Cooperation over Frequency-Selective Fading Relay Channels

We study information-rate calculations and coded-cooperation strategies for relay channels with frequency-selective (FS) fading. We develop suitable channel trellises for the multi-access and broadcast parts of the relay channel, and employ simulation-based techniques to calculate (approximate) ergodic information-rate bounds with FS Rayleigh fading. Our results show that frequency selectivity provides higher information rates than flat fading when the fading coefficients are known at the receiver, however, the improvement becomes marginal with increasing number of channel taps (when the overall signal to noise ratio is kept constant). Furthermore, we develop a distributed turbo-coding strategy and several decode-and-forward type detection/decoding schemes to ensure successful cooperative communication where the source and the relay may transmit simultaneously. We show that with suitable coding and iterative decoding, one can approach the approximate information-rate limits closely, and that detection schemes based on MMSE criterion provide a good performance/complexity trade-off.