Tethered UAV-based Communications for Under-connected Near-shore Maritime Areas

Maritime activities, including fisheries, maritime transportation, and surveillance, are expected to transfer multimedia data to remote users, which requires the establishment of reliable backhaul communication links from the marine vessels to the core network. Tethered Unmanned Aerial Vehicles (UAVs), which are connected to a sufficient power source and high-data-rate optical fiber, can be adopted in near-shore maritime communications for coverage extension. In this paper, we investigate the use of tethered UAVs in three scenarios, where the UAV can be either installed on the shore, tethered to the ship, or both. To study the coverage performance, we examine the outage probability in each scenario for both uplink and downlink, and we optimize it to derive the optimal UAV placement. Although the optimization problem, in terms of the UAV tether length and the angle it makes with the horizontal, is non-convex, we formulate and solve a simplified problem where the outage probability is minimized with respect to the channel gain to obtain the optimal UAV position. The simulation results show that using two UAVs, one onshore and one on the ship, provides more reliable connectivity on the uplink and downlink compared to the other two scenarios.