U-TDOA, or Uplink-Time Difference of Arrival, is a wireless location technology that relies on sensitive receivers typically located at the cell towers to determine the location of a mobile phone.
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How does U-TDOA work?
U-TDOA determines location based on the time it takes a signal to travel from a mobile phone to each of the sensitive receivers called Location Measurement Units (LMUs). By using the timing information from multiple LMUs, U-TDOA calculates the mobile phone’s location, using a technique called multilateration.
Because U-TDOA is a network-based location technology, it does not require the mobile phone to have any special chip, hardware, or software in it. As a result, it can locate any type of mobile phone.
Since U-TDOA requires physical access to the cellular network's cell towers (base transceiver stations or BTS), it is only available to the owner of the sensor network, which is typically the carrier. Therefore, the solution is generally not available when roaming.
Mission-critical safety and security
U-TDOA is uniquely suited for mission-critical safety and security applications:
U-TDOA vs. GPS
U-TDOA works with all mobile phones and is very accurate, typically identifying location within 50 meters.
GPS relies on special chipsets in wireless devices to calculate location in relationship to orbiting satellites. GPS can locate phones within 50 meters. However, not every wireless subscriber has a GPS-enabled phone. Also, GPS requires a clear view to multiple satellites in order to function, so GPS cannot locate a wireless caller who is indoors or surrounded by tall buildings.
Today, in the United States, Sprint and Verizon use a form of GPS known as Assisted GPS while AT&T Mobility and T-Mobile use U-TDOA for their E9-1-1 solutions.