Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/iau-comm31/pdf/2009_IAUGA_JD6/JD6_4_1952_Tuckey.pdf Дата изменения: Fri Aug 6 03:07:17 2010 Дата индексирования: Mon Feb 4 08:44:19 2013 Кодировка: Поисковые слова: annular solar eclipse

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


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 only 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


GPS and Galileo frequency bands

Galileo Joint Undertaking, 2005


Reminder of current GPS usage: s ignals
Signals used L1 (1575.42 MHz):


C/A code P code ("P1") carrier phase P code ("P2") carrier phase

L2 (1227.60 Mhz):



Reminder of current GPS usage: comparison methods
Common view, C/A code usually multi-satellite 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


Galileo


european GNSS 2 experimental satellites currently in orbit launch of 4 In Orbit Validation satellites by end 2010 fully operational (27+3 satellites) by end 2013







ESA ­ J. Huart


Galileo services
Open Service (OS) Safety of Life (SoL) Commercial Service (CS) Open access, free, dualfrequency OS + integrity, authentification, service guarantees Encrypted commercial data, service guarantees, higher precision Encrypted, high precision, robust signal, for security applications. Emergency beacon detection and return message forwarding

Public Regulated Service (PRS) Search and Rescue support service (SAR)


Galileo signals

Galileo Joint Undertaking, 2005


Galileo signal usage for time transfer metrology
Thus Galileo OS will provide 4 single-frequency signals:


E5A, E5B, E5, L1F

allowing 6 dual-frequency (ionosphere-free) combinations:


E5A-L1F, E5B-L1F, E5-L1F E5A-E5B, E5A-E5, E5-E5B


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.


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 of 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).


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.


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 calibration uncertainties ~ 0.8 ns -> P3 uncertainty ~ 2.3 ns -> link uncertainty ~ 3.2 ns


Thanks


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


Galileo services and signals
E5A E5B E6C OS SoL CS PRS x x x x x x x x E6 E6P L1F x x x x L1 L1P


More information on Galileo signals
Typical C/N0 dB-Hz E5A E5B E6C E6P L1F L1P 50 50 50 50 48 48 Chip rate Data rate Mcps 10.23 10.23 5.115 5.115 1.023 1.023 sps 50 250 1000 1000 250 250 Encryption Ranging Data

No No No Partial Commercial Governmental No Partial Governmental

Note: E5A + E5B = "E5" signal


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.