A family of minimum mean square error multiuser detectors for three-domain spread multi-carrier direct sequence-code division multiple access

This study presents a family of multiuser detectors (MUDs) for the uplink of spatial-frequency-time-domain (SFT-domain) spread, multi-carrier, direct sequence code division multiple access systems. More specifically, the family is comprised of a joint SFT MUD and six separate MUDs. The proposed joint SFT MUD achieves a significant performance gain because it is based on minimum mean square error (MMSE) decision criteria. For practical realisation, the main contribution of the study is that the authors further reduce the computational complexity by decomposing the complete received signal into several low-dimension signal components and implementing the corresponding separate MMSE MUDs to facilitate symbol detection. The authors also analyse the computational complexity and mean square error bound of the proposed MUDs. The results of simulations demonstrate that the joint SFT MMSE MUD outperforms the other proposed schemes; however, it requires the largest amount of computation. Meanwhile, the performance of the separate MMSE MUDs is effective and close to that of the joint SFT MMSE MUD, but the computational overhead is modest.