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EGNOS receivers

 

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To receive the EGNOS signals, an EGNOS compatible receiver (also called SBAS receiver or WAAS receiver) is required. It is like a GPS receiver but with special software enabling the receiver to lock onto the EGNOS satellites and apply the EGNOS corrections to the GPS signal. Today, most of the commercial GPS receivers provide EGNOS capability

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EGNOS Signal Format is described in the Appendix A of the Minimum Operational Performance Standards (MOPS) for Global Positioning System/Wide Area Augmentation System Airborne Equipment, RTCA/DO-229.
The RTCA DO229 WAAS MOPS documentation is available for sale at www.rtca.org
EGNOS Message Types (MT): The Message Type 0 (MT0) is used to indicate that the system is on test and cannot be used for safety critical applications they fall under the MOPS Do229A. Since April 2003, the Message Type 0/2 is implemented under the MOPS Do220C specs:. It consist of overlapping a message type 2, providing fast corrections, ionosphere corrections and ranging data, on the frame reserved to the message type 0. It still indicated that the system is on test mode, but it also optimizes the use of the SIS data capacity. There are a substantial number of receivers able to process EGNOS MT0/2 (Open Access Service), on the market.

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- Certified SoL receivers (for example aviation ones), implement all the requirements set in the applicable standards (RTCA Do-229()) in order to achieve the integrity levels necessary for SoL applications. These receivers will stop using EGNOS whenever the SoL service is discontinued (by adding a Message Type 0 to the signal). This can occur if a system degradation could render the use of EGNOS unsafe for SoL applications. Additionally, and depending on the application field, SoL receivers may require a certification stamp from the relevant authority (in aviation, EASA or FAA for ETSO or TSO certified equipment respectively)
- Open Service receivers, on the contrary may have implemented only a subset of the requirements in DO-229, in particular, they may ignore the MT0 if broadcasted and keep providing corrections even when SoL is not available. Typically these receivers only apply the EGNOS corrections to improve accuracy but no indication of protection levels or integrity alerts are provided.

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    Yes, any WAAS capable receiver shall work with the other SBAS (Satellite Based Augmentation System). Today two SBAS are already being operated: EGNOS in Europe and WAAS in the USA. Two other SBAS systems are being developed GAGAN in India and MSAS in Japan. These are all civil-controlled regional systems and there is a form of coordination to ensure that they are interoperable to provide a seamless worldwide navigation system so that you can use one single SBAS receiver for all of them.

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    Each EGNOS SIS has three modes of operation:
    Test Mode: This mode is defined by the broadcasting of the MT0 (Message Type 0) in the signal. It indicates that the system is on test and is not usable. Receipt of a message type 0 will normally prompt the receiver to terminate the use of any message.
    Non-Safety-Of-Life Mode: This mode still indicates that the system is on test, but allows receivers to compute EGNOS corrections, improving the use of the SIS data capacity, as long as the signal is only used for non-safety-of-life applications. The mode consists of overlapping a message type 2 on the frame reserved for the message type 0.
    Safety-Of-Life Mode: EGNOS SIS may be used for Safety of Life applications. In this case, no message Type 0 is broadcast and message type 2 is broadcast normally.

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    The pseudoranges corrections of EGNOS Operated GEOs, PRN120 and PRN124 are not considered by the receiver when computing the navigation position solution (even though there are almanac and ephemeris data provided in messages type 9 and 17), as these two satellites are declared as NON USABLE for EGNOS through the UDRE indicators provided in messages type 4 and type 6

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