Research On Low Earth Orbit Satellite Handover Strategy Based On Software-defined Satellite Network

With the development of 5G communication,satellite networks,which are backup and supplement of terrestrial networks,have been paid extensive attentions.In recent years,low earth orbit(LEO)satellites have become one of the newest hotpots of satellite communications due to their relatively short propagation delay and low costs.However,LEO satellite network is characterized by frequent handovers.In addition,the shortcomings of the satellite network itself:the difficulty of developing network protocols,the long path delay and the difficulty of being compatible with other protocols,also have negative effects on satellite communications.Software-defined networking provides a new way to solve these problems.Firstly,this thesis analyzes the current control strategy of software-defined satellite networks,that is,using ground equipment as the control plane and management plane device.Combining the characteristics of satellite networks and the idea of distributed control strategy,this thesis proposes a new policy based on on-board controller.The control policy of LEO satellite software-defined networking named SoftLEO(Software Defined Low Earth Orbit Satellite Network)uses on-board distributed controllers and divides satellites into different groups according to orbital planes.This strategy eliminates frequent handover between the controller and its switches.The simulation results prove that the SoftLEO strategy can reduce the propagation delay between the switch to its corresponding controller by 30%,reducing the waiting time for the user to send the first data packet by 20%,while the overall throughput remains essentially unchanged.Secondly,based on the control strategy SoftLEO,this thesis designs a new handover scheme named OBHOS(Onboard Handover Scheme),which is a LEO satellite software-defined network handover scheme.The handover scheme OBHOS combines handover scheme of software-defined networks with satellite visible time prediction,which reduces the propagation delay caused by signal exchange between switch and controller during handover.Compared with the software-defined wireless network handover procedure on the ground,OBHOS is more adaptable to the long path delay of satellite networks.The handover scheme OBHOS can reduce the handover delay and minimize the degradation time of link quality.What's more,this thesis designs an addressing method and flow table instructions,which provide the possibility of different constellations participating in data forwarding at the same time and make handover process more fluent.The simulation results show that the handover scheme OBHOS can reduce the handover delay by about 50%compared with the software-defined wireless network handover procedure on the ground,and can also reduce the link quality degradation time to 80%of ground procedure.