What is EGNOS?

I was asked this question at a job interview many years ago and I did not know the answer … I didn´t get the job, but I have no regrets! let me explain a bit …

The European Geostationary Navigation Overlay System (EGNOS) is an enhancement and extension of GNSS (GPS/GLONASS). It is the European SBAS (Satellite Based Augmentation System). The other SBAS systems are WAAS (Wide Area Augmentation System in the USA, MSAS in Japan, SNAS in China, etc. This fact sheet from ESA explains it all very well.


The fact that all the different systems from around the world work together is a testament to international cooperation/collaboration in this case through ICAO (International Civil Aviation Authority) so that the messages transmitted using the different SBAS systems can be interpreted by all the SBAS qualified GNSSS receivers.

The Overlay part of the system refers to the fact that EGNOS transmits from Geostationary orbit (36000 Km) on L1 (1575.42 MHz) a message with additional information to help GNSS users. This additional information helps users

The information transmitted by EGNOS is received similarly to the GPS and GLONASS navigation messages. The EGNOS message is used on-board the user receiver to provide integrity to the GNSS service (GPS/GLONASS). This integrity provides protection levels to the GNSS users against constellation problems and malfunctions and it can improve the positioning accuracy.

EGNOS is therefore considered the pre-cursor of Galileo “The European GNSS system”

Additional resources:


Salabert, F., “Interoperability, from Signals to Integrity”, GPS World, pp 10-12, Nov 2008.

Leave a Reply