Method and apparatus for estimating the location of a signal transmitter

• US 20070132577A1
• Filed: 12/09/2005
• Published: 06/14/2007
• Est. Priority Date: 12/09/2005
• Status: Abandoned Application

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Kolavennu, Soumitri
• Application Number:
  US11/298,822
• Publication Number:
  US 20070132577A1
• Time in Patent Office: Days
• US Class Current: 340/539.130
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0258 by combining or switching between measurements derived from different systems
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

In accordance with the principles of the present invention, a beaconing device transmits a radio signal that can be detected by a plurality of wireless receivers positioned at various known locations. The receivers form nodes of a wireless network that further includes a control node with which the receivers can communicate. Each receiver that receives the signal from the beaconing device records the signal strength at which it receives the signal from the beaconing device and sends that information to the control node. The control node processes the signal strength information received from all of the receivers and uses it to estimate the location of the beaconing device. Particularly, the controller solves an optimization problem for the coordinates of the beaconing device by determining the set of coordinates for the beaconing device that minimizes the squared error over all of the receivers that receive the signal from the beaconing device between (1) the Euclidian distance between the known coordinates of the receiving device and the estimated coordinates of the beaconing device and (2) the estimated distance between the beaconing device and the particular receiver based on signal strength at that receiver.

Claims

1. A method of estimating the location of an object based on estimates of distance between said object and a plurality of known locations, said method comprising the steps of:

obtaining estimates of the distance between said object and a plurality of known locations;

assigning a weighting factor to each of said estimates, said weighting factor being a function of a predicted accuracy of said estimate; and

determining said estimated location of said object to be a location that is selected from the group of;

an estimated location that minimizes a weighted squared error, over said plurality of estimates, between (a) said distance estimate and (b) a distance between said corresponding known location and said estimated location of said object; and

an estimated location that minimizes a weighted squared error, over said plurality of estimates, between (a) said distance estimate and (b) a distance between said corresponding known location and said estimated location of said object, and is within a set of predetermined physical boundaries.

2. The method of claim 1 wherein said distance estimates are based on a received signal strength of a signal received from said object.

3. The method of claim 2 wherein said signal is a radio frequency signal transmitted from said object.

4. The method of claim 1 wherein at least a first and a second one of said distance estimates are based on different technique for estimating said distance.

5. The method of claim 1 wherein each of said squared errors is multiplied by said weighting factor assigned to the corresponding estimated distance.

6. The method of claim 5 wherein each said weighting factor is a function of at least a technique by which said estimated distance was rendered.

7. The method of claim 5 wherein each said weighting factor is a function of at least the accuracy of the corresponding known location.

8. The method of claim 7 wherein each said weighting factor is a function of the technique by which the corresponding known location was determined.

9. The method of claim 5 wherein said distance estimates are based on a received signal strength of a signal received from said object and wherein said weighting factor is a function of at least said estimated distance.

10. The method of claim 5 wherein said distance estimates are based on a received signal strength of a signal received from said object and wherein said weighting factor is a function of at least said signal strength.

11. The method of claim 10 wherein each said weighting factor is inversely proportional to said corresponding estimated distance.

12. The method of claim 10 wherein each said weighting factor is inversely proportional to said corresponding signal strength.

13. The method of claim 1 wherein said estimated location is determined by solving:

$\underset{X_B,Y_B}{\min }<br><br>\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>w_i<br><br>J_i^2$

where

J_i=√

{square root over ((X_i−

X_B)²+(Y_i−

Y_B)²)}−

d_i

i=an index identifying a particular one of said known locations;

X_B, Y_B=the estimated Euclidian coordinates of said object;

X_i, Y_i=the estimated Euclidean coordinates of known location i;

d_i=said distance estimate corresponding to known location i;

w=said weighting factor; and

n=the number of said known locations.

14. The method of claim 1 wherein said estimated location is determined by solving:

$\underset{X_B,Y_B,Z_B}{\min }<br><br>\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>w_i<br><br>J_i^2$

where

J_i√

{square root over ((X_i−

X_B)²+(Y_i−

Y_B)²°

(Z_i−

Z_B)²)}−

d_i

i=an index identifying a particular one of said known locations;

X_B, Y_B, Z_B=the estimated Euclidian coordinates of said object;

X_i, Y_i, Z_i=the estimated Euclidean coordinates of known location i;

d=said distance estimate corresponding to known location i; and

n=the number of said known locations.

