Iterative soft QRD-M detection and decoding for single carrier block transmission systems

It has been long believed that the turbo equalizer leveraging a soft input/soft output (SISO) detector is effective for system performance enhancement in terms of bit error rate (BER). In practical applications, the implementation of SISO detection is usually challenging, due to its high computational-complexity. To address this issue, this paper proposes a low complexity SISO detector based on QR decomposition (QRD) and the M-search algorithm for single carrier block transmission systems. Benefiting from two unique properties called the aggregation property and the natural ordering property obtained by applying the QRD method into single carrier block transmission systems, the QRD-M based SISO detection algorithm can be dramatically simplified. Detailed analysis shows a linear growing computational-complexity. The extrinsic information transfer (EXIT) chart analysis tool is used to illustrate the performance of the proposed scheme. Both EXIT analysis and simulation results reveal that the turbo equalization with the proposed QRD-M detection algorithm could achieve a sub-optimal system performance close to the BER-optimal maximum a posteriori (MAP) detector at each iteration with a much lower computational-complexity.