Global Positioning System (GPS) pioneered the GNSS sector with the launch of its first satellite in 1978. Since then, the GNSS market has grown to include five additional constellations: BeiDou, Galileo, GLONASS, IRNSS, and QZSS.
Which constellation is ideal for your application? The answer depends on your customers’ requirements for reliability, performance, and coverage.
Global vs. Regional
GNSS stands for Global Navigation Satellite System. Although the acronym is frequently used as a catchall term for all six systems, only four of them provide global coverage:
- The GPS constellation consists of 31-plus satellites that ring the Earth. Each satellite circles the planet twice a day in one of six orbits.
- China’s BeiDou (BDS or Compass) started as a regional system but now provides full global coverage with 35 satellites.
- The European Space Agency’s Galileo became fully deployed globally in 2018 with 24 satellites launched, plus six spares.
- The Russian Federal Space Agency’s GLONASS is a global system with a focus on providing positioning in high latitudes.
The other two GNSS systems are focused on providing regional coverage:
- Japan’s Quasi-Zenith Satellite System (QZSS) serves eastern Asia-Oceania. It became fully operational in 2018 with four satellites.
- India’s IRNSS, or NavIC is focused on India and surrounding areas. It became fully operational in 2018 with seven satellites.
All six systems are continually evolving, with new satellites and new types of signals. This modernization benefits device OEMs, systems integrators, and end users by increasing performance and reliability.
For example, nearly every civilian GPS receiver supports the L1 signal at 1575.42 MHz. The GPS modernization program includes adding L1C, which will provide civilian users with better availability. L1C is among the new GPS signals expected to be available by the end of this decade. (For more information about the GPS modernization program, see https://www.gps.gov/systems/gps/modernization. And for a deeper dive into each GNSS system’s spectrum usage, see “How to Navigate the L1, L2, L5, E5a, E5b, and G2 Alphabet Soup of GNSS Constellations and Signals.”)
Combining GPS with Other GNSS Systems
GPS is an ideal choice for applications in North America, such as asset tracking. But there are a few caveats. For example, jamming and spoofing are increasingly common in other parts of the world, which obviously is a problem for applications where devices travel outside North America. Sometimes jamming is authorized, such as when the U.S. Air Force conducts training exercises designed to help pilots learn how to accommodate those kinds of attacks. This is rare but can be an issue for mission-critical applications in those areas.
If an application requires a continuous, 100% reliable source of positioning and/or timing information, then it’s worth considering a module and antenna system that support multiple GNSS bands and multiple GNSS constellations for redundancy. (For a deeper dive into this strategy, see “Get Out of a Jam: How GNSS Antennas Help Thwart Jamming Attacks.”)
Another consideration is the application’s latitude. If the devices are located above or travel above 55 degrees, GPS accuracy begins to suffer because its satellites rise only 45 degress above the horizon. This limits visibility of its satellites. A module and antenna system that supports GLONASS and/or Galileo enables the application to take advantage of constellations whose orbits provide better coverage in higher latitudes. (For more information about how latitude affects GPS accuracy, see “GNSS/INS Simulations of High-Latitude Operations.”)
