Dans la theorie du processement optimal d'antennes on représente généralement les champs aléatoires comme des processus stochastiques à deux indices stationnaires et homogènes. Avec ces représentations, l'antenne processe la... more
Dans la theorie du processement optimal d'antennes on représente généralement les champs aléatoires comme des processus stochastiques à deux indices stationnaires et homogènes. Avec ces représentations, l'antenne processe la fonction de covariance spatial et temporelle du champ réçu ou sa transformée de Eourier,c'est à dire, la fonction de fréquence/numéro d'onde. Pour obtenir des algorithmes récurrents, on modèle les champs réçus comme des sorties des systèmes stochastiques distribués. Dans le cas où on a des champs aléatoires directionels, modèles d'état on été fréquentment usés. Dans cet article, on considère le problème du modelage des champs aléatoires non stationnaires, homogènes et non directionels. Avec l'hypothèse de connaissance de la fonction de covariance espace/tenp, on demande que la représentation soit valide sur une antenne linéaire de longueur L. Pour représenter le champ aléatoire non directionel, on recourt à une série de Fourier spatial tronquée. En faisant usage du fait que cette série converge en moyenne quadratique sur la ligne dont la longueur est L, on mesure le degré d'approximation par l'erreur quadratique moyen. Les coefficients de la série sont des processus stochastiques temporels non stationnaires et correlés; ce processus vectoriel peut être interprété comme la sortie d'un système dynamique linéaire, à paramètres variables, avec des entrées stochastiques
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| The existence of doppler has always been an inconvenience for digital communications. Several schemes have been proposed to deal with the problem, often involving some kind of doppler tracking and/or compensation algorithm. All these... more
| The existence of doppler has always been an inconvenience for digital communications. Several schemes have been proposed to deal with the problem, often involving some kind of doppler tracking and/or compensation algorithm. All these schemes do, however, increase the complexity of the receiver. Furthermore, the need for exactness in the doppler tracking scheme adds an extra dimension to the space of potential failures. In this article, we will follow a di erent approach. By using time-frequency methods in the detection/decoding stage, we will be able to design receivers which are, in fact, doppler insensitive. The existence or non-existence of doppler e ect becomes irrelevant as far as the receiver performance
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The squared distance function is one of the standard functions on which an optimization algorithm is commonly run, whether it is used directly or chained with other functions. Illustrative examples include center of mass computation,... more
The squared distance function is one of the standard functions on which an optimization algorithm is commonly run, whether it is used directly or chained with other functions. Illustrative examples include center of mass computation, implementation of k-means algorithm and robot positioning. This function can have a simple expression (as in the Euclidean case), or it might not even have a closed form expression. Nonetheless, when used in an optimization problem formulated on non-Euclidean manifolds, the appropriate (intrinsic) version must be used and depending on the algorithm, its gradient and/or Hessian must be computed. For many commonly used manifolds a way to compute the intrinsic distance is available as well as its gradient, the Hessian however is usually a much more involved process, rendering Newton methods unusable on many standard manifolds. This article presents a way of computing the Hessian on connected locally-symmetric spaces on which standard Riemannian operations ...
