Joint Variable Threshold M-QAM and ARQ for Nakagami-m Fading Channel with Feedback Delay

Abstract

In this paper, we develop a cross-layer combining of adaptive M-ary quadrature amplitude modulation (M-QAM) and automatic repeat request (ARQ) protocol, which adapts the threshold of rate-region boundaries to the variation of feedback delay over the Nakagami-m fading (NMF) channels. We derive a threshold adaptation scheme to reduce the effect of the feedback delay on bit error rate (BER). Numerical results reveal that M-QAM with threshold adaptation is more reliable to the feedback delay than M-QAM with fixed thresholds. When we combine the proposed scheme with ARQ, the enhanced BER can lower the probability of packet loss and reduce the number of packet retransmissions.