Performance analysis of relay selection techniques with clustered fixed-gain relays

In this letter, we study the performance of two promising relay selection techniques, namely selection cooperation (SC) and opportunistic relaying (OPR), under a clustered fixed-gain relay setting. Such relay configuration finds applicability in practical ad-hoc and sensor networks, although it considers independent identically distributed channels among the links of each hop. Assuming Rayleigh fading and that all nodes are single-antenna devices, a comparative analysis between the selection strategies is performed in terms of the outage probability and average bit error rate. With this aim, closed-form expressions for the probability density function, cumulative distribution function, and moment generating function of the end-to-end signal-to-noise ratio (SNR) are derived. Our theoretical results are validated by means of Monte Carlo simulations, and show that, irrespective on the metric analyzed, OPR always yields higher performance than SC. Such conclusions differ from recent results reported in the open literature for decode-and-forward relays.