Radiolocation using path loss data

• US 8,264,402 B2
• Filed: 11/18/2011
• Issued: 09/11/2012
• Est. Priority Date: 07/28/2003
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Kaiser, Daryl A., Datla, Kirshnam Raju V.
• Primary Examiner(s): Sotomayor, John B
• Application Number:
  US13/300,475
• Publication Number:
  US 20120081249A1
• Time in Patent Office: 298 Days
• Field of Search: 702/150, 342/450, 342/174, 455/67.11, 455/456.1, 709/224
• US Class Current: 342/174
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0242 Determining the position of transmitters to be subsequently used in positioning G01S5/0289 takes precedence
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements
• CPC Class Codes: H04B 17/27 for locating or positioning the transmitter
• CPC Class Codes: H04W 12/122 Counter-measures against attacks; Protection against rogue devices
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Determining the location of a station in a wireless network including determining path losses between the wireless station of unknown location and at least some access points at known locations. The determining includes receiving measurements from the wireless station of unknown location, and measuring the received signal strengths as a result of respective transmissions from at least some of access points at known respective transmit powers and known or determined locations to obtained measured path losses. The method further includes determining a location for the wireless station using the measured path losses and a calibrated path loss model.

Claims

1. A method comprising:

receiving in a processing apparatus measurements from a particular wireless station having an unknown location, the measurements indicative of the received signal strengths at the particular wireless station resulting from transmissions at known respective transmit powers from at least some stations of a set of wireless stations; and

determining by the processing apparatus of a location for the particular wireless station using the received measurements and a calibrated path loss model.

2. A method as recited in claim 1, further comprising:

calibrating a radio loss model using data indicative of path losses between pairs of wireless stations of the set of wireless stations to determine the calibrated path loss model.

3. A method as recited in claim 2, wherein the calibrating includes comparing the path loss to the measured path loss for the known locations of the transmitting and receiving wireless stations to provide a sparse set of adjustment factors between a sparse set of known locations.

4. A method as recited in claim 3, wherein the adjustment factor between a known location and an unknown location is determined as a weighted sum of path losses between the known location and a sparse set of other known locations.

5. A method as recited in claim 2, wherein the first set of wireless stations is a set of managed access points of a managed wireless network, the managed access points being at known locations, and wherein the data indicative of path losses between pairs of wireless stations is determined by measuring the path loss between pairs of managed access points of the set of managed access points.

6. A method as recited in claim 5, wherein the determining of the location includes:

determining a set of likelihood components for each of a set of locations, each component corresponding to a respective managed access point whose transmissions are listened for at the particular station, and

determining an overall likelihood for each of the set of locations as the product of the likelihood components.

7. A method as recited in claim 6, wherein the determining of the location includes, for each managed access point whose transmitted signal is detected at the particular station, determining an inclusive likelihood component as a function of location using the measured path loss and calibrated path loss for the transmission from the respective managed access point to the particular wireless station, such that each inclusive likelihood component provides an indication of the likelihood at any location that the transmission from the access point whose transmission is detected could have been received at the location with the measured path loss.

8. A method as recited in claim 7, wherein the determining of location includes, for each managed access point whose transmitted signal is not detected at the particular station, determining an exclusive likelihood component as a function of location, such that each exclusive likelihood component provides an indication of the likelihood at any location that the transmission from the access point whose transmission is not detected could have been received at the location with an assumed signal strength for the transmitted power.

9. A non-transitory computer-readable medium configured with instructions that when executed by one or more processors cause at least one of the processors to implement a method comprising:

receiving measurements from each respective station of a set of wireless stations of a wireless network measuring the received signal strength at each of the respective stations resulting from transmission of a signal from a potential rogue access point, each station of the set being at a known or determined location; and

for each of a set of assumed transmit powers for the potential rogue access point, determining a location for the potential rogue access point using the received signal strengths at the stations of the third set and a calibrated path loss model.

10. A non-transitory computer-readable medium as recited in claim 9, wherein the method comprises:

calibrating a radio path loss model to determine the calibrated path loss model, the calibrating using measurements received from each respective wireless station of a first set of wireless stations of the wireless network measuring the received signal strengths at each of the respective wireless stations of the first set that receive signals as a result of transmissions by respective wireless stations of a second set of wireless stations of the wireless network, each respective transmission at a known respective transmit power, the locations of each station of the first and second set being known or determined.

11. A non-transitory computer readable medium as recited in claim 10, wherein the first set and the second set of stations include the same set of managed access points of a managed wireless network such that the calibration of the path loss model includes the receiving of measurements measuring the path loss between each of the set of managed access points and such that the calibrated path loss model provides a calibrated path loss at each location of the area of interest between each transmitting managed access point and each receiving managed access point.

