Investigation Of Trajectory Design And Radio Resource Allocation Technologies In Unmanned Aerial Vehicle Communication Systems

With the development of wireless communication technologies,the fifth generation mobile communication systems have been widely used to meet the needs of various communication services.However,in areas where communication infrastructure is missing or damaged,and in hot spots where large-scale access causes communication congestion,communication coverage requirements are still difficult to meet.With the characteristics of mobility and flexibility,the unmanned aerial vehicles(UAVs)can quickly adjust the deployment location according to the dynamic changes of the network,establish a strong line-of-sight transmission link,and provide on-demand and reliable communication services.Therefore,the UAV communication systems have received extensive attention and research.As the key technologies of UAV communication,trajectory design and radio resource allocation directly affect the quality of service(QoS)of users.The current research on UAV trajectory design and radio resource allocation mostly focuses on static scenarios.In the dynamic scenario,the dynamic changes of air-to-ground channel and user distribution state lead to frequent switching of user access state,and it is difficult for UAVs to provide stable communication coverage.In order to solve the above problems,this thesis mainly studies the trajectory design and radio resource allocation technologies in dynamic scenarios.The main work and innovations are as follows:(1)In the view of the limited communication performance and the difficulty for UAVs to provide stable coverage in dynamic scenarios,a joint optimization algorithm of trajectory design and power allocation for maximizing throughput is proposed.Firstly,considering the requirement of QoS,the constraints of user access and UAV mobility,a joint optimization is performed for user access,power allocation,and trajectory design to maximize the throughput.Secondly,the complexity and convergence of the proposed algorithm are analyzed and proved.Finally,the effectiveness of the algorithm is verified by simulation.The simulation results show that the proposed algorithm can significantly improve the throughput performance compared with the benchmark solution.(2)Considering the problem of limited coverage of a single UAV,a joint optimization algorithm of trajectory design and power allocation for multi-UAV communication systems based on swap-enabled matching algorithm is proposed.With the objective of maximizing the throughput of multi-UAV communication systems,a joint optimization problem of user access,power allocation and trajectory design is constructed to meet the requirement of QoS and the constraints of multi-UAV obstacle avoidance.To solve the complex non-convex optimization problem,this thesis decomposes it into three subproblems based on the idea of block coordinate descent,and solves them iteratively.Specifically,this thesis proposes a swap-enabled matching algorithm to solve the user access subproblem,derives a closed-form solution for the multi-UAV power allocation subproblem based on logarithmic approximation and Lagrange dual algorithm,and transforms the multi-UAV trajectory design subproblem into a convex optimization problem by successive convex approximation algorithm.The simulation results show that the algorithm can effectively improve the throughput performance of muti-UAV communication systems under the premise of meeting the differentiated QoS requirements of users.