Network Topology Design Of Low Earth Orbit Satellite Constellations

Satellite network is the key component of the “space-ground integrated information network”of our country and will play an important role in aerospace,transportation,industry and agriculture,disaster relief and smart city in the future.The network topology design,as the basis of the satellite networking design,has a huge impact on network performance,system robustness,and construction and maintenance costs.With the continuous enrichment of satellite constellation scale and configuration,the network topologies show the characteristics of high complexity,high dynamics and isomerization,which brings challenges to the network connectivity and stability,and universality of network topology design methods.Therefore,for the low-earth-orbit satellite networks,this thesis studies the characterization methods of the network topologies and proposes the intra-layer and inter-layer topology design methods for the double-layer constellations.The main innovations and contributions are as follows:1.A topology characterization method for Walker constellation is proposed.Based on the traditional three-element parameter set(T/ P/ F)of the Walker constellation,this method introduces the twisted factor U to characterize the inter-orbit connections,forming a fourelement parameter set(T/ P/ F/U).It not only reflects the basic parameters of the Walker constellations,but also maps the relationship between the inter-satellite link deployments and the topologies,eliminating the redundancy topologies,which can greatly improve the characterization efficiency of topologies and the universality of the characterization method.At the same time,the relationship between the twisted factor and the topology connectivity is analyzed.It is proved that the connectivity of 2D-Torus topology(U =0)is the lower bound of other topologies(U?0),which lays a theoretical foundation for the evaluation of network information-bearing capacity of Walker constellation.2.A Mobius topology for the Walker constellation is designed.By analyzing the average link distance and twisted factor of the topology design methods,it is proved that Mobius topology has the advantages of short link distance,high stability and strong scalability,which can effectively alleviate the connectivity deterioration of the Walker constellation as the network scale.The closed-form solution of the average hop count of Mobius topology is given,which reveals the mechanism that Mobius topology can shorten the average hop count of the intraorbit transmission through inter-orbit transmission.The impact of network scale and interorbit link deployment strategies(same identifier,shortest distance and Mobius topology)on the average hop count and average end-to-end propagation delay is analyzed by simulation,which proves the correctness and validity of the theoretical results.3.A low/medium-earth-orbit topology design method based on topology time slice evolution is proposed.This method defines the inter-layer topological performance evaluation index from topological stability and topological information-bearing capacity,and utilizes the time correlation of topology slices to greatly improve the efficiency of the topology design algorithm.The results show that the method is superior to the traditional link deployment method(the shortest distance)in terms of topology stability and information-bearing capacity.