2024/02/15 by Ahmed Elmaghraby, Thomas Krawinkel, Steffen Schön +5 · 1 voice
Engineering · Physics and Astronomy · #Advanced Frequency and Time Standards #GNSS positioning and interference #Geophysics and Sensor Technology
paper · doi:10.33012/2024.19592
openalex publication_date 2024/02/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29
Realizing a clock-based geodetic network with a relative uncertainty level of 10?18 has been a significant objective for the scientific community. This network can be utilized for realizing more accurate geodetic reference frames and for testing the fundamental laws of physics, such as the theory of relativity. Typically, optical fibers are connecting optical clocks in such a network. For the last decades, Global Navigation Satellite Systems (GNSSs) have built a trustful and easy-setup method for frequency and time transfer. However, recently optical fiber link networks showed better frequency instability. In this study, we investigate the limits of GNSS-based frequency transfer links with the help of an optical fiber link as ground truth. Therefore, we analyze the GNSS data acquired in a dedicated common-clock experiment over a 52 km baseline. We focus on developing two algorithms to estimate the receiver clock differences, hence the frequency instability. These are the single difference (SD) approach with ambiguity fixing as a common view technique, and precise point positioning as an all in-view technique. We discuss the frequency instability achieved by the optical fiber link as well. We evaluate further the performance by computing the modified Allan deviation for both cases. The results show that the ambiguity-fixed solution of SD-CV improves the relative frequency instability via GNSS to reach the order of 3–5 · 10^?17 at one day averaging time. In the optical fiber link, which is the basis of the common clock setup, the round-trip instability shows better performance for all averaging times.