Horizontal/vertical exclusion level determination scheme for RAIM fault detection and exclusion implementation

• US 6,847,893 B1
• Filed: 01/22/2003
• Issued: 01/25/2005
• Est. Priority Date: 01/22/2003
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Lupash, Lawrence O.
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): To, Tuan C
• Application Number:
  US10/350,390
• Time in Patent Office: 734 Days
• Field of Search: 701/213, 701/214, 701/215, 701/4, 375/371, 455/12.1, 455/427, 455/456.1, 342/357.01, 342/357.12, 342/357.06, 342/353, 342/357.08, 342/457, 340/970, 340/990, 340/995, 702/66
• US Class Current: 701/213
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment

Abstract

A method for satellite receiver autonomous integrity monitoring (RAIM) real time fault detection and exclusion implementation comprising the following steps: (1) continuously computing a horizontal protection level (HPL) and a vertical 32 protection level (VPL) associated with the effective configuration of real time measurement geometry; (2) if the HPL is less than or equal to the horizontal alert limit (HAL), and/or if the VPL is less than or equal to said vertical alert limit (VAL); declaring the RAIM detection function available; (3) continuously computing a horizontal exclusion level (HEL) and continuously computing a vertical exclusion level (VEL) associated with the effective configuration of real time measurement geometry; and (4) if the HEL is less than or equal to the HAL, and/or if the VEL is less than or equal to the VAL, declaring the RAIM fault exclusion function available.

Claims

1. A method for a satellite receiver autonomous integrity monitoring (RAIM) real time fault detection and exclusion implementation for each timing cycle of said satellite receiver;

said method comprising the steps of;

(a) identifying a default set of navigational measurements using a real time available GPS satellite constellation, and acquiring a plurality of GPS satellite signals by using a satellite receiver;

(b) for each timing cycle of said satellite receiver continuously determining an effective configuration of real time measurement geometry adjusted for a normalized weights factor associated with different error sources;

said effective configuration of real time measurement geometry adjusted for said normalized weights factor corresponds to said default set of navigational measurements;

(c) if said number of default navigational measurements is greater than or equal to a first predetermined number, for each timing cycle of said satellite receiver continuously computing a horizontal protection level (HPL) and a vertical protection level (VPL) associated with said effective configuration of real time measurement geometry adjusted for said normalized weights factor; and

(d) if said number of default navigational measurements is less than said first predetermined number, for each timing cycle of said satellite receiver adding an additional measurement to said default set of measurements and repeating said steps (a-c);

wherein said additional measurement is selected from the group consisting of;

{GPS measurement, GLONASS measurement, GALILEO measurement, a baro measurement, a clock measurement, and a pseudolite measurement}.

2. The method of claim 1, wherein said step (c) of continuously computing said horizontal protection level (HPL) and said vertical protection level (VPL) associated with said effective configuration of real time measurement geometry adjusted for said normalized weights factor;

further comprising the steps of;

(e) if said number of available navigational measurements is greater than or equal to said first predetermined number, checking whether said horizontal protection level (HPL) is less than or equal to a horizontal alert limit (HAL), and checking whether said vertical protection level (VPL) is less than or equal to a vertical alert limit (VAL); and

(f) if said number of default navigational measurements is less than said first predetermined number, adding an additional measurement to said set of available measurements, wherein said additional measurement is selected from the group consisting of;

{GPS measurement, GLONASS measurement, GALILEO measurement, a baro measurement, a clock measurement, and a pseudolite measurement}, and repeating said step (e).

3. The method of claim 2, wherein said step (e) of checking whether said horizontal protection level (HPL) is less than or equal to said horizontal alert limit (HAL), and checking whether said vertical protection level (VPL) is less than or equal to said vertical alert limit (VAL) further includes the steps of:

(g) if said horizontal protection level (HPL) is less than or equal to said horizontal alert limit (HAL), and/or if said vertical protection level (VPL) is less than or equal to said vertical alert limit (VAL);

declaring a receiver autonomous integrity monitoring (RAIM) detection function available based on said set of available measurements and declaring said set of available measurements as substantially sufficient;

(h) if said horizontal protection level (HPL) is greater than said horizontal alert limit (HAL), and/or if said vertical protection level (VPL) is greater than said vertical alert limit (VAL), adding an additional measurement to said set of available measurements and repeating said step (g);

wherein said additional measurement is selected from the group consisting of;

{GPS measurement, GLONASS measurement, GALILEO measurement, a baro measurement, a clock measurement, and a pseudolite measurement}; and

(i) if said horizontal protection level (HPL) is greater than said horizontal alert limit (HAL), and/or if said vertical protection level (VPL) is greater than said vertical alert limit (VAL), and if no additional measurement is available to add to said set of available measurements, declaring a receiver autonomous integrity monitoring (RAIM) detection function as not available and declaring said set of available measurements as not substantially sufficient.

