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Walid Hachem

  1. A CLT for Information-theoretic statistics of Non-centered Gram random matrices.

    Mon, 07/04/2011 - 15:01 — SomNambul
    Authors: Walid Hachem, Jamal Najim, Jack W. Silverstein, Malika Kharouf
    Subjects: Probability
    Abstract

    In this article, we study the fluctuations of the random variable: $$
    {\mathcal I}_n(\rho) = \frac 1N \log\det(\Sigma_n \Sigma_n^* + \rho I_N),\quad
    (\rho>0) $$ where $\Sigma_n= n^{-1/2} D_n^{1/2} X_n\tilde D_n^{1/2} +A_n$, as
    the dimensions of the matrices go to infinity at the same pace.

  2. A Subspace Estimator for Fixed Rank Perturbations of Large Random Matrices.

    Thu, 06/09/2011 - 15:01 — SomNambul
    Authors: Walid Hachem, Jamal Najim, Philippe Loubaton, Pascal Vallet, X. Mestre
    Subjects: Probability
    Abstract

    This paper deals with the problem of parameter estimation based on certain
    eigenspaces of the empirical covariance matrix of an observed multidimensional
    time series, in the case where the time series dimension and the observation
    window grow to infinity at the same pace. In the area of large random matrix
    theory, recent contributions studied the behavior of the extreme eigenvalues of
    a random matrix and their associated eigenspaces when this matrix is subject to
    a fixed-rank perturbation.

  3. Error exponents for Neyman-Pearson detection of a continuous-time Gaussian Markov process from noisy irregular samples.

    Sat, 09/26/2009 - 04:10 — SomNambul
    Authors: Walid Hachem, Eric Moulines, Francois Roueff
    Subjects: Information Theory
    Abstract

    This paper addresses the detection of a stochastic process in noise from
    irregular samples. We consider two hypotheses. The \emph{noise only} hypothesis
    amounts to model the observations as a sample of a i.i.d. Gaussian random
    variables (noise only). The \emph{signal plus noise} hypothesis models the
    observations as the samples of a continuous time stationary Gaussian process
    (the signal) taken at known but random time-instants corrupted with an additive
    noise. Two binary tests are considered, depending on which assumptions is
    retained as the null hypothesis.

  4. Performance Analysis over Slow Fading Channels of a Half-Duplex Single-Relay Protocol: Decode or Quantize and Forward.

    Mon, 08/31/2009 - 17:16 — SomNambul
    Authors: Nassar Ksairi, Philippe Ciblat, Pascal Bianchi, Walid Hachem
    Subjects: Information Theory
    Abstract

    In this work, a new static relaying protocol is introduced for half duplex
    single-relay networks, and its performance is studied in the context of
    communications over slow fading wireless channels. The proposed protocol is
    based on a Decode or Quantize and Forward (DoQF) approach. In slow fading
    scenarios, two performance metrics are relevant and complementary, namely the
    outage probability gain and the Diversity-Multiplexing Tradeoff (DMT).

  5. Resource Allocation for Downlink Cellular OFDMA Systems: Part I - Optimal Allocation.

    Mon, 08/31/2009 - 17:16 — SomNambul
    Authors: Nassar Ksairi, Philippe Ciblat, Pascal Bianchi, Walid Hachem
    Subjects: Information Theory
    Abstract

    In this pair of papers (Part I and Part II in this issue), we investigate the
    issue of power control and subcarrier assignment in a sectorized two-cell
    downlink OFDMA system impaired by multicell interference. As recommended for
    WiMAX, we assume that the first part of the available bandwidth is likely to be
    reused by different base stations (and is thus subject to multicell
    interference) and that the second part of the bandwidth is shared in an
    orthogonal way between the different base stations (and is thus protected from
    multicell interference).

  6. Resource Allocation for Downlink Cellular OFDMA Systems: Part II - Practical Algorithms and Optimal Reuse Factor.

    Mon, 08/31/2009 - 17:16 — SomNambul
    Authors: Nassar Ksairi, Pascal Bianchi, Walid Hachem, Phiippe ciblat
    Subjects: Information Theory
    Abstract

    In a companion paper, we characterized the optimal resource allocation in
    terms of power control and subcarrier assignment, for a downlink sectorized
    OFDMA system. In our model, the network is assumed to be one dimensional for
    the sake of analysis. We also assume that a certain part of the available
    bandwidth is likely to be reused by different base stations while that the
    other part of the bandwidth is shared in an orthogonal way between these base
    stations.

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