QoS-guaranteed cross-layer design for joint adaptive modulation and coding, power control, and ARQ protocol

Adaptive modulation and coding (AMC), power control (PC) and automatic repeat request protocols (ARQ) represent very important link adaptation (LA) techniques for future generations of wireless communication systems. In order to improve the efficiency of these systems, some combination schemes of these LA techniques have been proposed in the literature. Most of these schemes were interested in the combination of only two among the three LA techniques. We have proposed in [8] a novel combination scheme where all of the three LA techniques were optimally combined. The optimality criterion was the maximization of the average throughput efficiency, while meeting an average transmit power constraint, in order to reduce multiple access interference. QoS-sensitive services, like video streaming and IP voice, require a QoS constraint or, equivalently, a packet error probability (PEP) constraint. In this paper we are interested in the optimal combination of the three LA techniques, while satisfying a required PEP performance. More specifically, we derive the optimal AM switching thresholds as well as the optimal transmit power level, in order to achieve the highest average throughput efficiency, given the fading channel conditions and the required error performance. To assess the offered performance gain, the proposed LA scheme is compared to conventional scheme using exclusively AM in combination with ARQ without guaranteeing any QoS. Numerical and simulation results show significant average transmit power gains, with respect to AM-ARQ scheme, while still guaranteeing a satisfying error performance.