Iterative Soft QRD-M Decoding of Coded IFDMA Systems

We introduce an iterative decoding algorithm for the decoding of coded interleaved frequency division multiple access (IFDMA) system in this paper. The iterative decoding algorithm incorporates a low complexity a posterior probability (APP) detector based on breadth-first tree search algorithm with a soft-input soft-out (SISO) error-correcting codes (ECC) decoder. The proposed detector combines the principles of the M-algorithm with QR decomposition (QRD-M) to generate soft decision statistics in place of the conventional APP detector which has a high computational cost. We show through simulations that the purposed iterative decoding algorithm is able to achieve significant performance gain using only very small number of iterations. Furthermore, the simulated bit error rate (BER) performance of a system using the proposed algorithm not only exhibits similar diversity order as the hypothetical matched filter bound but also approaches it at high signal-to-noise ratio (SNR).