SYSTEM AND METHOD FOR MITIGATING SEVERE MULTIPATH INTERFERENCE FOR GEOLOCATION & NAVIGATION

• US 20130051434A1
• Filed: 03/18/2009
• Published: 02/28/2013
• Est. Priority Date: 03/18/2008
• Status: Active Grant

• Current Assignee: Argon St Incorporated (The Boeing Co.)
• Original Assignee: Argon St Incorporated (The Boeing Co.)
• Inventors: Draganov, Alexandr, Harlacher, Marc A., Haas, Franklin M. Jr.
• Granted Patent: US 8,406,280 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• 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 system and method for mitigating multipath interference of signals in environments to determine the line of sight signal propagation.

Claims

1. A method of mitigating multipath interference in a received signal comprising the steps of:

(a) receiving at a user a plurality of RF signals over time intervals from a transmitter, wherein at least one of the plurality of RF signals is a line-of-sight signal and wherein at least one of the plurality of RF signals is a multipath signal;

(b) correlating each of the plurality of received signals with delayed versions of a corresponding replica waveform to form a two dimensional matrix, where matrix elements in one dimension correspond to different time intervals;

(c) estimating a frequency spectrum of the two dimensional matrix; and

(d) identifying, and separating out a signal path of the at least one line-of-sight signal and the at least one multipath signal from the spectrum by a value of phase rates associated with these paths.

3. The method of claim 1 wherein the line-of-sight path is a first arriving signal.

4. The method of claim 1 wherein the step of correlating uses multiple correlators.

5. The method of claim 1 wherein the user is moving relative to the transmitter, and a second dimension of the two dimensional matrix is delayed in time.

6. The method of claim 1 wherein the plurality of RF signals is comprised of transmissions in multiple frequency channels, and a second dimension of the two dimensional matrix corresponds to correlations with each corresponding replica waveform in different frequency channels comprising the signal.

7. The method of claim 1 wherein the plurality of signals and the corresponding replica waveforms are filtered prior to computing correlation, such that a spectrum of each is limited to a band within the original spectrum, and second dimension of the two dimensional matrix corresponds to different bands.

9. The method of claim 1 wherein the corresponding replicated waveforms and delay are based on an estimated location of the transmitter and an estimated time of transmission.

10. The method of claim 3 wherein a delay for the line-of-sight path is estimated by combining data from correlators at different replica delays using early-minus late power correlators.

11. The method of claim 9 wherein the estimated location is based on an inertial navigation system.

12. The method of claim 1 further comprising the step of adjusting the two dimensional matrix as a function of an estimated motion of the user.

13. The method of claim 12 wherein the step of adjusting the two dimension matrix includes rotating phases of correlation measurements by an amount consistent with the estimated user motion.

14. The method of claim 13 further comprising the step of identifying the line-of-sight path as a function of a smallest phase rate change.

15. The method of claim 3 further comprising the steps of:

(f) estimating a pseudorange (PR) delay and Doppler for the line-of-sight path for a plurality of transmitters; and

(g) estimating a position of the user as a function of the PR and Doppler measurements.

16. The method of claim 15 wherein the step of estimating the user position includes use of a Kalman filter.

17. The method of claim 1 wherein the step of estimating the frequency spectrum includes using spectrum estimation-based beamforming and direction finding methods.

18. The method of claim 17 wherein the spectrum estimation based beamforming and direction finding methods include at least one of MUSIC, modified MUSIC, APES, maximum entropy methods, and subspace fitting methods.

19. The method of claim 1 wherein the step of estimating the frequency spectrum includes applying spectrum estimation-based beamforming and direction finding methods on data comprising temporal dimension of the two-dimensional matrix.

