Definition
What is GNSS (satellite navigation)?
GNSS (Global Navigation Satellite System) is the generic term for satellite systems that provide positioning, navigation and timing with global coverage, such as GPS, GLONASS, Galileo and BeiDou. A receiver measures how long signals from at least four satellites take to arrive and computes its position and the time. Augmentation services such as EGNOS improve accuracy and add integrity information.
- Technologies
- Updated
- Published by
- LETO SPACE
Satellite navigation tells a device where it is and what time it is. It runs in phones, vehicles, machines, ships, aircraft, power grids and telecom networks. This page explains how GNSS works, how GPS, Galileo and EGNOS relate to each other, how accurate a position is and where the limits are.
Definition
- GNSS (Global Navigation Satellite System)
GNSS is the generic term for satellite navigation systems that provide positioning with global coverage. It includes GPS, GLONASS, Galileo and BeiDou, as well as regional systems.
- Also called: satellite navigation, satnav; in German: Satellitennavigation
01Overview
Positioning, navigation and timing
GNSS delivers three things, often abbreviated as PNT Source: U.S. government, GPS.gov, accessed 6 October 2026U.S. government, GPS.govGPS.gov: What is GPS?accessed 6 October 2026Open source (opens gps.gov):
- Positioning: where a receiver is, as coordinates.
- Navigation: how it moves, derived from its position over time, and guidance along a route.
- Timing: a precise time signal, because every receiver computes the time as well as its position.
GPS is not another word for GNSS. It is one system, owned by the United States Source: U.S. government, GPS.gov, accessed 6 October 2026U.S. government, GPS.govGPS.gov: What is GPS?accessed 6 October 2026Open source (opens gps.gov). The other global systems are GLONASS, continued by the Russian Federation, the Chinese BeiDou system Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: GLONASS General Introductionaccessed 6 October 2026Open source (opens gssc.esa.int) and Galileo, Europe's own system under civilian control Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: Galileo General Introductionaccessed 6 October 2026Open source (opens gssc.esa.int). Many receivers use several systems at once. EUSPA notes that Galileo improves accuracy in urban canyons when used in multi-constellation receivers, because the additional satellites increase visibility and measurement redundancy Source: EU Agency for the Space Programme (EUSPA), 26 May 2026EU Agency for the Space Programme (EUSPA)EU Space Market Report 2026, Issue 126 May 2026Open source (opens euspa.europa.eu).
02Technology
How satellite positioning works
Each satellite carries atomic clocks and transmits navigation data from which the receiver computes where the satellite is. The receiver measures how long the signal took to arrive and multiplies this travel time by the speed of light. The result is its distance to the satellite Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: An intuitive approach to the GNSS positioningaccessed 6 October 2026Open source (opens gssc.esa.int).
Receivers have inexpensive quartz clocks, so every measured distance contains the same unknown clock error. The receiver therefore solves for four unknowns: three coordinates and its own clock offset. This is why it needs signals from at least four satellites Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: An intuitive approach to the GNSS positioningaccessed 6 October 2026Open source (opens gssc.esa.int). Because it solves for the clock offset, the receiver also knows the time precisely, which makes GNSS a time source as well as a position source.
The position of the satellites in the sky matters too. When they are bunched together, the same measurement error causes a larger position error, an effect called dilution of precision Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: An intuitive approach to the GNSS positioningaccessed 6 October 2026Open source (opens gssc.esa.int).
A navigation system has three parts: the satellites (space segment), the control centres and sensor stations on the ground (ground segment), and the receivers (user segment). EUSPA describes Galileo in these three segments Source: EU Agency for the Space Programme (EUSPA), accessed 6 October 2026EU Agency for the Space Programme (EUSPA)Galileoaccessed 6 October 2026Open source (opens euspa.europa.eu).
03Programmes
Galileo and EGNOS: Europe's satellite navigation
Galileo and EGNOS are two of the five components of the EU Space Programme, established by Regulation (EU) 2021/696 Source: European Union, EUR-Lex, 12 May 2021European Union, EUR-LexRegulation (EU) 2021/696 of 28 April 2021 establishing the Union Space Programme and the European Union Agency for the Space Programme12 May 2021Open source (opens eur-lex.europa.eu).
