  To develop a low-complexity multicast beamforming method for millimeter wave
communications, we first propose a channel gain estimation method in this
article. We use the beam sweeping to find the best codeword and its two
neighboring codewords to form a composite beam. We then estimate the channel
gain based on the composite beam, which is computed off-line by minimizing the
variance of beam gain within beam coverage. With the estimated channel gain, we
propose a multicast beamforming design method under the max-min fair (MMF)
criterion. To reduce the computational complexity, we divide the large antenna
array into several small-size sub-arrays, where the size of each sub-array is
determined by the estimated channel gain. In particular, we introduce a phase
factor for each sub-array to explore additional degree of freedom for the
considered problem. Simulation results show that the proposed multicast
beamforming design method can substantially reduce the computational complexity
with little performance sacrifice compared to the existing methods.
