Efficient Link Adaptation Using Joint Power Control, Adaptive Modulation and Coding with Enhanced ARQ Protocol

In this paper, we are interested in the optimal redistribution of the available budget in average transmit power per packet among potential packet transmission attempts for improved Automatic Repeat reQuest (ARQ) protocol. A conventional ARQ protocol was combined in [5], with both Adaptive Modulation and Coding (AMC) and Power Control (PC) to improve spectral efficiency, while satisfying an average transmit power constraint. The optimal power level as well as the most adequate modulation and coding scheme (MCS) are jointly selected, as a function of the channel state. However, the selected power level remains the same for all retransmission attempts of the same packet. We propose in this paper to wisely distribute this optimally selected power budget among potential retransmissions of a given packet, such that throughput is further maximized, while keeping a fixed average power spent by packet. To do this, a heuristic algorithm based on a dichotomic search approach is performed. The enhancement in performance brought by the improved version of the ARQ protocol to the joint AMC-PC-ARQ scheme is then assessed.