Enhancing the frequency stability of national time scale using EMD

Abstract

Almost all time keeping laboratories maintain the 5071A Cesium (Cs) frequency standard for generating their national time scales. The frequency stability of this standard is limited by different types of noise, especially the White Frequency Modulation noise. These noise types affect the stability of the resultant average Time Scale (TS). Kalman Filter (KF) is still applied until now within the time scale algorithm for de-noising and predicting improved resultant TS frequency stability. But, this method is very complicated and is based on difficult estimation techniques. In 2013, the Empirical Mode Decomposition (EMD) technique was applied for the first time on Cs atomic clock signal de-noising and frequency prediction. In this paper, the EMD technique is embedded in the TS generation algorithm for studying its effect on the stability of the resultant TS. Results show that the frequency stability of the resultant TS is improved for averaging times up to nearly 40 days due to EMD. These results are verified by comparing the effect of the EMD to that of the KF on the resultant TS frequency stability. Results show that the frequency stability of the resultant average TS is improved due to using EMD or KF for Cs clock signal de-noising for averaging times up to nearly 40 days. In addition, EMD is found to be more effective and simpler than the complicated KF.