To keep pace with the rapid growth of mobile traffic demands, densedeployment of small cells in millimeter wave (mmWave) bands has become apromising candidate for next generation wireless communication systems. With agreatly increased data rate from huge bandwidth of mmWave communications,energy consumption should be mitigated for higher energy efficiency. Due tocontent popularity, many content-based mobile applications can be supported bythe multicast service. mmWave communications exploit directional antennas toovercome high path loss, and concurrent transmissions can be enabled for bettermulticast service. On the other hand, device-to-device (D2D) communications inphysical proximity should be exploited to improve multicast performance. Inthis paper, we propose an energy efficient multicast scheduling scheme,referred to as EMS, which utilizes both D2D communications and concurrenttransmissions to achieve high energy efficiency. In EMS, a D2D path planningalgorithm establishes multi-hop D2D transmission paths, and a concurrentscheduling algorithm allocates the links on the D2D paths into differentpairings. Then the transmission power of links is adjusted by the power controlalgorithm. Furthermore, we theoretically analyze the roles of D2Dcommunications and concurrent transmissions in reducing energy consumption.Extensive simulations under various system parameters demonstrate the superiorperformance of EMS in terms of energy consumption compared with thestate-of-the-art schemes. Furthermore, we also investigate the choice of theinterference threshold to optimize network performance.
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