Performance Analysis Of Intelligent Reflecting Surface-aided Millimeter Wave Systems

Millimeter wave(Mm Wave)frequency band is capable of supporting multi-gigabit wireless access thanks to its abundant spectrum resource.However,mm Wave communication has very high path loss and is prone to blockage,especially in dense urban environment.In order to solve this problem,intelligent reflecting surface(IRS)is introduced into the mm Wave communication systems.IRS-aided communication is one of the promising 6G technologies that can control wireless propagation environments,increase the reflection path and improve the performance of communication system.This thesis focuses on the performance of IRS-aided mm Wave system in single user scenario and multi-user scenario.Major works are summarized as follows:(1)Single-IRS aided mm Wave massive MIMO system in single user scenario is discussed.First,the average achievable rate of system is derived.The performance difference between this technology and the traditional amplify and forward(AF)relay system is analyzed.The results show that the power gain of a single-IRS aided mm Wave system is proportional to the square of the number of IRS elements.Then,the condition that the average achievable rate of IRS system is higher than that of AF relay system is given.The simulation results verify the correctness of the proposed formulas,and point out that using IRS can improve the energy efficiency of the system.(2)Cooperative double-IRS aided mm Wave massive MIMO system in single user scenario is studied.First,the average achievable rate and its upper bound are derived and analyzed.The results show that the power gain of the cooperative double-IRS aided mm Wave system is proportional to the fourth power of the number of IRS elements.Then the optimal value of the number of IRS elements is analyzed to maximize the spectral efficiency of the system.The simulation results verify the correctness of the theories.Finally,the performance of this system is compared with that of a single-IRS aided system.The results show that when the large-scale fading meets certain conditions,the performance of cooperative double-IRS aided mm Wave system is higher than that of single-IRS aided system.(3)Distributed-IRS(D-IRS)aided mm Wave massive MIMO system in single user scenario is considered.First,when a large number of antennas at both transmitter and receiver,the low complexity optimal solutions of IRS phase shift matrix,precoding matrix,combining matrix and power allocation are given with the maximum achievable rate as the optimization objective,and the achievable rate of the system is derived.Results show that when the number of reflecting elements at each IRS is very large,the number of effective propagation paths provided by the IRS can be equal to the number of IRS.The received signal-to-noise ratio corresponding to each of the effective paths increases quadratically with the number of reflecting elements.Then,the problem of maximizing the average spectral efficiency constrained by the total number of IRS reflecting elements is analyzed when the equal power allocation strategy is adopted,and the lower bound of the average transmit power of the base station is given when the transmission rate is constant.Finally,the simulation results verify the correctness of the theories.(4)D-IRS aided mm Wave massive MIMO system in multi-user scenario is considered.The transmitter adopts hybrid precoding and the receiver adopts analog combining.First,a hybrid precoding scheme based on a phase shifter is presented,and the spectrum efficiency and energy efficiency of the system are analyzed.Theoretical analysis show that maximizing the average spectral efficiency of the system is only related to the large-scale fading parameters between IRSs and users.Then,the optimal value of the number of reflecting elements is analyzed to maximize the energy efficiency of the system.Simulation results verify the analysis results,and the proposed scheme is compared with the traditional singular value decomposition scheme.Finally,in view of the fact that the low complexity IRS reflecting matrix selection scheme can not provide more effective transmission paths,an alternative optimization algorithm is proposed to jointly optimize the hybrid precoding matrix,combining matrix and reflecting matrix.The simulation results show that this scheme can support more data streams and provide more effective transmission paths.Moreover this scheme is obviously better than the active and passive joint beamforming scheme with low complexity,but its implementation complexity is increased.