Research On Handover Schemes Of LEO Satellite Communication System

The thriving development of satellite communications technology continuously meeting the increasing traffic demands of mobile users,while the high-speed mobility of low earth orbit satellites also gives users links(links which between users and satellites)and feeder links(links between satellites and satellite satations)a huge challenge.As the number of users using satellite communications has increased,the demand for resource utilization of satellite systems and handover schemes has also been increasing.The subject of this paper is solving the handover schemes of user links and feeder links in LEO satellite communication system.Firstly,this paper clarifies the research background and significance of the subject,and at the same time it discusses and explains the main research content and the whole structure of the whole thesis.Based on the research on handover schemes in LEO satellite systems in domestic and abroad,the research focuses on the selection of handover paths for user links and feeder links,like user link handover scheme based on load balancing of satellite and feeder link handover scheme based on maximum matching algorithm of bipartite graph.Aiming at unbalanced satellite load caused by uneven distribution of user stations on the ground in low earth orbit satellite communication system and high-speed of satellite,this paper proposed user link handover algorithm based on load balancing of satellite.Firstly,I design a handover model based on user station's task sequence and directed graph.Then,in order to solve the unbalanced load of satellites(load of satellite means the number of user stations access to the satellite)and taking into the times of user station handover,I proposed the user link handover algorithm based on delete harmfull points.This algorithm is to planning a handover path for user station,which can result to handover frequency less and more balance of satellites load in the system according to the user station's task sequence.The simulation results show that the proposed algorithm increases the fairness of the load among the satellites compared with the minimum hop algorithm,reduces the number of handover failures and achieves satellite load balancing in the handover process.In the meantime,in order to handover the feeder link in LEO satellite system,this paper proposes a feeder link handover algorithm based on the maximum matching of the bipartite graph.According to the task sequence of the station,the central station models the gateway stations and satellites as a bipartite graph when it is necessary to do handover.In order to maximize the service time of all the satellites in the satellite system,the graph maximum matching algorithm calculates the target satellite and finally guides the handover of the gateway station.The simulation results show that the proposed handover algorithm based on maximum matching of bipartite graph can improve the utilization of satellites in the system.