Multiple-access interference-resistant acquisition for band-limited CDMA systems with random sequences

The problem of estimating the propagation delay of a new user in a coded band-limited DS/CDMA system in the presence of multiple access interference (MAI) is considered. MAI-resistant acquisition schemes are developed for a general CDMA system without the constraint that the spreading sequences of the users repeat every symbol period. It is assumed that the spreading sequences and delays of the interfering users are known. However, knowledge of their amplitudes, which would need estimation, is not assumed, and their unreliable code-symbol estimates are not used. Under this scenario, acquisition schemes are derived based on the maximum-likelihood (ML) criterion. The performance of an approximation to the ML scheme is analyzed using Gaussian approximations and by assuming that the chip boundaries of the new user are known a priori. Simulations show that the analysis is reasonably accurate for parameters in the realm of practical interest.