What is GNSS?

People say GPS when they mean satellite positioning in general, but GPS is the name of one system, run by the United States. GPS.gov defines GNSS as a general term for any satellite constellation that provides positioning, navigation and timing services on a global or regional basis, and notes that other nations have fielded their own systems to provide complementary, independent capability.

Every GNSS works on the principle described in how GPS works. Satellites with precise clocks broadcast their positions and the time, a receiver measures signal travel times to several satellites, and it solves for its position and its own clock error.

GPS.gov summarises the main systems as follows. The satellite counts are the figures it gives, and the GPS row is the US availability commitment.

GNSS can also refer to augmentation systems, which add corrections or integrity information on top of these constellations. GPS.gov notes there are too many international augmentations to list.

The global systems share a design but differ in detail.

• Orbits. GPS satellites orbit at about 20,200 km in six planes. Galileo’s nominal constellation is 24 satellites in three planes at 23,222 km, inclined at 56 degrees, according to Navipedia. Navipedia describes the GLONASS nominal constellation as 24 satellites in three planes inclined at 64.8 degrees, at an altitude of 19,100 km.
• Signals. GPS and Galileo separate satellites by giving each a different code on a shared frequency, a scheme called CDMA. GLONASS traditionally gave each satellite its own carrier frequency instead, a scheme Navipedia calls FDMA, and its newer GLONASS-K satellites add code-division (CDMA) signals alongside the old ones.
• Frequencies. Galileo transmits in four bands, E5a, E5b, E6 and E1, which Navipedia says supports both single- and dual-frequency positioning for receivers equipped for it.
• Services. Galileo’s Open Service includes OSNMA, a free authentication feature that lets a receiver check that the navigation message really came from Galileo and was not modified. The European GNSS Service Centre declared its initial service operational on 24 July 2025. Galileo also runs a search and rescue service that relays distress beacon signals.

A receiver that tracks several constellations has more satellites to choose from. Navipedia makes the point for Galileo: a larger number of satellites improves signal availability in dense cities, where tall buildings hide satellites that sit low on the horizon.

Phones expose this directly. Android’s GnssStatus API reports the constellation of each satellite the device is tracking, with constants for GPS, GLONASS, Galileo, BeiDou, QZSS, IRNSS and SBAS augmentation satellites. An app sees only the constellations the phone’s receiver actually tracks.

Independence matters too. GPS.gov describes the other systems as providing complementary, independent capability, and Navipedia says that by diversifying the sources of GNSS signals, Galileo offers users a more resilient service.

Using several systems does not make a receiver immune to interference. The European Union Aviation Safety Agency (EASA) describes jamming and spoofing as threats to GNSS reception in general, not to one system. GPS jamming explains what happens when radio noise drowns the signals, and how spoofing is detected covers counterfeit signals and the checks that catch them.

A GNSS fix is also only as trustworthy as the device that computed it. The receiver calculates its own position, and nothing in the satellite signal tells a remote server whether the number a phone reports is the one its receiver produced.