Efficient multi-stage decision-feedback multiuser detectors for multi-code DS-CDMA system over severe multipath channel

This paper presents efficient and high performance multiuser detectors (MUD) for multi-code DS-CDMA uplink system under different system loading over severe CM4 UWB indoor channel dispersion. Under low to moderate loading (up to 4 users), we first present a RAKE with parallel bi-directional decision feedback (RAKE-PBDDF) MUD for solving the intersymbol, multi-code, and multiple access interferences among all users. For heavier loading, an enhanced multi-stage MUD is then developed in successive interference cancellation (SIC) concept. Although the RAKE with SIC-BDDF (RAKE-SBDDF) MUD requires more latency duration, it leads to a performance close to the optimum performance in term of averaged single-user matched filter bound (SU-MFB). The simulation is conducted using a DS-MBOK UWB system with 32-chip orthogonal Gold code as spreading codes. The results show that even under the scenario of twelve 4-BOK uplink users, the RAKE-SBDDF MUD can work robustly.