Performance Evaluation of HARQ Schemes for Cooperative Regenerative Relaying

Two Hybrid ARQ (HARQ) schemes based on selective decode and forward are considered for a cooperative half-duplex relay channel. Two time slot types: T₁ slot for relay listening and T₂ slot for relay forwarding are assumed to accommodate half duplex relaying. The considered HARQ schemes differ in the frequency of the ARQ feedback: one is frame and the other is slot based where each frame is composed of one T₁ followed by one T₂ slot. Two types of encodings: repetition coding (RC) and unconstrained coding (UC) (also known as incremental redundancy) are assumed. Outage performance analysis is carried out for both RC and UC. The state transition models of the considered protocols are presented and are used to analytically calculate the HARQ throughput and latency performance; thus avoiding time consuming Monte Carlo based evaluations. The provided analysis enables us to predict the system performance and tune its transmission parameters (transmission rate and frame structure) for any combination of the signal to noise ratio (SNR) of the constituent links.