Research On Trajectory Optimization And Resource Allocation For UAV Multi-hop Relay Communication Systems

The unmanned aerial vehicle(UAV)relay system is one of the main use cases of the UAV communication.As an aerial relay,a UAV relay can provide an effective and reliable wireless connection between users far away from each other,expand the communication area,as well as improve the communication quality of the system.In the existing research,each hop of a UAV relay system usually uses the same bandwidth,which limits the communication performance of the system.This thesis considers a UAV multi-hop relay communication system where the bandwidth of each hop is adjusted dynamically.Specifically,in order to make full use of the limited communication resource and improve the communication performance of the UAV multi-hop relay system,this thesis jointly optimizes the channel bandwidth,transmit power and UAV flight trajectory.Two different communication environments for different user requirements are investigated separately.The main research contents and contributions of this thesis are summarized as follows.1.A UAV multi-hop relay system has been considered.Unlike the equal bandwidth allocation scheme in the existing research,which may limit the throughput of the multi-hop UAV relay system.This thesis dynamically optimizes the channel bandwidth of each hop to improve throughput.The performance of the system is maximized by optimizing the channel bandwidths,flight trajectories and transmit powers of the UAV relays.Specifically,the bandwidth of each hop link,the transmit power of each transmitting node,as well as the trajectories of the UAV relays are optimized to maximize end-to-end throughput.The considered optimization problem is non-convex and it is difficult to find the optimal solution.We propose an effective iterative algorithm to solve this problem suboptimally by using the alternating optimization and successive convex optimization methods.Computer simulation results show that as compared to other benchmark schemes,the proposed joint bandwidth,transmit power and trajectory optimization algorithm can achieve higher throughput.2.A cognitive UAV multi-hop relay communication system has been considered,where the UAV relays’ transmit powers,bandwidths,and trajectories are jointly optimized with the guarantee of protecting the primary users’ communications.The optimization is subject to the constraints of bandwidth,transmit power,UAV mobility,information causality,as well as the interference temperature of the primary users.The considered optimization problem is non-convex.In order to effectively solve this non-convex problem and reduce complexity,a heuristic algorithm is proposed to obtain the UAV relay flight trajectory,and then a sub-optimal method is used to find an approximate solution.As compared to other benchmark solutions,the proposed algorithm achieves higher throughput performance,which is shown by the computer simulation results.