An optimal power allocation scheme for cooperative CC-HARQ over block Rayleigh fading channels

In this paper, the optimal power allocation (OPA) problem for Chase combining (CC)-based cooperative hybrid automatic repeat request (HARQ) protocol over block Rayleigh fading channels is addressed. With the constraints of the targeted outage probability and the maximum number of transmission rounds, we aim at determining the optimal power sequences of the source and the relay to minimize the average total power consumption. Towards solving the problem, the asymptotic outage probability and the average total power consumption which are tight at the high SNR region are derived for cooperative CC-HARQ. Based on the approximations, the optimization problem is formulated and an equation set is derived to obtain the closed-form solution to the optimization problem. The results show that the OPA scheme for cooperative HARQ provides significant gains over the equal power allocation (EPA) scheme for cooperative HARQ and the OPA scheme for direct HARQ.