# Real-time free-running time scale with remote clocks on fiber-based frequency network

## TL;DR

This paper presents a real-time, robust free-running time scale using remote hydrogen masers connected via fiber links, demonstrating superior stability over long durations for applications like navigation and telecommunications.

## Contribution

It introduces a novel fiber-based frequency synchronization system for remote clocks, enabling a real-time, disturbance-resistant time scale with improved long-term stability.

## Key findings

- Time scale outperforms individual clocks after 10,000 seconds
- System maintains robustness against fiber link disturbances
- Continuous 224-day experiment validates stability and reliability

## Abstract

In this paper, we propose a real-time free-running time scale based on four remote hydrogen masers. The clocks in the ensemble were scattered around Beijing, connected by urban fiber links using a novel frequency synchronization system. The remote clock ensemble prevents the time scale from potential problems caused by correlation among co-located clocks. Insofar as it is real-time, it fulfills the requirements for applications such as navigation, telecommunications and so on. The free-running time scale is updated every 1200 s, and a disturbance-resistant algorithm makes it robust to fiber link disturbances and clock malfunctions. The results of a continuous experiment over 224 days are reported. The stability of the time scale outperformed any clock in the ensemble for averaging times of more than approximately 10000 s.