Adaptive delay tracking in asynchronous multiuser CDMA systems

Abstract

Published work on multiuser code division multiple access (CDMA) receivers often assume knowledge of most system parameters. But in a mobile system, it is unreasonable to assume perfect knowledge of the propagation delays for each mobile user at all times since these delays change when mobile units move. Therefore a method for tracking propagation delays in a practical asynchronous CDMA system is needed. In this paper, we introduce a multiuser detector which is able to track time-varying delays directly, and converges in a stationary environment to the decorrelating detector. It has the advantage of being a blind algorithm, in the sense that it does not require the use of training sequences, and therefore represents a more practical approach than other adaptive multiuser detectors based on linear filtering.