Low complexity demodulator for M-ary QAM

In this paper, a simple hard decision method for demodulating M-ary quadrature amplitude modulation (QAM) is presented. Traditionally, the M-ary QAM demodulator employs the maximum likelihood algorithm as the decision rule. It assumes equally likely message symbols. Accordingly, a maximum likelihood decoder computes the log-likelihood functions as metrics for all possible M message symbols, compares them, and then decides in favor of the maximum. When M is larger, the number of multiplications, additions, subtractions, and comparisons are significantly increased. As opposed to decode the received symbol, a new bit level decoding scheme is proposed based on the signal constellation. This bit decoding scheme is significantly simpler and faster than the conventional method. Simulation results show it presents the same bit error rate (BER) performance as the conventional method.