Joint variable threshold M-QAM and ARQ for Nakagami-m fading channel with feedback delay

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 MQAM 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.