An iterative near-far resistant algorithm for joint parameter estimation in asynchronous CDMA systems

An asynchronous multiuser communication system is considered where K users share an additive white Gaussian channel. Binary phase-shift keying and direct sequence spread spectrum signaling is employed for data modulation. In this work, we propose an algorithm for near-far resistant joint parameter estimation and data detection for multiuser systems: the successive interference cancellation scheme employs a stochastic approximation (SA) method for estimating delays, the expectation-maximization (EM) algorithm for obtaining carrier phase and amplitude estimates, and a multistage algorithm for data detection. Using an SA-scheme, the complexity of the receiver structure can be considerably reduced. Monte Carlo simulations illustrate the capability of the system to obtain parameter estimates even in the presence of strong interferers such that the near-far effect can be overcame.