Receiver autonomous integrity monitoring
Receiver Autonomous Integrity Monitoring (RAIM) is a technology for checking the integrity of GPS . It plays an important role especially in safety-critical applications such as aviation and shipping.
description
RAIM is used to detect errors in GPS measurements (pseudorange). Traditional RAIM only use Fault Detection (FD), newer GPS receivers operate with Fault Detection and Exclusion (FDE), which enables the measurement to be continued despite GPS errors.
RAIM works autonomously without the help of signals other than GPS, i.e. without a compass, altimeter or acceleration sensors. To get a position, signals from at least four satellites are necessary. (The system has to determine four variables: time and position in three dimensions of space.)
In order to determine that the measurement is incorrect, the signal from a fifth satellite is required; but then it is only known that some satellite is being measured incorrectly and no position can be determined. This corresponds to Fault Detection (FD).
In order to determine which satellite is incorrectly measured and then to determine the correct position from the remaining ones, the signals from six satellites are necessary. This is implemented by Fault Detection and Exclusion (FDE). However, due to the satellite geometry, more satellites (8-10) are often required; for example, when the satellites are on the same plane or two are close together.
Since z. If, for example, precision GPS-guided route, approach and departure navigation is becoming increasingly important in aviation, these RAIM processes (outages due to repositioning) are distributed worldwide using NOTAM (Notice to Airmen).
literature
- RG Brown: A Baseline RAIM Scheme and a Note on the Equivalence of Three RAIM Methods . In: Navigation: Journal of The Institute of Navigation 39 . No. 3 (Fall 1992): 301-316.
- BW Parkinson and P. Axelrad: Autonomous GPS Integrity Monitoring Using the Pseudorange Residual . In: Navigation 35 . No. 2 (Fall 1988): 255-274.
- BW Parkinson, JJ Spilker Jr. et al., Eds. (1996): The Global Positioning System: Theory and Applications; Volume I & II . In: Progress in Astronautics and Astronautics . American Institute of Aeronautics and Astronautics, Inc, Washington 1996.