无人机平台运动状态下节点间高精度时间同步

High precision time synchronization between nodes under motion scenario of UAV platforms

节点间的时间同步是无人机集群资源调度、协同定位、数据融合的基础,在同步精度要求较高的场景中常用双向时间同步进行节点间的时间同步。然而无人机的相对运动会导致两次同步消息的传播时延不等,进而引起时间同步误差。针对该问题,首先从线性方程组求解角度分析了时间同步误差的产生原因,提出了一种利用双触发双向时间同步以增加方程个数、并在节点匀速运动前提下减少未知量个数的方法。然后推导了该方法下钟差的求解公式,结果表明钟差求解与节点的匀速运动速度无关。随后比较了在加性高斯白噪声信道中双触发式双向时间同步方法与现有运动补偿方法的钟差估计性能,并分析了时间戳处理时延和速度改变对钟差求解精度的影响。最后通过外场实验验证了双触发式双向时间同步的有效性。仿真及实验结果表明,相比于传统双向时间同步,双触发式双向时间同步不会因节点的匀速运动导致主从节点间的时间同步出现系统偏差。

Time synchronization is the foundation for transmission resource scheduling,cooperative localization and data fusion in UAV clusters.Two-way time synchronization is commonly used to synchronize time between nodes in scenarios with high synchronization accuracy requirements.However,the relative motion of the UAVs will cause the propagation delays of the two synchronization messages to be unequal,thereby causing time synchronization errors.To solve this problem,the causes of synchronization deviation are analyzed from the perspective of solving linear equations.A method is proposed to increase the number of equations by conducting two-way time synchronization twice,with the number of unknown quantities being reduced under the premise of the uniform motion of nodes.The solution formula for the clock deviation under uniform motion of nodes is derived,and the derivation results show that the clock deviation solution is independent of the speed of the nodes.Synchronization performance is compared with that of existing compensation methods under the additive Gaussian white noise channel.The effect of time stamp deviation and speed changing on the accuracy of the clock deviation solution is analyzed.Finally,the effectiveness of the dual-trigger two-way time synchronization is verified through field experiments.Simulation and experiment results show that,compared with conventional two-way time synchronization,the dual-trigger two-way time synchronization does not cause systematic deviations by the uniform motion of nodes.