Search

US-20260126553-A1 - METHOD FOR MONITORING THE INTEGRITY OF A PLURALITY OF PSEUDORANGE MEASUREMENTS ACQUIRED BY A NAVIGATION SYSTEM

US20260126553A1US 20260126553 A1US20260126553 A1US 20260126553A1US-20260126553-A1

Abstract

This method for monitoring the integrity of a plurality of pseudorange measurements acquired by a navigation system from signals transmitted by a constellation of satellites includes: a first calculation, for each satellite of the constellation, of a first innovation (Inno) reflecting the deviation between the measured pseudorange from said satellite and a value of said pseudorange estimated after the event, produced by a Kalman filter; a first update of each first innovation (Inno); a second calculation of a first group of first test values (CM); maintaining the set of measured pseudoranges so as to calibrate the Kalman filter if all of the first test values (CM) are less than a first predetermined threshold, otherwise implementing a processing step.

Inventors

  • Yves BECHERET

Assignees

  • SAFRAN ELECTRONICS & DEFENSE

Dates

Publication Date
20260507
Application Date
20231002
Priority Date
20221003

Claims (10)

  1. 1 . A method for monitoring the integrity of a plurality of pseudorange measurements acquired by a navigation system from signals transmitted by a constellation of satellites, comprising the following steps: a step of a first calculation, for each satellite of the constellation, of a first innovation (Inno) reflecting the deviation between the measured pseudorange from said satellite and a value of said pseudorange estimated after the event, produced by a filter; a step of a first update of each first innovation depending on the mean of all of the first innovations so as to constitute a second innovation with which a variance is associated, the variance being equal to the mathematical expectation of the squares of the deviations from the mean of the second innovations; a step of a second calculation of a first group of first test values depending on all of the second innovations (Inno) and the variances thereof; a step of comparing all of the first test values with a first predetermined threshold; a step of maintaining the set of measured pseudoranges so as to calibrate the filter from the set of pseudoranges if all of the first test values are less than a first predetermined threshold; and a step of implementing a processing step if one of the first test values is greater than said first threshold, the implementation step comprising the following steps: a step of removing the set of pseudoranges of the pseudorange of which the second innovation is associated with the first highest test value as well as the first innovation that is associated with it from all of the first innovations; a step of a second update of each first innovation (Inno) depending on the mean of all of the first remaining innovations so as to constitute a third innovation with which a variance is associated, the variance being equal to the mathematical expectation of the squares of the deviations from the mean of the third innovations; a step of calculating a second group of second test values depending on the third innovations and the respective variances thereof; a step of comparing the second test values with said first predetermined threshold; a step of maintaining the remaining pseudoranges so as to calibrate the filter if all of the second test values are less than said first predetermined threshold; and a step of transmitting an alarm signal to the navigation system if at least one second test value is greater than said first predetermined threshold.
  2. 2 . Method according to claim 1 , wherein a notification is transmitted to the navigation system so as to configure the filter according to nominal ionospheric conditions when all of the first test values are less than a second predetermined threshold.
  3. 3 . Method according to claim 1 , wherein the alarm signal is transmitted to the navigation system so as to configure the filter according to degraded ionospheric conditions.
  4. 4 . Method according to claim 1 , wherein the satellite of which the pseudorange has been removed is excluded for an adjustable time.
  5. 5 . Method according to claim 1 , wherein the filter is a main filter.
  6. 6 . Device for monitoring the integrity of a plurality of pseudorange measurements acquired by a navigation system from signals transmitted by a constellation of satellites, the device comprising: calculation means capable, for each satellite of the constellation, of calculating a first innovation reflecting the deviation between the measured pseudorange from said satellite and a value of said pseudorange estimated after the event, produced by a filter, wherein the device comprises: means for updating each first innovation depending on the mean of all of the first innovations so as to constitute a second innovation with which a variance is associated, the variance being equal to the mathematical expectation of the squares of the deviations with the mean of the second innovations; a calculation unit capable of calculating a first group of first test values depending on all of the second innovations and the variances thereof; and processing means capable of comparing all of the first test values with a first predetermined threshold and of maintaining the set of measured pseudoranges so as to calibrate the filter if all of the first test values are less than a first predetermined threshold, the processing means being capable, if one of the first test values is greater than said first threshold, of performing: removing the pseudorange of which the second innovation is associated with the first highest test value as well as the first innovation associated with it; a second update of each first innovation depending on the mean of all of the first innovations so as to constitute a third innovation with which a variance is associated, the variance being equal to the mathematical expectation of the squares of the deviations from the mean of the third innovations; calculating a second group of second test values depending on the third innovations and the respective variances thereof; comparing the second test values with said first predetermined threshold; maintaining the remaining pseudoranges so as to calibrate the filter if all of the second test values are less than said first predetermined threshold; and transmitting an alarm signal to the navigation system if at least one second test value is greater than said first predetermined threshold.
  7. 7 . Device according to claim 6 , comprising transmission means intended to send a notification to the navigation system so as to configure the filter according to nominal ionospheric conditions when all of the first test values are less than a second predetermined threshold.
  8. 8 . Device according to claim 6 , wherein the processing means are capable of transmitting the alarm signal to the navigation system so as to configure the filter according to degraded ionospheric conditions.
  9. 9 . Device according to claim 6 , wherein the processing means are capable of excluding for an adjustable time the satellite of which the pseudorange has been removed.
  10. 10 . A navigation system comprising a receiver capable of acquiring pseudorange measurements from signals transmitted by a constellation of satellites, and a device for monitoring the integrity of said measurements according to claim 6 .

