO) structured channels arise when symbol extensions either in time or frequency are employed jointly with the spatial dimension in the design of the precoders. In this case, the rank constraint in the direct channels must explicitly be taken into account into the optimization problem to ensure that there is no degreesoffreedom (DoF) loss. To this end, we propose an algorithm that minimizes the interference leakage while ensuring that the direct links are full rank and the transmitters satisfy a power constraint. The algorithm is based upon an alternating optimization procedure, which solves a generalized eigenvalue problem at each step. We show through simulations the advantages of the proposed algorithm in several scenarios that use symbols extensions or improper (a.k.a. asymmetric) signalling.},
title = {An interference alignment algorithm for structured channels},
address = {Darmstadt, Germany},
author = {Lameiro, Christian and Gonz{\'a}lez, {\'O}scar and Santamar{\'i}a, Ignacio},
booktitle = {Proc. IEEE Work. Signal Process. Advances in Wireless Comm.},
month = {{J}une},
year = {2013},
doi = {10.1109/SPAWC.2013.6612059},
}
[Abstract]
In this paper we propose a new interference alignment (IA) algorithm specifically designed to work with structured channels (e.g., diagonal or blockdiagonal). Multipleinput multipleoutput (MIMO) structured channels arise when symbol extensions either in time or frequency are employed jointly with the spatial dimension in the design of the precoders. In this case, the rank constraint in the direct channels must explicitly be taken into account into the optimization problem to ensure that there is no degreesoffreedom (DoF) loss. To this end, we propose an algorithm that minimizes the interference leakage while ensuring that the direct links are full rank and the transmitters satisfy a power constraint. The algorithm is based upon an alternating optimization procedure, which solves a generalized eigenvalue problem at each step. We show through simulations the advantages of the proposed algorithm in several scenarios that use symbols extensions or improper (a.k.a. asymmetric) signalling.112Degreesoffreedom for the 4user SISO interference channel with improper signaling
(Christian Lameiro and Ignacio Santamaría)
Proc. IEEE Int. Conf. Comm., Budapest, Hungary, June 2013.
DOI:10.1109/ICC.2013.6655009.
[BibTeX]
@inproceedings{LameiroSantamaria:2013:DegreesofFreedomforthe4UserSISOInterference,
abstract = {It has been recently shown that for the 3user singleinput singleoutput (SISO) interference channel with constant channel coefficients, a maximum of 1.2 degreesoffreedom (DoF) are achievable using linear interference alignment schemes when improper (a.k.a. asymmetric) Gaussian signaling is applied. In this paper, we study the 4user SISO interference channel and provide inner and outer bounds for the total number of DoF achievable for this channel. We prove that at least 4/3 DoF are achievable for the 4user channel using also linear interference alignment techniques and improper signaling. A simple converse proof shows that no more than 8/5 DoF are achievable for this scheme. Simulation results seem to indicate that the inner bound is in fact tight for this channel, and serve to illustrate the sumrate improvement with respect to time division multiple access (TDMA) techniques.},
title = {Degreesoffreedom for the 4user {SISO} interference channel with improper signaling},
address = {Budapest, Hungary},
author = {Lameiro, Christian and Santamar{\'i}a, Ignacio},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {C}omm.},
month = {{J}une},
year = {2013},
doi = {10.1109/ICC.2013.6655009},
}
[Abstract]
It has been recently shown that for the 3user singleinput singleoutput (SISO) interference channel with constant channel coefficients, a maximum of 1.2 degreesoffreedom (DoF) are achievable using linear interference alignment schemes when improper (a.k.a. asymmetric) Gaussian signaling is applied. In this paper, we study the 4user SISO interference channel and provide inner and outer bounds for the total number of DoF achievable for this channel. We prove that at least 4/3 DoF are achievable for the 4user channel using also linear interference alignment techniques and improper signaling. A simple converse proof shows that no more than 8/5 DoF are achievable for this scheme. Simulation results seem to indicate that the inner bound is in fact tight for this channel, and serve to illustrate the sumrate improvement with respect to time division multiple access (TDMA) techniques.113Principal component analysis to extract blood oxygenation from theoretical modeling of total diffuse reflectance spectra
(Alma Eguizabal, Pilar GarciaAllende, Karin Jentoft, Panagiotis Symvoulidis, Jose LopezHiguera, Vasilis Ntziachristos and Olga M. Conde)
European Conferences on Biomedical Optics, Munich, Germany, May 2013. [BibTeX]
@inproceedings{EguizabalGarciaallendeJentoft:2013:PrincipalComponentAnalysistoextractblood,
abstract = {Endogenous tissue contrast such as decreased hemoglobin saturation aids in cancer localization. Principal component analysis is proposed for blindly oxygenation extraction from total diffuse reflectance spectra obtained by the diffusion approximation.},
title = {Principal component analysis to extract blood oxygenation from theoretical modeling of total diffuse reflectance spectra},
address = {Munich, Germany},
author = {Alma Eguizabal and Pilar GarciaAllende and Karin Jentoft and Panagiotis Symvoulidis and Jose LopezHiguera and Vasilis Ntziachristos and Olga M. Conde},
booktitle = {European Conferences on Biomedical Optics},
month = {{M}ay},
year = {2013},
}
[Abstract]
Endogenous tissue contrast such as decreased hemoglobin saturation aids in cancer localization. Principal component analysis is proposed for blindly oxygenation extraction from total diffuse reflectance spectra obtained by the diffusion approximation.114PowerCCA: maximizing the correlation coefficient between the power of projections
(D. Ramírez, P. J. Schreier, J. Vía and V. V. Nikulin)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Vancouver, Canada, May 2013.
DOI:10.1109/ICASSP.2013.6638864.
[BibTeX]
@inproceedings{RamirezSchreierVia:2013:PowerCCA:MaximizingtheCorrelationCoefficient,
abstract = {This work presents a variation of canonical correlation analysis (CCA), where the correlation coefficient between the instantaneous power of the projections is maximized, rather than between the projections themselves. The resulting optimization problem is not convex, and we have to resort to a suboptimal approach. Concretely, we propose a twostep solution consisting of the singular value decomposition (SVD) of a "coherence" matrix followed by a rankone matrix approximation. This technique is applied to blindly recovering signals in a model that is motivated by the study of neuronal dynamics in humans using electroencephalography (EEG) and magnetoencephalography (MEG). A distinctive feature of this model is that it allows recovery of amplitudeamplitude coupling between neuronal processes.},
title = {Power{CCA}: maximizing the correlation coefficient between the power of projections},
address = {Vancouver, Canada},
author = {D. Ram{\'i}rez and P. J. Schreier and J. V{\'i}a and V. V. Nikulin},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2013},
doi = {10.1109/ICASSP.2013.6638864},
}
[Abstract]
This work presents a variation of canonical correlation analysis (CCA), where the correlation coefficient between the instantaneous power of the projections is maximized, rather than between the projections themselves. The resulting optimization problem is not convex, and we have to resort to a suboptimal approach. Concretely, we propose a twostep solution consisting of the singular value decomposition (SVD) of a "coherence" matrix followed by a rankone matrix approximation. This technique is applied to blindly recovering signals in a model that is motivated by the study of neuronal dynamics in humans using electroencephalography (EEG) and magnetoencephalography (MEG). A distinctive feature of this model is that it allows recovery of amplitudeamplitude coupling between neuronal processes.115Optical coherence tomography assessment of vessel wall degradation in aneurysmatic thoracic aortas
(Eusebio Real, Alma Eguizabal, Alejandro Ponton, J. Fernando ValBernal, Marta Mayorga, Jose Revuelta, Jose LopezHiguera and Olga Conde)
European Conferences on Biomedical Optics, Munich, Germany, May 2013. [BibTeX]
@inproceedings{RealEguizabalPonton:2013:OpticalCoherenceTomographyAssesmentofVessel,
abstract = {OCT images of human aorta from aneurysms reveals elastin disorder and smooth muscle cell alteration when visualizing the intima and media layers of the aortic wall. Results correlate with pathologist diagnosis in aneurysmatic and control aortas.},
title = {Optical coherence tomography assessment of vessel wall degradation in aneurysmatic thoracic aortas},
address = {Munich, Germany},
author = {Eusebio Real and Alma Eguizabal and Alejandro Ponton and J. Fernando ValBernal and Marta Mayorga and Jose Revuelta and Jose LopezHiguera and Olga Conde},
booktitle = {European Conferences on Biomedical Optics},
month = {{M}ay},
year = {2013},
}
[Abstract]
OCT images of human aorta from aneurysms reveals elastin disorder and smooth muscle cell alteration when visualizing the intima and media layers of the aortic wall. Results correlate with pathologist diagnosis in aneurysmatic and control aortas.116Computing the degrees of freedom for arbitrary MIMO interference channels
(Óscar González, Christian Lameiro, Javier Vía, Carlos Beltrán and Ignacio Santamaría)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Vancouver, Canada, May 2013.
DOI:10.1109/ICASSP.2013.6638491.
[BibTeX]
@inproceedings{GonzalezLameiroVia:2013:ComputingtheDegreesofFreedomforArbitrary,
abstract = {In this paper we provide an efficient procedure to compute the total number of degrees of freedom (DoF), achievable by linear beamforming, of the $K$user multipleinput multipleoutput (MIMO) interference channel with an arbitrary number of TxRx antennas at each link. Firstly, we derive an analytical outer bound that generalizes the results that exist for the symmetric $K$user $M\timesN$ interference channel. Secondly, we obtain a tighter bound by solving a convex optimization problem that includes as constraints the DoF characterizations for pointtopoint MIMO links and for 2user interference channels. The solution to this convex problem admits an interesting waterfilling interpretation. Finally, exploiting this outer bound and using a recently proposed feasibility test, we show that it is possible to obtain the DoF for any interference channel in an efficient way. Some simulations results are included to illustrate the tightness of the derived bounds, as well as to study the DoF achievable for the 4user channel when we distribute the total number of antennas among users and between transmitters and receivers in different ways.},
title = {Computing the degrees of freedom for arbitrary {MIMO} interference channels},
address = {Vancouver, Canada},
author = {Gonz{\'a}lez, {\'O}scar and Lameiro, Christian and V{\'i}a, Javier and Beltr{\'a}n, Carlos and Santamar{\'i}a, Ignacio},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2013},
doi = {10.1109/ICASSP.2013.6638491},
}
[Abstract]
In this paper we provide an efficient procedure to compute the total number of degrees of freedom (DoF), achievable by linear beamforming, of the Kuser multipleinput multipleoutput (MIMO) interference channel with an arbitrary number of TxRx antennas at each link. Firstly, we derive an analytical outer bound that generalizes the results that exist for the symmetric Kuser MtimesN interference channel. Secondly, we obtain a tighter bound by solving a convex optimization problem that includes as constraints the DoF characterizations for pointtopoint MIMO links and for 2user interference channels. The solution to this convex problem admits an interesting waterfilling interpretation. Finally, exploiting this outer bound and using a recently proposed feasibility test, we show that it is possible to obtain the DoF for any interference channel in an efficient way. Some simulations results are included to illustrate the tightness of the derived bounds, as well as to study the DoF achievable for the 4user channel when we distribute the total number of antennas among users and between transmitters and receivers in different ways.117Quantizationloss reduction for signal parameter estimation
(Manuel Stein, Friederike Wendler, Amine Mezghani and Josef A. Nossek)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Vancouver, Canada, May 2013. [BibTeX]
@inproceedings{Stein:ICASSP:2013,
title = {Quantizationloss reduction for signal parameter estimation},
address = {Vancouver, Canada},
author = {Stein, Manuel and Wendler, Friederike and Mezghani, Amine and Nossek, Josef A.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2013},
}
[Abstract]118Quantizationloss analysis for array signalsource localization
(Manuel Stein, Amine Mezghani and Josef A. Nossek)
Proc. ITG Int. Work. Smart Ant., Stuttgart, Germany, March 2013. [BibTeX]
@inproceedings{Stein:WSA:2013,
title = {Quantizationloss analysis for array signalsource localization},
address = {Stuttgart, Germany},
author = {Stein, Manuel and Mezghani, Amine and Nossek, Josef A.},
booktitle = {{P}roc.\ {ITG} {I}nt.\ {W}ork.\ Smart Ant.},
month = {{M}arch},
year = {2013},
}
[Abstract]119Linear classifier and textural analysis of optical scattering images for tumor classification during breast cancer extraction
(Alma Eguizabal, Ashley M. Laughney, P. Beatriz GarciaAllende, Venkataramanan Krishnaswamy, Wendy A. Wells, Keith D. Paulsen, Brian W. Pogue, Jose LopezHiguera and Olga M. Conde)
SPIE Photonics West BIOS, VIII Biomedical Applications of Light Scattering, San Francisco, USA, February 2013. [BibTeX]
@inproceedings{EguizabalLaughneyGarciaallende:2013:Linearclassifierandtexturalanalysisofopticalscattering,
abstract = {Texture analysis of light scattering in tissue is proposed to obtain diagnostic information from breast cancer specimens. Light scattering measurements are minimally invasive, and allow the estimation of tissue morphology to guide the surgeon in resection surgeries. The usability of scatter signatures acquired with a microsampling reflectance spectral imaging system was improved utilizing an empirical approximation to the Mie theory to estimate the scattering power on a perpixel basis. Cooccurrence analysis is then applied to the scattering power images to extract the textural features. A statistical analysis of the features demonstrated the suitability of the autocorrelation for the classification of notmalignant (normal epithelia and stroma, benign epithelia and stroma, inflammation), malignant (DCIS, IDC, ILC) and adipose tissue, since it reveals morphological information of tissue. Nonmalignant tissue shows higher autocorrelation values while adipose tissue presents a very low autocorrelation on its scatter texture, being malignant the middle ground. Consequently, a fast linear classifier based on the consideration of just one straightforward feature is enough for providing relevant diagnostic information. A leaveoneout validation of the linear classifier on 29 samples with 48 regions of interest showed classification accuracies of 98.74% on adipose tissue, 82.67% on nonmalignant tissue and 72.37% on malignant tissue, in comparison with the biopsy H and E gold standard. This demonstrates that autocorrelation analysis of scatter signatures is a very computationally efficient and automated approach to provide pathological information in realtime to guide surgeon during tissue resection.},
title = {Linear classifier and textural analysis of optical scattering images for tumor classification during breast cancer extraction},
address = {San Francisco, USA},
author = {Alma Eguizabal and Ashley M. Laughney and P. Beatriz GarciaAllende and Venkataramanan Krishnaswamy and Wendy A. Wells and Keith D. Paulsen and Brian W. Pogue and Jose LopezHiguera and Olga M. Conde},
booktitle = {SPIE Photonics West BIOS, VIII Biomedical Applications of Light Scattering},
month = {{F}ebruary},
year = {2013},
}
[Abstract]
Texture analysis of light scattering in tissue is proposed to obtain diagnostic information from breast cancer specimens. Light scattering measurements are minimally invasive, and allow the estimation of tissue morphology to guide the surgeon in resection surgeries. The usability of scatter signatures acquired with a microsampling reflectance spectral imaging system was improved utilizing an empirical approximation to the Mie theory to estimate the scattering power on a perpixel basis. Cooccurrence analysis is then applied to the scattering power images to extract the textural features. A statistical analysis of the features demonstrated the suitability of the autocorrelation for the classification of notmalignant (normal epithelia and stroma, benign epithelia and stroma, inflammation), malignant (DCIS, IDC, ILC) and adipose tissue, since it reveals morphological information of tissue. Nonmalignant tissue shows higher autocorrelation values while adipose tissue presents a very low autocorrelation on its scatter texture, being malignant the middle ground. Consequently, a fast linear classifier based on the consideration of just one straightforward feature is enough for providing relevant diagnostic information. A leaveoneout validation of the linear classifier on 29 samples with 48 regions of interest showed classification accuracies of 98.74% on adipose tissue, 82.67% on nonmalignant tissue and 72.37% on malignant tissue, in comparison with the biopsy H and E gold standard. This demonstrates that autocorrelation analysis of scatter signatures is a very computationally efficient and automated approach to provide pathological information in realtime to guide surgeon during tissue resection.120Fractal analysis of scatter imaging signatures to distinguish breast pathologies
(Alma Eguizabal, Ashley M. Laughney, Venkataramanan Krishnaswamy, Wendy A. Wells, Keith D. Paulsen, Brian W. Pogue, Jose LopezHiguera and Olga M. Conde)
SPIE Photonics West BIOS, VIII Biomedical Applications of Light Scattering, San Francisco, USA, February 2013. [BibTeX]
@inproceedings{EguizabalLaughneyKrishnaswamy:2013:Fractalanalysisofscatterimagingsignatures,
abstract = {Fractal analysis combined with a labelfree scattering technique is proposed for describing the pathological architecture of tumors. Clinicians and pathologists are conventionally trained to classify abnormal features such as structural irregularities or high indices of mitosis. The potential of fractal analysis lies in the fact of being a morphometric measure of the irregular structures providing a measure of the object's complexity and selfsimilarity. As cancer is characterized by disorder and irregularity in tissues, this measure could be related to tumor growth. Fractal analysis has been probed in the understanding of the tumor vasculature network. This work addresses the feasibility of applying fractal analysis to the scattering power map (as a physical modeling) and principal components (as a statistical modeling) provided by a localized reflectance spectroscopic system. Disorder, irregularity and cell size variation in tissue samples is translated into the scattering power and principal components magnitude and its fractal dimension is correlated with the pathologist assessment of the samples. The fractal dimension is computed applying the boxcounting technique. Results show that fractal analysis of exvivo fresh tissue samples exhibits separated ranges of fractal dimension that could help classifier combining the fractal results with other morphological features. This contrast trend would help in the discrimination of tissues in the intraoperative context and may serve as a useful adjunct to surgeons.},
title = {Fractal analysis of scatter imaging signatures to distinguish breast pathologies},
address = {San Francisco, USA},
author = {Alma Eguizabal and Ashley M. Laughney and Venkataramanan Krishnaswamy and Wendy A. Wells and Keith D. Paulsen and Brian W. Pogue and Jose LopezHiguera and Olga M. Conde},
booktitle = {SPIE Photonics West BIOS, VIII Biomedical Applications of Light Scattering},
month = {{F}ebruary},
year = {2013},
}
[Abstract]
