Asset location system with enhanced accuracy

• US 20070018829A1
• Filed: 07/25/2005
• Published: 01/25/2007
• Est. Priority Date: 07/25/2005
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Singh, Ajeet, Pynadath, Renish, Subramanian, Krishnan, Rao, Abhijit
• Granted Patent: US 7,333,018 B2
• Time in Patent Office: Days
• US Class Current: 340/572.400
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G01S 5/0295 Proximity-based methods, e.g. position inferred from reception of particular signals
• CPC Class Codes: G06K 7/10079 the collision being resolved in the spatial domain, e.g. temporary shields for blindfolding the interrogator in specific directions

Abstract

An asset is located in an area by reading the asset, by making a first determination based on which of the readers are able to read the asset, by making a second determination based on which of the readers are not able to read the asset, and by locating the asset in the area based on both the first and second determinations.

Claims

1. A method of locating an asset in an area comprising:

reading the asset;

making a first determination based on which of a plurality of readers are able to read the asset;

making a second determination based on which of the readers are not able to read the asset; and

, locating the asset in the area based on both the first and second determinations.

2. The method of claim 1 wherein the area is divided into cells, wherein each of the readers is located to have a different cell coverage, wherein the making of a first determination comprises making the first determination based on the cells that are covered by the readers that are able to read the asset, wherein the making of a second determination comprises making the second determination based on the cells that are covered by the readers that are not able to read the asset, and wherein the locating of the asset comprises locating the asset in the area based on the cells that are covered by the readers that are able to read the asset and the cells that are covered by the readers that are not able to read the asset.

3. The method of claim 2 wherein the locating of the asset comprises:

forming an intersection of the cells that are covered by the readers that are able to read the asset;

forming a union of the cells that are covered by the readers that are not able to read the asset; and

, determining the location of the asset in the area from the intersection and the union.

4. The method of claim 3 wherein the determining of the location of the asset comprises determining the asset to be in the cells that are in the intersection and that are not in the union.

5. The method of claim 1 wherein the reading of the asset comprises receiving an RF signal from an RFID tag attached to the asset, wherein the making of a first determination comprises making the first determination based on which of the readers receive the RF signal, and wherein the making of a second determination comprises making a second determination based on which of the readers do not receive the RF signal.

6. The method of claim 5 wherein the area is divided into cells, wherein each of the readers includes an RF receiver and is located to have a different cell coverage, wherein the making of a first determination comprises making the first determination based on the cells that are covered by the receivers that receive the RF signal, wherein the making of a second determination comprises making the second determination based on the cells that are covered by the receivers that do not receive the RF signal, and wherein the locating of the asset comprises locating the asset in the area based on the cells that are covered by the receivers that receive the RF signal and the cells that are covered by the receivers that do not receive the RF signal.

7. The method of claim 6 wherein the locating of the asset comprises:

forming an intersection of the cells that are covered by the receivers that receive the RF signal;

forming a union of the cells that are covered by the receivers that do not receive the RF signal; and

,

determining the location of the asset in the area from the intersection and the union.

8. The method of claim 7 wherein the determining of the location of the asset comprises determining the asset to be in the cells that are in the intersection and that are not in the union.

9. The method of claim 1 wherein the first determination contains all of the cells covered by all of the readers in the event that none of the readers successfully read the asset.

10. A method of locating an asset by use of a plurality of readers comprising:

storing geographical information of a plurality of virtual cells defined by boundaries, wherein the virtual cells define an area known to contain the asset, and wherein the geographical information includes information about the cells covered by each of the readers;

identifying a first group of cells corresponding to those of the readers that read the asset;

identifying a second group of cells corresponding to those of the readers that do not read the asset; and

,

locating the asset based on both the first and second groups of cells.

11. The method of claim 10 wherein the locating of the asset comprises:

forming an intersection of the cells in the first group of cells;

forming a union of the cells in the second group of cells; and

,

determining the location of the asset in the area from the intersection and the union.

12. The method of claim 11 wherein the determining of the location of the asset comprises determining the asset to be in the cells that are in the intersection and that are not in the union.

13. The method of claim 10 wherein an RFID tag is attached to the asset, wherein the identifying of a first group of cells comprises identifying the first group of cells based on those readers that receive an RF signal from the RFID tag, and wherein the identifying of a second group of cells comprises identifying the second group of cells based on those readers that do not receive an RF signal from the RFID tag.

14. The method of claim 13 wherein the locating of the asset comprises:

forming an intersection of the cells in the first group of cells;

forming a union of the cells in the second group of cells; and

,

determining the location of the asset in the area from the intersection and the union.

15. The method of claim 14 wherein the determining of the location of the asset comprises determining the asset to be in the cells that are in the intersection and that are not in the union.

16. The method of claim 10 wherein the first group of cells contains all of the virtual cells in the event that none of the readers successfully read the asset.

17. A method of placing readers in an area defined by a plurality of virtual cells comprising:

computing an accuracy associated with each of a plurality of possible reader configurations, wherein each possible reader configuration corresponds to a possible configuration with which the readers can be placed in the area, and wherein each accuracy is dependent upon a number of possible cells in which an asset could be located as a function of a first number of cells covered by ones of the readers that are able to read the asset and a second number of cells covered by remaining ones of the readers that cannot read the asset; and

,

choosing the reader configuration that produces the highest accuracy.

18. The method of claim 17 further comprising determining a number of readers to be distributed among the cells according to a constraint.

19. The method of claim 18 wherein the constraint comprises a cost constraint.

20. The method of claim 17 further comprising determining the plurality of possible reader configurations according to P and K, wherein P comprises a number of possible locations of the readers in the area, and wherein K comprises the number of readers to be distributed throughout the area.

21. The method of claim 20 wherein the determining of the plurality of possible reader configurations according to P and K comprises determining a number L of possible configurations according to the following equation:

L=P!/(P−

K)!

for readers which have different ranges.

22. The method of claim 20 wherein the determining of the plurality of possible reader configurations according to P and K comprises determining a number L of possible configurations according to the following equation:

L=P!/(K!*(P−

K)!)

for readers having substantially equal ranges.

23. The method of claim 17 wherein the computing of an accuracy associated with each of a plurality of possible reader configurations comprises:

(a) determining a number n_i in accordance with a location i of the asset in each of the virtual cells, wherein the number n_i is dependent upon a corresponding number of possible cells within which the asset could be located as a function of a first number of cells covered by ones of the readers that are able to read the asset and a second number of cells covered by remaining ones of the readers that cannot read the asset for the asset in cell i;

(b) computing the accuracy associated with a possible configuration by summing all n_i for that configuration;

(c) repeating (a) and (b) for each of the possible reader configurations; and

,

choosing the reader configuration that produces the highest accuracy.

24. The method of claim 23 wherein (b) the computing of the accuracy associated with a possible configuration by summing all n_i for that configuration comprises:

dividing the sum of all n_i by the total number of virtual cells; and

,

inverting the division result.

25. The method of claim 17 wherein the choosing of the configuration that produces the highest accuracy comprises choosing of the configuration that produces the highest average accuracy.