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.