Ground-based system and method to extend the detection of excessive delay gradients using dual processing

• US 9,599,716 B2
• Filed: 04/15/2014
• Issued: 03/21/2017
• Est. Priority Date: 04/15/2014
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Weed, Douglas, Reuter, Randy J.
• Primary Examiner(s): LIU, HARRY K
• Application Number:
  US14/253,431
• Publication Number:
  US 20150293230A1
• Time in Patent Office: 1,071 Days
• Field of Search: 342/357.41
• US Class Current: 1/1
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/074 providing integrity data, e.g. WAAS
• CPC Class Codes: G01S 19/08 providing integrity information, e.g. health of satellites or quality of ephemeris data
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment

Abstract

A processing module to monitor a horizontal delay gradient in satellite signals is provided. The processing module includes a dual-processing-satellite-differencing module, a double differencing module, and a gradient estimator module. The dual-processing-satellite-differencing module is operable to: receive carrier phase measurements for at least two satellites from at least two reference receivers; implement a first processing mode to normalize first satellite differences between +λ/2 and −λ/2; implement a second processing mode configured to normalize second satellite differences between 0 and λ; and select for further processing one of: data indicative of the first satellite differences processed according to the first processing mode; and data indicative of the second satellite differences processed according to the second processing mode. The double differencing module forms double-differences based on the selected data input from the dual-processing-satellite-differencing module. The gradient estimator module estimates a magnitude of the horizontal delay gradient.

Claims

1. A processing module to monitor a horizontal delay gradient in satellite signals, the processing module comprising:

a dual-processing-satellite-differencing module;

wherein the dual processing-satellite-differencing module is configured to;

receive carrier phase measurements for at least two satellites from at least two reference receivers, the at least two satellites including a monitored satellite and at least one other satellite, wherein the at least two reference receivers have a known geometric relationship to each other; and

implement a first processing mode to normalize first satellite differences between +λ

/2 and −

λ

/2;

implement a second processing mode;

wherein the second processing mode is configured to normalize second satellite differences between 0 and λ

; and

select for further processing one of;

data indicative of the first satellite differences processed according to the first processing mode; and

data indicative of the second satellite differences processed according to the second processing mode;

a double differencing module;

wherein the double differencing module is configured to form double-differences between one or more pairs of the at least two reference receivers based on the selected data input from the dual-processing-satellite-differencing module; and

a gradient estimator module;

wherein the gradient estimator module is configured to estimate a magnitude of the horizontal delay gradient based on averaged compensated double-differences for the monitored satellite.

2. The processing module of claim 1, wherein the dual-processing-satellite-differencing module further comprises:

a first-processing-satellite-differences module;

wherein the first-processing-satellite difference module is configured to average normalized first satellite differences;

a first variance calculation module to compute a first variance of the normalized first satellite differences;

a second-processing-satellite-differences module;

wherein the second-processing-satellite-differences module is configured to average normalized second satellite differences;

a second variance calculation module to compute a second variance of the normalized second satellite differences; and

selection logic to select the output, for further processing, based on the first variance of the first satellite differences and the second variance of the second satellite differences.

3. The processing module of claim 1, wherein the first processing mode is further configured to:

compute the differences in the carrier phase measurements between satellite signals from the monitored satellite and at least one of the at least one other satellite;

compute an average of the first satellite differences normalized between +λ

/2 and −

λ

/2 at the first-processing-satellite-differences module; and

compute a first variance of the first satellite differences at a first variance calculation module in the dual-processing-satellite-differencing module, and wherein the second processing mode is further configured to;

compute an average of the second satellite differences normalized between 0 and λ

at the second-processing-satellite-differences module; and

compute a second variance of the second satellite differences at a second variance calculation module in the dual-processing-satellite-differencing module.

4. The processing module of claim 1, wherein the double differencing module is further configured to:

compensate the double-differences between the one or more pairs for one or more known difference-in-position of the reference receivers in the respective one or more pairs;

perform a modulo operation to limit the compensated double-differences to a range of minus one-half wavelength to plus one-half wavelength.

5. The processing module of claim 4, wherein the double differencing module is further configured to filter the compensated double-differences to reduce noise content.

6. The processing module of claim 4, wherein the double differencing module is further configured to average the compensated double-differences over time.

7. The processing module of claim 4, wherein the double differencing module is further configured to compensate for elevation and azimuth dependent antenna variations for antennas respectively associated with the at least two reference receivers.

8. The processing module of claim 1, wherein the gradient estimator module is further configured to compare the estimated magnitude of the delay gradient to a selected gradient threshold.

