| With the rapid development of the intelligent high-speed railway technology,higher requirements of wireless communication are required by train control systems and passengers,and future high-speed railway communication services are expected to need to achieve Gbps data rate.As a new and revolutionary technology,Reconfigurable Intelligent Surface(RIS)has a large number of independent units that can be controlled by software definition and can reconstruct wireless transmission channels.RIS beamforming technology has become an effective solution to improve cell coverage performance.Handover technology is the key to guarantee the reliability and security of train control and communication system in high-speed environment.However,traditional handover strategy does not take into account the uniqueness of rapid channel variation in HSR train-ground wireless communication,which leads to the degradation of handover performance.In this paper,based on millimeter-wave communication of high-speed railway,the joint optimization of RIS passive beamforming and base station active beamforming technology is studied to improve the coverage performance of RIS-assisted millimeter-wave communication of high-speed railway.Based on the study of intelligent handover algorithm in LTE-R scenario,the intelligent handover scheme of RIS-assisted millimeter-wave communication in high-speed railway is studied.By constructing RIS-assisted millimeter wave communication system model,simulation is provided to analyze and verify the performance of the proposed scheme.Firstly,in RIS-assisted HSR millimeter-wave wireless communication system,a joint optimization scheme of the RIS-assisted millimeter-wave communication in high speed railway beamforming is proposed.Aiming at the limitation of existing research results based on the perfect channel estimation and the characteristics of the millimeter wave communication system in highspeed railway,a joint optimization method of RIS passive beamforming and base station active beamforming based on GRNN neural network is proposed.The optimal RIS phase shift matrix is predicted by location and history channel state information.The results show that compared with traditional millimeter-wave communication system and RIS random phase shift control scheme,the proposed scheme can significantly improve the coverage performance of cell boundary communication,and the performance is close to the optimal RIS control strategy solved by SDR algorithm.Secondly,the handover algorithm of LTE-R system in high-speed rail scenario is studied,and an intelligent handover scheme based on GRNN neural network is proposed.The optimal training data set was selected with the count interrupt probability of handover as the index,and the intelligent handover strategy was realized by using GRNN neural network to adjust the handover parameters adaptively according to the train speed.Compared with the traditional LTE-R handover algorithm,the proposed scheme can significantly reduce the probability of ping-pong handover and improve the cumulative success rate of handover,and improve the performance of handover.Finally,based on the study of LTE-R intelligent handover strategy,an RIS-assisted intelligent handover scheme in high-speed railway millimeter-wave communication system was proposed.In RIS-assisted millimeter-wave communication system,the optimal RIS deployment scheme was analyzed to improve the performance of handover,and the handover parameters were adjusted adaptively by intelligent off-zone handover strategy.The simulation results show that the joint optimization scheme of RIS-assisted beamforming can be combined with the intelligent handover algorithm to further improve the handover performance of HSR millimeter-wave communication system. |
