Navigation System Using Hybridization by Phase Measurements

• US 20100324822A1
• Filed: 02/18/2009
• Published: 12/23/2010
• Est. Priority Date: 02/19/2008
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Juillaguet, Sebastien, Coatantiec, Jacques
• Granted Patent: US 8,311,728 B2
• Time in Patent Office: Days
• 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 being capable of acquiring and tracking at least one carrier received from a satellite, of measuring its phase and of demodulating its signal in order to recover at least one modulation code; and

one module for calculating navigation solutions by hybridization in at least one Kalman filter of the results from the first module with those of the second module,

wherein the 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 of the variables of the state vector of at least one of the Kalman filters represents a part of the errors on the code and phase measurements from the second positioning module due to the passage through the ionospheric layers of the atmosphere.

3. The navigation system according to claim 2, wherein the state variable or variables representing a part of the errors on the code and phase measurements from the second positioning module due to the passage through the ionospheric layers of the atmosphere are chosen from within the group comprising the ionospheric bias on the measurement of the code, the ionospheric bias on the measurement of the phase and the variation of the ionospheric environment.

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

5. The navigation system according to claim 1, wherein at least one of the variables of the state vector of at least one of the Kalman filters represents, at least partially, a part of the errors on the code and phase measurements from the second positioning module due to the errors in the satellite clock and in the ephemerides transmitted by the satellites.

6. The navigation system according to claim 1, wherein the internal errors of the receiver comprise the error due to the receiver clock, the error due to the thermal noise of said receiver and the residual error due to the processing loops of said receiver.

7. The navigation system according to claim 6, wherein the errors in the processing loops due to the dynamic behaviour of the aircraft are corrected by widening the range of variance of the loop noise as a function of said dynamic behaviour.

8. The navigation system according to claim 7, wherein the PLL errors due to the impact of a noisy signal are taken into account by rejecting the phase measurement variations corresponding to a low signal-to-noise ratio.

9. The navigation system according to claim 1, wherein the management structure of the receiver channels allows them to supply measurements meeting quality criteria which can be parameterized.

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

11. The navigation system according to claim 9, wherein the measurements of one channel 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 the results from the calculation module for the navigation solution are supplied to the first positioning module for correcting its measurements.

13. The navigation system according to claim 12, further comprising N Kalman filters in addition to 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 the calculation of the horizontal and vertical protection radii of the navigation solution.

15. The navigation system according to claim 1, wherein the results from the calculation module are not supplied to the second module in order to modify its 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 the output of the second positioning module prior to being hybridized with the 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 at least one of the variables of the state vector of at least one of the Kalman filters represents a part of the errors on the measurements of the baro-altimetric sensor.

20. The navigation system according to claim 1, wherein at least one of the variables of the state vector of at least one of the Kalman filters represents a part of the errors on the measurements of the inertial sensors.

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

a first positioning step using processing of inertial sensor measurements;

a second positioning step comprising at least one multi-channel radiofrequency reception step, each channel being capable of acquiring and tracking at least one 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 navigation solution calculation step using hybridization in at least one Kalman filter of the results from the first step with those of the second step,

wherein the navigation solution calculation step 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.