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The Safety App from 911Cellular, LLC 2 is a smartphone app that allows a person to make an E911 phone call from his/her smartphone at the time of an emergency. Just like any 911 call made from landline phones, the call could be due to the person having a serious medical emergency and needing immediate attention or a situation in which the person’s physical safety is at risk. Such calls are routed to PSAPs, whether they originated from landline or mobile phones. The PSAP would then dispatch emergency responders to attend to the person under distress. To do this, the PSAP needs to know the location of the person needing help. This is straightforward in the case of a 911 call made from a landline phone, because the address where the phone is located can be found in the telephone company database. The problem is much harder when the 911 call is made from a mobile phone, because the mobile phone is not tied to a particular location and it can be anywhere. This is called E911.

Presently, there are two main techniques for determining the location of an E911 call. One is triangulation based on the properties of the radio frequency (RF) signals received from the mobile phone at various cellular base stations that can hear the mobile phone. The properties of interest are the strength of the signal, the time of flight of the signal from the mobile phone to a base station, or the direction of arrival of the signal at the base station. A wide range of numbers have been reported for the accuracy of location determination based on signals received at base stations that could be away from a mobile phone on the order of kilometers. One paper 3 reports …