LEO Satellite Network Handover Technology For High-Speed Railway

With the rapid development of Chinese high-speed railway,not only the traffic burden of vehicle-ground communication is increasing,but also the physical security of land-based high-speed railway professional mobile communication system will inevitably be affected by complex environment.For example,the Lanzhou-Xinjiang high-speed Railway with a length of 1786 km is across the plateau snow mountains and desert gobi depopulated area,and the Saudi Mecca Madina high-speed Railway with a length of 450.25 km is in the desert hinterland.The physical safety of high-speed railway communication systems directly determines the safe operation capacity of highspeed railway.The research and application of Low Earth Orbit(LEO)satellite is one of the key technologies of B5G/6G,especially the integration of sky and ground communication network has received strong support and investment from the industry.For high-speed rail,LEO satellites can provide greater bandwidth,reduce the cost of professional communications infrastructure.The LEO satellite network can achieve global coverage,and effectively solve the problem of high-speed communications in remote areas,and in extreme disaster situation,which can take the place of ground infrastructure for high-speed communications services in some special cases.Mobility management brought by LEO satellites is one of the current research hot topics.This thesis mainly studies the handover between LEO satellites,aiming to design a new handover algorithm suitable for high-speed rail scenarios based on the existing research results.The specific research work of this thesis is as follows:First of all,in view of the handover scenario between different beams of highspeed rail in the same LEO satellite,it is analyzed that in this scenario,high-speed rail will frequently handover between different beam cells,or ping-pong handover between two adjacent beam cells,resulting in many handover times and high probability of link interruption.A beam to beam handover algorithm based on RSSI prediction and cell locking mechanism is proposed.We build the relationship between the use of space factor model of locking mechanism of cell,and then according to the grey model GM(1,1),we predict the next moment of high-speed railway of the received signal strength indicator(RSSI)in order to handover in advance,and design the corresponding signal process.Simulation results show that the algorithm can greatly reduce the number of handover times,avoid ping-pong handover and reduce the handover failure rate.Then,according to the handover scenario of high-speed railway between different LEO satellites,it is concluded that due to the deployment of large-scale LEO satellites,high-speed rail can be covered by multiple LEO satellites simultaneously,so it is necessary to choose the best satellite to handover.An inter-satellite handover algorithm for high-speed rail based on Q-learning is proposed.The algorithm takes into account a number of factors,including the longest available coverage time,channel available information and downlink carrier interference-to-noise ratio(CINR).And in the process of Q-learning action selection,the combination of Upper Confidence Bound(UCB)exploration and greedy strategy is used to replace the traditional greedy strategy,which improves the low efficiency of traditional action selection.Finally,the simulation results show that,compared with other typical algorithms,the proposed algorithm minimizes the number of long-term cumulative handoff interrupts,makes the cumulative handoff times close to the lower bound,and has a relatively high reachable transmission rate.