Variable Threshold M-QAM With Feedback Delay Over Nakagami-m Fading Channels

In this paper, we propose an adaptive M-ary quadrature amplitude modulation (M-QAM) with variable threshold, which adapts the threshold of rate-region boundaries to the variation of feedback delay between the transmitter and the receiver, over independent and identically-distributed (i.i.d) Nakagami-m fading (NMF) channel. The proposed scheme exploits the estimation of instantaneous bit error rate (BER) which is based on the maximum a posteriori (MAP) criterion in. Based on the proposed scheme, we derive the threshold adaptation algorithm to minimize the effect of the feedback delay on the spectral efficiency and the average BER. Numerical results show that our proposed scheme is more reliable to the feedback delay than conventional adaptive M-QAM with fixed thresholds.