Global Navigation Satellite Systems
The Global Navigation Satellite Systems (GNSS) rely on satellite constellations with global coverage that provide the user with positioning and timing information, allowing the determination of position to within a few meters (in addition to velocity and time), anywhere and anytime, using signals transmitted along a line of sight from satellites to special radio receivers.
Typically, a GNSS constellation consists of 20 to 30 Medium Earth Orbit (MEO) satellites, spread between several orbits, with inclinations of more than 50°, in order to achieve global coverage.
Full operational capability was declared in 1995
32 MEO satellites in 6 orbital planes. Requires 24 satellites for full operational capability.
First test satellite launched in 2005.
Initial operational capability expected in 2014.
Provides a global Search and Rescue (SAR) service.
Two experimental satellites available. Requires 30 MEO satellites.
Global coverage obtained in 1991, but then lost. System to be restored in 2011.
Requires 24 satellites for a full operational capability
Expected to be operational by 2020
5 satellites available. Requires 30 MEO and 5 GEO satellites.
GNSS Augmentation - Satellite Based Augmentation Systems (SBAS)
The SBAS systems provide a method of improving the accuracy, reliability, and availability, of the navigation systems by providing additional information through satellite-broadcast messages.
The systems are based on multiple strategically located ground stations that continuously track the GNSS satellites. Using the data collected from these ground stations, information messages are created and sent to one or more satellites for broadcast to the end users. The system offers an improvement in positioning accuracy from 3m to 1m, in a standalone scenario.
Established in 1994
Augmentation of GPS, with the goal of improving its accuracy, integrity, and availability
Expected to be fully operational from 2011
Augmentation of GPS, Galileo and GLONASS
First satellite launched in December 2010
Augmentation of the GPS and GLONASS over the Russian territory
GPS Aided Geo Augmented Navigation (GAGAN)
The system will be completed in 2011
Augmentation System of GPS to improve the accuracy of a GNSS receiver by providing reference signals
Multifunctional Transport Satellites (MTSAT)
Became partially operational in 2005
Regional augmentation system, with a series of weather and aviation control satellites
Regional Navigation Satellite Systems
A Regional Satellite System acts similar to the global one, by providing positioning and timing information to the user through radio signals sent from satellites, having the difference that the service is not provided globally, but to a geographically restricted area.
Operational since 2000
Consists of 3 satellites and has limited coverage and applications. It is going to be replaced in the future by the Compass system.
Quasi-Zenith Satellite System (QZSS)
Fully operational in 2013
A three-satellite regional time transfer system and enhancement for the Global Positioning System
Can only provide limited accuracy on its own and is not currently required in its specifications to work in a stand-alone mode
Indian Regional Navigational Satellite System (IRNSS)
Planned completion in 2014
Regional Positioning System
The information in tables above represents situation at the end of 2010.