Design and performance analysis of DA multiuser path trackers for long code DS-CDMA systems

We investigate timing recovery structures for a DS-CDMA multiuser uplink using codes with a period of several symbols named long codes and operating over frequency selective multipath and slowly Rayleigh fading channels. In order to implement RAKE reception the delays of the different paths have to be estimated and the estimates have to be updated. We extend interference mitigation to this estimation problem and design timing recovery schemes accounting for the intersymbol interference (ISI) and the multiple access interference (MAI) present in the signal. We first propose a multirate description of the long code DS-CDMA uplink. Then based on this formalism we revisit the optimum data-aided (DA) maximum likelihood (ML) delay estimation structure and the suboptimum early-late implementation. The sensitivity of the synchronizers to imperfect knowledge of path gains to the period of the long codes and to near-far situations is also investigated