Modulation diversity benefits in cooperative communications

In this paper we propose modulation diversity as a candidate diversity scheme for uncoded cooperative communication in wireless networks with decode-and-forward (DF) communication protocol. A performance analysis of such a scheme in Nakagami-m fading channels in the presence of additive white Gaussian noise (AWGN) is presented. An upper bound on the average probability of bit error (P_b) and average probability of symbol error (P_s) is derived for M-ary phase shift keying (MPSK) modulation schemes. It is shown that the system employing employing modulation diversity is able to provide a performance improvement of 5 dB at a bit error rate of 10^-4 as compared to the conventional cooperative communication systems. We introduce a power allocation factor and show that equal power allocation is not the optimal solution. Furthermore, we also analyze the effect of different rotation angles and power allocation on the system performance.