随着低轨巨型星座的快速部署和卫星互联网的快速发展,由大规模低地球轨道卫星组成的分布式卫星系统是空天地一体化的重要特点.在卫星网络中,低成本、高精度的时间同步技术是其中的核心技术之一.针对低轨卫星高动态、拓扑结构时变特性因素影响下的低轨通信星座的分布式时间同步问题,考虑低轨卫星场景下的通信时延特性,同时为解决现有方法在动态网络拓扑下同步精度和收敛速度方面的不足,提出了一种基于最大似然估计的低轨卫星时间同步方法,能有效解决分布式动态网络中的通信时延随机不可预测以及星间距离不对称的问题.仿真结果表明,低轨卫星动态场景和拓扑结构变化下,本文提出的基于最大似然估计的时间同步方法同步误差均小于5 ns.
Research on distributed time synchronization methods for LEO communication constellations based on maximum likelihood estimation
As the rapid deployment of low earth orbit(LEO)mega-constellations and the swift growth of satellite In-temet unfolds,distributed satellite systems composed of a large number of LEO satellites become a significant feature of the space-air-ground integrated networks.In satellite networks,low-cost,high-precision time synchronization tech-nology is one of the core technologies.The distributed timing synchronization problem of LEO communication con-stellations,influenced by the high dynamics and temporally varying topological structures of low orbit satellites was focused on.Considering the communication delay characteristics in the LEO satellite scenario,and addressing the de-ficiencies in synchronization accuracy and convergence speed of existing methods in dynamic network topologies,a timing synchronization method based on maximum likelihood estimation for LEO satellites was proposed.This method effectively solves the problem of unpredictable random communication delays and asymmetric inter-satellite distances in distributed dynamic networks.The simulation results show that the synchronization error of the time syn-chronization method based on maximum likelihood estimation is less than 5 ns under the dynamic scenario and topol-ogy of LEO satellites.
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