| Unmanned aerial vehicles(UAVs)have been widely deployed in various wireless communication scenarios as aerial base stations with flexible deployment,line-of-sight wireless transmission and high maneuverability advantages,which can cause problems in special areas(such as buildings,trees,etc.)channel congestion is a problem that cannot be ignored in communication systems.As a passive device,the intelligent reflective surface is proposed to bypass obstacles and play a role in the UAV communication system and enhance communication.This paper mainly studies the performance scheme design of using intelligent reflecting surface to assist UAV to establish air-to-ground communication system,and improving communication quality through joint optimization of UAV trajectory and intelligent reflecting surface passive beamforming,the details are as follows:(1)Aiming at the multi-intelligent reflecting surfaces-assisted UAV communication,a design scheme to maximize the energy efficiency of the communication system is proposed.Considering the phase shift of the intelligent reflecting surfaces and the UAV’s trajectory constraints,a nonlinear and multivariable coupling energy efficiency maximization problem is proposed.In order to solve the non-convex energy efficiency optimization problem,the signals of different paths are coherently combined at the user by fixing the UAV’s trajectory,and the closed expression of the optimal phase shift of the intelligent reflecting surface is derived.The continuous beamforming matrix is used for the intelligent reflecting surface.The successive convex approximation method solves the flight trajectory of the UAV,and obtains the high energy efficiency of the UAV communication system.In addition,related joint optimization algorithms are given,showing that the UAV’s trajectory presents different flight modes when the intelligent reflecting surface is deployed.(2)Aiming at the the multi-intelligent reflecting surfaces-assisted UAV multi-user communication system,a design scheme for maximizing users sum rate is proposed.Consider deploying intelligent reflecting surfaces to provide services for users in the UAV communication network.In order to rationally use spectrum resources to improve communication resources,to achieve the purpose of maximizing users sum rate,jointly optimizing the phase shift of intelligent reflecting surfaces and the UAV’s trajectory constraints.The optimization problem involves a non-convex problem that is difficult to obtain an optimal solution.A low-complexity algorithm is proposed to obtain the solution of the joint design problem.First,the phase shift sub-problem is solved based on the Riemann conjugate gradient method,and then used the successive convex approximation method is used to solve the trajectory design sub-problem.Compared with the simulation results without the intelligent reflecting surface-assisted communication scheme,the joint design algorithm achieves better performance.(3)Aiming at the intelligent reflecting surfaces-assisted UAV communication system based on the deep deterministic policy gradient algorithm,considering the UAV’s beamforming,the phase shift of the intelligent reflecting surface and the UAV’s trajectory constraints,a design for maximum user sum rate is proposed.When solving multi-variable coupling and rate optimization problems,an intelligent decision-making method that can learn independently and has strong generalization ability is used for joint optimization.Joint optimization of constrained variables using method based on the deep deterministic policy gradient algorithm in deep reinforcement learning,the constraint variables are jointly optimized,and the problem is transformed into a Markov decision process.First,a model of the action space is constructed based on the external real-time environment state and the joint optimization variables,and then based on the sum rate objective function design reward function,and finally verify the effectiveness and feasibility of the algorithm. |
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