GNSS constellations explained: GPS, GLONASS, Galileo and BeiDou compared
Key takeaways
- A GNSS constellation is a set of navigation satellites operated by one provider, with its own orbits, signals and reference frame.
- GPS, GLONASS, Galileo and BeiDou all provide global coverage; QZSS and NavIC are regional systems.
- GPS, Galileo and BeiDou share common centre frequencies such as 1575.42 MHz and 1176.45 MHz, which simplifies multi-constellation receivers.
- Tracking all constellations typically doubles or triples the satellites in view compared with GPS alone.
- More satellites do not remove the need for RTK or PPK corrections when centimetre accuracy is required.
What are GNSS constellations?
GNSS constellations are the groups of satellites that make up each global navigation satellite system (GNSS). A GNSS system is the complete service: the satellites, the ground control segment that monitors and updates them, and the signal specification that receivers use to compute position, navigation and timing (PNT).
Today four constellations provide global coverage: GPS, GLONASS, Galileo and BeiDou. Two more, QZSS and NavIC, serve specific regions, and satellite-based augmentation systems (SBAS) add correction and integrity data on top. The term GPS is often used for all of them, but GPS is only the US system; our article on GNSS vs GPS covers the terminology. This article compares the constellations themselves.
Each satellite broadcasts its orbit (ephemeris) and a precise clock time. A receiver measures the signal travel time from at least four satellites to solve for its three coordinates and its own clock error.
How do GPS, GLONASS, Galileo and BeiDou compare?
The four global constellations differ mainly in orbit altitude, number of orbital planes, signal design and operator, but all deliver similar standalone accuracy of a few metres.
| System | Operator | Orbit altitude (MEO) | Planes / inclination | Main civil signals | Global service |
|---|---|---|---|---|---|
| GPS | United States (US Space Force) | About 20,200 km | 6 planes, 55° | L1 C/A, L1C, L2C, L5 | Full operational capability 1995 |
| GLONASS | Russia | About 19,100 km | 3 planes, 64.8° | L1OF, L2OF (FDMA), newer CDMA L3OC | Full constellation restored 2011 |
| Galileo | European Union | About 23,200 km | 3 planes, 56° | E1, E5a, E5b, E6 | Initial Services from December 2016 |
| BeiDou (BDS-3) | China | About 21,500 km, plus IGSO and GEO | 3 MEO planes, 55° | B1I, B1C, B2a, B2b, B3I | Global service from 2020 |
The baseline GPS satellite constellation has 24 orbital slots, and around 30 satellites are usually operational. GLONASS is designed for 24 satellites, Galileo for 24 plus active spares, and BeiDou-3 uses 24 medium Earth orbit satellites plus inclined geosynchronous (IGSO) and geostationary (GEO) satellites that concentrate coverage over the Asia-Pacific region. Exact satellite counts change with launches and retirements, so check the operators' status pages for current numbers.
What is GPS and when was it invented?
GPS (Global Positioning System) is the satellite positioning system owned by the United States government and operated by the US Space Force; development began in 1973, the 1st GPS satellite was launched in 1978, and full operational capability was declared in 1995.
For surveyors, two milestones matter. In May 2000 the US switched off Selective Availability, the intentional degradation of civil accuracy, so early 2000s GPS receivers suddenly improved from roughly 100 m to around 10 m standalone. Later, modernised civil signals L2C and L5 were added, and GPS III satellites broadcast the new L1C signal designed to be interoperable with Galileo.
GPS applications today go far beyond navigation: surveying, machine guidance, precision farming, timing for telecom and power networks, and science. The official US government information site is gps.gov. For the signals in detail, see our guide to GPS frequencies L1, L2 and L5.
What is the GLONASS system?
The GLONASS system is Russia's global satellite navigation system, designed for 24 satellites in three orbital planes at about 19,100 km and 64.8° inclination.
The higher inclination gives GLONASS satellites better geometry at high latitudes, which is why the GLONASS satellite navigation system is especially useful in Scandinavia, Canada and Russia itself. The constellation reached full strength in 1995, declined in the following decade and was restored to full global coverage in 2011.
