Integrity in GNSS positioning refers to the system’s ability to provide timely and accurate warnings when its output should not be trusted for safety-critical navigation. Unlike accuracy (which measures how close a position is to truth) or availability (which measures how often a position is obtainable), integrity specifically addresses whether the system can be relied upon not to provide misleading information, a critical requirement for applications where incorrect positioning could endanger lives or cause significant harm.
The integrity concept originated in aviation, where navigation system failures during instrument approaches could lead to controlled flight into terrain. This safety imperative drove the development of integrity monitoring frameworks that have since been adapted for automotive, rail, and maritime applications. At its core, integrity requires systems to either provide positioning within specified error bounds or to alert users that the bounds cannot be guaranteed, ensuring that users are never unknowingly operating with hazardously incorrect position information.
Integrity is quantified through several key parameters. The Protection Level (PL) represents a statistical bound on position error, a calculated envelope within which the true position is assured to lie with high probability. The Alert Limit (AL) defines the maximum position error that can be tolerated for safe operation. The Integrity Risk is the probability that the actual error exceeds the alert limit without timely warning. When the computed protection level exceeds the alert limit, the system must trigger an alert, indicating that the position should not be used for safety-critical decisions.
Achieving high-integrity positioning requires comprehensive monitoring of all potential error sources and failure modes. This includes satellite signal quality checks, atmospheric anomaly detection, receiver autonomous integrity monitoring (RAIM), consistency verification between redundant sensors, and validation of correction data. For automotive applications, integrity monitoring extends to sensor fusion algorithms, ensuring that GNSS, IMU, odometry, and perception sensor outputs are mutually consistent. Meeting demanding integrity requirements like those specified for autonomous vehicles requires systematic engineering processes, rigorous testing, and ongoing monitoring throughout the system’s operational life.
