Acquisition of Orthogonal Modulated Signals in Rayleigh-Fading Channels

The problem of estimating propagation delays of the orthogonal modulated signals in asynchronous DS-CDMA system over fading channels is treated in this paper. The system under study resembles the uplink of an IS-95 system. The channel is assumed to be a time-varing flat Rayleigh-fading channel. The shortcoming of the sliding correlator as the standard method of code acquisition is examined and three robustified versions of delay estimators,namely whitened sliding correlator, subspace based delay estimator and MMSE based delay estimator are proposed to combat the multiple access interference (MAI) in the Rayleigh-fading channels. The performance of these estimators are compared with the computer simulations as a function of different parameters, e.g., the number of pilots, near-far resistance, signal to noise ratio,etc..