Galileo is the EU's global navigation satellite system. Unlike the other global systems, it is a civilian system. The EU owns the programme and the European Commission is its programme manager. EUSPA is responsible for the operational management of the services, and ESA is entrusted with the design and evolution of the system Source: EU Agency for the Space Programme (EUSPA), accessed 6 October 2026EU Agency for the Space Programme (EUSPA)Galileoaccessed 6 October 2026Open source (opens euspa.europa.eu). Galileo started its initial services on 15 December 2016 Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: Galileo General Introductionaccessed 6 October 2026Open source (opens gssc.esa.int).
For businesses, the question is which Galileo services they can use and on what terms:
| What it provides | Who can use it | |
|---|---|---|
| Open Service | Positioning, navigation and timing, as used in smartphones and vehicle navigation | Everyone, free of charge |
| High Accuracy Service (HAS) | Corrections for higher accuracy than the Open Service, typically below 25 cm horizontally | Everyone, free of charge, via the Galileo signal and the internet |
| OSNMA | Authentication of the navigation message, so that a receiver can check that the data comes from Galileo | Everyone, free of charge |
| Public Regulated Service (PRS) | Encrypted navigation with high continuity, more robust against malicious interference | Government-authorised users |
| Search and Rescue Service | Relays signals from distress beacons to rescue services | Distress beacons and rescue services |
The services are described by EUSPA Source: EU Agency for the Space Programme (EUSPA), 17 September 2026EU Agency for the Space Programme (EUSPA)Galileo services17 September 2026Open source (opens euspa.europa.eu). HAS went live in January 2023 as an initial service Source: EU Agency for the Space Programme (EUSPA), 24 January 2023EU Agency for the Space Programme (EUSPA)Galileo High Accuracy Service goes live!24 January 2023Open source (opens euspa.europa.eu), and the full service is still in preparation Source: European GNSS Service Centre (GSC), operated for EUSPA, accessed 7 October 2026European GNSS Service Centre (GSC), operated for EUSPAGalileo High Accuracy Service (HAS)accessed 7 October 2026Open source (opens gsc-europa.eu). OSNMA has been operational since 24 July 2025 Source: EU Agency for the Space Programme (EUSPA), 5 September 2025EU Agency for the Space Programme (EUSPA)From Testing to Operations: Galileo OSNMA Service Now Available to Users5 September 2025Open source (opens euspa.europa.eu). It authenticates the navigation message, not the ranging signal itself. EUSPA lists three further services under development: a Signal Authentication Service, which will add authentication of the ranging signal on E6, an Emergency Warning Satellite Service and a Timing Service Source: EU Agency for the Space Programme (EUSPA), 17 September 2026EU Agency for the Space Programme (EUSPA)Galileo services17 September 2026Open source (opens euspa.europa.eu).
EGNOS is Europe's regional satellite-based augmentation system (SBAS). Ground stations monitor the GPS signals and compute corrections and integrity messages, which three geostationary satellites broadcast to users Source: EU Agency for the Space Programme (EUSPA), accessed 6 October 2026EU Agency for the Space Programme (EUSPA)EGNOSaccessed 6 October 2026Open source (opens euspa.europa.eu). Its free Open Service improves GPS accuracy to 1 to 2 metres and needs no authorisation Source: EU Agency for the Space Programme (EUSPA), 19 November 2025EU Agency for the Space Programme (EUSPA)EGNOS services19 November 2025Open source (opens euspa.europa.eu). Since its certification for civil aviation in 2011, EGNOS has increased the safety and accessibility of airports, in particular small and regional airports and airfields. Its coverage is limited to Europe and some neighbouring countries. The next generation, EGNOS V3, is in preparation and will augment Galileo as well as GPS Source: EU Agency for the Space Programme (EUSPA), accessed 6 October 2026EU Agency for the Space Programme (EUSPA)EGNOSaccessed 6 October 2026Open source (opens euspa.europa.eu).
04Accuracy
How accurate is GNSS?
