Research And Simulation Implementation Of Clock Synchronization Mechanism In Satellite Time Sensitive Network

In recent years,with the rapid development of spatial information networks,time sensitive business pose new challenges to the deterministic transmission of data in spatial information networks.High-precision clock synchronization technology is the premise and foundation to ensure the real-time and deterministic transmission of time-sensitive business in spatial information networks.At present,in the satellite network,the clock synchronization between satellites and within satellites is mainly realized by satellite timing synchronization.The implementation process is too complex and needs the support of high-precision atomic clock,which is not a small cost for low-orbit small satellite system;Secondly,due to the high-speed movement between satellites,it is easy to cause the asymmetry of inter-satellite link propagation delay measurement,resulting in additional clock synchronization error.To solve the above problems,based on the IEEE802.1AS clock synchronization technology in Time Sensitive Networking(TSN),this paper designs a clock synchronization scheme to meet the high-precision synchronization requirements between LEO small satellites and their internal communication equipment.The main work is as follows :1.Aiming at the clock synchronization problem of inter-satellite and intra-satellite integration in LEO formation small satellite system.This paper designs inter-satellite and intra-satellite clock synchronization scheme based on IEEE 802.1AS synchronization technology.Firstly,according to the topology of LEO small satellites,the optimal master clock satellite node is selected as the reference clock source for inter-satellite synchronization,and the clock synchronization spanning tree is generated based on the optimal master clock satellite.Secondly,considering the frequency offset between the satellite airborne clock sources and the asymmetry of the inter-satellite link,the neighbor rate ratio and the symmetry ratio are introduced to characterize the inter-satellite synchronization process,and the synchronization between the clock satellite and the best master clock satellite is completed by synchronous information transmission.Finally,the airborne clock source in the current satellite node is used as the best main clock source in the satellite to realize the hierarchical clock synchronization in the satellite.2.For the problem of synchronization error caused by the asymmetric propagation path between satellites caused by the high-speed motion of satellites,a clock error correction scheme for relative motion based on bidirectional distance measurement is proposed.Firstly,the mathematical model of the satellite airborne clock source is established.Then,the motion of the satellite is analyzed based on the bidirectional distance measurement method.The mathematical model of the relative motion clock error is derived by referring to the knowledge of the radial velocity.The error sample set of multiple measurements is fitted by the least square method.Finally,the relative motion clock error is estimated by using the fitting results and the inter-satellite clock synchronization error is corrected.3.An inter-satellite and intra-satellite clock synchronization simulation prototype system is developed using EXata's open source discrete simulation model library.The simulation results show that the proposed scheme can ensure that the clock synchronization accuracy between satellites and within satellites is less than 1microsecond,which meets the synchronization requirements of time-sensitive service transmission in space-time sensitive network.