Wyner-Ziv coding for the half-duplex relay channel

Cover and El Gamal derived the tightest bounds on the capacity of the relay channel using random coding and proposed two coding strategies, namely decode-and-forward (DF) and compress-and-forward (CF), to provide the best known lower bounds of the achievable rate region. Depending on transmission parameters, either DF or CF could be superior. Several practical code designs based on DF have appeared recently. We present the first practical CF design for the half-duplex Gaussian relay channel based on Wyner-Ziv coding of the received source signal at the relay. Assuming ideal source and channel coding, our design achieves the lower bound of CF. It thus realizes the performance gain of CF over DF promised by the theory when the relay is close to the destination. Our practical implementation based on LDPC codes for error protection at the source and nested scalar quantization and IRA (irregular repeat-accumulate) codes for Wyner-Ziv coding at the relay comes as close as 0.76 dB to the theoretical limit of CF.