Research On Multi-parameter Collaborative Optimization Of UAV Links Based On Reconfigurable Intelligent Reflective Surfac

In wireless communication systems for urban environments,sudden services such as traffic dispatch,disaster relief,emergency communications,and large events are prone to traffic overload on ground facilities,leading to information congestion.Unmanned aerial vehicles(UAVs),as aerial relays,have become an important technology to expand the dimension of metropolitan communication networks due to their flexibility,ability to quickly establish communication links with ground equipment,and high efficiency of information transmission.However,the introduction of UAV relays can be affected by the uncertain urban environment,which in turn leads to a significant suppression of data transmission security,and the increase in tasks can cause a decrease in UAV communication transmission efficiency.In this paper,reconfigurable intelligent surface(RIS),which has the advantages of low cost and outstanding reflective capability,is introduced in the air-ground cooperative network to solve the problems of weak security performance and low transmission efficiency of the air-ground network in urban environments.To this end,based on the RIS-based UAV air-ground cooperative communication network in the urban environment,this study constructs a composite channel model based on Rayleigh fading and Rician fading,proposes an alternating optimization(AO)algorithm based on semidefinite relaxation and successive convex approximation,and solves the safe transmission problem of sensitive tasks in RIS-assisted air-ground channels.A joint optimization algorithm based on the alternating direction method of multipliers(ADMM)is also designed to optimize the effective throughput of the multiuser communication system for non-sensitive tasks.For the scenario that there are eavesdroppers in the RIS-assisted UAV communication system in sensitive tasks,an eavesdropping channel model for urban environment is built,and the influence of the equipment’s own hardware and external environment on the security performance of the UAV communication system is fully considered,and the criterion of maximizing the secrecy rate of the air-ground communication network is proposed based on convex optimization theory,combining the UAV trajectory,RIS passive beam assignment and power control based on convex optimization theory,and proposes an AO algorithm that combines UAV trajectory,RIS passive beam assignment and power control to achieve secure transmission in air-ground networks.In order to solve the problem of non-convex optimization caused by the coupling of multiple parameters,an ADMM-based optimization algorithm is designed to solve the non-convex optimization problem.A simulation environment is built to verify the performance of the proposed algorithm.The experimental results demonstrate the relationship between the secrecy rate and the number of reflective elements,RIS height,UAV height,UAV transmit power,and other factors of the alternate optimization algorithm designed for the physical layer security of the RIS-assisted communication system in this study;moreover,the experimental results show that the proposed joint optimization algorithm for multi-user service significantly outperforms similar algorithms in terms of performance such as average data transmission rate,energy consumption,and so on.Moreover,the proposed optimization algorithms in both scenarios provide important technical support for the rapid establishment and highquality transmission of information in future temporary communication networks.