Rate-Adaptation-Based Cooperative Hybrid-ARQ Relaying Scheme in Rayleigh Block-Fading Channels

We propose to optimize a decode-and-forward (DF) cooperative relaying scheme with Hybrid Automatic-Repeat-reQuest (HARQ) protocol for maximizing long-term average transmission rate (LATR) while satisfying the required maximum number of HARQ rounds and the required outage probability in Rayleigh block-fading channels. We analyze the outage probability and the LATR of the cooperative HARQ relaying scheme for varying placements of a source, a relay, and a destination. We formulate and numerically solve an optimization problem of the cooperative HARQ relaying scheme, which is called the CO-LATR, to maximize the LATR by finding optimal values of parameters: the round transmission rate, transmit power allocation ratio between source and relay, and allowable maximum number of HARQ rounds on the link between source and relay. The CO-LATR outperforms the direct-link HARQ scheme, which does not include a relay and outperforms the cooperative HARQ relaying scheme with the conventional method in terms of the LATR.