CDMA-synchronization: multi-user performance at single-user complexity

In this paper we present a large sample decoupled maximum likelihood time-delay estimator for multi-user CDMA systems in the presence of unknown and arbitrarily colored noise. The high-dimensional optimization problem is decoupled into the corresponding single-user problems, with lower dimensionality, where the dimensions correspond to the number of paths for the user of interest. This means that multi-user performance is achieved at the cost of a single-user estimator. The asymptotic statistical performance of the estimator is derived and compared with the Cramer-Rao bound and the estimator is shown to be asymptotically statistically efficient. Numerical simulations are also included to corroborate the analysis.