Fractal analysis combined with a labelfree scattering technique is proposed for describing the pathological architecture of tumors. Clinicians and pathologists are conventionally trained to classify abnormal features such as structural irregularities or high indices of mitosis. The potential of fractal analysis lies in the fact of being a morphometric measure of the irregular structures providing a measure of the object's complexity and selfsimilarity. As cancer is characterized by disorder and irregularity in tissues, this measure could be related to tumor growth. Fractal analysis has been probed in the understanding of the tumor vasculature network. This work addresses the feasibility of applying fractal analysis to the scattering power map (as a physical modeling) and principal components (as a statistical modeling) provided by a localized reflectance spectroscopic system. Disorder, irregularity and cell size variation in tissue samples is translated into the scattering power and principal components magnitude and its fractal dimension is correlated with the pathologist assessment of the samples. The fractal dimension is computed applying the boxcounting technique. Results show that fractal analysis of exvivo fresh tissue samples exhibits separated ranges of fractal dimension that could help classifier combining the fractal results with other morphological features. This contrast trend would help in the discrimination of tissues in the intraoperative context and may serve as a useful adjunct to surgeons.121Quantizationloss reduction for 1bit BOC positioning
(Friederike Wendler, Manuel Stein, Amine Mezghani and Josef A. Nossek)
ION Int. Tech. Meet., San Diego, USA, January 2013. [BibTeX]
@inproceedings{Wendler:ITM:2013,
title = {Quantizationloss reduction for 1bit {BOC} positioning},
address = {San Diego, USA},
author = {Wendler, Friederike and Stein, Manuel and Mezghani, Amine and Nossek, Josef A.},
booktitle = {{ION} {I}nt.\ {T}ech.\ Meet.},
month = {{J}anuary},
year = {2013},
}
[Abstract]122Small gain theorems for large scale systems and construction of ISS Lyapunov functions
(Sergey N. Dashkovskiy, Björn S. Rüffer and Fabian R. Wirth)
Proc. 51st IEEE Conf. Decis. Control, pp. 4165–4170, Maui, Hawaii, USA, 2012. [BibTeX]
@inproceedings{dashkovskiyrufferwirth2012smallgaintheoremsforlargescalesystemsandconstructionofisslyapunovfunctions,
abstract = {This invited paper is a significantly shortened excerpt of the article S. N. DASHKOVSKIY, B. S. R{\"U}FFER, AND F. R. WIRTH, Small gain theorems for large scale systems and construction of ISS Lyapunov functions, SIAM J. Control Optim., 48 (2010), pp. 4089–4118. We consider interconnections of n nonlinear subsystems in the inputtostate stability (ISS) framework. Foreach subsystem an ISS Lyapunov function is given that treats the other subsystems as independent inputs. A gain matrix is used to encode the mutual dependencies of the systems in the network. Under a small gain assumption on the monotone operator induced by the gain matrix, a locally Lipschitz continuous ISS Lyapunov function is obtained constructively for the entire network by appropriately scaling the individualLyapunov functions for the subsystems.},
title = {Small gain theorems for large scale systems and construction of {ISS} {L}yapunov functions},
address = {Maui, Hawaii, USA},
author = {Dashkovskiy, Sergey N. and R{\"u}ffer, Bj{\"o}rn S. and Wirth, Fabian R.},
booktitle = {{P}roc. 51st {IEEE} {C}onf. {D}ecis. {C}ontrol},
year = {2012},
pages = {4165–4170},
}
[Abstract]
This invited paper is a significantly shortened excerpt of the article S. N. DASHKOVSKIY, B. S. R"UFFER, AND F. R. WIRTH, Small gain theorems for large scale systems and construction of ISS Lyapunov functions, SIAM J. Control Optim., 48 (2010), pp. 4089–4118. We consider interconnections of n nonlinear subsystems in the inputtostate stability (ISS) framework. Foreach subsystem an ISS Lyapunov function is given that treats the other subsystems as independent inputs. A gain matrix is used to encode the mutual dependencies of the systems in the network. Under a small gain assumption on the monotone operator induced by the gain matrix, a locally Lipschitz continuous ISS Lyapunov function is obtained constructively for the entire network by appropriately scaling the individualLyapunov functions for the subsystems.123A cyclic smallgain condition and an equivalent matrixlike criterion for iISS networks
(Hiroshi Ito, ZhongPing Jiang, Sergey N. Dashkovskiy and Björn S. Rüffer)
Proc. 51st IEEE Conf. Decis. Control, pp. 4158–4164, Maui, Hawaii, USA, 2012. [BibTeX]
@inproceedings{itojiangdashkovskiyruffer2012acyclicsmallgainconditionandanequivalentmatrixlikecriterionforiissnetworks,
abstract = {This paper considers nonlinear dynamical networks consisting of individually iISS (integral inputtostatestable) subsystems which are not necessarily ISS (inputtostatestable). Stability criteria for internal and external stability of the networks are developed in view of both necessity and sufficiency. For the sufficiency, we show how we can construct a Lyapunov function of the network explicitly under the assumption that a cyclic smallgain condition is satisfied. The cyclic smallgain condition is shown to be equivalent to a matrixlike condition. The two conditions and their equivalence precisely generalize some central ISS results in the literature. Moreover, the necessity of the matrixlike condition is established. The allowable number of nonISS subsystems for stability of the network is discussed through several necessity conditions.},
title = {A cyclic smallgain condition and an equivalent matrixlike criterion for {iISS} networks},
address = {Maui, Hawaii, USA},
author = {Ito, Hiroshi and Jiang, ZhongPing and Dashkovskiy, Sergey N. and R{\"u}ffer, Bj{\"o}rn S.},
booktitle = {{P}roc. 51st {IEEE} {C}onf. {D}ecis. {C}ontrol},
year = {2012},
pages = {4158–4164},
}
[Abstract]
This paper considers nonlinear dynamical networks consisting of individually iISS (integral inputtostatestable) subsystems which are not necessarily ISS (inputtostatestable). Stability criteria for internal and external stability of the networks are developed in view of both necessity and sufficiency. For the sufficiency, we show how we can construct a Lyapunov function of the network explicitly under the assumption that a cyclic smallgain condition is satisfied. The cyclic smallgain condition is shown to be equivalent to a matrixlike condition. The two conditions and their equivalence precisely generalize some central ISS results in the literature. Moreover, the necessity of the matrixlike condition is established. The allowable number of nonISS subsystems for stability of the network is discussed through several necessity conditions.124From convergent dynamics to incremental stability
(Björn S. Rüffer, Nathan van de Wouw and Markus Mueller)
Proc. 51st IEEE Conf. Decis. Control, pp. 2958–2963, Maui, Hawaii, USA, 2012. [BibTeX]
@inproceedings{rufferwouwmueller2012fromconvergentdynamicstoincrementalstability,
abstract = {This paper advocates that the convergent systems property and incremental stability are two intimately related though different properties. Sufficient conditions for the convergent systems property usually rely upon first showing that a system is incrementally stable, as e.g. in the celebrated Demidovich condition. However, in the current paper it is shown that incremental stability itself does not imply the convergence property, or vice versa. Moreover, characterizations of both properties in terms of Lyapunov functions are given. Based on these characterizations, it is established that the convergence property implies incremental stability for systems evolving oncompact sets, and also when a suitable uniformity condition is satisfied.},
title = {From convergent dynamics to incremental stability},
address = {Maui, Hawaii, USA},
author = {R{\"u}ffer, Bj{\"o}rn S. and van de Wouw, Nathan and Mueller, Markus},
booktitle = {{P}roc. 51st {IEEE} {C}onf. {D}ecis. {C}ontrol},
year = {2012},
pages = {2958–2963},
}
[Abstract]
This paper advocates that the convergent systems property and incremental stability are two intimately related though different properties. Sufficient conditions for the convergent systems property usually rely upon first showing that a system is incrementally stable, as e.g. in the celebrated Demidovich condition. However, in the current paper it is shown that incremental stability itself does not imply the convergence property, or vice versa. Moreover, characterizations of both properties in terms of Lyapunov functions are given. Based on these characterizations, it is established that the convergence property implies incremental stability for systems evolving oncompact sets, and also when a suitable uniformity condition is satisfied.125GLRT for testing separability of a complexvalued mixture based on the strong uncorrelating transform
(D. Ramírez, P. J. Schreier, J. Vía and I. Santamaría)
Proc. IEEE Int. Work. Machine Learning for Signal Process., Santander, Spain, September 2012.
DOI:10.1109/MLSP.2012.6349785.
[BibTeX]
@inproceedings{RamirezSchreierVia:2012:GLRTForTestingSeparabilityOfAComplexValued,
abstract = {The Strong Uncorrelating Transform (SUT) allows blind separation of a mixture of complex independent sources if and only if all sources have distinct circularity coefficients. In practice, the circularity coefficients need to be estimated from observed data. We propose a generalized likelihood ratio test (GLRT) for separability of a complex mixture using the SUT, based on estimated circularity coefficients. For distinct circularity coefficients (separable case), the maximum likelihood (ML) estimates, required for the GLRT, are straightforward. However, for circularity coefficients with multiplicity larger than one (nonseparable case), the ML estimates are much more difficult to find. Numerical simulations show the good performance of the proposed detector.},
title = {{GLRT} for testing separability of a complexvalued mixture based on the strong uncorrelating transform},
address = {Santander, Spain},
author = {D. Ram{\'i}rez and P. J. Schreier and J. V{\'i}a and I. Santamar{\'i}a},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {W}ork.\ Machine Learning for Signal Process.},
month = {{S}eptember},
year = {2012},
doi = {10.1109/MLSP.2012.6349785},
}
[Abstract]
The Strong Uncorrelating Transform (SUT) allows blind separation of a mixture of complex independent sources if and only if all sources have distinct circularity coefficients. In practice, the circularity coefficients need to be estimated from observed data. We propose a generalized likelihood ratio test (GLRT) for separability of a complex mixture using the SUT, based on estimated circularity coefficients. For distinct circularity coefficients (separable case), the maximum likelihood (ML) estimates, required for the GLRT, are straightforward. However, for circularity coefficients with multiplicity larger than one (nonseparable case), the ML estimates are much more difficult to find. Numerical simulations show the good performance of the proposed detector.126The random monogenic signal
(S. C. Olhede, D. Ramírez and P. J. Schreier)
Proc. IEEE Int. Conf. Image Process., Orlando, Florida, USA, September 2012.
DOI:10.1109/ICIP.2012.6467404.
[BibTeX]
@inproceedings{OlhedeRamirezSchreier:2012:TheRandomMonogenicSignal,
abstract = {The monogenic signal allows us to decompose a twodimensional real signal into a local amplitude, a local orientation, and a local phase. In this paper, we introduce the random monogenic signal and study its secondorder statistical properties. The monogenic signal may be represented as a quaternionvalued signal. We show that for homogeneous random fields, we need exactly two quaternionvalued covariance functions for a complete secondorder description. We also introduce a stochastic model for unidirectional signals and a measure of unidirectionality.},
title = {The random monogenic signal},
address = {Orlando, Florida, USA},
author = {S. C. Olhede and D. Ram{\'i}rez and P. J. Schreier},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {I}mage {P}rocess.},
month = {{S}eptember},
year = {2012},
doi = {10.1109/ICIP.2012.6467404},
}
[Abstract]
The monogenic signal allows us to decompose a twodimensional real signal into a local amplitude, a local orientation, and a local phase. In this paper, we introduce the random monogenic signal and study its secondorder statistical properties. The monogenic signal may be represented as a quaternionvalued signal. We show that for homogeneous random fields, we need exactly two quaternionvalued covariance functions for a complete secondorder description. We also introduce a stochastic model for unidirectional signals and a measure of unidirectionality.127Pre and postFFT Interference Leakage Minimization for MIMO OFDM networks
(Christian Lameiro, Óscar González, Javier Vía, Ignacio Santamaría and Robert W. Heath Jr.)
Proc. Int. Symp. Wireless Comm. Syst., Paris, France, August 2012.
DOI:10.1109/ISWCS.2012.6328429.
[BibTeX]
@inproceedings{LameiroGonzalezVia:2012:Pre–andPostFFTInterferenceLeakage,
abstract = {Interference alignment (IA) has been shown to achieve the maximum degrees of freedom in the multipleinput multipleoutput (MIMO) Kuser interference channel (IFC). In the presence of frequencyselective channels, orthogonal frequencydivision multiplexing (OFDM) is typically used to deal with the multipath nature of the channel. While IA techniques can be applied in a persubcarrier basis (postFFT), the existence of symbol timing offsets (STOs) between the desired and the interfering OFDM symbols decreases the system performance dramatically. To solve this problem, we design preFFT precoders and decoders for singlebeam MIMO IFCs for OFDM transmissions. Since the IA decoders operate before the FFT, they mitigate the interference before synchronization takes place. We show that our proposed scheme improves the system performance when STOs occur, in comparison with traditional postFFT IA techniques. We provide simulation results to compare post and preFFT beamforming techniques and to illustrate the performance of the proposed method.},
title = {Pre and post{FFT} Interference Leakage Minimization for {MIMO OFDM} networks},
address = {Paris, France},
author = {Lameiro, Christian and Gonz{\'a}lez, {\'O}scar and V{\'i}a, Javier and Santamar{\'i}a, Ignacio and Heath Jr., Robert W.},
booktitle = {Proc. Int. Symp. Wireless Comm. Syst.},
month = {{A}ugust},
year = {2012},
doi = {10.1109/ISWCS.2012.6328429},
}
[Abstract]
Interference alignment (IA) has been shown to achieve the maximum degrees of freedom in the multipleinput multipleoutput (MIMO) Kuser interference channel (IFC). In the presence of frequencyselective channels, orthogonal frequencydivision multiplexing (OFDM) is typically used to deal with the multipath nature of the channel. While IA techniques can be applied in a persubcarrier basis (postFFT), the existence of symbol timing offsets (STOs) between the desired and the interfering OFDM symbols decreases the system performance dramatically. To solve this problem, we design preFFT precoders and decoders for singlebeam MIMO IFCs for OFDM transmissions. Since the IA decoders operate before the FFT, they mitigate the interference before synchronization takes place. We show that our proposed scheme improves the system performance when STOs occur, in comparison with traditional postFFT IA techniques. We provide simulation results to compare post and preFFT beamforming techniques and to illustrate the performance of the proposed method.128The locally most powerful invariant test for detecting a rankP Gaussian signal in white noise
(D. Ramírez, J. Iscar, J. Vía, I. Santamaría and L. L. Scharf)
Proc. IEEE Sensor Array and Multichannel Signal Process. Work., Hoboken, NJ, USA, June 2012.
DOI:10.1109/SAM.2012.6250547.
[BibTeX]
@inproceedings{RamirezIscarVia:2012:TheLocallyMostPowerfulInvariant,
abstract = {Spectrum sensing has become one of the main components of a cognitive transmitter. Conventional detectors suffer from noise power uncertainties and multiantenna detectors have been proposed to overcome this difficulty, and to improve the detection performance. However, most of the proposed multiantenna detectors are based on nonoptimal techniques, such as the generalized likelihood ratio test (GLRT), or even heuristic approaches that are not based on first principles. In this work, we derive the locally most powerful invariant test (LMPIT), that is, the optimal invariant detector for close hypotheses, or equivalently, for a low signaltonoise ratio (SNR). The traditional approach, based on the distributions of the maximal invariant statistic, is avoided thanks to Wijsman's theorem, which does not need these distributions. Our findings show that, in the low SNR regime, and in contrast to the GLRT, the additional spatial structure imposed by the signal model is irrelevant for optimal detection. Finally, we use Monte Carlo simulations to illustrate the good performance of the LMPIT.},
title = {The locally most powerful invariant test for detecting a {rank$P$} {G}aussian signal in white noise},
address = {Hoboken, NJ, USA},
author = {D. Ram{\'i}rez and J. Iscar and J. V{\'i}a and I. Santamar{\'i}a and L. L. Scharf},
booktitle = {{P}roc.\ {IEEE} {S}ensor {A}rray and {M}ultichannel {S}ignal {P}rocess. {W}ork.},
month = {{J}une},
year = {2012},
doi = {10.1109/SAM.2012.6250547},
}
[Abstract]
Spectrum sensing has become one of the main components of a cognitive transmitter. Conventional detectors suffer from noise power uncertainties and multiantenna detectors have been proposed to overcome this difficulty, and to improve the detection performance. However, most of the proposed multiantenna detectors are based on nonoptimal techniques, such as the generalized likelihood ratio test (GLRT), or even heuristic approaches that are not based on first principles. In this work, we derive the locally most powerful invariant test (LMPIT), that is, the optimal invariant detector for close hypotheses, or equivalently, for a low signaltonoise ratio (SNR). The traditional approach, based on the distributions of the maximal invariant statistic, is avoided thanks to Wijsman's theorem, which does not need these distributions. Our findings show that, in the low SNR regime, and in contrast to the GLRT, the additional spatial structure imposed by the signal model is irrelevant for optimal detection. Finally, we use Monte Carlo simulations to illustrate the good performance of the LMPIT.129Bayesian multiantenna sensing for cognitive radio
(J. MancoVásquez, M. LazaroGredilla, D. Ramírez, J. Vía and I. Santamaría)
Proc. IEEE Sensor Array and Multichannel Signal Process. Work., Hoboken, NJ, USA, June 2012.
DOI:10.1109/SAM.2012.6250566.
[BibTeX]
@inproceedings{MancoVasquezLazaroGredillaRamirez:2012:BayesianMultiantennaSensingforCognitive,
abstract = {In this paper, the problem of multiantenna spectrum sensing in cognitive radio (CR) is addressed within a Bayesian framework. Unlike previous works, our Bayesian model places priors directly on the spatial covariance matrices under both hypotheses, as well as on the probability of channel occupancy. Specifically, we use inversegamma and complex inverseWishart distributions as conjugate priors for the null and alternative hypotheses, respectively; and a Bernoulli distribution as the prior for channel occupancy. At each sensing period, Bayesian inference is applied and the posterior of channel occupancy is thresholded for detection. After a suitable approximation, the posteriors are employed as priors for the next sensing frame, which can be beneficial in slowly timevarying environments. By means of simulations, the proposed detector is shown to outperform the Generalized Likelihood Ratio Test (GLRT) detector.},
title = {Bayesian multiantenna sensing for cognitive radio},
address = {Hoboken, NJ, USA},
author = {J. MancoV{\'a}squez and M. LazaroGredilla and D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a},
booktitle = {{P}roc.\ {IEEE} {S}ensor {A}rray and {M}ultichannel {S}ignal {P}rocess. {W}ork.},
month = {{J}une},
year = {2012},
doi = {10.1109/SAM.2012.6250566},
}
[Abstract]
In this paper, the problem of multiantenna spectrum sensing in cognitive radio (CR) is addressed within a Bayesian framework. Unlike previous works, our Bayesian model places priors directly on the spatial covariance matrices under both hypotheses, as well as on the probability of channel occupancy. Specifically, we use inversegamma and complex inverseWishart distributions as conjugate priors for the null and alternative hypotheses, respectively; and a Bernoulli distribution as the prior for channel occupancy. At each sensing period, Bayesian inference is applied and the posterior of channel occupancy is thresholded for detection. After a suitable approximation, the posteriors are employed as priors for the next sensing frame, which can be beneficial in slowly timevarying environments. By means of simulations, the proposed detector is shown to outperform the Generalized Likelihood Ratio Test (GLRT) detector.130A distributed algorithm for twoway multiplerelay networks
(Christian Lameiro, Javier Vía and Ignacio Santamaría)
Proc. IEEE Sensor Array and Multichannel Signal Process. Work., Hoboken, NJ, USA, June 2012.
DOI:10.1109/SAM.2012.6250440.
