Comparative Study of Time Scale Algorithms

Abstract

The statistical generation of an accurate, stable and reliable time scale from a clock ensemble calls for an efficient algorithm. Here we present a comparative study which points out conceptual differences and similarities between two different types of time scale algorithm used worldwide:1. ALGOS (BIPM), which produces, bimonthly, the international reference TAI (temps atomique international) at the Bureau International des Poids et Mesures (Sèvres, France), and2. AT1 (NIST), from which is obtained, in real-time, the AT1 time scale at the National Institute of Standards and Technology (Boulder, Colorado, USA).These two algorithms rely basically upon weighted averages of clock readings, but the weight determination and the frequency prediction are of different types because they are adapted to different needs and to the peculiarities of the available time measurements.

The evaluation of uncertainties in [UTC−UTC(k)]

“…EAL is a worldwide weighted average of a large number of free-running, effectively uncalibrated, frequency standards [1][2][3]. The uncertainty in the determination of EAL, TAI and UTC, as steps in the realization of Terrestrial Time (TT), is affected by three major elements: clock variations, the means of comparisons of remote clocks (time transfer) and the time-scale algorithm.…”

The New Generation System of Japan Standard Time at NICT

“…The algorithm for NET in the former JST system [2] was based on a standard theory of timescale algorithm [3,4]. First, the rate of each Cs atomic clock at a moment is estimated from the past behavior.…”

Development of automatic intercomparison system for generation of time scale ensembling several atomic clocks

“…National physical laboratory India (NPLI) has five commercial cesium atomic clocks and one H-maser. One of these clocks maintains coordinated universal time (UTC) [1] of NPLI. It is being planned to utilize all these clocks in an ensemble manner to generate a smoother time scale.…”