# The EGNOS Augmentation in Maritime Navigation +
## 2 EGNOS Background  
ESA initiated the agreements for a European SBAS in 1995. The development of EGNOS started in 1999, following the agreements between ESA, the EC, Eurocontrol and national service providers air navigation. On the first of April 2009, EGNOS was handed over to the EC and starting from the first of October 2009 the corrective data were transmitted free of charge to public users [12]. EGNOS consists of a ground segment, a support segment, a space segment and a user segment. The ground segment contains 40 Ranging and Integrity Monitoring Stations (RIMS), two Mission Control Centers (MCCs) and six Navigation Land Earth Station (NLES). The communication between the components of the ground segment is guaranteed by the EGNOS Wide Area Network (EWAN). RIMS stations cover all of Europe and collect data from GNSS satellites. The Central Processing Facilities (CPF) broadcast the collected data to the MCC every second. At the MCC, the data are processed, and corrections are generated in the form of EGNOS messages. These messages are then forwarded to the NLES by the MCC's CPF. EGNOS messages are sent to the GEO satellites by the NLES. The support segment consists of a Performance Assessment and Checkout Facility (PACF) and the Application Specific Qualification Facility (ASQF). The support segment is controlled by the EGNOS Service Provider: the ESSP. The space segment of EGNOS is composed by three GEO satellites that are in 36,000 km altitude circular orbits and downlink EGNOS messages to the user segment at the L1 (1575.42 MHz) frequency band [12]. EGNOS GEO satellites are Astra Ses-5 (PRN 136), Astra 5B (PRN 123) and Inmarsat 4F2 Emea (PRN 126) that are currently part of the EGNOS operational platform and are transmitting the operational Signal-In-Space (SIS) to be used by EGNOS users. From 23 March 2020 onwards, the PRN123 and PRN136 satellites are operational while the PRN126 is in test mode. Inmarsat is an initiative established by the IMO in 1979 for safer maritime navigation [12]. Finally, the user segment includes anyone with an EGNOS enabled receiver. EGNOS provides three services: the Open Service (OS), the Commercial Data Distribution Service (CDDS) and the Safety of Life (SoL) service [15; 16; 17]. The OS provides EGNOS data freely to anyone in Europe with an EGNOS enabled GNSS receiver and provides a horizontal position accuracy of 1 to 3 m, and a vertical position accuracy of 2 to 4 m for GPS [17]. The SoL service is able to provide highly accurate positioning and integrity data for safety-critical application areas. This service is primarily provided for aviation, and subsequently it is also widely used in the maritime, rail and road applications sectors. Alerts are sent to the user in the event that accuracy worsens, so that the user can react to degraded navigation signals without serious consequences [16]. The CDDS is a service designed for professional users and provides EGNOS data via EGNOS Data Access Service (EDAS). This service offers raw GPS, GLONASS and EGNOS observation data to the user with an update rate of one second [15]. There are multiple EDAS services depending on the user's application. Among them, the EDAS Signal in Space (SiS) service through the Internet (SISNet) provides the user with EGNOS messages using the Internet. These data are provided according to the SISNeT protocol, and the user must be registered to access the service. The EGNOS messages are also available for post-processing purposes via EDAS FTP. This service provides EDAS/EGNOS data in different formats and at different time intervals. A standard FTP client is used to access this service and the user must register. EDAS is available also from the network transport of RTCM (Radio Technical Commission for Maritime Services organization) via Internet Protocol (NTRIP). The data available through this service are DGNSS corrections and carrier phase measurements. This service also provides messages for Real-Time Kinematic (RTK) applications [15]. The EGNOS functional architecture is shown in Figure 1.