Cooperative OFDM systems for UWAC with SNR-based relay selection schemes

In this paper, we investigate a multi-carrier multi-relay cooperative system with amplify-and-forward relaying over frequency-selective underwater acoustic channels. Relay selection rules rely on the maximization of signal-to-noise ratio (SNR). We basically use two distinct relay selection schemes; one bases on SNR-summation and the other bases on selecting the relay which gives the best SNR among chosen the worst SNRs of all subcarriers in each relay (best of worst). These are used in conjunction with so-called per-subcarrier, all-subcarriers or subcarrier grouping approaches in which one or more relays are selected. We present an extensive Monte Carlo simulation study to evaluate the error rate performance of the UWAC system with different relay selection schemes under consideration and point out differences with terrestrial radio-frequency (RF) systems.Our simulation results indicate that although SNR summation relay selection rule performs slightly better than best of worst relay selection rule for all subcarrier basis approach, best of worst scheme can extract the diversity gain for subcarrier grouping basis approach.