Research On Multi-user MISO Beamforming Assisted By Intelligent Reflecting Surface

With the popularity of the Internet of Things,the number of user equipments groups is increasing,and the traffic demand of communication is growing rapidly.This makes the contradiction between the increasing communication demand and the maximum capability of communication system increasingly prominent.How to further improve the channel capacity of wireless communication has become an urgent problem to be solved.As one of the key technologies of 6G in the future,intelligent reflecting surface(IRS)assisted wireless communication technology is considered to be an effective scheme to improve the communication data rate.This scheme can not only improve the communication data rate of the system,but also greatly reduce the hardware energy consumption and communication cost,so it has attracted the attention of the industry.In this thesis aiming at improving the channel capacity of multiple input single output(MISO)users,the beamforming design scheme assisted by multiple IRS and the beamforming design scheme based on IRS location optimization are studied respectively for single user and multi-user scenarios.The main contents and contributions are as follows:(1)In order to further improve the communication capacity of single user in MISO scenario,a scheme of multi IRS cooperative downlink transmission is proposed.By deploying multiple IRS between the base station and the user,and jointly optimizing the beamforming vector parameters of the base station and the IRS,the useful signals of the user's receiver can be enhanced and the interference signals can be effectively suppressed.Considering the fairness of users,the joint optimization of active beamforming vector and IRS reflected beamforming vector is established to maximize the data rate.Then an optimization algorithm based on dichotomy and alternating iteration algorithm is proposed to solve the problem.Simulation results show that the proposed multi-IRS assisted communication scheme can effectively improve the single user communication capacity in MISO scenario.(2)In order to further improve the multi-user communication capacity in MISO scenario,a joint optimization scheme of IRS position and beamforming vector is proposed.Under the assumption of strong Los channel,the communication quality can be further improved by adjusting the position of IRS.Furthermore,considering the fairness of users,the joint optimization of IRS location,active beamforming vector of base station and transmit beamforming vector of IRS is established to maximize the data rate.The alternating iterative optimization algorithm is used to solve the problem.Finally,the simulation results show that the location optimization can improve the communication capacity.