Research On Joint Active And Passive Beamforming Techniques Of Intelligent Reflecting Surface-Assisted Wireless Communication Systems

Nowadays,the rapid development of the Internet of Things has led to a dramatic increase in the number of network-connected devices and energy consumption,and how to design energy-efficient wireless communication technologies has become one of the research hotspots.The emergence of intelligent reflecting surface(IRS)provides a new idea to solve the energy consumption problem of devices,which can intelligently modify the wireless propagation environment to improve the channel gain of the system and effectively reduce the energy consumption of the system,and has a broad application potential in wireless communication systems.Against this background,this thesis deeply investigates the joint active and passive beamforming techniques for IRS-assisted wireless communication systems.The main contributions of this thesis are listed as follows.Firstly,the wireless communication scenario of IRS-assisted active user is considered,including multi-antenna base station,multiple IRSs and active user,where the IRSs are used to reflect the base station signal to the active user to complete the transmission of effective information.In this regard,a transmission rate optimization scheme based on IRS selection and joint active and passive beamforming is proposed to maximize the information transmission rate of the system as the optimization objective,and to jointly design the active and passive beamforming by an alternating optimization algorithm under the premise of the restricted transmit power of the base station,and to select a suitable IRS to provide a virtual auxiliary link.The simulation results show that the proposed scheme is significantly better than the traditional polling scheduling scheme and the non-IRS-assisted transmission scheme in terms of information transmission rate.Secondly,the IRS-assisted simultaneous wireless information and power transfer communication scenario is considered,including multi-antenna base station,IRS and passive node,where the IRS is used to reflect the base station signal to passive node to complete the simultaneous transmission of energy and information.In this regard,a transmit power optimization scheme based on IRS joint active and passive beamforming is proposed.With the system’s base station transmit power minimization as the optimization objective,the active and passive beamforming is jointly designed by an alternating optimization algorithm under the premise that the signal-to-noise ratio of passive node’ information decoding and the energy harvesting for maintaining information interaction are limited.The simulation results show that with the increase of the number of IRS reflective elements,the transmit power of the base station can be significantly reduced while ensuring the communication quality of service,and it is superior to the random phase adjustment scheme.Finally,the simultaneous wireless information and power transfer communication security scenario with IRS-assisted passive node is considered,including multi-antenna base station,IRS,passive node,and eavesdropping node,where IRS is used to reflect the base station signal to passive node to complete the transmission of energy and confidential information,and the presence of eavesdropping node to attack confidential information transmission.In this regard,a secrecy rate optimization scheme based on IRS joint active and passive beamforming is proposed.With the objective of maximizing the secrecy rate of the system,the active and passive beamforming vectors are jointly designed with the help of convex optimization tools and alternating optimization algorithms under the premise of maximum eavesdropping information rate of the eavesdropping node,energy harvesting for maintaining information interaction and restricted transmitting power of the base station.The simulation results show that the proposed optimization scheme significantly improves the secrecy rate of the IRS-assisted simultaneous wireless information and power transfer communication network compared with the random phase adjustment scheme.