Systems and methods for positioning using multipath signals

• US 7,679,561 B2
• Filed: 01/19/2006
• Issued: 03/16/2010
• Est. Priority Date: 01/19/2005
• Status: Active Grant

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Dowdle, John R., Gustafson, Donald E., Elwell, John M. Jr.
• Primary Examiner(s): Issing; Gregory C
• Application Number:
  US11/335,160
• Publication Number:
  US 20080198072A1
• Time in Patent Office: 1,517 Days
• Field of Search: 342/453, 342/353, 342/451
• US Class Current: 342/453
• CPC Class Codes: G01C 21/206 specially adapted for indoor navigation
• CPC Class Codes: G01S 19/428 using multipath or indirect path propagation signals in position determination
• CPC Class Codes: G01S 5/02525 Gathering the radio frequency fingerprints
• CPC Class Codes: G01S 5/0273 using multipath or indirect path propagation signals in position determination

Abstract

A signal processing technique for RF active, passive, or aided localization approaches that utilizes multipath signals as additional measurements with a filter or estimator, e.g., a nonlinear filter. The filter uses indirect and direct path measurements or any other available signals to build parametric models of observable indirect paths. If one or more direct path measurements are subsequently lost (e.g., due to obstruction), the filter maintains an estimate of the position of the person or object of interest using indirect path measurements.

Claims

1. A method for positioning using a multipath wireless signal, the method comprising the steps of:

receiving a plurality of wireless signals comprising multipath signals;

processing the plurality of wireless signals to identify at least one indirect path;

determining an initial estimate for {r}, wherein {r} is a position of a receiver;

determining initial estimates of and {w_n, τ

_0n} for the at least one indirect path based on a parametric model relating {r} to a length of the at least one indirect path, the parametric model assuming, without prior knowledge of a local infrastructure or propagation channels associated with the at least one indirect path, that at least one multipath signal has experienced at least one specular reflection off a planar surface along the at least one indirect path before reaching the receiver;

receiving a subsequent plurality of wireless signals comprising multipath signals; and

updating the initial estimates of {r} and {w_n, τ

_0n} using a nonlinear filter and the subsequent plurality of wireless signals applied to that filter,

wherein w_n is a unit vector in a direction of the at least one indirect path from a reflecting surface closest to the receiver and τ

_0n is a scalar geometry-dependent offset associated by the parametric model to the length of the at least one indirect path.

2. The method of claim 1 wherein determining an initial estimate for {r} comprises:

receiving, at a plurality of positions, at least one transmitted signal;

determining the magnitude of the at least one signal received at each position; and

using the determined signal magnitudes and a statistical model to estimate the initial position.

3. The method of claim 2 wherein the statistical model comprises data indicative of signal propagation characteristics associated with a signal space between the receiver and one or more transmitters.

4. The method of claim 1 wherein determining an initial estimate for {r} comprises computing a plurality of candidate locations and selecting a most likely location therefrom.

5. The method of claim 4 wherein the most likely location is determined using a statistical test.

6. The method of claim 1 wherein the wireless signals are generated by a Global Positioning System (GPS) transmitter.

7. The method of claim 1 wherein the wireless signals are generated by a transmitter.

8. The method of claim 1 wherein determining an initial estimate for {r} comprises making a direct path measurement of an initial position of the receiver.

9. The method of claim 8 wherein the direct path measurement is a measurement of received signal strength.

10. The method of claim 1 wherein determining an initial estimate for {r} comprises utilizing prior knowledge of an initial position of the receiver.

11. The method of claim 1 wherein processing the plurality of wireless signals to identify the at least one indirect path comprises modeling path lengths using ordinary least squares analysis and a polynomial model.

12. An apparatus for positioning using a multipath wireless signal, the apparatus comprising:

a receiver for receiving a plurality of wireless signals comprising multipath signals; and

a processor configured to (i) process the plurality of wireless signals to identify at least one indirect path, (ii) determine an initial estimate of {r}, wherein {r} is a position of the receiver, (iii) determine initial estimates of {w_n, τ

_0n} for the at least one indirect path based on a parametric model relating {r} to a length of the at least one indirect path, the parametric model assuming, without prior knowledge of a local infrastructure or propagation channels associated with the at least one indirect path, that at least one multipath signal has experienced at least one specular reflection off a planar surface along the at least one indirect path before reaching the receiver, and (iv) update the initial estimates of {r} and {w_n, τ

_0n} using a nonlinear filter and subsequent wireless signals applied to that filter,

wherein w_n is a unit vector in a direction of the at least one indirect path from a reflecting surface closest to the receiver and τ

_0n is a scalar geometry-dependent offset associated by the parametric model to the length of the at least one indirect path.

13. The apparatus of claim 12 wherein the wireless signals are generated by a Global Positioning System (GPS) transmitter.

14. The apparatus of claim 12 wherein the wireless signals are generated by a transmitter.