Compress and Forward Coding for Half Duplex Gaussian Relay Channels

Abstract

Cooperative communication has become one of the fastest growing domain of wireless communication and is likely to become one of the mainstream technologies in future due to its e cient use of spectrum. This interest in cooperation is not undeserved since it o ers advantages of diversity and multiplexing which make it highly desirable for use in wireless channels. A three node network known as relay channel forms the basic building block of cooperative networks. Therefore a large body of research specially in the realm of information theory has been dedicated to relay channel. Since its inception, several coding schemes have been proposed to enable cooperation between nodes. They can mainly be classi ed into Decode and Forward, Compress and Forward and Amplify and Forward. This monologue presents a multi-level compress and forward coding scheme for a three-node relay network in which all transmissions are constrained to be from an M-ary PAM constellation. The proposed framework employs a uniform scalar quantizer followed by Slepian-Wolf coding at the relay. We rst obtain a performance benchmark for the proposed scheme by deriving the corresponding information theoretical achievable rate. A practical coding scheme involving multi-level codes is then discussed. At the source node, we use multi-level low-density parity-check codes for error protection. At the relay node, we propose a multi-level distributed joint source-channel coding scheme that uses irregular repeat-accumulate codes, the rates of which are carefully chosen using the chain rule of entropy. For a block length of 2 105 symbols, the proposed scheme operates within 0:56 and 0:63 dB of the theoretical limits at transmission rates of 1:0 and 1:5 bits/sample, respectively.