Spatial filtering for WCDMA: A semi-blind subspace approach

This paper proposes a spatial filtering technique for the reception of pilot-aided multi-rate multi-code DS/CDMA systems such as WCDMA. These systems introduce a code-multiplexed pilot sequence that can be used for the estimation of the filter weights, but the presence of the traffic signal (transmitted at the same time as the pilot sequence) corrupts that estimation up to the point that it might render the filter completely useless. The traffic and pilot signals are designed to be orthogonal, but the frequency selectivity of the channel degrades this orthogonality in the received signal. Here we propose a semi-blind technique that eliminates the self-noise caused by the code-multiplexing. We derive analytically the asymptotic performance of both the training-only and the semi-blind techniques and compare it with the actual simulated performance. It is shown, both analytically and via simulation, that high gains can be achieved with respect to training-only based techniques.