Multi-Relay Cooperative Retransmission Strategies over Time-Correlated Channels

Time-varying property of practical wireless channels affects the performance of cooperative protocol in multi-relay networks. In this paper, we evaluate and compare four decode-and-forward (DF) retransmission strategies over time-correlated Rayleigh channels, which are the combinations of two relay selection (RS) schemes and two repeater switching patterns: RS can be based on either statistical or outdated channel state information (CSI); in the static switching pattern all forwardings are executed by the same relay that is selected at the beginning, while in the dynamic pattern relays that have not recovered the source message keep receiving from the forwarding relay to extend the decoding subset, from which the activated relay for next retransmission is reselected. Numerical simulations validate that statistical information is more beneficial than outdated CSI over weakly correlated channels. On the other hand, the dynamic switching pattern generally outperforms the static one especially with relatively large maximum transmission number, at the cost of higher complexity of decoding and signalling.