There is no single answer: accuracy depends on the method and on the conditions. Typical values from the operators and from ESA's GNSS reference:
Show as table
| Typical accuracy | What it needs | |
|---|---|---|
| GPS without augmentation | Around 5 m in open sky | A standard receiver |
| EGNOS Open Service | 1 to 2 m | An EGNOS-enabled receiver within the coverage area |
| Galileo HAS | Below 25 cm horizontally | A receiver that processes HAS corrections, received via the Galileo signal or the internet |
| PPP (precise point positioning) | Centimetres to decimetres | Precise orbit and clock corrections; standard PPP needs many tens of minutes to converge |
| RTK (real-time kinematic) | A few centimetres | A base station within about 10 to 20 km and a real-time link to it |
Sources: EUSPA for GPS without augmentation and EGNOS Source: EU Agency for the Space Programme (EUSPA), 19 November 2025EU Agency for the Space Programme (EUSPA)EGNOS services19 November 2025Open source (opens euspa.europa.eu) and for HAS Source: EU Agency for the Space Programme (EUSPA), 24 January 2023EU Agency for the Space Programme (EUSPA)Galileo High Accuracy Service goes live!24 January 2023Open source (opens euspa.europa.eu); ESA Navipedia for PPP Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: Precise Point Positioningaccessed 6 October 2026Open source (opens gssc.esa.int) and RTK Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: RTK Fundamentalsaccessed 6 October 2026Open source (opens gssc.esa.int). How construction companies choose between these corrections is covered under GNSS machine guidance and surveying.
Accuracy is only one requirement. Integrity describes whether a system warns its user in time when a position should not be trusted. EGNOS adds an integrity message for this purpose Source: EU Agency for the Space Programme (EUSPA), accessed 6 October 2026EU Agency for the Space Programme (EUSPA)EGNOSaccessed 6 October 2026Open source (opens euspa.europa.eu), and its Safety of Life Service is used mainly in civil aviation Source: EU Agency for the Space Programme (EUSPA), 19 November 2025EU Agency for the Space Programme (EUSPA)EGNOS services19 November 2025Open source (opens euspa.europa.eu). For critical national infrastructure, the UK Blackett review of 2018 recommends that procurers specify requirements for accuracy, integrity, availability and continuity Source: UK GO-Science, UK Government Office for Science, 30 January 2018UK Government Office for ScienceSatellite-derived time and position: a study of critical dependencies (Blackett review)30 January 2018Open source (opens gov.uk).
05Use cases
What GNSS is used for
GNSS applications in industry rely on position, on time, or on both. EUSPA describes, among others, centimetre-level surveying and machine guidance with RTK networks, the time synchronisation of phasor measurement units in power grids and the alignment of time and frequency between the base stations of mobile networks Source: EU Agency for the Space Programme (EUSPA), 26 May 2026EU Agency for the Space Programme (EUSPA)EU Space Market Report 2026, Issue 126 May 2026Open source (opens euspa.europa.eu). The use cases in our library that rely on satellite navigation:
- UC-17
GNSS machine guidance and surveying in construction
How GNSS with RTK corrections guides construction machines and supports surveying, what Galileo adds, and where satellite positioning reaches its limits.
- UC-13
GNSS timing for power grids
Why power grids depend on GNSS timing: phasor measurement units, microsecond synchronisation, Galileo next to GPS and resilient grid timing.
- UC-22
GNSS jamming and spoofing: protecting business operations
How a business protects operations that depend on GNSS position or time against jamming and spoofing: find dependencies, harden receivers, plan a backup.
- UC-21
Fleet tracking by satellite beyond mobile coverage
How vehicles, containers and vessels are tracked without a mobile network: GNSS for the position, satellite links for the transmission, and the limits of both.
- UC-26
Crop monitoring and precision farming with satellite data
How satellites help farms monitor crops and apply fertiliser, seed and water precisely: Sentinel-2 vegetation data, GNSS guidance, benefits and limits.
- UC-11
Pipeline and grid corridor monitoring with satellite data
How operators monitor pipelines and power line corridors with satellite data: ground motion, vegetation and third-party interference, with limits.
- UC-10
Site selection with satellite data
How satellite data on radiation, wind, terrain, land cover and ground motion narrows the search for solar, wind and industrial sites, and what to check on site.
- UC-05
Land use change detection with satellite data
How satellite data tracks land take, sealing and urban expansion, which Copernicus layers a region can use, and where their limits are.
- UC-25
Insurance claims verification with satellite data
How insurers use satellite images to map a flood or storm footprint, check claims against it, plan loss adjusters, and where site visits remain necessary.
