  Millimeter-wave (mmWave) communication plays a vital role to efficiently
disseminate large volumes of data in beyond-5G networks. Unfortunately, the
directionality of mmWave communication significantly complicates efficient data
dissemination, particularly in multicasting, which is gaining more and more
importance in emerging applications (e.g., V2X, public safety). While
multicasting for systems operating at lower frequencies (i.e., sub-6GHz) has
been extensively studied, they are sub-optimal for mmWave systems as mmWave has
significantly different propagation characteristics, i.e., using the
directional transmission to compensate for the high path loss and thus
promoting spectrum sharing. In this paper, we propose novel multicast
scheduling algorithms by jointly exploiting relaying and spatial sharing gains
while aiming to minimize the multicast completion time. We first characterize
the min-time mmWave multicasting problem with a comprehensive model and
formulate it with an integer linear program (ILP). We further design a
practical and scalable distributed algorithm named mmDiMu, based on gradually
maximizing the transmission throughput over time. Finally, we carry out
validation through extensive simulations in different scales and the results
show that mmDiMu significantly outperforms conventional algorithms with around
95% reduction on multicast completion time.
