SUMMARY
In this paper, we analyze a new cross layer combining scheme of adaptive modulation and coding (AMC) at the physical layer and hybrid automatic repeat request (HARQ) protocol at the data link layer. Our purpose is to improve the performance of the communication system in terms of throughput and errors. We propose a new adaptive HARQ protocol based on the estimated mutual information in addition to signal to noise ratio as channel state information (CSI), which are unavailable at the receiver. Unlike the traditional protocols, the transmitter is aware of the transmission mode only, not the instantaneous CSI, which minimize the load on the feedback channel. The transmission is supposed to be done over block fading channel. Mathematical formulation is improved for the performance criterions, in terms of throughput of the new HARQ, average number of transmissions and the spectral efficiency of the AMC/HARQ. The comparison with the traditional variable rate HARQ shows that our new adaptive HARQ protocol provides an upper bound for the throughput. In addition, the simulation results show that, a small number of transmissions, is enough to reach the maximum spectral efficiency while maintaining the error probabilities under certain acceptable level.