- UC-19
Traffic hub monitoring with satellite data
Which satellite data show the state of ports and traffic hubs a supply chain depends on: satellite AIS, radar and optical imagery, GNSS and satellite links.
06Limits
Limits
Limit 01
Weak signals can be jammed or spoofed
GNSS signals reach the ground well below the level of ambient noise, and more powerful transmissions in the GNSS band can overwhelm a receiver Source: UK GO-Science, UK Government Office for Science, 30 January 2018UK Government Office for ScienceSatellite-derived time and position: a study of critical dependencies (Blackett review)30 January 2018Open source (opens gov.uk). Jamming blocks the signals, spoofing feeds false ones Source: European Union Aviation Safety Agency (EASA), 3 July 2026European Union Aviation Safety Agency (EASA)Global Navigation Satellite System (GNSS) outages and alterations3 July 2026Open source (opens easa.europa.eu). Our use case on GNSS jamming and spoofing explains how to protect operations.
Limit 02
No signal indoors or underground
GNSS is not available indoors or underground Source: UK GO-Science, UK Government Office for Science, 30 January 2018UK Government Office for ScienceSatellite-derived time and position: a study of critical dependencies (Blackett review)30 January 2018Open source (opens gov.uk). Near buildings, signals reflected by walls reach the antenna by several paths and distort the measurement Source: ESA Navipedia, European Space Agency (ESA), Navipedia, 2011European Space Agency (ESA), NavipediaNavipedia: Multipath2011Open source (opens gssc.esa.int).
Limit 03
Published accuracy is conditional
The figures above apply under nominal conditions. Satellite geometry Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: An intuitive approach to the GNSS positioningaccessed 6 October 2026Open source (opens gssc.esa.int), the antenna and reflecting structures nearby Source: ESA Navipedia, European Space Agency (ESA), Navipedia, 2011European Space Agency (ESA), NavipediaNavipedia: Multipath2011Open source (opens gssc.esa.int) change the result, so accuracy needs testing where it matters.
Limit 04
Dependence is often hidden
Systems that look independent of GNSS, such as some network time services, can take their time from GNSS receivers. Even careful operators may not know how much they rely on it Source: UK GO-Science, UK Government Office for Science, 30 January 2018UK Government Office for ScienceSatellite-derived time and position: a study of critical dependencies (Blackett review)30 January 2018Open source (opens gov.uk).
07Key terms
Key terms
- PNT: positioning, navigation and timing, the three services GNSS provides.
- Constellation: the set of satellites that make up a navigation system.
- Pseudorange: the distance to a satellite computed from the signal travel time, still containing the receiver's clock error.
- SBAS: satellite-based augmentation system, such as EGNOS, which broadcasts corrections and integrity information via geostationary satellites.
- RTK: real-time kinematic positioning, which uses corrections from a nearby base station to reach a few centimetres.
- PPP: precise point positioning, which uses precise satellite orbits and clocks to position a single receiver without a nearby base station.
- Integrity: the ability of a system to warn its users in time when it should not be used.
- Multipath: signals that reach the antenna by reflection as well as directly, which distorts the measurement.
- OSNMA: Galileo Open Service Navigation Message Authentication, which lets receivers check that navigation data is genuine.
- Jamming and spoofing: deliberate interference that blocks GNSS signals, or counterfeit signals that make a receiver compute a wrong position or time.
08Next steps
How we help
We help organisations decide whether satellite positioning or timing fits a task, which accuracy, integrity and continuity it needs, and how to specify and procure a solution that delivers it. If you are new to the field, start with the definition of space-enabled solutions, which places satellite navigation next to Earth observation, satellite communication and AI.
Frequently asked questions
Q1What is the difference between GPS and GNSS?
GNSS is the generic term for satellite navigation systems with global coverage Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: GNSS (glossary entry)accessed 6 October 2026Open source (opens gssc.esa.int). GPS is one of them, owned by the United States Source: U.S. government, GPS.gov, accessed 6 October 2026U.S. government, GPS.govGPS.gov: What is GPS?accessed 6 October 2026Open source (opens gps.gov). GLONASS, Galileo and BeiDou are the others. Many receivers combine several systems, which gives them more satellites to work with.
Q2How accurate is GNSS?
