| With the gradual deployment of the fifth generation mobile communication system around the world,various countries have successively carried out the research of the sixth generation(6G)mobile communication system.In order to satisfy the application requirements of 6G communication networks,high-frequency technologies such as millimeter-wave and terahertz have received extensive attention.High-frequency communication has abundant spectrum resources and can achieve ultra-high-speed data transmission.However,high propagation loss limits communication distance and signal coverage,which is becoming an urgent problem for high-frequency communication.Multiple-Input Multiple-Output(MIMO)antenna technology can increase communication distance and signal coverage through beamforming,thereby ensures high-frequency communication performance.Establishing an accurate high-frequency MIMO channel model is the basis for the design,evaluation,and optimization of 6G high-frequency communication networks.Compared with low-frequency Single-Input Single-Output channels,high-frequency MIMO channels have significant differences in propagation loss,space-time-frequency correlation,and spatial consistency.Accurately describing the characteristics of high-frequency MIMO propagation channels is the main challenge for 6G wireless channel research.This thesis investigates the modeling and simulation of high-frequency MIMO channel based on geometry theory,and the main contributions of the thesis are summarized as follows:(1)For MIMO channel modeling at millimeter-Wave bands in mobile scenarios,the research on spatial consistency simulation and modeling of time-varying channels is carried out.For the time domain,the terminal moving trajectory is segmented,and the large-scale channel parameters between segments are determined by characterizing the correlated shadow fading and Line-of-Sight/ Non-Line-of-Sight scenarios.In addition,the Markov chain is introduced to achieve the dynamic evolution of the number of clusters between channel segments.Finally,the smooth evolution of the small-scale parameters within the channel segment is realized based on geometry theory,which ensures the simulation of spatial consistency.For the array domain,the accurate channel simulation of different links is realized by characterizing the response of the antenna array.The channel correlation between different antenna elements and the influence of the antenna angle on the correlation are analyzed,which improves the accuracy of the channel simulation.(2)For ultra massive MIMO channel modeling at terahertz bands,the path loss in free space and molecular absorption loss of terahertz signal are simulated and analyzed.Combined with the novel graphene nano-antenna material,a regular geometry-based terahertz ultra massive MIMO channel model is proposed.According to the characteristics of graphene material and the geometric position of the transceiver,the second-order channel statistical characteristics expressions such as space-time-frequency correlation function and Doppler power density spectrum are deduced.The influence of some channel parameters,such as carrier frequency and Fermi energy,on statistical properties is investigated.The results show that in the terahertz band,the reduction of the Fermi energy in the graphene-material ultra massive MIMO antenna can significantly reduce the antenna element spacing,resulting in a slower decline of the channel correlation function.Moreover,higher frequencies can significantly increase the decline rate of the correlation function.(3)In order to improve the simulation efficiency of high-frequency ultra massive MIMO channel and validate the proposed theoretical model,the angle parameters of the proposed model are discretized to construct the simulation model.The Modified Method of Equal Areas method and the Riemann Sum method are used to solve the discrete angle data set of multipath components.The correlation functions obtained by the two methods are compared with the theoretical model,which evaluate the accuracy of the simulation model.On this basis,the accuracy of the theoretical model is evaluated and verified by comparing the measured power delay profile with the simulation model.To sum up,this thesis focuses on 6G high-frequency MIMO modeling and establishes the millimeter-wave MIMO time-varying channel model and the terahertz ultra-massive MIMO channel model.It also provides support for the design of 6G high-frequency communication systems. |
