3D trajectory design and resource management for UAV-assisted multi-user two-way transmission system

With the advantages of mobility and high spectrum efficiency, the unmanned aerial vehicle (UAV) enabled two-way relay technology has practical significance in improving the network's throughput. This paper proposes a UAV-enabled two-way relaying framework, in which a UAV assists the exchange of information between multiple pairs of ground users (GUs) based on the physical layer network coding. We consider the probabilistic line-of-sight (LoS) links of the UAV-GU channels, and formulate an optimization problem with the goal of maximizing the overall rate of the two-way relaying network, by jointly optimizing the time-slots pairing, power allocation, and three-dimensional (3D) trajectory of the UAV. To address the formulated non-convex problem, we first propose an efficient offline algorithm that decomposes the problem into four low-complex subproblems, which are optimized iteratively by using the successive convex approximation (SCA) technique and the coordinate descent (BCD) method. To fully utilize the instantaneous channel state information (CSI) of the two-way relaying network during the flight of the UAV, we also propose a hybrid offline-online algorithm to further improve the performance of the network on the basis of the offline algorithm. The simulation results demonstrate that the proposed hybrid offline-online algorithm improves the network's rate by about 20 percent compared to the offline algorithm, and validate that the 3D UAV trajectory optimization is superior to boost the overall rate compared to the traditional two-dimensional (2D) UAV trajectory optimization.(c) 2022 Elsevier Inc. All rights reserved.