Performance evaluation of a flexible amplify and forward (AF) combined with HARQ

A Hybrid ARQ (HARQ) scheme employing a flexible amplify and forward (AF) relaying is considered for a cooperative relay channel. Two phase types with flexible length: one phase for relay reception and another phase for relay forwarding are assumed to accommodate half duplex relaying. We assume two types of encoding: repetition coding (RC) and unconstrained coding (UC). The outage performance of the considered flexible AF scheme is analytically derived for any number of retransmissions, and both RC and UC encoding used by the considered HARQ. The state transition models of the considered protocols are presented and then the HARQ throughput and latency performance are analytically calculated; As a result time consuming Monte Carlo based evaluations are avoided. The provided analysis enables us to predict the performance and adjust transmission rate and frame structure for any combination of the signal to noise ratio (SNR) of the involved links. Performance gains of up to 1 and 1.5 dB are observed for the considered simulation scenarios thanks to the flexible AF combined with properly designed HARQ protocols. Also the flexible AF is able to attain its performance over all the range of SNRs of the constituent links while the conventional AF is only efficient on a restricted range of SNRs.