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2008 IEEE International Symposium on Circuits and Systems (ISCAS 2008), vol.1

作者： Feng Wan Wei-Ping Zhu M.N.S. Swamy Centre for Signal Processing and Communications Department of Electrical and Computer Engineering Concordia University Montreal QUE Canada

In this paper, a perturbation analysis of two subspace-based semi-blind MIMO channel estimation approaches is conducted. Our analysis shows that, in the noise-free case, the whitening-rotation (WR)-based algorithm is subject to a signal perturbation error, while the nulling-based algorithm is a signal perturbation free scheme with an ideal nulling constraint imposed on the channel matrix. This explains why the WR-based method is efficient only in the low SNR case, and concludes that the nulling-based approach is better for moderate to high SNRs. A novel closed-form mean square error (MSE) expression is also derived for the nulling-based blind estimation method, in which an appealing scheme for the determination of the weighting factor is presented. The nulling-based method with the proposed weighting scheme is validated via computer simulations, showing a very high estimation accuracy of our semi-blind solution in terms of the MSE of the channel estimate.

关键词： MIMO Channel estimation signal processing algorithms signal analysis Mean square error methods Receiving antennas Algorithm design and analysis Maximum likelihood estimation Phase estimation computer errors

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A Lattice Structure for Linear-Phase Perfect Reconstruction Filter Banks with Mirror Image Symmetric Frequency Response

A Lattice Structure for Linear-Phase Perfect Reconstruction ...

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2008 IEEE International Symposium on Circuits and Systems (ISCAS 2008), vol.9

作者： Chao Wu Wei-Ping Zhu M.N.S. Swamy Centre for Signal Processing and Communications Department of Electrical and Computer Engineering Concordia University Montreal QUE Canada

In this paper, the lattice structure of a class of filter banks that possesses both the linear-phase property and the mirror-image symmetry, referred to as MIS-LPPRFB, has been investigated. By combining the MIS and the LP constraints and proposing a new simplified scheme, a reduced lattice structure with fewer parameters has been developed. It is shown that the introduction of the MIS has imposed certain constraints on the invertible matrices in the lattice structure of the conventional LPPRFBs, reducing the number of free parameters by nearly one-half. Using the new lattice structure, the optimization design problem of MIS-LPPRFBs is also addressed with an objective of achieving a high performance filter bank for its use in image compression coding.

关键词： Lattices Image reconstruction Filter bank Mirrors Frequency response Image coding Gallium nitride Chaotic communication signal processing Design optimization

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Semi-Blind Channel Estimation of MIMO-OFDM Systems with Pulse Shaping

Semi-Blind Channel Estimation of MIMO-OFDM Systems with Puls...

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2008 IEEE International Symposium on Circuits and Systems (ISCAS 2008), vol.1

作者： Feng Wan Wei-Ping Zhu M.N.S. Swamy Centre for Signal Processing and Communications Department of Electrical and Computer Engineering Concordia University Montreal QUE Canada

Most of the existing MIMO-OFDM channel estimation methods do not take into account the effect of the pulse-shaping filter in the transmitter nor of the matched filter in the receiver, thus leading to an estimation solution for the composite channel including the pulse-shaping and matched filters, instead of for the pure wireless channel. This solution is neither directly applicable to practical communication systems nor sufficiently accurate due to the extra length of the composite channel induced by the two filters. In this paper, a semi-blind channel estimation method is proposed for pulse-shaped MIMO-OFDM systems. By utilizing the knowledge of pulse-shaping and matched filters, a time domain semi-blind estimation method is developed for the pure multi-path channel. In order to reduce the computational burden of the time-domain algorithm, a frequency-domain alternative is derived. A number of computer simulation-based experimentations are conducted, and these simulations confirm the effectiveness of the proposed semi-blind method.

关键词： Channel estimation Pulse shaping methods Matched filters MIMO OFDM Transmitters Computational modeling computer simulation Wireless communication Receiving antennas

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A Spectro-Temporal Algorithm for Pitch Frequency Estimation from Noisy Observations

A Spectro-Temporal Algorithm for Pitch Frequency Estimation ...

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2008 IEEE International Symposium on Circuits and Systems (ISCAS 2008), vol.5

作者： C. Shahnaz W.-P. Zhu M. O. Ahmad Centre for Signal Processing and Communications Department of Electrical and Computer Engineering Concordia University Montreal QUE Canada

A novel algorithm for pitch frequency (PF) estimation from non-stationary noise-corrupted speech observations is presented in this paper based on both spectral pre-processing and temporal representation. A modified power spectral subtraction based de-noising scheme that allows tracking the time-variation of the underlying non-stationary noise is put forward to enhance speech prior to PF estimation. The de-noised speech is then utilized to propose a squared difference function of the Linear Prediction (LP) residual which is expected to reveal more prominent dips at integral multiples of the pitch period compared to that revealed by the LP residual. The dips at different pitch-harmonic locations are added and weighted by a periodicity dependent weighting factor for every possible pitch period thus yielding a weighted and harmonically summed temporal function which is globally minimized to extract the desired PF. Simulation results using the Keele database show the superior efficacy of the proposed method in the presence of a multi-talker babble noise relative to some of the existing methods.

