Time delay tracking for multiuser synchronization in CDMA networks

Multipath propagation, multiple access interference and non-line of sight propagation, etc. have impeded the accuracy in mobile data measurements. Multiuser receivers in asynchronous Code Division Multiple Access (CDMA) systems require the knowledge of several parameters such as timing delay between users. In this paper, the problem of time delay estimation for CDMA systems is examined by proposing an approach based on blind nonlinear least mean squares (LMS) based early-late delay tracker. A system model is developed and a delay tracking algorithm is presented. The simulation results of the proposed delay tracker are compared with the classical delay-locked loop (DLL) approach in a multipath scenario and these show that the proposed delay tracker provides very good performance in challenging cases of closely spaced multipath delays.