Joint decision-directed feedback multiuser channel gain and delay estimation for DS-CDMA uplink

This paper addresses the issue of channel parameter estimation for uplink direct-sequence code-division multiple-access (DS-CDMA) system. A frequency-selective multipath channel is considered, and a feedback (FB) structure to jointly estimate path delays and complex gains is developed. The proposed algorithms are extensions of those from , where only path-delay estimation is considered. In the current paper, a detailed mathematical analysis of the coupling between the different parallel feedback loops is carried out. From this analysis, results are derived pertaining to system dynamics and jitter variance. Furthermore, a novel operating mode, called improved decision-directed (IDD), is proposed as an improvement of the standard decision-directed (DD) mode. The resulting performance will be measured in terms of mean-square estimation errors (MSEEs) and benchmarked against the corresponding modified Crame´r-Rao bounds (MCRBs). Finally, the impact of the accuracy of the estimated complex gains on the jitter of the path delay trackers (and vice versa) is investigated.