User recognition and time delay estimation with near far robustness in asynchronous bandlimited DS-CDMA systems

An algorithm for user recognition and time delay estimation (UR/TDE) in an asynchronous bandlimited DS-CDMA system in a near far scenario is presented. The algorithm, which is based on the subspace concept, consists of preprocessing (UR) and postprocessing (TDE). In the preprocessing, by estimating the noise subspace, we propose a method to determine whether a user transmits a signal while requiring only a priori knowledge of the user's signature codes. If a user is active, an initial and coarse TDE is available, and the following postprocessing is needed, which is designed to get a fine estimation by an efficient search strategy for active users. Simulations are carried out. It is shown that the algorithm is near far resistant, the accuracy of TDE with noise subspace estimator outperforms TDE without it.