What is EGNOS?

EGNOS is Europe’s first venture into satellite navigation. It currently augments the positioning signals provided by the GPS and makes them suitable for safety critical applications such as flying aircraft or navigating ships through narrow channels. In the near future, EGNOS will be upgraded to augment Galileo signals, in addition to GPS.

What is the difference between GPS and EGNOS?

GPS is a global navigation satellite system (GNSS) that allows anyone with a GPS receiver to navigate from anywhere in the world. EGNOS is a satellite-based augmentation system (SBAS) that makes the GPS signal more precise. EGNOS also provides an integrity signal about GPS performance by broadcasting error corrections to the users in Europe via three geostationary satellites. This means that without a GPS signal, EGNOS will not work.

Who uses EGNOS?

EGNOS increases the accuracy and integrity of the GNSS signal, making it suitable for use by aircraft, ships, trains and other forms of transport as well as agriculture. 

How does EGNOS work?

EGNOS provides the information needed to use GNSS navigational signals for safety critical applications. It improves the accuracy of GNSS position measurements, informs users of the errors in the position measurements and warns of disruptions to the satellite signals.

The EGNOS signal is transmitted by three geostationary satellites: two Inmarsat-3 satellites, one over the eastern part of the Atlantic the other over the Indian Ocean, and the ESA Artemis satellite above Africa. Unlike GPS satellites, these satellites do not have signal generators on board. A transponder transmits signals up-linked to the satellites from the ground, where all the signal processing takes place.

The EGNOS ground segment consists of 34 Ranging and Integrity Monitoring Stations (RIMS), four Master Control Centres (MCC) and six Up Link Stations (ULS).

The RIMS measure the positions of each EGNOS satellite and compare accurate measurements of the positions of each GNSS satellite with measurements obtained from the satellites’ signals. The RIMS then send this data to the MCCs via a purpose-built communications network.

The MCCs determine the accuracy of the GNSS signals received at each station and determine position inaccuracies due to disturbances in the ionosphere. All the deviation data is then incorporated into a signal and sent via the secure communications link to the up-link stations, which are spread across Europe. The up-link stations send the signal to the three EGNOS satellites, which then transmit it for reception by users with an EGNOS-enabled GNSS receiver.

The GNSS-like signals from the three transponders can be used as additional signals to fix a user’s position. They also provide information about the accuracy of the position measurements delivered by GNSS so that users can assess whether the position is accurate enough to rely on.

The information, or integrity data, is modulated onto the ranging signal. It includes accurate information on the position of each GNSS satellite, the accuracy of the atomic clocks on board the satellites and information about disturbances within the ionosphere that might affect the accuracy of the positioning measurements.

Considerable redundancy is built into EGNOS so that the service can be guaranteed practically all the time. At any one time, only one MCC will be ‘the master’, with another on stand-by to take over instantaneously should the first one fail. There is redundancy in the up-link stations, too. Only three are needed to operate EGNOS, one for each satellite. The other three are in reserve in case of a failure.

How much should I pay for EGNOS?

Anyone with an EGNOS-enabled receiver can use EGNOS’ services free of charge.

Is EGNOS the only SBAS?

In addition to EGNOS, two other SBAS are currently operational: WAAS in the USA,  MSAS in Japan and KAAS in Korea.

Each of these systems complies with a common global standard, meaning they are both:

  • Compatible: the systems do not interfere with each other
  • Interoperable: a user with a standard receiver can benefit from the same level

of service and performance regardless of what coverage area they are in.

Who designed and developed EGNOS?

EGNOS has been developed through a tripartite agreement between the European Space Agency (ESA), the European Commission (EC) and Eurocontrol, the European Organisation for the Safety of Air Navigation. The agreement was signed in 1998.

Who operates EGNOS?

While the exploitation of EGNOS is the responsibility of EUSPA, the operational management and maintenance of EGNOS is assigned to the EGNOS service provider under a contract with EUSPA. The current service provider is ESSP (European Satellite Services Provider).

Who owns EGNOS?

EGNOS is owned by European Union citizens. The European Commission took over ownership of the EGNOS infrastructure from the European Space Agency (ESA) on behalf of the European Union on 1 April 2009. On 1 January 2014, the European Commission fully delegated the exploitation of EGNOS to EUSPA.

Can EGNOS provide an accurate time reference?

Yes, EGNOS provides a real-time distribution of Coordinated Universal Time (UTC) for the benefit of time/frequency users. EGNOS uses a system time known as EGNOS Network Time (ENT), which is linked to UTC, notably through the installation of an EGNOS ground station at the Observatoire de Paris, which itself provides UTC reference time for France.

All the differential corrections broadcast by EGNOS are referenced according to ENT. Thus, the time obtained by the user when they calculate their position using EGNOS data is also referenced in ENT and not GPS time. In addition, EGNOS broadcasts a specific message containing several parameters that allow the receiver to estimate UTC. The user then has a precise, reliable time directly synchronised with UTC. The accuracy obtained relative to UTC is less than 50 nanoseconds.

Can the EGNOS service area be extended?

EGNOS is designed so its services can be extended to other areas within the broadcast area of the geostationary satellites. Such extensions can be made by building additional monitoring stations and without interrupting the EGNOS signal. Africa, South America and Asia could benefit from such extensions.

Is the EGNOS signal encrypted or affected by interference?

The EGNOS signal is neither encrypted nor should it normally be affected by interference. There is a constant monitoring of the EGNOS signal to prevent interference that may significantly impact the system’s operations.

What is the difference between the ESTB and EGNOS architecture?

ESTB (EGNOS System Test Bed) is a reduced version of EGNOS that uses dedicated monitoring stations and processing devices. Since February 2000, ESTB has been offering an experimental signal to help navigation equipment manufacturers and application developers test their products. The experimental signal also allows users to become familiar with EGNOS and allows tests to be conducted so EGNOS can expand its services outside of Europe.

EGNOS and ESTB are two independent systems making use of their own ground segment infrastructure and different geostationary satellites. EGNOS and ESTB also broadcast two different signals. The ESTB signal cannot and does not provide the availability and integrity that EGNOS provides. Therefore, it cannot be used in any safety critical applications.

Will a receiver be able to process EGNOS, MSAS, WAAS and KAAS signals?

Yes, all receivers compliant with RTCA/DO-229C MOPS will work with any SBAS. All SBAS service providers meet on a regular basis to ensure signal compatibility and system interoperability.