In flight detection

1. A method, in a mobile device, for in-flight detection, the method comprising:

providing two acceleration indicators {A i-1 , A i };

determining, by the mobile device, a difference acceleration (dÂ) between the two acceleration indicators {A i-1 , A i };

splitting, by the mobile device, the difference acceleration (dÂ) into orthogonal components comprising an estimated horizontal acceleration (d H ) and an estimated vertical acceleration (d V ) based on an estimated direction of gravitational acceleration;

comparing, by the mobile device, an acceleration value comprising a vertical acceleration with a first threshold (Th 1 ) to determine a first comparison result;

comparing, by the mobile device, a value comprising the estimated horizontal acceleration (d H ) with a second threshold (Th 2 ) to determine a second comparison result; and

setting, by the mobile device, an in-flight indicator, indicating whether the mobile device is in flight within an airplane, based on the first and second comparison results.

2. The method of claim 1 , wherein the two acceleration indicators {A i-1 , A i } each comprise a three-dimensional acceleration vector.

3. The method of claim 1 , wherein the two acceleration indicators {A i-1 , A i } comprises:

a first acceleration (A i ) of the two acceleration indicators {A i-1 , A i } comprises a sum of a first sequence of sequential accelerometer measurements {a j , a j-1 , a j-2 , . . . }; and

a second acceleration (A i-1 ) of the two acceleration indicators {A i-1 , A i } comprises a sum of a second sequence of sequential accelerometer measurements {a k , a k-1 , a k-2 , . . . }.

4. The method of claim 1 , wherein the two acceleration indicators {A i-1 , A i } comprises:

a first acceleration (A i-1 ) of the two acceleration indicators {A i , A i-1 } indicates an acceleration at a first time (t i-1 ); and

a second acceleration (A i ) of the two acceleration indicators {A i , A i-1 } indicates an acceleration at a second time (t i );

wherein a difference in time between the second time (t i ) and the first time (t i-1 ) is less than 10000 seconds.

5. The method of claim 4 , wherein the difference in time between the second time (t i ) and the first time (t i-1 ) is between 1 to 30 seconds.

6. The method of claim 1 , wherein the estimated direction of gravitational acceleration comprises a first acceleration (A i ) of two acceleration indicators {A i-1 , A i } wherein the first acceleration (A i-1 ) represents an earlier acceleration than a second acceleration (A i ).

7. The method of claim 1 , wherein the estimated direction of gravitational acceleration comprises a second acceleration (A i ) of two acceleration indicators {A i-1 , A i } wherein the second acceleration (A i ) represents a later acceleration than a first acceleration (A i-1 ).

8. The method of claim 1 , wherein the estimated direction of gravitational acceleration comprises an average acceleration based on the two acceleration indicators {A i-1 , A i }.

9. The method of claim 1 , wherein the act of comparing the acceleration comprising the vertical acceleration comprises comparing the difference acceleration (dÂ) with the first threshold (Th 1 ).

10. The method of claim 1 , wherein the act of comparing the acceleration comprising the vertical acceleration comprises comparing the estimated vertical acceleration (d V ) with the first threshold (Th 1 ).

11. The method of claim 1 , wherein the act of comparing the value comprising the estimated horizontal acceleration (d H ) with the second threshold (Th 2 ) comprises comparing the estimated horizontal acceleration (d H ) with the second threshold (Th 2 ).

12. The method of claim 1 , wherein the act of comparing the value comprising the estimated horizontal acceleration (d H ) with the second threshold (Th 2 ) comprises comparing the second threshold (Th 2 ) to a ratio of the orthogonal components {d H , d v }.

13. The method of claim 1 , wherein the act of comparing the value comprising the estimated horizontal acceleration (d H ) with the second threshold (Th 2 ) comprises comparing the estimated horizontal acceleration (d H ) to the estimated vertical acceleration (d V ).

