Robust Clock Parameters Tracking for IEEE 1588 With Asymmetric Packet Delays in Industrial Networks

Clock synchronization is a prerequisite for the proper operation of industrial networks. IEEE 1588 Precision Time Protocol (PTP) can provide tight synchronization for a vast number of industrial applications. However, the joint tracking of clock skew and offset for IEEE 1588 under the more realistic delay asymmetries scenario is a challenging problem in sophisticated industrial networks. In this paper, we first investigate the biased estimation problem for clock parameters tracking in the presence of delay asymmetries, which significantly degrade the synchronization accuracy. Based on the investigation, a state-space model is developed that is capable of overcoming the uncertainty caused by the unknown packet delay distribution. A recursive joint clock skew and offset tracking scheme that employs the robust three-step recursive Kalman filter (R3SRKF) is proposed to estimate the time-varying clock parameters in a minimum-variance unbiased manner under the asymmetric packet delays scenario. Also, a variant of the R3SRKF is derived to joint track clock skew and offset with asymmetric packet delays in multi-hop networks. Simulation results indicate the effectiveness and performance enhancement of the presented robust tracking scheme.