Detection and Identification of Phase and Frequency Drifts in Clock Ensembles

Christian Trainotti and Gabriele Giorgi

Abstract:	A stable system time scale is a fundamental part of Global Navigation Satellite Systems (GNSSs). The composite clock approach provides a method for the generation of a stable and robust time scale. However, it can still be impacted by failures in single clocks. This paper describes two dedicated statistical tests aiming to detect and identify slow deviations from the clocks’ nominal behavior. First, the batch test is described, which computes the overlapping Allan deviation (OADEV) of differential clock measurements over a sliding window and compare it to a nominal model. Second, the envelope test is developed. It compares the measured phase deviations with the expected value at each time step. The tests are derived for an arbitrary size of the ensemble, while their performance are evaluated with simulations and on a real testbed using three cesium frequency standards. Two fault scenarios are analyzed. The first case involves a linearly increasing frequency bias, while the second includes an oscillating frequency behavior, which intends to simulate a bias with period signature. The fault detection capabilities of the statistical tests are given in terms of time-to-detect and minimum detectable biases.
Published in:	Proceedings of the 51st Annual Precise Time and Time Interval Systems and Applications Meeting January 21 - 24, 2020 Hyatt Regency Mission Bay San Diego, California
Pages:	347 - 365
Cite this article:	Trainotti, Christian, Giorgi, Gabriele, "Detection and Identification of Phase and Frequency Drifts in Clock Ensembles," Proceedings of the 51st Annual Precise Time and Time Interval Systems and Applications Meeting, San Diego, California, January 2020, pp. 347-365. https://doi.org/10.33012/2020.17310
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