System and method for multiple range estimation location
A system and method of determining the location of a mobile station by determining the time of transmission of a signal by a mobile station and determining range rings at a plurality of reference stations receiving the transmitted signal, where the range rings represent the distance of the mobile station from the plurality of reference stations.
1. A method of determining the location of a mobile device in a network having a plurality of base stations, in which a base station communicates with the mobile device in a downlink transmission and the mobile device communicates with a base station in uplink transmission, comprising the steps of:
(a) transmitting a downlink transmission from a first base station to a mobile device;
(b) receiving an uplink transmission from the mobile device to a first base station at the reference station;
(c) measuring a time of arrival of the uplink transmission at the reference station;
(d) determining a total distance from the first base station to the reference station as a function of the time of transmission of the downlink signal and the measured time of arrival of the uplink transmission, wherein the total distance includes (a) the distance from the reference station to the mobile device and (b) the distance from the first base station to the mobile device.
2. The method of claim 1 wherein the downlink transmission includes timing information for the mobile device and wherein the total distance is determined as a function of the timing information.
3. The method of claim 2 wherein the timing information includes timing advance.
4. The method of claim 1 wherein the first base station is a serving base station and the reference station is co-located with first base station.
5. The method of claim 1 wherein the step of measuring the time of arrival is performed at a sensor co-located at a second base station.
6. The method of claim 1 wherein the determined total distance circumscribes a range ring in the shape of an ellipse having foci at the first base station and the reference station.
7. The method of claim 4 wherein the determined total distance circumscribes a range ring in the shape of a circle centered on the first base station.
8. The method of claim 1 further comprising the steps:
(e) receiving the uplink transmission at a plurality of base stations;
(f) measuring a time of arrival of the uplink transmission at each of the plurality of base stations;
(g) determining a total distance from each of the plurality of base stations to the first base station as a function of the time of transmission of the downlink signal and the measured time of arrival of the uplink transmission at each of the respective plurality of base stations, wherein the total distance includes (a) the distance from the a respective one of the plurality of base stations to the mobile device and (b) the distance from the first base station to the mobile device.
9. The method of claim 8 further comprising the step of determining the geographic location of the mobile device as a function of the determined total distances.