Method for navigation of moving platform by using satellite data supplemented by satellite-calibrated baro data

• US 6,205,377 B1
• Filed: 04/27/1999
• Issued: 03/20/2001
• Est. Priority Date: 04/27/1999
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Wlad, Joseph M., Lupash, Lawrence O.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Beaulieu, Yonel
• Application Number:
  US09/300,934
• Time in Patent Office: 693 Days
• Field of Search: 701/13, 701/200, 701/207, 701/213, 701/214, 701/215, 342/357.06, 342/357.08, 342/357.11, 342/357.12, 342/357.15, 455/12.1, 455/13.2
• US Class Current: 701/13
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/45 by combining measurements of signals from the satellite radio beacon positioning system with a supplementary measurement

Abstract

The method of supplementing the satellite data by the satellite-calibrated baro data when the receiver autonomous integrity monitoring function (RAIM) is unavailable and when the horizontal protection level (HPL) does not satisfy the horizontal alert limit (HAL) requirement is disclosed. The baro data is calibrated with satellite data if maximum weighted vertical dilution of precision with one satellite removed at one time (max {SubWVDOP}) is less than a predetermined threshold (TSUB) and if a test statistic is less than a predetermined test statistic threshold (TST). The HPL is re-computed using the satellite-calibrated baro data. The re-computed HPL could satisfy the HAL requirement which would make the RAIM function available when it would be otherwise unavailable.

Claims

1. A method for satellite supplementary navigation of a moving platform using a satellite data supplemented by a satellite- calibrated baro data;

said moving platform including a satellite receiver and a barosensor;

said method comprising the steps of;

(a) checking whether a satellite configuration is substantially sufficient;

(b) if said satellite configuration is substantially sufficient, acquiring a plurality of satellite signals from said substantially sufficient satellite configuration;

(c) checking whether a set of satellite data obtained from said substantially sufficient satellite configuration utilizing said satellite receiver is substantially sufficient;

(d) if said satellite configuration is substantially sufficient, and if said satellite data obtained from said substantially sufficient satellite configuration utilizing said satellite receiver is substantially sufficient, utilizing said satellite data for obtaining position fixes of said moving platform; and

(e) if said satellite configuration is not substantially sufficient, or if said satellite data obtained from said substantially sufficient satellite configuration is not substantially sufficient, supplementing said satellite data by said satellite-calibrated baro data obtained utilizing said barosensor.

2. The method of claim 1, wherein said step of checking whether said satellite configuration is substantially sufficient further includes the steps of:

continuously determining a number N of visible satellites being tracked by said satellite receiver, N being an integer; and

declaring said satellite configuration as substantially sufficient if said number N of satellites being tracked is greater than a predetermined number K, K being an integer.

3. The method of claim 1, wherein said step of checking whether said satellite configuration is substantially sufficient further includes the steps of:

continuously determining a number N of visible GPS satellites being tracked by a GPS receiver, N being an integer; and

declaring said satellite configuration as substantially sufficient if said number N of GPS satellites being tracked is greater than a predetermined number 4 for a three-dimensional determination of position fixes of said moving platform.

4. The method of claim 1, wherein said step of checking whether said satellite configuration is substantially sufficient further includes the steps of:

continuously determining a number N of visible GPS satellites being tracked by said GPS receiver, N being an integer; and

declaring said satellite configuration as substantially sufficient if said number N of GPS satellites being tracked is greater than a predetermined number 3 for a two-dimensional determination of position fixes of said moving platform.

5. The method of claim 1, wherein said step of checking whether said satellite data obtained from said substantially sufficient satellite configuration is substantially sufficient further includes the steps of:

continuously computing a horizontal protection level (HPL) and a vertical protection level (VPL);

checking whether said horizontal protection level (HPL) is less than a horizontal alert limit (HAL);

if said horizontal protection level (HPL) is less than said horizontal alert limit (HAL), declaring a receiver autonomous integrity monitoring (RAIM) function available and declaring said satellite data obtained by using said satellite receiver as substantially sufficient for obtaining position fixes of said moving platform;

and

if said horizontal protection level (HPL) is greater than said horizonal alert limit (HAL), declaring said receiver autonomous integrity monitoring (RAIM) function unavailable and declaring said satellite data obtained by using said satellite receiver as not substantially sufficient for obtaining position fixes of said moving platform.