[BibTeX]
@inproceedings{LameiroViaSantamaria:2012:ADistributedAlgorithmforTwoWayMultipleRelay,
abstract = {In this paper we propose an efficient transmission strategy for the twoway relay channel (TWRC) with multiple relays, when these are multipleinput multipleoutput (MIMO) transceivers that apply the amplifyandforward (AF) protocol. Although the optimal beamforming strategy is known, it requires a central node, with channel state information (CSI) of the entire network, to compute all the beamforming matrices, which is impractical. To reduce the overhead, in this paper we present a distributed algorithm for the computation of the relay beamforming matrices. The proposed algorithm divides the problem in two stages. First, each relay computes its own beamforming matrix in parallel using only local CSI. Next, a distributed beamforming is applied to make the signals add up coherently at the nodes. Although the proposed algorithm is suboptimal, we show through simulations that it performs very close to the optimal achievable rate region.},
title = {A distributed algorithm for twoway multiplerelay networks},
address = {Hoboken, NJ, USA},
author = {Lameiro, Christian and V{\'i}a, Javier and Santamar{\'i}a, Ignacio},
booktitle = {{P}roc.\ {IEEE} {S}ensor {A}rray and {M}ultichannel {S}ignal {P}rocess. {W}ork.},
month = {{J}une},
year = {2012},
doi = {10.1109/SAM.2012.6250440},
}
[Abstract]
In this paper we propose an efficient transmission strategy for the twoway relay channel (TWRC) with multiple relays, when these are multipleinput multipleoutput (MIMO) transceivers that apply the amplifyandforward (AF) protocol. Although the optimal beamforming strategy is known, it requires a central node, with channel state information (CSI) of the entire network, to compute all the beamforming matrices, which is impractical. To reduce the overhead, in this paper we present a distributed algorithm for the computation of the relay beamforming matrices. The proposed algorithm divides the problem in two stages. First, each relay computes its own beamforming matrix in parallel using only local CSI. Next, a distributed beamforming is applied to make the signals add up coherently at the nodes. Although the proposed algorithm is suboptimal, we show through simulations that it performs very close to the optimal achievable rate region.131ICAguided delineation of breast cancer pathology
(Alma Eguizabal, Ashley M. Laughney, P. Beatriz GarciaAllende, Venkataramanan Krishnaswamy, Wendy A. Wells, Keith D. Paulsen, Brian W. Pogue, Jose M. LopezHiguera and Olga M. Conde)
IEEE 9th International Symposium on Biomedical Imaging, Barcelona, Spain, May 2012. [BibTeX]
@inproceedings{EguizabalLaughneyGarciaallende:2012:ICAguideddelineationofbreastcancer,
abstract = {A surgeonguided independent component analysis from optical reflectance measurements is proposed for breast tumor delineation. Independent Component Analysis is first applied to extract the most relevant features from local measures of broadband reflectance and then a tumor probability indicator is obtained and provided utilizing surgeon assistance to resolve the inherent ambiguities in the independent component calculation. A set of 29 breast tissue samples have been diagnosed achieving a sensitivity of 90.57%, and specificity of 93.98%.},
title = {{ICA}guided delineation of breast cancer pathology},
address = {Barcelona, Spain},
author = {Alma Eguizabal and Ashley M. Laughney and P. Beatriz GarciaAllende and Venkataramanan Krishnaswamy and Wendy A. Wells and Keith D. Paulsen and Brian W. Pogue and Jose M. LopezHiguera and Olga M. Conde},
booktitle = {IEEE 9th International Symposium on Biomedical Imaging},
month = {{M}ay},
year = {2012},
}
[Abstract]
A surgeonguided independent component analysis from optical reflectance measurements is proposed for breast tumor delineation. Independent Component Analysis is first applied to extract the most relevant features from local measures of broadband reflectance and then a tumor probability indicator is obtained and provided utilizing surgeon assistance to resolve the inherent ambiguities in the independent component calculation. A set of 29 breast tissue samples have been diagnosed achieving a sensitivity of 90.57%, and specificity of 93.98%.132Textural analysis of optical scattering for identification of cancer in breast surgical specimens
(Alma Eguizabal, Ashley M. Laughney, P. Beatriz GarciaAllende, Venkataramanan Krishnaswamy, Wendy A. Wells, Keith D. Paulsen, Brian W. Pogue, Jose M. LopezHiguera and Olga M. Conde)
IEEE 9th International Symposium on Biomedical Imaging, Barcelona, Spain, May 2012. [BibTeX]
@inproceedings{EguizabalLaughneyGarciaallende:2012:Texturalanalysisofopticalscattering,
abstract = {Textural analysis of tissue scattering images is proposed for healthy versus tumor discrimination. Scattering center density varies from normal to tumor tissues and this variation is translated into different textures in the scattering power map. Adipose tissue shows low autocorrelation values while tumor tissues present higher entropies than normal tissue. Consequently, a combination of autocorrelation and entropy values allows ready tissue discrimination by a supervised linear classifier. The proposed approach has been validated over a set of 29 breast tissue samples achieving a sensitivity of 73.59% and specificity of 82.40%.},
title = {Textural analysis of optical scattering for identification of cancer in breast surgical specimens},
address = {Barcelona, Spain},
author = {Alma Eguizabal and Ashley M. Laughney and P. Beatriz GarciaAllende and Venkataramanan Krishnaswamy and Wendy A. Wells and Keith D. Paulsen and Brian W. Pogue and Jose M. LopezHiguera and Olga M. Conde},
booktitle = {IEEE 9th International Symposium on Biomedical Imaging},
month = {{M}ay},
year = {2012},
}
[Abstract]
Textural analysis of tissue scattering images is proposed for healthy versus tumor discrimination. Scattering center density varies from normal to tumor tissues and this variation is translated into different textures in the scattering power map. Adipose tissue shows low autocorrelation values while tumor tissues present higher entropies than normal tissue. Consequently, a combination of autocorrelation and entropy values allows ready tissue discrimination by a supervised linear classifier. The proposed approach has been validated over a set of 29 breast tissue samples achieving a sensitivity of 73.59% and specificity of 82.40%.133Multisatellite timedelay estimation for reliable highresolution GNSS receivers
(Christoph Enneking, Manuel Stein, Mario Castañeda, Felix Antreich and Josef A. Nossek)
Proc. IEEE/ION Pos. Nav. Symp., Myrtle Beach, USA, April 2012. [BibTeX]
@inproceedings{Enneking:PLANS:2012,
title = {Multisatellite timedelay estimation for reliable highresolution {GNSS} receivers},
address = {Myrtle Beach, USA},
author = {Enneking, Christoph and Stein, Manuel and Casta{\~n}eda, Mario and Antreich, Felix and Nossek, Josef A.},
booktitle = {{P}roc.\ {IEEE}{\/}{ION} {P}os. {N}av.\ Symp.},
month = {{A}pril},
year = {2012},
}
[Abstract]134The locally most powerful test for multiantenna spectrum sensing with uncalibrated receivers
(D. Ramírez, J. Vía and I. Santamaría)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Kyoto, Japan, March 2012.
DOI:10.1109/ICASSP.2012.6288655.
[BibTeX]
@inproceedings{RamirezViaSantamaria:2012:TheLocallyMostPowerfulTest,
abstract = {Spectrum sensing is a key component of the cognitive radio (CR) paradigm. Among CR detectors, multiantenna detectors are gaining popularity since they improve the detection performance and are robust to noise uncertainties. Traditional approaches to multiantenna spectrum sensing are based on the generalized likelihood ratio test (GLRT) or other heuristic detectors, which are not optimal in the NeymanPearson sense. In this work, we derive the locally most powerful invariant test (LMPIT), which is the optimal detector, among those preserving the problem invariances, in the low SNR regime. In particular, we apply Wijsman's theorem, which provides us an alternative way to derive the ratio of the distributions of the maximal invariant statistic. Finally, numerical simulations illustrate the performance of the proposed detector.},
title = {The locally most powerful test for multiantenna spectrum sensing with uncalibrated receivers},
address = {Kyoto, Japan},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}arch},
year = {2012},
doi = {10.1109/ICASSP.2012.6288655},
}
[Abstract]
Spectrum sensing is a key component of the cognitive radio (CR) paradigm. Among CR detectors, multiantenna detectors are gaining popularity since they improve the detection performance and are robust to noise uncertainties. Traditional approaches to multiantenna spectrum sensing are based on the generalized likelihood ratio test (GLRT) or other heuristic detectors, which are not optimal in the NeymanPearson sense. In this work, we derive the locally most powerful invariant test (LMPIT), which is the optimal detector, among those preserving the problem invariances, in the low SNR regime. In particular, we apply Wijsman's theorem, which provides us an alternative way to derive the ratio of the distributions of the maximal invariant statistic. Finally, numerical simulations illustrate the performance of the proposed detector.135Interference leakage minimization for convolutive MIMO interference channels
(Óscar González, Christian Lameiro, Javier Vía, Ignacio Santamaría and Robert W. Heath Jr.)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Kyoto, Japan, March 2012.
DOI:10.1109/ICASSP.2012.6288506.
[BibTeX]
@inproceedings{GonzalezLameiroVia:2012:InterferenceLeakageMinimizationforConvolutive,
abstract = {An alternating optimization algorithm was recently proposed for the Kuser multipleinput multipleoutput (MIMO) interference channel. For flatfading channels and feasible problems, this algorithm successfully aligns the interfering signals exploiting the spatial dimensions. In this paper, we consider the case in which all pairwise MIMO channels are frequencyselective (convolutive), and the users transmit broadband signals using a singlecarrier scheme. Unlike the flatfading case, for frequencyselective channels it is necessary to add a spectral mask in the frequency response of the precoders and decoders to avoid trivial solutions. We show in the paper that each step of the alternating minimization algorithm can be reformulated as a convex optimization problem in which the autocorrelation function of the precoders or decoders is obtained. Upon convergence, a final spectral factorization stage must be applied to obtain the precoders and decoders from their autocorrelation functions. Simulation results are provided to illustrate the performance of the proposed algorithm.},
title = {Interference leakage minimization for convolutive {MIMO} interference channels},
address = {Kyoto, Japan},
author = {Gonz{\'a}lez, {\'O}scar and Lameiro, Christian and V{\'i}a, Javier and Santamar{\'i}a, Ignacio and Heath Jr., Robert W.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}arch},
year = {2012},
doi = {10.1109/ICASSP.2012.6288506},
}
[Abstract]
An alternating optimization algorithm was recently proposed for the Kuser multipleinput multipleoutput (MIMO) interference channel. For flatfading channels and feasible problems, this algorithm successfully aligns the interfering signals exploiting the spatial dimensions. In this paper, we consider the case in which all pairwise MIMO channels are frequencyselective (convolutive), and the users transmit broadband signals using a singlecarrier scheme. Unlike the flatfading case, for frequencyselective channels it is necessary to add a spectral mask in the frequency response of the precoders and decoders to avoid trivial solutions. We show in the paper that each step of the alternating minimization algorithm can be reformulated as a convex optimization problem in which the autocorrelation function of the precoders or decoders is obtained. Upon convergence, a final spectral factorization stage must be applied to obtain the precoders and decoders from their autocorrelation functions. Simulation results are provided to illustrate the performance of the proposed algorithm.136Regularized linear equalization for multipath channels with imperfect channel estimation
(Jun Tong and Peter J. Schreier)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 3009–3012, March 2012.
DOI:10.1109/ICASSP.2012.6288548.
[BibTeX]
@inproceedings{TongSchreier:2012:Regularizedlinearequalizationformult,
abstract = {This paper deals with different techniques for linear equalization (LE) of multipath channels with imperfect channel estimation (CE). We develop a unified framework based on Krylov subspace expansion, which allows us to compare the performance of the conjugate gradient (CG) method, diagonal loading (DL), and a hybrid scheme. Our analysis shows that the DL method generally outperforms its alternatives, but at the cost of higher complexity. However, we also demonstrate that a proper implementation of the lowcomplexity CG method can also approach the performance of DL. Finally, we show that preconditioning degrades performance when the CE is poor.},
title = {Regularized linear equalization for multipath channels with imperfect channel estimation},
author = {Tong, Jun and Schreier, Peter J.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}arch},
year = {2012},
pages = {3009–3012},
doi = {10.1109/ICASSP.2012.6288548},
}
[Abstract]
This paper deals with different techniques for linear equalization (LE) of multipath channels with imperfect channel estimation (CE). We develop a unified framework based on Krylov subspace expansion, which allows us to compare the performance of the conjugate gradient (CG) method, diagonal loading (DL), and a hybrid scheme. Our analysis shows that the DL method generally outperforms its alternatives, but at the cost of higher complexity. However, we also demonstrate that a proper implementation of the lowcomplexity CG method can also approach the performance of DL. Finally, we show that preconditioning degrades performance when the CE is poor.137Blind breast tissue diagnosis using independent component analysis of localized backscattering response
(Alma Eguizabal, Ashley M. Laughney, P. Beatriz GarciaAllende, Venkataramanan Krishnaswamy, Wendy A. Wells, Keith D. Paulsen, Brian W. Pogue, Jose LopezHiguera and Olga M. Conde)
SPIE Photonics West BIOS, VI Biomedical Applications of Light Scattering, San Francisco, USA, January 2012. [BibTeX]
@inproceedings{EguizabalLaughneyGarciaallende:2012:Blindbreasttissuediagnosis,
abstract = {A blind separation technique based on Independent Component Analysis (ICA) is proposed for breast tumor delineation and pathologic diagnosis. Tissue morphology is determined by fitting local measures of tissue reflectance to a Mie theory approximation, parameterizing the scattering power, scattering amplitude and average scattering irradiance. ICA is applied on the scattering parameters by spatial analysis using the Fast ICA method to extract more determinant features for an accurate diagnostic. Neither training, nor comparisons with reference parameters are required. Tissue diagnosis is provided directly following ICA application to the scattering parameter images. Surgically resected breast tissues were imaged and identified by a pathologist. Three different tissue pathologies were identified in 29 samples and classified as notmalignant, malignant and adipose. Scatter plot analysis of both ICA results and optical parameters where obtained. ICA subtle ameliorates those cases where optical parameter's scatter plots were not linearly separable. Furthermore, observing the mixing matrix of the ICA, it can be decided when the optical parameters themselves are diagnostically powerful. Moreover, contrast maps provided by ICA correlate with the pathologic diagnosis. The time response of the diagnostic strategy is therefore enhanced comparing with complex classifiers, enabling near realtime assessment of pathology during breastconserving surgery.},
title = {Blind breast tissue diagnosis using independent component analysis of localized backscattering response},
address = {San Francisco, USA},
author = {Alma Eguizabal and Ashley M. Laughney and P. Beatriz GarciaAllende and Venkataramanan Krishnaswamy and Wendy A. Wells and Keith D. Paulsen and Brian W. Pogue and Jose LopezHiguera and Olga M. Conde},
booktitle = {SPIE Photonics West BIOS, VI Biomedical Applications of Light Scattering},
month = {{J}anuary},
year = {2012},
}
[Abstract]
A blind separation technique based on Independent Component Analysis (ICA) is proposed for breast tumor delineation and pathologic diagnosis. Tissue morphology is determined by fitting local measures of tissue reflectance to a Mie theory approximation, parameterizing the scattering power, scattering amplitude and average scattering irradiance. ICA is applied on the scattering parameters by spatial analysis using the Fast ICA method to extract more determinant features for an accurate diagnostic. Neither training, nor comparisons with reference parameters are required. Tissue diagnosis is provided directly following ICA application to the scattering parameter images. Surgically resected breast tissues were imaged and identified by a pathologist. Three different tissue pathologies were identified in 29 samples and classified as notmalignant, malignant and adipose. Scatter plot analysis of both ICA results and optical parameters where obtained. ICA subtle ameliorates those cases where optical parameter's scatter plots were not linearly separable. Furthermore, observing the mixing matrix of the ICA, it can be decided when the optical parameters themselves are diagnostically powerful. Moreover, contrast maps provided by ICA correlate with the pathologic diagnosis. The time response of the diagnostic strategy is therefore enhanced comparing with complex classifiers, enabling near realtime assessment of pathology during breastconserving surgery.138Enhanced tumor contrast during breast lumpectomy provided by independent component analysis of localized reflectance measures
(Alma Eguizabal, Ashley M. Laughney, P. Beatriz GarciaAllende, Venkataramanan Krishnaswamy, Wendy A. Wells, Keith D. Paulsen, Brian W. Pogue, Jose LopezHiguera and Olga M. Conde)
SPIE Photonics West 2012BIOS, VI Biomedical Applications of Light Scattering, San Francisco, USA, January 2012. [BibTeX]
@inproceedings{EguizabalLaughneyGarciaallende:2012:Enhancedtumorcontrastduringbreastlumpectomy,
abstract = {A spectral analysis technique to enhance tumor contrast during breast conserving surgery is proposed. A set of 29 surgicallyexcised breast tissues have been imaged in local reflectance geometry. Measures of broadband reflectance are directly analyzed using Principle Component Analysis (PCA), on a per sample basis, to extract areas of maximal spectral variation. A dynamic selection threshold has been applied to obtain the final number of principal components, accounting for interpatient variability. A blind separation technique based on Independent Component Analysis (ICA) is then applied to extract diagnostically powerful results. ICA application reveals that the behavior of one independent component highly correlates with the pathologic diagnosis and it surpasses the contrast obtained using empirical models. Moreover, blind detection characteristics (no training, no comparisons with training reference data) and no need for parameterization makes the automated diagnosis simple and time efficient, favoring its translation to the clinical practice. Correlation coefficient with modelbased results up to 0.91 has been achieved.},
title = {Enhanced tumor contrast during breast lumpectomy provided by independent component analysis of localized reflectance measures},
address = {San Francisco, USA},
author = {Alma Eguizabal and Ashley M. Laughney and P. Beatriz GarciaAllende and Venkataramanan Krishnaswamy and Wendy A. Wells and Keith D. Paulsen and Brian W. Pogue and Jose LopezHiguera and Olga M. Conde},
booktitle = {SPIE Photonics West 2012BIOS, VI Biomedical Applications of Light Scattering},
month = {{J}anuary},
year = {2012},
}
[Abstract]
A spectral analysis technique to enhance tumor contrast during breast conserving surgery is proposed. A set of 29 surgicallyexcised breast tissues have been imaged in local reflectance geometry. Measures of broadband reflectance are directly analyzed using Principle Component Analysis (PCA), on a per sample basis, to extract areas of maximal spectral variation. A dynamic selection threshold has been applied to obtain the final number of principal components, accounting for interpatient variability. A blind separation technique based on Independent Component Analysis (ICA) is then applied to extract diagnostically powerful results. ICA application reveals that the behavior of one independent component highly correlates with the pathologic diagnosis and it surpasses the contrast obtained using empirical models. Moreover, blind detection characteristics (no training, no comparisons with training reference data) and no need for parameterization makes the automated diagnosis simple and time efficient, favoring its translation to the clinical practice. Correlation coefficient with modelbased results up to 0.91 has been achieved.139A smallgain theorem and construction of sumtype Lyapunov Functions for Networks of iISS systems
(Hiroshi Ito, ZhongPing Jiang, Sergey N. Dashkovskiy and Björn S. Rüffer)
Proc. IEEE American Contr. Conf., pp. 1971–1977, 2011. [BibTeX]
@inproceedings{itojiangdashkovskiyruffer2011asmallgaintheoremandconstructionofsumtypelyapunovfunctionsfornetworksofiisssystems,
abstract = {This paper gives a solution to the problem of verifying stability of networks consisting of integral inputtostate stable (iISS) subsystems. The iISS smallgain theorem developed recently has been restricted to interconnection of two subsystems. For largescale systems, stability criteria relying only on gaintype information have been successful only in dealing with inputtostate stable stable (ISS) subsystems. To address the stability problem involving iISS subsystems interconnected in general structure, this paper shows how to construct Lyapunov functions of the network by means of nonlinear sum of individual Lyapunov functions of subsystems given in a dissipation formulation under an appropriate smallgain condition.},
title = {A smallgain theorem and construction of sumtype {L}yapunov Functions for Networks of {iISS} systems},
author = {Ito, Hiroshi and Jiang, ZhongPing and Dashkovskiy, Sergey N. and R{\"u}ffer, Bj{\"o}rn S.},
booktitle = {{P}roc. {IEEE} {A}merican {C}ontr. {C}onf.},
year = {2011},
pages = {1971–1977},
}
[Abstract]
This paper gives a solution to the problem of verifying stability of networks consisting of integral inputtostate stable (iISS) subsystems. The iISS smallgain theorem developed recently has been restricted to interconnection of two subsystems. For largescale systems, stability criteria relying only on gaintype information have been successful only in dealing with inputtostate stable stable (ISS) subsystems. To address the stability problem involving iISS subsystems interconnected in general structure, this paper shows how to construct Lyapunov functions of the network by means of nonlinear sum of individual Lyapunov functions of subsystems given in a dissipation formulation under an appropriate smallgain condition.140Spatial rank estimation in cognitive radio networks with uncalibrated multiple antennas (invited paper)
(G. VazquezVilar, D. Ramírez, R. LópezValcarce, J. Vía and I. Santamaría)
Proc. Int. Conf. on Cognitive Radio and Advanced Spectrum Management, Barcelona, Spain, October 2011.
DOI:10.1145/2093256.2093291.
[BibTeX]
@inproceedings{VazquezVilarRamirezLopezValcarce:2011:SpatialrankestimationinCognitive,
abstract = {Spectrum sensing is a key component of the Cognitive Radio paradigm. Multiantenna detectors can exploit different spatial features of primary signals in order to boost detection performance and robustness in very low signaltonoise ratios. However, in several cases these detectors require additional information, such as the rank of the spatial covariance matrix of the received signal. In this work we study the problem of estimating this rank under Gaussianity assumption using an uncalibrated receiver, i.e. with different (unknown) noise levels at each of the antennas.},
title = {Spatial rank estimation in cognitive radio networks with uncalibrated multiple antennas (invited paper)},
address = {Barcelona, Spain},
author = {G. VazquezVilar and D. Ram{\'i}rez and R. L{\'o}pezValcarce and J. V{\'i}a and I. Santamar{\'i}a},
booktitle = {Proc.\ Int. Conf. on Cognitive Radio and Advanced Spectrum Management},
month = {{O}ctober},
year = {2011},
doi = {10.1145/2093256.2093291},
}
[Abstract]
Spectrum sensing is a key component of the Cognitive Radio paradigm. Multiantenna detectors can exploit different spatial features of primary signals in order to boost detection performance and robustness in very low signaltonoise ratios. However, in several cases these detectors require additional information, such as the rank of the spatial covariance matrix of the received signal. In this work we study the problem of estimating this rank under Gaussianity assumption using an uncalibrated receiver, i.e. with different (unknown) noise levels at each of the antennas.141Recent advances in multiantenna spectrum sensing: complexity, noise uncertainty, and signal rank issues
(G. VazquezVilar, D. Romero, R. LópezValcarce, D. Ramírez, J. Vía, I. Santamaría and J. Sala)
Int. Work. COST Action IC0902, Barcelona, Spain, October 2011.
