A novel downlink beamforming scheme for FDD/SDMA systems

Abstract

When beamforming is employed in the uplink without feedback channel, the beam pattern for the downlink can be generated using the weight used for uplink beamforming. However, this scheme may result in significantly performance degradation in the frequency division duplex (FDD) because of carrier frequency offset between the uplink and downlink. In this paper we propose a novel downlink beamforming algorithm based on least square method with some constraint points which have same gain in the up/downlink beam pattern. From the constraint points, we generate downlink weight and also propose how to choose the constraint points in order to satisfy the desired signal-to-interference power ratio. Simulation results show that the proposed method can sufficiently reduce the interference from other space division multiple access (SDMA) signals, providing interference-free spatial channel.