Effect of Downscaling the Frequency Offset of Clock Ensemble on the Stability of the Time Scale

Abstract

Improving the stability of national time scale (TS) is a main target for all time keepers. The stability of TS can be improved by either increasing the number of atomic clocks in the ensemble or by adding clocks of higher stability. In both cases, a large financial budget is needed which may be unaffordable by some developing economics. In this paper, we propose a new method for improving the stability of national TS by a factor approaching 50% with zero expenses by replacing the real clocks in the ensemble by virtual clocks (VCs). The VCs are obtained by downscaling (DS) the frequency offset of the real clocks. The DS process improves the frequency stability of the clocks and hence that of the resultant average TS. Since the downscaled clocks are correlated to the original ones, they replace the real clocks and not added to the ensemble. The performance of the proposed method is verified by applying it on the daily clocks comparison data of the Observatory of Paris (OP) published on the time department server of the Bureau International des Poids et Measures. The performance of the proposed method is compared with that of Kalman filter (KF) method presented in the literature. It is found that the proposed method is simpler and acting as a wider bandwidth de-noising filter than KF method for achieving the same performance.