Adaptive threshold logic implementation for RAIM fault detection and exclusion function

• US 6,798,377 B1
• Filed: 05/31/2003
• Issued: 09/28/2004
• Est. Priority Date: 05/31/2003
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Lupash, Lawrence O., Wlad, Joseph
• Primary Examiner(s): Issing, Gregory C.
• Assistant Examiner(s): Mull, Fred H
• Application Number:
  US10/449,340
• Time in Patent Office: 486 Days
• Field of Search: 342/357.02, 342/357.06, 342/357.13, 342/357.14
• US Class Current: 342/357.29
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/33 Multimode operation in different systems which transmit time stamped messages, e.g. GPS/GLONASS

Abstract

A method for improving a satellite receiver autonomous integrity monitoring (RAIM) availability and fault detection and exclusion (FDE) function by using an adaptive threshold logic. The method comprises the following steps: (A) pre-computing a database of thresholds; (B) selecting in real time from the database a plurality of thresholds corresponding to a set of available measurements; and (C) determining an optimum RAIM/FDE function corresponding to the set of available measurements by using the adaptive threshold logic that utilizes the plurality of thresholds corresponding to the set of available measurements. The set of available measurements is selected from the group consisting of: {a GPS measurement, a GLONASS measurement, a GALILEO measurement, a baro measurement, a clock measurement, and a pseudolite measurement}.

Claims

1. A method for improving a satellite autonomous integrity monitoring (RAIM) availability and fault detection and exclusion (FDE) function by using an adaptive threshold logic;

said method comprises the steps of;

(A) pre-computing a database of thresholds including multiple sets of thresholds;

(B) selecting in real time from said database one set of thresholds, the set comprising a plurality of thresholds corresponding to a set of available measurements; and

(C) determining an optimum RAIM/FDE function corresponding to said set of available measurements by using said adaptive threshold logic that utilizes said plurality of thresholds corresponding to said set of available measurements;

wherein said set of available measurements is selected from the group consisting of;

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

2. The method of claim 1, wherein said step (A) of pre-computing said database of thresholds including said multiple sets of thresholds further includes the steps of:

(A1) selecting a navigation scenario from the group consisting of;

{a Standard Positioning System (SPS) navigation scenario;

a Precise Positioning System (PPS) navigation scenario; and

a navigation scenario including a combination of said SPS navigation scenario and said PPS navigation scenario}; and

(A2) generating a table of thresholds for said selected navigation scenario.

3. The method of claim 2;

wherein said step of (A1) of selecting said navigation scenario further includes the step of;

(A1,

     1) determining a degree of freedom parameter (dof) for said selected navigation scenario, wherein said dof is equal to an integer K of available measurements corresponding to said selected navigation scenario minus four measurements; and

wherein said integer K of available measurements corresponding to said selected navigation scenario is selected from the group consisting of;

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

and wherein said step (A2) of generating said table of thresholds for said selected navigation scenario further includes the steps of;

(A2,

     1) selecting a probability of false alert (pfa) for said selected navigation scenario;

(A2,

     2) selecting a probability of missed detection (pmd)for said selected navigation scenario; and

(A2,

     3) selecting a probability of false exclusion (pfe) for said selected navigation scenario.

4. The method of claim 3 further including the steps of:

(A2,

     4) for each said degree of freedom parameter (dof), using said probability of false alert (pfa) to determine a table of fault detection (FD) normalized thresholds (td_table of T_D); and

(A2,

     5) for each said degree of freedom parameter (dof), using said table of fault detection normalized thresholds (td_table of T_D), using said probability of missed detection (pmd), and using said probability of false alert (pfa) to determine a table of normalized thresholds for fault detection availability (pb_table of pbiasb) based on a parity vector method.

5. The method of claim 3 further including the step of

(A2, 6) for each said degree of freedom parameter (dof), using said probability of false exclusion (pfe) to determine a table of fault exclusion (FE) normalized thresholds (te_table of T_E).

