EGNOS Receivers

EGNOS
Title	EGNOS Receivers
Author(s)	GMV.
Level	Basic
Year of Publication	2011

To receive EGNOS signals an EGNOS compatible receiver is required. There are many receivers available on the market from a variety of manufacturers.

An EGNOS receiver is like a GPS receiver but with special software inside that allows the receiver to lock onto the code used by the EGNOS satellites and compute the EGNOS corrections to the GPS signals. Apart from this, an EGNOS receiver is just like a GPS receiver. This means that it can pick up GPS signals as well. An EGNOS receiver is the same size as a GPS receiver and uses the same type of antenna.

Receiver types

EGNOS receiver used for test and validation purposes.

EGNOS-enabled receivers depend on the targeted application, the EGNOS functions that will be used and the integration constraints. In choosing a receiver, users should establish whether it correctly supports EGNOS, then select the interface type and check if the protocols supported by the receiver allow retrieval of the data required for the targeted application.

EGNOS-enabled receivers can be designed using a chipset, hybrid component or an auxiliary card.

• Chipset: consists of one or two components that must be installed on a circuit board. The routing of the RF part is sensitive. This compact solution is also the least expensive.
• Hybrid component: consists of a single component integrating the RF and signal processing parts to be installed on a circuit board. Routing is easier compared to chipsets. The price is higher than for the chipset solution.
• Auxiliary card (piggyback): all the receiver and peripheral components are integrated on a ready-to-use card connected to the final product’s main circuit board. It is an ideal solution for prototyping embedded applications. This is the most expensive solution.

Communications protocols

Manufacturers generally use proprietary protocols which give access to almost all the data (pseudoranges, satellite navigation messages, SBAS messages, etc.) associated with a standardised protocol, NMEA 0183. Some receivers also generate data in RINEX (Receiver INdependent EXchange) format.

RINEX is an exchange format that is independent of the receiver. It was developed by the Astronomical Institute of the University of Bern in order to provide data in a single format that has been collected in proprietary formats by different brands of receiver. This format is generally supported by professional receivers. It is also used by IGS servers for supplying GNSS data. In this format, the GNSS data are provided as text files. A description of this format described by the University of Bern is available free of charge on http://igscb.jpl.nasa.gov/igscb/data/format/rinex210.txt.

Manufacturer’s specifications

EGNOS Receiver market.

Although some manufacturers clearly specify that EGNOS is supported, others indicate that their receivers are “WAAS Capable” or “WAAS Enabled”, with WAAS referring to both the North American satellite-based augmentation system (SBAS) and the SBAS standard. In practice, “WAAS Capable” means that the receiver can use SBAS services but the user must activate this function once only, or each time it starts up. “WAAS Enabled” usually means that the receiver activates SBAS reception by default.

It is important to bear in mind that navigation services are developing swiftly, so it is vital to keep in pace with international standards.

Safety-of-Life and Open Service Receivers

For the Safety-of-Life (SoL) service, the EGNOS user equipment shall be compliant (certified) against several standards. For instance, civil aviation SBAS equipment shall demonstrate (see SBAS standards):

• Full compliance to RTCA SBAS MOPS DO-229 (airborne equipment).
• Full compliance to the RTCA SBAS MOPS 228 and 301 (antenna requirements).
• Compliance to RTCA TSO (C190, C145b, C146b) for SBAS equipment.
• Compatibility to other avionics equipment, in particular Flight Management Systems (FMS).

The SoL civil aviation certified equipment is in the highest rank with respect its cost. There exist a large number of certified receivers manufacturers worldwide both in the US (GARMIN, Honeywell, Rockwell Collins, General Avionics, etc) and in Europe (see complete list in EASA homepage).

The Open Service (OS) targets low cost, general purpose GNSS equipment that uses the SBAS SIS to provide the user with an enhanced accuracy performance in comparison with the one provided by a standalone GPS device. In comparison with the certification requirements of the user equipment above, user equipment is not necessarily compliant with the RTCA MOPS DO 229 processing rules, but might only make use of the processing algorithms that render the accuracy corrections provided by the SBAS SIS.

Helios produced a list of receivers compatible with EGNOS as part of a market study completed in 2008 on behalf of the GNSS Supervisory Authority. It is a non-exhaustive list but it provides, for each receiver, the degree to which its SBAS capability is recorded, as well as the GNSS chipset used (where this information is available). This information is available in the EGNOS compatible receiver list produced by the GSA.

Many devices are suitable, and marketed, for more than one of the market segments identified here. Outdoor recreation devices, for example, cross over into the maritime and general aviation segments.

The survey divided the receivers into several categories, depending on the level of processing of the SBAS information:

• Category 1: Full use of SBAS corrections.
• Category 2: Capability of receiving the signal from the SBAS satellites.
• Category 3: The receiver is known to be SBAS compatible, but the receiver does not make use of this ability and does not process the augmentation data. Products in this category would require a more extensive receiver firmware upgrade to make use of SBAS.
• Category 4: Receivers for which the SBAS capability of the device/chipset is unknown.

In any case, it should be noted that this classification is not aligned with the equipment operational classes defined in the MOPS RTCA DO 229 D.