Downlink beamforming for frequency division duplex systems

We propose a downlink beamforming method for an adaptive antenna system utilizing our new spatial covariance matrix transformation (SCMT). Therefore we first estimate the azimuthal power spectrum (APS) of the received uplink data for all users within the same physical channel. Afterwards we modify the APS of the user and the interference to prevent beampointing errors for the desired user and improve the nulling capabilities. Finally we construct the spatial covariance matrices at the downlink frequency and use this spatial information for antenna weight calculation. The approach is applicable for any adaptive antenna system with FDD. It outperforms direction of arrival based methods by at least 10 dB in SNIR. Applying the SCMT we approach the upper downlink limit within 4 dB in urban environments.