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Cell Phone Location
By Matt | February 13, 2010
Fascinating — I didn’t know the difference between CDMA & GMS in how they locate phones, or the more sophisticated time based triangulation by T-Mobile:
The Federal Communications Commission’s “Enhanced 911″ (E911) requirements allowed rough estimates to be transformed into precise coordinates. Wireless carriers using CDMA networks, such as Verizon Wireless and Sprint Nextel, tend to use embedded GPS technology to fulfill E911 requirements. AT&T and T-Mobile comply with E911 regulations using network-based technology that computes a phone’s location using signal analysis and triangulation between towers.
T-Mobile, for instance, uses a GSM technology called Uplink Time Difference of Arrival, or U-TDOA, which calculates a position based on precisely how long it takes signals to reach towers. A company called TruePosition, which provides U-TDOA services to T-Mobile, boasts of “accuracy to under 50 meters” that’s available “for start-of-call, midcall, or when idle.”
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