EM-based receiver design of LDPC-coded MIMO systems over unknown fading channels

We consider an LDPC-coded MIMO system operating in a fading environment, where channel state information is assumed to be unavailable both to the transmitter and the receiver. We propose at the component level a modified EM-based MIMO detector, which completely removes positive feedback between input and output extrinsic information and provide much better performance as compared to the regular EM-based detector that has strong correlations. At the structural level, motivated by the turbo iterative decoding strategy, a new LDPC-coded MIMO receiver is constructed in a novel manner where the soft MIMO detector and LDPC variable node decoder form one super soft decoding unit and the LDPC check node decoder the other component of the iterative decoding scheme. Based on the analysis of the extrinsic information transfer characteristic of the component soft decoders, a simple and efficient LDPC code optimization approach is also provided. Numerical and simulation results are provided to further confirm the optimality of the proposed design approach for the coded MIMO system.