System and method for asset location in wireless networks

• US 7,778,649 B2
• Filed: 04/04/2008
• Issued: 08/17/2010
• Est. Priority Date: 02/25/2005
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Katz, Joseph, Sharony, Jacob
• Primary Examiner(s): Eng; George
• Assistant Examiner(s): Miller; Brandon J
• Application Number:
  US12/062,725
• Publication Number:
  US 20080182593A1
• Time in Patent Office: 865 Days
• Field of Search: 455/456.1, 455/456.2, 455/456.3, 455/456.5, 455/456.6, 370/338, 370/328, 340/539.13, 340/825.49
• US Class Current: 455/456.1
• CPC Class Codes: G01S 5/02521 using a radio-map
• 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: H04W 4/029 Location-based management or tracking services
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Described is a system and method for tracking an asset. The system may include a plurality of wireless access points and a computing arrangement communicating with the access points. The arrangement determines a location area of the device as a function of first data and a location of each of at least three access points of the plurality of the access points. The first data includes at least one of first signal strength data and second signal strength data. The first signal strength data is indicative of a strength of a first signal transmitted by the device and received by the at least three access points. The second signal strength data is indicative of a strength of a second signal transmitted by the at least three access points and received by the device. The location area is an area within a predetermined reception range of the at least three local access points. The arrangement determines the location of the device within the location area as a function of second data and a further location of each of the at least three further access points of the plurality of access points. The second data is indicative of a travel time of a third signal from the device to each of the at least three further access points.

Claims

1. A method for locating a wireless communication device, comprising:

determining a first location of the wireless communication device, the determining including;

initiating each of three access points to transmit a respective signal to the wireless communication device,

receiving at each of the three access points an acknowledgment signal from the wireless communication device, the acknowledgment signal including a first signal strength of the respective signals from the three access points,

determining at each of the three access points a second signal strength of the acknowledgment signal, and

determining the first location as a function of at least one of the first signal strength and the second signal strength; and

determining a second location of the wireless communication device, the determining of the second location including;

directing from each of the three access points a respective beam to the first location,

receiving at each of the three access points a return signal from the wireless communication device a signal,

determining the second location of the wireless communication device as a function of the return signal.

2. The method as recited in claim 1, wherein the first location corresponds to a coarse location.

3. The method as recited in claim 1, wherein the second location corresponds to a fine location.

4. The method as recited in claim 1, wherein the determining of the second location includes determining a time of arrival of the return signal at each of the three access points.

5. The method as recited in claim 1, wherein the determining of the first location is performed by a server in communication with the three access points.

6. The method as recited in claim 1, wherein the determining of the second location is performed by a server in communication with the three access points.

7. The method as recited in claim 1, further comprising:

storing at the three access points a signal strength of a prior transmission from the wireless communication device, wherein the determining of the first location is based on the signal strength of the prior transmission.

8. The method as recited in claim 1, further comprising:

storing at the three access points a signal strength information received in a prior transmission from the wireless communication device, wherein the determining of the first location is based on the signal strength of the prior transmission.

9. The method as recited in claim 1, wherein the wireless communication device includes one of a PDA, a laptop computer, a network card, and a handheld computer.

10. The method as recited in claim 1, wherein the directing of the respective beam includes providing to the three access points instructions from a server for steering the beam from each of the three access points.

11. The method as recited in claim 1, wherein the directing of the respective beam includes providing to the three access points the first location, wherein the three access points determines the manner by which to direct their respective beams based on the first location.

12. A system for locating a wireless communication device, comprising:

means for determining a first location of the wireless communication device, the means for determining including;

means for initiating each of three access points to transmit a respective signal to the wireless communication device,

means for receiving at each of the three access points an acknowledgment signal from the wireless communication device, the acknowledgment signal including a first signal strength of the respective signals from the three access points,

means for determining at each of the three access points a second signal strength of the acknowledgment signal, and

means for determining the first location as a function of at least one of the first signal strength and the second signal strength; and

means for determining a second location of the wireless communication device, the means for determining the second location including;

means for directing from each of the three access points a respective beam to the first location,

means for receiving at each of the three access points a return signal from the wireless communication device a signal,

means for determining the second location of the wireless communication device as a function of the return signal.

13. The system as recited in claim 12, wherein the first location corresponds to a coarse location.

14. The system as recited in claim 12, wherein the second location corresponds to a fine location.

15. The system as recited in claim 12, wherein the means for determining the second location includes means for determining a time of arrival of the return signal at each of the three access points.

16. The system as recited in claim 12, wherein the means for determining the first location includes a server in communication with the three access points.

17. The system as recited in claim 12, wherein the means for determining the second location includes a server in communication with the three access points.

18. The system as recited in claim 12, further comprising:

means for storing at the three access points a signal strength of a prior transmission from the wireless communication device, wherein the determining of the first location is based on the signal strength of the prior transmission.

19. The system as recited in claim 12, further comprising:

means for storing at the three access points a signal strength information received in a prior transmission from the wireless communication device, wherein the determining of the first location is based on the signal strength of the prior transmission.

20. A system for determining a first location and a second location of a wireless communication device, comprising:

at least three access points;

a processing device in communication with the at least three access points, wherein the processing device initiates in the at least three access points a first location operation and a second location operation, wherein;

in the first location operation;

each of the three access points transmit a respective signal to a wireless communication device,

each of the three access points receive an acknowledgment signal from the wireless communication device, the acknowledgment signal including a first signal strength of the respective signals from the three access points,

each of the three access points determines a second signal strength of the acknowledgment signal, and

the first location is determined as a function of at least one of the first signal strength and the second signal strength; and

in the second location operation;

each of the three access points directs a respective beam to the first location,

each of the three access points receives a return signal from the wireless communication device a signal,

the second location of the wireless communication device is determined as a function of the return signal.