Global Navigation Satellite System

A Global Navigation Satellite System (GNSS) is a constellation of satellites and supporting infrastructure that broadcasts signals for positioning, navigation, and timing worldwide.

Trilateration: A method for locating a point from its distances to known reference points. A receiver estimates its distances from satellites and solves for its position by trilateration.
Satellite constellation: A coordinated group of satellites arranged to provide coverage or perform a shared task. GNSS coverage depends on multiple satellites occupying carefully planned orbital planes.
Global Positioning System: The United States satellite navigation system that provides positioning, navigation, and timing services worldwide. GPS is the best-known GNSS, but it is only one of several independent systems.
Inertial navigation system: A navigation system that estimates motion and position from accelerometers and gyroscopes. Unlike GNSS, it needs no external signals but accumulates errors as it runs.
Pseudorange: An apparent signal travel distance calculated from the transmission and reception times of a radio signal. GNSS receivers derive these measurements from satellite signals before correcting clock errors.
Radio navigation: Navigation that determines position or direction using transmitted and received radio signals. GNSS is a global form of radio navigation based on one-way satellite broadcasts.
Galileo: The European Union's global satellite navigation system. Galileo provides an independent civil constellation that receivers can combine with other GNSS.
Pseudolite: A ground-based transmitter that imitates satellite navigation signals for local positioning. Pseudolites extend GNSS-like positioning indoors or locally, where satellite coverage is poor.
Atomic clock: A clock that measures time using the frequency of an atomic transition. Precise satellite clocks let receivers infer signal travel times from arrival times.
Geodesy: The science of measuring Earth's shape, gravity field, and positions on its surface. GNSS positions rely on geodetic models and reference frames tied to Earth.

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