In critical applications, the reliability of GNSS receivers must always be ensured. Protection level information is calculated in real-time by GNSS receivers to quantify the reliability of positioning information, improve data quality and protect the safety of personnel and assets.
The protection level of a GNSS receiver indicates the maximum possible positioning error with a certain confidence level. For example, if a GNSS receiver has a protection level of 1 meter with a 95% confidence level, there is only a 5% chance that the reported fix is more than 1 meter away from the true fix. Like the accuracy of a GNSS receiver's position information, the level of protection will fluctuate, and all sources of error in GNSS will affect the level of protection. The protection level continuously provides an upper bound on the expected error of the GNSS receiver, allowing the application to adjust its behavior based on the quality of the received information and to discard unreliable values.
The figure above is an example of protection level application. Black represents the true localization of the robotic lawnmower, and gray represents the measured localization. The receiver continuously calculates a position accuracy estimate, represented by a dotted dot. The Protection Level is represented by a dotted circle around the reported position, which provides an estimate of the positioning accuracy and defines an area with a high degree of confidence in the true positioning of the GNSS receiver. robot navigation
In robotic navigation, protection levels help ensure that equipment, such as a robotic lawn mower, stays within a geofence (and away from a neighbor's flowerbed). If the protection level is too high, the robot can adjust its behavior to slow down or move backwards to a "safe" position, taking into account the poor quality of the localization estimate. If the protection level value cannot be calculated, the device can stop and wait for various sources of environmental error (such as radio frequency interference, adverse atmospheric conditions, etc.) to disappear or return to normal until a valid protection level value is obtained. Drones and UAVs
For drones and other UAVs (unmanned aerial vehicles), the level of protection can be used to determine the reliability of GNSS positioning, determining whether it is sufficient to support delicate maneuvers such as landing and strict avoidance of no-fly zones. If the protection level exceeds a threshold, the drone may return to a previously known location. Only if the protection level value is below a threshold, the drone lands and, if needed, hovers in place until the protection level indicates that the quality of the position estimate has improved. Cars, Electric Scooters
Cars, electric scooters, and other connected mobility solutions can use the protection level feature to assess the quality of the vital location data they report to their servers. Parked vehicles, for example, only report their location when the protection level falls below established limits, making it easier for workers and customers to find them. The level of protection required, from basic protection level to functional safety, varies by application and largely depends on the expected reliability of the GNSS receiver and how critical its position estimate is. For a specific asset tracking solution, a GNSS receiver with an accuracy of 2 meters and a protection level of 3.5 meters at a 95% confidence level may be well suited. Self-driving cars, on the other hand, may have much more stringent requirements, requiring a 99.9999% confidence level of protection. Basic protection levels add value to many consumer and industrial applications , but critical automotive-grade applications require more stringent levels of protection to achieve "functional safety" as defined in the ISO 26262 standard.