Timing Calibration of a GPS/Galileo Combined Receiver
NAVAL OBSERVATORY WASHINGTON DC
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Navigation users will soon benefit from multiple GNSS satellite constellations, potentially doubling or tripling the number of usable GNSS satellites. The improved satellite visibility, and reduced dilution of precision DOP, will be particularly useful in urban canyon environments where sky visibility is challenged. The independent GNSS navigation time scales are typically traceable to UTC module whole seconds to better than 50 nanoseconds. To be useful for precision navigation solutions, this error needs to be reduced to below 5 nanoseconds. Therefore in 2004, GPS and Galileo agreed to develop and jointly broadcast a GPS-to-Galileo Time Offset GGTO message, which user receivers may use for system-to-system navigation timing traceability. Working in cooperation, USNO representing GPS and ESA Galileo Project have agreed upon several methods to compute and coordinate the GGTO values. During the initial stages of the coordination, and throughout Galileos In-Orbit Validation IOV campaign, the different methods will provide validation to the GGTO computations, ensuring the most accurate results. One of the techniques to be employed by USNO will utilize a GPSGalileo combined receiver. For its proper application, the special GGTO monitoring receiver must be precisely calibrated to account for its internal time delays among all of the GPS and Galileo channels. In September of 2012, USNO and ESA teamed up to perform calibrations of the USNO and ESA GGTO receivers using a combined GPSGalileo multiconstellation simulator Spirent, located at the European Space Research and Technology Centre ESTEC in Noordwijk, Netherlands. This paper details the procedures and the results of the experiment.
- Test Facilities, Equipment and Methods
- Navigation and Guidance