The EGNOS signal is broadcast by two Inmarsat-3 satellites – one positioned east of the Atlantic and the other above Africa – and by the European Space Agency’s (ESA) Artemis satellite, also located above Africa. These three satellites’ orbits are in the equatorial plane, at three different longitudes, allowing each to broadcast EGNOS services across Europe.
As with GPS satellites, each EGNOS satellite is allocated a unique pseudo-random noise (PRN) number, which allows a user to identify it.
The National Marine Electronics Association (NMEA) standard, used in output mode by most commercially available receivers, allocates a unique identifier to each EGNOS satellite, as described in the table below.
|INMARSAT AOR-E||120||33||15.5 W|
|INMARSAT IOR-W||126||39||25 E|
As a general rule, two out of the three available satellites are used operationally to broadcast the EGNOS message. The third is used for maintenance, testing and validation purposes (currently PRN126).
EGNOS consists of three core services:
- Open Service: free and open to the public, the Open Service is used by mass-market receivers and common user applications;
- EGNOS Data Access Service (EDAS): offered on a controlled access basis (i.e. via the internet and mobile phones) for customers requiring enhanced performance for professional use;
- Safety of Life Service (SoL): for safety-critical transport applications, including civil aviation, which require enhanced and guaranteed performance and an integrity warning system.
Additional information on these services can be found here.
More detailed information on EDAS and how to access this service is available here.