Iterative Multiuser Detectors for Spatial–Frequency–Time-Domain Spread Multi-Carrier DS-CDMA Systems

This paper presents three low-complexity, yet effective, multiuser detectors (MUDs) for the uplink of spatial-frequency-time-domain (SFT-domain) spread multicarrier (MC) direct-sequence code-division multiple-access (DS-CDMA) systems. Each MUD first converts a received signal into the corresponding format. It then detects the transmitted symbols iteratively by using a one-domain (1D) minimum-mean-square-error (MMSE) detector and a two-domain (2D) MMSE detector alternately. The weights of the 1D detector are updated to minimize the mean-square error (MSE) of the detection output by setting the weights of the 2D detector at the values determined in the previous iteration, and vice versa. Performance analyses of the bit-error-rate (BER) bound, the convergence, and the required computational complexity are conducted to assess the feasibility of the proposed MUDs. Finally, the results of computer simulations demonstrate that the performance of the proposed schemes is close to that of the joint SFT-domain MMSE MUD in most scenarios but with lower computational overheads.