Optimization Scheme Of UAV Communication System Based On Reconfigurable Intelligent Surface

Unmanned Aerial Vehicle(UAV)mobile communication technology is considered to be a key technology for building an air-space-ground-sea integrated network in the sixth-generation mobile communication system.By mounting communication equipment and flexibly adjusting its position,UAV can facilitate the establishment of line-of-sight communication links and effectively combat channel fading,which has important practical significance.However,the performance of UAV communication systems is limited by the limited duration of service.Therefore,how to save the energy consumption of UAVs is an important challenge for future UAV communication.On the one hand,the flight power consumption can be reduced through the trajectory design of the UAV;on the other hand,the communication energy consumption can be reduced by mounting the communication equipment with less energy consumption on the UAV.Reconfigurable Intelligent Surface(RIS)is a nearly passive metasurface,which can actively change the wireless propagation environment and effectively improve the channel capacity and spectral efficiency of wireless communication systems.Therefore,the RIS can be used as the communication device of the UAV and optimized the trajectory of the UAV,saving the energy consumption of the UAV.This thesis mainly investigates the UAV communication system based on RIS,and designs RIS-assisted UAV Wireless Sensor Networks(WSN)communication system,RISassisted UAV wireless sensor network(WSN)communication system for the uplink and downlink information transmission scenarios of RISassisted UAV.The multi-UAV WSN communication system and the RISassisted UAV Orthogonal Frequency Division Multiple Access(OFDMA)communication system improve the system performance by optimizing the system model and algorithm design.The main work of this thesis is as follows:(1)Aiming at the scenario of RIS-assisted downlink information relay of a single UAV,a multi-user OFDMA-oriented RIS-assisted single UAV relay communication scheme is proposed.This scheme considers a RISassisted relay UAV to provide communication services for multiple users in a limited flight period.By jointly optimizing the time-frequency resource block allocation of the base station,the UAV trajectory and the RIS phase shift,the sum rate of the system is maximized.Simulation results show that,compared with the existing UAV relay communication methods,the proposed RIS-assisted UAV OFDMA communication method can significantly improve the system performance.(2)Aiming at the scenario of RIS-assisted UAV uplink information transmission,a RIS-based single UAV WSN data transmission scheme suitable for WSN scenarios is proposed.By utilizing the block coordinate descent method,Alternating Optimization(AO),and Successive Convex Approximation(SC A)related optimization techniques,a joint optimization of UAV trajectory,wake-up scheduling,wireless sensor network nodes energy and RIS phase shift matrix is proposed to maximize the average reachable rate of all wireless network nodes.A method to sense the average reachability rate of nodes.The simulation results verify that the proposed method can effectively improve the system performance in the scenario of UAV data transmission.(3)Aiming at the scenario of increasing sensor nodes and communication coverage,a multi-UAV WSN data transmission scheme based on RIS is proposed.The transmission scheme divides the data transmission task into different data transmission areas and completes the data transmission by the optimal UAV,thereby reducing the workload of a single UAV.By jointly optimizing multiple UAV trajectories,sensor nodes scheduling,and energy consumption and RIS phase shift design,the minimum data transmission rate of all sensor nodes is maximized for a limited period of time.Considering that the UAV is limited by the maximum speed and collision avoidance constraints,the original problem is a non-convex optimization problem that is difficult to solve.Transform and solve by introducing auxiliary variables,equivalent transformation and perfect squared difference formula.Simulation results verify the performance of the algorithm under different conditions,and the performance is significantly improved compared with the two benchmark schemes of the multi-UAV data transmission system without RIS assistance and the multi-UAV data transmission system with fixed RIS position.