European Geostationary Navigation Overlay Service
The European Geostationary Navigation Overlay Service (EGNOS) is a satellite-based augmentation system (SBAS) developed by the European Space Agency and EUROCONTROL on behalf of the European Commission. Currently, it supplements the GPS by reporting on the reliability and accuracy of their positioning data and sending out corrections. The system will supplement Galileo in a future version. EGNOS consists of 40 Ranging Integrity Monitoring Stations, 2 Mission Control Centres, 6 Navigation Land Earth Stations, the EGNOS Wide Area Network (EWAN), and 3 geostationary satellites. Ground stations determine accuracy data of the satellite navigation systems and  transfer it to the geostationary satellites; users may freely obtain this data from those satellites using an EGNOS-enabled receiver, or over the Internet. One main use of the system is in aviation. According to specifications, horizontal position accuracy when using EGNOS-provided corrections should be better than seven metres. In practice, the horizontal position accuracy is at the metre level. Similar service is provided in North America by the Wide Area Augmentation System (WAAS), in Russia by the System for Differential Corrections and Monitoring (SDCM), and in Asia, by Japan's Multi-functional Satellite Augmentation System (MSAS) and India 's GPS-aided GEO augmented navigation (GAGAN). Galileo and EGNOS budget for the 2021–2027 period is €9 billion History and roadmap. The system started its initial operations in July 2005, with accuracy better than two metres and availability above 99%. As of July 2005, EGNOS has been broadcasting a continuous signal, and at the end of July 2005 the system was again used to track cyclists in the Tour de France road race. In 2009, the European Commission announced it had signed a contract with the company European Satellite Services Provider to run EGNOS. The official start of operations  was announced by the European Commission on 1 October 2009. The system was certified for use in safety of life applications in March 2011. An EGNOS Data Access Service became available in July 2012. Initial work to extend EGNOS coverage to the Southern Africa region is being done under a project called ESESA - EGNOS Service Extension to South Africa. The European Commission is defining the roadmap for the evolution of the EGNOS mission. This roadmap should cope with legacy and new missions: Satellites and SISNeT. Similar to WAAS, EGNOS is mostly designed for aviation users who enjoy unperturbed reception of  direct signals from geostationary satellites up to very high latitudes. The use of EGNOS on the ground, especially in urban areas, is limited due to relatively low elevation of geostationary satellites: about 30° above horizon in central Europe and much less in the North of Europe. To address this problem, ESA released in 2002 SISNeT, an Internet service designed for continuous delivery of EGNOS signals to ground users. The first experimental SISNeT receiver was created by the Finnish Geodetic Institute. The commercial SISNeT receivers have been developed by Septentrio. PRN #136 was placed into the Operational Platform from 23/08/2018  at 10:00 UTC and PRN #120 was placed into Test Platform from 30/08/2018 at 13:00 UTC. Architecture. EGNOS is divided into four functional segments: 1. Ground segment: comprises a network of 40 Ranging Integrity Monitoring Stations (RIMS), 2 Mission Control Centres (MCC), 2 Navigation Land Earth Stations (NLES) per Geostationary Earth Orbit (GEO), and the EGNOS Wide Area Network (EWAN), which provides the communication network for all the components of the ground segment. 2. Support segment: In addition to the above-mentioned stations/centres, the system has other ground support installations involved in system operations planning and performance assessment, namely  the Performance Assessment and Checkout Facility (PACF) and the Application Specific Qualification Facility (ASQF) which are operated by the EGNOS Service Provider (ESSP). 3. Space Segment: composed of at least three geostationary satellites broadcasting corrections and integrity information for GPS satellites in the L1 frequency band (1575.42 MHz). This space segment configuration provides a high level of redundancy over the whole service area in the event of a failure in the geostationary satellite link. EGNOS operations are handled in such a way that, at any point in time, at least two GEOs broadcast an operational signal. 4. User Segment: the  EGNOS user segment consists of EGNOS receivers that enable their users to accurately compute their positions with integrity. To receive EGNOS signals, the end user must use an EGNOS-compatible receiver. Currently, EGNOS compatible receivers are available for such market segments as agriculture, aviation, maritime, rail, mapping/surveying, road and location based services (LBS). Aviation. In March 2011, the EGNOS Safety-of-Life Service was deemed acceptable for use in aviation. This allows pilots throughout Europe to use the EGNOS system as a form of positioning during an approach, and allows pilots to land the aircraft in IMC using a  GPS approach. As of September 2018 LPV (Localizer performance with vertical guidance) landing procedures, which are EGNOS-enabled, were available at more than 180 airports across Europe.