12. A non-transitory computer-readable medium as recited in claim 11, wherein the set of wireless stations includes managed access points of the set of access points of the wireless network.

13. A non-transitory computer-readable medium as recited in claim 11, wherein the set of wireless stations includes wireless clients of at least one managed access point of the wireless network, the method further including determining the location of each client by a radiolocation method that includes receiving measurements, measuring the received signal strengths at the wireless client resulting from respective transmissions from at least some of the managed access points, said each of the respective transmissions being at a known corresponding transmit power;

and determining a location for the wireless client using the received signal strengths and the calibrated path loss model.

14. A non-transitory computer-readable medium as recited in claim 11, wherein the determining of the location includes:

determining a set of likelihood components for each of a set of locations, each component corresponding to a respective managed access point whose transmissions are listened for at the particular station, and

determining an overall likelihood for each of the set of locations as the product of the likelihood components.

15. A non-transitory computer readable medium as recited in claim 14, wherein the determining of the location includes, for each managed access point whose transmitted signal is detected at the particular station, determining an inclusive likelihood component as a function of location using the measured path loss and calibrated path loss for the transmission from the respective managed access point to the particular wireless station, such that each inclusive likelihood component provides an indication of the likelihood at any location that the transmission from the access point whose transmission is detected could have been received at the location with the measured path loss.

16. A non-transitory computer-readable medium as recited in claim 15, wherein the determining of the location includes, for each managed access point whose transmitted signal is not detected at the particular station, determining an exclusive likelihood component as a function of location, such that each exclusive likelihood component provides an indication of the likelihood at any location that the transmission from the access point whose transmission is not detected could have been received at the location with an assumed signal strength for the assumed transmitted power.

17. A non-transitory computer-readable medium as recited in claim 14, wherein the method further comprises displaying the overall likelihood to the user on a user interface showing the area of interest.

18. A non-transitory computer-readable medium as recited in claim 10, wherein the calibrating includes comparing the path loss to the measured path loss for the known locations of the transmitting and receiving stations to provide a sparse set of adjustment factors between a sparse set of known locations.

19. A non-transitory computer readable medium as recited in claim 18, wherein the adjustment factor between a known location and an unknown location is determined as a weighted sum of path losses between the known location and a sparse set of other known locations.

20. A non-transitory computer readable medium configured with one or more code segments to instruct one or more processors of a processing system to execute a method comprising:

causing respective transmissions at known respective transmit powers from at least some stations of a first set of wireless stations;

receiving measurements from a particular wireless station having an unknown location, the measurements indicative of the received signal strengths at the particular wireless station resulting from the caused respective transmissions; and

determining a location for the particular wireless station using the received measurements and a calibrated path loss model.

21. A non-transitory computer-readable medium as recited in claim 20, further comprising:

calibrating a path loss model using the data indicative of path losses between pairs of wireless stations of the first set of wireless stations to determine the calibrated path loss model between the receiving and transmitting wireless stations, the data provided by measuring the path loss between pairs of the first set of wireless stations, the wireless stations being at known or determined locations.

22. An apparatus comprising:

a processing system including a memory and a network interface to couple the apparatus to a network including a set of wireless stations of a wireless network at known or determined locations, the processing system configured to;

receive measurements from a particular wireless station having an unknown location, the measurements indicative of the received signal strengths at the particular wireless station resulting from transmissions at known respective transmit powers from at least some of the stations of the set of wireless stations; and

determining by the processing apparatus of a location for the particular wireless station using the received measurements and a calibrated path loss model.

23. An apparatus as recited in claim 22, wherein the processing system is further configured to:

calibrate a radio loss model using data indicative of path losses between pairs of wireless stations of a first set of wireless stations to determine the calibrated path loss model.

24. A method comprising:

determining a measured path loss between a particular wireless station having an unknown location and at least some of wireless stations of a wireless network by receiving measurements from the particular wireless station, wherein in the case the wireless station having the unknown location is known not to be a rogue access point, the determining uses measurements received from the particular wireless station having the unknown location measuring the received signal strength as a result of respective transmissions from at least some of the wireless stations, each of the respective transmissions being at a known respective transmit power, and wherein, in the case the wireless station having the unknown location is a potential rogue access point, the determining uses measurements received from each of at least some of the wireless stations measuring the received signal strength at each of the wireless stations resulting from transmission of a signal from the potential rogue access point for each of a set of assumed transmit powers for the potential rogue access point; and

determining a location for the particular wireless station having the unknown location using the measured path loss and a calibrated path loss model.

25. A method as recited in claim 24, further comprising:

calibrating a path loss model in an area of interest to determine the calibrated path loss model using path loss determined from measurements between wireless stations of the wireless network at known locations, the measurements received from some of the wireless stations measuring their received signal strengths resulting from respective transmissions from respective wireless stations, each respective transmission at a known respective transmit power.