Research On Architecture Optimization Technologies And Topology Control Methodolgies In Space Information Network

As air-space-ground of an integrated network system,space information network(SIN)will be used for a wide of application to provide future global data communication services,such as national defense,aerospace engineering,emergency rescue,smart city.Compared with the traditional information network,SIN adopts the network architecture of satellite constellation and air-ground cooperation to improve the transmission performance,coverage percent and stability of the network.Due to the multitudinous node and its hierarchical layers,it is difficult to design the complicated architecture of SIN.On the other hand,each node of the SIN is in a state of high-speed operation.The dynamic of nodes leads to the rapid change of the whole network topology,which has brought new challenges to the topology control of the SIN.Under this background,two specific aspects of the construction of SIN: architecture optimization technologies and topology control methodologies in SIN are discussed in this dissertation.The main contributions of the dissertation are as follows:In order to solve the optimal deployment problem of space segment of SIN,we develop a unified framework for constellation optimization design in LEO satellite broadband networks.Several design criteria including network performance and coverage capability are combined into the design process.Firstly,the quality of service(Qo S)metrics is presented to evaluate the performance of the LEO satellite broadband network.Also,we propose a network stability model for the rapid change of the satellite network topology.Besides,a mathematical model of constellation optimization design is formulated by considering the network cost-efficiency and stability.Then,an optimization algorithm based on non-dominated sorting genetic algorithm-?(NSGA-?)is provided for the problem of constellation design.Finally,the proposed method is further evaluated through numerical simulations.Simulation results validate the proposed method and show that it is an efficient and effective approach for solving the problem of constellation design in LEO satellite broadband networks.Due to lack of continuous connectivity in the underlying topology,most traditional topology control methods are not applicable to SIN.This thesis solves the topology control problem in SIN where the dynamic topology is known a priori or can be predicted over time.First,this dynamic topology is modeled by a directed space-time graph that includes spatial and temporal information.Second,the topology control problem of the predictable SIN is formulated as building a sparse structure.For any pair devices,there is an efficient path connecting them to improve the efficiency of the generated structure.Then,a topology control strategy is proposed for this optimization problem by using a kth shortest paths algorithm.Finally,simulations are conducted on random networks and a synthetic space network.The results demonstrate that the proposed method can significantly improve the efficiency of the generated structure and reduce the total cost.SIN is a large space-time scale and dynamic network,thus may result in end-to-end delay increasing.To solve this problem,a topology control method satisfying the delay constraint is proposed.Firstly,the evolving graph model of SIN is established to describe the temporal connectivity of the network by using the reachability of the evolving graph.The time-connected interval satisfying the time-delay constraint in the network is defined as the transitive closure at a time slot.Secondly,a topology control algorithm with the minimum cost that satisfies the delay constraint is proposed.The algorithm uses a recursive approach to search the path with the minimum cost in each transitive closure and combines all the paths with the minimum cost to finally generate a new network topology.Finally,a cost-efficient topology control algorithm satisfying the time delay constraint is proposed,which can construct spanner in each transitive closure of the network to ensure the spanning ratio of the generated network.The experimental results show that the two algorithms can not only maintain the time connectivity but also reduce the energy consumption of the network.Because there are a lot of lossy links in the space information network,this will leads to a decrease in the reliability of the network data transmission.A topology control method satisfying the reliability requirements is proposed.Firstly,the probabilistic evolving graph model of lossy SIN is established,in which the connection probability of a directed edge represents a reliability of data transmission between two nodes.Secondly,the most reliable path topology control algorithm satisfying the time delay constraint is proposed.The algorithm uses recursion to search the most reliable path between any nodes of each transitive closure in the network.Finally,a minimal cost topology control algorithm is proposed to satisfy the reliability constraint.The algorithm uses the inclusion and exclusion principle to construct the path between any nodes of each transitive closure that satisfies the reliability threshold and the minimum cost.The experimental results show that both algorithms can realize reliable data transmission in a sparse network with low energy consumption.