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U-TDOA – Uplink Time Difference of ArrivalA high-yield, high-performance location technology, TruePosition's Uplink Time Difference of Arrival (U-TDOA), relies upon multilateration, using cell towers, which makes U-TDOA especially well suited for indoor and urban environments. Because it is completely network based (calculating location based on a normal cellular signal) no additional chip or software needs to be installed into the handset, which means U-TDOA can locate every mobile phone anywhere. U-TDOA determines a mobile phone's location by comparing the times at which a cell signal reaches multiple Location Measurement Units (LMUs) installed at the operator's base stations. Accuracy is determined by the network layout and deployment density of LMUs to Base Transceiver Stations (BTSs). U-TDOA technology works very well in urban, suburban, and indoor environments — suffering only in extreme rural conditions where the cell sites are arranged in a "string of pearls" configuration. In such scenarios, TruePosition can supplement its U-TDOA technology with Angle of Arrival (AOA) technology, which computes locations based on the angle at which signal reached two base stations. TDOA should not be confused with Time of Arrival or TOA. Even though a TDOA call flow would look virtually the same as a TOA call flow, there is a difference in how the location is calculated. TDOA and TOA are similar, but there is a difference. TOA differs in the fact that it uses the absolute time of arrival at a certain base station rather than the difference between two stations. The distance can be directly calculated from the time of arrival because signals travel with a known velocity. Time of arrival data from two base stations will narrow a position to two points and data from a third base station is required to resolve the precise position. U-TDOA Highlights
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