GPS/GNSS receivers can calculate not only the position but also the accurate time by receiving satellite signals. Accurate time information is used in infrastructure such as cell phone base stations, digital terrestrial broadcasting stations, and wireless systems that require time synchronization and accurate frequency.
This glossary mainly focuses on time and explains various associated terms. In addition, related general GPS/GNSS terms will also be explained. The content relates to Furuno's GNSS timing and frequency receivers GF/GT-88 series.
Please note that a"*" denotes a Furuno's original terminology.
28 July 2016
|GLONASS||Navigation Radiosignal in Bands L1, L2
|Galileo||EUROPEAN GNSS(GALILEO) OPEN
Issue 1 revision 3
29 January 2018
13 April 2018
|GPS||1||32||Same as the PRN No|
|GLONASS||65||96||Same as the PRN No|
|Galileo||1||36||Same as the PRN No|
|QZSS L1C/A||93||99||PRN No minus 100|
|QZSS L1S||83||89||PRN No minus 100|
|SBAS||33||51||PRN No minus 87|
|WARMUP||WARMUP is the state in which the internal VCLK frequency is waiting to reach stability immediately after power-on.|
|PULL-IN||PULL-IN is the state in which the GNSS satellite signals are received and the PPS and the VCLK frequency are beginning to be synchronized with UTC time or a GNSS time.|
|COARSE LOCK||COARSE LOCK is the state in which GNSS satellite signals are received and the PPS and the VCLK frequency are roughly synchronized with UTC time or a GNSS time.|
|FINELOCK||FINE LOCK is the state in which GNSS satellite signals are received and the PPS and the VCLK frequency are precisely synchronized with UTC time or a GNSS time.|
|HOLDOVER||HOLDOVER is the state in which GNSS satellite signals are no longer received after the learning period was completed and the PPS and the VCLK frequency are maintained to a certain accuracy and stability, by automatically taking into account the frequency aging characteristic and frequency-temperature characteristic of the oscillator, providing better performances than in free-running mode.|
|OUT OF HOLDOVER||OUT OF HOLDOVER is the state in which GNSS satellite signals are no longer received either for period of time greater than the holdover period or before the learning period was completed. In this state the accuracy and stability of the PPS and the VCLK frequency are not maintained. The oscillator is in free-running mode.|
|Position estimation refers to the process of calculating a position fix with insufficient accuracy. The results of such calculation is referred to as the estimated position.|
|NAV mode||NAV mode stands for Navigation Mode. In this mode the GNSS receiver calculates the latitude, longitude, altitude, speed, azimuth, and time every second.
A GNSS receiver dedicated to time sensitive applications must be set in NAV mode if it is used in non-static applications.
|TO mode||TO mode stands for Time Only mode. In this mode the GNSS receiver must operate in static position, must already know its precise position, and only calculates the time every second.
In TO mode, a GNSS receiver outputs a more accurate and stable time, PPS and VCLK frequency. In TO mode a GNSS receiver can continue to calculate the time even when it receives only one GNSS satellite signal.
|SS mode||SS mode stands for Self-Survey mode. In this mode the GNSS receiver must operate in static position and calculates the latitude, longitude, altitude and time every second. It calculates its static position with a high accuracy based on the positional information obtained over a long period of time. To do so it must receive four or more GNSS satellite signals, excluding SBAS satellite signals.
In SS mode, even if at a time less than four but more than one GNSS satellite signals are received, the GNSS receiver can continue to output accurate time using the fixed position information calculated up to that point of time and the same processing technic as in TO mode. This allows the GNSS receiver to keep outputting accurate time, PPS or VCLK frequency.
The SS mode is suitable for situations where the use of TO mode is desired but the exact static position of the GNSS receiver is unknown and must first be determinated. Once the GNSS receiver has calculated its static position for a long enough period of time and/ or with a certain accuracy (configurable), it automatically transitions into TO mode.
|CSS mode||CSS mode stands for Continuous Self-Survey mode.
While in SS mode, the GNSS receiver discards its surveyed position when powering off, in CSS mode, it backs it up in BBRAM (back-up memory) and continues calculating its position after powering on again, starting from the backed-up position.
|Fixed position||The fixed position is the 3D position (latitude, longitude, altitude) of the fixed point to be set in the GNSS receiver when using the TO mode.|
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