A CDE Definition
(Enhanced Observed Time Difference) See mobile positioning.
The ability to pinpoint the location of a vehicle or mobile caller in transit. Also called "geotracking," these location-based services (LBS) are used for emergency purposes as well as proximity marketing, traffic updates, fleet management and asset and people tracking. They are also used for social purposes; for example, the WhosHere app for smartphones identifies other WhosHere users 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).
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 email or text message if the A-GPS device moves outside a defined area. See vehicle tracking, Wi-Fi, GPS and iBeacon.
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