Optimum joint Adaptive Modulation and Coding and Power Control for packet transmission over fading channels using the ARQ protocol

Mobile radio communication systems employ either Adaptive Modulation and Coding (AMC) combined with an Automatic Repeat reQuest (ARQ) protocol, or Power Control (PC) to handle channel variations, but never a combination of these link adaptation techniques. In this paper we propose a novel scheme which optimally combines PC with AMC, using the ARQ protocol. More specifically, the optimal power level and the appropriate modulation and coding set (MCS) are jointly determined, as a function of the fading channel conditions, to achieve the highest average throughput efficiency, for a fixed average transmit power constraint. To assess the offered performance gain, the proposed technique is compared to a conventional system using exclusively the AMC technique. Numerical results show that the proposed scheme provides significant average transmit power gains. In particular, for a given average throughput, no less than 2 dB gain in transmitted power is achieved, yielding a substantial decrease in interference to other systems/users.