Positioning system

1. A method of determining a position of an active tag using a system comprising an application server and a plurality of fixed location beacons, comprising:

synchronizing the plurality of active tags and the plurality of beacons continuously to a common time base for ranging during assigned time slots;

performing two-way ranging between the beacons and the tags perform in the assigned time slots by:

ranging the active tag to at least a portion of the plurality of beacons during the beacon assigned ranging time slots; and

reporting a position of the active tag to at least a beacon of the plurality of beacons; and

determining a position of an active tag by:

providing the common time base for the plurality of fixed location beacons;

receiving a synchronization message from each of the plurality of fixed location beacons in a fixed time slot for each beacon;

registering the active tag to the common time base based on the received synchronization message; and

receiving active tag ranging information from at least one of the plurality of beacons;

drift compensating the plurality of beacons and the active tag, using an internal clock count B c n of a beacon synchronization message and an internal clock count T c n of the active tag for a current update cycle n of the system, by determining a correction factor D to correct for clock drift versus the common time base using the formula

D

=

T

c

n

-

T

c

n

-

1

B

c

n

-

B

c

n

-

1

.

;

and

wherein time of flight between a beacon and the active tag is T f , wherein a response delay between a beacon and an active tag is T d , and wherein the application server is further configured to apply the correction factor to a two-way ranging round trip flight time as T RT =2T f +T d *D.

2. The method of claim 1 , wherein each beacon of the plurality of beacons listens for a two-way ranging poll from a tag of the plurality of active tags in a predefined window.

3. The method of claim 1 , wherein the plurality of active tags has a global reporting time slot.

4. The method of claim 1 , wherein each tag of the plurality of active tags is configured to determine its position based on two-way ranging between it and at least one beacon of the plurality of beacons.

5. The method of claim 4 , wherein each tag of the plurality of tags is configured to determine its position based on two-way ranging between it and at least three beacons.

6. The method of claim 1 , wherein the processing unit is further configured to update positions of the plurality of tags at a rate dependent upon determined conditions of the tags.

7. The method of claim 1 , including providing an application server configured to register the active tag by:

listening by the active tag for synchronization messages from the plurality of beacons;

sending a registration message upon receipt of a synchronization message from a beacon of the plurality of beacons;

receiving a confirmation message from the beacon of the plurality of beacons at the tag; and

initiating listening for a tag position report in a tag position report time slot.

8. The method of claim 1 , including providing an application server configured to provide a synchronization message by providing the synchronization message within a range of predetermined beacon time synchronization time slots in an update cycle for the system.

9. The method of claim 8 , wherein the application server is further configured to issue two-way ranging signals within a globally designated window in an update cycle of the system.

10. The method of claim 1 , including providing an application server configured to register the active tag by registering the active tag within a range of predetermined tag registration time slots in an update cycle for the system.

11. The method of claim 10 , including ranging the active tag by ranging the active tag within a range of time slots in the update cycle after the tag registration time slots.

12. The method of claim 1 , including providing an application server configured to range the active tag by:

issuing from the active tag a two-way ranging signal;

receiving at the active tag return signals from at least three beacons of the plurality of beacons; and

calculating a position of the active tag at the active tag using the common time base and the received return signals.

13. The method of claim 12 , including issuing a two-way ranging signal by issuing to a determined one of the plurality of beacons.

14. The method of claim 13 , including ranging to range to more than one beacon of the plurality of beacons within an update cycle of the system.

15. The method of claim 1 , including:

connecting the plurality of beacons and an application server with a wireless communication network; and

transferring mobile tag information from the plurality of beacons to the application server.

16. The method of claim 1 , including monitoring a plurality of tags, and updating at least one tag of the plurality of tags at a rate slower than other tags, depending upon determined conditions of the at least one tag.