Satellite-Based Positioning Receiver with Improved Integrity and Continuity

• US 20080129586A1
• Filed: 01/03/2006
• Published: 06/05/2008
• Est. Priority Date: 01/20/2005
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Martin, Nicolas
• Granted Patent: US 7,504,996 B2
• Time in Patent Office: Days
• US Class Current: 342/357.03
• CPC Class Codes: G01S 19/43 using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial

Abstract

The invention relates to a receiver of signals of a satellite-based radionavigation system intended to calculate the position of a carrier very precisely. The receiver comprises several digital signal processing channels each associated with a satellite and each providing a first digital datum representing a pseudo-distance between the receiver and the satellite in the form of an instantaneous temporal position of a pseudo-random code and a second digital datum representing this pseudo-distance in the form of an instantaneous phase of the carrier of the signal transmitted by the satellite. According to the invention, the receiver comprises an extended Kalman filter comprising:

• • means for calculating an instantaneous position of the receiver;
  • means for calculating propagation of a state vector;
  • means for calculating registration of the state vector on the basis of observations relating to each satellite and of a matrix of observations;
  • means for calculating observations;
  • means for calculating an estimated instantaneous pseudo-distance for each satellite.

Claims

1. A satellite-based positioning receiver, comprising several digital signal processing channels each intended to be associated with a respective satellite and each providing a first digital datum representing a pseudo-distance between the receiver and the satellite calculated on the basis of an instantaneous phase of a pseudo-random code present in the signal transmitted by the satellite and a second digital datum representing this pseudo-distance calculated on the basis of an instantaneous phase of the carrier of the signal transmitted by the satellite, comprising an:

extended Kalman filter comprising including;

means for calculating a position of the receiver in a terrestrial reference frame on the basis of a previously calculated position and of an error in this position;

means for calculating propagation of an estimated state vector comprising the error in the calculated position of the receiver, on the basis of a matrix propagation equation involving a propagation matrix,

means for calculating registration of the state vector on the basis of observations relating to each satellite and of a matrix of observations relating the state vector and the observations,

means for calculating observations, receiving the first and the second digital datum a to calculate an estimated pseudo-distance between the receiver and each satellite, so as to establish observations to be applied to the input of the registration calculation means,

means for calculating an estimated pseudo-distance for each satellite, by calculating the distance between the calculated position of the receiver in the terrestrial reference frame and each satellite.

2. The receiver as claimed in claim 1, wherein the means for calculating observations comprise means for subtracting the estimated pseudo-distance from the first and from the second digital datum and applying the result of the subtraction to the input of the registration calculation means.

3. The receiver as claimed in claim 1, wherein the matrix propagation equation brings into the state vector a component representing the ambiguity of the measurement of the carrier pseudo-distance, per satellite.

4. The receiver as claimed in claim 1, wherein the matrix propagation equation brings into the state vector a component representing an error related to the propagation of the signal in the ionosphere, per satellite.

5. The receiver as claimed in claim 1, wherein the matrix propagation equation brings into the state vector at least one component representing an error related to the propagation of the carrier in the troposphere, per satellite.

6. The receiver as claimed in claim 1, wherein each channel associated with a satellite comprises two sub-channels receiving signals at different carrier frequencies from this satellite, the sub-channels producing respective instantaneous pseudo-distances and the first and the second digital data being linear combinations of these pseudo-distances.

7. The receiver as claimed in claim 1, wherein each channel associated with a satellite comprises two sub-channels receiving signals at different carrier frequencies from this satellite, each of the sub-channels producing respective instantaneous pseudo-distances which are all applied, in the form of first and second digital data respectively, to the input of the means for calculating observations.

8. The receiver as claimed in claim 1, wherein the Kalman filter constitutes a main filter providing a position calculated in the terrestrial reference frame on the basis of observations made on m satellites identified by their rank i (i integer from 1 to m), and in that the receiver moreover comprises m auxiliary Kalman filters of rank i, an auxiliary filter of rank i receiving the signals from all the satellites with the exception of the satellite of rank i.

9. The receiver as claimed in claim 8, comprising means for calculating a protection radius on the basis of the outputs of the various Kalman filters and means for verifying that this protection radius does not exceed a determined threshold.

