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The ability to pinpoint the location of a mobile caller or vehicle in transit. These location-based services (LBS) are used for emergency purposes as well as enhanced business applications such as location-sensitive billing, traffic updates, fleet management and asset and people tracking. They are also used for social purposes; for example, the WhosHere app for the iPhone tells you what other WhosHere users are in the vicinity. Mobile positioning systems use the following methods to locate a person or vehicle. In some cases, all three are used (cellular, Wi-Fi and GPS).

Cell Towers
The most basic method is cell of origin (COO), which identifies the cell tower closest to the user; however, accuracy is typically around 1,500 feet. Using additional reference beacons and antennas, accuracy can be greatly improved with methods known as Enhanced Observed Time Difference (E-OTD), Time of Arrival (TOA) and Angle of Arrival (AOA). See E-911.

Wi-Fi and A-GPS
Wi-Fi hotspots are also used for location detection. Databases of known hotspots are constantly updated, and positioning accuracy can be within 100 feet. However, Wi-Fi only works well in dense urban areas, and it serves to augment cellular positioning rather than be the sole locating method.

     GPS offers the greatest accuracy (15-75 feet), but requires line of sight to the satellites. Since this cannot be assured in cities with tall buildings, most smartphones employ Assisted GPS (A-GPS), which helps them get the initial fix on the satellites by obtaining orbit and clock data from nearby cell towers.

A-GPS Is Used to Track Everything
Assisted GPS (A-GPS) devices are available to track cars, pets, children as well as anything that may move or be moved. Users can locate the device on the Web or be alerted via e-mail or text message if the A-GPS device moves outside a defined area. See vehicle tracking, Wi-Fi and GPS.