Nonlinear filters based on neural networks can be used for adaptive signal processing in a wide range of applications, e.g. underwater acoustic communications. In this paper, a radial basis function (RBF) neural network is used for blind... more
Nonlinear filters based on neural networks can be used for adaptive signal processing in a wide range of applications, e.g. underwater acoustic communications. In this paper, a radial basis function (RBF) neural network is used for blind adaptive equalization with higher order statistics. The RBF network proposed in this paper has several features which make it a suitable structure for
Research Interests: Radial Basis Function, Neural Network, Adaptive Signal Processing, Performance Analysis, Blind Equalization, and 11 moreIEEE, Unsupervised Learning, Higher order statistics, Radial Basis Function Neural Network, Nonlinear Filter, Fuzzy Adaptive Equalizer, Training Algorithm, OCEANS Conference, Underwater Acoustic Communication, Adaptive Equalizer, and Real time implementation
Abstract—We address the problem of joint source symbol detection and multi-channel estimation in time-selective digital communication scenarios. Our approach is based on a statistical model which decouples the time dy-namics of the... more
Abstract—We address the problem of joint source symbol detection and multi-channel estimation in time-selective digital communication scenarios. Our approach is based on a statistical model which decouples the time dy-namics of the multi-channel vector in amplitude and direction. We com-pute the most probable emitted symbol sequence and channel realization for this statistical model, given the set of array observations. Our maxi-mum a posterior (MAP) receiver consists of a bank of parallel processors. Each processor finds the most probable channel realization for a given sym-bol sequence via a relaxed semidefinite programming (SDP) re-formulation of the original estimation problem. Computer simulations are included to assess the capability of our technique in acquiring fast-changing flat-fading channels. I. PROBLEM FORMULATION C ONSIDER a wireless communication scenario in which a multiple antenna receiver observes a mobile digital source, as depicted in figure 1. The source transmi...
We address the problem of space-time codebook design for non-coherent communications in multiple-antenna wireless systems. In contrast with other approaches, the channel matrix is modeled as an unknown deterministic parameter at both the... more
We address the problem of space-time codebook design for non-coherent communications in multiple-antenna wireless systems. In contrast with other approaches, the channel matrix is modeled as an unknown deterministic parameter at both the receiver and the transmitter, and the Gaussian observation noise is allowed to have an arbitrary correlation structure, known by the transmitter and the receiver. In order to handle the unknown deterministic space-time channel, a generalized likelihood ratio test (GLRT) receiver is considered. A new methodology for space-time codebook design under this non-coherent setup is proposed. It optimizes the probability of error of the GLRT receiver’s detector in the high signal-to-noise ratio (SNR) regime by solving a high-dimensional nonlinear non-smooth optimization problem in a two-step approach. (i) Firstly, a convex semidefinite programming (SDP) relaxation of the codebook design problem yields a rough estimate of the optimal codebook. (ii) This is th...
Research Interests: Algorithm, Multidisciplinary, Parameter estimation, Optimization, Optimization Problem, and 15 moreAntenna arrays, Geometry, Geodesic, Computer Simulation, Relaxation, Colored Noise, Convex Programming, Antenna Array, High Dimensionality, Codebook, Gaussian noise, optimal algorithm, Multiple Antennas, Probability of Error, and Deterministic Approach
The design of adaptive equalizers is an important topic for practical implementation of ecient digital communica-tions. In this paper, the application of a radial basis func-tion neural network (RBF) for blind channel equalization is... more
The design of adaptive equalizers is an important topic for practical implementation of ecient digital communica-tions. In this paper, the application of a radial basis func-tion neural network (RBF) for blind channel equalization is analysed. This architecture is well suited for equalization of nite impulse response (FIR) channels partly because the network model closely matches the data model. This al-lows a rather straightforward design of an optimal receiver, in a Bayesian sense. It also provides a simple framework for data classication, in which more complex nonlinear distor-tions can be accomodated with virtually no modications. A clustering algorithm for dynamic creation and combina-tion of local units is proposed, which eliminates the need for channel order estimation. An initialization procedure for the output linear layer is also presented. The network performance is illustrated with Monte Carlo simulations for a family of random channels. 1.
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2 DETERMINISTIC METHODS 9 2.1 INSTANTANEOUS MIXTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1.1 ILSP and ILSE algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11... more
2 DETERMINISTIC METHODS 9 2.1 INSTANTANEOUS MIXTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1.1 ILSP and ILSE algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.1.2 Analytical constant modulus algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.1.3 Closed form solution based on linear coding . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.2 SUBSPACE METHOD FOR ISI CANCELLATION . . . . . . . . . . . . . . . . . . . . . . . . . . 22
This paper examines an extension of QR-RLS lattice filtering to the case of multiple input signals. The proposed adaptation algorithm is based on a compact square-root array formulation that is amenable to hardware implementation due to... more
This paper examines an extension of QR-RLS lattice filtering to the case of multiple input signals. The proposed adaptation algorithm is based on a compact square-root array formulation that is amenable to hardware implementation due to its scalar-only nature, parallelizability and numerical robustness. A technique that provides increased design flexibility by allowing unequal filter lengths to be specified for different input channels is also presented.