It depends on the method. A GPS receiver without augmentation typically reaches around 5 metres in open sky, and the EGNOS Open Service improves this to 1 to 2 metres Source: EU Agency for the Space Programme (EUSPA), 19 November 2025EU Agency for the Space Programme (EUSPA)EGNOS services19 November 2025Open source (opens euspa.europa.eu). The free Galileo High Accuracy Service typically reaches below 25 centimetres horizontally Source: EU Agency for the Space Programme (EUSPA), 24 January 2023EU Agency for the Space Programme (EUSPA)Galileo High Accuracy Service goes live!24 January 2023Open source (opens euspa.europa.eu), and RTK corrections from a nearby base station reach a few centimetres Source: ESA Navipedia, European Space Agency (ESA), Navipedia, accessed 6 October 2026European Space Agency (ESA), NavipediaNavipedia: RTK Fundamentalsaccessed 6 October 2026Open source (opens gssc.esa.int).
Q3What is the Galileo High Accuracy Service?
The High Accuracy Service (HAS) is a free Galileo service that sends precise point positioning corrections worldwide, through the Galileo signal and over the internet. Under nominal conditions it typically reaches an accuracy below 25 centimetres horizontally. It serves professional applications such as surveying, precision agriculture and civil engineering Source: EU Agency for the Space Programme (EUSPA), 24 January 2023EU Agency for the Space Programme (EUSPA)Galileo High Accuracy Service goes live!24 January 2023Open source (opens euspa.europa.eu). Its initial service started in January 2023, and the full service is still in preparation Source: European GNSS Service Centre (GSC), operated for EUSPA, accessed 7 October 2026European GNSS Service Centre (GSC), operated for EUSPAGalileo High Accuracy Service (HAS)accessed 7 October 2026Open source (opens gsc-europa.eu).
Q4What are jamming and spoofing?
Jamming is radio interference that stops a receiver from locking onto the satellite signals. Spoofing broadcasts counterfeit signals, so the receiver computes a wrong position, navigation or time Source: European Union Aviation Safety Agency (EASA), 3 July 2026European Union Aviation Safety Agency (EASA)Global Navigation Satellite System (GNSS) outages and alterations3 July 2026Open source (opens easa.europa.eu). How organisations protect their operations is described in our use case on GNSS jamming and spoofing.
Q5Is Galileo free to use?
The Open Service, the High Accuracy Service and the authentication service OSNMA are free of charge. The encrypted Public Regulated Service is reserved for government-authorised users Source: EU Agency for the Space Programme (EUSPA), 17 September 2026EU Agency for the Space Programme (EUSPA)Galileo services17 September 2026Open source (opens euspa.europa.eu).
Sources (19)
- Navipedia: GNSS (glossary entry) (opens gssc.esa.int)
- GPS.gov: What is GPS? (opens gps.gov)
- Navipedia: GLONASS General Introduction (opens gssc.esa.int)
- Navipedia: An intuitive approach to the GNSS positioning (opens gssc.esa.int)
- Galileo (opens euspa.europa.eu)
- Navipedia: Galileo General Introduction (opens gssc.esa.int)
- Regulation (EU) 2021/696 of 28 April 2021 establishing the Union Space Programme and the European Union Agency for the Space Programme (opens eur-lex.europa.eu)
- Galileo services (opens euspa.europa.eu)
- Galileo High Accuracy Service goes live! (opens euspa.europa.eu)
- Galileo High Accuracy Service (HAS) (opens gsc-europa.eu)
- From Testing to Operations: Galileo OSNMA Service Now Available to Users (opens euspa.europa.eu)
- EGNOS (opens euspa.europa.eu)
- EGNOS services (opens euspa.europa.eu)
- Navipedia: Precise Point Positioning (opens gssc.esa.int)
- Navipedia: RTK Fundamentals (opens gssc.esa.int)
- Navipedia: Multipath (opens gssc.esa.int)
- Satellite-derived time and position: a study of critical dependencies (Blackett review) (opens gov.uk)
- Global Navigation Satellite System (GNSS) outages and alterations (opens easa.europa.eu)
- EU Space Market Report 2026, Issue 1 (opens euspa.europa.eu)
Contact
Need a position or a time signal you can rely on? We help you specify it.
Prefer to talk?
Tell one of our experts about your project. Together we work out where you stand, whether satellite data and AI can help and what a sensible next step would be.
Both calls are free of charge and take place online. You choose a date in our booking calendar.