Research On The Key Technologies In Space-based Internet System Based On LEO Constellations

Due to the wide coverage of satellite,satellite communication is still the most effective solution for network coverage in deserts,mountains and marine Regions.It is of great economic value and strategic significance to develop space-based Internet system(SIS)based on Low-Earth orbit(LEO)constellations.Compared with traditional satellite communication system,SIS has the characteristics of broad bandwidth and low delay.And Compared with the terrestrial network,in SIS,the topology changes drastically,the link error rate is high,the switching is frequent,and the on-board power and processing capacity are limited.This paper introduces the composition,working patterns and features of SIS.The research includes LEO constellation design,inter-satellite link analysis,the efficient routing algorithm and the optimization of gateway placement.The main work is as follows.1.Design of Large-scale LEO constellations and analysis of inter-satellite link.Street of coverage(SOC)method is adopted to solve the LEO satellite constellation providing continuous coverage,the number of constellation satellites rapidly increases with a limited single coverage.Effects of constellation parameters on the constellation configuration are investigated by dividing constellations into inclined orbit,symmetric and asymmetric polar orbit constellations.The optimal constellations with the least number of satellites in three different constellations are compared.Results shows that asymmetric polar constellation requires the least satellites.The influence of constellation parameters on the topological characteristics and communication performance of the permanent inter-orbit inter-satellite link is analyzed.2.Research of a Dynamic Distributed Packet Routing(DDPR)algorithm based on the fusion of terrestrial networks.Due to the drastic topological changes,high transmission error rate,limited onboard computational resources and complex network management system,in SIS,a DDPR algorithm based on the fusion of terrestrial networks is proposed.With the idea of wireless mesh networks(MSN),gateway nodes and routers are introduced into the satellite networks.Thus,satellite coverage of the packet destination is not required,which simplifies the routing problem.Virtual node method is improved to shield network dynamics by updating the satellite virtual address based on latitude range change of satellites.Candidate Path Set(CPS)concept is proposed for determining next hop direction in packet forwarding.Considering maximizing the path selection space,the strategy of remaining hop priority path(RHPP)is proposed to determine the direction of next hop to obtain better network balance.The validity of routing algorithm is verified by scenario simulations.3.Modeling and solution in optimization of gateway placement.Taking into account the non-uniform distribution of global traffic,an optimization model of gateway placement problem is proposed using above-mentioned routing algorithm to resolve network performance as objective function.The simulation results reveal that network balance is significantly improved under the optimized solution.