6. The method of claim 5, wherein said step of supplementing said satellite data by said satellite-calibrated baro data further includes the steps of:

checking whether said baro data is satellite-calibrated;

if said baro data is satellite-calibrated, adding said satellite-calibrated baro data to said satellite data to recompute said horizontal protection level (HPL) in order to obtain a baro-calibrated horizontal protection level (HPL_baro) and in order to activate said receiver autonomous integrity monitoring (RAIM) function;

checking whether said baro-calibrated horizontal protection level (HPL_baro is less than said horizontal alert limit (HAL);

if said baro-calibrated horizontal protection level (HPL_baro) is less than said horizontal alert limit (HAL), declaring said receiver autonomous integrity monitoring (RAIM) function available; and

if said baro data is not satellite-calibrated, declaring said receiver autonomous integrity monitoring (RAIM) function unavailable.

7. The method of claim 5, wherein said step of supplementing said satellite data by said satellite-calibrated baro data further includes the step of:

calibrating said baro data with said satellite data.

8. The method of claim 7, wherein said step of calibrating said baro data with said satellite data further includes the steps of:

checking whether a raw baro data is available and valid;

if said raw baro data is available and valid, computing a maximum weighted vertical dilution of precision with one satellite removed at one time (max {SubWVDOP});

checking whether said max {SubWVDOP} is less than a predetermined threshold (TSUB);

if said max {SubWVDOP} is less than said TSUB, checking whether a test statistic is less than a predetermined test threshold (TST);

if said max {SubWVDOP} is less than said TSUB and if said test statistic is less than said TST, calibrating said satellite data with said baro data; and

if max {SubWVDOP} is greater than said TSUB, or if said test statistic is greater than said TST, declaring said satellite data as unfit for calibrating said raw baro data.

9. The method of claim 8, wherein said step of computing said maximum weighted vertical dilution of precision with one satellite removed at one time (max {SubWVDOP}) further includes the steps of:

using a pre-computed vertical protection level (VPL) in each configuration of said visible satellites for computation of a vertical slope maximum (VSLOPEMAX), wherein said vertical slope maximum (VSLOPEMAX) is a maximum vertical slope of said visible satellites;

identifying an estimated vertical error (EVE) for said visible satellites;

inputting said pre-computed vertical slope maximum (VSLOPEMAX) and said pre-computed estimated vertical error (EVE);

computing an unnormalized maximum weighted vertical dilution of precision with one satellite removed at one time Un_normalized_max {SubWVDOP} for said visible satellites by utilizing said EVE and said VSLOPEMAX; and

computing a normalized maximum weighted vertical dilution of precision Normalized_max {SubWVDOP} by using said Un_normalized_max {SubWVDOP}.

10. The method of claim 5, wherein said step of supplementing said satellite data by said satellite-calibrated baro data further includes the step of:

calibrating said baro data with a GPS satellite data.

11. The method of claim 10, wherein said step of calibrating said baro data with said GPS data further includes the steps of:

checking whether a raw baro data is available and valid;

if said raw baro data is available and valid, computing a maximum weighted vertical dilution of precision with one satellite removed at one time (max {SubWVDOP});

checking whether said max {SubWVDOP} is less than a predetermined threshold (TSUB);

if said max {SubWVDOP} is less than said TSUB, checking whether a test statistic is less than a predetermined test threshold (TST);

if said max {SubWVDOP} is less than said TSUB and if said test statistic is less than said TST, calibrating said GPS data with said baro data; and

if max {SubWVDOP} is greater than said TSUB, or if said test statistic is greater than said TST, declaring said GPS data as unfit for calibrating said raw baro data.

12. The method of claim 11, wherein said step of computing said maximum weighted vertical dilution of precision with one GPS satellite removed at one time (max {SubWVDOP}) further includes the steps of:

using a pre-computed vertical protection level (VPL) in each configuration of said visible GPS satellites for computation of a vertical slope maximum (VSLOPEMAX), wherein said vertical slope maximum (VSLOPEMAX) is a maximum vertical slope of said visible GPS satellites;

identifying an estimated vertical error (EVE) for said visible GPS satellites;

inputting said pre-computed vertical slope maximum (VSLOPEMAX) and said pre-computed estimated vertical error (EVE);

computing an unnormalized maximum weighted vertical dilution of precision with one GPS satellite removed at one time Un_normalized_max {SubWVDOP} for said visible GPS satellites by utilizing said EVE and said VSLOPEMAX; and

computing a normalized maximum weighted vertical dilution of precision Normalized_max {SubWVDOP} by using said Un_normalized_max {SubWVDOP}.