System and method for mitigating severe multipath interference for geolocation and navigation

• US 9,304,184 B1
• Filed: 02/22/2013
• Issued: 04/05/2016
• Est. Priority Date: 03/18/2008
• Status: Active Grant

• Current Assignee: Argon St Incorporated (The Boeing Co.)
• Original Assignee: The Boeing Co.
• Inventors: Draganov, Alexandr, Haas, Franklin M. Jr., Harlacher, Marc A.
• Primary Examiner(s): Liu, Harry
• Application Number:
  US13/774,961
• Time in Patent Office: 1,138 Days
• Field of Search: 342/451, 342/357.77
• US Class Current: 1/1
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial
• CPC Class Codes: G01S 5/0273 using multipath or indirect path propagation signals in position determination
• CPC Class Codes: H04B 1/711 the interference being multi-path interference
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A method for increasing accuracy of geolocation based on timing measurements of RF signals. The method includes: (a) receiving at a user one or more RF signals transmitted over time, (b) correlating the received signals with a plurality of replica waveforms, (c) creating a first set of estimates of the time or arrivals of the signals at the user, (d) using the first set of estimates to create a plurality of models, wherein each model assumes that some of the measurements are affected by multipath or interference, (e) testing the models to estimate the likelihood of timing measurements for each model, and (f) determining the set of LOS measurements as one associated with a model having the largest likelihood.

Claims

1. A method to increase accuracy of geolocation of a user device based on timing measurements of RF signals, the method comprising:

(a) receiving, at a user device, one or more RF signals transmitted over time from a transmitter;

(b) correlating, at the user device, the received signals with a plurality of replica waveforms;

(c) creating, at the user device, a first set of estimates of times of arrival of the received signals at the user device;

(d) using the first set of estimates to create a plurality of models at the user device, wherein each model assumes at least one of the first set of estimates is affected by multipath or interference;

(e) processing, at the user device, the plurality of models to estimate the likelihood of times of arrival for each model;

(f) determining, at the user device, a set of line of sight (LOS) measurements for the user device using a model having the largest likelihood;

(g) determining, at the user device, a location of the user device as a function of the determined set of LOS measurements.

2. The method of claim 1 wherein creating the plurality of models and estimating their likelihoods uses an Interacting Multiple Models (IMM) method.

3. The method of claim 1 wherein creating the plurality of models uses a Genetic Algorithms method.

4. The method of claim 1 wherein the processing includes using Bayesian Likelihood.

5. The method of claim 1 wherein the step of creating the plurality of models includes the use of likelihood gradients to estimate the likelihoods of the plurality of models, which may be created at the next time interval.

6. The method of claim 1 wherein the processing includes removing a model if its likelihood is lower than a threshold likelihood.

7. The method of claim 6 wherein the threshold likelihood is dynamically adjusted to keep some reasonable number of models.

8. The method of claim 1 wherein the processing includes calculating a priori likelihood for the plurality of models.

9. The method of claim 1 wherein the processing includes calculating posteriori likelihood for the plurality of models.

10. The method of claim 1 wherein the step of creating a first set of estimates includes estimating amplitude and Doppler of the received signals at the user device, and the processing the plurality of models includes testing the plurality of models to estimate the likelihood of amplitude and Doppler measurements for each model.

11. A method of locating a user device having a signal receiver in an environment having a plurality of transmitters, and a plurality of reference stations of known location for receiving signals transmitted by the transmitters, the method comprising:

(a) receiving, at a plurality of reference stations, a first signal transmitted by a first one of a plurality of transmitters;

(b) estimating, at a reference station in the plurality of reference stations, the location of the first transmitter using time difference of arrival of the first signal at pairs of the plurality of reference stations;

(c) transmitting, from the reference station to the user device, signal timing information and estimated pseudo ranges from the first transmitter to the plurality of reference stations;

(d) forming, at the user device, a linear combination of multiple time differences of arrival, each time difference of arrival comprising a time of receipt of the first signal at the user device and at a particular reference station of the plurality of reference stations;

(e) processing, at the user device, the linear combination of time differences of arrival to compute an estimate of a location of the user device; and

(f) repeating steps (a)-(e) for each of the plurality of transmitters.

12. The method of claim 11 further comprising forming navigation equations that express dependence of the estimated pseudo ranges on timing errors at the plurality of reference stations and on positional errors of the plurality of transmitters.

13. The method of claim 12 wherein the step of forming linear combinations cancels the timing and positional errors.

14. A method of estimating a location of a user device in a propagation environment having a plurality of transmitters

(a) receiving an RF signal at a user device where the RF signal is transmitted over time from a transmitter;

(b) correlating, at the user device, the received RF signal with a plurality of delayed replica waveforms;

(c) testing, at the user device, a plurality of estimated distances from the user device to the transmitter;

(d) accessing, at the user device, a database of historical statistics for a plurality of correlation values;

(e) comparing, at the user device, calculated statistics for each of the plurality of estimated distances with the accessed historical statistics; and

(f) estimating, at the user device, a pseudo range between the user device and the transmitter as a function of the comparison.

15. The method of claim 14 wherein the step of comparing includes characterizing the received RF signal as being comprised of noise and a transmitter-generated signal, the noise having propagation delay.

16. The method of claim 14 wherein the steps of (a)-(f) are repeated for the plurality of transmitters, and the location of the user device is determined as a function of the estimated pseudo ranges between the user device and the plurality of transmitters.

17. The method of claim 14 wherein the step of correlating uses a bank of correlators.

18. The method of claim 14 wherein the each of the plurality of replica waveforms is an expected received signal delayed in time.

19. The method of claim 18 wherein the expected received signal is based on an estimated location of the transmitter.

20. The method of claim 14 wherein the location of the user device is estimated based on an inertial navigation system.

21. The method of claim 15, wherein the step of testing an estimated distance includes determining a Bayesian likelihood of having a portion of the received RF signal between the noise and the transmitter-generated signal, the noise having the delay associated with the estimated distance.