Downlink Beamforming for FDD Systems with Precoding and Beam Steering

Abstract

A practical downlink beamforming technique is proposed for an FDD system to mitigate the interference and enhance the SINR performance at the mobile user. Most of the closed loop beamforming techniques require a large number of feedback bits that make them impractical for standards such as LTE where only a limited number of feedback bits is available in the feedback channel. Therefore, a downlink beamforming scheme is introduced at the base station where the antenna elements are grouped into a collection of ports. We propose to apply codebook beamforming over the ports and perform beam steering at each port to further direct the transmitted energy and reduce the interference to the rest of the users. Simulation results reveal that, with significantly fewer number of feedback bits, our proposed technique outperforms diversity transmission scheme, especially in the low SNR regime, in a system with the same total number of antenna elements where a larger number of feedback bits is required.