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InFormAtion theory: New challenges and new interdisciplinary tools.

First Meeting Abstracts

  • Author: A. Proutiere and T. Bonald
    Title: Maximum stability of networks with non-convex capacity constraints

    Abstract: Wireless networks where base stations interact through interference typically have non-convex rate regions. By scheduling the extremal points of the rate region only, one can ensure maximum stability in the sense that the stability region is the convex hull of the rate region. This typically requires the cooperation of the base stations, however. In this talk, we analyse the ability of usual allocations like proportional fairness, for which decentralized schemes exist, to ensure maximum stability.

  • Author: Nicolas Bonneau
    Title: Correlated Equilibrium for multi-user OFDMA

  • Author: C. D. Charalambous
    Title: Control of Uncertain Dynamical Systems via Limited Capacity Communication Channels

    Abstract: In this presentation, an information theoretic framework is discussed for controlling uncertain dynamical systems over limited capacity uncertain communication channels. The methodology employs tools from Shannon's theory of reliable communication and robustness of uncertain dynamical systems, as follows. 1) The classical information theoretic measures of entropy rate and channel capacity are defined for a family of source distributions and channel transition distributions, respectively. 2) The classical Shannon rate distortion lower bound is defined for a family of source distributions. 3) The notions of observability and stabilizability of a family of control dynamical systems is related to rate distortion of the source and its reconstruction. By invoking 1)-3) and the information transmission theorem, necessary condition for the existence of an encoder, decoder and feedback controller over the communication channel are derived for uniform stabilizability and observability of the dynamical system. When applied to Gauss Markov controlled processes, the necessary condition states that the capacity of the channel should be at least equal to the sum of the logarithms of the unstable eigenvalues associated with the open loop Gauss Markov process.

  • Author: N. Hegde
    Title: Combined Cell Selection and Inter-Cell Scheduling in Wireless Data Networks

    Abstract: We examine the potential capacity gains in wireless data networks such as UMTS/HSDPA and CDMA 1xEV-DO from cell coordination which combines inter-cell scheduling and optimal cell selection. The inter-cell scheduling involves coordinating the activity phases of interfering base stations so as to avoid inter-cell interference and boost the transmission rates. The cell selection aims at improving the performance by assigning users to base stations based on load and other relevant considerations in addition to signal strength conditions. We consider a dynamic setting where users come and go over time as governed by the arrival and completion of random finite-size data transfers, and evaluate the capacity gains in terms of the maximum sustainable network throughput for a given spatial traffic pattern. We demonstrate that the relative merits of inter-cell scheduling and cell selection strongly depend on the network topology

  • Author: F. Baccelli
    Title: Summary of related research activity at TREC

  • Author: M. Dirani
    Title: Ressource allocation in heterogenes environnements.

  • Author: Can Emre Koksal
    Title: Perspectives on Time Varying Wireless Communication Networks

    Abstract: The quality of communication over a wireless channel depends on many different parameters. It can vary dramatically over time and is known to change with slight environmental changes. Therefore, treating network layer issues such as network delay, routing and traffic engineering, separately from physical layer issues such as channel modeling, detection and coding leads to a loss of complete understanding.
    In this work, we introduce a model that captures the time varying characteristics of a wireless channel in a form that could be directly translated into network and application layer quality constraints. In a sense, the model projects certain parameters of the physical layer onto the space of networking parameters which enables us to better understand the impact of physical layer variability on the networking performance. First, we show that the channel variability may affect the networking performance quite differently depending on its time scale. Then we establish further connections between the two layers using the notion of ``effective number of transmissions'' (ENT). ENT is motivated by the idea of effective bandwidths which is used to model variable rate sources in many traffic engineering problems. We illustrate that ENT captures the statistical properties of the channel in such a way that problems of routing and opportunistic multiple access over variable channels resemble those in fixed (wired) channels. We also present experimental results taken from sensor and mesh networks for further illustration.

  • Author: E. Altman (joint work with K. Avratchenkov, G. Miller and R. Marquez)
    Title: A stochastic game framework for obtaining capacity limits for Markovian channels under adversarial conditions

    Abstract: We study an uplink power control problem in a CDMA network. A group of subscribers transmit data to a base station over wireless channels, in the presence of a malicious node that tries to jam the communication. The transmission power of the subscribers is assumed to be controlled by the base station which transmits the requested power levels. Both the subscribers' terminals as well as the jamming terminal have constraints on their average transmission power. Using a zero-sum game formulation, we identify the most harmful behavior of the jammer as well as a robust power control policy for the subscribers' terminals that guarantee the best performance under worst case jamming conditions.
    E. Altman, K. Avrachenkov, R. Marquez and G. Miller, "Zero-sum constrained stochastic games with independent state processes", Math. Meth. Oper. Res., Vol. 62, pp. 375-386, Dec. 2005.
    E. Altman, A. Konstantin, G. Miller, B. Prabhu, "Uplink dynamic discrete power control in cellular networks", Inria Research Report, RR-5818, 2006. Availablr as INRIA Research Report