4. The method of claim 3, wherein said step (g) of declaring said receiver autonomous integrity monitoring (RAIM) detection function available based on said available set of measurements and declaring said available set of measurements as substantially sufficient further includes the steps of:

(k) if said number of available navigational measurements is greater than or equal to a second predetermined number, for each timing cycle of said satellite receiver, continuously computing a horizontal exclusion level (HEL) and continuously computing a vertical exclusion level (VEL) associated with said effective configuration of real time measurement geometry adjusted for said normalized weights factor; and

(l) if said number of available navigational measurements is less than said second predetermined number, for each timing cycle of said satellite receiver adding an additional measurement to said set of available measurements and repeating said step k;

wherein said additional measurement is selected from the group consisting of;

{GPS measurement, GLONASS measurement, GALILEO measurement, a baro measurement, a clock measurement, and a pseudolite measurement}.

5. The method of claim 4, wherein said step (k) of continuously computing said horizontal exclusion level (HEL) and continuously computing said vertical exclusion level (VEL) further includes the steps of:

(k1) computing said horizontal exclusion level (HEL) by using a prior two-dimensional horizontal plane data obtained in said step (e) of checking whether said horizontal protection level (HPL) is less than or equal to said horizontal alert limit (HAL);

(k2) computing said vertical exclusion level (VEL) by using a prior one-dimensional vertical data obtained in said step (e) of checking whether said vertical protection level (VPL) is less than or equal to said vertical alert limit (VAL);

(k3) if said horizontal exclusion level (HEL) is less than or equal to said horizontal alert limit (HAL), and/or if said vertical exclusion level (VEL) is less than or equal to said vertical alert limit (VAL);

declaring said RAIM fault exclusion function available;

(k4) if said horizontal exclusion level (HEL) is greater than said horizontal alert limit (HAL), and/or if said vertical exclusion level (VEL) is greater than said vertical alert limit (VAL);

adding an additional measurement to said set of available measurements; and

repeating said steps (k1-k3);

wherein said additional measurement is selected from the group consisting of;

{GPS measurement, GLONASS measurement, GALILEO measurement, a baro measurement, a clock measurement, and a pseudolite measurement}; and

(k5) if said horizontal exclusion level (HEL) is greater than said horizontal alert limit (HAL), and/or if said vertical exclusion level (VEL) is greater than said vertical alert limit (VAL), and if no additional measurement is available, declaring said RAIM fault exclusion function not available.

6. The method of claim 5, wherein said step (k1) of computing said horizontal exclusion level (HEL) by using said prior data obtained in said step (e) further includes the steps of:

(k1,

     1) computing said horizontal exclusion level (HEL) by excluding one measurement at a time from said available set of measurements;

(k1,

     2) calculating a horizontal protection level (HPL_k) for each said subset of measurements obtained from said available set of measurements with one excluded measurement; and

(k1,

     3) maximizing said (HPL_k) over all ‘

k’

values;

‘

k’

is an integer less than or equal to the number of available measurements.

7. The method of claim 5, wherein said step (k2) of computing said vertical exclusion level (VEL) by using said prior data obtained in said step (e) further includes the steps of:

(k2,

     1) computing said vertical exclusion level (VEL) by excluding one measurement at a time from said available set of measurements;

(k2,

     2) calculating a vertical protection level (VPL_i) for each said subset of measurements obtained from said available set of measurements with one excluded measurement; and

(f2,

     3) maximizing said (VPL_i) over all ‘

i’

values;

‘

i’

is an integer less than or equal to the number of available measurements.

8. A method for a satellite receiver autonomous integrity monitoring (RAIM) real time fault detection and exclusion implementation by performing at least one re-initialization cycle;

said method comprising the steps of;

(a) identifying a default set of navigational measurements using a real time available GPS satellite constellation, and acquiring a plurality of GPS satellite signals by using a satellite receiver;

(b) performing a re-initialization cycle of said satellite receiver by computing and storing in a HEL/VEL database a plurality of HEL values and a plurality of VEL values for at least two consecutive timing cycles;

each said HEL value corresponding to one said timing cycle;

each said VEL value corresponding to one said timing cycle;

(c) determining and storing in said HEL/VEL database the difference between one said HEL value and a selected threshold HAL for each said re-initialization cycle; and

(d) determining and storing in said HEL/VEL database the difference between one said VEL value and a selected threshold VAL for each said re-initialization cycle.

9. The method of claim 8 further including the steps of:

if said default set of measurements has been updated to include an updated set of measurements by adding or eliminating at least one measurement selected from the group consisting of;

{GPS measurement, GLONASS measurement, GALILEO measurement, a baro measurement, a clock measurement, and a pseudolite measurement};

(e) computing and storing in said HEL/VEL database a plurality of updated HEL values and a plurality of updated VEL values corresponding to said updated set of measurements for at least two consecutive timing cycles;

each said updated HEL value corresponding to one said timing cycle;

each said updated VEL value corresponding to one said timing cycle;

(f) determining and storing in said HEL/VEL database the difference between one said updated HEL value and a selected threshold HAL for each said re-initialization cycle; and

(g) determining and storing in said HEL/VEL database the difference between one said updated VEL value and a selected threshold VAL for each said re-initialization cycle.