Description

TECHNICAL FIELD The present invention relates to satellite navigation systems and pertains more particularly to the detection and exclusion of faulty satellites. PRIOR ART The guidance systems currently used in automotive, avionics or even maritime navigation are generally hybrid INS/GNSS (‘Inertial Navigation System’ and ‘Global Navigation Satellite System’) equipment. This hybrid equipment simultaneously uses two measurement sources of physical variables intended to be used so as to provide the location data necessary for the navigation of the vehicle. A first measurement source may be an inertial system of which the physical variables are acquired by inertial sensors such as accelerometers or gyroscopes. Such measurements are subsequently exploited so as to provide accurate location, speed and orientation data in the short term which, nevertheless, tend to drift in the long term. To circumvent this problem, a second measurement source may be a constellation of satellites that thus deliver accurate data in the long term but of which the processing retains noise and therefore makes the operation thereof difficult. These satellite data are known as ‘pseudoranges’ and make it possible to obtain the associated positions and dates of the receiving antenna of the vehicle. To combine the data from said measurement sources, guidance (or navigation) systems generally include a bank of Kalman filters. More precisely, the bank of Kalman filters includes a main filter intended to use the set of pseudoranges, and a series of secondary filters using only part of the available pseudoranges. Nevertheless, when one of the satellites of said constellation is faulty, the satellite signal that it transmits may lead to pseudorange measurement errors. To protect against a possible satellite failure and the consequences thereof, the Kalman filter is configured to determine a reset value so as to reduce the influence of errors associated with degraded satellite signals. The reset value is then generated by comparing a measurement external to the filter, known as an observation, with a measurement processed by said filter. The deviation between the two measurements is known as ‘innovation’ and thus serves as a reset value. There are a plurality of algorithms intended to process a set of observations. By way of example, the object of the so-called ‘separation’ algorithm is to perform, for each reset cycle, intermediate innovation tests. Each observation is then dependent on the previous observations. However, such an algorithm may lead to more or less significant consequences depending on the order for processing the erroneous pseudorange. Thus, if the measurement of the erroneous pseudorange is processed in the last position by this algorithm, the reset value will be consistent. Nevertheless, when said measurement is processed first by the algorithm, the error propagates through the successive intermediate innovation tests. The variance of the innovations is then higher and the erroneous pseudoranges become difficult to detect. A first solution consists in modifying the program instructions of this algorithm to compare each pseudorange measurement acquired by the navigation system with the same measurement processed by the filter and which is associated with the observation processed first. Nevertheless, the standard deviation of innovations is higher. The reset values are then dispersed and random. There is therefore a need to improve the detection and exclusion of faulty satellites before navigation begins. DISCLOSURE OF THE INVENTION In view of the foregoing, the object of the invention is a method for monitoring the integrity of a plurality of pseudorange measurements acquired by a navigation system from signals transmitted by a constellation of satellites, comprising: a first calculation, for each satellite of the constellation, of a first innovation reflecting the deviation between the measured pseudorange from said satellite and a value of said pseudorange estimated after the event, produced by a filter;a first update of each first innovation depending on the mean of all of the first innovations so as to constitute a second innovation with which a variance is associated, the variance being equal to the mathematical expectation of the squares of the deviations from the mean of the second innovations;a second calculation of a first group of first test values depending on all of the second innovations and the variances thereof,maintaining the set of measured pseudoranges so as to calibrate the filter from the set of pseudoranges if all of the first test values are less than a first predetermined threshold, otherwise implementing a processing step that comprises the following sub-steps: removing the set of pseudoranges of the pseudorange of which the second innovation is associated with the first highest test value as well as removing the first innovation associated with it from all of the first innovations;a second up