Energy Efficiency Analysis And Optimization Of Intelligent Reflecting Surface Aided MIMO System

Green communication is an inevitable requirement for the sustainable development of communication industry.Energy efficiency(EE),defined as the ratio of data transmission rate to total power consumption,is considered a key indicator to measure the performance of 5G green communication.In order to improve EE,it is necessary not only to improve the transmission rate,but also to reduce the power consumption of the system as much as possible.Intelligent reflecting surface(IRS)is a planar array device with a large number of low-cost passive reflection elements integrated on its surface,which can control the amplitude and phase of the reflected signal without the use of an RF link,thereby co-implementing passive reflection beamforming to enhance signal reception power and improve system EE.At present,in the research on energy efficiency of IRS-aided MIMO system,the proposed power consumption(PC)model is mostly theoretical,which has a significant gap with the actual PC of 5 G base station.By refining each PC module of 5G base station,the thesis proposed a PC model that conforms to the actual 5G base station architecture in Sub6GHz and millimeter wave(mmWave)frequency range.On this basis,the thesis analyzes the factors that affect EE in IRS-aided MIMO system and the methods to improve EE,and designs an algorithm to optimize EE.Firstly,the proposed PC model is used to model the EE of digital beamforming(DBF),hybrid beamforming(HBF)and analog beamforming(ABF)systems respectively for IRS-aided MIMO systems,and the influence of different configurations on EE is compared through simulation.Simulation results show that,higher EE can be obtained by deploying IRS,and EE can be improved by increasing the number of IRS reflection units;HBF and ABF systems can get higher EE than DBF systems when serving the same number of users;in DBF system,there are an optimal transmitting power and an optimal number of antennas to make EE reach the maximum value;in HBF and ABF systems,there is an optimal transmitting power to maximize EE,and EE can be improved by increasing the number of antennas.Next,considering IRS-aided HBF multi-user MIMO systems,the thesis derives a tractable upper-bound on achievable sum-rate of users,and use the proposed PC model to model EE as a function of transmitting power and number of users.Then,under the constraints of maximum transmitting power,minimum and maximum number of active users,and minimum peruser rate,an optimization problem is established to maximize EE,and an iterative optimization algorithm is designed to achieve the global maximum value of EE through joint optimization of transmitting power and user number.