Study Intelligent Reflecting Surface Aided Simultaneous Wireless Information And Power Transfer System

With the rapid development of the fifth-generation wireless network and the Internet of Things,the number of low-power network connection devices increases rapidly,which makes the simultaneous wireless information and power transfer(SWIPT)technology attract much attention.In SWIPT systems,information and power are carried by the same radio frequency signal which not only achieves communication but also solves the problem of unsustainable power supply for low-power devices.Meanwhile,intelligent reflecting surface(IRS)technology can improve the frequency spectrum efficiency and realize more efficient communication by intelligently improving the wireless communication environment.This thesis combines SWIPT and IRS technologies,and makes an in-depth study of the improvement of transmission rate and energy efficiency in IRS-assisted SWIPT systems.The specific research content is as follows.First of all,in the IRS-assisted SWIPT system,different from the traditional scheme adopting single IRS,this paper uses double IRSs to reflect the information beam from the base station,and maximizes the information transmission rate by jointly optimizing the transmitting beamforming vector,power splitting ratio and the phase shift matrices at the IRSs.The corresponding optimization problem is a non-convex problem with multi-variable coupling.Hence,the alternative optimization method is utilized to obtain the solution.Numerical results show that adopting double IRSs to reflect signal achieves higher transmission rate than adopting single IRS.Secondly,in a single IRS-assited single-user SWIPT system,the energy-bearing signal is introduced into the system.By utilizing beamforming technology,the superposition of information signal beam and energy signal beam is sent at the base station,and the energy efficiency of the system is maximized by jointly optimizing the signal beams at the base station and the phase shift matrix at the IRS.This optimization problem is also a non-convex problem with multi-variable coupling,it is solved by alternative optimization method along with convex-concave procedure and successive convex approximation algorithm.Numerical results show that introducing energy-bearing signal and optimizing it jointly with the information-bearing signal and the phase shift can greatly improve the energy efficiency of the system.Finally,the previous research is extended to the IRS-assisted multi-user SWIPT system,where the base station tranmits the superposition of the information signal beam and the energy signal beam.This thesis maximizes the energy efficiency of the system by jointly optimizing the two beams and the phase shift matrix.The problem is still non-convex and multi-variable coupling.Therefore,the alternative optimization method is still utilized to decouple the variables.And during solving the sub-problems,Dinkelbach algorithm and semi-positive definite relaxation method are adopted.Numerical results show that the system with the proposed scheme is superior in energy efficiency to the system without IRS and that with IRS but without energy-bearing signal.