The Researh On Key Planning Technologies For Multi-Stage Constructed LEO Satellite Constellation Networks

Satellite communication system is an extension and complement for terrestrial communication systems,it mainly provides communication services for the people in remote areo and the people with special requirements.Due to global coverage,low propagation delay and low power consuming,the Low-Earth Orbit(LEO)satellite constellation network(SCN)with inter-satellite links(ISLs)and on-board processing(OBP)ability,could be independent of ground gateway stations and will be the hot research point around the world.From the point of service provider,the target of network planning is to provide service for the most users by means of the least network resources.Since satellites are hardly to update themselves when they have been launched to the sky,it is significant to design network topology and dimension link capacity for LEO SCN to accommodate as many user requests as possible without wasting network resources.Furthermore,the LEO SCN typically needs several stages and during each stage only a few LEO satellites could be inserted into target positions.Thus,another key planning technology is to optimize the construction process such that the best service could be provided for users during the construction period.However,the LEO satellite's relative position to the earth and the set of its visible satellites change continuously as it moves along its orbit.And these will introduce challenges to the planning technologies for LEO SCN.Recently,extensive research on LEO SCN has been started.However,there still exist some problems: 1)Design network topology;2)Dimension the link capacity;3)Optimize the construction process.To solve the above problems,the detailed work is as follows:1,Network topology design for LEO SCNThe LEO satellite's relative position to the earth and the set of its visible satellites change continuously as it moves along its orbit,and the communication terminals(CTs)equipped on each LEO satellite is less than its visible satellites.As a result,ISLs for each LEO satellite should be dynamically established and deleted according to its visible satellite set.To avoid the waste of network resources,link assignment scheme based on perfect match model(LAS-PMM)is proposed to assign all CTs equipped to establish ISLs.Finally,simulation results for Next-generation LEO System(NeLS)constellation network show that our LAS-PMM could achieve better performaces in terms of the average node-to-node distance and CT utilization,compared to the regular and random greedy link assignment schemes in both static and dynamic situations.2,Link capacity dimensioning for LEO SCNISLs for each LEO satellite should be dynamically established and deleted according to its visible satellite set.Network topology is decided by link assignment,while different network topologies will result in different routings and different link bandwidth assignments.As a result,these three subproblems of link assignment,routing and link bandwidth assignment are closely coupled and essentially influence both installation and operation costs.Therefore,LAS-PMM is used to design appropriate topology such that shorter path could be routed and less link bandwidth is required.Finally,simulation results show that link capacity requirements and average delay based on topology generated by LAS-PMM could be reduced by 24.8% and 12.4% respectively,compared to the regular topology.3,The optimization of construction process for LEO SCNDuring the construction period of SCN,the relay communication service could be provided by a partially constructed constellation through buffering data and forwarding it at a later time.However,it is hard to update the hardware since satellites have been launched and this strategy will introduce extra end-to-end delay during the construction period.Therefore,we propose a scheme to minimize the delay by designing an optimal construction process.We also evaluate the delay performance in the construction period.In each stage,our scheme decides the positions which satellites should be inserted into,and we analyze its fuel cost and time cost.Finally,simulation results for Globalstar constellation network indicate that our scheme can reduce the average end-to-end delay by 70.1% and storage requirements by 42.8% respectively,compared to the traditional scheme which inserts the satellites into one orbtal plane in each stage.