15. An apparatus for estimating the location of an object based on estimates of distance between said object and a plurality of known locations comprising:

a beaconing device adapted to wirelessly transmit a beacon signal;

a plurality of anchor devices each adapted to be positioned at various locations throughout a space to be monitored, said anchor devices further adapted to detect said beacon signal transmitted by said beaconing device;

a first circuit adapted to determine an estimated distance between each said anchor device and said beaconing device based on said receipt of said signal transmitted by said beaconing device; and

a second circuit adapted to determine an estimated location of said beaconing device to be a location that is selected from the group of;

an estimated location that minimizes the weighted squared error, over said plurality of estimates, between (a) said distance estimate and (b) a distance between a location of said anchor device and said estimated location of said beaconing device; and

an estimated location that minimizes a weighted squared error, over said plurality of estimates, between (a) said distance estimate and (b) a distance between said corresponding known location and said estimated location of said object, and is within a set of predetermined physical boundaries.

16. The apparatus of claim 15 wherein said anchor devices are further adapted to detect said signal transmitted by said beaconing device and determine strength of said signal as received by the anchor device, and wherein said distance estimates are based on said received signal strength.

17. The apparatus of claim 16 further comprising:

a controller adapted to receive said signal strengths transmitted from said plurality of anchor devices, and wherein said first and second circuits form part of said controller.

18. The apparatus of claim 17 wherein said anchor devices are further adapted to wirelessly transmit said signal strengths to said controller.

19. The apparatus of claim 17 wherein said beacon signal is a radio frequency signal transmitted from said object.

20. The apparatus of claim 15 wherein at least a first and a second one of said anchor devices use different techniques for estimating said distance.

21. The apparatus of claim 15 wherein said second circuit multiplies each of said distance estimates by said weighting factor assigned to the corresponding estimated distance.

22. The apparatus of claim 21 wherein each said weighting factor is a function of at least a technique by which said estimated distance was rendered.

23. The apparatus of claim 21 wherein each said weighting factor is a function of at least the accuracy to which the location of the corresponding anchor device is known.

24. The method of claim 23 wherein each said weighting factor is a function of the technique by which the location of the corresponding anchor device was determined.

25. The apparatus of claim 21 wherein said anchor devices are further adapted to detect said signal transmitted by said beaconing device and determine a strength of said signal as received by the anchor device, and wherein said distance estimates are based on said received signal strength and wherein said weighting factor is a function of at least said distance estimate.

26. The apparatus of claim 15 wherein said second circuit determines said estimated location by solving:

$\underset{X_B,Y_B}{\min }<br><br>\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>w_i<br><br>J_i^2$

where

J_i=√

{square root over ((X_i−

X_B)²+(Y_i−

Y_B)²)}−

d_i

i=an index identifying a particular one of said known locations;

X_B, Y_B=the estimated Euclidian coordinates of said object;

X_i, Y_i=the estimated Euclidean coordinates of known location i;

d_i=said distance estimate corresponding to known location i; and

n=the number of said known locations.

27. The apparatus of claim 15 wherein said second circuit determines said estimated location by solving:

$\underset{X_B,Y_B,Z_B}{\min }<br><br>\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>w_i<br><br>J_i^2$

where

J_i=√

{square root over ((X_i−

X_B)²+(Y_i−

Y_B)²+(Z_i−

Z_B)²)}−

d_i

i=an index identifying a particular one of said known locations;

X_B, Y_B, Z_B=the estimated Euclidian coordinates of said object;

X_i, Y_i, Z_i=the estimated Euclidean coordinates of known location i;

d_i=said distance estimate corresponding to known location i; and

n=the number of said known locations.

28. The apparatus of claim 15 wherein said beaconing device transmits said signal at intervals and wherein said apparatus further comprises:

a third circuit adapted to track movement of said beaconing device based on said estimates over a multiplicity of said signals transmitted by said beaconing device.