A semiblind adaptive beamformer using a parallel pilot signal for WCDMA systems

A semiblind beamformer using a parallel pilot signal in the adaptive algorithm is investigated for wideband code-division multiple-access (WCDMA) systems. Although the pilot signal and traffic channels are designed to be transmitted using orthogonal codes in the downlink direction, time dispersion and frequency-selective fading in the transmission channel severely degrade this orthogonality at the receiver. As a result, the traffic signal of a target base station appears as interference coming from the same direction as the pilot signal, and causes poor performance of a pilot-only training-based beamformer. In order to mitigate this effect, we propose a semiblind beamforming algorithm that jointly exploits the pilot signal and the traffic channel signals. A modified version of the semiblind beamformer simultaneously suppresses self-interference and cochannel interference from other base stations. The proposed semiblind techniques outperform the conventional pilot-only approach as demonstrated via computer simulations.