10. The receiver as claimed in claim 1, wherein each digital processing channel associated with a satellite and processing the signals transmitted by this satellite furthermore receives from a reference positioning receiver placed in a ground station, a first code phase correction and a second carrier phase correction that relate to this satellite, so as to formulate respectively the first and the second digital data by taking account of these corrections.

11. The receiver as claimed in claim 1, for a relative position measurement, wherein each digital processing channel associated with a satellite and processing the signals transmitted by this satellite furthermore receives from a mobile reference positioning receiver a correction consisting of a measured pseudo-distance between the satellite and the reference positioning receiver, so as to formulate respectively the first and the second digital datum by differences of the pseudo-distances and in that the cue delivered by the receiver is a relative position with respect to the mobile reference receiver.

12. The receiver as claimed in claim 10, comprising, other Kalman filters termed auxiliary filters of rank j, j integer varying from 1 to M, and M greater than 1, and in that each digital processing channel receives corrections from M reference receivers, and calculates:

an average of the M first corrections and an average of the M second corrections, these averages serving as corrective terms to formulate the first and second digital data for the main filter

for each rank j, an average of M−

1 first corrections and an average of M−

1 second corrections, excluding the corrections arising from the receiver of rank j, these averages serving as corrective terms to formulate the first and second digital data for the filter of rank j.

13. The receiver as claimed in claim 12, comprising means for calculating a protection radius on the basis of the outputs of the various Kalman filters and means for verifying that this protection radius does not exceed a determined threshold.

14. The receiver as claimed in claim 10, comprising means for calculating a protection radius on the basis of the outputs of a single Kalman filter supplied with M observations composed of the differences between a vector of main observations whose m components are equal to the arithmetic average of the M observations by the M reference receivers and the M vectors of average observations whose m components are equal to the arithmetic average of M−

1 observations by the reference receivers, and means for verifying that this protection radius does not exceed a determined threshold.

15. The receiver as claimed in claim 2, wherein the matrix propagation equation brings into the state vector a component representing the ambiguity of the measurement of the carrier pseudo-distance, per satellite.

16. The receiver as claimed in claim 2, wherein the matrix propagation equation brings into the state vector a component representing an error related to the propagation of the signal in the ionosphere, per satellite.

17. The receiver as claimed in claim 2, wherein the matrix propagation equation brings into the state vector at least one component representing an error related to the propagation of the carrier in the troposphere, per satellite.

18. The receiver as claimed in claim 2, wherein each channel associated with a satellite comprises two sub-channels, receiving signals at different carrier frequencies from this satellite, each of the sub-channels, producing respective instantaneous pseudo-distances which are all applied, in the form of first and second digital data respectively, to the input of the means for calculating observations.

19. The receiver as claimed in claim 2, wherein the Kalman filter constitutes a main filter providing a position calculated in the terrestrial reference frame on the basis of observations made on m satellites identified by their rank i (i integer from 1 to m), and in that the receiver moreover comprises m auxiliary Kalman filters of rank i, an auxiliary filter of rank i receiving the signals from all the satellites with the exception of the satellite of rank i.

20. The receiver as claimed in claim 2, for a relative position measurement, wherein each digital processing channel associated with a satellite and processing the signals transmitted by this satellite furthermore receives from a mobile reference positioning receiver a correction consisting of a measured pseudo-distance between the satellite and the reference positioning receiver, so as to formulate respectively the first and the second digital datum by differences of the pseudo-distances and in that the cue delivered by the receiver is a relative position with respect to the mobile reference receiver.

21. The receiver as claimed in claim 11, comprising, other Kalman filters termed auxiliary filters of rank j, j integer varying from 1 to M, and M greater than 1, and in that each digital processing channel receives corrections from M reference receivers, and calculates:

an average of the M first corrections and an average of the M second corrections, these averages serving as corrective terms to formulate the first and second digital data for the main filter

for each rank j, an average of M−

1 first corrections and an average of M−

1 second corrections, excluding the corrections arising from the receiver of rank j, these averages serving as corrective terms to formulate the first and second digital data for the filter of rank j.

22. The receiver as claimed in claim 11, comprising means for calculating a protection radius on the basis of the outputs of a single Kalman filter supplied with M observations composed of the differences between a vector of main observations whose m components are equal to the arithmetic average of the M observations by the M reference receivers and the M vectors of average observations whose m components are equal to the arithmetic average of M−

1 observations by the reference receivers, and means for verifying that this protection radius does not exceed a determined threshold.