Extended abstract [BibTeX]
@inproceedings{VazquezVilarRomeroLopezValcarce:2011:Recentadvancesinmultiantennaspectrum,
title = {Recent advances in multiantenna spectrum sensing: complexity, noise uncertainty, and signal rank issues},
address = {Barcelona, Spain},
author = {G. VazquezVilar and D. Romero and R. L{\'o}pezValcarce and D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a and J. Sala},
booktitle = {Int. Work. COST Action IC0902},
month = {{O}ctober},
year = {2011},
note = {Extended abstract},
}
[Abstract]142Experimental evaluation of Interference Alignment under imperfect channel state information
(J. A. GarcíaNaya, L. Castedo, Ó. González, D. Ramírez and I. Santamaría)
Proc. Eur. Signal Process. Conf., Barcelona, Spain, September 2011. [BibTeX]
@inproceedings{GarciaNayaCastedoGonzalez:2011:ExperimentalEvaluationofInterferenceAlignment,
abstract = {Interference Alignment (IA) has been revealed as one of the most attractive transmission techniques for the Kuser in terference channel. In this work, we employ a multiuser MultipleInput MultipleOutput (MIMO) testbed to analyze, in realistic indoor scenarios, the impact of channel state information errors on the sumrate performance of IA. We restrict our study to a 3user interference network in which each user transmits a single data stream using two transmit and two receive antennas. For this MIMO interference network, only two different IA solutions exist. We also evaluate the performance gain obtained in practice by using the IA solution that maximizes the sumrate.},
title = {Experimental evaluation of {I}nterference {A}lignment under imperfect channel state information},
address = {Barcelona, Spain},
author = {J. A. Garc{\'i}aNaya and L. Castedo and {\'O}. Gonz{\'a}lez and D. Ram{\'i}rez and I. Santamar{\'i}a},
booktitle = {{P}roc.\ {E}ur.\ {S}ignal {P}rocess.\ {C}onf.},
month = {{S}eptember},
year = {2011},
}
[Abstract]
Interference Alignment (IA) has been revealed as one of the most attractive transmission techniques for the Kuser in terference channel. In this work, we employ a multiuser MultipleInput MultipleOutput (MIMO) testbed to analyze, in realistic indoor scenarios, the impact of channel state information errors on the sumrate performance of IA. We restrict our study to a 3user interference network in which each user transmits a single data stream using two transmit and two receive antennas. For this MIMO interference network, only two different IA solutions exist. We also evaluate the performance gain obtained in practice by using the IA solution that maximizes the sumrate.143Precoder design and convergence analysis of MIMO systems with Krylov subspace receivers
(Jun Tong, Peter J. Schreier and Steven R. Weller)
Proc. IEEE Int. Symp. Inform. Theory, pp. 2914–2918, August 2011.
DOI:10.1109/ISIT.2011.6034110.
[BibTeX]
@inproceedings{TongSchreierWeller:2011:Precoderdesignandconvergenceanalysis,
abstract = {This paper studies the design and analysis of large multipleinput multipleoutput (MIMO) systems with linear precoding and Krylov subspace receivers. We design precoders that can improve performance with lowrank receivers. We then introduce a tool based on potential theory to analyze the convergence behavior of the meansquared error (MSE). The effectiveness of the proposed precoder and the superexponential convergence of the MSE are demonstrated1.},
title = {Precoder design and convergence analysis of {MIMO} systems with {Krylov} subspace receivers},
author = {Tong, Jun and Schreier, Peter J. and Weller, Steven R.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {S}ymp.\ {I}nform.\ {T}heory},
month = {{A}ugust},
year = {2011},
pages = {2914–2918},
doi = {10.1109/ISIT.2011.6034110},
}
[Abstract]
This paper studies the design and analysis of large multipleinput multipleoutput (MIMO) systems with linear precoding and Krylov subspace receivers. We design precoders that can improve performance with lowrank receivers. We then introduce a tool based on potential theory to analyze the convergence behavior of the meansquared error (MSE). The effectiveness of the proposed precoder and the superexponential convergence of the MSE are demonstrated1.144Multisensor beamsteering based on the asymptotic likelihood for colored signals
(D. Ramírez, J. Vía, I. Santamaría and L. L. Scharf)
Proc. IEEE Work. Stat. Signal Process., Nice, France, June 2011.
DOI:10.1109/SSP.2011.5967644.
[BibTeX]
@inproceedings{RamirezViaSantamaria:2011:MultiSensorBeamsteeringBasedontheAsymptotic,
abstract = {In this work, we derive a maximum likelihood formula for beamsteering in a multisensor array. The novelty of the work is that the impinging signal and noises are wide sense stationary (WSS) time series with unknown power spectral densities, unlike in previous work that typically considers white signals. Our approach naturally provides a way of fusing frequencydependent information to obtain a broadband beamformer. In order to obtain the compressed likelihood, it is necessary to find the maximum likelihood estimates of the unknown parameters. However, this problem turns out to be an ML estimation of a blockToeplitz matrix, which does not have a closedform solution. To overcome this problem, we derive the asymptotic likelihood, which is given in the frequency domain. Finally, some simulation results are presented to illustrate the performance of the proposed technique. In these simulations, it is shown that our approach presents the best results.},
title = {Multisensor beamsteering based on the asymptotic likelihood for colored signals},
address = {Nice, France},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a and L. L. Scharf},
booktitle = {{P}roc.\ {IEEE} {W}ork.\ {S}tat.\ {S}ignal {P}rocess.},
month = {{J}une},
year = {2011},
doi = {10.1109/SSP.2011.5967644},
}
[Abstract]
In this work, we derive a maximum likelihood formula for beamsteering in a multisensor array. The novelty of the work is that the impinging signal and noises are wide sense stationary (WSS) time series with unknown power spectral densities, unlike in previous work that typically considers white signals. Our approach naturally provides a way of fusing frequencydependent information to obtain a broadband beamformer. In order to obtain the compressed likelihood, it is necessary to find the maximum likelihood estimates of the unknown parameters. However, this problem turns out to be an ML estimation of a blockToeplitz matrix, which does not have a closedform solution. To overcome this problem, we derive the asymptotic likelihood, which is given in the frequency domain. Finally, some simulation results are presented to illustrate the performance of the proposed technique. In these simulations, it is shown that our approach presents the best results.145Multiantenna detection under noise uncertainty and primary user's spatial structure
(D. Ramírez, G. VazquezVilar, R. LópezValcarce, J. Vía and I. Santamaría)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Prague, Czech Republic, May 2011.
DOI:10.1109/ICASSP.2011.5946275.
[BibTeX]
@inproceedings{RamirezVazquezVilarLopezValcarce:2011:Multiantennadetectionundernoise,
abstract = {Spectrum sensing is a challenging key component of the Cognitive Radio paradigm, since primary signals must be detected in the face of noise uncertainty and at signaltonoise ratios (SNRs) well below decodability levels. Multiantenna detectors exploit spatial independence of receiver thermal noise to boost detection performance and robustness. Here, we study the problem of detecting Gaussian signals with unknown rank$P$ spatial covariance matrix when the noise at the receiver is independent across the antennas and with unknown power. A generic diagonal noise covariance matrix is allowed to model calibration uncertainties in the different antenna frontends. We derive the generalized likelihood ratio test (GLRT) for this detection problem. Although, in general, the corresponding statistic must be obtained by numerical means, in the low SNR regime the GLRT does admit a closed form. Numerical simulations show that the proposed asymptotic detector offers good performance even for moderate SNR values.},
title = {Multiantenna detection under noise uncertainty and primary user's spatial structure},
address = {Prague, Czech Republic},
author = {D. Ram{\'i}rez and G. VazquezVilar and R. L{\'o}pezValcarce and J. V{\'i}a and I. Santamar{\'i}a},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2011},
doi = {10.1109/ICASSP.2011.5946275},
}
[Abstract]
Spectrum sensing is a challenging key component of the Cognitive Radio paradigm, since primary signals must be detected in the face of noise uncertainty and at signaltonoise ratios (SNRs) well below decodability levels. Multiantenna detectors exploit spatial independence of receiver thermal noise to boost detection performance and robustness. Here, we study the problem of detecting Gaussian signals with unknown rankP spatial covariance matrix when the noise at the receiver is independent across the antennas and with unknown power. A generic diagonal noise covariance matrix is allowed to model calibration uncertainties in the different antenna frontends. We derive the generalized likelihood ratio test (GLRT) for this detection problem. Although, in general, the corresponding statistic must be obtained by numerical means, in the low SNR regime the GLRT does admit a closed form. Numerical simulations show that the proposed asymptotic detector offers good performance even for moderate SNR values.146Multiplechannel detection of a Gaussian time series over frequencyflat channels
(D. Ramírez, J. Vía, I. Santamaría and L. L. Scharf)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Prague, Czech Republic, May 2011.
DOI:10.1109/ICASSP.2011.5947194.
[BibTeX]
@inproceedings{RamirezViaSantamaria:2011:MultipleChannelDetectionofaGaussianTime,
abstract = {This work addresses the problem of deciding whether a set of realizations of a vectorvalued time series with unknown temporal correlation are spatially correlated or not. Specifically, the spatial correlation is induced by a colored source over a frequencyflat singleinput multipleoutput (SIMO) channel distorted by independent and identically distributed noises with temporal correlation. The generalized likelihood ratio test (GLRT) for this detection problem does not have a closedform expression and we have to resort to numerical optimization techniques. In particular, we apply the successive convex approximations approach which relies on solving a series of convex problems that approximate the original (nonconvex) one. The proposed solution resembles a power method for obtaining the dominant eigenvector of a matrix, which changes over iterations. Finally, the performance of the proposed detector is illustrated by means of computer simulations showing a great improvement over previously proposed detectors that do not fully exploit the temporal structure of the source.},
title = {Multiplechannel detection of a {G}aussian time series over frequencyflat channels},
address = {Prague, Czech Republic},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a and L. L. Scharf},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2011},
doi = {10.1109/ICASSP.2011.5947194},
}
[Abstract]
This work addresses the problem of deciding whether a set of realizations of a vectorvalued time series with unknown temporal correlation are spatially correlated or not. Specifically, the spatial correlation is induced by a colored source over a frequencyflat singleinput multipleoutput (SIMO) channel distorted by independent and identically distributed noises with temporal correlation. The generalized likelihood ratio test (GLRT) for this detection problem does not have a closedform expression and we have to resort to numerical optimization techniques. In particular, we apply the successive convex approximations approach which relies on solving a series of convex problems that approximate the original (nonconvex) one. The proposed solution resembles a power method for obtaining the dominant eigenvector of a matrix, which changes over iterations. Finally, the performance of the proposed detector is illustrated by means of computer simulations showing a great improvement over previously proposed detectors that do not fully exploit the temporal structure of the source.147Capacity region of the twoway multiantenna relay channel with analog TxRx beamforming
(Christian Lameiro, Alfredo Nazábal, Fouad Gholam, Javier Vía and Ignacio Santamaría)
Proc. Int. ICST Conf. Mobile Lightweight Wireless Syst., Bilbao, Spain, May 2011.
DOI:10.1007/9783642294792_1.
[BibTeX]
@inproceedings{LameiroNazabalGholam:2011:CapacityRegionoftheTwoWayMultiAntenna,
abstract = {In this paper we study the multipleinput multipleoutput twoway relay channel (MIMOTWRC) when the nodes use analog beamforming. Following the amplifyandforward (AF) strategy, the problem consists of finding the transmit and receive beamformers of the nodes and the relay, and the power allocated to each one, that achieve the boundary of the capacity region. We express the optimal node beamformers in terms of the relay beamformers, and show that the capacity region can be efficiently characterized using convex optimization techniques. Numerical examples are provided to illustrate the results of this paper, and to compare the capacity region achieved by analog beamforming against the conventional MIMO schemes that operate at the baseband.},
title = {Capacity region of the twoway multiantenna relay channel with analog {TxRx} beamforming},
address = {Bilbao, Spain},
author = {Lameiro, Christian and Naz{\'a}bal, Alfredo and Gholam, Fouad and V{\'i}a, Javier and Santamar{\'i}a, Ignacio},
booktitle = {Proc. Int. ICST Conf. Mobile Lightweight Wireless Syst.},
month = {{M}ay},
year = {2011},
doi = {10.1007/9783642294792_1},
}
[Abstract]
In this paper we study the multipleinput multipleoutput twoway relay channel (MIMOTWRC) when the nodes use analog beamforming. Following the amplifyandforward (AF) strategy, the problem consists of finding the transmit and receive beamformers of the nodes and the relay, and the power allocated to each one, that achieve the boundary of the capacity region. We express the optimal node beamformers in terms of the relay beamformers, and show that the capacity region can be efficiently characterized using convex optimization techniques. Numerical examples are provided to illustrate the results of this paper, and to compare the capacity region achieved by analog beamforming against the conventional MIMO schemes that operate at the baseband.148Linear precoding for timevarying MIMO channels with lowcomplexity receivers
(Jun Tong, Peter J. Schreier, Steven R. Weller and Louis L. Scharf)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 3092–3095, May 2011.
DOI:10.1109/ICASSP.2011.5946312.
[BibTeX]
@inproceedings{TongSchreierWeller:2011:LinearprecodingfortimevaryingMIMOc,
abstract = {This paper considers linear precoding for timevarying multiple input multipleoutput (MIMO) channels. We show that linear minimum meansquared error (LMMSE) equalization based on the conjugate gradient (CG) method can result in significantly reduced complexity compared with conventional approaches. This reduction is achieved by incorporating a condition number constraint into the precoder optimization framework, which leads to clustered eigen values of the measurement covariance matrix. The cost is a small increase in MSE compared to the optimal precoder.},
title = {Linear precoding for timevarying {MIMO} channels with lowcomplexity receivers},
author = {Tong, Jun and Schreier, Peter J. and Weller, Steven R. and Scharf, Louis L.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2011},
pages = {3092–3095},
doi = {10.1109/ICASSP.2011.5946312},
}
[Abstract]
This paper considers linear precoding for timevarying multiple input multipleoutput (MIMO) channels. We show that linear minimum meansquared error (LMMSE) equalization based on the conjugate gradient (CG) method can result in significantly reduced complexity compared with conventional approaches. This reduction is achieved by incorporating a condition number constraint into the precoder optimization framework, which leads to clustered eigen values of the measurement covariance matrix. The cost is a small increase in MSE compared to the optimal precoder.149Experimental validation of Interference Alignment Techniques using a Multiuser MIMO testbed
(Ó. González, D. Ramírez, I. Santamaría, J. A. GarcíaNaya and L. Castedo)
Proc. Int. ITG Work. on Smart Antennas, Aachen, Germany, February 2011.
DOI:10.1109/WSA.2011.5741921.
[BibTeX]
@inproceedings{GonzalezRamirezSantamaria:2011:ExperimentalValidationofInterferenceAlignment,
abstract = {Hardware platforms and testbeds are an essential tool to evaluate, in realistic scenarios, the performance of wireless communications systems. In this work we present a multiuser MultipleInput MultipleOutput (MIMO) testbed made up of 6 nodes, each one with 4 antennas, which allows us to evaluate Interference Alignment (IA) techniques in indoor scenarios. We specifically study the performance of IA for the 3user interference channel in the 5 GHz band. Our analysis identifies the main practical issues that potentially degrade the IA performance such as channel estimation errors or collinearity between the desired signal and interference subspaces.},
title = {Experimental validation of {I}nterference {A}lignment Techniques using a Multiuser {MIMO} testbed},
address = {Aachen, Germany},
author = {{\'O}. Gonz{\'a}lez and D. Ram{\'i}rez and I. Santamar{\'i}a and J. A. Garc{\'i}aNaya and L. Castedo},
booktitle = {Proc.\ Int.\ ITG Work.\ on Smart Antennas},
month = {{F}ebruary},
year = {2011},
doi = {10.1109/WSA.2011.5741921},
}
[Abstract]
Hardware platforms and testbeds are an essential tool to evaluate, in realistic scenarios, the performance of wireless communications systems. In this work we present a multiuser MultipleInput MultipleOutput (MIMO) testbed made up of 6 nodes, each one with 4 antennas, which allows us to evaluate Interference Alignment (IA) techniques in indoor scenarios. We specifically study the performance of IA for the 3user interference channel in the 5 GHz band. Our analysis identifies the main practical issues that potentially degrade the IA performance such as channel estimation errors or collinearity between the desired signal and interference subspaces.150Multiantenna spectrum sensing: the case of wideband rankone primary signals
(D. Ramírez, J. Vía and I. Santamaría)
Proc. IEEE Sensor Array and Multichannel Signal Process. Work., Israel, October 2010.
DOI:10.1109/SAM.2010.5606502.
[BibTeX]
@inproceedings{RamirezViaSantamaria:2010:Multiantennaspectrumsensing:Thecase,
abstract = {One of the key problems in cognitive radio (CR) is the detection of primary activity in order to determine which parts of the spectrum are available for opportunistic access. In this work, we present a new multiantenna detector which fully exploits the spatial and temporal structure of the signals. In particular, we derive the generalized likelihood ratio test (GLRT) for the problem of detecting a wideband rankone signal under spatially uncorrelated noise with equal or different power spectral densities. In order to simplify the maximum likelihood (ML) estimation of the unknown parameters, we use the asymptotic likelihood in the frequency domain. Interestingly, for noises with different distributions and under a low SNR approximation, the GLRT is obtained as a function of the largest eigenvalue of the spectral coherence matrix. Finally, the performance of the proposed detectors is evaluated by means of numerical simulations, showing important advantages over previously proposed approaches.},
title = {Multiantenna spectrum sensing: the case of wideband rankone primary signals},
address = {Israel},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a},
booktitle = {{P}roc.\ {IEEE} {S}ensor {A}rray and {M}ultichannel {S}ignal {P}rocess. {W}ork.},
month = {{O}ctober},
year = {2010},
doi = {10.1109/SAM.2010.5606502},
}
[Abstract]
One of the key problems in cognitive radio (CR) is the detection of primary activity in order to determine which parts of the spectrum are available for opportunistic access. In this work, we present a new multiantenna detector which fully exploits the spatial and temporal structure of the signals. In particular, we derive the generalized likelihood ratio test (GLRT) for the problem of detecting a wideband rankone signal under spatially uncorrelated noise with equal or different power spectral densities. In order to simplify the maximum likelihood (ML) estimation of the unknown parameters, we use the asymptotic likelihood in the frequency domain. Interestingly, for noises with different distributions and under a low SNR approximation, the GLRT is obtained as a function of the largest eigenvalue of the spectral coherence matrix. Finally, the performance of the proposed detectors is evaluated by means of numerical simulations, showing important advantages over previously proposed approaches.151Improperness measures for quaternion random vectors
(J. Vía, D. Ramírez, I. Santamaría and L. Vielva)
Proc. IEEE Int. Work. Machine Learning for Signal Process., Finland, August 2010.
DOI:10.1109/MLSP.2010.5589225.
