Investigation of uplink and downlink performance of directivity controlled constrained beamforming algorithms for CDMA-based systems

The growth of wireless cellular communication based on DS-CDMA requires an increase in spectral efficiency. One promising way to do this is to deploy antenna arrays at the base station in order to perform space-time processing. This paper investigates the applicability of the blind DoA-based maximum directivity (MD) beamformer to CDMA-based systems in uplink and downlink. Our approach is based on DoA (direction of arrival) estimation and consequently does not require any pilot signal or training sequence. It is shown how knowledge of the DoA can be used to generate a most robust beam pattern in order to perform spatial filtering of multipath components in uplink and downlink. Robustness is achieved by maximising the directivity of the beam pattern as well as by generating broad nulls. Analytical results are presented and different aspects of directivity controlled beamforming are discussed.