I. Introduction
Thanks to the highly flexibility contrast to conventional base station, unmanned aerial vehicles (UAVs) are given strong expectations in 5G wireless networks [1]. Now, UAV has been widely adopted as aerial access points to provide communication services for Internet of Things (IoT) devices. For example, UAV as aerial relay nodes for dynamic routing, while mitigating the impact of occlusions on the terrestrial links [2]. However, in some scenarios, like video stream services and monitoring tasks [3], the data rate requirements cannot be satisfied with conventional communication technologies. Fortunately, Millimeter-Wave (MmWave) communications with multi-gigahertz bandwidth availability enables high speed data rate transmission for UAV [4]. UAV MmWave communications with flexible coverage, low latency and sufficient bandwidth, has been extensively studied [5].