Definition
GNSS (Global Navigation Satellite System) refers to all satellite positioning systems, including the United States GPS, China's Beidou, Russia's GLONASS, and the European Union's Galileo. Industrial terminals obtain latitude, longitude, speed, and time through GNSS modules for vehicle, asset, and personnel positioning.
Multi-system integration
Multi-mode GNSS receivers can simultaneously receive signals from multiple systems, increasing the number of satellites visible and improving positioning availability (in obstructed or multipath environments) and accuracy. In China and surrounding areas, GPS+BeiDou dual-mode can significantly improve positioning performance. Timing applications (power, communication, finance) highly rely on GNSS time synchronization, and multiple systems can enhance timing reliability.
Accuracy and Enhancement
Standard positioning accuracy is approximately 5–10 m; SBAS (satellite-based augmentation), ground-based augmentation (CORS/RTK) can achieve decimeter to centimeter-level accuracy. High-precision applications (autonomous driving, precision agriculture, surveying and mapping) require RTK or PPP technology. When selecting industrial terminals, the accuracy requirements, whether multi-system support is needed, and whether timing output is required should be determined according to the application scenario.
Use Cases
Applications include vehicle networking, logistics tracking, ship positioning, personnel inspection, asset tracking, power inspection, and geological disaster monitoring. Combined with RTLS indoor positioning and Geofencing geofencing, integrated indoor and outdoor positioning services can be realized.
Satellites in view and dilution of precision
Global satellite navigation is the name of a family of systems. Which constellations a receiver uses at the same time is decided by the antenna, the radio front end, and the ephemeris together. A large number of satellites in view only says there is signal. Dilution of precision says whether those satellites are spread across the sky. When they bunch in one direction, the horizontal position or the height is stretched, and the satellite count still looks normal. The value of several constellations is mainly to fill a missing direction where the sky is blocked, not to erase the error in open country. Timing looks at the offset between receiver time and system time, and at whether the one-pulse-per-second output is stable. A positioning lamp that is on does not mean the pulse is usable.
The conditions start at the antenna: clear sky above, distance from heat and from transmitting antennas, feeder loss left inside the budget, and the supply voltage of an active antenna arriving at the antenna. A vehicle roof, a lamp post, and a mast are mounted in different directions. Sticking the antenna to a metal side is blocking half the sky yourself. A city, a forest, and a workshop door have to accept multipath. Multipath slides the position along the reflecting surface. Smoothing can make the track look tidy, and it cannot restore the stretch that the reflection pulled aside. Metre-level or centimetre-level work needs corrections of its own. The status word of a standalone fix must not be labeled as a differential fix.
Datums and antenna mounting
The interface description has to say which geodetic datum the longitude and latitude belong to. If the map, the fence, and the site control points are not in the same datum, there is a shift in a fixed direction. The shift does not jitter with time, so it looks like an installation offset, and it is actually a conversion that was never done. Ellipsoidal height and orthometric height are not the same number. Comparing ellipsoidal height with a benchmark height leaves a systematic height error on a pond or a roadbed. Taking many digits after the decimal does not add real precision. The number of digits should match the state of the current solution.
Cold, warm, and hot starts differ in whether the ephemeris and the time are still valid. A slow first fix after a long power-off is expected. Do not use that duration to judge tracking performance. Under a metal box, in a basement, and under a dense canopy the output should be invalid, not an extrapolation of the last point with no mark that it is extrapolated. When the receiver is combined with an inertial sensor, position during a satellite outage is a dead-reckoned value. When lock returns it may jump back. The application has to accept that jump or limit it. After snow, paint, or a newly installed piece of equipment shades the antenna, the carrier-to-noise ratio falls across the board. Check the antenna before replacing the receiver module.
Correction age and the extrapolation mark
A standalone solution, a differential solution, and a precise solution are not in the same error class. The status word has to change with whether the corrections are valid. If corrections stop and the status is still written as differential, a fence and a mileage total downstream will trust it too far. A position held by extrapolation or by inertial sensors must be marked. It must not share a quality class with a satellite solution. The jump when lock returns is a correction, not a new movement. Mileage should skip that jump or book it separately.
When snow, a coating, or newly installed equipment shades the antenna, the carrier-to-noise ratio falls together. Clean and check the installation before suspecting the receiver. Account for feeder loss and antenna gain at the frequency in use. Changing band without changing the antenna reduces the number of satellites. Before height is used to tell one level from another, confirm whether the output is ellipsoidal height or orthometric height, and leave margin in the threshold. Truncate decimal places to the current state, so a standalone solution is not displayed as centimetres. Count the first fix after a long shutdown on its own. Do not let it stand for tracking performance.
When dilution of precision grows, horizontal or height error stretches even if the satellite count did not fall. A threshold on count alone will treat that solution as high quality. When several constellations are used together, the receiver estimates the time offset of each. In the first minutes before that estimate has converged, position may jump, and that stretch of track should be down-weighted. The antenna phase center and the device reference point are not the same place. The lever arm from a roof antenna to the center of the vehicle has to be removed in the application, or the track swings outward in a turn. Before a height threshold is used for a slope or a floor, confirm what the output height means, and avoid the heavy multipath under a bridge. A break in the correction source has to show up in the status word within a second. The application should see the status change before it decides whether to keep using the point.