LDPC-coded MIMO receiver design over unknown fading channels

We consider an LDPC-coded MIMO system composed of M transmit and N receive antennas operating in a flat fading environment. The channel state information is assumed to be unavailable both to the transmitter and the receiver. A soft iterative receiver structure is developed which consists of three main blocks, a soft MIMO detector and two LDPC component soft decoders. Without forming any specific channel estimate, we propose several soft MIMO detectors at the component level that offer an effective tradeoff between complexity and performance. At the structural level, the LDPC-coded MIMO receiver is constructed in a unconventional manner where the soft MIMO detector and LDPC variable node decoder form one super soft-decoding unit, and the LDPC check node decoder forms the other component of the iterative decoding scheme. By exploiting the proposed receiver structure, tractable extrinsic information transfer functions of the component soft decoders are obtained, which further lead to a simple and efficient LDPC code degree profile optimization algorithm with proven global optimality and guaranteed convergence from any initialization. Finally, numerical and simulation results are provided to confirm the advantages of the proposed design approach for the coded system