NAVIOR-24S
™
CHAPTER IV
Operation and Performance
64
NAVIOR-24S ™
Revision
V1.00 20.05.2008
GPS/GLONASS Timing
In many timing applications, such as time/frequency standards, site synchronization systems and
event measurement systems, GPS/GLONASS receivers are used to discipline local oscillators.
The GPS constellation consists of 24 orbiting satellites. Each GPS satellite contains a highly-stable
atomic (Cesium) clock, which is continuously monitored and corrected by the GPS control segment.
Consequently, the GPS constellation can be considered a set of 24 orbiting clocks with worldwide
24-hour coverage.
GPS receivers use the signals from these GPS “clocks” to correct its internal clock, which is not as
stable or accurate as the GPS atomic clocks. GPS receivers like the NAVIOR-24S GPS/GLONASS
receiver output a highly accurate timing pulse (PPS) generated by its internal clock, which is
constantly corrected using the GPS clocks. This timing pulse is synchronized to GPS within ±25 ns.
In addition to serve as a highly accurate stand-alone time source, GPS/GLONASS receivers are
used to synchronize distant clocks in communication or data networks. This synchronization is
possible since all GPS/GLONASS satellite clocks are corrected to a common master clock.
Therefore, the relative clock error is the same, regardless of which satellite or satellites are used.
For timing applications requiring a “common clock”, GPS is the ideal solution.
The position and time errors are related by the speed of light.
The hardware and software implementation affects the GPS/GLONASS receiver's PPS accuracy
level. The receiver's clocking rate determines the PPS steering resolution.
The NAVIOR-24S GPS/GLONASS receiver clocking rate is 40.0 MHz. This rate corresponds to a
steering resolution of ±25 ns.
When using both systems (GPS and GLONASS) in NAVIOR-24S receiver time, except
coordinates, on one of these systems is determined. After that time displacement between these
systems is determined. Moreover, transmitted from satellites data contain the information about the
deviation of UTC time from GPS scale and the deviation UTC (SU) from GLONASS scale. Using
time of chosen system user can get time value in any of these scales.
