Maximum likelihood detection with arbitrary modulations in cooperative relay channels

This paper proposes a simple combining technique with arbitrary modulations for a cooperative relay scheme based on a Detect-and-Forward (DEF) relay protocol. Here we present Maximum Likelihood (ML) criterion detection at the destination which considers individual symbol error rate (SER) to facilitate the detection in noisy relay networks. In particular, our proposed algorithm is flexible to signals with different modulation formats as detection is done on a symbol-bysymbol basis. If different modulations are used at the source and the relays, we propose that lower modulation constellation is used at the source. By computer simulations, the results show that significant Packet Error Rate (PER) performance can be achieved by the proposed scheme and we compare it against Cooperative-Maximum Ratio Combining (C-MRC) and Selection Combining (SC). KeywordsCooperative Relay; Detect-and-Forward; Maximum-Likelihood criterion detection.