Improving uplink adaptive antenna algorithms for WCDMA by covariance matrix compensation

This document addresses the estimation of long-term spatial covariance matrices. Many beamforming techniques are based on those matrices. In the past, they often have been assumed to be perfectly known, since long averaging processes can be applied. However, a systematic error is committed when using conventional methods for the estimation. We discuss the occurrence and the performance impact of this error. A simple compensation scheme is introduced which completely removes this error. Simulation results are presented for a multiuser WCDMA environment. For beamforming methods based on maximizing the signal power, gains of more than 2 dB are observed. The impact of the systematic error on SINR maximizing algorithms is minor, so that the improvement of the compensation scheme is slight. The results show that an estimate for the interference covariance is needed in all cases, either for compensating the signal covariance or for SINR based techniques.