Enhanced Observed Time Difference A position-location method for
GSM networks in which the phone measures the difference in the
time of arrival signals from different towers. Essentially, the
phone triangulates its position using signals from the towers,
the reports the position back to the network. E-OTD is one of
several technologies that carriers can deploy to meet E-911
requirements. Unlike competing U-TDOA technology, the phone
actively participates in the location process. Therefore, E-OTD
only works with phones that specifically include E-OTD
technology. Most major U.S. carriers that tested E-OTD for E-911
compliance decided against it and opted for U-TDOA technology
instead. The main proponent and provider of E-OTD technology is
a company called Cambridge Positioning Systems (CPS).