A Novel Multi-Layer Cooperative Decode and Forward Scheme

Decode-and-forward (DF) is one of the most popular approach to transmit information over a cooperative relay channel. In DF, information coming from different sources is simply combined regardless of their respective link qualities, and thus DF is not optimized for any propagation conditions. In this paper, we propose a novel transmit cooperation scheme that exploits asymmetric link qualities by using layered higher order modulation. A partial forwarding approach is followed by taking advantage of the layered structure: one part of the information is forwarded by a relay for increasing the robustness of the direct link and the rest of the information flows through the boosted direct link. Moreover, our scheme is based on a distributed serially concatenated encoding structure that can accommodate iterative decoding to further improve its performance. The complexity of our scheme is seemingly identical to DF scheme. Performance evaluation shows that our scheme provides a better spectral efficiency in asymmetric propagation conditions than DF scheme for both non-iterative and iterative decoding.