Global Navigation Satellite System (GNSS) is the standard generic term
for satellite navigation systems that provide autonomous geo-spatial positioning
with global coverage. A GNSS allow small electronic receivers to determine their
location (longitude, latitude, and altitude) to within a few metres using time
signals transmitted along a line of sight by radio from satellites. Receivers on
the ground with a fixed position can also be used to calculate the precise time
as a reference for scientific experiments.
As of 2007, the United States NAVSTAR Global Positioning System (GPS) is the
only fully operational GNSS. The Russian GLONASS is a GNSS in the process of
being restored to full operation. The European Union's Galileo positioning
system is a next generation GNSS in the initial deployment phase, scheduled to
be operational in 2010. China has indicated it may expand its regional Beidou
navigation system into a global system.
GNSS classification
GNSS that provide enhanced accuracy and integrity monitoring usable for civil
navigation are classified as follows:
- GNSS-1 is the first generation system and is the combination of existing
satellite navigation systems (GPS and GLONASS), with Satellite Based
Augmentation Systems (SBAS) or Ground Based Augmentation Systems (GBAS). In
the United States, the satellite based component is the Wide Area Augmentation
System (WAAS), in Europe it is the European Geostationary Navigation Overlay
Service (EGNOS), and in Japan it is the Multi-Functional Satellite
Augmentation System (MSAS). Ground based augmentation is provided by systems
like the Local Area Augmentation System (LAAS).
- GNSS-2 is the second generation of systems that independently provides a
full civilian satellite navigation system, exemplified by the European Galileo
positioning system. These systems will provide the accuracy and integrity
monitoring necessary for civil navigation. This system consists of L1 and L2
frequencies for civil use and L5 for system integrity. Development is also in
progress to provide GPS with civil use L2 and L5 frequencies, making it a
GNSS-2 system.
A GNSS may have several layers of infrastructure:
- Core Satellite navigation systems, currently GPS, Galileo and GLONASS.
- Global Satellite Based Augmnetation Systems (SBAS) such as Omnistar and
Stafire.
- Regional SBAS including WAAS(US) , EGNOS (EU), MSAT (Japan) and GAGAN
(India).
- Regional Satellite Navigation Systems such a QZSS (Japan), IRNSS (India)
and Beidou (China).
- Continental scale Ground Based Augmentaion Systems (GBAS) for example the
Australian GRAS and the US Department of Transportation National Differential
GPS (DGPS) service.
- Regional scale GBAS such as CORS networks.
- Local GBAS typified by a single GPS reference station operating Real Time
Kinematic (RTK) corrections.