Granted Patent B2

US 9,207,331 · App. 13/734,352 · Granted Dec 8, 2015

Abstract

Claims (31)

1. A method for improving the accuracy of a tracking device where the tracking device cannot achieve a complete fix using a location determination mechanism, the method comprising:

determining a current position for the tracking device using incomplete information from the location determination mechanism;

adding the current position to a historical table of previous position determinations;

calculating a normalized center position from the current position and previous position determinations;

inferring the position of the tracking device from the normalized center position;

detecting the movement of the tracking device using an inertia sensor; and

clearing the historical table of previous positions in response to the detection of movement.

2. The method of claim 1 wherein the location determination mechanism is GPS.

3. The method of claim 1 wherein the failure to achieve a complete fix is caused by the tracking device being in a low observability position relative to the GPS satellites.

4. The method of claim 1 wherein the normalized center position is a weighted normalized center position.

5. The method of claim 1 further comprising calculating an acceptable error radius around the normalized center position.

6. The method of claim 5 further comprising rejecting a current position determination if it is outside the acceptable error radius.

7. The method of claim 1 further comprising calculating a fault radius around the normalized center position, wherein the fault radius is used to detect failure of an inertia sensor in the tracking device.

8. A system for improving the accuracy of a tracking device where the tracking device cannot achieve a complete fix using a location determination mechanism, the system comprising:

one or more tracking devices, each tracking device having a location determination mechanism for determining a current position for the tracking device, wherein the tracking device is operable to calculate a current position using incomplete information from the location determination mechanism, each of the one or more tracking devices including a communications interface and an inertia sensor in each of the one or more tracking devices, the inertia sensor used to detect the movement of the tracking device; and

a monitoring center monitoring each of the one or more tracking devices using the communications interface of each tracking device;

wherein the system is operable to calculate a normalized center position from the current position and a historical table of previous position determinations for each tracking device, and to infer the position of each of the tracking devices from the normalized center position, and wherein the historical table of previous position determinations is cleared when movement of the tracking device is detected.

9. The system of claim 8 wherein the calculation of a normalized center position is performed by the tracking device.

10. The system of claim 8 wherein the calculation of a normalized center position is performed by the monitoring center.

11. The method of claim 8 wherein the system calculates an acceptable error radius around the normalized center position and rejects a current position determination if it is outside the acceptable error radius.

12. The method of claim 8 wherein the system calculates a fault radius around the normalized center position, wherein the fault radius is used to detect failure of an inertia sensor in the tracking device.

13. A method for improving the accuracy of a tracking device where the tracking device cannot achieve a complete fix using GPS, the method comprising:

determining a current position for the tracking device using incomplete information from the GPS;

adding the current position to a historical table of previous position determinations;

calculating a normalized weighted center position from the current position and previous position determinations;

inferring the position of the tracking device from the normalized weighted center position;

calculating an acceptable error radius around the normalized center position;

detecting the movement of the tracking device using an inertia sensor; and

clearing the historical table of previous positions in response to the detection of movement.

14. The method of claim 13 further comprising rejecting a current position determination if it is outside the acceptable error radius.

15. The method of claim 13 further comprising calculating a fault radius around the normalized center position, wherein the fault radius is used to detect failure of an inertia sensor in the tracking device.

Assignments (11)