Channel estimation-assisted demapping algorithm of high-order QAM within shrunk search range

QAM (Quadrature Amplitude Modulation) is broadly used in various communication systems thanks to its high power efficiency and bandwidth utilization. High-order QAM, because of its wide search range, may result in high demapping complexity. In order to solve this problem, a novel concept of soft-decision contribution factor is introduced to evaluate the contribution of reference constellation to the demapping, and a demapping algorithm of high-order QAM within shrunk search range is proposed. Then, some boundary conditions of the algorithm are discussed, and an adaptive selection scheme of search range is finally presented with the assistance of channel estimation. Simulated results indicate that (1) the proposed algorithm downsizes the search range without any sacrifice of BER performance; (2) 4096-QAM and 1024-QAM respectively shrink their search range to 12.7% and 19.7% of that of the whole constellation; and (3) as the proposed algorithm makes good tradeoff between performance and demapping complexity, it has a good prospect of engineering application.