Time References in GNSS

Fundamentals
Title	Time References in GNSS
Author(s)	J. Sanz Subirana, J.M. Juan Zornoza and M. Hernández-Pajares, Technical University of Catalonia, Spain.
Level	Basic
Year of Publication	2011

Regarding the GNSS, the GPS Time (GPST), GLONASS Time (GLONASST), Galileo System Time (GST) and BeiDou Time (BDT) are the reference times used in GPS, GLONASS and Galileo applications, respectively.

GPST is defined by the GPS Control segment on the basis of a set of atomic clocks aboard the satellites and in the Monitor Stations. It is synchronised with the UTC(USNO) at nanosecond level. The origin epoch of GPS time is 0^h UTC (midnight) of January 5th to 6th 1980 (6^d· 0). At that epoch, the difference TAI−UTC was 19 seconds, thence GPS−UTC=n − 19^s.

GLONASST is generated by the GLONASS Central Synchroniser and the difference between the UTC(SU) and GLONASST should not exceed 1 millisecond plus three hours (i.e.,[math]\displaystyle{ GLONASS=UTC(SU)+3^h-\tau }[/math], where [math]\displaystyle{ |\tau|\lt 1 milisec. }[/math]).

GST will be maintained by the Galileo Central Segment and synchronised with TAI with a nominal offset below 50 ns. The GST start epoch is 0^h UTC on Sunday, 22 August 1999 (midnight between 21 and 22 August).

BDT started at 0^h UTC on January 1st, 2006 and is synchronised with UTC in [math]\displaystyle{ 100 ns }[/math] (modulo one second), [BeiDou-SIS-ICD-Test, 2011].

References

• BeiDou-SIS-ICD-Test, 2011. Technical report. BeiDou Navigation Satellite System Signal In Space. Interface Control Document (Test version), December 2011.