UAV-Enabled Accompanying Coverage for Hybrid Satellite-Uav-Terrestrial Maritime Communications

Despite of constantly-developing satellites and terrestrial fifth generation (5G) communications, there is still a large gap for maritime broadband coverage. In this paper, we explore the potential gain of unmanned aerial vehicles (UAVs) for maritime communications. A hybrid satellite-UAV-terrestrial network is considered, where the UAV is employed to offer an accompanying coverage for mobile ships. We optimize both the trajectory and transmit power of UAV to maximize the minimum of ship's achievable rate. Different from previous studies, we consider a typical composite channel model containing both large-scale and small-scale fading, to cope with the practical propagation environment. Moreover, we assume only the large-scale channel state information (CSI) is known for optimization, because the dynamic small-scale fading cannot be obtained before UAV's flight, whereas the large-scale CSI can be estimated according to the position information of ships. Under this context, an optimization problem is formulated, subject to constraints on UAV's kinematics and communication limitation. We solve the problem which is proved to be non-convex by problem decomposition, successive convex optimization and bisection searching tools. Simulation results have corroborated the superiority of the proposed accompanying coverage of UAV.