[BibTeX]
@inproceedings{ViaRamirezSantamaria:2010:ImpropernessMeasuresforQuaternionRandom,
abstract = {It has been recently proved that the two main kinds of quaternion improperness require two different kinds of widely linear process ing. In this work, we show that these definitions satisfy some im portant properties, which include the invariance to quaternion lin ear transformations and right Clifford translations, as well as some clear connections with the case of proper complex vectors. More over, we introduce a new kind of quaternion properness, which clearly relates the two previous definitions, and propose three mea sures for the degree of improperness of a quaternion vector. The proposed measures are based on the KullbackLeibler divergence between two zeromean quaternion Gaussian distributions, one of them with the actual augmented covariance matrix, and the other with its closest proper version. These measures allow us to quan tify the entropy loss due to the improperness of the quaternion vec tor, and they admit an intuitive geometrical interpretation based on KullbackLeibler projections onto sets of proper augmented co variance matrices.},
title = {Improperness measures for quaternion random vectors},
address = {Finland},
author = {J. V{\'i}a and D. Ram{\'i}rez and I. Santamar{\'i}a and L. Vielva},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {W}ork.\ Machine Learning for Signal Process.},
month = {{A}ugust},
year = {2010},
doi = {10.1109/MLSP.2010.5589225},
}
[Abstract]
It has been recently proved that the two main kinds of quaternion improperness require two different kinds of widely linear process ing. In this work, we show that these definitions satisfy some im portant properties, which include the invariance to quaternion lin ear transformations and right Clifford translations, as well as some clear connections with the case of proper complex vectors. More over, we introduce a new kind of quaternion properness, which clearly relates the two previous definitions, and propose three mea sures for the degree of improperness of a quaternion vector. The proposed measures are based on the KullbackLeibler divergence between two zeromean quaternion Gaussian distributions, one of them with the actual augmented covariance matrix, and the other with its closest proper version. These measures allow us to quan tify the entropy loss due to the improperness of the quaternion vec tor, and they admit an intuitive geometrical interpretation based on KullbackLeibler projections onto sets of proper augmented co variance matrices.152Capacity region of the multiantenna gaussian broadcast channel with analog TXRX beamforming
(Ignacio Santamaría, Javier Vía, Alfredo Nazábal and Christian Lameiro)
Proc. Int. ICST Conf. Comm. and Networking in China, Beijing, China, August 2010. [BibTeX]
@inproceedings{SantamariaViaNazabal:2010:CapacityregionofthemultiantennaGaussian,
abstract = {In this paper we characterize the capacity boundary of the twouser multipleinput multipleoutput (MIMO) broadcast channel (BC) when the multiantenna terminals use analog beamforming at both sides of the link. Basically, the problem reduces to finding the optimal transmit direction and the optimal power allocation between users to operate at any point on the boundary. We show that both optimization problems can be solved in closed form. First, exploiting the fact that any Pareto optimal pair of rates must also be Pareto optimal of a convex region defined by the channel energies, the optimal transmit direction is shown to be the principal eigenvector of a matrix. Second, the optimal power allocation is obtained by exploiting again the Pareto optimality of the sought pair of rates. Although this paper focuses on the BC, the obtained results also serve to characterize the dual multipleaccess channel (MAC). Moreover, this explicit characterization of the boundary can be extended to a $K$user system for $K>2$. Numerical examples are provided to illustrate the results of the paper, and to show the enlargement of the capacity region achieved by analog beamforming in comparison to a singleinput singleoutput (SISO) BC.},
title = {Capacity region of the multiantenna gaussian broadcast channel with analog {TXRX} beamforming},
address = {Beijing, China},
author = {Santamar{\'i}a, Ignacio and V{\'i}a, Javier and Naz{\'a}bal, Alfredo and Lameiro, Christian},
booktitle = {Proc. Int. ICST Conf. Comm. and Networking in China},
month = {{A}ugust},
year = {2010},
}
[Abstract]
In this paper we characterize the capacity boundary of the twouser multipleinput multipleoutput (MIMO) broadcast channel (BC) when the multiantenna terminals use analog beamforming at both sides of the link. Basically, the problem reduces to finding the optimal transmit direction and the optimal power allocation between users to operate at any point on the boundary. We show that both optimization problems can be solved in closed form. First, exploiting the fact that any Pareto optimal pair of rates must also be Pareto optimal of a convex region defined by the channel energies, the optimal transmit direction is shown to be the principal eigenvector of a matrix. Second, the optimal power allocation is obtained by exploiting again the Pareto optimality of the sought pair of rates. Although this paper focuses on the BC, the obtained results also serve to characterize the dual multipleaccess channel (MAC). Moreover, this explicit characterization of the boundary can be extended to a Kuser system for K>2. Numerical examples are provided to illustrate the results of the paper, and to show the enlargement of the capacity region achieved by analog beamforming in comparison to a singleinput singleoutput (SISO) BC.153Multiantenna spectrum sensing: detection of spatial correlation among timeseries with unknown spectra
(D. Ramírez, J. Vía, I. Santamaría, R. LópezValcarce and L. L. Scharf)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Dallas, USA, March 2010.
DOI:10.1109/ICASSP.2010.5496151.
[BibTeX]
@inproceedings{RamirezViaSantamaria:2010:MultiantennaSpectrumSensing:Detection,
abstract = {One of the key problems in cognitive radio (CR) is the detection of primary activity in order to determine which parts of the spectrum are available for opportunistic access. This detection task is challenging, since the wireless environment often results in very low SNR conditions. Moreover, calibration errors and imperfect analog components at the CR spectral monitor result in uncertainties in the noise spectrum, making the problem more difficult. In this work, we present a new multiantenna detector which is based on the fact that the observation noise processes are spatially uncorrelated, whereas any primary signal present should result inspatial correlation. In particular, we derive the generalized likelihood ratio test (GLRT) for this problem, which is given by the quotient between the determinant of the sample covariance matrix and the determinant of its blockdiagonal version. For stationary processes the GLRT tends asymptotically to the integral of the logarithm of the Hadamard ratio of the estimated power spectral density matrix. Additionally, we present an approximation of the frequency domain detector in the low SNR regime, which results in computational savings. The performance of the proposed detectors is evaluated by means of numerical simulations, showing important advantages over existing detectors.},
title = {Multiantenna spectrum sensing: detection of spatial correlation among timeseries with unknown spectra},
address = {Dallas, USA},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a and R. L{\'o}pezValcarce and L. L. Scharf},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}arch},
year = {2010},
doi = {10.1109/ICASSP.2010.5496151},
}
[Abstract]
One of the key problems in cognitive radio (CR) is the detection of primary activity in order to determine which parts of the spectrum are available for opportunistic access. This detection task is challenging, since the wireless environment often results in very low SNR conditions. Moreover, calibration errors and imperfect analog components at the CR spectral monitor result in uncertainties in the noise spectrum, making the problem more difficult. In this work, we present a new multiantenna detector which is based on the fact that the observation noise processes are spatially uncorrelated, whereas any primary signal present should result inspatial correlation. In particular, we derive the generalized likelihood ratio test (GLRT) for this problem, which is given by the quotient between the determinant of the sample covariance matrix and the determinant of its blockdiagonal version. For stationary processes the GLRT tends asymptotically to the integral of the logarithm of the Hadamard ratio of the estimated power spectral density matrix. Additionally, we present an approximation of the frequency domain detector in the low SNR regime, which results in computational savings. The performance of the proposed detectors is evaluated by means of numerical simulations, showing important advantages over existing detectors.154Widely and semiwidely linear processing of quaternion vectors
(J. Vía, D. Ramírez, I. Santamaría and L. Vielva)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Dallas, USA, March 2010.
DOI:10.1109/ICASSP.2010.5495787.
[BibTeX]
@inproceedings{ViaRamirezSantamaria:2010:Widelyandsemiwidelylinearprocessing,
abstract = {In this paper the two main definitions of quaternion properness (or second order circularity) are reviewed, showing their connection with the structure of the optimal quaternion linear processing. Specifically, we present a rigorous generalization of the most common multivariate statistical analysis techniques to the case of quaternion vectors, and show that the different kinds of quaternion improperness require different kinds of widely linear processing. In general, the optimal linear processing is \emph{fullwidely linear}, which requires the joint processing of the quaternion vector and its involutions over three pure unit quaternions. However, in the case of jointly $\mathbb{Q}$proper and $\mathbb{C}^{\eta}$proper vectors, the optimal processing reduces, respectively, to the \emph{conventional} and \emph{semiwidely linear processing}, with the latter only requiring to operate on the quaternion vector and its involution over the pure unit quaternion $\eta$. Finally, a simulation example poses some interesting questions for future research.},
title = {Widely and semiwidely linear processing of quaternion vectors},
address = {Dallas, USA},
author = {J. V{\'i}a and D. Ram{\'i}rez and I. Santamar{\'i}a and L. Vielva},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}arch},
year = {2010},
doi = {10.1109/ICASSP.2010.5495787},
}
[Abstract]
In this paper the two main definitions of quaternion properness (or second order circularity) are reviewed, showing their connection with the structure of the optimal quaternion linear processing. Specifically, we present a rigorous generalization of the most common multivariate statistical analysis techniques to the case of quaternion vectors, and show that the different kinds of quaternion improperness require different kinds of widely linear processing. In general, the optimal linear processing is fullwidely linear, which requires the joint processing of the quaternion vector and its involutions over three pure unit quaternions. However, in the case of jointly mathbbQproper and mathbbC^etaproper vectors, the optimal processing reduces, respectively, to the conventional and semiwidely linear processing, with the latter only requiring to operate on the quaternion vector and its involution over the pure unit quaternion eta. Finally, a simulation example poses some interesting questions for future research.155Coherent fusion of information for optimal detection in sensor networks
(D. Ramírez, J. Vía and I. Santamaría)
Proc. IEEE Work. Stat. Signal Process., Cardiff, UK, September 2009.
DOI:10.1109/SSP.2009.5278473.
[BibTeX]
@inproceedings{RamirezViaSantamaria:2009:CoherentFusionofInformationforOptimal,
abstract = {In this work, we consider the problem of centralized detection in wireless sensor networks when the sensors transmit coherently through a multiple access channel. We derive the optimal weighting at each sensor that maximizes the error exponent. Firstly, the noiseless case is considered and a closedform solution to the problem is found. Secondly, we generalize the formulation to consider additive noise at the fusion center. For the noisy case, we propose a suboptimal approach which allows us to find a closedform solution. Interestingly, the proposed approaches reduce to the extraction of a normalized eigenvector of a generalized eigenvalue problem. The performance of the proposed scheme is illustrated by means of numerical results, showing that the suboptimal approach has a similar performance to that of the optimal one; and that the proposed scheme outperforms other techniques, such as orthogonal transmissions or the maximization of the signaltonoise ratio.},
title = {Coherent fusion of information for optimal detection in sensor networks},
address = {Cardiff, UK},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a},
booktitle = {{P}roc.\ {IEEE} {W}ork.\ {S}tat.\ {S}ignal {P}rocess.},
month = {{S}eptember},
year = {2009},
doi = {10.1109/SSP.2009.5278473},
}
[Abstract]
In this work, we consider the problem of centralized detection in wireless sensor networks when the sensors transmit coherently through a multiple access channel. We derive the optimal weighting at each sensor that maximizes the error exponent. Firstly, the noiseless case is considered and a closedform solution to the problem is found. Secondly, we generalize the formulation to consider additive noise at the fusion center. For the noisy case, we propose a suboptimal approach which allows us to find a closedform solution. Interestingly, the proposed approaches reduce to the extraction of a normalized eigenvector of a generalized eigenvalue problem. The performance of the proposed scheme is illustrated by means of numerical results, showing that the suboptimal approach has a similar performance to that of the optimal one; and that the proposed scheme outperforms other techniques, such as orthogonal transmissions or the maximization of the signaltonoise ratio.156Entropy and KullbackLeibler divergence estimation based on Szegö's theorem
(D. Ramírez, J. Vía, I. Santamaría and P. Crespo)
Proc. Eur. Signal Process. Conf., Glasgow, Scotland, August 2009. [BibTeX]
@inproceedings{RamirezViaSantamaria:2009:EntropyandKullbackLeiblerdivergenceestimation,
abstract = {In this work, a new technique for the estimation of the Shannon's entropy and the KullbackLeibler (KL) divergence for one dimensional data is presented. The estimator is based on the Szeg\"o's theorem for sequences of Toeplitz matrices, which deals with the asymptotic behavior of the eigenvalues of those matrices, and the analogy between a probability density function (PDF) and a power spectral density (PSD), which allows us to estimate a PDF of bounded support using the wellknown spectral estimation techniques. Specifically, an AR model is used for the PDF PSD estimation, and the entropy is easily estimated as a function of the eigenvalues of the autocorrelation Toeplitz matrix. The performance of the Szeg\"o's estimators is illustrated by means of Monte Carlo simulations and compared with previously proposed alternatives, showing a good performance.},
title = {Entropy and {K}ullback{L}eibler divergence estimation based on {S}zeg\"o's theorem},
address = {Glasgow, Scotland},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a and P. Crespo},
booktitle = {{P}roc.\ {E}ur.\ {S}ignal {P}rocess.\ {C}onf.},
month = {{A}ugust},
year = {2009},
}
[Abstract]
In this work, a new technique for the estimation of the Shannon's entropy and the KullbackLeibler (KL) divergence for one dimensional data is presented. The estimator is based on the Szeg"o's theorem for sequences of Toeplitz matrices, which deals with the asymptotic behavior of the eigenvalues of those matrices, and the analogy between a probability density function (PDF) and a power spectral density (PSD), which allows us to estimate a PDF of bounded support using the wellknown spectral estimation techniques. Specifically, an AR model is used for the PDF PSD estimation, and the entropy is easily estimated as a function of the eigenvalues of the autocorrelation Toeplitz matrix. The performance of the Szeg"o's estimators is illustrated by means of Monte Carlo simulations and compared with previously proposed alternatives, showing a good performance.157The Wiener filter for locally stationary stochastic processes is rarely locally stationary
(Patrik Wahlberg and Peter J. Schreier)
Proc. 17th European Signal Process. Conf., pp. 2465–2469, August 2009. [BibTeX]
@inproceedings{WahlbergSchreier:2009:TheWienerfilterforlocallystationary,
abstract = {The Wiener filter (i.e., linear minimum mean squared error filter) for widesense stationary stochastic processes is translationinvariant, i.e., its impulse response, like the covariance function, is only a function of the timeshift. We investigate whether there is a generalization of this result to continuoustime stochastic processes that are locally stationary in Silverman's sense: Is the optimal filter for locally stationary processes locally stationary itself? The answer is surprisingly negative: Even though the optimal filter can be locally stationary in special cases, it rarely is, even when the covariance functions have Gaussian shape.},
title = {The {Wiener} filter for locally stationary stochastic processes is rarely locally stationary},
author = {Wahlberg, Patrik and Schreier, Peter J.},
booktitle = {{P}roc.\ 17th\ {E}uropean {S}ignal {P}rocess.\ {C}onf.},
month = {{A}ugust},
year = {2009},
pages = {2465–2469},
}
[Abstract]
The Wiener filter (i.e., linear minimum mean squared error filter) for widesense stationary stochastic processes is translationinvariant, i.e., its impulse response, like the covariance function, is only a function of the timeshift. We investigate whether there is a generalization of this result to continuoustime stochastic processes that are locally stationary in Silverman's sense: Is the optimal filter for locally stationary processes locally stationary itself? The answer is surprisingly negative: Even though the optimal filter can be locally stationary in special cases, it rarely is, even when the covariance functions have Gaussian shape.158On ICA of improper and noncircular sources
(Peter J. Schreier, Tülay Adali and Louis L. Scharf)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 3561–3564, April 2009.
DOI:10.1109/ICASSP.2009.4960395.
[BibTeX]
@inproceedings{SchreierAdaliScharf:2009:OnICAofimproperandnoncircularsourc,
abstract = {We provide a review of independent component analysis (ICA) for complexvalued improper and noncircular random sources. An improper random signal is correlated with its complex conjugate, and a noncircular random signal has a rotationally variant probability distribution. We present methods for ICA using secondorder statistics, and higherorder statistics. For ICA based on secondorder statistics, we emphasize the key role played by the circularity coefficients, which are the canonical correlations between the source and the complex conjugate. For ICA based on higherorder statistics, we show how to extend algorithms for realvalued ICA to the complex domain using Wirtinger calculus.},
title = {On {ICA} of improper and noncircular sources},
author = {Schreier, Peter J. and Adali, T{\"u}lay and Scharf, Louis L.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{A}pril},
year = {2009},
pages = {3561–3564},
doi = {10.1109/ICASSP.2009.4960395},
}
[Abstract]
We provide a review of independent component analysis (ICA) for complexvalued improper and noncircular random sources. An improper random signal is correlated with its complex conjugate, and a noncircular random signal has a rotationally variant probability distribution. We present methods for ICA using secondorder statistics, and higherorder statistics. For ICA based on secondorder statistics, we emphasize the key role played by the circularity coefficients, which are the canonical correlations between the source and the complex conjugate. For ICA based on higherorder statistics, we show how to extend algorithms for realvalued ICA to the complex domain using Wirtinger calculus.159Impact of signaling schemes on iterative linear minimummeansquareerror detection
(Li Ping, Jun Tong, Xiaojun Yuan and Qinghua Guo)
Proc. IEEE Global Telecomm. Conf., pp. 1–5, December 2008.
DOI:10.1109/GLOCOM.2008.ECP.665.
[BibTeX]
@inproceedings{PingTongYuan:2008:Impactofsignalingschemesoniterative,
abstract = {In this paper, we study the iterative detection problem for a coded system with multiary modulation. We show that, with iterative linear minimummeansquareerror (LMMSE) detection, superposition coded modulation (SCM) can provide performance superior to that with other traditional signaling schemes used in trellis coded modulation (TCM) and bitinterleaved coded modulation (BICM). This finding provides a useful guideline for system design considering intersymbol interference (ISI) and other forms of interference. Simulation results are provided to illustrate the efficiency of the iterative LMMSE detection with different signaling schemes.},
title = {Impact of signaling schemes on iterative linear minimummeansquareerror detection},
author = {Ping, Li and Tong, Jun and Yuan, Xiaojun and Guo, Qinghua},
booktitle = {{P}roc.\ {IEEE} {G}lobal {T}elecomm.\ {C}onf.},
month = {{D}ecember},
year = {2008},
pages = {1–5},
doi = {10.1109/GLOCOM.2008.ECP.665},
}
[Abstract]
In this paper, we study the iterative detection problem for a coded system with multiary modulation. We show that, with iterative linear minimummeansquareerror (LMMSE) detection, superposition coded modulation (SCM) can provide performance superior to that with other traditional signaling schemes used in trellis coded modulation (TCM) and bitinterleaved coded modulation (BICM). This finding provides a useful guideline for system design considering intersymbol interference (ISI) and other forms of interference. Simulation results are provided to illustrate the efficiency of the iterative LMMSE detection with different signaling schemes.160Iterative detection techniques for clipped OFDM systems
(Jun Tong and Li Ping)
Proc. IEEE Global Telecomm. Conf., pp. 1–5, December 2008.
DOI:10.1109/GLOCOM.2008.ECP.225.
[BibTeX]
@inproceedings{TongPing:2008:Iterativedetectiontechniquesforclipp,
abstract = {This paper studies orthogonal frequencydivision multiplexing (OFDM) systems employing coded modulation. Clipping is applied to reduce the peaktoaveragepowerratio (PAPR) of the transmit signal. A soft compensation method is proposed to combat the clipping effect. It is shown that the proposed method can outperform conventional clipping effect mitigation methods. The impact of signaling schemes of the coded modulation on system performance is investigated. The average variance analysis and numerical results demonstrate that superposition coded modulation (SCM) together with the proposed detection technique provides a simple and efficient solution to clipped OFDM transmission.},
title = {Iterative detection techniques for clipped {OFDM} systems},
author = {Tong, Jun and Ping, Li},
booktitle = {{P}roc.\ {IEEE} {G}lobal {T}elecomm.\ {C}onf.},
month = {{D}ecember},
year = {2008},
pages = {1–5},
doi = {10.1109/GLOCOM.2008.ECP.225},
}
[Abstract]
This paper studies orthogonal frequencydivision multiplexing (OFDM) systems employing coded modulation. Clipping is applied to reduce the peaktoaveragepowerratio (PAPR) of the transmit signal. A soft compensation method is proposed to combat the clipping effect. It is shown that the proposed method can outperform conventional clipping effect mitigation methods. The impact of signaling schemes of the coded modulation on system performance is investigated. The average variance analysis and numerical results demonstrate that superposition coded modulation (SCM) together with the proposed detection technique provides a simple and efficient solution to clipped OFDM transmission.161Performance analysis of multiary systems with iterative linear minimummeansquareerror detection
(Li Ping, Jun Tong, Xiaojun Yuan and Qinghua Guo)
5th Int. Symp. Turbo Codes & Rel. Top., pp. 192–197, September 2008.
