Simplified universal soft demapper for gray-mapped constellation

Bit-interleaved coded modulation (BICM) systems with high order constellations and signal space diversity (SSD) are deployed in DVB-T2 and recommended for potential use in 3GPP-LTE standards for its high spectral efficiency and diversity gain. However, in such systems, previous soft demapping algorithms show either extremely high computational complexity or poor performance under imbalanced In-phase/Quadrature (IQ) fading channel due to SSD. In this paper, a simplified universal soft demapping algorithm for Gray-mapped Mary constellation with O(logM) computational complexity is proposed. According to the average mutual information analysis and bit error rate (BER) simulation, the proposed algorithm shows almost the same performance as the Max-Log-MAP algorithm under conventional channel and a little SNR loss under imbalanced IQ fading channel.