The GPS (Global Positioning System) originally Navstar GPS, is a radio navigation system that provides location, velocity, and time synchronization based on a global satellite system. It is one of the Global Navigation Satellite Systems (GNSS) that provides geolocation and time information. The system made up of at least 24 satellites. Some GPS receivers are so accurate they can establish their location within 1 centimetre (0.4 inches).
There are four main satellite constellations used worldwide as follows;
- GPS (United States)
- GLONASS ( Russia )
- BeiDou ( China )
- Galileo ( European Union )
For the GPS itself, The US military first used it in the year 1960, then the GPS project was launched in 1973 to overcome the limitations of previous navigation systems, by putting together the ideas from several predecessors, including classified engineering design studies from the 1960s. The US Department of Defense’s developed the system and became fully operational in 1985. They were made available for civilian use in the 1980s. Nowadays, GPS is everywhere and is being used in most of the modern applications that we use daily, such as smartphone and smartwatch.
Global Positioning System (GPS), consists of three main segments: space, control and user segment.
- Space segment – It consists of 24 satellites that transmit one-way signals that provide current GPS position and time of the satellite. Satellites act like the stars in constellations, and we know where they are because they invariably send out signals.
- Control segment – It consists of monitoring and controlling stations that ensure of correct satellite performance, maintain condition and status of the satellite constellation. Also known as the ground station.
- User segment – It consists of equipment that receives signals from the GPS satellites and calculates the user’s dimensional position and time. We can find a receiver in our phone or our car. It constantly seeks for the signals from the satellites. The receiver figures out how far away they are from some of the satellites. Once the receiver calculates its distance from four or more satellites, it knows exactly where we are