Adaptive symbol and parameter estimation in asynchronous multiuser CDMA detectors

Existing multiuser code division multiple access (CDMA) detectors either have to rely on strict power control or near-perfect parameter estimation for reliable operation. In this paper, a novel adaptive multiuser CDMA detector structure is introduced. Using either an extended Kalman lter (EKF) or a recursive least squares (RLS) formulation, adaptive algorithms which jointly estimate the transmitted bits of each user and individual amplitudes and time delays may be derived. The proposed detectors work in a tracking mode after initial delay acquisition is accomplished using other techniques not discussed here. Through computer simulations, we show that the algorithms perform better than a bank of single-user receivers in terms of near-far resistance. Practical issues such as the selection of adaptation parameters are also discussed in some detail.