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

• US 20050195109A1
• Filed: 03/05/2004
• Published: 09/08/2005
• 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.
• Granted Patent: US 7,205,938 B2
• Time in Patent Office: Days
• US Class Current: 342/463
• 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 known locations, the strength of RF signals transmitted by the plurality of radio transceivers;

dynamically updating at least one parameter value used in a wireless node location algorithm based on the detected strength of the RF signals transmitted by at least some of the radio transceivers.

2. The method of claim 1 wherein the wireless node location algorithm estimates the respective distances between at least three identified radio transceivers 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 identified radio transceivers and the wireless node.

3. The method of claim 1 wherein the at least one parameter value characterizes the attenuation of a radio signal as a function of distance.

4. The method of claim 3 wherein the at least one parameter value is a path loss exponent.

5. The method of claim 2 wherein the at least one parameter value is a path loss exponent, and wherein the wireless node location algorithm estimates the respective distances between at least three identified radio transceivers 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 the path loss exponent.

6. The method of claim 1 further comprising

applying an adjustment factor to the at least one parameter, wherein the adjustment factor is based on an evaluation of the difference in signal attenuation observed at two, vertically spaced planes in a physical space.

7. The method of claim 4 further comprising

applying an adjustment factor to the path loss exponent, wherein the adjustment factor is based on an evaluation of the difference in signal attenuation observed at two, vertically spaced planes in a physical space.

8. In a wireless network system comprising a plurality of radio transceivers placed in known locations, a method facilitating the location of a wireless node, comprising

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

dynamically updating at least one parameter value used in a wireless node location algorithm based on the detected strength of the RF signals.

9. The method of claim 8 wherein the wireless node location algorithm estimates the respective distances between at least three identified radio transceivers 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 identified radio transceivers and the wireless node.

10. The method of claim 8 wherein the at least one parameter value characterizes the attenuation of a radio signal as a function of distance.

11. The method of claim 10 wherein the at least one parameter value is a path loss exponent.

12. The method of claim 9 wherein the at least one parameter value is a path loss exponent, and wherein the wireless node location algorithm estimates the respective distances between at least three identified radio transceivers 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 the path loss exponent.

13. The method of claim 8 wherein the updating step is performed in response to a request to locate a wireless node.

14. 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 known locations, the strength of RF signals transmitted by the plurality of radio transceivers;

identifying the radio transceivers in the plurality of radio transceivers that detect a desired wireless node;

updating a parameter used in a wireless node location algorithm based on the detected strength of the RF signals associated with the identified radio transceivers.

15. The method of claim 14 wherein the wireless node location algorithm estimates the respective distances between at least three identified radio transceivers 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 identified radio transceivers and the wireless node.

16. The method of claim 14 wherein the parameter characterizes the attenuation of a radio signal as a function of distance.

17. The method of claim 16 wherein the parameter is a path loss exponent.

18. The method of claim 15 wherein the parameter is a path loss exponent, and wherein the wireless node location algorithm estimates the respective distances between at least three identified radio transceivers 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 the path loss exponent.

19. The method of claim 14 wherein the wireless node location algorithm estimates the respective distances between at least three identified radio transceivers 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 identified radio transceivers and the wireless node.

20. 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 known locations, the strength of RF signals transmitted by the plurality of radio transceivers;

identifying the radio transceivers in the plurality of radio transceivers that detect a desired wireless node;

computing path loss exponents for at least three of the identified radio transceivers based on the strength of the signals, detected at at least some of the known locations, associated with the identified radio transceivers;

estimating the distances between the desired wireless node and the at least three identified radio transceivers based on the corresponding path loss exponents and the strength of the signals transmitted by the wireless node and detected by the at least three identified radio transceivers; and

locating the desired wireless node using the estimated distances.

21. The method of claim 20 wherein the locating step comprises triangulating the location of the wireless node based on the estimated distances between the at least three identified radio transceivers and the wireless node.

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

a wireless node location model operative to compute the location of a wireless node based on attributes of the signal transmitted by the wireless node and detected by a plurality of radio transceivers disposed in known locations;

wherein the wireless node location model includes at least one parameter involved in computing the location of the wireless node;

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

means to dynamically adjust the at least one parameter in the wireless node location model based on observed attributes of the signals transmitted between the plurality of radio transceivers.

23. The apparatus of claim 22 wherein the attributes of the signals are signal strength.

24. A system according to claim 22 further comprising a plurality of radio transceivers operatively connected to the apparatus.

25. The apparatus of claim 22 wherein the wireless node location model estimates the respective distances between at least three identified radio transceivers 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 identified radio transceivers and the wireless node.

26. The apparatus of claim 22 wherein the parameter characterizes the attenuation of a radio signal as a function of distance.

27. The apparatus of claim 22 wherein the parameter is a path loss exponent.

28. The apparatus of claim 25 wherein the parameter is a path loss exponent, and wherein the wireless node location model estimates the respective distances between at least three identified radio transceivers 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 the path loss exponent.

29. The apparatus of claim 22 wherein the wireless node location model estimates the respective distances between at least three identified radio transceivers 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 identified radio transceivers and the wireless node.

30. 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

dynamically adjust one or more parameters in a wireless node location model based on the signal strength data characterizing the propagation of signals between the access elements;

apply the wireless node location model to estimate the location of a wireless node.

31. The system of claim 30 wherein the wireless node location module resides in a network management system.

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

33. The system of claim 30 wherein the wireless node location module maintains a signal strength matrix including values representing the strength of signals detected between the access elements.

34. The system of claim 30 wherein the wireless node location model estimates the respective distances between at least three identified 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.

35. The system of claim 30 wherein the parameter characterizes the attenuation of a radio signal as a function of distance.

36. The system of claim 30 wherein the parameter is a path loss exponent.

37. The system of claim 34 wherein the parameter is a path loss exponent, and wherein the wireless node location model estimates the respective distances between at least three identified 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 access elements and the path loss exponent.

38. The system of claim 30 wherein the wireless node location model estimates the respective distances between at least three identified 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 access elements, and triangulates the location of the wireless node based on the estimated distances between the at least three identified access elements and the wireless node.

39. 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

dynamically adjust one or more parameters in a wireless node location model based on the signal strength data characterizing the propagation of signals between the access elements;

apply the wireless node location model to estimate the location of a wireless node.

40. The system of claim 39 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.

41. The system of claim 39 wherein the wireless node location module resides in a network management system.

42. The system. of claim 39 wherein the wireless node location module resides in the central control element.

43. The system of claim 39 wherein the wireless node location module maintains a signal strength matrix including values representing the strength of signals detected between the access elements.