Efficient combination of HARQ-I with AMC and power control operating in tracking mode

In this paper, we develop an energy efficient cross-layer design which optimally combines adaptive modulation and coding (AMC) and power control (PC), at the physical layer, with type-I hybrid automatic repeat request protocol (HARQ-I), at the data link layer. The objective is to maximize the average throughput efficiency under a prescribed average transmit power constraint. We have shown in [6] that the optimum transmission strategy is a function of an unknown parameter, referred to γ, which depends on both the average transmit power and the time-varying channel statistics. Since the channel statistics are a priori unknown at the transmitter, we here recourse to an adaptive algorithm, operating in tracking mode, to follow this parameter. We show that the obtained Monte-Carlo simulation results are in perfect agreement with the numerical results based on a perfect knowledge of γ. The obtained results show a significant performance improvement with respect to a conventional cross-layer design using exclusively AMC at the physical layer and HARQ-I at the data link layer.