Estimation Of Visibility Region And Research On Wireless Transmission Method In Extra-large Scale Of Massive MIMO

With the expansion of the commercialization scale of the 5th generation mobile communication technology in the world,the design and development of the 6th generation mobile communication technology(6G)have been started.In order to further exploit space resources and make better use of high-frequency spectrum resources,researchers have proposed an extra-large scale of massive multiple-input multiple-output(MIMO)transmission technology with thousands or more antennas in base station,which is a further evolution base on massive MIMO.However,the deployment of extra-large scale of antennas makes the channel exhibit near-field propagation and spatial non-stationarity,and the energy dispersion of the propagation paths will cause the terminal to see only a portion of the base station antenna array,which is called Visibility Region(VR).The performance of the extra-large scale of massive MIMO is highly dependent on the channel characteristics and the information of VR.Therefore,this paper mainly studies the impact of VR estimation on the ergodic sum-rate and the average spectral efficiency of extra-large scale of massive MIMO system.Specific contributions of this article are as follows:Firstly,for the time division duplexing(TDD)mode,an optimal VR threshold detection design method based on VR estimation for extra-large scale of massive MIMO is proposed.Considering a wireless communication system with multiple single-antenna users and a base station employed with an extra-large scale of uniform linear array,the probabilities of two types of error detection in VR estimation are derived by estimating the user’s VR using the uplink received training signal.Using the above VR information,the channel corresponding to the VR estimation is estimated by least squares estimation,the maximum ratio transmission precoding method is used in the downlink transmission,and the deterministic expression of the ergodic sum-rate and the average spectral efficiency is derived by the large system approximation method.By maximizing the deterministic equivalent expression of the average spectral efficiency,an optimal VR detection threshold is designed.The simulation results show that the derived deterministic equivalent expression has a good approximation effect,and the proposed VR estimation method can effectively improve communication performance of the system.Secondly,for the frequency division duplex(FDD)mode,an optimal VR threshold detection design method for extra-large scale of massive MIMO based on VR estimation is proposed.Considering the FDD system unlike TDD,the system also includes an extra-large scale of uniform linear array base station and multiple single-antenna users.The training signal received by the uplink is used to estimate the VR of the users.Based on the above VR information,the pilot is sent in the downlink to estimate the channel by minimum mean squared error estimation.Through the feedback of the uplink channel state information(CSI),the base station obtains the CSI and the maximum ratio transmission precoding method is used for data processing in the downlink.The expression of the system’s ergodic sum-rate and the average spectral efficiency is obtained.By maximizing the average spectral efficiency,an optimal VR detection threshold is designed.The simulation results show that the proposed design method is superior to the TDD system,which can effectively improve the communication performance of the system while reducing the pilot overhead and system calculation complexity.