Philippe Ciblat

Bio: Philippe Ciblat is an academic researcher from Télécom ParisTech. The author has contributed to research in topics: Hybrid automatic repeat request & Orthogonal frequency-division multiplexing. The author has an hindex of 33, co-authored 223 publications receiving 3316 citations. Previous affiliations of Philippe Ciblat include ParisTech & Université catholique de Louvain.

Asynchronous distributed optimization using a randomized alternating direction method of multipliers

Abstract: Consider a set of networked agents endowed with private cost functions and seeking to find a consensus on the minimizer of the aggregate cost. A new class of random asynchronous distributed optimization methods is introduced. The methods generalize the standard Alternating Direction Method of Multipliers (ADMM) to an asynchronous setting where isolated components of the network are activated in an uncoordinated fashion. The algorithms rely on the introduction of randomized Gauss-Seidel iterations of Douglas-Rachford splitting leading to an asynchronous algorithm based on the ADMM. Convergence to the sought minimizers is provided under mild connectivity conditions.

Age-optimal constrained cache updating

Abstract: We consider a system where a local cache maintains a collection of N dynamic content items that are randomly requested by local users. A capacity-constrained link to a remote network server limits the ability of the cache to hold the latest version of each item at all times, making it necessary to design an update policy. Using an age of information metric, we show under a relaxed problem formulation that an asymptotically optimal policy updates a cached item in proportion to the square root of the item's popularity. We then show experimentally that a physically realizable policy closely approximates the asymptotic optimal policy.

Asymptotic analysis of blind cyclic correlation based symbol rate estimation

Abstract: We consider symbol rate estimation of an unknown signal linearly modulated by a sequence of symbols. We rely on the received signal is cyclostationarity, and consider an existing estimator obtained by maximizing in the cyclic domain a (possibly weighted) sum of modulus squares of cyclic correlation estimates. Although widely used, this estimate seems not to have been studied rigorously when the number of samples N is large. In this paper, we study rigorously the asymptotic behavior of this estimate. We establish consistency and asymptotic normality of the estimate, prove that its convergence rate is N3'2, and calculate in closed form its asymptotic variance. The obtained formula allows us to discuss in relevant way on the influence of the number of estimated cyclic correlation coefficients to take into account in the cost function to maximize.

Explicit Convergence Rate of a Distributed Alternating Direction Method of Multipliers

Abstract: Consider a set of $N$ agents seeking to solve distributively the minimization problem $\inf_{x}\sum_{n=1}^{N}f_{n}(x)$ where the convex functions $f_{n}$ are local to the agents. The popular Alternating Direction Method of Multipliers has the potential to handle distributed optimization problems of this kind. We provide a general reformulation of the problem and obtain a class of distributed algorithms which encompass various network architectures. The rate of convergence of our method is considered. It is assumed that the infimum of the problem is reached at a point $x_{\star}$ , the functions $f_{n}$ are twice differentiable at this point and $\sum abla^{2}f_{n}(x_{\star}) >0$ in the positive definite ordering of symmetric matrices. With these assumptions, it is shown that the convergence to the consensus $x_{\star}$ is linear and the exact rate is provided. Application examples where this rate can be optimized with respect to the ADMM free parameter $\rho$ are also given.

Accurate digital frequency offset estimator for coherent PolMux QAM transmission systems

Abstract: An accurate blind frequency offset estimator adapted to QAM modulated signal is proposed. For coherent 100Gbit/s QAM PolMux transmission, frequency offset can be recovered with an accuracy of a few kHz.

Table Of Integrals Series And Products

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Linear systems

Abstract: Most of the signal processing that we will study in this course involves local operations on a signal, namely transforming the signal by applying linear combinations of values in the neighborhood of each sample point. You are familiar with such operations from Calculus, namely, taking derivatives and you are also familiar with this from optics namely blurring a signal. We will be looking at sampled signals only. Let's start with a few basic examples. Local difference Suppose we have a 1D image and we take the local difference of intensities, DI(x) = 1 2 (I(x + 1) − I(x − 1)) which give a discrete approximation to a partial derivative. (We compute this for each x in the image.) What is the effect of such a transformation? One key idea is that such a derivative would be useful for marking positions where the intensity changes. Such a change is called an edge. It is important to detect edges in images because they often mark locations at which object properties change. These can include changes in illumination along a surface due to a shadow boundary, or a material (pigment) change, or a change in depth as when one object ends and another begins. The computational problem of finding intensity edges in images is called edge detection. We could look for positions at which DI(x) has a large negative or positive value. Large positive values indicate an edge that goes from low to high intensity, and large negative values indicate an edge that goes from high to low intensity. Example Suppose the image consists of a single (slightly sloped) edge:

IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems Draft Amendment: Management Information Base Extensions

Abstract: This document provides updates to IEEE Std 802.16's MIB for the MAC, PHY and asso- ciated management procedures in order to accommodate recent extensions to the standard.