Near-optimum iterative multiuser detection in time-frequency-domain spread multicarrier DS-CDMA systems

In this contribution we propose and study a novel iterative time-frequency-domain (TF-domain) multiuser detector (MUD) for the multicarrier direct-sequence code-division multiple-access system employing both T-domain and F-domain spreading, which, for brevity, is referred to as the TF/MC DSCDMA system. The proposed iterative TF-domain MUD consists of a set of T-domain soft-input soft-output MUDs (SISO-MUDs) and a set of F-domain SISO-MUDs, which exchange information through two multiuser interference (MUI) cancellation units. Both the T-domain and F-domain SISO-MUDs are operated under the maximum a-posteriori (MAP) principles. In this contribution the complexity and bit error rate (BER) performance of the TF/MC DS-CDMA employing the proposed iterative TF-domain MUD are investigated and also compared with the other existing MUD schemes, including the optimum MUD and the joint/separate minimum mean-square error (MMSE) MUDs. Our study shows that the iterative TF-domain MUD is capable of achieving nearly the same BER performance as the optimum MUD, but at much lower complexity.