VEHICLE NAVIGATION SYSTEM WITH DEAD RECKONING

• US 20130116921A1
• Filed: 11/05/2012
• Published: 05/09/2013
• Est. Priority Date: 11/03/2011
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: KASARGOD, Sandeep, RAO, Sandeep, RAMASUBRAMANIAN, Karthik, PANDE, Tarkesh, MURALI, Sriram
• Granted Patent: US 8,825,397 B2
• Time in Patent Office: Days
• US Class Current: 701/472
• CPC Class Codes: G01C 21/12 executed aboard the object being navigated; Dead reckoning
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 19/45 by combining measurements of signals from the satellite radio beacon positioning system with a supplementary measurement

Abstract

A vehicle navigation system includes a GNSS position engine (GPE) that uses GNSS satellite measurements to compute a first position and velocity of a vehicle and a first quality metric associated with the position and velocity. The system also includes a dead reckoning engine (DRE) that operates parallel with the GPE that computes a second position and velocity and a second quality metric associated with the dead reckoning. The GPE is configured to use the second position and velocity to detect a set of outliers in an incoming GNSS measurement; use the second position and velocity as an initial estimate of its position and velocity for a particular time instant, which is then refined by GNSS measurements received at that particular time instant; and to replace the first position and velocity with the second position and velocity.

Claims

1. A vehicle navigation system comprising:

a GNSS position engine (GPE) that uses GNSS satellite measurements to compute a first position and velocity of a vehicle and a first quality metric associated with the position and velocity;

a dead reckoning engine (DRE) that operates parallel with the GPE, and computes a second position and velocity and a second quality metric associated with the dead reckoning;

wherein in the GPE is configured to;

use the second position and velocity to detect a set of outliers in an incoming GNSS measurement;

use the second position and velocity as an initial estimate of its position and velocity for a particular time instant, which is then refined by GNSS measurements received at that particular time instant; and

replace the first position and velocity with the second position and velocity.

2. The vehicle navigation system of claim 1, wherein the DRE is configured to seed its dead reckoning with the first position and velocity.

3. The vehicle navigation system of claim 2, wherein the DRE is configured to compare the first quality metric with the second quality metric prior to reseeding its position and velocity with the position and velocity of the GPE, and configured to check if the GPEs recent fixes, including a current one, correspond to a trajectory on a map network.

4. The vehicle navigation system of claim 1, wherein the GPE detects the set of outliers in the incoming GNSS measurements by checking the consistency between each of the psuedorange measurements and the position computed by the DRE;

and by checking the consistency between each of the pseudorange rate measurements and the velocity computed by the DRE.

5. The vehicle navigation system of claim 1, wherein, the GPE and the satellite receiver chain is configured to be in a sleep state for a period of time to save power.

6. The vehicle navigation system of claim 5, wherein the GPE and the satellite receiver chain is configured to be in an active state after the sleep state based on one of a fixed period, based on one of a condition:

when the quality of the DREs position as determined by the second quality metric falls below a threshold;

when the DRE is approaching an intersection where the difference in degrees between possible turns is less than another threshold; and

when the DRE is approaching a set of intersections where the distance between consecutive intersections is less than yet another threshold.

7. The vehicle navigation system of claim 5, wherein the first and second quality metric is computed in units of distance.

8. A method of computing a quality metric for a sensor and map based dead reckoning in a vehicle navigation system, comprising:

initializing a position uncertainty of a dead reckoned position that seeds dead reckoning;

increasing the position uncertainty by a fraction of a distance travelled along a road segment when the vehicle is traveling in a current road segment;

increasing the position uncertainty by a certain amount when a lane change by the vehicle is detected; and

reinitializing the position uncertainty when a new road segment is identified subsequent to a turn from the current road segment, wherein the quality metric is used in conjunction with sensor information from the vehicle, a map database and GNSS measurements for accurate positioning of the vehicle navigation system.

9. The method of claim 8, wherein the sensor and map based dead reckoning comprises:

receiving, at a dead reckoning engine, a start of a turn signal when the vehicle starts a turn on a current road segment;

storing a last known position of the vehicle;

receiving an end of turn signal when the vehicle finishes the turn; and

identifying, from a map database, a nearest intersection in the current road segment and the next road segment at this intersection based on satisfaction of a set of conditions;

10. The method of claim 9, wherein the set of conditions comprises:

checking if the nearest intersection is within a first threshold from the last known position of the vehicle, wherein the first threshold is based on distance;

checking if there is a turn at the nearest intersection that matches with a cumulative angle of the turn within a second threshold, wherein the second threshold is based on the cumulative angle; and

checking to confirm that there are no other turns than the turn at the nearest intersection, within a certain angle of the turn.

11. The method of claim 9, wherein a turn detection engine generates the start of a turn signal and the end of a turn signal and calculates the cumulative angle.

12. The method of claim 8, wherein increasing the position uncertainty by a fraction of a distance travelled along a road segment comprises calculating the fraction by calibrating a wheel tick sensor that provides a speed input.

13. The method of claim 8, wherein generating the start of a turn signal comprises:

monitoring a sequence of yaw rate readings from a gyroscope;

generating the start of the turn signal when a set of parameters exceeds a third threshold, wherein the set of parameters comprises one of a cumulative turn in time or distance and yaw rate readings.

14. The method of claim 8, wherein generating the end of turn signal comprises:

accumulating the sequence of yaw rate readings;

detecting an end of turn event when a set of parameters falls below a fourth threshold, wherein the set of parameters comprises one of a cumulative turn in time or distance and yaw rate readings.

15. A method of removing erroneous satellite measurements in a vehicle navigation system, comprising:

identifying a direction of a vehicle at an instant;

calculating a sequence of displacements, at one or more subsequent instances, from an initial position of the vehicle using speed and yaw rate measurements;

using the sequence of displacements to relate a set of GNSS pseudorange measurements from the instant to the one or more subsequent instances, to the initial position of the vehicle navigation system;

detecting and removing inconsistent GNSS psuedorange measurements; and

using a set of remaining psuedorange measurements to compute the initial position of the vehicle navigation system.

16. The method of claim 15, wherein the method of identifying a direction of a vehicle at an instant, comprises:

calculating a sequence of headings, at one or more subsequent instances, in terms of the heading of the vehicle at that instant, using yaw rate measurements;

using the sequence of headings to relate a set of GNSS Doppler measurements from the instant to one or more subsequent instances, to the initial heading of the vehicle at the instant

detecting and removing inconsistent GNSS Doppler measurements; and

using a set of remaining doppler measurements to compute the initial direction of the vehicle.