6. The method of claim 1, wherein, for each timing cycle of said satellite receiver, said step of (C) determining said optimum RAIM/FDE function corresponding to said set of available measurements by using said adaptive threshold logic further includes the steps of:

(C1) identifying a default set of available measurements by using a real time available GPS satellite constellation, and acquiring a plurality of GPS satellite signals by using a satellite receiver;

(C2) if said number of default available measurements is greater than or equal to a first predetermined number, substantially continuously determining said optimum RAIM/FDE function corresponding to said set of available measurements; and

(C3) if said number of default available measurements is less than said first predetermined number, and if at least one additional measurement is available, adding said at least one additional measurement to said set of available measurements and repeating said steps (C1-C3);

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}.

7. The method of claim 6, wherein, for each timing cycle, said step (C2) of continuously determining said optimum RAIM/FDE function corresponding to said set of available measurements further includes the steps of:

(C2,

     1) counting an integer L of timing cycles by using a counter;

(C2,

     2) tracking said set of used available measurements; and

(C2,

     3) if said integer L of timing cycles is not a multiple of a second predetermined number, or if said integer L of timing cycles is not equal to one;

or if said set of tracked used available measurements does not change from a prior timing cycle, starting the process of determining said optimum RAIM/FDE function.

8. The method of claim 6, wherein, for each timing cycle, said step (C2) of continuously determining said optimum RAIM/FDE function corresponding to said set of available measurements further includes the steps of:

(C2,

     1) counting an integer L of timing cycles by using a counter;

(C2,

     2) tracking said set of used available measurements; and

(C2,

     3) if said integer L of timing cycles is a multiple of said second predetermined number, or if said integer L of timing cycles is equal to one;

or if said set of tracked used available measurements does change from a prior timing cycle, starting a process of selecting a set of adaptive thresholds.

9. The method of claim 8, wherein said step (C2, 3) of selecting said set of adaptive thresholds further includes the steps of:

determining a set of measurement weights;

checking if there is an operator'"'"'s overrule command;

if there is no operator'"'"'s overrule command, determining a composite weighting scalar factor by using said set of measurement weights;

based on said composite weighting scalar factor, selecting a navigation scenario from the group consisting of;

{a Standard Positioning System (SPS) navigation scenario;

a Precise Positioning System (PPS) navigation scenario; and

a navigation scenario including a combination of said SPS navigation scenario and said PPS navigation scenario}; and

based on said selected navigation scenario, and based on said degree of freedom (dof), selecting from said pre-computed off-line database of thresholds a set of thresholds including said table of fault detection (FD) normalized thresholds (td_table of T_D);

including said table of fault exclusion (FE) normalized thresholds (te_table of T_E); and

including said table of normalized thresholds for fault detection availability (pb_table of pbiasb).

10. The method of claim 8, wherein said step (C2, 3) of selecting said set of adaptive thresholds further includes the steps of:

determining a set of measurement weights;

checking if there is an operator'"'"'s overrule command;

if there is an operator'"'"'s overrule command, based on said operator'"'"'s overrule command, selecting a navigation scenario from the group consisting of;

{a Standard Positioning System (SPS) navigation scenario;

a Precise Positioning System (PPS) navigation scenario; and

a navigation scenario including a combination of said SPS navigation scenario and said PPS navigation scenario}; and

based on said selected navigation scenario, and degree of freedom (dof), selecting from said pre-computed off-line database of thresholds a set of thresholds including said table of fault detection (FD) normalized thresholds (td_table of T_D);

including said table of fault exclusion (FE) normalized thresholds (te_table of T_E); and

including said table of normalized thresholds for fault detection availability (pb_table of pbiasb).

11. The method of claim 9, wherein said step of determining said set of measurement weights further includes the steps of:

decoding from a received GPS navigation message a user range accuracy (URA) index for each said satellite measurement that is used in a navigation solution;

determining a user range error (URE) corresponding to a plurality of errors selected from the group consisting of {a plurality of space segment errors; and

a plurality of control segment errors} for said URA index for each said satellite measurement;

evaluating a user equipment error (UEE) corresponding to a plurality of errors selected from the group consisting of {a receiver noise error;

a multipath error;

a ionosphere delay uncompensated error; and

a troposphere delay uncompensated error} for each said satellite measurement; and

determining a user equivalent range error (UERE) based on said calculated URE and based on said calculated UEE for said URE value for each said satellite measurement.