BER analysis and optimization for differential cooperative networks with relay selection

In this paper, we investigate a cooperative communication system which consists of a source, a destination and N_R relays. The differential modulation and relay selection (DM-RS) are combined in the system, where the best relay is selected to assist the source node with detect-and-forward (DetF) protocol. We consider general fading scenarios where the channel variances of different links are not equal, the average bit error rate (ABER) performance and power allocation strategy are investigated. Firstly, a theoretical ABER expression of the scheme with differential M-ary phase shift keying (DMPSK) modulation is derived. Then, to gain more insightful understanding, we look into the high signal-to-noise ratio (SNR) regime and provide a simple and informative asymptotic ABER expression, which reveals that the scheme can achieve a full diversity order. Furthermore, based on the simple asymptotic ABER expression, the optimum power allocation strategy is determined to improve the system ABER performance. Simulation and numerical results show that the optimum power allocation strategy yields significant performance improvement over the equal power allocation strategy.