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— We study how 2nd order statistics (SOS) can be exploited in two signal processing problems, blind separation of binary sources and trained-based multi-user channel identification, in a Bayesian context where a prior on the mixing... more
— We study how 2nd order statistics (SOS) can be exploited in two signal processing problems, blind separation of binary sources and trained-based multi-user channel identification, in a Bayesian context where a prior on the mixing channel matrix is available. It is well known that the SOS of the received data permit to resolve the unknown mixing matrix, up to an orthogonal factor. In a Bayesian framework, this residual orthogonal mixing matrix becomes a random object in its own right, with an associated distribution over the group of orthogonal matrices. This distri-bution is induced by the prior on the mixing matrix, and must be known for optimum statistical processing. We rely on a previous theoretical work to provide these answers, and discuss applications for this induced probabil-ity density function (pdf) over the orthogonal group, in the two aforemen-tioned signal processing problems. Preliminary results, obtained through computer simulations, demonstrate the effectiveness o...
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Research Interests: System Identification, Multidisciplinary, Coding, Parameter estimation, Channel Estimation, and 12 moreComputer Simulation, Correlation, MIMO channel modeling, TSP, Second Order, Boolean Satisfiability, MIMO System, Finite Impulse Response (FIR), Multiple Input Multiple Output, Blind Identification, Finite Impulse Response Filter, and Order statistic
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AbstractAn array-based algorithm for multichannel lattice filtering is proposed. The filter is formed by a set of units that are adapted locally and concurrently using recursions that closely match those for single-channel lattice... more
AbstractAn array-based algorithm for multichannel lattice filtering is proposed. The filter is formed by a set of units that are adapted locally and concurrently using recursions that closely match those for single-channel lattice filters. The design, based on a known modular ...
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ABSTRACT Broadband phase conjugation using a time-reversal mir-ror may be used to focus acoustic waves in inhomoge-neous media. This technique has been successfully ap-plied in the ocean over distances of a few kilometers, stimulating... more
ABSTRACT Broadband phase conjugation using a time-reversal mir-ror may be used to focus acoustic waves in inhomoge-neous media. This technique has been successfully ap-plied in the ocean over distances of a few kilometers, stimulating research into possible ...
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We have extended our approach of video compression of underwater images [1,2] to standard test video sequences. Our technique based on Gabor filters to segment underwater images [1] is applied to standard test video sequences to segment... more
We have extended our approach of video compression of underwater images [1,2] to standard test video sequences. Our technique based on Gabor filters to segment underwater images [1] is applied to standard test video sequences to segment the blocks with motion. After ...
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... the real signal under analysis, a phase function cp(t). How-ever, interpreting cp'(t) as the IFt leads to physically un-acceptable results in all but a few special cases [2]. Recent work by Loughlin and Tacer [5] has come to... more
... the real signal under analysis, a phase function cp(t). How-ever, interpreting cp'(t) as the IFt leads to physically un-acceptable results in all but a few special cases [2]. Recent work by Loughlin and Tacer [5] has come to shed additional light on the inappropriateness of that ...
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... This will happen for both the tra-ditional definition (dash-dot line) and the symmetry based one (solid line). ... 5, No 4, April 1998. Kumaresan, Fbmdas, and Rao, Ashwin, "Algorithm for Decomposing an Analytic Signal into AM and... more
... This will happen for both the tra-ditional definition (dash-dot line) and the symmetry based one (solid line). ... 5, No 4, April 1998. Kumaresan, Fbmdas, and Rao, Ashwin, "Algorithm for Decomposing an Analytic Signal into AM and Pos-itive FM Components", Proc. ...
