Optimized timing error detector for DS-CDMA applications in multipath scenarios

An extension to the timing error detector (TED) for timing/code tracking loops used inside RAKE receivers in CDMA systems is presented. In contrast to the conventional TED, it is well suited for the case of multipath propagation channels. In order to accomplish this task, the conventional early-late TED is replaced by an FIR filter which is optimized for the instantaneous multipath scenario. This optimization minimizes the overall distortions inside the timing tracking loop of each of the fingers of the RAKE receiver. The filter coefficients are calculated using the knowledge on the relative delays of all paths and their respective powers. An optimization becomes necessary whenever closely spaced paths have to be tracked. This fact makes this algorithm a favorable candidate for indoor scenarios where individual paths can be spaced even more closely than one chip. The performance of the scheme is assessed by means of simulation