UTC and GNSS system time access using PPP with broadcast ephemerides

Abstract

The application of precise point positioning with broadcast ephemerides (PPP-BCE) is discussed as an alternative to the established all-in-view technique for multi-GNSS time transfer. It combines the use of broadcast ephemerides with low-noise carrier-phase observations for accessing GNSS system time scales and Coordinated Universal Time (UTC) with improved precision, and can be employed on stationary as well as mobile receivers in offline or real-time analyses. Using calibrated timing receivers, the method is shown to provide estimates of the GNSS-to-GNSS time offsets (XYTOs) with an accuracy at the 2 ns level. In the absence of prior calibrations, 0.5 ns consistency across different stations is achieved for GPS, Galileo, and BeiDou-3 after adjustment of systematic biases in comparison with calibrated reference stations or broadcast XYTO values. Furthermore, access to GNSS-specific UTC realizations can be obtained through predictions of the UTC offset from GNSS system time as provided in the broadcast ephemerides of individual constellations. The overall quality of the PPP-BCE-derived receiver clock offsets from UTC is assessed using calibrated receivers at various timing laboratories along with BIPM-provided UTC-UTC(k) measurements. Over the 1.5 years covered in the study, an accuracy of 1.8 ns for GPS and 2.5 ns for Galileo is demonstrated. For BeiDou, a slightly worse accuracy of 3 ns is obtained for a single timing laboratory over 9 months.

Real-Time Precise Point Positioning Method Considering Broadcast Ephemeris Discontinuities

“…BRD_est is a BE-PPP mode that still uses the raw broadcast ephemeris but incorporates an SISRE parameter estimation algorithm. This method has been proven effective in previous studies (Carlin et al, 2022;G. Chen et al, 2022).…”

“…The stations used in this study, information regarding observations, and PPP processing configurations are presented in Table 1, Table 2, and Table 3. In general, the ephemeris update interval is 2 h for GPS, 1 h for BDS-3, and 10 min for Galileo. The clock discontinuity for BDS-3 is the most significant, resulting in an average distance conversion of approximately 0.3 m, sometimes exceeding 1 m. In contrast, GPS exhibits a smaller discontinuity, typically within 0.2 m, whereas Galileo experiences an extremely low discontinuity, usually less than 5 cm (Carlin et al, 2022;G. Chen et al, 2022).…”

“…Carlin et al (2021) conducted GPS/Galileo-integrated BE-PPP and estimated the signal-in-space range error (SISRE), which represents the projected orbit and clock errors introduced by the broadcast ephemeris, and obtained a significant improvement in positioning accuracy. Time transfer experiments using a similar method achieved an accuracy of 0.5 ns (Carlin et al, 2022). The researchers reported that the discontinuity of the orbit and clock offset is caused by the handover of broadcast ephemeris and developed a model to account for variations in these errors using the SISRE process noise.…”

Galileo High Accuracy Service in Real-Time PNT, Geoscience and Monitoring Applications

“…Therefore, due to site-specific hardware biases and alternative GNSS data processing technique, i.e. double-differencing, utilized by the IGS, the estimated receiver clock errors differ from the IGS Final clock product [30]. With CNS corrections, the extreme biases, i.e.…”