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Page 1. BLIND SDMA WITH A SIGNAL SPACE GEOMETRY MATCHED ALGORITHM Joho Xavier Victor Barroso Instituto Superior TCcnico - Instituto de Sistemas e Rob6tica AV. Rovisco Pais, 1096 Lisboa Codex, Portugal { jxavier,vab}Qisr. ist .utl.pt ...
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Experiments on phase conjugation have shown that the temporal stability of the underwater acoustic propagation channel may be larger than what had been previously anticipated. Using a source/receiver array to implement a time-reversal... more
Experiments on phase conjugation have shown that the temporal stability of the underwater acoustic propagation channel may be larger than what had been previously anticipated. Using a source/receiver array to implement a time-reversal mirror, acoustic energy was successfully refocused back at the source position with small temporal dispersion. The focusing effect proved to be quite robust, and was still observed
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ABSTRACT
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ABSTRACT The design of adaptive equalizers is an important topic for practical implementation of efficient digital communica-tions. In this paper, the application of a radial basis func-tion neural network (RBF) for blind channel... more
ABSTRACT The design of adaptive equalizers is an important topic for practical implementation of efficient digital communica-tions. In this paper, the application of a radial basis func-tion neural network (RBF) for blind channel equalization is analysed. This architecture is well suited ...
Research Interests: Monte Carlo Simulation, Digital Communication, Performance Evaluation, Blind Equalization, Network Performance, and 8 moreRadial Basis Function Neural Network, Data Model, Data classification, Network Model, Nonlinear Distortion, Channel Equalization, Finite Impulse Response (FIR), and Adaptive Equalizer
Research Interests: Computer Architecture, Modulation, OFDM, MIMO, Channel Estimation, and 9 moreImpulse response, Robots, Signal Processing for Wireless Communications, Computational Efficiency, Channel model, Decision Feedback Equalizer, Multicarrier Modulation, Multiple Input Multiple Output, and Minimum Mean Square Error
Research Interests: Wireless Communications, Underwater Communication, Digital Communication, OFDM, Protocols, and 10 moreBroadband Networks, Feedback, Time Reversal, Demodulation, Radio Transmitters, Communication Protocol, Communication protocols, Decision Feedback Equalizer, Underwater Acoustic Communication, and Multiple Input Multiple Output
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ABSTRACT
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Research Interests: Information Geometry, Parameter estimation, Gaussian processes, Variance, Cramer Rao Lower Bound, and 11 moreRiemannian Geometry, Fisher information, Structural Change, Quantum Cellular Automata, Covariance Matrix, Lower Bound, Statistical Model, Probability Density Function, Geodesic Distance, Fisher Information Matrix , and quotient space
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Is there a limit to the maximum resolution one can achieve when representing the signal's energy in the time-frequency plane? Some authors sustain that such a limit exists, and ignoring it is the cause of the known... more
Is there a limit to the maximum resolution one can achieve when representing the signal's energy in the time-frequency plane? Some authors sustain that such a limit exists, and ignoring it is the cause of the known difficulties with some joint time-frequency distributions; others maintain that there is no such limit. In this article, we propose to analyze the merits
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The complexity of real-life transients, coupled with the incomplete (or absent) knowledge of their statistical structure or defining features has motivated the interest on the use of blind, data driven detection schemes. One such scheme,... more
The complexity of real-life transients, coupled with the incomplete (or absent) knowledge of their statistical structure or defining features has motivated the interest on the use of blind, data driven detection schemes. One such scheme, proposed by Jones and Sayeed (1995), uses time-frequency distributions to implement sub-optimal quadratic detectors which, under certain conditions, approach the performance of optimal quadratic detectors. However, their use of Fisher's discriminants to obtain class separation has some drawbacks, which we solve by using a simple perceptron to obtain the discriminant. Also, more often than not, we will have a multiclass situation, implying the use of different time-frequency distributions, each one of them tuned for a given class of transients. The different nature of these distributions (bias, type of cross-terms, time-frequency resolution, etc.) will hamper the performance of the algorithm, forcing the need for experimental validation of its heuristical aspects. The algorithm will be applied to real data, and its performance investigated
