Local positioning system
A local positioning system (LPS) is a navigation system that provides location information in all weather, anywhere within the coverage of the network, where there is an unobstructed line of sight to three or more signaling beacons of which the exact position on earth is known. A special type of LPS is the Real-time locating system; which also allows real-time tracking of an object or person in a confined area such as a building.
Use
Unlike GPS or other global navigation satellite systems, local positioning systems don't provide global coverage. Instead, they use (a set of) beacons which have a limited range, hence requiring the user to be near these. Beacons include cellular base stations, Wi-Fi access points, and radio broadcast towers.
In the past, long-range LPS's have been used for navigation of ships and aircraft. Examples are the Decca Navigator System and LORAN.
Nowadays, local positioning systems are often used as complementary (and in some cases alternative) positioning technology to GPS, especially in areas where GPS does not reach or is weak, for example, inside buildings, or urban canyons. Local positioning using cellular and broadcast towers can be used on cell phones that do not have a GPS receiver. Even if the phone has a GPS receiver, battery life will be extended if cell tower location accuracy is sufficient.
Techniques
An LPS can use any of the following to calculate the position of an object: