The Global Navigation Satellite System (GNSS) is a fundamental concept and a global system of systems that provides autonomous geospatial positioning, navigation, and timing (PNT) services. The concept originated from the discovery in 1957 that the signal from the Soviet Union's Sputnik 1 could be tracked to determine an observer's position. The problem it solved was the need for continuous, all-weather, and highly accurate location and time data, which led the US to develop the Global Positioning System (GPS), with the first satellite launched in 1978 under the NAVSTAR program.
The mechanism of GNSS relies on three segments: Space, Control, and User. Satellites in medium Earth orbit (MEO) transmit radio signals containing their precise orbit information and a time stamp from their on-board atomic clocks. A receiver on Earth calculates the distance (range) to each satellite by measuring the time difference between the signal's broadcast and reception. To determine a three-dimensional position (latitude, longitude, and altitude) and correct the receiver's internal clock, the receiver must simultaneously receive signals from at least four satellites, using a mathematical process called trilateration.
GNSS is a collective term for all such systems, which include the US GPS, Russia's GLONASS, the European Union's Galileo, and China's BeiDou Navigation Satellite System (BDS). For an informed Indian reader, the most relevant connection is the regional system, the Indian Regional Navigation Satellite System (IRNSS), which is operationally named NavIC (NAVigation with Indian Constellation). India developed NavIC to ensure strategic independence after facing issues with reliance on foreign systems during the Kargil war.
The technology is constantly changing, with a recent shift to Multi-Constellation and Multi-Band receivers that use signals from multiple systems and frequencies for enhanced accuracy and reliability. The US is upgrading its system with the GPS III series, which provides four times the accuracy and eight times the anti-jamming capability of previous versions, with the final satellite launched in April 2026. India is also upgrading NavIC with new satellites (NVS series) launched since 2023 to broadcast signals in the L1, L5, and S bands, with plans to expand its coverage from regional to global.