Using EMD for Smoothing Atomic Clock Error in National Time Scale Algorithm

Enhancing the frequency stability of the national Time Scale (TS) is a main target of all time keeping laboratories around the world. The Empirical Mode Decomposition (EMD), as a new adaptive simple signal processing technique, is used previously for enhancing the frequency stability of national TS by denoising atomic clock's signal. But, this requires removing the trend of clock phase measurement data (clock detrending) outside the main TS algorithm before applying EMD to obtain real variations of the signal. In this paper, a new more effective use of EMD in the TS algorithm for enhancing frequency stability of national TS is introduced. The EMD is used directly for smoothing atomic clocks errors used in the TS ensemble algorithm without detrending. Then, the smoothed clocks errors are used for building an average TS to improve its resultant frequency stability and hence that of national TS. The use of EMD for smoothing atomic clock error is compared to that of the Kalman Filter (KF) as a famous signal processing technique for the same purpose. Obtained results show that the simple EMD achieves an average TS frequency stability improvement factor of 44% as compared to 41% of the complicated KF. Also, this new proposed use of EMD saves the processing effort and time required for clock detrending step before denoising.