What’s the Difference Between GNSS and GPS?
Global Navigation Satellite System (GNSS) is a broad term encompassing different types of satellite-based positioning, navigation, and timing (PNT) systems used globally. Global Positioning System (GPS) is one such type of GNSS.
Originally known as Navigation Satellite Timing and Ranging or NAVSTAR, GPS was developed by the U.S. Department of Defense for military use back in the 1970s. After the first satellite launch in 1978 technology using 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.
GNSSs 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 GNSSs. 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 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
In addition to 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 Keysight
Keysight’s GNSS simulator, which was the first simulator made commercially available, now comprises a huge number of constellations and signals, including for complementary positioning technologies such as inertial sensors.
Keysight's GPS Navstar Simulator