On the performance of AF opportunistic relaying with adaptive transmission over Rayleigh fading channels

We analyze the performance of the amplify-and-forward (AF) opportunistic relaying technique in cooperative systems with adaptive transmission over Rayleigh fading channels. We first consider four adaptive transmission techniques: optimal power and rate adaptation, constant power with optimal rate adaptation, truncated channel inversion with fixed rate, and total channel inversion with fixed rate. We present closed-form expressions for the average channel capacity and outage probability for each adaptation policy. We then consider a rate-adaptive M-QAM modulation technique and we derive closed-form expressions for the average spectral efficiency, outage probability and the average bit error rate. Using numerical evaluations the performances of different cases are compared to show the advantages of each adaptive modulation policy in conjunction with the opportunistic relaying in a cooperative communication over Rayleigh fading channels.