Optimization of a timing-error-detector used in RAKE receivers

We consider a DS-CDMA system operating in downlink mode in a multi-user multipath channel scenario. We propose a new version of a standard timing error detector (TED), the early-late detector, for the code tracking loops used inside RAKE receivers. The proposed modification consists in inserting a prefilter in each loop. This concept of prefiltering has already been studied by the authors for a single path channel in the multi-user CDMA context (E. Simon et al., 2003), and here it is generalized to the case of multipath channel. It is explained how to design the optimum pre filters for the minimization of jitter due to the other users and other paths. The prefilter permits in addition to track unresolvable paths. The analysis shows improved tracking performance in comparison to the standard early-late algorithm.