Research On Contact Plan Design In Space Communication Networks

With the development of satellite communication technology and various aerospace communication platform technologies,the space communication networks will provide necessary guarantees for many fields such as future space scientific detection,ground disaster emergency rescue,ocean communication,and real-time navigation.In the space communication networks,due to the relative motions and orbital height differences between various types of space nodes,the network topology state and contact properties are dynamically changed,and the contact is frequently interrupted,which brings great challenges to the efficient execution of space tasks.This thesis takes the space communication networks composed of the near space layer and satellite network as the research background,and studies the contact plan design(CPD)around the cost-effectiveness,reliability,and load balance of the contact in the space communication networks.The main work of this thesis is summarized as follows:(1)The CPD scheme based on directional space-time graph is proposed.Aiming at the problem of space-time connectivity in space communications,considering the contact cost and contact reliability,three CPD schemes based on directional space-time graph were proposed.First,a two-layer space communication network model consisting of the satellite network and the near space layer is constructed.Then,a directional space-time graph is designed to statically discretize the dynamic network by analyzing the time evolution characteristics of the network and the predictability of node trajectories.After that,in order to minimize network contact costs and maximize network contact reliability,the contact cost and the contact reliability based on spatial distance and carrier frequency are defined.Finally,the CPD problem is divided into a collection of multiple subproblems by introducing the idea of a greedy algorithm,and three CPD schemes solved by greedy algorithm are proposed.The simulation results show that the proposed CPD scheme can effectively improve network contact reliability and reduce network contact costs.Moreover,as the network density increases,the cost-effectiveness is higher.(2)The load balancing CPD scheme based on inter-layer cooperation is proposed.Aiming at the problem of unbalanced or even congested load of spatial contact caused by the change of ground relay traffic,two load balancing CPD schemes based on inter-layer cooperation are proposed.First,in order to fully exploit the inter-layer collaboration capabilities of the space communication networks,a space communication network structure based on virtual group management is constructed by comprehensively considering the mobility,coverage and processing capabilities of the space nodes in each layer.Then,comprehensively consider the correlation between the space contact load,the ground relay traffic and the number of ground communication equipment,the global contact plan of the relay layer is calculated after the ground relay traffic is predicted by the management layer.At the same time,in view of the problem that the global contact plan cannot adapt to the sudden local load fluctuation of the relay layer,a relay layer local contact management strategy is designed by considering the remaining time capacity.Finally,two CPD schemes are proposed,aiming to achieve load balancing of spatial contacts through the inter-layer cooperation method of global contact plan by the management layer and local contact management by the relay layer.The simulation results show that the proposed CPD scheme can optimize the performance of packet loss rate,average end-to-end delay,and load balancing during data transmission in the space communication networks.