Optimization of symbol timing recovery for multi-user DS-CDMA receivers

We consider a direct-sequence code-division multiple-access system operating in the downlink. We propose to improve the performances of a conventional delay tracking algorithm, i.e. the early-late algorithm, by prefiltering the received signal. This concept has been studied by A.N. D\´Andrea and M. Luise (see IEEE Trans. Commun., vol.44, p.399-406, 1996) for the clock recovery scheme proposed by F.M. Gardner (see IEEE Trans. Commun., vol.34, p.423-9, 1986). Our main contribution is to extend this concept in a multi-user CDMA context. We treat multiple-access interference and deal with the two "timing scales", i.e. symbol and chip duration, due to the spread spectrum. The analysis shows improved tracking performances in comparison to the standard early-late algorithm.