WPR.6 - Relaying and cooperation in networks

Objectives

This WP will address the potential of cooperative behavior in the view of obtaining significant capacity and multiplexing gain in wireless communications. This encompasses strategies and codes (including error correcting codes, linear precoders or both) which exploit relaying diversity in order to realize seamless communication and reduce complexity of routing in highly volatile/mobile networks.

Description of work

Task TR6.1: Design of distributed Space-Time/Frequency codes for Multiuser OFDM systems with relay, relaying strategies and resource allocation.

6.1.1. Space-Time/Frequency codes will be investigated and designed for multiuser systems based on OFDM and relays. Assuming first CSI at the receiver side, codes will be optimized from the point of view of diversity gain. For CSI available at the transmitter side, the power allocation and the carrier allocation will be optimized for various criterions. These designs will be addressed for different relaying strategies (DF, AF, …), and various levels of knowledge about the CSI. The optimization of MIMO relays will also be considered. The linear processing operated by the relay will be optimized for a number of criteria.

Main players: UCL, CNRS, CTTC

6.1.2. Distributed space-time coding schemes will be investigated for cooperative networks. One of the challenges in cooperative systems is that since there is no central control unit, often the cooperating nodes are not aware of each other. Randomized space-time coding schemes have been shown to attain diversity gains even when the number of cooperative nodes are unknown. However, these coding schemes take advantage of diversity gain inherent in the channel only, one can provide further gains in spectral efficiency by designing space-time codes exploiting spatial multiplexing gains as well. In this subtask, we will investigate randomized distributed space-time codes that can provide varying levels of diversity-multiplexing tradeoffs. Practical issues such as the decoding complexity and the asynchronism among the nodes will also be addressed

6.1.3. Another aspect is to design “universal” estimate-and-forward protocols that are based on joint source-channel coding. Ideally the proposed scheme should be able to approximate any reference strategies such as amplify-and-forward and decode-and-forward in the regime where each of these strategies dominates the others. Additionally we want to address the receiver design, which has to be optimally adapted to the chosen relaying scheme. This issue appears in half duplex relay channel and can be critical for relays under bad reception conditions. Additionally we will address these issues both from the PHY- and cross-layer standpoints.

Main players: Bilkent, CNRS

Task TR6.2: Oblivious cooperation protocols and scaling laws for relay networks

6.2.1. This robust method of cooperation addresses topological uncertainty, namely where the user is unaware whether a helper (relay) is present or not. Yet it benefits in cases such a helper exists and is not damaged if this is not the case. The research will be guided by information theoretic considerations, adhering to these practical assumptions. Within this procedure techniques will also be investigated that take advantage of side information present at the receiving end, as well as different broadcast and incremental Wyner-Ziv joint source-channel coding techniques.

6.2.2. Another aspect considered in this task is devoted to how the capacity scales with the use of relay nodes (virtual MIMO) in the case of full and partial cooperation between the nodes. We will focus our attention in particular in the case partial CSI and correlated channels with or without line of sight. The framework will use asymptotic results of random matrix theory.

Main players: Technion, CNRS, CTTC

Task TR6.3: Cooperation in mobile ad-hoc networks (Virtual Antenna Arrays/VAAs)

The following issues concerning cooperation in VAAs will be considered: (1) which neighbours should assist the transmission, (2) how to perform the cooperative relaying so the battery life of a mobile relay node is kept at a reasonable level, (3) which spatial-temporal processing technique to employ, (4) how to efficiently secure such a transmission.

This task will target the selection of the appropriate network layer protocol and cross-layer optimisation technique. The examination and the choice of the network layer protocol and optimisation across multiple OSI layers is essential so that additional routing information can be used for the purposes of organising cooperative relaying at the link layer. A possible selection is the well-known Optimised Link State Routing protocol (OLSR) which features some advanced neighbour discovery and pre-selection mechanisms that seem also applicable for selecting the mobile relays forming VAAs.

Main players: PUT, Chalmers