关键词： Frequency estimation Speech enhancement Noise reduction Speech analysis signal processing algorithms Personal digital assistants Degradation Additive noise signal to noise ratio Filters

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The extended invariance principle applied to joint time-delay, frequency, and DOA estimation

The extended invariance principle applied to joint time-dela...

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International Conference on Acoustics, Speech, and signal processing (ICASSP)

作者： Felix Antreich Josef A. Nossek Gonzalo Seco A. Lee Swindlehurst Institute for Communications and Navigation German Aerospace Center Wessling Germany Institute for Circuit Theory & Signal Processing Munich University of Technology Germany Department of Telecommunications & Systems Engineering Universitat Autonoma de Barcelona Spain Department of Electrical Engineering & Computer Science University of California Irvine CA USA

This paper deals with the joint estimation of temporal (time- delay, Doppler frequency) and spatial (direction-of-arrival, DOA) parameters of several replicas of a known signal in an unknown spatially correlated field. Unstructured and structured models have been proposed in the literature. The former suffers from a severe performance degradation in some scenarios, whereas the latter involves huge complexity. It is shown how the extended invariance principle (EXIP) can be applied to obtain estimates with the quality of those of the structured model, but with the complexity of the unstructured one. We present a method to improve the quality of the time- delay and Doppler estimates obtained with an unstructured spatial model when an estimate of the DOAs is available. Exemplarily, simulation results for time-delay estimation for GPS (global positioning system) are included and confirm that our proposal approaches the Cramer-Rao lower bound (CRLB) of the structured model even when suboptimal DOA estimates obtained by ESPRIT are introduced.

关键词： Frequency estimation Direction of arrival estimation Global Positioning System Delay estimation Data models Sensor arrays signal processing Gaussian noise Aerospace engineering Navigation

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4D wavelet noise suppression of MR diffusion tensor data

4D wavelet noise suppression of MR diffusion tensor data

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International Conference on Acoustics, Speech, and signal processing (ICASSP)

作者： Hesamoddin Jahanian Azadeh Yazdan-Shahmorad Hamid Soltanian-Zadeh Department of Radiology Henry Ford Health System Image Analysis and Communications Laboratory Detroit MI USA Department of Biomedical Engineering University of Michigan Ann Arbor MI USA Controll and Intelligent Processing Center of Excellence Department of Electrical and Computer Engineering University of Tehran Tehran Iran

Diffusion tensor imaging (DTI) is known to be promising for providing anatomical information about white-matter fiber bundles that cannot be obtained by other non-invasive in vivo imaging methods. However, its application is limited because of its low signal-to-noise ratio and significant imaging artifacts. To improve the accuracy of tissue structural and architectural characterization with diffusion tensor imaging 4D wavelet denoising technique is used to improve the signal to noise ratio (SNR) of diffusion tensor images. To evaluate the proposed method, a high SNR data set is built by repeating and averaging the data acquisition several times and is compared to the denoised data. Our results revealed that wavelets would effectively reduce the noise in DTI data with less blurring of tissue types, especially in the white matter. It would suggest that by using the 4D wavelet noise suppression, one could decrease the acquisition time and still have an acceptable SNR.

关键词： Tensile stress Diffusion tensor imaging signal to noise ratio Noise reduction Magnetic noise Anisotropic magnetoresistance Eigenvalues and eigenfunctions In vivo Magnetic resonance imaging Wavelet analysis

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Ultrabroadband Biphotons Generated via Chirped Quasi-Phase-Matched Optical Parametric Down-Conversion

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Physical Review Letters 2008年第18期100卷 183601-183601页

作者： Magued B. Nasr Silvia Carrasco Bahaa E. A. Saleh Alexander V. Sergienko Malvin C. Teich Juan P. Torres Lluis Torner David S. Hum Martin M. Fejer Quantum Imaging Laboratory* Departments of Electrical & Computer Engineering and Physics Boston University Boston Massachusetts 02215 USA ICFO-Institut de Ciencies Fotoniques and Department of Signal Theory and Communications Universitat Politecnica de Catalunya Mediterranean Technology Park 08860 Castelldefels (Barcelona) Spain E. L. Ginzton Laboratory Stanford University Stanford California 94305 USA

We generate ultrabroadband biphotons via the process of spontaneous parametric down-conversion (SPDC) in quasi-phase-matched nonlinear gratings that have a linearly chirped wave vector. By using these ultrabroadband biphotons (300-nm bandwidth), we measure the narrowest Hong-Ou-Mandel dip to date, having a full width at half maximum of 7.1 fs. This enables the generation of a high flux of nonoverlapping biphotons with ultrabroad bandwidth, thereby promoting the use of SPDC light in many nonclassical applications.

