GNSS vs GPS: Decoding Satellite Navigation’s Alphabet Soup


People casually use GPS and GNSS interchangeably as if they’re the same. Although they are related, the two terms refer to different things. You can’t treat them as synonymous, especially in the GNSS community.

Put simply, the Global Positioning System (GPS) is an example of a Global Navigation Satellite System (GNSS).

But what are the differences and how do they impact consumer, professional, and military users?

What is GPS?

People think GPS and GNSS are the same because America’s Global Positioning System is the original GNSS.

Throughout history, imprecise or error-prone positioning techniques hampered navigation, surveying, and other activities. American academic and military researchers in the 1960s explored using satellites as navigation beacons. An orbital network with enough satellites to guarantee at least four are visible would provide accurate positioning for ships, aircraft, and ground vehicles anywhere on Earth.

By the early 1970s, this research had progressed enough to justify the creation of a Joint Program Office to combine the best technologies into a single system. Things moved quickly, with the first prototype GPS satellite reaching medium Earth orbit (MEO) in 1978. GPS became fully operational in 1995, guaranteeing at least 24 operational MEO satellites for global coverage.

However, GPS was not limited to military users. Commercial and consumer applications proliferated, and “GPS” became universally recognized as how you navigate by satellite.

What is GNSS?

Of course, GPS was not the only satellite-based navigation system. The Soviet Union (and later Russia) was not far behind. GLONASS has as many satellites as GPS but at a higher inclination to cover polar regions.

With the development of multiple satellite positioning services, the industry settled on GNSS to describe the overall category and product features that use more than one GNSS network.

What are the other GNSS options?

By the end of the 20th Century, GPS and GLONASS were publicly available worldwide. Some countries developed independent GNSS networks to improve local service and avoid reliance on Russia and the United States.

The European Union began developing its Galileo service in 1999. Galileo provides global coverage similar to GPS, with the same number of satellites in similar MEO inclinations. However, Galileo uses new technologies to provide more accurate positioning than the original GPS.

China developed its BeiDou GNSS system at the same time as Europe. In its current iteration, BeiDou-3 consists of thirty satellites in MEO, geostationary orbit (GEO), and geosynchronous orbit (GSO). BeiDou’s architecture provides global coverage with support for high-precision positioning in China and the surrounding regions.

India’s Navigation with Indian Constellation (NavIC) consists of seven satellites in either GEO or GSO. This structure lets NavIC deliver accurate positioning within India and surrounding regions.

What is GNSS Augmentation?

Although GPS provided unprecedented accuracy, its signals weren’t accurate enough for certain applications. Ships and aircraft could use it exclusively far from land, but not in busy air and sea lanes. Another reason to augment GPS signals was the potential for intentional degradation of GPS signal accuracy. Selective Availability was an initial feature of GPS, but the United States deactivated it in 1990 to support commercial applications.

Ground-based and satellite-based augmentation systems (GBAS and SBAS, respectively) combine GPS signals with additional reference signals to achieve more precise positioning.

QZSS: Japan launched its Quasi-Zenith Satellite System (QZSS) in 2010. One GEO and three GSO satellites improve GPS reception in Japan’s dense urban landscape.

GBAS and WAAS: The Federal Aviation Administration supports civil aviation by augmenting GPS in the United States with ground and satellite signals. Aircraft approaching an airport can use signals from the FAA’s GBAS to correct errors in GPS reception. The satellite-based Wide Area Augmentation System (WAAS) improves vertical accuracy for more precise approaches under instrument flight rules.

EGNOS: The EU augments GPS and Galileo with signals from the European Geostationary Navigation Overlay Service (EGNOS). This satellite-based augmentation system improves transportation safety in Europe’s crowded airspace and sea lanes.

Are GNSS receivers and GPS receivers the same thing?

Confusingly, sometimes they’re the same, and sometimes they aren’t. Marketing departments play fast and loose with language. Since the public uses the term GPS generically for satellite navigation, marketers often do the same.

For example, Apple’s iPhones come with “Precision dual-frequency GPS.” The technical specifications show that iPhones have GNSS receivers supporting GPS, Galileo, BeiDou, QZSS, and GLONASS signals.

GNSS receivers detect signals from multiple satellite networks to improve positioning accuracy. Receiving signals from a dozen or more satellites lets a receiver calculate its position more precisely. In addition, GNSS receivers can deliver accurate positioning when terrain, trees, or buildings obscure satellites near the horizon.

Strictly speaking, GPS receivers only use signals broadcast from GPS satellites — an essential feature for American defense applications. Military GPS receivers have full access to the system’s capabilities, making them resistant to adversarial jamming and spoofing.

What’s next for GPS and GNSS?

The latest-generation Block III GPS satellites are part of America’s GPS Modernization program. New civilian signals will improve accuracy and reliability while supporting interoperability with the Galileo network. A third civilian signal will enhance precision navigation for air, sea, and land transportation.

M-code is a new military signal that will improve positioning performance and resistance to jamming and spoofing. In addition, the high-gain antennas on modernized GPS satellites can broadcast a spot beam to increase signal strength for military GPS receivers in specific regions.

Other GNSS networks have modernization programs of their own. For example, the Galileo program may not be fully operational, but second-generation satellites will launch in a few years.

GPS vs. GNSS: A genuine distinction

The general public — and marketing departments — may always use GPS and GNSS interchangeably. GPS has become as generic in the public mind as bandaid, kleenex, or velcro.

However, accuracy matters in the world of navigation and positioning. If you say GPS, you better mean GPS.

July 28, 2023