Vehicle navigation system with adaptive gyroscope bias compensation

1. A method for improving the accuracy of a vehicle navigation module including a gyroscope and a navigation filter, the method comprising:

storing average gyroscope biases as a function of temperature, the average gyroscope biases as a function of temperature obtained by averaging gyroscope biases over a plurality of temperature cycles;

computing gradients of gyroscope bias as a function of temperature from the average gyroscope biases as a function of temperature;

estimating a gyroscope bias at a first temperature based on a reference rotation rate when the reference rotation rate is available by: (i) measuring a rotation rate at the first temperature using the gyroscope, and (iii) comparing the measured rotation rate with the reference rotation rate; and,

estimating a gyroscope bias at the first temperature, when no reference rotation rate is available, via linear extrapolation from a known bias value at a second temperature, the linear extrapolation taking into account a difference between the first temperature and the second temperature and a gradient of gyroscope bias at the second temperature from the computed gradients of gyroscope bias.

2. The method of claim 1 further comprising storing the computed gradients of gyroscope bias as a function of temperature.

3. The method of claim 1 further comprising:

updating the average gyroscope biases as a function of temperature using the estimated gyroscope bias at the first temperature based on the reference rotation rate.

4. The method of claim 1 wherein computing gradients of gyroscope bias comprises:

excluding average gyroscope biases for which a number of gyroscope biases used to compute the average gyroscope biases is less than a specified minimum number of gyroscope biases.

5. The method of claim 1 wherein computing gradients of gyroscope bias comprises:

excluding average gyroscope biases for which a variance of gyroscope biases used to compute the average gyroscope biases is greater than a specified maximum variance.

6. The method of claim 1 , wherein the reference rotation rate is estimated from attitude rates or changes determined from GNSS velocity data.

7. The method of claim 1 , wherein the reference rotation rate is estimated from attitude rates or changes determined by map-matching techniques.

8. The method of claim 1 , wherein the reference rotation rate is estimated from attitude rates or changes determined from video data.

9. The method of claim 1 , wherein estimating gyroscope bias at the first temperature based on a reference rotation rate is performed when the gyroscope is stationary and the reference rotation rate is zero.

10. The method of claim 1 , wherein the navigation module is installed in a vehicle, and the method is performed regardless of whether the vehicle is turned on or off.

11. The method of claim 1 , wherein the navigation module is installed in a vehicle and is programmed to be turned on periodically whenever electrical power is available even if the vehicle is not turned on.

12. A vehicle navigation module comprising:

a MEMS gyroscope; and,

a navigation filter configured to:

store average gyroscope biases as a function of temperature, the average gyroscope biases as a function of temperature obtained by averaging gyroscope biases over a plurality of temperature cycles;

compute gradients of gyroscope bias as a function of temperature from the average gyroscope biases as a function of temperature;

estimate a gyroscope bias at a first temperature based on a reference rotation rate when the reference rotation rate is available by: (i) measuring a rotation rate at the first temperature using the gyroscope, and (iii) comparing the measured rotation rate with the reference rotation rate; and,

estimate a gyroscope bias, when no reference rotation rate is available, via linear extrapolation from a known bias value at a second temperature, the linear extrapolation taking into account a difference between the first temperature and the second temperature and a gradient of gyroscope bias at the second temperature from the computed gradients of gyroscope bias.

13. The vehicle navigation module of claim 12 , wherein the navigation filter is further configured to store the computed gradients of gyroscope bias.

14. The vehicle navigation module of claim 12 , wherein the navigation filter is further configured to update the average gyroscope biases as a function of temperature using the estimated gyroscope bias at the first temperature based on the reference rotation rate.

15. The vehicle navigation module of claim 12 , wherein the navigation filter is further configured to exclude average gyroscope biases for which a number of gyroscope biases used to compute the average gyroscope biases is less than a specified minimum number of gyroscope biases.

16. The vehicle navigation module of claim 12 , wherein the navigation filter is further configured to exclude average gyroscope biases for which a variance of gyroscope biases used to compute the average gyroscope biases is greater than a specified maximum variance.

17. The vehicle navigation module of claim 12 , wherein the reference rotation rate is estimated from attitude rates or changes determined from GNSS velocity data.

18. The vehicle navigation module of claim 12 , wherein the reference rotation rate is estimated from attitude rates or changes determined by map-matching techniques.

19. The vehicle navigation module of claim 12 , wherein the reference rotation rate is estimated from attitude rates or changes determined from video data.

20. The vehicle navigation module of claim 12 , wherein the navigation filter is configured to estimate the gyroscope bias at the first temperature based on the reference rotation rate when the gyroscope is stationary and the reference rotation rate is zero.