Maximum likelihood time delay estimation for Direct-Spread CDMA multipath transmissions using importance sampling

In this paper, we address the problem of time delay estimation for Direct-Spread CDMA (DS-CDMA) multipath transmissions. We observe that the attractive post-correlation model (PCM) of the despread data allows for exploiting results provided in array signal processing and we introduce a new time delay estimator based on the maximum likelihood (ML) criterion. The new technique finds the global maximum of the compressed likelihood function in an efficient way using the importance sampling (IS) technique. Simulation results show that the new estimator provides very good performance in challenging cases of very closely-spaced delays even with a single antenna and transmitted symbol. The Cramer-Rao lower bound (CRLB) for multipath delays is also provided.