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.
White Paper: Countermeasure for GNSS receiver failure (Multipath, Jamming, Spoofing, Interruption of GNSS signal)
Telecommunication article: Basics of Network Time Synchronization
|WARMUP||A state in which the receiver is waiting for the oscillator to have reached stability immediately after power-on.|
|PULL-IN||GNSS satellite signals are received and the VCLK frequency and PPS are being synchronized to the synchronization target based on the time obtained from the GNSS satellite signals.|
|COARSE LOCK||GNSS satellite signals are received and the VCLK frequency and PPS are synchronized to the synchronization target based on the time obtained from GNSS satellite signals. However, the synchronization precision is still coarse.|
|FINELOCK||GNSS satellite signals are received and the VCLK frequency and PPS are precisely synchronized to the synchronization target based on the time obtained from GNSS satellite signals.|
|HOLDOVER||When the GNSS satellite signals can no longer be received, it transitions into this mode if the learning period has been completed in advance. It automatically provides optimal control of the oscillator, taking into account its frequency aging characteristics and frequency-temperature characteristics, to maintain the accuracy and stability of the VCLK frequency and PPS at a much higher level than in free-running condition.|
|OUT OF HOLDOVER||It transitions into this mode after the holdover period has reached its maximum or when the GNSS satellite signals can no longer be received while the learning is not yet completed.|
|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. The time precision of this mode is inferior to TO mode, but it must be used for non-static applications, in in-vehicle applications. In this mode, at least four or more satellites, except SBAS satellites, must be received.|
|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. It is possible to set the receiver in TO mode, by sending a command to the receiver with its precise position coordinates.
In TO mode, a GNSS receiver outputs a more accurate and stable PPS and VCLK frequency. In this 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. SS mode is the mode for position estimation processing, which calculates the latitude, longitude, altitude of the static antenna installation location and time every second.
The SS mode is suitable for applications where the use of TO mode is desired but the exact static position of the GNSS receiver is unknown and must be first determined. Once the GNSS receiver has calculated its static position for a long enough period of time (24 hours by default) and/ or with a certain accuracy (configurable), it automatically transitions into TO mode.
We provide technical white papers for each of the typical failures caused by GNSS receiver. For each failures, our experts in time synchronization explain details about countermeasures on receiver side, using diagrams to show the effectiveness, and how to select products. If you are considering a GNSS receiver for the first time, please take a look.
A basic explanation of how NTP/PTP works! Basics of Network Time Synchronization
A special download of the feature article "Basics of Network Time Synchronization," which published in the December 2021 issue of Telecommunication, is available.
The magazine covered multiple companies, resulting in a comprehensive article that is not biased toward any one company.
You can view the PDF as it looks in the magazine.
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