Thinking on GNSS System Time Scale and Interoperability

Nikolai B. Kosheliaevskii

Abstract:	The more global satellite navigational systems become operational more frequently arises issues on interoperabil-ity these systems. As an example let us look at ICG meeting discussion: Jörg Hahn, “Galileo Implementation Status and Performance”, Werner Enderle, Erik Schoenemann, “ESA Proposal for Multi GNSS Ensemble Time - MGET”. Some of these proposals for example call upon Galileo-GPS Timing Offset (GGTO) as a system contribution to achieve tighter interoperability. In this case, there has to be a special agreement between corresponding providers and GGTO has to be broadcasted in GNSS navigation message. The other solution proposes new time scale - Multi GNSS Ensemble Time – MGET. This decision suppose special institution (for example IGS) responsible for generation MGET. Ones more – this solution supposes that particular GNSS (k) provider has to upload in GNSS navigation message MGET- System (k) Time. On other hand, even now we have a good example of maintenance GNSS System Time referring to the world refer-ence time scale UTC - strictly speaking to its local real time realization UTC (k). For example, the uncertainty uA, (Standard Deviation) of the UTC(USNO) - GPS ST < 2 ns, UTC(SU) - GLO ST < 3 ns. On other hand corresponding RMS values UTC - UTC(USNO) < 2 ns and UTC - UTC(SU) < 2 ns. So total GPS ST – GLO ST uncertainty < 5 ns without any contrivance. The achieved level is well above initial services target for GPS/GALILEO - 20 ns (95%). It seems there is no need to introduce any other time reference scale to solve GGTO problem but UTC. Proposals to refer to UTCr does not look correct because of only UTC ensure worldwide time scale traceability. UTCr looks like a prompt in a classroom. Perhaps the only issue to be defined by ICG is Recommendation or even Agreement between GNSS providers on UTC - GNSS(k) ST value.
Published in:	Proceedings of the 50th Annual Precise Time and Time Interval Systems and Applications Meeting January 28 - 31, 2019 Hyatt Regency Reston Reston, Virginia
Pages:	117 - 121
Cite this article:	Kosheliaevskii, Nikolai B., "Thinking on GNSS System Time Scale and Interoperability," Proceedings of the 50th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, January 2019, pp. 117-121. https://doi.org/10.33012/2019.16767
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