260
14 Pseudo-Ranging Radio Navigation Systems
Fig. 14.8 GALILEO orbital
constellation
Fig. 14.9 Spectrum of navigation radio signals of GALILEO system
been formed, which also ensures the participation of the international community in
defining and maintaining the GTRF coordinate system.
The Galileo System Time (GST) system time scale is a continuous atomic time
scale with a constant offset of an integer number of seconds relative to TAI international atomic time. The GST has a variable discrepancy with the UTC time scale by
an integer number of seconds.
The GST scale is maintained by a system of atomic frequency standards based
on active hydrogen generators. To correct the GST, the GALILEO ground control
complex synchronization system receives information on the TAI time scale from the
International Bureau of Weights and Measures. According to the technical requirements for the GALILEO system, the discrepancy between GST and TAI should not
exceed 50 ns with a probability of 95%.
Information on the discrepancy magnitude of the GST time scale relative to the
TAI and UTC scales is included in the navigation message for transmission to users.
The time in the navigation message is transmitted in a format similar to GPS, in
the form of the week number and the number of seconds within the current week.
In the navigation message, in comparison with GPS, the number of digits intended
for transmitting information on the week number has been increased. This provides
time measurement for 4096 weeks (over 78 years), which is more than the analogous
parameter of the GPS, where the interval is 1024 weeks or 19.5 years.
14 Pseudo-Ranging Radio Navigation Systems
Fig. 14.8 GALILEO orbital
constellation
Fig. 14.9 Spectrum of navigation radio signals of GALILEO system
been formed, which also ensures the participation of the international community in
defining and maintaining the GTRF coordinate system.
The Galileo System Time (GST) system time scale is a continuous atomic time
scale with a constant offset of an integer number of seconds relative to TAI international atomic time. The GST has a variable discrepancy with the UTC time scale by
an integer number of seconds.
The GST scale is maintained by a system of atomic frequency standards based
on active hydrogen generators. To correct the GST, the GALILEO ground control
complex synchronization system receives information on the TAI time scale from the
International Bureau of Weights and Measures. According to the technical requirements for the GALILEO system, the discrepancy between GST and TAI should not
exceed 50 ns with a probability of 95%.
Information on the discrepancy magnitude of the GST time scale relative to the
TAI and UTC scales is included in the navigation message for transmission to users.
The time in the navigation message is transmitted in a format similar to GPS, in
the form of the week number and the number of seconds within the current week.
In the navigation message, in comparison with GPS, the number of digits intended
for transmitting information on the week number has been increased. This provides
time measurement for 4096 weeks (over 78 years), which is more than the analogous
parameter of the GPS, where the interval is 1024 weeks or 19.5 years.