Enhancing Accuracy and Robustness of Frequency Transfer Using Synchronous Ethernet and Multiple Network Paths

Distributed measurement and control systems often rely on time synchronization protocols over Ethernet. Recently, it has been shown that estimating and compensating for not only time offsets, but also frequency skews is of crucial importance to meet the accuracy requirements of high-end applications. In this respect, this paper presents a new technique capable of: 1) measuring the jitter of multiple reference signals received by a single node over different network paths and 2) combining them in order to synthesize a downstream signal with a more stable frequency than using a single reference. The proposed algorithm can exploit the native frequency transport of Synchronous Ethernet and relies on a module for outlier identification and removal, a Kalman filter, and a linear quadratic regulator that drives a local voltage-controlled oscillator. The algorithm performance has been evaluated through both simulations and experiments using a prototype platform based on a field-programmable gate array. Simulation and experimental results confirm that the proposed approach can strongly decrease the jitter and wander of the generated signal. For instance, the time deviation is reduced on average by about 30% when three stable input references are merged and by several orders of magnitude when one of the input signals is affected by a large frequency step.