An Asymptotically Capacity-Achieving Scheme for the Gaussian Relay Channel with Relay-Destination Cooperation

This paper shows that the capacity of the relay channel can be asymptotically achieved by allowing relay-destination cooperation. Consider a scheme with rate splitting and second-order superposition block Markov encoding at the source, partial decode-forward (PDF) relaying and joint decoding over two consecutive blocks at the relay, and quantize-forward relaying and backward decoding at the destination. This scheme includes as special cases the classical PDF scheme and the destination feedback scheme of the relay channel. In Gaussian channels, the proposed scheme outperforms noisy network coding scheme except for weak source-relay link. For all channel gains, it asymptotically achieves the capacity by reaching the cutset bound as the destination power approaches infinity.