  With the exponential growth of mobile data, there are increasing interests to
deploy small cells in millimeter wave (mmWave) bands to underlay the
conventional homogeneous macrocell network as well as in exploiting
device-to-device (D2D) communications to improve the efficiency of the
multicast service that supports content-based mobile applications. To
compensate for high propagation loss in the mmWave band, high-gain directional
antennas have to be employed, while it is critical to optimize multicast
service in order to improve the network performance. In this paper, an
efficient multicast scheduling scheme is proposed for small cells in the mmWave
band, called MD2D, where both D2D communications in close proximity and
multi-level antenna codebook are utilized. Specifically, a user partition and
multicast path planning algorithm is proposed to partition the users in the
multicast group into subsets and to determine the transmission node for each
subset, so as to achieve optimal utilization of D2D communications and
multi-level antenna codebook. Then a multicast scheduling algorithm schedules
the transmission for each subset. Furthermore, in order to optimize the network
performance, the optimal choice of user partition thresholds is analyzed.
Performance evaluation demonstrate that the MD2D achieves the best performance,
in terms of network throughput and energy efficiency, compared with other
existing schemes. MD2D improves the network throughput compared with the
second-best scheme by about 27\%.
