Universal soft demodulation schemes for M-ary phase shift keying and quadrature amplitude modulation

In this study, the authors propose an efficient universal soft demodulation method for M-ary phase shift keying (PSK) and quadrature amplitude modulation (QAM) schemes. The proposed method achieves the same performance as the Max-log method with much lower, linear-order complexity. The proposed demodulator recursively maps the detected symbol to a specific region in the first quadrant, so that finally there is only one constellation symbol left in the region, and thus it requires approximately one distance estimation per bit. The authors first derive the equations to estimate soft decision bit information for a few well-known M-ary PSK and QAM schemes, and subsequently present compact universal equations applicable to any M-ary PSK and QAM schemes, respectively. The simulation results reveal that the proposed method produces exactly the same performance as the Max-log method with greatly reduced computational complexity.