Global Navigation Satellite Systems (GNSS)
provide Position, Navigation and Timing (PNT)
services, 24 hours a day, seven days a week, in all types of weather.
The first and best known GNSS is the US Global Positioning System (GPS),
which has been fully operational since 1995. The second and less well known system is the Russian Glonass, which is also now operational.
GNSS is a term applied to what are, in reality, three classes of satellite navigation systems. These are:
- True Global systems such as the United States’ GPS and Russia’s Glonass
- Regional Navigation Satellite Systems (RNSS) such as Japan’s QZSS or India’s IRNSS
- Satellite Based Augmentation Systems (SBAS) such as the European EGNOS.
China plans to start with an RNSS, which will develop into a GNSS over time.
GNSS provide the primary signals, free of charge, which can be used by receiving equipment anywhere on the Earth’s surface to derive position, navigation and timing. RNSS do the same, but over a limited portion of the globe. SBAS provide an integrity signal, which alerts the GNSS receiving equipment if the GNSS or RNSS they are using develop a fault. SBAS are designed primarily for the safe navigation of commercial aircraft but have a wide range of other users including land transport, agriculture and spatial information.
GNSS comprise constellations of between 24-32 Mid-Earth Orbiting (MEO) satellites. RNSS constellations are smaller (three to seven constellations) and can be both MEO and Geostationary (GEO) satellites. SBAS only consist of Geostationary satellites.
The number of GNSS and RNSS satellites is steadily increasing as the system providers execute their launch programs. The chart shown here illustrates the projected growth in satellites to 2013 based on current launch schedules. As GNSS and RNSS expand, earth based GNSS receiving equipment are able to “see” more satellites.
By 2020, Australia is projected to be in the GNSS “hot-spot” with access to over 40 GNSS and RNSS satellites at any time.
The advantages of being in this hotspot include better availability of navigation signals in high-rise urban areas and under tree canopies, which are places where GPS might struggle to work today. GPS is undergoing a modernisation program and, along with some of the new GNSS (such as Europe’s Galileo system), users can expect improved accuracy in the future.
For more information on GNSS, visit the United Nation International Committee on Global Navigation Satellite Systems.