Soft QRD-M decoding for coded IFDMA systems

In this paper, a low complexity a posterior probability (APP) detector based on breadth-first tree search algorithm is purposed for coded interleaved frequency division multiple access (IFDMA) system. The proposed detector combines the principles of the M-algorithm with QR decomposition (QRD-M) to generate soft decision statistics in place of the full APP detector which has a high computational cost. We first demonstrate that an IFDMA system can be viewed as a MIMO system at the receiver and then derive the proposed detector. Simulated results show that the bit error rate (BER) performance of a system using the proposed QRD-M detector performs better than a system using frequency domain equalizer, especially for channels with greater diversity. Moreover, the simulated BER performance exhibits similar diversity order as the maximum channel diversity order.