Method for RF fingerprinting

• US 7,346,359 B2
• Filed: 07/29/2004
• Issued: 03/18/2008
• Est. Priority Date: 07/31/2003
• Status: Expired due to Fees

• Current Assignee: InnerWireless Incorporated (Black Box Ltd.)
• Original Assignee: Pando Networks Incorporated (Microsoft Corporation)
• Inventors: Damarla, Chanakya, Ivers, James, Pollard, Mark, Kompanek, Andrew J., Trammell, Brian H.
• Primary Examiner(s): D AGOSTA, STEPHEN M
• Application Number:
  US10/902,510
• Publication Number:
  US 20050040968A1
• Time in Patent Office: 1,328 Days
• Field of Search: 4554561-457, 455/456.3, 4554141- 4, 455/404.2, 455/432.1, 455/435.1, 455440-441, 701/207, 701213-214, 340/988, 342/357.1, 342/357.06, 342/357.12, 342/450, 342/457
• US Class Current: 455/456.1
• CPC Class Codes: G01S 5/02526 using non-dedicated equipment, e.g. user equipment or crowd-sourcing
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

The invention provides a novel method for preparing a wireless environment for location determination of a wireless mobile unit, and for location determination of a wireless mobile unit. In preparing the physical environment, the invention utilizes novel techniques, including novel techniques to place transmitters, the removal of outlying data in the creation of reference RF fingerprints, and algorithms to obtain accurate reference RF fingerprints. In determining the location of a wireless mobile unit, the invention utilizes novel techniques, including novel techniques to select transmitters, the removal of outlying data in the creation of reference RF fingerprints, and algorithms to obtain accurate reference RF fingerprints.

Claims

1. A method of collecting reference radio frequency (RF) measurements to form RF fingerprints for a reference database to facilitate subsequent location determination of a mobile unit, the method comprising steps of:

providing at least two transmitters that are detectable by said mobile unit at a first location in an area serviced by the at least two transmitters;

collecting a plurality of measurements, each obtained at a respective successive time slice, the plurality of measurements indicative of RF signals transmitted between said mobile unit and a first transmitter of the at least two transmitters at the first location in said area; and

determining a characteristic value based on at least some of the plurality of measurements, the characteristic value forming a first portion of a reference RF fingerprint associated with the first location, wherein determining the characteristic value comprises;

determining if a transmitter of the at least two transmitters for which a plurality of measurements are being collected is out of range or temporarily unobservable for said mobile unit at a particular location in said area;

applying a mathematical function to said plurality of measurements that are not temporarily unobservable or out of range and obtaining the characteristic value from said application of said mathematical function; and

using the characteristic value to form a portion of a reference RF fingerprint to be applied to the database of reference RF fingerprints.

2. The method of claim 1 wherein collecting the plurality of measurements comprises collecting a plurality of measurements at each of a plurality of orientations, and wherein determining the characteristic value comprises determining a characteristic value for each of the plurality of orientations based on at least some of the respective plurality of measurements, the characteristic values forming portions of respective reference RF fingerprints associated with the first location.

3. The method of claim 1 wherein determining the characteristic value comprises averaging the at least some of the plurality of measurements.

4. The method of claim 2 wherein the plurality of orientations includes a plurality of directions between the mobile unit and the first transmitter such that a plurality of measurements is collected at each of the plurality of directions at the first location.

5. The method of claim 1 wherein determining the characteristic value includes ignoring any of the plurality of measurements that are substantially zero and determining the characteristic value based on at least some of the remaining measurements.

6. The method of claim 1 wherein determining the characteristic value comprises identifying which, if any, of the plurality of measurements is an outlier with respect to other of the plurality of measurements based on at least one statistical measurement, and determining the characteristic value based on at least some of the plurality of measurements not identified as outliers.

7. The method of claim 6 wherein a measurement of the plurality of measurements is identified as an outlier if the measurement has a value greater than N standard deviations of an average of said plurality of measurements.

8. The method of claim 6 wherein a measurement of the plurality of measurements is identified as an outlier if the measurement has a value over N units from an average of said plurality of measurements.

9. The method of claim 1 wherein said step of determining if the transmitter is out of range or temporarily unobservable for the mobile unit at the particular location is accomplished by determining that the transmitter is out of range if the transmitter has not been observed in a predetermined number of preceding time slices, and determining that the transmitter is temporarily unobservable if the transmitter has been observed in at least one of the predetermined number of preceding time slices, but is not observable in a current time slice.

