Enhanced MRC for Decode-and-Forward Cooperative Diversity Systems

In this letter, we propose a novel enhanced maximal-ratio combining (E-MRC) scheme for multi-branch decode-and-forward (DF) cooperative diversity systems consisting of a source, a destination, and multiple relays. This scheme employs adjustable parameters at the relays and the destination which enable this scheme to appropriately adapt to variations in the source-relay and relay-destination channel gains. For the proposed E-MRC scheme, we analyze the asymptotic error rate performance for high signal-to-noise ratios and Rayleigh fading. Based on the obtained analytical expressions, we find the optimal parameters that lead to minimization of the asymptotic error rate. Furthermore, we compare the error rate performance as well as the feedback overhead of E-MRC with those of important DF schemes, namely, cooperative MRC (C-MRC) and two DF schemes based on the link adaptive regeneration (LAR) concept, namely, LAR-α_inst and LAR-α. We show that although the feedback requirements of E-MRC are similar to those of LAR-α, E-MRC achieves a performance similar to that of LAR-α_inst, which has a substantially higher feedback overhead.