A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. A satellite navigation system with global coverage may be termed a global navigation satellite system (GNSS).
United States’ GPS was the first global satellite navigation system and was the first to be provided as a free global service.
GNSS
A global navigation satellite system (GNSS) is the general term for any of the satellite constellations that broadcast positioning, navigation, and timing (PNT) data.
The multiple groups of satellites, known as constellations, that broadcast signals to master control stations and users of GNSS across the planet. These three segments – space, control, and user – are all considered part of GNSS.
Satellite Constellations
| GNSS | Operator | Country | Coverage | Satellites |
|---|---|---|---|---|
| GPS | US Space Force | USA | Global | 31 |
| GLONASS | Roscosmos | Russia | Global | 24 |
| Galileo | GSA and ESA | Europe | Global | 26 |
| BeiDou (BDS) | CNSA | China | Global | 48 |
| QZSS | JAXA | Japan | Regional | 4 |
| IRNSS/NavIC | ISRO | India | Regional | 8 |
All GNSS providers have offered free use of their systems to the international community. All providers have developed International Civil Aviation Organization (ICAO) Standards and Recommended Practices to support the use of these constellations for aviation.
GPS and GLONASS have the capability to provide accurate position and time information worldwide. The accuracy provided by both systems meets aviation requirements for en-route through a non-precision approach, but not the requirements for precision approach.
GNSS Augmentation
Augmentation of a global navigation satellite system (GNSS) is a method of improving the navigation system’s attributes, such as accuracy, reliability, and availability, through the integration of external information into the calculation process. There are many such systems in place and they are generally named or described based on how the GNSS sensor receives the external information.
GPS
The Global Positioning System (GPS) is a space-based radio-navigation system consisting of a constellation of satellites broadcasting navigation signals and a network of ground stations and satellite control stations used for monitoring and control.
GPS is the most prevalent GNSS. The good news for the aviation community is that GPS is constantly being improved and modernized.
GPS system consists of three segments: the space segment, the control segment, and the user segment. The pace and control segment develops, maintains, and operates by the U.S. Space Force.
The Global Positioning System (GPS) provides the following positional information on a worldwide basis. The information can comprise:
- Latitude
- Longitude
- Altitude
- Time
- Speed
GPS offers seamless satellite navigation services for aviation users to increase the safety and efficiency of flight. Space-based position and navigation enable three-dimensional position determination for all phases of flight from departure, en-route, and arrival, to airport surface navigation.
GPS Augmentation Systems
A GPS augmentation is any system that aids GPS by providing accuracy, integrity, availability, or any other improvement to positioning, navigation, and timing that is not inherently part of GPS itself.
The accuracy of current GPS is within 20 meters horizontally and a bit more vertically. This is sufficient for en-route navigation with greater accuracy than required. However, departures and approaches require more stringent accuracy. Integration of the wide-area augmentation system (WAAS) improves GPS accuracy to within 7.6 meters.
Wide Area Augmentation System (WAAS)
To increase the accuracy of GPS for aircraft navigation, the wide-area augmentation system (WAAS) was developed by FAA. It consists of approximately 25 precisely surveyed ground stations that receive GPS signals and ultimately transmit correction information to the aircraft.
WAAS is an extremely accurate navigation system developed for civil aviation.
