Wireless node location mechanism responsive to observed propagation characteristics of wireless network infrastructure signals

• US 7,205,938 B2
• Filed: 03/05/2004
• Issued: 04/17/2007
• Est. Priority Date: 03/05/2004
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Airespace, Inc. (Cisco Systems, Inc.)
• Inventors: Davi, Gregg Scott, Dietrich, Paul F., Hills, Alexander H.
• Primary Examiner(s): Issing; Gregory C.
• Application Number:
  US10/794,842
• Publication Number:
  US 20050195109A1
• Time in Patent Office: 1,138 Days
• Field of Search: None
• US Class Current: 342/451
• CPC Class Codes: G01S 11/06 using intensity measurements
• CPC Class Codes: G01S 5/0226 Transmitters
• CPC Class Codes: G01S 5/02527 Detecting or resolving anomalies in the radio frequency fingerprints of the radio-map
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

A wireless node location mechanism that dynamically adapts to changes to a surrounding physical environment that affect the propagation of radio signals. The wireless node location mechanism assesses radio signals from transmitters associated with a wireless node location infrastructure to adjust one or more parameters used to estimate location of a wireless node. In one implementation, path loss exponents are re-computed based on the signals transmitted between infrastructure radio transceivers. These path loss exponents are used, in one implementation, to compute the distance between a wireless node and a given infrastructure radio transceiver and, ultimately, to determine the location of the wireless node based on triangulation. In one implementation, path loss exponents are computed on demand based on the signals observed between infrastructure radios that detect the wireless node whose location is to be estimated.

Claims

1. A method facilitating the location of a wireless node in an RF environment, the RF environment including a plurality of radio transceivers placed in known locations, comprising:

detecting, at the known locations of the plurality of radio transceivers, the strength of RF signals transmitted by the plurality of radio transceivers;

receiving a request to locate a wireless node;

selecting radio transceivers that detect RF signals transmitted by the wireless node;

then, for pairs of the selected radio transceivers;

determining a distance between a first and second radio transceiver, wherein the first and second radio transceivers detected RF signals from each other in the detecting step;

determining an observed path loss between the first and second radio transceivers; and

computing a path loss exponent based on the determined distance and the observed path loss; and

then, for each selected radio transceiver, computing an average path loss exponent based on all path loss exponents associated with a respective radio transceiver; and

estimating the location of the wireless node based on respective estimated distances between the selected radio transceivers and the wireless node, wherein the respective estimated distances are determined according to a path loss model using the average path loss exponents corresponding to a given radio transceiver and the strength of the RF signal transmitted by the wireless node and detected by the given radio transceiver.

2. The method of claim 1 wherein the dynamically updated path loss exponents are calculated based on an average of path loss exponents values calculated over a period of time.

3. The method of claim 1 wherein the dynamically updated path loss exponents are calculated based on an moving average of path loss exponents values calculated over a period of time.

4. The method of claim 1 wherein the dynamically updated path loss exponents are calculated based on a weighted average of path loss exponents values calculated over a period of time.

5. The method of claim 1 wherein the default path loss exponent is a path loss exponent previously computed for the first identified radio transceiver.

6. The method of claim 1 wherein additional radio transceivers, beyond the at least three identified radio transceivers, are used for error correction.

7. The method of claim 1 wherein the detected strength of RF signals sent between the first and second radio transceivers are averaged.

8. The method of claim 1 wherein an RF signal of a largest-detected signal strength is selected of the RF signals sent between the first and second radio transceivers.

9. The method of claim 1 wherein a last-detected strength of RF signals transmitted is selected of the RF signals sent between the first and second radio transceivers is selected.

10. The method of claim 1 wherein a default path loss is utilized if the first or second transceiver can not detect the other transceiver.

11. An apparatus facilitating the location of a wireless node in an RF environment, comprising:

means to monitor the strength of signals transmitted between the plurality of radio transceivers;

means for receiving a request to locate a wireless node;

means to select radio transceivers that detect RF signals transmitted by the wireless node;

then, for pairs of the selected radio transceivers;

means to determine a distance between a first and second radio transceiver, wherein the first and second radio transceivers detected signals from each other in the monitor step;

means to determine an observed path loss between the first and second radio transceivers; and

means to compute a path loss equivalent based on the determined distance and the observed path loss; and

then, for each selected radio transceiver, means to compute an average path loss exponent based on all path loss exponents associated with a respective radio transceiver; and

means to estimate the location of the wireless node based on respective estimated distances between the selected radio transceivers and the wireless node, wherein the respective estimated distances are determined according to a path loss model using the average path loss exponents corresponding to a given radio transceiver and the strength of the RE signal transmitted by the wireless node and detected by the given radio transceiver.

12. The apparatus of claim 11 wherein the default path loss exponent is a path loss exponent previously computed for the first identified radio transceiver.

13. The apparatus of claim 11 wherein additional radio transceivers, beyond the at least three identified radio transceivers, are used for error correction.

