Architecture of WNT

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CGSIC 11 SEP 2001
Latest Developments in using an SBAS for Time
Transfer
Bill Klepczynski Innovative Solutions
International
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Outline

• NovAtel Conversion Program
• CGGTTS Format
• Expansion of Participating Laboratories
• USNO NRC BIPM NIST
• Brief Results of Recent Experiments
• Conclusions

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Conversion toCGGTTS Format

• Pat Fenton, Vice President for RD at NovAtel,
  has developed a program to convert output of a
  NovAtel Receiver to CGGTTS Format
• Facilitates Time Comparisons between Timing Labs
  
• References for CGGTTS Format
• D.W. Allan and C. Thomas, Technical Directives
  for Standardization of GPS Time Receiver
  Software, Metrologia, 31, 1994, pp. 67-79.
• J. Azoubib, W. Lewandowski, CGGTTS GPS/GLONASS
  Data Format Version 02 Document submitted to
  the 7th CGGTTS, 30 November 1998, Reston,
  Virginia, USA, 4 pages.

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Configuration File(Input to CGGTTS Program)

• Required Arguments
• Laboratory Acronym, Coordinates of Lab, Input
  Files, Output File, Precise Ephemeris File
• Optional Arguments
• GEO Satellites, Ionospheric Correction Choice,
  Various Delays, Comments, etc.
• Ionospheric Choices
• L1L2, WAAS Broadcast, EGNOS Broadcast, Klobuchar
  Model, Code-Carrier (Relative)

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CGGTTS Format (Output of Program)
SAT CL MJD STTIME TRKL ELV AZTH REFSV
SRSV REFSYS SRSYS DSG IOE ...
hhmmss s .1dg .1dg .1ns .1ps/s .1ns
.1ps/s .1ns
SAT Satellites Vehicle GPS 1..32, GLONASS
100slot, WAAS/EGNOS Wdd (where dd prn -
100) e.g WAAS prn 122 ? W22, EGNOS 120 ? W20
CL Hexadecimal class byte assigned by BIPM for
scheduled data. No unit.
. . .
REFSV Reference clock-satellite clock at the
mid point of the track. In 0.1 ns
REFSYS Reference clock-satellite system time at
the mid point of the track. In 0.1 ns
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Participating Labs

• USNO - U. S. Naval Observatory, Washington, DC
• NRC - National Research Council, Ottawa, Canada
• BIPM - International Bureau of Weights and
  Measures, Sevres, France
• NIST - National Institute of Standards and
  Technology, Boulder, CO
• FAA has been participating in this effort

These labs have, both, an omnidirectional and a
dish antenna.
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Time Transfer between 2 Labs
USNO - WAAS X BIPM - WAAS A USNO- BIPM X -
A USNO - EGNOS Y BIPM - EGNOS B USNO- BIPM
Y - B
EGNOS AOR-E
WAAS AOR-W
BIPM
USNO
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Discussion - I

• BIPM while it is in the footprint of AOR-W, a
  hill blocks it view
• NIST is out of the footprint of AOR-E

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BIPM - AOR-E (27-28 AUG 2001)
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USNO - AOR-E (27-28 AUG 2001)
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BIPM - USNO (AOR-E)(27-28 AUG 2001)
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NIST - USNO (AOR-W)(27-28 AUG 2001)
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NRC - USNO (6-21 NOV 1999)
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Composite
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Discussion - II

• Remember with GPS SA, two forms of dither - Clock
  Ephemeris.
• Clock Dither did not affect Common View Time
  Transfer.
• Ephemeris Dither would have.
• Time Transfer Error is a function of geometry and
  separation distance.
• Here we see the effect of Geo orbit upload and
  GEO orbit error on Time Transfer.

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Time Transfer between 2 SBAS
USNO - WAAS X USNO - EGNOS Y WAAS - EGNOS Y
- X BIPM - WAAS A BIPM - EGNOS B WAAS -
EGNOS B - A
EGNOS
WAAS
BIPM
USNO
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WAAS - EGNOS via USNO (27-28 AUG 01)
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Conclusions

• Interest in using SBAS for Time Transfer is
  increasing and new developments are continually
  taking place.
• Improvement in the orbits of the geostationary is
  needed in order to take full advantage of the
  benefits of an SBAS.
• Need participation or development of group like
  IGS to get improved orbits. Navigation would
  also benefit.