Energy Efficient Trajectory Design for Fixed-Wing UAV Enabled Two-Way Amplify-and-Forward Relaying

paper investigates optimal trajectory design for an unmanned aerial vehicle (UAV) enabled two-way relaying, where a fixed-wing UAV employs an amplify-and-forward protocol to assist data exchange between two ground users. With the aim of maximizing the system energy efficiency (EE), an optimization problem corresponding to the UAV's trajectory design is formulated, where the UAV's initial/final speed and location constraints in addition to the acceleration constraint of the UAV are considered. The initial optimization problem is intractable due to its non-concave objective function and nonconvex constraints. To this end, slack variables are introduced, and then the successive convex approximation (SCA) method and the Dinkelbach's algorithm are applied to transform it into a convex optimization problem, which is solved by a proposed iterative algorithm. Simulation results show that the proposed iterative algorithm converges quite quickly, and with the trajectory design, the two-way UAV relaying is much more superior than the compared benchmark schemes in terms of EE.