20. The method of claim 19 wherein the spectrum estimation based beamforming and direction finding methods include the steps of:

(i) identifying signal paths from data which are associated with at least one of replica delay, frequency channel, or spectral band;

(ii) computing beamforming weights for each signal path;

(iii) applying beamforming weights to data for at least one other of replica delays, frequency channels, or spectral bands;

(iv) estimating amplitudes, phase rates and residual delays of isolated signal paths; and

(v) identifying line-of-sight path as a function of at least one of the following criteria;

smallest residual delay, smallest phase rates, and sufficiently large amplitude.

2. (canceled)

8. (canceled)

21. A method to increase accuracy of geolocation based on timing measurements of RF signal comprising the steps of:

(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, move amplitude and Doppler to dependent claims amplitudes and Doppler measurements 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, [amplitude and Doppler] measurements for each model; and

(f) determining the set of LOS measurements as one associated with a model having the largest likelihood.

22. The method of claim 21 wherein the steps of creating the models and estimating their likelihoods use an Interacting Multiple Models (IMM) method.

23. The method of claim 21 wherein the step of creating the models use a Genetic Algorithms method.

24. The method of claim 21 wherein the testing includes using Bayesian Likelihood.

25. The method of claim 21 wherein the step of creating includes the use of likelihood gradients to estimate the likelihoods of models, which may be created at the next time interval.

26. The method of claim 21 wherein the step of testing includes removing a model if its likelihood is lower than a threshold likelihood.

27. The method of claim 26 wherein the threshold likelihood is dynamically adjusted to keep some reasonable number of models.

28. The method of claim 21 wherein the location of the user is determined as a function of the determined set of LOS signals.

29. The method of claim 21 wherein the testing includes calculating a priori likelihood for the models.

30. The method of claim 21 wherein the testing includes calculating posteriori likelihood for the models.

31. The method of claim 21 wherein the step of creating a first set of estimates includes estimating amplitude and Doppler of the signals at the user, and the step of testing the models includes testing the models to estimate the likelihood of amplitude and Doppler measurements for each model.

32. A method of locating a user 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, comprising the steps of:

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

(b) estimating 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 to the user the signal timing information and the estimated pseudo ranges from the first transmitter to reference stations;

(d) forming a linear combination of multiple time differences of arrival, each time difference of arrival being comprised of the timing of the received signal at the user and at a particular reference station; and

(e) processing the linear combination of time differences of arrival to estimate or update an estimate of the user position.

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

(g) fanning navigation equations that express dependence of the estimated pseudo range on timing errors at the reference stations.

33. The method of claim 32 wherein the step of forming navigation equations includes forming navigation equations that express dependence of the estimated pseudo range on positional errors of the transmitters.

34. The method of claim 33 wherein the step of forming linear combinations cancels the timing and positional errors.

35. A method of estimating the location of a user in an environment having a plurality of transmitters

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

(b) correlating the received signals with a plurality of delayed replica waveforms;

(c) testing multiple hypotheses of having an estimated distance from the user to the transmitter;

(d) accessing a database of historical statistics for the plurality of correlation values and selecting a statistic, which is associated with propagation path characteristics similar to the current propagation environment;

(e) comparing the calculated statistics for each hypothesis with the accessed historical statistics; and

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

36. The method of claim 35 wherein the step of comparing includes characterizing the received signals as being comprised of noise and the transmitter-generated signal, the transmitter generated noise having certain propagation delay.

37. The method of claim 35 wherein the steps of (a)-(g) are repeated for a plurality of transmitters, and the location of the user is determined as a function of the estimated pseudo ranges between the user and the plurality of transmitters.

38. The method of claim 35 wherein the step of correlating uses a bank of correlators.

39. The method of claim 35 wherein the replica waveform is an expected received signal delayed in time.

40. The method of claim 39 wherein the expected signal is based on the estimated location of the transmitter.

41. The method of claim 35 wherein the estimated location is based on an inertial navigation system.

42. The method of claim 35 wherein the step of testing a hypothesis is determined using Bayesian likelihood of having the partition of the received signal between the noise and the transmitter-generated signal, the transmitter-generated noise having the delay associated with the current hypothesis.