Enhanced location methodology for a location system

• US 6,515,623 B2
• Filed: 06/29/2001
• Issued: 02/04/2003
• Est. Priority Date: 06/29/2001
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Johnson, Mark J.
• Primary Examiner(s): Phan, Dao
• Application Number:
  US09/897,007
• Publication Number:
  US 20030001777A1
• Time in Patent Office: 585 Days
• Field of Search: 342/387, 342/457, 342/450, 342/453, 342/463, 455/455, 455/456
• US Class Current: 342/387
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial

Abstract

A first device (100) transmits a first signal to a second device (300) at a first time. A third device (110) detects a second signal from the second device (300) at a second time. The second signal was transmitted in response to detection of the first signal. Based on the first and second times, a sum of a first propagation delay (200) and a second propagation delay (210) is estimated. The first propagation delay (200) is between the first device (100) and the second device (300), and the second propagation delay (210) is between the second device (300) and the third device (110). The sum of the first and second propagation delays (200, 210) is then used to estimate a location of the second device (300).

Claims

1. A location method used in a location system, the method comprising the steps of:

at a first device, transmitting a first signal to a second device at a first time;

at a third device, detecting a second signal from the second device at a second time, wherein the second signal was transmitted in response to detection of the first signal;

based on the first and second times, estimating a sum of a first propagation delay and a second propagation delay, wherein the first propagation delay is between the first device and the second device, and the second propagation delay is between the second device and the third device; and

using the sum of the first and second propagation delays to estimate a location of the second device.

2. The method of claim 1 further comprising the step of using the sum of the first and second propagation delays to define a first locus of points on which the second device is located.

3. The method of claim 2 further comprising the steps of:

defining a second locus of points on which the second device is located; and

estimating a location of the second device based on an intersection of the first locus of points and the second locus of points.

4. The method of claim 3 wherein the step of defining a second locus of points comprises one of the following steps:

estimating a difference between the first and second propagation delays;

estimating at least one of the first and the second propagation delays; and

estimating a direction from which the second signal originated.

5. The method of claim 1 wherein the step of estimating a sum is further based on a delay time, wherein the delay time is a time between detection of the first signal at the second device and transmission of the second signal by the second device.

6. The method of claim 5 further comprising the step of establishing the delay time a priori at at least one of the following devices:

the first device, the second device, the third device, and a fourth device.

7. The method of claim 5 further comprising the step of reporting the delay time to at least one of the following devices:

the first device, the second device, the third device, and a fourth device.

8. The method of claim 1 wherein the first device and the third device are not a part of a common system.

9. The method of claim 1 further comprising the step of synchronizing the first device and the third device with each other.

10. The method of claim 1 further comprising the step of synchronizing the first device and the third device with a reference source.

11. A location method used in a location system comprising the steps of:

at a first device, detecting a first signal from a second device, and responsive to detection of the first signal, transmitting a second signal to a third device;

estimating a first time when the first signal was transmitted from the second device;

estimating a second time when the second signal was received at the third device;

based on the first time and the second time, estimating a sum of a first propagation delay and a second propagation delay, wherein the first propagation delay is between the first device and the second device, and the second propagation delay is between the first device and the third device; and

using the sum of the first and second propagation delays to estimate a location of the first device.

12. The method of claim 11 further comprising the step of detecting the second signal at the second device.

13. The method of claim 11 further comprising the step of detecting the first signal at the third device.

14. A location method used in a location system, the method comprising the steps of:

at a first device, detecting a first signal from a second device at a first time;

at the first device, detecting a second signal from a third device at a second time, wherein the second signal was transmitted from the third device in response to detecting the first signal from the second device at the third device;

based on the first time and the second time, estimating a difference between a first propagation delay and a sum of a second propagation delay and a third propagation delay, wherein the first propagation delay is between the first device and the second device, the second propagation delay is between the second device and the third device, and the third propagation delay is between the first device and the third device; and

using the difference between the first propagation delay and the sum of the second and third propagation delays to estimate a location of the second device.

15. The method of claim 14 further comprising the step of defining a first locus of points based on a difference between the first propagation delay and a sum of the second and third propagation delays.

16. The method of claim 14 wherein the first device and the second device are not a part of a common system.

17. A location method used in a location system, the method comprising the steps of:

at a first device, transmitting a first signal at a first time, and detecting a second signal at a second time, wherein the second signal was transmitted from a second device in response to detecting the first signal from the first device at a third device;

based on the first time and the second time, estimating a sum of a first propagation delay and a second propagation delay, wherein the first propagation delay is between the first device and the second device and the second propagation delay is between the first device and the third device; and

using the sum of the first and second propagation delays to estimate a location of the first device.

18. The method of claim 17 further comprising the step of using the sum of the first and second propagation delays to define a first locus of points on which the first device is located.

19. The method of claim 18 further comprising the steps of:

defining a second locus of points on which the first device is located; and

estimating a location of the first device based on an intersection of the first locus of points and the second locus of points.

20. The method of claim 17 wherein the step of estimating a sum is further based on a delay time, wherein the delay time is a time between detection of the first signal at the second device and transmission of the second signal by the second device.