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ABSTRACT
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A procedure for parameter estimation of multicomponent polynomial phase signals is presented. This scheme, while restricted to high SNRs, has the advantage of being extremely simple. It is also insensitive to the equal-coefficient... more
A procedure for parameter estimation of multicomponent polynomial phase signals is presented. This scheme, while restricted to high SNRs, has the advantage of being extremely simple. It is also insensitive to the equal-coefficient identifiability problem of the HAF (high-order ambiguity function) based methods. It poses, however, some restrictions on the component amplitudes. Its performance in noise is investigated, and confirmed with several examples
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Research on underwater acoustic communication has shown that throughput and reliability can be improved if the spatial dimension is exploited to create multiple parallel channels in the ocean. This work proposes a technique for creating... more
Research on underwater acoustic communication has shown that throughput and reliability can be improved if the spatial dimension is exploited to create multiple parallel channels in the ocean. This work proposes a technique for creating such channels that builds on the concept of a time-reversal mirror, a retroreflective array that focuses signals at a given point in the ocean by
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Research Interests: Signal Processing, Digital Signal Processing, Coding, Hardware, Remotely Operated Vehicles, and 14 moreData Collection, Bit Error Rate, Communication Channels, TCM, Encoding, Delays, Doppler effect, Bandwidth, Trellis Coded Modulation, Receiver, Fixed Point Arithmetic, Underwater Acoustic Communication, Channel Equalization, and fixed point
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ABSTRACT Recently, wave focusing using a uniform time-reversal array has been demonstrated in the ocean with very encouraging results. This technique may be used to regenerate a mildly distorted signal at the input of a digital underwater... more
ABSTRACT Recently, wave focusing using a uniform time-reversal array has been demonstrated in the ocean with very encouraging results. This technique may be used to regenerate a mildly distorted signal at the input of a digital underwater acoustic receiver, hence reducing its ...
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... so that the output magnitude approaches a desired value R. As the CMA cost function does not ... 8 shows the MSE for equalizer orders 20 and 130 as a function of frame index. ... N. Jablon, Jointblind equalization, carrier recovery,... more
... so that the output magnitude approaches a desired value R. As the CMA cost function does not ... 8 shows the MSE for equalizer orders 20 and 130 as a function of frame index. ... N. Jablon, Jointblind equalization, carrier recovery, and tim-ing recovery for high-order QAM signal ...
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Abstract In the framework of project ASIMOV, an autonomous underwater vehicle and an autonomous surface craft cooperate to jointly carry out complex missions at sea. Exchange of positioning data between the two vehicles ensures that they... more
Abstract In the framework of project ASIMOV, an autonomous underwater vehicle and an autonomous surface craft cooperate to jointly carry out complex missions at sea. Exchange of positioning data between the two vehicles ensures that they remain vertically aligned, ...
Research Interests: Acoustic Communication, Channel Coding, Underwater Acoustics, Underwater Communication, Autonomous Underwater Vehicle, and 10 moreHardware, Remotely Operated Vehicles, Robustness, High Speed, Underwater vehicles, OCEANS Conference, Frequency shift keying, Underwater Acoustic Communication, Synchronisation, and Vents
ABSTRACT The super-exponential algorithm is a block-based tech-nique for blind channel equalization and system identifi-cation. Due to its fast convergence rate, and no a pri-ori parameterization other than the block length, it is a... more
ABSTRACT The super-exponential algorithm is a block-based tech-nique for blind channel equalization and system identifi-cation. Due to its fast convergence rate, and no a pri-ori parameterization other than the block length, it is a useful tool for linear equalization gf moderately ...