Monitoring and Performance Assessment of GNSS Inter-constellation Timescale Biases

Yoaz Bar-Sever, Robert Meyer, Kannan Muthuraman, Zoltan Biacs

Abstract: Consistent inter-constellation timing is key to GNSS interoperability. We report a new capability, based on JPL’s Global Differential GPS (GDGPS) System, to monitor, assess, and predict GNSS inter-constellation timescale biases, globally, robustly, and in real-time. We demonstrate sub-nanosecond (one sigma) accuracy in determining the inter-constellation timescale bias on a sub-daily basis among all GNSS constellations with a global footprint, and a somewhat reduced accuracy relative to the regional GNSS constellations. The timescale of a specific GNSS constellation is an attribute of its broadcast ephemeris, and can only be indirectly realized through positioning (and timing) of a receiver (or preferably multiple receivers) relative to another timescale. But that process gets inevitably entangled with receiver timing biases, which are receiver-specific, installation-specific, temperature dependent, signal dependent, and constellation dependent… Therein lies the challenge of accessing, monitoring and inter-comparing the timescales expressed in the broadcast of the GNSS constellations. We compare two approaches for determining the biases between GPS and all other GNSS constellations: GLONASS, BeiDou, Galileo, QZSS, and NAVIC. Both approaches leverage the GDGPS global real-time GNSS tracking network of 60+ geodetic-quality receivers, many of which are in well-controlled environments, including several timing labs. Having so many receivers enable robust quality control and error assessment. We compare our estimates of inter-constellation biases to the values broadcasted by a variety of constellations over the last couple of years, and found general agreement at the few nsec level RMS, but also periods of large discrepancies, depending on the broadcasting constellation. We will discuss the inter-operability implications of errors in the relative timescale, and briefly describe our offering for real-time monitoring and prediction of these timescales.
Published in: Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021)
September 20 - 24, 2021
Union Station Hotel
St. Louis, Missouri
Pages: 1903 - 1916
Cite this article: Bar-Sever, Yoaz, Meyer, Robert, Muthuraman, Kannan, Biacs, Zoltan, "Monitoring and Performance Assessment of GNSS Inter-constellation Timescale Biases," Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021), St. Louis, Missouri, September 2021, pp. 1903-1916. https://doi.org/10.33012/2021.17983
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