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External Ground Monitoring v. Receiver Monitoring

Published online by Cambridge University Press:  21 October 2009

R. Johannessen
R. Johannessen
Affiliation:
(STC Technology Ltd)
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Extract

The transmissions from GPS and GLONASS navigation satellites include information about the state of those transmissions as perceived by the control centre. In the case of GPS, for example, this information is contained in the data stream in Subframe 1 Word 3. However, with some of the failure conditions that can arise there is a delay of the order of half an hour before this message is altered to signal that a failure exists. A situation can therefore arise when the satellite signals that all is well, whereas in fact it is not. The very high levels of integrity which civil aviation require before satellite navigation can be used with confidence therefore means that the warning messages from the satellite must be augmented by some other form of monitoring. Two alternatives exist: (1) to have a monitor at some fixed and surveyed ground location which broadcasts a warning to the navigating aircraft when there is a malfunction (ground monitoring), or (2) to arrange for the navigating receiver to perform its own internal monitoring, known as receiver autonomous integrity monitoring (RAIM). Each alternative is beneficial in its own way.

Keywords

1. Air navigation.2. Satellites.
Type
Research Article
Information
The Journal of Navigation , Volume 44 , Issue 1 , January 1991 , pp. 11 - 24
Copyright
Copyright © The Royal Institute of Navigation 1991

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