DOI:10.1109/TURBOCODING.2008.4658696.
[BibTeX]
@inproceedings{PingTongYuan:2008:Performanceanalysisofmultiarysystem,
abstract = {This paper is concerned with coded multiary systems over linear channels. Based on a semianalytical evolution technique, the impact of signaling schemes on the performance of lowcost iterative linear minimummeansquareerror (LMMSE) detection is studied. It is shown that superposition coded modulation (SCM) maximizes the output signaltonoise ratio (SNR) of LMMSE detectors. Consequently, SCM may potentially outperform other conventional signaling schemes when LMMSE detectors are used. Numerical examples are provided to verify the theoretical analysis.},
title = {Performance analysis of multiary systems with iterative linear minimummeansquareerror detection},
author = {Ping, Li and Tong, Jun and Yuan, Xiaojun and Guo,Qinghua},
booktitle = {5th\ {I}nt.\ {S}ymp.\ {T}urbo {C}odes \& {R}el.\ {T}op.},
month = {{S}eptember},
year = {2008},
pages = {192–197},
doi = {10.1109/TURBOCODING.2008.4658696},
}
[Abstract]
This paper is concerned with coded multiary systems over linear channels. Based on a semianalytical evolution technique, the impact of signaling schemes on the performance of lowcost iterative linear minimummeansquareerror (LMMSE) detection is studied. It is shown that superposition coded modulation (SCM) maximizes the output signaltonoise ratio (SNR) of LMMSE detectors. Consequently, SCM may potentially outperform other conventional signaling schemes when LMMSE detectors are used. Numerical examples are provided to verify the theoretical analysis.162Optimal MIMO transmission schemes with adaptive antenna combining in the RF path
(I. Santamaría, V. Elvira, J. Vía, D. Ramírez, J. Pérez, J. Ibáñez, R. Eickhoff and F. Ellinger)
Proc. Eur. Signal Process. Conf., Lausanne, Switzerland, August 2008. [BibTeX]
@inproceedings{SantamariaElviraVia:2008:OptimalMIMOtransmissionschemes,
abstract = {In this paper we study spacetime coding schemes for a novel MIMO transceiver which performs adaptive signal combining in radiofrequency (RF). The limitations of the RF circuitry make necessary to develop specific designs for this architecture. For instance, the space and time encoders must operate separately (the former works in the RF domain and the latter works in baseband), and at different time scales: the spatial encoder or RF beamformer must remain fixed dur ing the transmission of a probably large number of symbols, whereas the timeencoder can work at the symbol rate. We show in the paper that although the multiplexing gain of the system is limited to one, we are still able to achieve the full spatial diversity of the MIMO channel as well as to increase the received signaltonoise ratio through array gain. Specifically, when perfect channel state information (CSI) is available only at the receiver we propose to use a scheme referred to as orthogonal beam division multiplexing (OBDM). With this scheme the symbols are timeprecoded with a unitary discrete Fourier transform (DFT) matrix, then they are successively transmitted through orthogonal direc tions and, finally, we use a receiver comprising maximal ra tio combining (MRC) followed by a minimum meansquare error (MMSE) decoder. The performance of the proposed techniques in terms of outage capacity and bit error rate is illustrated by means of several simulations examples.},
title = {Optimal {MIMO} transmission schemes with adaptive antenna combining in the {RF} path},
address = {Lausanne, Switzerland},
author = {I. Santamar{\'i}a and V. Elvira and J. V{\'i}a and D. Ram{\'i}rez and J. P{\'e}rez and J. Ib{\'a}{\~n}ez and R. Eickhoff and F. Ellinger},
booktitle = {{P}roc.\ {E}ur.\ {S}ignal {P}rocess.\ {C}onf.},
month = {{A}ugust},
year = {2008},
}
[Abstract]
In this paper we study spacetime coding schemes for a novel MIMO transceiver which performs adaptive signal combining in radiofrequency (RF). The limitations of the RF circuitry make necessary to develop specific designs for this architecture. For instance, the space and time encoders must operate separately (the former works in the RF domain and the latter works in baseband), and at different time scales: the spatial encoder or RF beamformer must remain fixed dur ing the transmission of a probably large number of symbols, whereas the timeencoder can work at the symbol rate. We show in the paper that although the multiplexing gain of the system is limited to one, we are still able to achieve the full spatial diversity of the MIMO channel as well as to increase the received signaltonoise ratio through array gain. Specifically, when perfect channel state information (CSI) is available only at the receiver we propose to use a scheme referred to as orthogonal beam division multiplexing (OBDM). With this scheme the symbols are timeprecoded with a unitary discrete Fourier transform (DFT) matrix, then they are successively transmitted through orthogonal direc tions and, finally, we use a receiver comprising maximal ra tio combining (MRC) followed by a minimum meansquare error (MMSE) decoder. The performance of the proposed techniques in terms of outage capacity and bit error rate is illustrated by means of several simulations examples.163Performance analysis of OFDMIDMA systems with peakpower limitation
(Jun Tong, Qinghua Guo and Li Ping)
IEEE 10th Int. Symp. Spread Spectrum Techn. & Appl., pp. 555–559, August 2008.
DOI:10.1109/ISSSTA.2008.109.
[BibTeX]
@inproceedings{TongGuoPing:2008:PerformanceanalysisofOFDMIDMAsystem,
abstract = {This paper is concerned with orthogonal frequencydivision multiplexing interleavedivision multipleaccess (OFDMIDMA) systems over frequencyselective fading channels. Deliberate clipping is applied to reduce the peaktoaverage power ratio (PAPR) of each user's transmitted signal. An iterative multiuser detection (MUD) technique is developed to recover the performance loss due to clipping. A semianalytical signaltonoise ratio (SNR) evolution technique is proposed, which can provide quick and accurate prediction of the iterative MUD performance. Numerical results show that the performance of OFDMIDMA is not sensitive to the frequency selectivity of channels, and OFDMIDMA is more powerefficient than other alternative multicarrier transmission techniques},
title = {Performance analysis of {OFDMIDMA} systems with peakpower limitation},
author = {Tong, Jun and Guo, Qinghua and Ping, Li},
booktitle = {{IEEE} 10th\ {I}nt.\ {S}ymp.\ {S}pread {S}pectrum {T}echn.\ \& {A}ppl.},
month = {{A}ugust},
year = {2008},
pages = {555–559},
doi = {10.1109/ISSSTA.2008.109},
}
[Abstract]
This paper is concerned with orthogonal frequencydivision multiplexing interleavedivision multipleaccess (OFDMIDMA) systems over frequencyselective fading channels. Deliberate clipping is applied to reduce the peaktoaverage power ratio (PAPR) of each user's transmitted signal. An iterative multiuser detection (MUD) technique is developed to recover the performance loss due to clipping. A semianalytical signaltonoise ratio (SNR) evolution technique is proposed, which can provide quick and accurate prediction of the iterative MUD performance. Numerical results show that the performance of OFDMIDMA is not sensitive to the frequency selectivity of channels, and OFDMIDMA is more powerefficient than other alternative multicarrier transmission techniques164A timefrequency formula for LMMSE filters for nonstationary underspread continuoustime stochastic processes
(Patrik Wahlberg and Peter J. Schreier)
Proc. 16th European Signal Process. Conf., August 2008. [BibTeX]
@inproceedings{WahlbergSchreier:2008:AtimefrequencyformulaforLMMSEfilte,
abstract = {We study linear minimum mean square error (LMMSE) filters for estimating a nonstationary secondorder continuoustime stochastic process from a noisy observation. The equation for the optimal filter is treated in the Weyl symbol domain, and the involved Weyl symbols are assumed to belong to certain modulation spaces. By discretizing this equation using a Gabor frame we transform it into a matrix equation and obtain a formula for the filter by matrix inversion. The inverse matrix has offdiagonal decay at a rate that increases the more underspread the process is.},
title = {A timefrequency formula for {LMMSE} filters for nonstationary underspread continuoustime stochastic processes},
author = {Wahlberg, Patrik and Schreier, Peter J.},
booktitle = {{P}roc.\ 16th\ {E}uropean {S}ignal {P}rocess.\ {C}onf.},
month = {{A}ugust},
year = {2008},
}
[Abstract]
We study linear minimum mean square error (LMMSE) filters for estimating a nonstationary secondorder continuoustime stochastic process from a noisy observation. The equation for the optimal filter is treated in the Weyl symbol domain, and the involved Weyl symbols are assumed to belong to certain modulation spaces. By discretizing this equation using a Gabor frame we transform it into a matrix equation and obtain a formula for the filter by matrix inversion. The inverse matrix has offdiagonal decay at a rate that increases the more underspread the process is.165Multiplechannel signal detection using the generalized coherence spectrum
(D. Ramírez, J. Vía and I. Santamaría)
Proc. IAPR Work. Cognitive Information Process., Santorini, Greece, June 2008. [BibTeX]
@inproceedings{RamirezViaSantamaria:2008:MultipleChannelSignalDetectionusing,
abstract = {Recently, a generalization of the magnitude squared coherence (MSC) spectrum for more than two random processes has been proposed. The generalized MSC (GMSC) spectrum definition, which is based on the largest eigenvalue of a matrix containing all the pairwise complex coherence spectra, provides a frequencydependent measure of the linear relationship among several stationary random processes. Moreover, it can be easily estimated by solving a generalized eigenvalue problem. In this paper we apply the GMSC spectrum for detecting the presence of a common signal from a set of linearly distorted and noisy observations. Specifically, the new statistic for the multiplechannel detection problem is the integral of the square root of the GMSC, which can be estimated as the sum of the $P$ largest generalized canonical correlations (typically $P=1$ is enough in practice). Unlike previous approaches, the new statistic implicitly takes into account the spectral characteristics of the signal to be detected (e.g., its bandwidth). Finally, the performance of the proposed detector is compared in terms of its receiver operating characteristic (ROC) curve with the generalized coherence (GC) showing a clear improvement in most scenarios.},
title = {Multiplechannel signal detection using the generalized coherence spectrum},
address = {Santorini, Greece},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a},
booktitle = {Proc.\ {IAPR} Work.\ Cognitive Information Process.},
month = {{J}une},
year = {2008},
}
[Abstract]
Recently, a generalization of the magnitude squared coherence (MSC) spectrum for more than two random processes has been proposed. The generalized MSC (GMSC) spectrum definition, which is based on the largest eigenvalue of a matrix containing all the pairwise complex coherence spectra, provides a frequencydependent measure of the linear relationship among several stationary random processes. Moreover, it can be easily estimated by solving a generalized eigenvalue problem. In this paper we apply the GMSC spectrum for detecting the presence of a common signal from a set of linearly distorted and noisy observations. Specifically, the new statistic for the multiplechannel detection problem is the integral of the square root of the GMSC, which can be estimated as the sum of the P largest generalized canonical correlations (typically P=1 is enough in practice). Unlike previous approaches, the new statistic implicitly takes into account the spectral characteristics of the signal to be detected (e.g., its bandwidth). Finally, the performance of the proposed detector is compared in terms of its receiver operating characteristic (ROC) curve with the generalized coherence (GC) showing a clear improvement in most scenarios.166A generalization of the magnitude squared coherence spectrum for more than two signals: definition, properties and estimation
(D. Ramírez, J. Vía and I. Santamaría)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Las Vegas, USA, April 2008.
DOI:10.1109/ICASSP.2008.4518473.
[BibTeX]
@inproceedings{RamirezViaSantamaria:2008:Ageneralizationofthemagnitudesquaredcoherence,
abstract = {The coherence spectrum is a wellknown measure of the linear statistical relationship between two time series. In this paper, we extend this concept to several processes and define the generalized magnitude squared coherence (GMSC) spectrum as a function of the largest eigenvalue of a matrix containing all the pairwise complex coherence spectra. The GMSC is bounded between zero and one, and attains its maximum when all the processes are perfectly correlated at a given frequency. Furthermore, three different GMSC spectrum estimators, extending those previously proposed for the MSC of two processes, are presented. Specifically, we compare the Welch method, the minimum variance distortionless response (MVDR) estimator and a new estimator based on canonical correlation analysis (CCA).},
title = {A generalization of the magnitude squared coherence spectrum for more than two signals: definition, properties and estimation},
address = {Las Vegas, USA},
author = {D. Ram{\'i}rez and J. V{\'i}a and I. Santamar{\'i}a},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{A}pril},
year = {2008},
doi = {10.1109/ICASSP.2008.4518473},
}
[Abstract]
The coherence spectrum is a wellknown measure of the linear statistical relationship between two time series. In this paper, we extend this concept to several processes and define the generalized magnitude squared coherence (GMSC) spectrum as a function of the largest eigenvalue of a matrix containing all the pairwise complex coherence spectra. The GMSC is bounded between zero and one, and attains its maximum when all the processes are perfectly correlated at a given frequency. Furthermore, three different GMSC spectrum estimators, extending those previously proposed for the MSC of two processes, are presented. Specifically, we compare the Welch method, the minimum variance distortionless response (MVDR) estimator and a new estimator based on canonical correlation analysis (CCA).167The degree of impropriety (noncircularity) of complex random vectors
(Peter J. Schreier)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 3909–3912, April 2008.
DOI:10.1109/ICASSP.2008.4518508.
[BibTeX]
@inproceedings{Schreier:2008:Thedegreeofimproprietynoncircularit,
abstract = {A complex random vector is called improper (noncircular) if it is correlated with its complex conjugate. We consider measures for the degree of impropriety that are invariant under linear transformation. These measures are functions of the canonical correlations between the vector and its complex conjugate, which have been termed the circularity coefficients. However, we show that these circularity coefficients do not tell the whole story: Two random vectors with identical covariance matrix and identical circularity coefficients can still behave differently in secondorder estimation and detection.},
title = {The degree of impropriety (noncircularity) of complex random vectors},
author = {Schreier, Peter J.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{A}pril},
year = {2008},
pages = {3909–3912},
doi = {10.1109/ICASSP.2008.4518508},
}
[Abstract]
A complex random vector is called improper (noncircular) if it is correlated with its complex conjugate. We consider measures for the degree of impropriety that are invariant under linear transformation. These measures are functions of the canonical correlations between the vector and its complex conjugate, which have been termed the circularity coefficients. However, we show that these circularity coefficients do not tell the whole story: Two random vectors with identical covariance matrix and identical circularity coefficients can still behave differently in secondorder estimation and detection.168Nearcapacity turbo equalization using optimized turbo codes
(Vladimir D. Trajkovic, Minyue Fu and Peter J. Schreier)
Proc. Australasian Telecomm. Netw. Applic. Conf., pp. 480–484, December 2007.
DOI:10.1109/ATNAC.2007.4665276.
[BibTeX]
@inproceedings{TrajkovicFuSchreier:2007:Nearcapacityturboequalizationusingo,
abstract = {In this paper we analyze a turbo equalization scheme that combines maximum a posteriori probability (MAP) equalization and turbo decoding. Our aim is to optimize the turbo equalizer in order to approach the information capacity limit for channels with severe intersymbol interference (ISI). For this purpose, we perform an extensive search for turbo codes that give an SNRBER performance closest to the channel information capacity limit. Our results show that the optimized turbo equalizer can approach the information capacity limit to within 0.7 dB. We also optimize the turbo equalizer in terms of the minimum number of required turbo decoding iterations. Our results show that a turbo decoder within a turbo equalization loop requires only a small number of iterations. Finally, our analysis reveals that when there are turbo codes with similar extrinsic information transfer characteristics, the computational complexity can be reduced by choosing the code with the smallest constraint length with no loss in SNRBER performance.},
title = {Nearcapacity turbo equalization using optimized turbo codes},
author = {Trajkovic, Vladimir D. and Fu, Minyue and Schreier, Peter J.},
booktitle = {{P}roc.\ {A}ustralasian {T}elecomm. {N}etw.\ {A}pplic.\ {C}onf.},
month = {{D}ecember},
year = {2007},
pages = {480–484},
doi = {10.1109/ATNAC.2007.4665276},
}
[Abstract]
In this paper we analyze a turbo equalization scheme that combines maximum a posteriori probability (MAP) equalization and turbo decoding. Our aim is to optimize the turbo equalizer in order to approach the information capacity limit for channels with severe intersymbol interference (ISI). For this purpose, we perform an extensive search for turbo codes that give an SNRBER performance closest to the channel information capacity limit. Our results show that the optimized turbo equalizer can approach the information capacity limit to within 0.7 dB. We also optimize the turbo equalizer in terms of the minimum number of required turbo decoding iterations. Our results show that a turbo decoder within a turbo equalization loop requires only a small number of iterations. Finally, our analysis reveals that when there are turbo codes with similar extrinsic information transfer characteristics, the computational complexity can be reduced by choosing the code with the smallest constraint length with no loss in SNRBER performance.169Correlation coefficients for complex random vectors
(Peter J. Schreier)
Proc. 41st Asilomar Conf. Signals Syst. Computers, pp. 577–581, November 2007.
DOI:10.1109/ACSSC.2007.4487279.
[BibTeX]
@inproceedings{Schreier:2007:CorrelationCoefficientsforComplexRan,
abstract = {We consider the assessment of multivariate association between two complex random vectors. For complex data, there are three types of correlation coefficients, which account for rotational, reflectional, and total (i.e., rotational and reflectional) dependencies. We define and analyze these three types for different correlation coefficients, based on two popular correlation analysis techniques: canonical correlation analysis and multivariate linear regression (also known as halfcanonical correlation analysis).},
title = {Correlation coefficients for complex random vectors},
author = {Schreier, Peter J.},
booktitle = {{P}roc.\ 41st\ {A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {{N}ovember},
year = {2007},
pages = {577–581},
doi = {10.1109/ACSSC.2007.4487279},
}
[Abstract]
We consider the assessment of multivariate association between two complex random vectors. For complex data, there are three types of correlation coefficients, which account for rotational, reflectional, and total (i.e., rotational and reflectional) dependencies. We define and analyze these three types for different correlation coefficients, based on two popular correlation analysis techniques: canonical correlation analysis and multivariate linear regression (also known as halfcanonical correlation analysis).170Frequencydomain properties of locally stationary improper secondorder stochastic processes
(Patrik Wahlberg and Peter J. Schreier)
Proc. 41st Asilomar Conf. Signals Syst. Computers, pp. 1093–1097, November 2007.
DOI:10.1109/ACSSC.2007.4487391.
[BibTeX]
@inproceedings{WahlbergSchreier:2007:Frequencydomainpropertiesoflocallys,
abstract = {This paper concerns continuoustime secondorder complex improper stochastic processes that satisfy Silverman's condition of local stationarity, which is a generalization of widesense stationarity (WSS). We study their spectral relations, proving a necessary condition that is related to a characterizing inequality of the pair of complementary spectral measure and spectral measure in the WSS case.},
title = {Frequencydomain properties of locally stationary improper secondorder stochastic processes},
author = {Wahlberg, Patrik and Schreier, Peter J.},
booktitle = {{P}roc.\ 41st\ {A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {{N}ovember},
year = {2007},
pages = {1093–1097},
doi = {10.1109/ACSSC.2007.4487391},
}
[Abstract]
This paper concerns continuoustime secondorder complex improper stochastic processes that satisfy Silverman's condition of local stationarity, which is a generalization of widesense stationarity (WSS). We study their spectral relations, proving a necessary condition that is related to a characterizing inequality of the pair of complementary spectral measure and spectral measure in the WSS case.171Turbo equalization with irregular turbo codes
(Vladimir D. Trajkovic, Minyue Fu and Peter J. Schreier)
Proc. 4th Int. Symp. Wireless Comm. Syst., pp. 153–157, October 2007.
DOI:10.1109/ISWCS.2007.4392320.
