Maximum likelihood combining in cooperative relay networks with different modulations

This paper proposes a novel combining strategy with different modulations for cooperative relay networks. We model a Maximum Likelihood (ML) detection at the destination with higher order modulations such as quadrature amplitude modulation (QAM) which accounts individual symbol error rate (SER) to facilitate the detection. Our proposed algorithm is flexible to signals with different modulations as detection is done symbol-by-symbol basis. If different modulations are used at the source and the relays, we propose that lower modulation is used at the source. By computer simulations, significant Packet Error Rate (PER) performance can be obtained by the proposed scheme against Cooperative-Maximum Ratio Combining (C-MRC).