Research On Optimization Of Intelligent Reflector-assisted Wireless Relay System Based On RF Power Suppl

With the increase in working frequency bands of the new generation wireless communication systems(such as the terahertz frequency band in 6G systems),achieving seamless and large-scale coverage at low cost is a critical challenge that wireless communication networks urgently need to address.Wireless relay can expand the coverage range of wireless communication systems at low cost.On the other hand,intelligent reflecting surface(IRS)can improve the signal power received by wireless receivers by adjusting the phase shift of the reflected signal through passive components,thereby effectively improving the spectrum efficiency of wireless communication.As a new power supply technology,radio frequency(RF)energy harvesting can solve the energy-limited problem of wireless nodes,and its application in wireless relaying and IRS can make the deployment of wireless relaying and IRS more flexible and convenient.This thesis focuses on the design and optimization of the RF energy-based intelligent reflecting surface-assisted wireless relaying system,providing a reference scheme for achieving seamless and large-scale coverage of the new generation wireless communication systems.Firstly,we conduct research on the RF energy-based intelligent reflecting surface-assisted wireless relaying system,considering the stability of the rechargeable battery energy buffer of wireless relaying and IRS.In the first place,a new protocol is proposed to increase the RF energy harvesting capability of wireless relay and IRS and improve their energy utilization efficiency.Under this protocol,the relay and IRS can adaptively switch between two working modes based on the rechargeable battery energy status and system channel link status,which allows for flexible switching between energy harvesting and assisted information transmission.Based on the proposed protocol,we establish a corresponding system optimization problem that considers the stability constraint of the energy queues of relaying and IRS,aiming to jointly optimize the transmission signal power of relay,the phase shift of the intelligent reflecting surface,and the time allocation to maximize the system throughput.Since the established optimization problem is a stochastic programming problem,it is difficult to solve directly.Therefore,based on the Lyapunov optimization theory,we convert the problem into a deterministic optimization problem and use convex optimization methods to solve the transformed deterministic optimization problem,thereby proposing a corresponding system optimization algorithm to improve the system throughput performance.Secondly,to evaluate the system throughput performance obtained from the Lyapunov optimization-based system optimization algorithm,further research was conducted on the RF energy harvesting assisted intelligent reflecting surface(IRS)aided wireless relay system using dynamic programming.In the first place,assuming that the non-causal information of the energy status and system channel state information of multiple time frames of the IRS and relay can be known in advance,a new protocol was designed to allow the IRS and relay to select more working modes.Then,based on the non-causal information assumption and the designed new protocol,the corresponding system optimization problem was established.Although the optimization problem is a deterministic optimization problem,the resource allocation of each time frame is mutually coupled and difficult to solve directly.Therefore,based on dynamic programming theory,the problem was decomposed into optimization problems of single time frames and solved using convex optimization theory to obtain the optimal solution of the corresponding optimization problem.Thus,a corresponding system optimization algorithm was proposed,and the upper bound of system throughput performance was obtained.Finally,the performance of the proposed system optimization algorithm was verified through computer simulations.The simulation results show that the IRS-assisted wireless relay cooperative transmission scheme proposed in this paper can significantly improve the system throughput compared to the cooperative communication scheme with only a wireless relay or only an IRS assistance.Moreover,the multi-mode working protocol proposed in this paper can significantly improve the system throughput performance compared to the baseline scheme with only one working mode.In addition,the simulation results also show that the system throughput performance obtained by the Lyapunov optimization-based algorithm proposed in this paper is close to the upper bound of throughput performance obtained by the dynamic programming-based optimization algorithm.