[BibTeX]
@inproceedings{TrajkovicFuSchreier:2007:TurboEqualizationWithIrregularTurbo,
abstract = {We analyze a turbo equalization system that combines maximum a posteriori probability (MAP) equalization with irregular turbo codes. Our goal is to approach the information capacity limit for severe intersymbol interference (ISI) channels. To this end, we optimize the degree profile of irregular turbo codes by maximizing the minimum distance between the mutual information transfer functions for the MAP equalizer and decoder. We show that turbo equalizers employing such optimized irregular turbo codes can approach the information capacity limit of some severe ISI channels within 0.75 dB.},
title = {Turbo equalization with irregular turbo codes},
author = {Trajkovic, Vladimir D. and Fu, Minyue and Schreier, Peter J.},
booktitle = {{P}roc.\ 4th\ {I}nt.\ {S}ymp.\ {W}ireless {C}omm.\ {S}yst.},
month = {{O}ctober},
year = {2007},
pages = {153–157},
doi = {10.1109/ISWCS.2007.4392320},
}
[Abstract]
We analyze a turbo equalization system that combines maximum a posteriori probability (MAP) equalization with irregular turbo codes. Our goal is to approach the information capacity limit for severe intersymbol interference (ISI) channels. To this end, we optimize the degree profile of irregular turbo codes by maximizing the minimum distance between the mutual information transfer functions for the MAP equalizer and decoder. We show that turbo equalizers employing such optimized irregular turbo codes can approach the information capacity limit of some severe ISI channels within 0.75 dB.172Performance of STBC transmissions with real data
(J. A. GarcíaNaya, T. M. FernándezCaramés, H. J. PérezIglesias, M. GonzálezLópez, L. Castedo, D. Ramírez, I. Santamaría, J. Pérez, J. Vía and J. M. TorresRoyo)
Proc. IST Mobile & Wireless Comms. Summit, Budapest, Hungary, July 2007.
DOI:10.1109/ISTMWC.2007.4299296.
[BibTeX]
@inproceedings{GarciaNayaFernandezCaramesPerezIglesias:2007:PerformanceofSTBCtransmissionswith,
abstract = {This paper presents a comparative study of three SpaceTime Block Coding (STBC) techniques in realistic indoor scenarios. In particular, we focus on the Alamouti orthogonal scheme considering two types of Channel State Information (CSI) estimation: a conventional pilotaided technique and a new blind method based on Second Order Statistics (SOS). We also considered a Differential (noncoherent) SpaceTime Block code (DSTBC) that can be optimally decoded without CSI estimation, although it incurs in a 3 dB loss in performance. Experimental evaluation is carried out with a flexible and easytouse $2 \times 2$ MIMO platform at 2.4 GHz. Results show the excellent performance of the blind channel estimation technique in either LineOfSight (LOS) and NonLOS (NLOS) indoor scenarios.},
title = {Performance of {STBC} transmissions with real data},
address = {Budapest, Hungary},
author = {J. A. Garc{\'i}aNaya and T. M. Fern{\'a}ndezCaram{\'e}s and H. J. P{\'e}rezIglesias and M. Gonz{\'a}lezL{\'o}pez and L. Castedo and D. Ram{\'i}rez and I. Santamar{\'i}a and J. P{\'e}rez and J. V{\'i}a and J. M. TorresRoyo},
booktitle = {Proc.\ IST Mobile $\&$ Wireless Comms.\ Summit},
month = {{J}uly},
year = {2007},
doi = {10.1109/ISTMWC.2007.4299296},
}
[Abstract]
This paper presents a comparative study of three SpaceTime Block Coding (STBC) techniques in realistic indoor scenarios. In particular, we focus on the Alamouti orthogonal scheme considering two types of Channel State Information (CSI) estimation: a conventional pilotaided technique and a new blind method based on Second Order Statistics (SOS). We also considered a Differential (noncoherent) SpaceTime Block code (DSTBC) that can be optimally decoded without CSI estimation, although it incurs in a 3 dB loss in performance. Experimental evaluation is carried out with a flexible and easytouse 2 times 2 MIMO platform at 2.4 GHz. Results show the excellent performance of the blind channel estimation technique in either LineOfSight (LOS) and NonLOS (NLOS) indoor scenarios.173Spectra of multidimensional complex improper (almost) cyclostationary processes
(Patrik Wahlberg and Peter J. Schreier)
Proc. IEEE Int. Symp. Inform. Theory, pp. 971–975, June 2007.
DOI:10.1109/ISIT.2007.4557350.
[BibTeX]
@inproceedings{WahlbergSchreier:2007:Spectraofmultidimensionalcompleximpr,
abstract = {We analyze the spectral measure and complementary spectral measure for strongly harmonizable cyclostationary and almost cyclostationary multidimensional complex improper processes. We show that the offdiagonal components of the spectral measure are absolutely continuous with respect to the diagonal component, which is a generalization of a result for scalar processes. For scalar almost cyclostationary processes, we derive representation formulas for the complementary spectral measure and the offdiagonal components of the spectral measure, in terms of the diagonal component of the spectral measure. These results are similar to the cyclostationary case, with some modifications concerning the offdiagonal components of the complementary spectral measure.},
title = {Spectra of multidimensional complex improper (almost) cyclostationary processes},
author = {Wahlberg, Patrik and Schreier, Peter J.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {S}ymp.\ {I}nform.\ {T}heory},
month = {{J}une},
year = {2007},
pages = {971–975},
doi = {10.1109/ISIT.2007.4557350},
}
[Abstract]
We analyze the spectral measure and complementary spectral measure for strongly harmonizable cyclostationary and almost cyclostationary multidimensional complex improper processes. We show that the offdiagonal components of the spectral measure are absolutely continuous with respect to the diagonal component, which is a generalization of a result for scalar processes. For scalar almost cyclostationary processes, we derive representation formulas for the complementary spectral measure and the offdiagonal components of the spectral measure, in terms of the diagonal component of the spectral measure. These results are similar to the cyclostationary case, with some modifications concerning the offdiagonal components of the complementary spectral measure.174A new interpretation of bilinear timefrequency distributions
(Peter J. Schreier)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 1133–1136, April 2007.
DOI:10.1109/ICASSP.2007.366884.
[BibTeX]
@inproceedings{Schreier:2007:ANewInterpretationofBilinearTimeFr,
abstract = {Wigner's theorem states that there exists no bilinear timefrequency distribution (TFD) that has correct marginals and is nonnegative everywhere. This means that any attempt to interpret a bilinear TFD as an energy or power distribution must be fraught with problems. In this paper, an alternative perspective is proposed, which allows a local interpretation at a point in the timefrequency plane. This approach is based on analyzing the properties of a chirping ellipse that, at a given time instant, gives the best local approximation of the signal from a given frequency. This chirping ellipse is described in terms of its mean shape, orientation, and direction of polarization (counterclockwise or clockwise). A timefrequency coherence measures the quality of the approximation that this ellipse presents. The ellipse parameters and the timefrequency coherence can be expressed in terms of the Rihaczek TFD},
title = {A new interpretation of bilinear timefrequency distributions},
author = {Schreier, Peter J.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{A}pril},
year = {2007},
pages = {1133–1136},
doi = {10.1109/ICASSP.2007.366884},
}
[Abstract]
Wigner's theorem states that there exists no bilinear timefrequency distribution (TFD) that has correct marginals and is nonnegative everywhere. This means that any attempt to interpret a bilinear TFD as an energy or power distribution must be fraught with problems. In this paper, an alternative perspective is proposed, which allows a local interpretation at a point in the timefrequency plane. This approach is based on analyzing the properties of a chirping ellipse that, at a given time instant, gives the best local approximation of the signal from a given frequency. This chirping ellipse is described in terms of its mean shape, orientation, and direction of polarization (counterclockwise or clockwise). A timefrequency coherence measures the quality of the approximation that this ellipse presents. The ellipse parameters and the timefrequency coherence can be expressed in terms of the Rihaczek TFD175Causal cyclic Wiener filtering
(Mark S. Spurbeck, Peter J. Schreier and Louis L. Scharf)
Proc. 40th Asilomar Conf. Signals Syst. Computers, pp. 1425–1429, November 2006.
DOI:10.1109/ACSSC.2006.354993.
[BibTeX]
@inproceedings{SchreierSpurbeckScharf:2006:CausalcyclicWienerfiltering,
abstract = {We develop a causal filter bank implementation of the cyclic Wiener filter for periodically correlated (PC, or cyclostationary) time series. By converting the PC time series into a vectorvalued widesense stationary (WSS) time series, we may utilize the existing literature on factorization of spectral density matrices. However, because PC analytic and equivalent baseband signals are generally improper, spectral factorization algorithms must be modified for the improper case. Then, given the spectral density matrix for the equivalent WSS vector process, a causal cyclic Wiener filter can be implemented as a multirate filter bank or an equivalent polyphase structure.},
title = {Causal cyclic {Wiener} filtering},
author = {Spurbeck, Mark S. and Schreier, Peter J. and Scharf, Louis L.},
booktitle = {{P}roc.\ 40th\ {A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {{N}ovember},
year = {2006},
pages = {1425–1429},
doi = {10.1109/ACSSC.2006.354993},
}
[Abstract]
We develop a causal filter bank implementation of the cyclic Wiener filter for periodically correlated (PC, or cyclostationary) time series. By converting the PC time series into a vectorvalued widesense stationary (WSS) time series, we may utilize the existing literature on factorization of spectral density matrices. However, because PC analytic and equivalent baseband signals are generally improper, spectral factorization algorithms must be modified for the improper case. Then, given the spectral density matrix for the equivalent WSS vector process, a causal cyclic Wiener filter can be implemented as a multirate filter bank or an equivalent polyphase structure.176A flexible testbed for the rapid prototyping of MIMO baseband modules
(D. Ramírez, I. Santamaría, J. Pérez, J. Vía, A. Tazón, J. A. GarciaNaya, T. M. FernandezCarames, M. Gonzalez Lopez, H. J. Pérez Iglesias and L. Castedo)
Proc. Int. Symp. on Wireless Comm. Systems, Valencia, Spain, September 2006.
DOI:10.1109/ISWCS.2006.4362407.
[BibTeX]
@inproceedings{RamirezSantamariaPerez:2006:Aflexibletestbedfortherapidprototyping,
abstract = {Hardware platforms and testbeds are an essential tool to evaluate, in realistic scenarios, the performance of MultipleInputMultipleOuput (MIMO) systems. In this work we present a simple and easily reconfigurable $2 \times 2$ MIMO testbed for the rapid prototyping of the signal processing baseband functions. The signal generation module consists of a host PC equipped with a board that contains two high performance 100 MHz DACs and a 1 GB memory module that allows the transmission of extremely large frames of data. At the receiver side, we use another host PC equipped with two 105 MHz ADCs, another 1 GB memory module and a trigger that starts the acquisition process when the presence of signal is detected. The platform has been designed to operate at the ISM band of 2.4 GHz with a RF bandwidth of 20 MHz. In order to minimize the number of DAC and ADC circuits, signals are generated and acquired at an IF of 15 MHz. Upconversion to RF is performed with two RF vectorial signal generators (Agilent E4438C) and downconversion with two specific circuits designed from commercial components. Transmitter and receiver signal processing functions are implemented offline in Matlab. To illustrate the performance and capabilities of the platform, we present the results of two experiments of a $2 \times 2$ MIMO transmission with Alamouti coding.},
title = {A flexible testbed for the rapid prototyping of {MIMO} baseband modules},
address = {Valencia, Spain},
author = {D. Ram{\'i}rez and I. Santamar{\'i}a and J. P{\'e}rez and J. V{\'i}a and A. Taz{\'o}n and J. A. GarciaNaya and T. M. FernandezCarames and M. Gonzalez Lopez and H. J. P{\'e}rez Iglesias and L. Castedo},
booktitle = {Proc.\ Int. Symp. on Wireless Comm. Systems},
month = {{S}eptember},
year = {2006},
doi = {10.1109/ISWCS.2006.4362407},
}
[Abstract]
Hardware platforms and testbeds are an essential tool to evaluate, in realistic scenarios, the performance of MultipleInputMultipleOuput (MIMO) systems. In this work we present a simple and easily reconfigurable 2 times 2 MIMO testbed for the rapid prototyping of the signal processing baseband functions. The signal generation module consists of a host PC equipped with a board that contains two high performance 100 MHz DACs and a 1 GB memory module that allows the transmission of extremely large frames of data. At the receiver side, we use another host PC equipped with two 105 MHz ADCs, another 1 GB memory module and a trigger that starts the acquisition process when the presence of signal is detected. The platform has been designed to operate at the ISM band of 2.4 GHz with a RF bandwidth of 20 MHz. In order to minimize the number of DAC and ADC circuits, signals are generated and acquired at an IF of 15 MHz. Upconversion to RF is performed with two RF vectorial signal generators (Agilent E4438C) and downconversion with two specific circuits designed from commercial components. Transmitter and receiver signal processing functions are implemented offline in Matlab. To illustrate the performance and capabilities of the platform, we present the results of two experiments of a 2 times 2 MIMO transmission with Alamouti coding.177Superposition coding with peakpower limitation
(Jun Tong, Li Ping and Xiao Ma)
Proc. IEEE Int. Conf. Comm., pp. 1718–1723, June 2006.
DOI:10.1109/ICC.2006.254967.
[BibTeX]
@inproceedings{TongPingMa:2006:Superpositioncodingwithpeakpowerlim,
abstract = {This paper presents a peakpowerlimited superposition coding scheme based on clipping. A lowcomplexity soft compensation algorithm (SCA) for combating the clipping effect is investigated. It can be easily combined with softinput softoutput (SISO) decoding algorithms in an iterative manner. Various numerical results show that the SCA can effectively mitigate the performance loss due to clipping.},
title = {Superposition coding with peakpower limitation},
author = {Tong, Jun and Ping, Li and Ma, Xiao},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {C}omm.},
month = {{J}une},
year = {2006},
pages = {1718–1723},
doi = {10.1109/ICC.2006.254967},
}
[Abstract]
This paper presents a peakpowerlimited superposition coding scheme based on clipping. A lowcomplexity soft compensation algorithm (SCA) for combating the clipping effect is investigated. It can be easily combined with softinput softoutput (SISO) decoding algorithms in an iterative manner. Various numerical results show that the SCA can effectively mitigate the performance loss due to clipping.178Blind decoding of MISOOSTBC systems based on principal component analysis
(J. Vía, I. Santamaría, J. Pérez and D. Ramírez)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., Toulouse, France, May 2006.
DOI:10.1109/ICASSP.2006.1661026.
[BibTeX]
@inproceedings{ViaSantamariaPerez:2006:BlinddecodingofMISOOSTBCsystems,
abstract = {In this paper, a new secondorder statistics (SOS) based method for blind decoding of orthogonal space time block coded (OSTBC) systems with only one receive antenna is proposed. To avoid the in herent ambiguities of this problem, the spatial correlation matrix of the source signals must be nonwhite and known at the receiver. In practice, this can be achieved by a number of simple linear preco ding techniques at the transmitter side. More specifically, it is shown in the paper that if the source correlation matrix has different eigen values, then the decoding process can be formulated as the problem of maximizing the sum of a set of weighted variances of the signal estimates. Exploiting the special structure of OSTBCs, this problem can be reduced to a principal component analysis (PCA) problem, which allows us to derive computationally efficient batch and adap tive blind decoding algorithms. The algorithm works for any OSTBC (including the popular Alamouti code) with a single receive antenna. Some simulation results are presented to demonstrate the potential of the proposed procedure.},
title = {Blind decoding of {MISOOSTBC} systems based on principal component analysis},
address = {Toulouse, France},
author = {J. V{\'i}a and I. Santamar{\'i}a and J. P{\'e}rez and D. Ram{\'i}rez},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2006},
doi = {10.1109/ICASSP.2006.1661026},
}
[Abstract]
In this paper, a new secondorder statistics (SOS) based method for blind decoding of orthogonal space time block coded (OSTBC) systems with only one receive antenna is proposed. To avoid the in herent ambiguities of this problem, the spatial correlation matrix of the source signals must be nonwhite and known at the receiver. In practice, this can be achieved by a number of simple linear preco ding techniques at the transmitter side. More specifically, it is shown in the paper that if the source correlation matrix has different eigen values, then the decoding process can be formulated as the problem of maximizing the sum of a set of weighted variances of the signal estimates. Exploiting the special structure of OSTBCs, this problem can be reduced to a principal component analysis (PCA) problem, which allows us to derive computationally efficient batch and adap tive blind decoding algorithms. The algorithm works for any OSTBC (including the popular Alamouti code) with a single receive antenna. Some simulation results are presented to demonstrate the potential of the proposed procedure.179A statistical test for impropriety of complex random signals
(Peter J. Schreier, Louis L. Scharf and Alfred Hanssen)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 796–799, May 2006.
DOI:10.1109/ICASSP.2006.1660774.
[BibTeX]
@inproceedings{SchreierScharfHanssen:2006:AStatisticalTestforImproprietyofCo,
abstract = {A complex random vector is called improper if it is correlated with its complex conjugate. In this paper, we present a generalized likelihood ratio test (GLRT) for impropriety. This test is compelling because it displays the right invariances: The proposed GLR is invariant to linear transformations on the data, including rotation and scaling, just as propriety is preserved by linear transformations. Because canonical correlations make up a complete, or maximal, set of invariants for the Hermitian and complementary covariance matrices under linear transformations, the GLR can be shown to be a function of the squared canonical correlations between the data and its complex conjugate. This validates our intuition that the internal coordinate system should not matter for this hypothesis test},
title = {A statistical test for impropriety of complex random signals},
author = {Schreier, Peter J. and Scharf, Louis L. and Hanssen, Alfred},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2006},
pages = {796–799},
doi = {10.1109/ICASSP.2006.1660774},
}
[Abstract]
A complex random vector is called improper if it is correlated with its complex conjugate. In this paper, we present a generalized likelihood ratio test (GLRT) for impropriety. This test is compelling because it displays the right invariances: The proposed GLR is invariant to linear transformations on the data, including rotation and scaling, just as propriety is preserved by linear transformations. Because canonical correlations make up a complete, or maximal, set of invariants for the Hermitian and complementary covariance matrices under linear transformations, the GLR can be shown to be a function of the squared canonical correlations between the data and its complex conjugate. This validates our intuition that the internal coordinate system should not matter for this hypothesis test180Iterative decoding of superposition coding
(Jun Tong and Li Ping)
6th Int. Symp. Turbo Codes & Rel. Top., pp. 1–6, April 2006. [BibTeX]
@inproceedings{TongPing:2006:Iterativedecodingofsuperpositioncodi,
abstract = {Clipping is applied to superposition coding systems to reduce the peaktoaverage power ratio (PAPR) of the transmitted signal. The performance limit is investigated through evaluating the mutual information driven by the induced peakpowerlimited input signals. It is shown that the channel capacity can be approached by clipped superposition coding systems. To alleviate the performance degradation due to clipping noises, we develop a soft compensation algorithm that is combined with softinputsoftoutput (SISO) decoding algorithms in an iterative manner. Simulation results show that with the proposed algorithm, most performance loss can be recovered.},
title = {Iterative decoding of superposition coding},
author = {Tong, Jun and Ping, Li},
booktitle = {6th\ {I}nt.\ {S}ymp.\ {T}urbo {C}odes \& {R}el.\ {T}op.},
month = {{A}pril},
year = {2006},
pages = {1–6},
}
[Abstract]
Clipping is applied to superposition coding systems to reduce the peaktoaverage power ratio (PAPR) of the transmitted signal. The performance limit is investigated through evaluating the mutual information driven by the induced peakpowerlimited input signals. It is shown that the channel capacity can be approached by clipped superposition coding systems. To alleviate the performance degradation due to clipping noises, we develop a soft compensation algorithm that is combined with softinputsoftoutput (SISO) decoding algorithms in an iterative manner. Simulation results show that with the proposed algorithm, most performance loss can be recovered.181A geometric interpretation of the Rihaczek timefrequency distribution for stochastic signals
(Peter J. Schreier, Louis L. Scharf and Alfred Hanssen)
Proc. IEEE Int. Symp. Inform. Theory, pp. 966–969, September 2005.
DOI:10.1109/ISIT.2005.1523481.