The main technical difference is the signal structure. Traditional GLONASS satellites use frequency division (FDMA): each satellite transmits on a slightly different frequency around 1602 MHz (L1) and 1246 MHz (L2). This creates inter-channel biases that RTK engines must handle, especially when base and rover receivers come from different manufacturers. Newer GLONASS satellites also broadcast code division (CDMA) signals, such as L3OC near 1202 MHz, similar in design to the other systems.
In a GPS vs GLONASS comparison, standalone accuracy is broadly similar. The value of GLONASS satellites for surveyors is the extra geometry, not a different accuracy class.
What is the Galileo navigation system?
The Galileo navigation system is the European Union's civil global navigation satellite system, with satellites in three orbital planes at about 23,200 km and 56° inclination. The Galileo global navigation satellite system is sometimes called the EU GPS or the Galileo GPS system, but it is an independent system with its own satellites, ground segment and time scale.
The EU Galileo project was led by the European Commission with the European Space Agency (ESA) responsible for design and procurement; the European Union Agency for the Space Programme (EUSPA) now manages service provision, and publishes status on euspa.europa.eu. Galileo Initial Services began in December 2016.
Key features of the Galileo satellite navigation system for professional users:
- Four signal bands: E1 (1575.42 MHz, shared with GPS L1), E5a (1176.45 MHz, shared with GPS L5), E5b (1207.14 MHz) and E6 (1278.75 MHz). E5a and E5b together form the wideband E5 AltBOC signal, known for low noise and strong multipath resistance.
- High Accuracy Service (HAS): free precise orbit and clock corrections broadcast on E6 and online, with initial service declared in 2023 and a target of decimetre-level horizontal accuracy.
- Precise clocks: passive hydrogen maser and rubidium clocks on each satellite.
In Galileo vs GPS terms, Galileo signals are modern from the start, while GPS is still replacing older satellites. For a survey crew, the practical benefit of the Galileo satellite constellation is simply more high-quality satellites in view.
What is BeiDou, and how does BeiDou vs GPS compare?
BeiDou (BDS) is China's global navigation satellite system; its third generation, BDS-3, began global service in 2020 and combines medium Earth orbit satellites with IGSO and GEO satellites.
The GEO and IGSO satellites stay over Asia and the western Pacific, so BeiDou often provides the largest number of satellites in view in that region. Elsewhere it contributes its global MEO satellites. BDS-3 broadcasts the legacy B1I and B3I signals and the newer B1C (1575.42 MHz) and B2a (1176.45 MHz), which share centre frequencies with GPS L1 and L5. BeiDou also offers services the others do not, such as short message communication and the PPP-B2b precise point positioning corrections over the Asia-Pacific region.
In BeiDou vs GPS terms, standalone accuracy is similar worldwide. The decision for a buyer is not which one to choose, but whether the receiver tracks both: GPS and BeiDou together give much better geometry in eastern Asia than either alone.
Which regional systems and augmentations add to GNSS?
Besides the four global systems, regional constellations and SBAS improve availability and accuracy in specific areas.
| System | Type | Coverage | What it adds |
|---|---|---|---|
| QZSS | Regional constellation (Japan) | Japan and Asia-Oceania | GPS-compatible signals at high elevation, plus L6 centimetre-level corrections in Japan |
| NavIC | Regional constellation (India) | India and about 1,500 km around it | Extra satellites on L5 and S-band, newer satellites also on L1 |
| SBAS (e.g. WAAS, EGNOS, MSAS, GAGAN) | Augmentation by geostationary satellites | Continental | Corrections and integrity for sub-metre to metre-level accuracy |
| Precise point positioning services | Satellite or internet corrections | Global or regional | Decimetre to centimetre accuracy after convergence |
A full-band receiver can use all of these. Our S20 smart antenna for vehicles, for example, lists GPS, GLONASS, Galileo, BeiDou, QZSS, NavIC and SBAS.
Why do multi-constellation GNSS receivers matter for surveying?
Multi-constellation GNSS receivers matter because more satellites from more directions mean faster RTK initialisation, more reliable fixes and usable results in places where a GPS-only receiver fails.
In open sky a GPS-only receiver typically sees around 8 to 12 satellites. With all four global constellations, survey-grade GNSS receivers routinely track 30 to 40 or more. Our engineers see the difference most in four situations:
- Urban canyons and building corners, where half the sky is blocked.
