Adaptive protocol for differentially modulated cooperative communications

In this paper, an adaptive protocol is proposed for differentially encoded cooperative communications achieving full rate with an amplify-and-forward protocol.The proposed protocol achieves the maximum achievable diversity gain available in such system based on minimizing a tight approximate bound on bit error rate (BER), and is able to optimally choose the best cooperation partners under the slowly-varying fading channels. A sub-optimum power allocation for such systems is also studied, based on a guideline of an optimum power allocation for coherent systems. Simulation results show that the proposed adaptive protocol yields a remarkably lower BER in comparison with existing protocols. Furthermore, the proposed adaptive protocol with sub-optimum power allocation yields significant performance improvement in comparison with the equal power allocation scheme.