Global Navigation Satellite System (GNSS) is the universal term encompassing all satellite-based positioning, navigation, and timing (PNT) systems that provide global or regional coverage. While ‘GPS’ has become colloquial shorthand for satellite navigation, GNSS correctly refers to the broader category including GPS (United States), GLONASS (Russia), Galileo (European Union), BeiDou (China), and regional systems like QZSS (Japan) and NavIC (India).

GNSS technology fundamentally operates through precise timing measurements. Each navigation satellite carries atomic clocks and continuously broadcasts signals containing its position (ephemeris) and exact transmission time. A GNSS receiver measures the time delay between signal transmission and reception, multiplying by the speed of light to determine the distance (pseudorange) to each satellite. With pseudoranges to four or more satellites and knowledge of their positions, the receiver solves a system of equations to determine its three-dimensional position and clock offset.

The accuracy of standalone GNSS positioning is limited by various error sources: ionospheric delays (signals slow as they pass through the charged upper atmosphere), tropospheric delays (moisture and pressure variations in the lower atmosphere), satellite clock and orbital errors, multipath (signals reflecting off nearby surfaces), and receiver noise. Standard single-frequency GNSS receivers typically achieve positioning accuracy of 3-10 meters under open-sky conditions, adequate for navigation and many consumer applications but insufficient for precision uses.

GNSS correction services overcome these limitations through various techniques. Satellite-Based Augmentation Systems (SBAS) like WAAS provide free 1-3 meter accuracy over continental regions. Differential GNSS (DGNSS) achieves sub-meter accuracy using local reference stations. Real-Time Kinematic (RTK) and Precise Point Positioning (PPP) deliver centimeter-level accuracy for surveying, autonomous vehicles, precision agriculture, and construction applications. The combination of multi-constellation reception (accessing 30+ satellites instead of 8-12), multi-frequency processing (enabling ionospheric delay estimation), and sophisticated correction services has transformed GNSS from a navigation aid into a precision positioning infrastructure supporting countless industries.