Near-far resistant channel estimation for the DS-CDMA uplink

Joint detection is a means to overcome the near-far problem and to improve the spectrum efficiency in the DS-CDMA uplink in terrestrial mobile communications. Detection requires knowledge of the channel parameters which are distinct for every user. Due to inter-user interference (IUI) conventional estimation of these parameters is unreliable if some signals are weaker than others. Consequently, the performance of a subsequent joint detector gets degraded. We study a new method to jointly estimate these parameters for fading multipath channels. The joint channel estimator uses the RAKE outputs at the symbol rate. These samples are multiplied by pilot or detected symbols. Before low-pass filtering a decorrelator removes the IUI. The resulting channel parameter estimates are shown to be independent of the power levels of the interfering users and therefore near-far resistant. Simulation results evaluating the mean-square error are given for the conventional and the proposed joint estimation of multipath channels with Doppler fading. We also investigate the influence of the estimator on the detector performance