Energy Efficiency Optimization Of Communication System Based On Reconfigurable Intelligent Surface

The universal popularization of 5G has brought a new era of wireless communication construction boom to the world.Advanced transmission technology has brought users faster and faster communication experience,but also brought many largescale energy consumption problems contrary to the green economy.The Reconfigurable Intelligent Surface(RIS)is a new and revolutionary technology,which can configure the wireless communication environment by integrating a large number of low-cost passive circuit elements on the plane,thereby improving the performance of wireless communication systems.This dissertation mainly focuses on the energy efficiency of wireless communication system based on reconfigurable intelligent surface.On the one hand,in the wireless communication system,dual RIS are used to cooperate with each other to optimize the total energy efficiency of system users.On the other hand,simultaneous transmission and reflection reconfigurable intelligent surfaces(STARRIS)is introduced to ensure user fairness by optimizing the minimum energy efficiency of users in the system.Aiming at the optimization of total energy efficiency and minimum energy efficiency of system users in wireless communication system based on reconfigurable intelligent surface,the main work of this dissertation is as followed:(1)Aiming at the problem of user total energy efficiency optimization in wireless communication system,a model of multi-user wireless communication system assisted by double reconfigurable intelligent surface was established.Based on the joint optimization of base station transmitting power distribution and intelligent surface module phase shift planning,the problem of maximizing the total energy efficiency of the system is proposed.Aiming at the challenging total user energy efficiency optimization problem,the non-convex maximization problem is transformed into two equivalent sub-problems based on the mean square error(MSE)method.The transmitting beamforming matrix and intelligent surface phase shift matrix are optimized by Lagrange method and semidefinite relaxation(SDR)technique respectively.Finally,alternating maximization strategy is used to solve the intelligent surface phase shift planning optimization with fixed power beamforming and the base station power allocation optimization with fixed surface phase shift.(2)Aiming at the user optimization problem of minimum energy efficiency in communication system,this dissertation proposes a cooperative communication downlink multi-user communication model based on simultaneous transmission and reflection intelligent surface.According to the location of users and STAR-RIS,users are divided into reflected signal users and transmitted signal users.Solve base station beamforming and surface phase shift planning problems to optimize minimum energy efficiency.Aiming at the non-convexity of the target problem,the original problem is divided into two sub-problems,and the alternating optimization method(AO)algorithm is applied to optimize the two sub-problems iteratively.Firstly,the nonconvex optimization problem is transformed into convex form by fractional programming method,convex function difference(DC)programming and optimization minimization(MM)method.Then,the continuous convex approximation(SCA)is used to solve the convex problem that can substitute the original problem,and the semidefinite programming(SDP)is used to solve the sub-problem of the simultaneous transmission and reflection intelligent surface phase shift fixed condition.A sequence constraint relaxation algorithm is used to solve the optimization problem of joint beamforming with transmission and reflection.