Exploiting Device-to-Device Communications to Enhance Spatial Reuse for Popular Content Downloading in Directional mmWave Small Cells

摘要

With the explosive growth of mobile demand, small cells in millimeter wave(mmWave) bands underlying the macrocell networks have attracted intenseinterest from both academia and industry. MmWave communications in the 60 GHzband are able to utilize the huge unlicensed bandwidth to provide multiple Gbpstransmission rates. In this case, device-to-device (D2D) communications inmmWave bands should be fully exploited due to no interference with themacrocell networks and higher achievable transmission rates. In addition, dueto less interference by directional transmission, multiple links including D2Dlinks can be scheduled for concurrent transmissions (spatial reuse). With thepopularity of content-based mobile applications, popular content downloading inthe small cells needs to be optimized to improve network performance andenhance user experience. In this paper, we develop an efficient schedulingscheme for popular content downloading in mmWave small cells, termed PCDS(popular content downloading scheduling), where both D2D communications inclose proximity and concurrent transmissions are exploited to improvetransmission efficiency. In PCDS, a transmission path selection algorithm isdesigned to establish multi-hop transmission paths for users, aiming at betterutilization of D2D communications and concurrent transmissions. Aftertransmission path selection, a concurrent transmission scheduling algorithm isdesigned to maximize the spatial reuse gain. Through extensive simulationsunder various traffic patterns, we demonstrate PCDS achieves near-optimalperformance in terms of delay and throughput, and also superior performancecompared with other existing protocols, especially under heavy load.