SYSTEMS AND METHODS FOR CALIBRATING UNSTABLE SENSORS

• US 20170363423A1
• Filed: 08/31/2017
• Published: 12/21/2017
• Est. Priority Date: 09/09/2016
• Status: Active Grant

• Current Assignee: NextNav, LLC
• Original Assignee: NextNav, LLC
• Inventors: DORMODY, Michael, PATTABIRAMAN, Ganesh, KUMAR, Abijith, WOLF, Thomas, PARSONS, Gary, GATES, Christian, JOSEPH, Deepak, NAGARAJAN, Badrinath
• Granted Patent: US 10,514,258 B2
• Time in Patent Office: Days
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01C 21/10 by using measurements of speed or acceleration G01C21/24, G01C21/26 take precedence
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01C 5/06 by using barometric means
• CPC Class Codes: G01L 27/002 Calibrating, i.e. establishing true relation between transducer output value and value to be measured, zeroing, linearising or span error determination
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude
• CPC Class Codes: G01S 5/012 Identifying whether indoors or outdoors
• CPC Class Codes: G01S 5/017 Detecting state or type of motion
• CPC Class Codes: G01S 5/02 using radio waves using satellite radio beacon systems for determining position G01S19/00

Abstract

Calibrating an unstable sensor of a mobile device. Systems and methods for calibrating a sensor of a mobile device determine a first estimated position of the mobile device without using any measurement from the sensor of the mobile device, generate a second estimated position of the mobile device using a measurement from the sensor, estimate a sensor error of the sensor using the first estimated position and the second estimated position, and use the sensor error to determine a calibration value for adjusting one or more measurements from the sensor.

Claims

1. A method for calibrating a sensor of a mobile device, the method comprising:

determining a first estimated position of the mobile device without using any measurement from the sensor of the mobile device;

generating a second estimated position of the mobile device using a measurement from the sensor;

estimating a sensor error of the sensor using the first estimated position and the second estimated position; and

using the sensor error to determine a calibration value for adjusting one or more measurements from the sensor.

2. The method of claim 1, wherein the sensor is a pressure sensor that produces an inaccurate measurement of pressure relative to true pressure.

3. The method of claim 1, wherein the first estimated position is determined using positioning signals received from beacons of a satellite system or a network of terrestrial transmitters.

4. The method of claim 1, wherein the first estimated position is determined by:

identifying an event, a thing, or a condition;

identifying a stored position that is associated with the identified event, thing or condition;

receiving the stored position; and

determining that the first estimated position is the stored position.

5. The method of claim 1, wherein the first estimated position is determined by:

determining whether the mobile device is inside a building;

after determining that the mobile device is inside the building, determining a floor of the building at which the mobile device resides; and

identifying an altitude of the floor, wherein an altitude of the first estimated position is the altitude of the floor or the altitude of the floor adjusted by a predefined value.

6. The method of claim 1, wherein the first estimated position is determined by:

determining whether the mobile device is outside; and

after determining that the mobile device is outside, determining a ground-level altitude, wherein an altitude of the first estimated position is the ground-level or the ground level adjusted by a predefined value.

7. The method of claim 6, wherein determining whether the mobile device is outside comprises:

estimating a non-vertical velocity of the mobile device;

determining whether the estimated velocity exceeds a threshold amount of velocity; and

if the estimated velocity is determined to exceed the threshold amount of velocity, determining that the mobile device is outside.

8. The method of claim 1, wherein the first estimated position is determined by:

identifying a time period during which the measurement from the sensor is measured on a first day;

identifying a stored position that is associated with the time period, wherein the stored position includes an estimate of a position the mobile device was at during the time period on a second day that precedes the first day; and

determining that the first estimated position is the stored position.

9. The method of claim 1, wherein the first estimated position is determined by:

determining that a battery of the mobile device is charging on a first day;

identifying a time period during which the battery of the mobile device is charging;

identifying a stored position that is associated with the time period, wherein the stored position includes an estimate of a position the mobile device was at when a battery of the mobile device was charging during the time period on a second day that precedes the first day; and

determining that the first estimated position is the stored position.

