Improving the rates in wireless relay systems through superposition coding

We introduce a new two-step relaying scheme based on superposition coding, SC-relaying. In Step 1, the source A_S broadcasts a message, created by superposition coding, to the relay A_R and the destination A_D. After decoding the information from A_S, A_R relays a part of this message in Step 2, by using a codebook that is adapted to the link A_R - A_D. The information-theoretic design shows that the proposed scheme can improve the spectral efficiency, attaining almost optimal value. We demonstrate that the SC-relaying can be ported even to the case of uncoded systems, where it is shown how to select the transmission scheme in order to maximize the throughput between the source and the destination.