A New Transmit Beamforming Technique for Physical-Layer Multicasting in Cellular Downlink Systems

This paper investigates the design of physical-layer multicasting in the cellular downlink systems, where antennas at a base station are used to transmit a common signal to multiple single-antenna users. The central design problem of the physical multicasting is the search of the optimal beamforming vector that maximizes the multicast rate and has been known as an NP-hard problem in the literature. In this paper, a new method based on a two-user approximation is proposed for optimizing the beamforming vector. The method is shown to achieve a much higher multicast rate than the existing methods and provides an attractive tradeoff between performance and complexity, especially for the case of using a large number of antennas.