Enabling & Support

Method to determine the integrity of positioning information in a Global Positioning System

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ESA / Enabling & Support / Space Engineering & Technology

557 - Abstract:

The European Space Agency is offering an innovative mathematical tool for accurate, simpler and fully-controlled determination of the positioning information provided by the Global Positioning System (GPS). Such a tool can be applied in any navigation system where safety is a top priority, for example in an aircraft’s landing phase. More generally, such an advanced algorithm can significantly enhance accuracy of civil aviation, harbour docking, ship and rail navigation and transportation procedures.

Description of the offer

The proposed innovative method allows identifying the integrity of the positioning information provided by the Global Positioning System (GPS).

As a matter of fact, GPS and Galileo satellites or space vehicles self-monitor their positions, therefore in order to detect failure operations that could affect the accuracy and the reliability of the position information, a more reliable method than existing ones should be implemented.

If failure occurs, the calculation of the positioning might be affected by strong inaccuracy, because it is determined using the position of the sending satellite and the run length of the signal, which is directly affected by failure.

The innovation of the method proposed relies in the fact that it determines the integrity of the positioning information. The integrity is based on two factors:

1. Measure of trust in the correctness and reliability of the information provided by the GPS/Galileo, especially for safety critical applications (e.g. landing of airplanes).
2. Evaluation of the integrity performance indicator which is the Integrity Risk, i.e. the probability to exceed a predetermined threshold without being detected or without receiving an alert

Currently the Integrity Risk (or Protection Level) parameter is determined with Receiver Autonomous Integrity Algorithm (RAIM) using either:

External integrity data sources (for example SBAS) or
External integrity data provided by the navigator message

The innovation of the proposed method relies is based on:

First Probability: when the position error exceeds the error threshold because of undetected abnormal conditions of the space vehicle
Second Probability: probability of occurrence of a single Failure event
Third Probability: probability of an impact of the occurrence of the single failure event on the positioning information determination.

The new positioning calculation is therefore based on a combination of the three above mentioned parameters, determining the integrity parameter on the basis of the input parameter and on the basis of a first relation between the integrity parameter and the input parameter and the plurality of integrity information parameters. In brief, such method of calculation is exact.