关键词： Photons

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Towards an inclusive computational model of visual cortex

Towards an inclusive computational model of visual cortex

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IEEE Symposium on Bioinformatics and Bioengineering (BIBE)

作者： M. Gheiratmand H. Soltanian-Zadeh H. Khaloozadeh Electrical Engineering Department K.N. Toosi University of Technology Tehran Iran Radiology Department Henry Ford Health System Image Analysis and Communications Laboratory Detroit MI USA School of Cognitive Sciences Institute for Studies Theoretical Physics and Mathematics (IPM) Tehran Iran Control and Intelligent Processing Center of Excellence Electrical and Computer Engineering Department University of Tehran Tehran Iran

Understanding the primatespsila visual system has been one of the challenging problems of different groups of scientists for years. Though many studies, from physiology and neuroscience to computer vision, are done on different aspects of visual processing in the cortex, a comprehensive computational model of visual cortex is still missing. We have implemented a computational model of object recognition in ventral visual pathway in our previous work. This hierarchical model covers visual areas V1/V2, V4/PIT, and AIT sending inputs to the Prefrontal Cortex (PFC) for categorization. To extend our model, in this work, we have added a simple model of motion detection in neurons of areas V1 and MT of the dorsal stream to our previous model. This has enabled the model to perform another principal function of the visual cortex, i.e., motion perception.

关键词： Brain modeling Computational modeling Neurons Biological system modeling Object recognition Motion analysis Solid modeling Visual system computer vision Motion detection

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Time delay estimation in a spatially structured model using decoupled estimators for temporal and spatial parameters

Time delay estimation in a spatially structured model using ...

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ITG Workshop on Smart Antennas

作者： Felix Antreich Josef A. Nossek Gonzalo Seco A. Lee Swindlehurst German Aerospace Center (DLR) Inst. for Communications and Navigation Wessling Germany Inst. for Circuit Theory & Signal Processing Munich University of Technology (TUM) Germany Department of Telecommunication & Systems Engineering Universitat Authnòma de Barcelona Spain Dept. of Telecommunications & Systems Engineering Universitat Autonoma de Barcelona (UAB) Spain Dept. of Electrical Engineering & Computer Science The University of California Irvine CA U.S.A.

This paper deals with the joint estimation of time-delay and spatial (direction-of-arrival, DOA) parameters of several replicas of a known signal in an unknown spatially correlated field. Unstructured and structured models have been proposed for maximum likelihood (ML) estimators in the literature. The former suffers from a severe performance degradation in some scenarios, whereas the latter involves huge complexity. It is shown how the extended invariance principle (EXIP) can be applied to obtain estimates with the quality of those of the structured model, but with the complexity of the unstructured one. We present a method to improve the quality of the time-delay estimates obtained with an unstructured spatial model when an estimate of the DOAs is available. Exemplarily, simulation results for time-delay estimation for GPS (Global Positioning System) are included and confirm that our proposal approaches the Cramer-Rao lower bound (CRLB) of the structured model even when suboptimal DOA estimates obtained by ESPRIT are introduced.

关键词： Delay estimation Delay effects

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Digitally Enhanced Analog Circuits: System Aspects

Digitally Enhanced Analog Circuits: System Aspects

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2008 IEEE International Symposium on Circuits and Systems (ISCAS 2008), vol.2

作者： Boris Murmann Christian Vogel Heinz Koeppl Department of Electrical Engineering University of Stanford Stanford CA USA Signal Processing and Speech Communication Laboratory Graz University of Technology Graz Austria School of Communication and Computer Sciences EPF Lausanne Lausanne Switzerland

An overview of digital enhancement techniques for analog circuits is presented. Recent research suggests that the high density and low energy of digital circuits can be leveraged to enable a new generation of interface electronics that is based on minimal precision, low complexity analog blocks. Today, examples of enhancement schemes can be found in diverse applications and include nonlinearity compensation of ADCs, predistortion of power amplifiers and mismatch calibration in radio receivers. Since it is often difficult to identify commonalities among these different, but conceptually related schemes, this tutorial paper aims to provide a unified and system-oriented perspective of the field.

关键词： Analog circuits Calibration signal processing Microprocessors Circuit noise Digital circuits Linearity Power dissipation signal resolution Digital signal processing

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