Receiver Autonomous Integrity Monitoring

Receiver Autonomous Integrity Monitoring ( RAIM ) is a technology to verify the integrity of GPS. It plays an important role, especially in safety-critical applications such as air and sea travel.

Description

RAIM is used for the detection of errors from the GPS measurements ( pseudo-range ). RAIM traditional use only fault detection ( FD), newer GPS receiver to operate with Fault Detection and Exclusion (FDE), which enables the continuation of the measurement in spite of GPS errors.

RAIM operates autonomously without help from other than GPS signals, ie, without a compass, altimeter or accelerometer. To obtain position signals from at least four satellites are necessary. ( The system must determine four variables: ., The time and the position in three dimensions )

To determine that the measurement is erroneous, the signal of a fifth satellite is required; but then it is only known that any satellite is measured incorrectly and there can be no position can be determined. This corresponds to the Fault Detection ( FD).

To determine which satellite is measured incorrectly, and then determine the correct position of the rest of the signals of six satellites are necessary. The implements Fault Detection and Exclusion ( FDE). However, often more satellites (8-10 ) required by the satellite geometry; For example, if the satellites are in a plane or two close together.

For example, since in aviation PräzisionsGPS - guided en-route, approach and departure navigation is becoming increasingly important these RAIM processes ( Outages due to repositioning ) distributed worldwide by NOTAM ( Notice to Airmen ).