Link calibration against receiver calibration: an assessment of GPS time transfer uncertainties

Abstract

We present a direct comparison between two different techniques for the relative calibration of time transfer between remote time scales when using the signals transmitted by the Global Positioning System (GPS). Relative calibration estimates the delay of equipment or the delay of a time transfer link with respect to reference equipment. It is based on the circulation of some travelling GPS equipment between the stations in the network, against which the local equipment is measured. Two techniques can be considered: first a station calibration by the computation of the hardware delays of the local GPS equipment; second the computation of a global hardware delay offset for the time transfer between the reference points of two remote time scales. This last technique is called a ‘link’ calibration, with respect to the other one, which is a ‘receiver’ calibration. The two techniques require different measurements on site, which change the uncertainty budgets, and we discuss this and related issues. We report on one calibration campaign organized during Autumn 2013 between Observatoire de Paris (OP), Paris, France, Observatoire de la Côte d'Azur (OCA), Calern, France, and NERC Space Geodesy Facility (SGF), Herstmonceux, United Kingdom. The travelling equipment comprised two GPS receivers of different types, along with the required signal generator and distribution amplifier, and one time interval counter. We show the different ways to compute uncertainty budgets, leading to improvement factors of 1.2 to 1.5 on the hardware delay uncertainties when comparing the relative link calibration to the relative receiver calibration.

Combining GPS, BeiDou, and Galileo Satellite Systems for Time and Frequency Transfer Based on Carrier Phase Observations

“…Considering the existence of hardware delays in the receiver, antenna, and cables when conveying the internal electrical signal, the receiver clock offset usually contains these delays, which can be calibrated in the area of the time and frequency transfer [41,42]. Therefore, this is not included in the present study.…”

Modeling and Assessment of Precise Time Transfer by Using BeiDou Navigation Satellite System Triple-Frequency Signals

“…At present, time transfer can be performed using BPM/BPL (ground-based radio stations that broadcast short-wave and long-wave time signals, respectively), two-way satellite time and frequency transfer (TWSTFT), optical fiber (OP), and global navigation satellite system (GNSS) [ 1 ]. Among these approaches, GNSS time transfer is preferable because of its portability and low cost [ 2 ].…”

Study of time link calibration based on GPS carrier phase observation

“…Compared with the former two techniques, the link calibration based on GPS shows the characteristics of portable and low cost. It is also well adapted to the current structure of time links evaluated by the Bureau International des Poids et Mesures (BIPM) in the realisation of UTC [2, 3].…”