Multiuser DD-ML estimation of multipath channel delays for a DS-CDMA uplink

We consider a direct sequence code division multiple access (DS-CDMA) system 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. Starting from the maximum likelihood (ML) approach we derive a decision-directed (DD) early-late synchronizer and its tracking performance is studied. The advantage of the interference mitigating synchronizer is illustrated. The sensitivity of the synchronizer to near-far situations is also investigated