Method and apparatus for geolocating a wireless communications device

• US 20060187119A1
• Filed: 04/19/2006
• Published: 08/24/2006
• Est. Priority Date: 03/18/2002
• Status: Active Grant

• Current Assignee: Christopher J. Hall, Clay S. Turner, Jimmy C. Ray
• Original Assignee: Christopher J. Hall, Clay S. Turner, Jimmy C. Ray
• Inventors: Hall, Christopher J., Ray, Jimmy C., Turner, Clay S.
• Granted Patent: US 7,256,737 B2
• Time in Patent Office: Days
• US Class Current: 342/387
• CPC Class Codes: G01S 5/0205 Details
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04M 2207/18 wireless networks
• CPC Class Codes: H04M 2242/30 Determination of the location of a subscriber
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

The time difference of arrival for a signal received at two or more receiving sites as transmitted from a wireless communications device, is determined by a frequency domain technique. The constituent frequencies of the signals received at the two or more receiving sites are determined, including the phase, or a value representative of the phase, of each frequency component. The phase values for the same frequency are subtracted to yield a phase difference values as a function of frequency. The slope of the function represents the time difference of arrival for the wireless communications device signal as received at the two receiving sites. To determine the mobile location based on the determined time difference of arrival values, a seed or initial location is first assumed for the wireless communications device and the distance difference of arrival (the time difference of arrival multiplied by the speed of light) is calculated. The calculated time difference of arrival is then used to adjust the distance difference of arrival by continuously iterating the position of the wireless communications device until the calculated distance of arrival and the calculated time difference of arrival (as multiplied by the speed of light) are within a predetermined margin.

Claims

1. A method for determining the location of a transmitting unit transmitting a signal, in response to the time difference of arrival of the signal at two or more receiving sites, comprising:

(a) selecting a location estimate for the transmitting unit;

(b) determining the pairwise distance difference of arrival from the location estimate to at least two of the two or more receiving sites;

(c) determining the error in the location estimate in response to the distance difference of arrival value determined at the step (b); and

(d) updating the location estimate in response to the error.

2. The method of claim 1 further comprising determining a predetermined threshold value and a step (e), repeating the steps (b) through (d) until the error is less than the threshold value.

3. The method of claim 1 wherein the distance difference of arrival value is the product of the time difference of arrival and the speed of light.

4. The method of claim 1 wherein the (a) further comprising selecting a location estimate of the geographic center of the two or more receiving sites.

5. The method of claim 1 wherein the step (c) further comprises:

(c1) determining a linear differential equation relating the distance difference of arrival, the geographic location of the two or more receiving sites, the location estimate and the error in the location estimate; and

(c2) solving the linear differential equation to determine the error in the location estimate.

6. The method of claim 5 wherein the step (c2) further comprises solving the linear differential equation according to a least squared error process.

7. The method of claim 1 wherein the step (b) further comprises determining the distance difference of arrival for the pairwise combinations of the receiving sites, wherein the error in the location estimate according to the step (c) further comprises the error in the location estimate with respect to each of the pairwise combinations of receiving sites.

8. The method of claim 1 wherein the location estimate includes a location estimate in three dimensions.