What is GPS?

The USA’s NAVSTAR Global Positioning System (GPS) is the most widely used global navigation satellite system (GNSS) in the world. It is widely used for navigation by the public, businesses and other organisations. Today, GPS is embedded in an increasing variety of positioning devices such as smart phones.

GPS constellation

GPS, which is owned and operated by the US military, operates on two levels. GPS’ Precise Positioning Service (PPS) is reserved for authorised, controlled users, generally the US military. The system’s Standard Positioning Service (SPS) is available globally for free to anyone with a GPS-capable receiver.

Accuracy and integrity

The free signal provides a location accuracy of within 17 metres (the horizontal specification for 95% of the measurements), a range which is inadequate for certain applications. Similarly, it does not provide a guarantee of the position or time calculated by the user’s receiver. EGNOS augments GPS by improving the accuracy of the GPS signal to within three metres and by providing integrity alerts confirming the signal can be used for navigation.