DS-CDMA SYNCHRONIZATION IN TIME-VARYING FADING CHANNELS

Herein, the problem of estimating propagation delays of the transmitte d signals in a direct-sequence code-division multiple access (DS-CDMA) system operating over fading channels is considered. Even though this study is limited to the case when the propagation delays are fixed du ring the observation interval, the channel gain and phase are allowed to vary in time. Special attention is given to the near-far problem wh ich is catastrophic for the standard acquisition algorithm. An estimat or based on subspace identification techniques is proposed, and the Cr amer-Rao bound, which serves as an optimality criterion, is derived. T he Cramer-Rao bound is shown to be independent of the near-far problem , which implies that there is no fundamental reason for propagation de lay estimators to be near-far limited. Furthermore, the proposed algor ithm is experimentally shown to be robust against the near-far problem .