14. The method of claim 1 , further comprising displaying a message to a user based on the in-flight indicator.

15. The method of claim 1 , further comprising disabling circuitry base on the in-flight indicator.

16. The method of claim 1 , further comprising putting circuitry into a low power mode base on the in-flight indicator.

17. The method of claim 1 , wherein the act of setting the in-flight indicator based on the first and second comparison results comprises filtering a series of in-flight indicators.

18. The method of claim 1 , wherein the act of setting the in-flight indicator based on the first and second comparison results comprises performing a logical AND operation using the first and second comparison results.

19. A mobile device for in-flight detection, the device comprising:

an accelerometer providing raw samples;

an averager coupled to the accelerometer to receive the raw sample and provide averaged samples;

a delay T unit coupled to the averager to receive the averaged samples;

a difference unit coupled to the averager and the delay T unit to compute and provide a difference acceleration;

a gravity direction estimator coupled to the accelerometer to provide an estimate of a direction of gravity;

a vector splitter coupled to the difference unit and gravity direction estimator to find a vertical component and a horizontal component of the difference acceleration;

a first comparator coupled to a first threshold and coupled to the vector splitter to receive the vertical component and to provide a first comparison result;

a second comparator coupled to the vector splitter to receive the vertical component and the horizontal component and to provide a second comparison result; and

a logic gate coupled to the first and second comparators to process the first and second comparison results into an in-flight indicator, indicating whether the mobile device is in flight within an airplane.

20. A mobile device for in-flight detection, the device comprising:

means for providing two acceleration indicators {A i-1 , A i };

means for determining a difference acceleration (dÂ) between the two acceleration indicators {A i-1 , A i };

means for splitting the difference acceleration (dÂ) into orthogonal components comprising an estimated horizontal acceleration (d H ) and an estimated vertical acceleration (d V ) based on an estimated direction of gravitational acceleration;

means for comparing an acceleration comprising a vertical acceleration with a first threshold (Th 1 ) to determine a first comparison result;

means for comparing a value comprising the estimated horizontal acceleration (d H ) with a second threshold (Th 2 ) to determine a second comparison result; and

means for setting an in-flight indicator, indicating whether the mobile device is in flight within an airplane, based on the first and second comparison results.

21. The device of claim 20 , further comprising means for summing a first sequence of sequential accelerometer measurements {a j , a j-1 , a j-2 , . . . } and for summing a second sequence of sequential accelerometer measurements {a k , a k-1 , a k-2 , . . . } to form the two acceleration indicators {A i , A i-1 }.

22. A device comprising a processor and a memory wherein the memory includes software instructions to:

provide two acceleration indicators {A i-1 , A i };

determine a difference acceleration (dÂ) between the two acceleration indicators {A i-1 , A i };

split the difference acceleration (dÂ) into orthogonal components comprising an estimated horizontal acceleration (d H ) and an estimated vertical acceleration (d V ) based on an estimated direction of gravitational acceleration;

compare an acceleration comprising a vertical acceleration with a first threshold (Th 1 ) to determine a first comparison result;

compare a value comprising the estimated horizontal acceleration (d H ) with a second threshold (Th 2 ) to determine a second comparison result; and

set an in-flight indicator, indicating whether the device is in flight within an airplane, based on the first and second comparison results.

23. A non-transitory computer-readable medium including program code stored thereon, comprising program code to:

provide two acceleration indicators {A i-1 , A i };

determine a difference acceleration (dÂ) between the two acceleration indicators {A i-1 , A i };

split the difference acceleration (dÂ) into orthogonal components comprising an estimated horizontal acceleration (d H ) and an estimated vertical acceleration (d V ) based on an estimated direction of gravitational acceleration;

compare an acceleration comprising a vertical acceleration with a first threshold (Th 1 ) to determine a first comparison result;

compare a value comprising the estimated horizontal acceleration (d H ) with a second threshold (Th 2 ) to determine a second comparison result; and

set an in-flight indicator, indicating whether a device is in flight within an airplane, based on the first and second comparison results.