Navigation system using hybridization by phase measurements

• US 8,311,728 B2
• Filed: 02/18/2009
• Issued: 11/13/2012
• Est. Priority Date: 02/19/2008
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Coatantiec, Jacques, Juillaguet, Sébastien
• Primary Examiner(s): Tarcza, Thomas
• Assistant Examiner(s): Alharbi, Nagi
• Application Number:
  US12/918,204
• Publication Number:
  US 20100324822A1
• Time in Patent Office: 1,364 Days
• Field of Search: None
• US Class Current: 701/216
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial

Abstract

The invention relates to a navigation system for aircraft comprising inertial sensors, a GNSS receiver and potentially a baro-altimeter. The measurements from the inertial sensors are hybridized with the code and phase measurements from the receiver within a main Kalman filter and, possibly, secondary filters. The said measurements are corrected for several types of errors, notably those due to the passage of the satellite signals through the ionospheric layers. The precision of the determination of the position of the aircraft is greatly improved, both in the horizontal plane and in the vertical direction. This is also the case for the corresponding protection radii, which allows margins to be created in order to satisfy the integrity constraints for the navigation solution.

Claims

1. A navigation system for a moving craft, comprising:

a first positioning module for processing of inertial sensor measurements;

a second positioning module comprising at least one multi-channel radiofrequency receiver, each channel of the at least one multi-channel radiofrequency receiver is capable of acquiring and tracking at least one carrier received from a satellite, of measuring the carrier'"'"'s phase and of demodulating the carrier'"'"'s signal in order to recover at least one modulation code; and

a calculation module for calculating navigation solutions by hybridization in at least one hybridization Kalman filter of results from the first positioning module with results of the second positioning module, wherein the calculation module for calculating the navigation solution includes in the hybridization at least one measurement of pathway increment carried out on at least one channel by integration of the measurements of the carrier phase tracked by said channel.

2. The navigation system according to claim 1, wherein at least one variable of a state vector of the at least one hybridization Kalman filter represents a part of errors on pseudo-random code and the carrier'"'"'s phase measurements from the second positioning module due to a passage through ionospheric layers of atmosphere.

3. The navigation system according to claim 2, wherein the at least one variable represents a part of the errors on the pseudo-random code and the carrier'"'"'s phase measurements from the second positioning module due to passage through ionospheric layers of atmosphere are chosen from a group comprising an ionospheric bias on a measurement of the pseudo-random code, an ionospheric bias on a measurement of the carrier'"'"'s phase and a variation of the ionospheric environment.

4. The navigation system according to claim 1, wherein a part of errors on pseudo-random code and the carrier'"'"'s phase measurements from the second positioning module due to multiple pathways of received signals are modeled in the calculation module for the navigation solution by two states, one for the pseudo-random code and one for the carrier'"'"'s phase.

5. The navigation system according to claim 1, wherein at least one of variables of state vector of the at least one of hybridization Kalman filter represents, at least partially, a part of errors on the pseudo-random code and the carrier'"'"'s phase measurements from the second positioning module due to errors in satellite clock and in ephemerides transmitted by the satellite.

6. The navigation system according to claim 1, wherein internal errors of the at least one multi-channel radiofrequency receiver comprise an error due to a receiver clock, an error due to a thermal noise of the at least one multi-channel radiofrequency receiver and a residual error due to processing loops of the at least one multi-channel radiofrequency receiver.

7. The navigation system according to claim 6, wherein the residual error caused by in the processing loops of dynamic behavior of the moving craft are corrected by widening range of variance of loop noise as a function of the dynamic behavior.

8. The navigation system according to claim 7, wherein phase lock loop errors due to a noisy signal are taken into account by rejecting the carrier'"'"'s phase measurement variations corresponding to a low signal-to-noise ratio.

9. The navigation system according to claim 1, wherein management structure of the at least one multi-channel radiofrequency receiver allows channels of the at least one multi-channel radiofrequency receiver to supply measurements meeting quality criteria which can be parameterized.

10. The navigation system according to claim 9, wherein the measurements of one channel of the at least one multi-channel radiofrequency receiver are only used after a chosen delay following a reception of an indication of an availability status of said channel.

11. The navigation system according to claim 9, wherein the measurements of one channel of the at least one multi-channel radiofrequency receiver are only used beyond chosen thresholds in elevation of the satellite being tracked and in signal-to-noise ratio of the received signal.

12. The navigation system according to claim 1, wherein results from the calculation module for the navigation solution are supplied to the first positioning module for correcting inertial sensor measurements.

13. The navigation system according to claim 12, further comprising N Kalman filters in addition to the at least one hybridization Kalman filter, one per channel corresponding to a satellite in view.

14. The navigation system according to claim 13, wherein the N Kalman filters are used for calculating horizontal and vertical protection radii of the navigation solution.

15. The navigation system according to claim 1, wherein results from the calculation module are not supplied to the second positioning module in order to modify the carrier'"'"'s phase measurements.

16. The navigation system according to claim 1, further comprising at least one narrow double-delta correlator.

17. The navigation system according to claim 1, wherein a partial navigation solution is calculated at an output of the second positioning module prior to being hybridized with outputs of the first positioning module.

18. The navigation system according to claim 1, wherein the second positioning module also comprises a baro-altimetric measurement sensor.

19. The navigation system according to claim 2, wherein the at least one variable of the state vector of the at least one hybridization Kalman filter represents a part of errors on measurements of the baro-altimetric sensor.

20. The navigation system according to claim 1, wherein at least one variable of state vector of the at least one hybridization Kalman filter represents a part of errors on the inertial sensor measurements.

21. A navigation method for a moving craft, the method comprising:

a first step of processing measurements from inertial sensors;

a second step of processing positioning signals from a multi-channel radiofrequency receiver, each channel being capable of acquiring and tracking at least one radiofrequency carrier received from a satellite, of measuring its phase and of demodulating the signal in order to recover at least one modulation code; and

a step of calculating a navigation solution by hybridizing the output from the first step with the output of the second step in a processor comprising at least one Kalman filter, wherein said calculating step includes in the hybridization at least one measurement of pathway increment carried out on at least one satellite channel by integration of the measurements of the radiofrequency carrier phase tracked by said satellite channel.