3D Trajectory Optimization for Fixed-Wing UAV Communications With Full UAV Dynamics

Unmanned Aerial Vehicle (UAV)-aided communication is a promising technology for future wireless systems by providing communication access from the sky. However, existing mobility models for UAV-aided communication with fixed-wing UAVs do not characterize the full UAV dynamics that needs to consider the forces manipulating the UAV as the model inputs. As a result, the planned trajectories are usually a sequence of non-smooth piece-wise line segments which are difficult to implement in practice for fixed-wing UAVs. To tackle this problem, a control-based design framework is proposed in this paper for fixed-wing UAVs by modeling their realistic dynamics in the three-dimensional (3D) space. By leveraging the state-space model, the trajectory optimization problem for fixed-wing UAV communication is formulated as a state-constrained optimal control problem, subject to the practical constraints on the UAV's flying speed, altitude and flight path angle. A solution method based on control parametrization is proposed, which converts the original infinite-dimensional optimization problem into a new finite-dimensional nonlinear program. With the proposed method, a smooth 3D UAV trajectory is obtained, which is easy to realize in practice by directly implementing the designed control variables such as thrust force and lift force. Extensive numerical examples are provided to illustrate the effectiveness of the proposed solution as compared to existing solutions.