Research On Resource Allocation Optimization Of Intelligent Reflecting Surface Assisted SWIPT System

In recent years,as the life expectancy of wireless Internet of Things devices has become higher and higher,continuous power supply for wireless Internet of Things devices has become a key issue in practice.So as to solve the problem,Simultaneous Wireless Information and Power Transfer(SWIPT)is proposed,which can transmit information and energy wirelessly together.But the long-distance transmission can make wireless Io T devices very inefficient.The intelligent reflecting surface(IRS)can intelligently reconstruct the propagation environment of the wireless signal by controlling the coefficient of the reflection unit integrated on it,thereby improving the performance of the wireless communication network and reducing the energy consumption of the wireless communication.This makes IRS a very effective solution to the fundamental performance constraints of the SWIPT system.First of all,this paper considers a passive IRS-assisted non-orthogonal multiple access(NOMA)SWIPT multi-user cooperative system.As a candidate technology for 6G,IRS has the characteristics of low cost,low energy consumption,and high reliability.In addition,NOMA has the advantages of large-scale access,high spectral efficiency and low transmission delay.Therefore,applying IRS to NOMA network can further improve spectrum efficiency and reduce system cost.At the same time,because the user at the edge of the cell is relatively far away from the transmitter,the quality of the received signal becomes poor.Therefore,this paper proposes to adopt the method of multi-user cooperation,and multiple users in the center of the cell assist in forwarding signals to the edge users of the cell,so as to achieve the purpose of cooperation,and finally satisfy the minimum threshold condition of each user throughput and the NOMA constraint.The transmitter power is minimized and optimized.The optimization problem includes the active beamforming of the transmitter,the passive beamforming of the IRS,and the power split ratio.This optimization problem is non-convex because the optimization variables are coupled.In order to solve this non-convex optimization problem,Alternate Optimization technology is used to decouple the optimization variables,and a joint optimization of active beamforming vector,power split ratio and IRS phase offset matrix(JO-BAT-PR-PSM)algorithm.Finally,the scheme proposed in this paper is compared with the benchmark scheme,and it is verified that the scheme proposed in this paper can further reduce the power of the transmitter under the NOMA constraint and user quality of service requirements.Secondly,so as to improve the throughput performance of the system,this paper combines the active IRS and the passive IRS to form a double IRS,so as to study the problem of maximizing the throughput of the system,and at the same time avoid the cost problem caused by all the active IRS.Compared with passive IRS,active IRS can not only change the phase angle of the incident signal,but also adjust the amplitude of the incident signal,thus providing higher beamforming gain.The use of active IRS in double-IRS assisted SWIPT system brings a new degree of freedom to the information rate maximization problem.In addition,the active IRS amplification power constraint increases the difficulty and complexity of IRS beamforming optimization,and it uses an active reflection unit,the thermal noise at the IRS will also be amplified,and this part of the noise cannot be ignored.In this paper,under the power constraints of the transmitter,the energy threshold requirements of the energy harvesting user,the power constraints of the active IRS,and the modulo-1 constraint of the reflection coefficient of the passive IRS,the passive beamforming and transmission of the active IRS and the passive IRS are jointly optimized.Active beamforming at the end to maximize the total throughput of the system.Since there is a reflection link between the two IRSs,the optimization variables are highly coupled and cannot be solved directly.This paper proposes to jointly optimize the beamforming at the transmitting end,the active IRS1 phase offset matrix and the passive IRS2 phase offset matrix(JO-BAT-PSM1-PSM2)algorithm.Through simulation,it is verified that the throughput performance of the double-IRS assisted SWIPT system scheme composed of active IRS and passive IRS proposed in this paper is better than that of the benchmark scheme.