How GPS functions

The Global Positioning System more popularly referred to by the acronym GPS, is a navigational tool that makes use of the 24 NAVSTAR satellites to deliver accurate location and time data. The acronym NAVSTAR is short for Navigation Satellite Timing and Ranging. These satellites have the capacity to make an orbit around the Earth every 12 hours. They are orbiting at an attitude that will see them cover the same distance every 23hours 56minutes.

Each 24 NAVSTAR satellite is equipped with an atomic clock. This enables it to provide accurate location and time signals. Handheld GPS receivers then pick up these signals from multiple satellites. The GPS receiver makes use of mathematical algorithms to analyse all these signals and provide a location that is accurate to about 50ft. The accuracy of this system is affected by a number of factors, including vegetation cover, atmospheric conditions, buildings etc. The new SiRE star III chipset has been designed to give better accuracy.

Most GPS gadgets have been fitted with Wide Area Augmentation System technology, also referred to as WAAS. This system utilises 25 ground reference stations that are located large distances apart. Each of these stations receives GPS signals and analyses them for accuracy. The signals are then transmitted to a Wide Area Master Station that further refines the data and uploads it to a satellite. The data is then broadcast on a frequency similar to that of GPS. Handheld GPS receivers pick up these messages, provided that they are in the same range as the WAAS broadcast area.