10. The method of claim 1 wherein said step of determining if the transmitter is out of range or temporarily unobservable for a mobile unit at a location is accomplished by determining that the transmitter is out of range if the transmitter has not been observed in a predetermined percentage of time slices.

11. The method of claim 1 further comprising:

collecting a plurality of measurements for each of the at least two transmitters, the plurality of measurements indicative of RF signals between the mobile unit and a respective one of the at least two transmitters at the first location;

determining a characteristic value for each of the plurality of measurements collected from respective ones of the at least two transmitters, the characteristic values forming, at least in part, the reference RF fingerprint associated with the first location.

12. The method of claim 1, wherein providing at least two transmitters includes providing at least two transmitters that are located along different axes with respect to a plurality of locations in said area.

13. A method of collecting reference radio frequency (RF) measurements to form RF fingerprints for a reference database to facilitate subsequent location determination of a mobile unit, the method comprising steps of:

providing at least two transmitters that are detectable by said mobile unit at a first location in an area serviced by the at least two transmitters;

collecting a plurality of measurements, each obtained at a respective successive time slice, the plurality of measurements indicative of RF signals transmitted between said mobile unit and a first transmitter of the at least two transmitters at the first location in said area; and

determining a characteristic value based on at least some of the plurality of measurements, the characteristic value forming a first portion of a reference RF fingerprint associated with the first location,

wherein collecting the plurality of measurements comprises collecting a plurality of measurements at each of a plurality of orientations, and wherein determining the characteristic value comprises determining a characteristic value for each of the plurality of orientations based on at least some of the respective plurality of measurements, the characteristic values forming portions of respective reference RF fingerprints associated with the first location, and wherein the plurality of orientations includes a plurality of directions between the mobile unit and the first transmitter such that a plurality of measurements is collected at each of the plurality of directions at the first location, and wherein the plurality of orientations includes a plurality of elevations between the mobile unit and the first transmitter such that a plurality of measurements is collected at each of the plurality of elevations at the first location.

14. A method of determining a location of a mobile unit in an area serviced by a wireless network, the wireless network configured for wireless location determination of said mobile unit and capable of being accessed from within the area via at least one of a plurality of wireless transmitters, the wireless network having a database of reference radio frequency (RF) fingerprints indicative of RF signal levels at a plurality of locations in the area, the method comprising steps of:

collecting a plurality of measurements from each of the plurality of wireless transmitters, the plurality of measurements for each of the plurality of wireless transmitters indicative of RF signal strengths transmitted between said mobile unit and a respective one of the plurality of wireless transmitters at a current location of the mobile unit in the area, each of the plurality of measurements for the respective one of the plurality of wireless transmitters obtained at a respective successive time slice;

determining, for each of the plurality of measurements, a characteristic value based on at least some of the respective plurality of measurements, to form a plurality of characteristic values, each associated with a respective one of the plurality of wireless transmitters, the plurality of characteristic values forming, at least in part, a target RF fingerprint for the mobile device at the current location, wherein determining the characteristic value includes identifying transmitters determined to be out of range or temporarily unobservable by determining if the transmitter has not been observed in a selectable number of preceding time slices, and determining that the transmitter is temporarily unobservable if the transmitter has been observed in said selectable number of preceding time slices, but is not observable in a current time slice; and

determining the location of the mobile device by, at least in part, comparing the target RF fingerprint with the database of reference RF fingerprints,

wherein determining the characteristic value includes identifying which, if any, of the plurality of measurements is an outlier with respect to other of the plurality of measurements based on at least one statistical measurement, and determining the characteristic value based on at least some of the plurality of measurements not identified as outliers.

15. The method of claim 14 wherein determining a characteristic value includes determining a mode, median, or mean of the plurality of measurements not identified as an outlier.

16. The method of claim 14 wherein a measurement is identified as an outlier if the measurement is outside N standard deviations of an average of the plurality of measurements.

17. The method of claim 14 wherein a measurement is identified as an outlier if the measurement is over N units from an average of the plurality of measurements.

18. The method according to claim 14 further comprising determining that a transmitter is out of range if the transmitter has not been observed in a selectable percentage of time slices for the mobile unit at said respective location.

19. The method of claim 14 wherein the selectable number of preceding slices is selected based, at least in part, on motion of the mobile unit.

20. The method of claim 18 wherein the selectable percentage of time slices is selected based, at least in part, on motion of the mobile unit.

21. The method of claim 14, wherein determining the characteristic value includes averaging the plurality of measurements not identified as being out of range or temporarily unobservable.