Efficient combination of hybrid ARQ with Adaptive Modulation and Coding and Power Control operating in tracking mode

In this paper, we develop an energy efficient cross-layer design which optimally combines Adaptive Modulation (AMC) and Coding and Power Control (PC), at the physical layer, with type-I Hybrid Automatic Repeat reQuest (HARQ-I) protocol, 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 [7] that the optimum transmission strategy is a function of an unknown parameter, referred to λ, 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 estimate and track this parameter. In contrast with our previous work, which relied on a block-fading model, we adopt a time-correlated fading channel model based on the Jakes model. We show that the obtained Monte-Carlo simulation results are in perfect agreement with the numerical results based on a perfect knowledge of λ. 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. More precisely, simulation results show that more than 5 dB gain in average transmit power is achieved for low and high average data rates, and no less than 2 dB for medium average data rates.