[BibTeX]
@inproceedings{SchreierScharfHanssen:2005:AgeometricinterpretationoftheRihacz,
abstract = {Based on the CramerLoeve spectral representation for a harmonizable random process, the Rihaczek distribution is a time and frequencyshift covariant, bilinear timefrequency distribution. It can be expressed as a complex Hilbert space inner product between the time series and its infinitesimal stochastic Fourier generator. We show that we may attach an illuminating geometry to this inner product, wherein the cosinesquared of the angle between the time series and its infinitesimal stochastic Fourier generator is given by the Rihaczek distribution. We propose to construct estimators of the Rihaczek distribution using a factored kernel in Cohen's class of bilinear timefrequency distributions},
title = {A geometric interpretation of the {Rihaczek} timefrequency distribution for stochastic signals},
author = {Schreier, Peter J. and Scharf, Louis L. and Hanssen, Alfred},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {S}ymp.\ {I}nform.\ {T}heory},
month = {{S}eptember},
year = {2005},
pages = {966–969},
doi = {10.1109/ISIT.2005.1523481},
}
[Abstract]
Based on the CramerLoeve spectral representation for a harmonizable random process, the Rihaczek distribution is a time and frequencyshift covariant, bilinear timefrequency distribution. It can be expressed as a complex Hilbert space inner product between the time series and its infinitesimal stochastic Fourier generator. We show that we may attach an illuminating geometry to this inner product, wherein the cosinesquared of the angle between the time series and its infinitesimal stochastic Fourier generator is given by the Rihaczek distribution. We propose to construct estimators of the Rihaczek distribution using a factored kernel in Cohen's class of bilinear timefrequency distributions182A note on aliasing in higher order spectra
(Peter J. Schreier)
Proc. 6th Australian Comm. Theory Works., pp. 184–188, February 2005.
DOI:10.1109/AUSCTW.2005.1624249.
[BibTeX]
@inproceedings{Schreier:2005:Anoteonaliasinginhigherorderspect,
abstract = {There are two types of aliasing in higher order spectra: ``regular aliasing'' due to sampling below the Nyquist frequency, and ``higher order aliasing''. Spectra of discretetime signals may suffer from higherorder aliasing if the signals are not sufficiently oversampled. By providing some insight into the cause of higher order aliasing, we show that higher order aliasing can just as well occur in second order spectra. More importantly, we demonstrate that spectra of stationary random signals defined as ensembleaverages and spectra of ergodic random signals defined as the Fourier transform of infinite timeaverages never exhibit higher order aliasing},
title = {A note on aliasing in higher order spectra},
author = {Schreier, Peter J.},
booktitle = {{P}roc.\ 6th\ {A}ustralian {C}omm.\ {T}heory {W}orks.},
month = {{F}ebruary},
year = {2005},
pages = {184–188},
doi = {10.1109/AUSCTW.2005.1624249},
}
[Abstract]
There are two types of aliasing in higher order spectra: ``regular aliasing'' due to sampling below the Nyquist frequency, and ``higher order aliasing''. Spectra of discretetime signals may suffer from higherorder aliasing if the signals are not sufficiently oversampled. By providing some insight into the cause of higher order aliasing, we show that higher order aliasing can just as well occur in second order spectra. More importantly, we demonstrate that spectra of stationary random signals defined as ensembleaverages and spectra of ergodic random signals defined as the Fourier transform of infinite timeaverages never exhibit higher order aliasing183An adaptive channel tracking method for MIMOOFDM systems
(Jun Tong, Yaohuan Gong and Shengxian Sun)
Int. Conf. Comm. Circuits Syst., pp. 354–358, June 2004.
DOI:10.1109/ICCCAS.2004.1346098.
[BibTeX]
@inproceedings{TongGongSun:2004:Anadaptivechanneltrackingmethodfor,
abstract = {The tracking of the timevarying channel is crucial for MIMOOFDM wireless communication systems. Aiming at doublyselective fading MIMO channels, we present a novel pilot pattern and the corresponding adaptive channel tracking algorithm. Compared with the traditional pilot patterns, the new pattern has higher frequency efficiency and is more suitable for large transmit arrays. The computational complexity, frequency efficiency and BER performance of the system assisted by the proposed channel tracking scheme are analyzed. Simulation results demonstrate that the proposed scheme can track the timevarying channel effectively.},
title = {An adaptive channel tracking method for {MIMOOFDM} systems},
author = {Tong, Jun and Gong, Yaohuan and Sun, Shengxian},
booktitle = {{I}nt.\ {C}onf.\ {C}omm.\ {C}ircuits {S}yst.},
month = {{J}une},
year = {2004},
pages = {354–358},
doi = {10.1109/ICCCAS.2004.1346098},
}
[Abstract]
The tracking of the timevarying channel is crucial for MIMOOFDM wireless communication systems. Aiming at doublyselective fading MIMO channels, we present a novel pilot pattern and the corresponding adaptive channel tracking algorithm. Compared with the traditional pilot patterns, the new pattern has higher frequency efficiency and is more suitable for large transmit arrays. The computational complexity, frequency efficiency and BER performance of the system assisted by the proposed channel tracking scheme are analyzed. Simulation results demonstrate that the proposed scheme can track the timevarying channel effectively.184Polyspectra of analytic signals
(Peter J. Schreier and Louis L. Scharf)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 473–476, May 2004.
DOI:10.1109/ICASSP.2004.1326297.
[BibTeX]
@inproceedings{SchreierScharf:2004:Polyspectraofanalyticsignals,
abstract = {For complex signals, nth order moment functions can be defined in 2n different ways, depending on the placement of complex conjugates. We demonstrate that, for stationary analytic signals, only a few of these different moments are actually required for a complete nth order description. Which, and how many of them, depends on the signal's spectrum. We investigate properties of nth order moments and spectra with different conjugation patterns and show how they provide different information about the signal.},
title = {Polyspectra of analytic signals},
author = {Schreier, Peter J. and Scharf, Louis L.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2004},
pages = {473–476},
doi = {10.1109/ICASSP.2004.1326297},
}
[Abstract]
For complex signals, nth order moment functions can be defined in 2n different ways, depending on the placement of complex conjugates. We demonstrate that, for stationary analytic signals, only a few of these different moments are actually required for a complete nth order description. Which, and how many of them, depends on the signal's spectrum. We investigate properties of nth order moments and spectra with different conjugation patterns and show how they provide different information about the signal.185Widelylinear beamforming
(Todd McWhorter and Peter J. Schreier)
Proc. 37th Asilomar Conf. Signals Syst. Computers, pp. 753–759, November 2003.
DOI:10.1109/ACSSC.2003.1292015.
[BibTeX]
@inproceedings{McWhorterSchreier:2003:Widelylinearbeamforming,
abstract = {In this paper we describe a beamforming algorithm based on widelylinear rather than linear data models. Initially, we develop this beamformer by generalizing the Capon (MVDR) optimization problem. That is, if the objective is to minimize output power while maintaining a specified directional gain, then we show that the output power of the widelylinear beamformer is less than or equal to the output power of the Capon (MVDR) beamformer. This result is valid regardless of the ``true'' distribution of the data. We also derive the widelylinear beamformer by considering beamforming to be an estimation problem. Linear models assume that the composite covariance matrix formed from the real and imaginary parts of the arraysnapshot has a particular structure. This structure is often summarized by stating that the covariance formed from the array snapshot and its transpose (not Hermitian transpose) is zero. We could also call these data ``proper'' Gaussian vectors. The beamformers in this paper are appropriate for situations in which these implicit assumptions are violated.},
title = {Widelylinear beamforming},
author = {McWhorter, Todd and Schreier, Peter J.},
booktitle = {{P}roc.\ 37th\ {A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {{N}ovember},
year = {2003},
pages = {753–759},
doi = {10.1109/ACSSC.2003.1292015},
}
[Abstract]
In this paper we describe a beamforming algorithm based on widelylinear rather than linear data models. Initially, we develop this beamformer by generalizing the Capon (MVDR) optimization problem. That is, if the objective is to minimize output power while maintaining a specified directional gain, then we show that the output power of the widelylinear beamformer is less than or equal to the output power of the Capon (MVDR) beamformer. This result is valid regardless of the ``true'' distribution of the data. We also derive the widelylinear beamformer by considering beamforming to be an estimation problem. Linear models assume that the composite covariance matrix formed from the real and imaginary parts of the arraysnapshot has a particular structure. This structure is often summarized by stating that the covariance formed from the array snapshot and its transpose (not Hermitian transpose) is zero. We could also call these data ``proper'' Gaussian vectors. The beamformers in this paper are appropriate for situations in which these implicit assumptions are violated.186Canonical coordinates are the right coordinate system for transform coding of noisy sources
(Peter J. Schreier, Louis L. Scharf, Tianjian Hu and Stephen D. Voran)
Proc. IEEE Works. Statistical Signal Proces., pp. 234–237, September 2003.
DOI:10.1109/SSP.2003.1289387.
[BibTeX]
@inproceedings{SchreierScharfHu:2003:Canonicalcoordinatesaretherightcoor,
abstract = {Historically, transform coding of noisy sources has been performed by first estimating the message and then quantizing this estimate. We show that it is also optimum to first transform the noisy observations into canonical coordinates, quantize, apply a Wiener filter in this coordinate system, and then transform the result back to the original coordinates. Canonical coordinates are uncorrelated, and quantizing and Wiener filtering are applied to each component independently. Optimality of this approach can be proved assuming additive white quantization noise. Half canonical coordinates minimize the meansquared error by minimizing the trace of the error covariance matrix and full canonical coordinates maximize information rate by minimizing the determinant of the error covariance matrix.},
title = {Canonical coordinates are the right coordinate system for transform coding of noisy sources},
author = {Schreier, Peter J. and Scharf, Louis L. and Hu, Tianjian and Voran, Stephen D.},
booktitle = {{P}roc.\ {IEEE} {W}orks.\ {S}tatistical {S}ignal {P}roces.},
month = {{S}eptember},
year = {2003},
pages = {234–237},
doi = {10.1109/SSP.2003.1289387},
}
[Abstract]
Historically, transform coding of noisy sources has been performed by first estimating the message and then quantizing this estimate. We show that it is also optimum to first transform the noisy observations into canonical coordinates, quantize, apply a Wiener filter in this coordinate system, and then transform the result back to the original coordinates. Canonical coordinates are uncorrelated, and quantizing and Wiener filtering are applied to each component independently. Optimality of this approach can be proved assuming additive white quantization noise. Half canonical coordinates minimize the meansquared error by minimizing the trace of the error covariance matrix and full canonical coordinates maximize information rate by minimizing the determinant of the error covariance matrix.187A unified approach to performance comparisons between linear and widely linear processing
(Peter J. Schreier, Louis L. Scharf and Clifford T. Mullis)
Proc. IEEE Works. Statistical Signal Proces., pp. 114–117, September 2003.
DOI:10.1109/SSP.2003.1289353.
[BibTeX]
@inproceedings{SchreierScharfMullis:2003:Aunifiedapproachtoperformancecompar,
abstract = {Recently, a number of papers have been published that show significant performance gains can be obtained by accounting for the fact that communication signals can be improper. In this paper, we derive a general result comparing the performance of conventional processing, which ignores the improper nature of signals, with processing that takes it into account. In particular, for an estimation and a detection problem, we find that the performance gain, as measured by meansquared error and deflection, respectively, can be as large as a factor of 2, but no larger. In a communications example, we show how this finding generalizes the result that coherent processing enjoys a 3 dB gain over noncoherent processing.},
title = {A unified approach to performance comparisons between linear and widely linear processing},
author = {Schreier, Peter J. and Scharf, Louis L. and Mullis, Clifford T.},
booktitle = {{P}roc.\ {IEEE} {W}orks.\ {S}tatistical {S}ignal {P}roces.},
month = {{S}eptember},
year = {2003},
pages = {114–117},
doi = {10.1109/SSP.2003.1289353},
}
[Abstract]
Recently, a number of papers have been published that show significant performance gains can be obtained by accounting for the fact that communication signals can be improper. In this paper, we derive a general result comparing the performance of conventional processing, which ignores the improper nature of signals, with processing that takes it into account. In particular, for an estimation and a detection problem, we find that the performance gain, as measured by meansquared error and deflection, respectively, can be as large as a factor of 2, but no larger. In a communications example, we show how this finding generalizes the result that coherent processing enjoys a 3 dB gain over noncoherent processing.188The KarhunenLoève expansion of improper complex random signals with applications in detection
(Peter J. Schreier and Louis L. Scharf)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 717–720, April 2003.
DOI:10.1109/ICASSP.2003.1201782.
[BibTeX]
@inproceedings{SchreierScharf:2003:TheKarhunenLoeveexpansionofimproper,
abstract = {Nonstationary complex random signals are in general improper (not circularly symmetric), which means that their complementary covariance is nonzero. Since the KarhunenLoeve expansion in its known form is only valid for proper processes, we derive the improper version of this expansion. It produces two sets of eigenvalues and an improper internal description. We use the KarhunenLoeve expansion to solve the problem of detecting nonstationary improper complex random signals in additive white Gaussian noise. Using the deflection criterion we compare the performance of conventional processing, which ignores complementary covariances, with processing that takes these into account. The performance gain can be as great as a factor of 2.},
title = {The {KarhunenLo{\`{e}}ve} expansion of improper complex random signals with applications in detection},
author = {Schreier, Peter J. and Scharf, Louis L.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{A}pril},
year = {2003},
pages = {717–720},
doi = {10.1109/ICASSP.2003.1201782},
}
[Abstract]
Nonstationary complex random signals are in general improper (not circularly symmetric), which means that their complementary covariance is nonzero. Since the KarhunenLoeve expansion in its known form is only valid for proper processes, we derive the improper version of this expansion. It produces two sets of eigenvalues and an improper internal description. We use the KarhunenLoeve expansion to solve the problem of detecting nonstationary improper complex random signals in additive white Gaussian noise. Using the deflection criterion we compare the performance of conventional processing, which ignores complementary covariances, with processing that takes these into account. The performance gain can be as great as a factor of 2.189Reducing interference in stochastic timefrequency analysis without losing information
(Peter J. Schreier and Louis L. Scharf)
Proc. 36th Asilomar Conf. Signals Syst. Computers, pp. 1565–1570, November 2002.
DOI:10.1109/ACSSC.2002.1197041.
[BibTeX]
@inproceedings{SchreierScharf:2002:Reducinginterferenceinstochastictime,
abstract = {The analytic signal is commonly used in stochastic timefrequency analysis in Cohen's class to reduce interference terms. However, we show that the usual timefrequency representation (TFR) based on the analytic signal gives only an incomplete signal description. This is because the analytic signal constructed from a nonstationary real signal is in general improper, which means that it has nonzero complementary correlation. We show how to augment the standard TFR by a complementary TFR to obtain a complete secondorder characterization of the signal while still reducing interference terms compared to the TFR of the real signal.},
title = {Reducing interference in stochastic timefrequency analysis without losing information},
author = {Schreier, Peter J. and Scharf, Louis L.},
booktitle = {{P}roc.\ 36th\ {A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {{N}ovember},
year = {2002},
pages = {1565–1570},
doi = {10.1109/ACSSC.2002.1197041},
}
[Abstract]
The analytic signal is commonly used in stochastic timefrequency analysis in Cohen's class to reduce interference terms. However, we show that the usual timefrequency representation (TFR) based on the analytic signal gives only an incomplete signal description. This is because the analytic signal constructed from a nonstationary real signal is in general improper, which means that it has nonzero complementary correlation. We show how to augment the standard TFR by a complementary TFR to obtain a complete secondorder characterization of the signal while still reducing interference terms compared to the TFR of the real signal.190Canonical coordinates for reducedrank estimation of improper complex random vectors
(Peter J. Schreier and Louis L. Scharf)
Proc. IEEE Int. Conf. Acoustics, Speech and Signal Process., pp. 1153–1156, May 2002.
DOI:10.1109/ICASSP.2002.5744004.
[BibTeX]
@inproceedings{SchreierScharf:2002:Canonicalcoordinatesforreducedranke,
abstract = {We consider the problem of minimum mean squared error (MMSE) estimation of complex random vectors in the improper case. Accounting for the information present in the complementary covariance requires the use of widely linear transformations. Based on these, we present the eigenanalysis of improper complex random vectors. This paves the way for a study of two different rankreduced implementations of the complex Wiener Filter that make use of canonical coordinates: one that is optimum with respect to maximizing mutual information and one that minimizes mean squared error.},
title = {Canonical coordinates for reducedrank estimation of improper complex random vectors},
author = {Schreier, Peter J. and Scharf, Louis L.},
booktitle = {{P}roc.\ {IEEE} {I}nt.\ {C}onf.\ {A}coustics, {S}peech and {S}ignal {P}rocess.},
month = {{M}ay},
year = {2002},
pages = {1153–1156},
doi = {10.1109/ICASSP.2002.5744004},
}
[Abstract]
We consider the problem of minimum mean squared error (MMSE) estimation of complex random vectors in the improper case. Accounting for the information present in the complementary covariance requires the use of widely linear transformations. Based on these, we present the eigenanalysis of improper complex random vectors. This paves the way for a study of two different rankreduced implementations of the complex Wiener Filter that make use of canonical coordinates: one that is optimum with respect to maximizing mutual information and one that minimizes mean squared error.191Lowrank approximation of improper complex random vectors
(Peter J. Schreier and Louis L. Scharf)
Proc. 35th Asilomar Conf. Signals Syst. Computers, pp. 597–601, November 2001.
DOI:10.1109/ACSSC.2001.986993.
[BibTeX]
@inproceedings{SchreierScharf:2001:Lowrankapproximationofimpropercompl,
abstract = {In reducedrank signal processing for radar, sonar, and digital communications, we seek the right tradeoff between model bias and model variance for reconstructing signals from noisy data. Here, we extend the classical theory by considering the lowrank approximation of complex random vectors, which may or may not be proper. We show that, in general, widely linear approximation is superior to strictly linear approximation, unless the vector to be approximated is proper, in which case the optimum procedure is strictly linear. We analyze the case where the approximated random vector becomes proper in its internal coordinate system. This class of random vector, which we call generalized proper, possesses qualities similar to proper random vectors.},
title = {Lowrank approximation of improper complex random vectors},
author = {Schreier, Peter J. and Scharf, Louis L.},
booktitle = {{P}roc.\ 35th\ {A}silomar {C}onf.\ {S}ignals {S}yst.\ {C}omputers},
month = {{N}ovember},
year = {2001},
pages = {597–601},
doi = {10.1109/ACSSC.2001.986993},
}
[Abstract]
In reducedrank signal processing for radar, sonar, and digital communications, we seek the right tradeoff between model bias and model variance for reconstructing signals from noisy data. Here, we extend the classical theory by considering the lowrank approximation of complex random vectors, which may or may not be proper. We show that, in general, widely linear approximation is superior to strictly linear approximation, unless the vector to be approximated is proper, in which case the optimum procedure is strictly linear. We analyze the case where the approximated random vector becomes proper in its internal coordinate system. This class of random vector, which we call generalized proper, possesses qualities similar to proper random vectors.192MAP decoding of linear block codes based on a sectionalized trellis of the dual code
(Peter J. Schreier and Daniel J. Costello, Jr.)
Proc. Int. Zurich Seminar Broadband Comm., pp. 271–278, February 2000.
DOI:10.1109/IZSBC.2000.829262.
[BibTeX]
@inproceedings{SchreierCostello:2000:MAPdecodingoflinearblockcodesbased,
abstract = {Block codes for use in turbo coding schemes provide an alternative to punctured convolutional codes when high rate component codes are needed. Since block codes have large, timevarying trellis diagrams, full maximum a posteriori (MAP) softin softout decoders are very complex. It is shown how to modify the MAP algorithm to utilize a sectionalized trellis diagram of the dual code for decoding, which minimizes computational complexity for high rate component codes. This paper also gives simulation results for some high rate block turbo codes},
title = {{MAP} decoding of linear block codes based on a sectionalized trellis of the dual code},
author = {Schreier, Peter J. and {Costello, Jr.}, Daniel J.},
booktitle = {{P}roc.\ {I}nt.\ {Z}urich {S}eminar {B}roadband {C}omm.},
month = {{F}ebruary},
year = {2000},
pages = {271–278},
doi = {10.1109/IZSBC.2000.829262},
}
[Abstract]
Block codes for use in turbo coding schemes provide an alternative to punctured convolutional codes when high rate component codes are needed. Since block codes have large, timevarying trellis diagrams, full maximum a posteriori (MAP) softin softout decoders are very complex. It is shown how to modify the MAP algorithm to utilize a sectionalized trellis diagram of the dual code for decoding, which minimizes computational complexity for high rate component codes. This paper also gives simulation results for some high rate block turbo codes