Channel allocation and downlink beamforming in an SDMA mobile radio system

On the downlink of an SDMA mobile radio system, co-channel interference has to be kept down by beamforming. In this paper two DOA-based beamforming approaches are presented minimizing array signal power while maintaining given signal-to-noise-and-interference ratios for all users. The linear approach is computationally cheap, so that it is suited for channel allocation as well, quickly evaluating the spatial separability of a specific mobile radio scenario. The nonlinear algorithm yields optimum results but only converges quickly, if provided with a good starting point. Therefore, its basic application is burst-to-burst updating of the beamformer