- Tree cover and field edges, where signals are weakened and reflected.
- Open pits and valleys, where low satellites are masked by terrain.
- Long days, where geometry with one system has weak periods.
What extra satellites do not do is replace corrections. Standalone multi-GNSS is still metre-level; centimetre work needs RTK, network RTK over NTRIP, or post-processing, as explained in our NTRIP and CORS guide. Multi-constellation tracking also benefits other users: GNSS for ADAS systems in vehicles, drones and timing receivers all gain availability from more satellites.
How to choose GNSS receivers and antennas for all constellations
Choose a receiver and antenna that track all four global constellations on at least two, preferably three, frequency bands, and confirm that the RTK engine actually uses every system in the solution.
- Check constellations and signals. Look for GPS, GLONASS, Galileo and BeiDou, with modern signals such as L5, E5a/E5b and B2a, not only L1/L2.
- Check the antenna. Base stations and CORS sites need a full-band antenna with a stable phase centre and good multipath rejection.
- Check correction formats. Your base or network must broadcast multi-constellation RTCM 3 MSM messages, or the rover cannot use all satellites.
- Test where you work. Compare fix time and fix rate under trees or near buildings, not just in an open car park.
Our E1 GNSS RTK receiver uses a 1408-channel full-constellation engine and works as base, radio rover or network rover. For fixed bases, the SA102 geodetic GNSS antenna tracks GPS, BDS, GLONASS, Galileo, QZSS, SBAS and L-Band, with Galileo E1, E5a, E5b and AltBOC. Crews working inside CORS coverage can use the 409 g Mini network RTK rover, which has the same 1408-channel engine. Our GNSS RTK receiver buying guide covers the other criteria, and you can request a quote for a complete kit.
Frequently asked questions
How many GNSS constellations are there?
There are four global GNSS constellations: GPS from the United States, GLONASS from Russia, Galileo from the European Union and BeiDou from China. Two regional systems, QZSS in Japan and NavIC in India, add satellites over their regions, and SBAS services such as WAAS and EGNOS add corrections. Survey-grade receivers can use all of them together.
Is Galileo more accurate than GPS?
Standalone accuracy of Galileo and GPS is similar, typically a few metres for a single-frequency user and better with dual-frequency signals. Galileo has modern signals and precise clocks, and its free High Accuracy Service targets decimetre-level accuracy. For centimetre surveying, both still need RTK or PPK corrections, and using both together gives better results than either alone.
What is the difference between GLONASS and Galileo?
In GLONASS vs Galileo terms, the main differences are orbit and signal design. GLONASS orbits lower at about 19,100 km with a 64.8° inclination, which helps at high latitudes, and uses frequency division signals. Galileo orbits at about 23,200 km and uses code division signals that share frequencies with GPS, which simplifies receiver design and processing.
Does GPS work in Russia?
Yes. GPS satellites broadcast worldwide, so GPS signals are available in Russia as everywhere else, and most receivers sold there combine GPS and GLONASS. As in any region, local interference or jamming near sensitive areas can disrupt reception at times, which is another reason professional users prefer receivers that track several constellations and frequencies.
What is PNT vs GPS?
PNT stands for positioning, navigation and timing, the three services a satellite navigation system provides. GPS is one specific system that delivers PNT. Other PNT sources include the other GNSS constellations, inertial sensors and terrestrial radio systems. Critical infrastructure planners use the term PNT because they want resilience that does not depend on one system alone.
What is the difference between DGPS vs GPS?
Standalone GPS computes position from satellite signals alone, with accuracy of a few metres. Differential GPS (DGPS) adds corrections from a reference station or SBAS, improving accuracy to around sub-metre to a metre. RTK goes further, using carrier phase for centimetre accuracy. Our article on GNSS correction methods compares DGPS, RTK, PPK and PPP in detail.
Are sat nav and GPS the same thing?
Not exactly. Sat nav is an everyday term for satellite navigation, often meaning an in-car navigation device, while GPS is the US satellite system that most such devices use. In a sat nav vs GPS comparison, the sat nav is the product and GPS, often with Galileo, GLONASS and BeiDou, is the signal source it relies on.
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