Single-user timing estimation in DS-CDMA mobile communication systems using a receiving antenna array

The synchronization of a desired user transmitting a known training sequence in a direct-sequence (DS) asynchronous code-division multiple-access (CDMA) system is addressed. This is an essential issue in mobile communication systems because of two reasons. First, it has been shown that the ability to achieve synchronization in a near-far environment may limit the capacity of those systems. In the second place, most multiuser detectors require precise knowledge of the users ' timings, powers and carrier phases in order to work properly. We propose a synchronization technique that makes eÆcient use of the structure of the signals in both the space and time domains, employing usual lengths of the training sequence. A frequency-nonselective slowly fading channel is assumed for the estimator derivation. Finally, it is shown that the use of space-time diversity in the receiver is indispensable for the correct synchronization in heavily loaded systems and in the presence of external interference