Tracking performance of DA and DD multiuser timing synchronizersfor short code DS-CDMA systems

摘要

We consider a direct-sequence code-division multiple-access systemnoperating over frequency-selective multipath and slowly Rayleigh fadingnchannels. In order to implement RAKE reception, the delays of thendifferent paths have to be estimated and the estimates have to benupdated. We extend interference mitigation to this estimation problemnand design timing recovery schemes accounting for the intersymbolninterference and the multiple-access interference present in the signal.nStarting from the maximum likelihood approach, we derive data-aided andndecision-directed early-late synchronizers and study their trackingnperformance. The advantage of the interference mitigating synchronizernis illustrated. The sensitivity of the synchronizer to imperfectnknowledge of path gains and to near-far situations is also investigated