Mobile devices can make use of several different approaches to determine their current location. Some of these – such as Cell Identification, Up-Link Time Difference of Arrival (U-TDOA), Advanced Forward Link Trilateration (AFLT), and Enhanced Observed Time Difference (E-OTD) – rely to some extent on the cellular network. Another popular method, used by devices that support Wireless LAN (WLAN), is to map known WLAN access points then use this information to approximate a device’s current location. However, since the majority of these approaches have limitations, including accuracy and availability, the most common method employed in mobile devices today is to use the Global Positioning System (GPS).
GPS is a Global Navigation Satellite System that has been fully operational since 1993. Devices with embedded GPS receiving capability are able to accurately compute their current position almost anywhere on earth that the satellite signals can be received. The reliability, accuracy, and availability of this technology has driven widespread adoption.
Mobile devices with GPS have two options to use when determining their current location:
1) Conventional standalone GPS capabilities and 2) Assisted GPS (A-GPS)