10. The method of claim 1, wherein the first estimated position is determined by:

recording movement by the mobile device;

determining that the recorded movement by the mobile device matches one or more stored values of previous movement by the mobile device;

identifying a stored position that is associated with the one or more stored values of previous movement by the mobile device, wherein the stored position includes an estimate of a position the mobile device arrived at after the one or more stored values of movement were recorded; and

determining that the first estimated position is the stored position.

11. The method of claim 1, wherein the first estimated position is determined by:

determining that the mobile device is connected to a local area network;

identifying a stored position that is associated with the local area network, wherein the stored position includes an estimate of a position the mobile device was at when the mobile device was previously connected to the local area network; and

determining that the first estimated position is the stored position.

12. The method of claim 1, wherein the first estimated position is determined by:

capturing a first image using a camera of the mobile device;

identifying a second image that matches the first image;

identifying a stored position that is associated with the second image, wherein the stored position includes an estimate of a position the mobile device was at when the camera of the mobile device captured the second image; and

determining that the first estimated position is the stored position.

13. The method of claim 1, wherein the first estimated position is determined by:

determining that a battery of the mobile device is charging;

determining an initial estimated position of the mobile device using positioning signals from beacons of a satellite system or a network of terrestrial transmitters, wherein the initial estimated position is generated in response to determining that the battery of the mobile device is charging;

identifying a stored position that is within a threshold amount of distance from the initial estimated position; and

determining that the first estimated position is the stored position.

14. The method of claim 1, wherein using the sensor error to determine a calibration value for adjusting one or more measurements from the sensor comprises:

retrieving one or more previously estimated sensor errors of the sensor from storage;

computing an average sensor error by averaging the estimated sensor error and the one or more previously estimated sensor errors; and

using the average sensor error as the calibration value.

15. The method of claim 1, wherein the sensor is a pressure sensor of the mobile device, and wherein the calibration value is determined by:

identifying a pressure sensor calibration equation that includes calibration coefficient values;

identifying temperature measurements of the pressure sensor and corresponding sensor error measurements for the pressure sensor, wherein each temperature measurement of the identified temperature measurements was measured when the pressure sensor made a corresponding measurement of pressure that was used to determine a corresponding sensor error measurement of the identified sensor error measurements;

determining calibration coefficient adjustment values by performing a polynomial fit using the identified temperature measurements and corresponding sensor error measurements;

determining an adjusted pressure sensor calibration equation by using the calibration coefficient adjustment values to adjust the calibration coefficient values of the pressure sensor calibration equation; and

determining the calibration value using the adjusted sensor calibration equation.

16. The method of claim 1, wherein sensor error is estimated by:

determining a difference in distance between the first estimated position and the second estimated position;

determining an estimated difference in pressure between the first estimated position and the second estimated position by applying a scaling factor to the difference in distance; and

setting the sensor error to the estimated difference in pressure.

17. The method of claim 1, wherein the calibration value is determined by:

setting the calibration value to the sensor error or an average of the sensor error and other previously stored sensor errors.

18. One or more non-transitory machine-readable media embodying program instructions that, when executed by one or more machines, cause the one or more machines to implement a method for calibrating a sensor of a mobile device, the method comprising:

determining a first estimated position of the mobile device without using any measurement from the sensor of the mobile device;

generating a second estimated position of the mobile device using a measurement from the sensor;

estimating a sensor error of the sensor using the first estimated position and the second estimated position; and

using the sensor error to determine a calibration value for adjusting one or more measurements from the sensor.

19. A system for calibrating a sensor of a mobile device, the system comprising:

the sensor; and

one or more machines that are operable to perform a method for calibrating a sensor of a mobile device, the method comprising;

determining a first estimated position of the mobile device without using any measurement from the sensor of the mobile device;

generating a second estimated position of the mobile device using a measurement from the sensor;

estimating a sensor error of the sensor using the first estimated position and the second estimated position; and

using the sensor error to determine a calibration value for adjusting one or more measurements from the sensor.