Delay trackers for multiuser CDMA receivers

Two types of coherent delay-locked loops (DLL) are considered in this paper as delay trackers in multiuser CDMA receivers. The first approach is based on the parallel interference cancellation (PIC) method. PIC based delay trackers require the estimation of channel parameters and data symbols of all users to construct the multiple-access interference (MAI) estimates. The other method is based on decision-directed single-user coherent DLLs. According to the numerical results, the PIC based DLL yields better steady state tracking performance at high SNRs, whereas the single-user coherent DLL performs better at low SNRs with reasonably low interference levels. The single-user DLL in a PIC based receiver is more robust against other user delay errors, which resulted in better transient state performance.