Abstract
A simplified soft demapper for non-square quadrature amplitude modulation (QAM) provided by fifth generation of high-speed data-over-cable systems (DOCSIS 3.1) is proposed. By using the geometric tendency of the non-square QAM constellation and “fold-and-overlap” approach, the non-linear log likelihood ratio (LLR) equation based on the max-log maximum a posteriori (MAP) algorithm can be approximated to linear equations. With this approximation, the proposed method can be applied to high-order non-square QAM, up to 8192 QAM, with negligible bit error rate performance degradation under additive white Gaussian noise and multipath flat-fading channels. Computational complexity is reduced by at least 93% compared to the LLR calculation based on the max-log MAP algorithm.
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