Low-complexity soft demodulation of MIMO-BICM using the line-search detector

Bit-interleaved coded modulation (BICM) is an attractive transmission scheme for MIMO wireless communications over fast fading channels. BICM receivers employing maximum-likelihood decoding require a soft demodulator (demapper) that calculates log-likelihood ratios (LLRs) for the coded bits. Because in the MIMO case the calculation of LLRs tends to he excessively complex, there is a strong demand for efficient soft demodulation algorithms that calculate approximate LLRs. Here, we develop the novel soft line-search demodulator (SLSD) by extending the recently introduced line-search detector (LSD) such that approximate LLRs are obtained with little extra computations. We show that the SLSD´s BER performance Ls close to that of the list extension of the sphere decoding algorithm even though the complexity is significantly smaller.