On multicast beamforming and admission control for UMTS-LTE

Transmit beamforming for physical layer multicasting is emerging as an appealing transmission modality for next-generation cellular wireless systems, notably UMTS-LTE. Optimal design of the transmit beamformer(s) from a quality of service perspective is a hard computational problem; however, convex approximation tools have been shown to yield high-quality approximate solutions. Recently, Lozano proposed a particularly simple adaptive multicast beamforming algorithm that aims to serve a certain percentage of users. In parallel, convex approximation algorithms were developed for the more general problem of joint co-channel multicast beamforming and admission control. In this paper, we focus on the important (in view of recent standardization activity) special case of a single multicast group, and put the two approaches to the test. Through simple examples, we pinpoint issues regarding convergence of Lozano's algorithm. In numerical experiments with measured channel data, we show that a convex approximation approach is preferable performance- wise. At the same time, we find merits in the simplicity of Lozano's approach, and suggest a way to improve its performance.