Coordinated Trajectory Planning for Efficient Communication Relay Using Multiple UAVs

This paper investigates the use of small UAVs as communication relay nodes for expanding communications links and improving communication quality, primarily for a fleet of ground or navy vessels. An airborne relay in ground/maritime space can effectively connect to units operating over the horizon, beyond normal communication range, or under limited satellite communication environments. For efficient UAV communication relay, this paper firstly deals with the UAV deployment for stationary communication nodes, which finds the fixed optimal location of UAVs to improve the connectivity of a wireless network. Then, considering movements of vessels and constraints of the fixed-wing UAV in a dynamic environment, this paper proposes a decentralised nonlinear model predictive trajectory planning strategy. By exploiting motion estimates of vessels and states of UAVs, the trajectory planning algorithm finds a control input sequence over a certain time horizon, which optimises network connectivity. Numerical simulations are performed with different number of UAVs for both stationary and manoeuvring naval vessels to verify the feasibility and benefit of the proposed approach.