Trajectory Optimization And Resource Allocation For UAV Relaying Communications

Unmanned aerial vehicles(UAVs)have be envisioned to have many applications in wireless communications due to their unique abilities such as swift on demand deployment,high maneuverability,and high probability of achieving line-of-sight communication links with nodes on the ground.For UAV-assisted wireless communications,one of the main use cases is UAV relay,where UAVs are deployed as flying relays in the sky,providing long-distance wireless connectivity between remote users without reliable direct communication links.In the UAV relay communication system,appropriate designing the trajectory of the UAV relays and the resource allocation of the system can maximize the throughput of the system and thus improve the transmission performance.Based on two practical application scenarios,this thesis proposes joint trajectory and resource allocation optimization algorithms for UAV relay communication systems with different setups.The considered problem is non-convex,and thus is difficult to solve.Based on alternating optimization and successive convex optimization method,this thesis proposes an effective iterative algorithm to tackle the problem.The thesis includes the following aspects.(1)A multi-hop UAV relay communication system is studied,in which information is relayed from the source node to the destination node via multiple UAV relays in multi-hop way.Subject to mobility and collision avoidance constraints of the UAV,the information causal constraints of the multi-hop transmission,and the average and peak transmit power constraints of the source and the UAV relays,the end-to-end throughput is maximized.Computer simulation results have verified the effectiveness of the proposed algorithm,as compared to the three benchmark schemes.(2)A UAV relay communication system with limited backhaul is studied,in which information is relayed from the backhaul node to multiple users via a UAV relay.Subject to the UAV mobility constraints,the information causal constraints of the relaying transmission,the bandwidth constraints of the communication links,and the average and peak transmit power constraints of the backhaul nodes and the UAV relays,the weighted sum of the user rates is maximized.Computer simulation results show that the proposed algorithm significantly improves the weighted sum rate performance of the system,as compared to three benchmark schemes.