Optimal beam scheduling for multicasting in wireless networks

We consider the problem of efficient link-layer multicasting in wireless networks with switched beamforming antennas. The inherent tradeoff between multicasting and beamforming -- the broadcast advantage of low-gain omni-directional transmissions versus the high-gain but spatially restricted transmissions of beamforming antennas -- makes this problem especially challenging. In this paper, we design and evaluate optimal algorithms, and easy-to-implement greedy algorithms with performance guarantees, that generate and schedule efficient beam patterns for multicast transmissions. These algorithms are built upon the novel usage of composite beams that provide a knob to control the operating point of the tradeoff curve. This is in contrast to the sub-optimal usage of either purely directional or omni-directional beams by existing schemes. We further consider two models for composite beam pattern generation: one in which transmit power is (a) equally split, and (b) asymmetrically split between the constituent main lobes. A systematic evaluation, using real world traces obtained from measurements using an eight element switched beamforming antenna in an indoor office environment, indicates significant gains of about four folds over omni and two folds over prior art schemes.