10. The method of claim 8 further including the steps of:

if said user dynamics exceed a pre-determined dynamics, or if said user is pre-selecting a high dynamics option;

(e) computing and storing in said HEL/VEL database a plurality of updated HEL values and a plurality of updated VEL values corresponding to said high dynamics option for at least two consecutive timing cycles;

each said updated HEL value corresponding to one said timing cycle;

each said updated VEL value corresponding to one said timing cycle;

(f) determining and storing in said HEL/VEL database the difference between one said updated HEL value and a selected threshold HAL for each said re-initialization cycle; and

(g) determining and storing in said HEL/VEL database the difference between one said updated VEL value and a selected threshold VAL for each said re-initialization cycle.

11. The method of claim 8 further including the steps of:

if a plurality of last stored HEL/VEL values includes a plurality of ‘

old’

HEL/VEL values, that is if each said ‘

old’

HEL value was updated at least at an absolute timing coordinate greater than a predetermined timing coordinate, and/or if each said ‘

old’

VEL value was updated at least at an absolute timing coordinate greater than said predetermined timing coordinate;

(e) computing and storing in said HEL/VEL database a plurality of updated HEL values and a plurality of updated VEL values for at least two consecutive timing cycles;

each said updated HEL value corresponding to one said timing cycle;

each said updated VEL value corresponding to one said timing cycle;

(f) determining and storing in said HEL/VEL database the difference between one said updated HEL value and a selected threshold HAL for each said re-initialization cycle; and

(g) determining and storing in said HEL/VEL database the difference between one said updated VEL value and a selected threshold VAL for each said re-initialization cycle.

12. The method of claim 8 further including the steps of:

if a plurality of last computed HEL/VEL values includes a plurality of HEL values and a plurality of VEL values, and at least one said last computed HEL value is greater than or equal to a selected threshold HAL; and

/or at least one said last computed VEL value is greater than or equal to a selected threshold VAL;

(e) computing and storing in said HEL/VEL database a plurality of updated HEL values and a plurality of updated VEL values for at least two consecutive timing cycles;

each said updated HEL value corresponding to one said timing cycle;

each said updated VEL value corresponding to one said timing cycle;

(f) determining and storing in said HEL/VEL database the difference between one said updated HEL value and a selected threshold HAL for each said re-initialization cycle; and

(g) determining and storing in said HEL/VEL database the difference between one said updated VEL value and a selected threshold VAL for each said re-initialization cycle.

13. The method of claim 8 further including the step of:

if a plurality of last computed HEL/VEL values includes a plurality of HEL values and a plurality of VEL values computed at a prior timing cycle;

executing the process of prediction of a plurality of predicted HEL/VEL values based on said HEL/VEL database, wherein each said predicted HEL value is extrapolated from at least two said prior HEL values stored in said HEL/VEL database;

wherein each said predicted VEL value is extrapolated from at least two said prior VEL values stored in said HEL/VEL database.

14. The method of claim 13, wherein said step of executing the process of prediction of said plurality of predicted HEL/VEL values further includes the steps of:

extrapolating each said predicted HEL value from at least two said prior HEL values stored in said HEL/VEL database by using a linear extrapolation; and

extrapolating each said predicted VEL value from at least two said prior VEL values stored in said HEL/VEL database by using said linear extrapolation.

15. The method of claim 13, wherein said step of executing the process of prediction of said plurality of predicted HEL/VEL values further includes the steps of:

extrapolating each said predicted HEL value from at least two said prior HEL values stored in said HEL/VEL database by using a cubic extrapolation; and

extrapolating each said predicted VEL value from at least two said prior VEL values stored in said HEL/VEL database by using said cubic extrapolation.

16. The method of claim 13, wherein said step of executing the process of prediction of said plurality of predicted HEL/VEL values further includes the steps of:

extrapolating each said predicted HEL value from at least two said prior HEL values stored in said HEL/VEL database by using a spline prediction method; and

extrapolating each said predicted VEL value from at least two said prior HEL values stored in said HEL/VEL database by using said spline prediction method.

17. The method of claim 13, wherein said step of executing the process of prediction of said plurality of predicted HEL/VEL values further includes the steps of:

extrapolating each said predicted HEL value from at least two said prior HEL values stored in said HEL/VEL database by using a fuzzy logic method; and

extrapolating each said predicted VEL value from at least two said prior HEL values stored in said HEL/VEL database by using said fuzzy logic method.

18. The method of claim 13 further including the steps of:

if a plurality of predicted HEL/VEL values includes a plurality of HEL values and a plurality of VEL values, and if each said predicted HEL is greater than or within a selected interval around a predetermined HAL; and

/or if each said predicted VEL is greater than or within said selected interval around a predetermined VAL;

computing and storing in said HEL/VEL database a plurality of updated HEL values and a plurality of updated VEL values for at least two consecutive timing cycles;

each said updated HEL value corresponding to one said timing cycle;

each said updated VEL value corresponding to one said timing cycle;

determining and storing in said HEL/VEL database the difference between one said updated HEL value and a selected threshold HAL for each said re-initialization cycle; and

determining and storing in said HEL/VEL database the difference between one said updated VEL value and a selected threshold VAL for each said re-initialization cycle.