Philippe Ciblat

Resource allocation for the downlink of OFDMA cellular networks and optimization of the reuse factor

In this paper, we investigate the issue of power control and sub-carrier assignment in a downlink OFDMA system. We assume that a certain part of the available bandwidth is likely to be reused by the different base stations (and is thus subject to multicell interference) and that the other part of the bandwidth is shared in an orthogonal way between them (and is thus protected from multicell interference). Although this problem of multicell resource allocation is non-convex, we provide, in the limit of large number of users, the general form of its global solution. As a byproduct, we characterize the optimal value of the frequency reuse factor.

Chapter 2 – Synchronization

Synchronization is fundamental to the proper operation of communication systems. The focus of this chapter is on time and carrier synchronization when a reference is available. In this context, both single and multi-carrier systems, both single and multi-user scenarios, and both flat-fading and non-flat-fading (frequency-selective) channels will be considered. The last section of this chapter will also provide a brief review of the network time synchronization problem, commonly used protocols and performance metrics. Both broadcast protocols and distributed schemes are discussed.

Outage performance of a novel relaying protocol: Decode or Quantize and Forward

In this paper, we propose a novel half duplex relaying protocol which belongs to the class of hybrid decode and forward schemes, and we study its performance in the context of communications over slow fading channels. Our protocol is based on a Decode or Quantize and Forward (DoQF) approach. In slow fading contexts, the outage probability Po is of central importance. As the exact evaluation of the outage probability for all possible values of the signal-to-noise ratio (SNR) is a difficult problem for most relaying protocols, we analyze the behaviour of Po as the SNR rho tends to infinity. In that case, rho2Po converges to a constant xi, which we will refer to as the outage gain. The proposed DoQF protocol is shown to outperform the classical DF protocol in terms of outage gain. Moreover, at high SNR, the proposed scheme is shown to be optimal in the wide class of hybrid DF protocols.

A static protocol to achieve optimal Diversity-Multiplexing Tradeoff for high diversity gains in half-duplex relay channels

In this paper, we study the Diversity-Multiplexing Tradeoff (DMT) of a novel Decode or Quantize and Forward (DoQF) protocol for the half duplex single relay channel. It is well-known that the so-called Dynamic Decode and Forward (DDF) achieves the Multiple-Input-Single-Output (MISO) bound in the range of multiplexing gains r < 0.5. But to the best of our knowledge, no practical coding scheme allows the implementation of the DDF, so that it essentially remains a theoretical protocol. On the opposite, the proposed DoQF protocol is based on a practical static coding-decoding strategy. Our results show that the DoQF achieves the MISO bound in the range of multiplexing gains r < 0.25 (and still has an attractive performance for r < 0.37). To the best of our knowledge, this makes the DoQF the only static protocol that achieves the MISO upperbound without any feedback link between nodes.