GNSS (or Global Navigation Satellite System) is a broad term encompassing different types of satellite-based positioning, navigation and timing (PNT) systems used globally. GPS (or Global Positioning System) is one such type of Global Navigation Satellite System.
Originally known as “NAVSTAR” (Navigation Satellite Timing and Ranging), GPS was developed by the US Department of Defense for military use back in the 1970s. After the first satellite launch in 1978 technology utilizing GPS evolved quickly, and it began to infiltrate various aspects of our daily lives. However, it wasn’t until after 2000 that it became truly ubiquitous – following the switching-off of Selective Availability. For more information about Selective Availability please see our blog on its conception, lifetime, and abrupt end: Selective Availability – A Bad Memory for GPS Developers and Users
GNSS use constellations of satellites and are based on the concept of trilateration. Put simply, this means that GNSS receivers accurately determine their own location by measuring the distance to four or more satellites. Initially these satellites would all have been from one GNSS, but multi-GNSS receivers are now commonplace.
For a long time, GPS and its Russian-owned counterpart (GLONASS) were the only available GNSS. As the more reliable of the two systems through this period – GLONASS went through a long period of disrepair – GPS became the most widely used GNSS, and that remains the case to this day.
However, with the regeneration of GLONASS, and the advent of Europe’s Galileo system and China’s BeiDou, users and developers are now presented with a broader range of signals and all the benefits that this brings with it. These include:
Greater reliability as more satellites are available at any given time
Greater precision as combinations of signals and frequencies can help to mitigate effects such as atmospheric interference on GNSS precision
Greater robustness as receivers using multi-GNSS are less susceptible to errors introduced in the space segment, and are harder to spoof/jam
Regional and augmentation systems
As well as the global systems, there are several regional and augmentation systems:
Japan’s Quasi-Zenith Satellite System (QZSS) uses a mixture of geostationary (GEO) and Highly Elliptical Orbit (HEO) satellites to augment GPS, improving GNSS signal performance in Japan and nearby areas of Eastern Asia.
Navigation Indian Constellation (NAVIC) uses geostationary satellites to similar effect.
Satellite-based augmentation systems (SBAS) such as the Wide Area Augmentation System (WAAS) for North America and the European Geostationary Navigation Overlay Service (EGNOS) have long been established as a method to provide a positioning service for critical applications such as commercial aviation.
Testing GNSS-enabled systems with Spirent
Over 35 years ago, Spirent delivered the first commercial GPS simulator. Since then we’ve added a huge number of constellations and signals, including for complementary positioning technologies such as inertial sensors.
Learn more about GNSS simulators and how they are enabling the next generation of precise and robust GNSS-enabled technology.
This blog was originally published in October 2018 and republished with updates.