14. The apparatus of claim 11 wherein the strength of RF signals sent between the first and second radio transceivers are averaged.

15. The apparatus of claim 11 wherein a stronger RF signal is selected of the RF signals sent between the first and second radio transceivers is selected.

16. The apparatus of claim 11 wherein a last-received RF signal is selected of the RF signals sent between the first and second radio transceivers is selected.

17. The apparatus of claim 11 wherein a default path loss is utilized if the first or second transceiver can not detect the other transceiver.

18. A wireless network system facilitating the location of a wireless node, comprising

a plurality of access elements for wireless communication with at least one remote client element and for communication with a central control element;

wherein the access elements are each operative to

establish and maintain, in connection with a central control element, wireless connections with remote client elements;

detect the strength of received signals;

append a signal strength value to frames received from wireless nodes; and

transmit received frames to a central control element;

at least one central control element for supervising the access elements, wherein the central control element is operative to

manage wireless connections between the access elements and corresponding remote client elements, and

store signal strength data appended to frames transmitted by the plurality of access elements in association with wireless node identifiers; and

a wireless node location module operative to

receive a request to locate the wireless node;

select access elements that detect RF signals transmitted by the wireless node;

then, for pairs of the selected access elements;

determine a distance between a first and second access element, wherein the first and second access elements detected RF signals from each other;

determine an observed path loss between the first and second radio transceivers; and

compute a path loss exponent based on the determined distance and the observed path loss; and

then, for each selected radio transceiver, compute an average path loss exponent based on all path loss exponents associated with a respective radio transceiver; and

estimate the location of the wireless node based on respective estimated distances between the selected access elements and the wireless node, wherein the respective estimated distances are determined according to a path loss model using the average path loss exponents corresponding to a given access element and the strength of the RF signal transmitted by the wireless node and detected by the given access element.

19. The system of claim 18 wherein the wireless node location module resides in a network management system.

20. The system of claim 18 wherein the wireless node location module resides in the central control element.

21. The system of claim 18 wherein the wireless node location module maintains a signal strength matrix including values representing the strength of signals detected between the access elements.

22. The system of claim 18 wherein the wireless node location model estimates the distances between at least three identified access elements of the selected access elements and the wireless node based on the strength of the signals transmitted by the wireless node detected by the at least three identified radio transceivers, and triangulates the location of the wireless node based on the estimated distances between the at least three access elements and the wireless node.

23. The system of claim 18 wherein the strength of RF signals sent between the first and second radio transceivers are averaged.

24. The system of claim 18 wherein a stronger RF signal is selected of the RF signals sent between the first and second radio transceivers is selected.

25. The system of claim 18 wherein a last-received RF signal is selected of the RF signals sent between the first and second radio transceivers is selected.

26. The system of claim 18 wherein a default path loss is utilized if the first or second transceiver can not detect the other transceiver.

27. A wireless network system facilitating the location of a wireless node, comprising

a plurality of access elements for wireless communication with at least one remote client element and for communication with a central control element;

wherein the access elements are each operative to

detect the strength of received signals;

append a signal strength value to frames received from wireless nodes; and

transmit received frames to a central control element;

at least one central control element for supervising the access elements, wherein the central control element is operative to

store signal strength data appended to frames transmitted by the plurality of access elements in association with wireless node identifiers; and

a wireless node location module operative to

receive a request to locate a wireless node;

select access elements that detect RF signals transmitted by the wireless node;

then, for pairs of the selected access elements;

determine a distance between first and second access elements, wherein the first and second access elements detected RF signals from each other in the detect step;

determine an observed path loss between the first and second access elements; and

compute a path loss equivalent based on the determined distance and the observed pathloss; and

then, for each selected access elements, compute an average path loss exponent based on all path loss exponents associated with a access elements respective radio transceiver; and

estimate the location of the wireless node based on respective estimated distances between the selected access elements and the wireless node, wherein the respective estimated distances are determined according to a path loss model using the average path loss exponents corresponding to a given access element and the strength of the RF signal transmitted by the wireless node and detected by the given access element.

28. The system of claim 27 wherein the access elements are further operative to establish and maintain, in connection with a central control element, wireless connections with remote client elements;

and wherein the central control element is further operative to manage wireless connections between the access elements and corresponding remote client elements.

29. The system of claim 27 wherein the wireless node location module resides in a network management system.

30. The system of claim 27 wherein the wireless node location module resides in the central control element.

31. The system of claim 27 wherein the wireless node location module maintains a signal strength matrix including values representing the strength of signals detected between the access elements.

32. The system of claim 27 wherein the strength of RE signals sent between the first and second access elements are averaged.

33. The system of claim 27 wherein a stronger RE signal is selected of the RE signals sent between the first and second access elements is selected.

34. The system of claim 27 wherein a last-received RE signal is selected of the RE signals sent between the first and second access elements is selected.

35. The system of claim 27 wherein a default path loss is utilized if the first or second access element can not detect the other access element.