9. A method of monitoring for a delay gradient in signals from a monitored satellite, the method comprising:

receiving carrier phase measurements from at least two reference receivers at a dual-processing-satellite-differencing module of a processing module, wherein the at least two reference receivers substantially simultaneously receive radio frequency signals from the monitored satellite and at least one other satellite;

implementing a first processing mode at a first-processing-satellite-differences module in the dual-processing-satellite-differencing module to normalize computed first satellite differences between +λ

/2 and −

λ

/2;

implementing a second processing mode at a second-processing-satellite-differences module in the dual-processing-satellite-differencing module to normalize computed second satellite differences between 0 and λ

at the second-processing-satellite-differences module;

selecting for further processing one of;

data indicative of the first satellite differences processed according to the first processing mode; and

data indicative of the second satellite differences processed according to the second processing mode;

forming double-differences between one or more pairs of the at least two reference receivers based on the selected data input from the dual-processing-satellite-differencing module at a double differencing module in the processing module; and

estimating, at a gradient estimator module in the processing module, a magnitude of the horizontal delay gradient based on averaged compensated double-differences for the monitored satellite.

10. The method of claim 9, wherein implementing the first processing mode further comprises:

computing the differences in the carrier phase measurements between the radio frequency signals from the monitored satellite and at least one other satellite for the at least two reference receivers at the first-processing-satellite-differences module;

averaging the first satellite differences normalized between +λ

/2 and −

λ

/2; and

computing a first variance of the normalized first satellite differences.

11. The method of claim 10, wherein implementing the second processing mode further comprises:

averaging the second satellite differences normalized between 0 and λ

;

computing the second variance of the normalized second satellite differences, wherein the selecting for further processing is based on the first variance and the second variance.

12. The method of claim 9, further comprising:

performing a modulo operation on compensated double-differences to limit the compensated double-differences to a range of minus one-half wavelength to plus one-half wavelength.

13. The method of claim 9, further comprising:

determining if the estimated magnitude of the horizontal delay gradient exceeds a selected gradient threshold.

14. The method of claim 13, further comprising:

issuing an alert if the estimated magnitude of the horizontal delay gradient exceeds the selected gradient threshold; and

excluding satellites from providing navigation system data to an aircraft based on the issuing of the alert.

15. The method of claim 13, further comprising:

excluding the monitored satellite from providing navigation system data to an aircraft if the estimated magnitude of the horizontal delay gradient exceeds the selected gradient threshold.

16. A ground based system to monitor for a horizontal delay gradient to a monitored satellite, the system comprising:

at least two reference receivers positioned in a known geometric relationship to each other, the at least two reference receivers configured to substantially simultaneously receive radio frequency signals from the monitored satellite and at least one other satellite; and

a processing module communicatively coupled to the at least two reference receivers, the processing module including a dual-processing-satellite-differencing module;

wherein the dual-processing-satellite-differencing module is configured to;

receive carrier phase measurements for at least two satellites from at least two reference receivers, the at least two satellites including a monitored satellite and at least one other satellite, wherein the at least two reference receivers have a known geometric relationship to each other, and

implement a first processing mode to normalize first satellite differences between +λ

/2 and −

λ

/2;

implement a second processing mode configured to normalize second satellite differences between 0 and λ

; and

select for further processing one of;

data indicative of the first satellite differences processed according to the first processing mode; and

data indicative of the second satellite differences processed according to the second processing mode.

17. A ground based system of claim 16, wherein the dual-processing-satellite-differencing module includes:

a first-processing-satellite-differences module;

wherein the first-processing-satellite-differences module is configured to average normalized first satellite differences;

a first variance calculation module to compute a first variance of the normalized first satellite differences;

a second-processing-satellite-differences module configured to average normalized second satellite differences;

a second variance calculation module to compute a second variance of the normalized second satellite differences; and

selection logic to select output for further processing, based on the first variance and the second variance.

18. The ground based system of claim 16, wherein the processing module further includes a double differencing module;

wherein the double differencing module is configured to;

form double-differences between pairs of the at least two reference receivers;

compensate the double-differences between the pairs for a known difference-in-position of the reference receivers in the pairs;

perform a modulo operation to limit the compensated double-differences to a range of minus one-half wavelength to plus one-half wavelength.

19. The ground based system of claim 16, wherein the processing module further comprises:

a gradient estimator module;

wherein the gradient estimator module is configured to estimate a magnitude of the horizontal delay gradient based on averaged compensated double-differences for the monitored satellite.

20. The ground based system of claim 19, wherein the gradient estimator module is further configured to compare the estimated magnitude of the delay gradient to a selected gradient threshold.