Abstract
The problem of estimating propagation delays of orthogonally modulated signals in asynchronous DS-CDMA systems over time-varing Rayleigh-fading channels is treated in this paper. The maximum likelihood (ML) estimator and its unaffordable complexity for implementation are discussed. Some suboptimal solutions, e.g., whitened sliding correlator, MMSE estimator, subspace-based estimator, approximate ML estimator, are proposed to combat the multiple access interference in the fading channels. The performance of these estimators are evaluated with the computer simulations and shown to have better acquisition performance than the standard sliding correlator. They also achieve reduced computational complexity compared with the ML estimator, while maintaining an acceptable performance degradation.