A downlink beamforming in consideration of common pilot and phase mismatch

A new spatial covariance-based downlink beamforming method is proposed. This is suitable for a cellular mobile system with FDD duplexing method and a coherent PSK detection scheme where phase reference is made with respect to a common pilot signal. As opposed to the conventional method which implicitly assumes a dedicated pilot for phase reference, the common pilot-based method compromises performance due to the inevitable phase mismatch between the common pilot signal and the traffic signals at the mobile. Instead, it has an advantage that the channels (e.g., code channels in CDMA system) originally allocated for dedicated pilots can be saved and utilized to accommodate more traffic users. Moreover, its performance approximates that of the conventional method when angular spread gets smaller. Statistical characteristics of the proposed method in comparison with the conventional method are demonstrated through computer simulations to support the proposed algorithm.