SLIDE 1
The use of Galileo signals for time transfer metrology
Pierre Uhrich, Philip Tuckey LNE-SYRTE Observatoire de Paris, LNE, CNRS, UPMC
6 August 2009 JD6, IAU XXVII General Assembly, Rio de Janeiro
SLIDE 2 Global Navigation Satellite System (GNSS) time transfer metrology
Objective is to measure the time offset between two clocks in distant laboratories, using a GNSS receiver in each laboratory. The GNSS serves
- nly as a transfer system.
Used for:
- comparisons between time scales
- comparisons between frequency standards
GNSS data essentially always post-processed, with more or less sophistication
SLIDE 3 GPS and Galileo frequency bands
Galileo Joint Undertaking, 2005
SLIDE 4 Reminder of current GPS usage: signals
Signals used L1 (1575.42 MHz):
- C/A code
- P code (“P1”)
- carrier phase
L2 (1227.60 Mhz):
- P code (“P2”)
- carrier phase
SLIDE 5 Reminder of current GPS usage: comparison methods
Common view, C/A code
Common view, dual-frequency P-code
- in particular the ionosphere-free linear
combination P3 = 2.5457xP1 - 1.5457xP2 All-in-view
- all visible satellites are used to link each receiver
to IGS time (common view not needed) Precise Point Positioning (PPP)
- carrier phase and code between two receivers,
taking IGS products as fixed data
SLIDE 6 Galileo
- european GNSS
- 2 experimental
satellites currently in
- rbit
- launch of 4 In Orbit
Validation satellites by end 2010
satellites) by end 2013
ESA – J. Huart
SLIDE 7
Galileo services
Open Service (OS) Open access, free, dual- frequency Safety of Life (SoL) OS + integrity, authentification, service guarantees Commercial Service (CS) Encrypted commercial data, service guarantees, higher precision Public Regulated Service (PRS) Encrypted, high precision, robust signal, for security applications. Search and Rescue support service (SAR) Emergency beacon detection and return message forwarding
SLIDE 8 Galileo signals
Galileo Joint Undertaking, 2005
SLIDE 9 Galileo signal usage for time transfer metrology
Thus Galileo OS will provide 4 single-frequency signals:
allowing 6 dual-frequency (ionosphere-free) combinations:
- E5A-L1F, E5B-L1F, E5-L1F
- E5A-E5B, E5A-E5, E5-E5B
SLIDE 10
As with GPS, use of the all-in-view and PPP methods, relying on IGS products, will be beneficial. The combined use of GPS and Galileo (and other GNSS) data will also improve measurements. Timing receivers: provision for external clock and frequency input, existence of a well-defined temporal reference point.
SLIDE 11 Access to further Galileo signals
For GPS, civil user access to the P code signals, in addition to C/A, has been of great importance for the development of applications and for the monitoring of GPS itself. Galileo and future GPS civil signals take account
- f lessons learned by providing multi-frequency
signals, code improvements over C/A, etc. Nevertheless, it is to be expected that scientific user access to Galileo CS (or PRS) signals, in particular on E6, would bring advantages (e.g. multi-frequency combinations for phase ambiguity resolution).
SLIDE 12 A comment on the CGGTTS format
A file format used in the time metrology community for exchanging GPS and GLONASS receiver data for common view, code-based
- comparisons. For GPS data, C/A, P1, P2 and P3
codes are provided for. In 2006, CCTF approved a modification creating an identifier for Galileo satellites. We also need to define identifiers for the 10 different single-frequency Galileo OS signals and their dual-frequency combinations.
SLIDE 13 Recent LNE-SYRTE work related to Galileo
Participation in the GST to UTC link development. Relative calibration of GPS receivers of participating laboratories: P1 and P2 code delays. Individual P1 and P2 calib- ration uncertainties ~ 0.8 ns
- > P3 uncertainty ~ 2.3 ns
- > link uncertainty ~ 3.2 ns
SLIDE 14
Thanks
SLIDE 15 Future GPS civil signals
Future GPS civil signals
- 2005: L2C (L2CM and L2CL)
- 2009: L5C
- 2013: L1C
- 2015: end of civil access to P code
SLIDE 16
Galileo services and signals
E5A E5B E6 L1 E6C E6P L1F L1P OS x x x SoL x x x CS x x x x PRS x x
SLIDE 17
More information on Galileo signals
Typical C/N0 dB-Hz Chip rate Mcps Data rate sps Encryption Ranging Data E5A 50 10.23 50 No No E5B 50 10.23 250 No Partial E6C 50 5.115 1000 Commercial E6P 50 5.115 1000 Governmental L1F 48 1.023 250 No Partial L1P 48 1.023 250 Governmental
Note: E5A + E5B = “E5” signal
SLIDE 18
Triple-frequency combinations
Dual frequency combinations allow the ionospheric contribution to be removed, leaving the geometrical information and errors (code delays, multi-path, receiver noise, phase ambiguities). Triple (and more) frequency combinations allow the geometrical information to also be removed, leaving only the remaining error terms (a frequency-weighted average), which will facilitate their study and mitigation.
