Method and apparatus for geolocating a wireless communications device

• US 7,256,737 B2
• Filed: 04/19/2006
• Issued: 08/14/2007
• Est. Priority Date: 03/18/2002
• Status: Expired due to Term

• 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., Turner, Clay S., Ray, Jimmy C.
• Primary Examiner(s): Tarcza; Thomas H.
• Assistant Examiner(s): MULL, FRED H
• Application Number:
  US11/407,314
• Publication Number:
  US 20060187119A1
• Time in Patent Office: 482 Days
• Field of Search: 342/387, 342/451, 342/458, 342463-465
• 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, comprising:

(a) transforming the signal received at a first site to a frequency domain representation comprising first component signals each having a frequency and a phase angle parameter and transforming the signal received at a second site to a frequency domain representation comprising second component signals each having a frequency and a phase angle parameter;

(b) operating in the frequency domain, determining a Hermitian product of first and second component signals having a same frequency parameter;

(c) operating in the frequency domain, determining a phase angle parameter of each Hermitian product determined at the step (b);

(d) determining a relationship between the phase angle parameter and the frequency parameter for a plurality of Hermitian products;

(e) determining a time difference of arrival of the signal from the relationship.

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

(g) determining a distance difference of arrival from the location estimate to the first and the second sites, the distance difference of arrival responsive to the time difference of arrival;

(h) determining an error in the location estimate in response to the distance difference of arrival value; and

(i) 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 (i), repeating the steps (g) through (i) 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 the step (f) 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 (h) further comprises:

(h1) determining a linear differential equation relating the distance difference of arrival, the geographic location of the first and the second receiving sites, the location estimate and the error in the location estimate; and

(h2) solving the linear differential equation to determine the error in the location estimate.

6. The method of claim 5 wherein the step (h2) further comprises solving the linear differential equation according to a least squares error process.

7. The method of claim 1 wherein the step (g) further comprises determining a distance difference of arrival for pairwise combinations of a plurality of receiving sites, wherein the error in the location estimate according to the step (h) 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.