Geolocation of cellular phone using supervisory audio tone transmitted from single base station

Abstract

In order to geolocate a wireless communication device (cellular phone) initiating a 911 call, a base station transceiver transmits a supervisory audio tone (SAT), which is automatically looped back by the calling cellular phone. Returned SAT signals are correlated with those transmitted to determine the range of the cellular phone. In addition, incoming signals from the cellular phone, such as the returned SAT signals, are received by a phased array antenna and subjected to angle of arrival processing to determine the direction of the cellular phone relative to the base station. Given this angle of arrival and range information the cellular phone is geolocated. Since the total travel distance of SAT signals between the base station and the cellular phone traverses a two-way path from the base station to the cellular phone and back, plus a loopback path through the circuitry of the phone, the range R of the cellular phone from the base station is calculated in accordance with the equation R=C×m/2−k, where C is the velocity of light, m is a correlation time shift interval, and k is a correction factor associated with the loopback path, and varies with manufacturer and phone type. The value of k is provided by the phone manufacturer and is accessed using equipment serial number information conveyed in the incoming control channel call establishment request from the calling phone.