Systems and methods of location and tracking
A system for computing accurate position location coordinates of tags used for tracking assets and people include a first network of access points to help compute a first approximation of the tag position location, a second network of access points underlying the first network for fine position location determination, and a position location server for controlling the second network of access points and computing position location based on round trip delay measurements between tags and the access points.
1. A location determination system having mobile tags and zone tags comprising:
first network configured to obtain first approximate position location coordinates of the mobile tags;
second network underlying the first network, configured to obtain second position location estimates as round trip delay measurements between the mobile tags and the zone tags; and,
a position location server configured to determine the first position location coordinate of said mobile tags and second position location estimates of said zone tags using measurements sent by the mobile and zone tags, wherein position location coordinates of at least three zone tags are manually initialized as configured zone tags and wherein
configured zone tags make round trip delay RTD measurements with non-configured zone tags and send measurements to position location server; and the position location server computes the position coordinates of the non-configured zone tags using the RTD measurements between the zone tags and coordinates of the configured zone tags, and adds the non-configured zone tags to the list of configured zone tags.
2. The system of claim 1 , further comprising:
a reference zone tag configured to broadcast a message carrying frame timing information to neighboring zone tags, neighboring zone tags configured to receive the broadcast message from the reference zone tags,
wherein the neighboring zone tags are configured to estimate their frame timing offset with respect to that of the reference zone tag and aligning their frame timing to that of the reference zone tag; and
zone tags that correct their frame timing act as new reference zone tags, configured to broadcast messages to their neighboring zone tags whose frame timing are not yet corrected.
3. The system of claim 2 , wherein the position location server is configured to associate each mobile tag to a nearby zone tag; and the mobile tag receives a frame alignment message from the associated zone tag and aligns its frame timing to that of the associated zone tag.
4. The system of claim 2 wherein the mobile tags and zone tags are configured to periodically carry out frame timing alignment.
5. A location determination system having mobile tags and zone tags comprising:
first network configured to obtain first approximate position location coordinates of the mobile tags;
second network underlying the first network, configured to make second position location estimates as round trip delay measurements between the mobile tags and the zone tags; and,
a position location server configured to determine the first and second position location estimates of said mobile tags using measurements sent by the mobile and zone tags, wherein the position location server is configured to schedule a measurement time interval for each mobile tag, to inform the mobile tags of the measurement time interval using the first network of the measurement interval, wherein the zone tags are configured to wake prior to the beginning of the scheduled measurement period, and to contend for and get access to a channel, and wherein the zone tags are configured to send a preamble message to each mobile tag, the mobile tag configured to detect the preamble message sent by the zone tags, and configured to send a message back to the zone tags for round trip delay measurement, and send the measured round trip delay values between mobile tags and zone tags to the position location server.
6. The system of claim of 5 wherein the zone tags are configured to seize a channel before the end of the inter-frame spacing time interval during channel idle times, to speed up channel acquisition time.
7. The system of claim 5 wherein the position location server is configured to schedule multiple round trip delay measurements between certain zone tags and mobile tags, and averages the multiple round trip delay measurements to improve the accuracy of the measurement.
8. The system of claim 5 wherein the position location server is configured to uses the measured round trip delay values to determine whether or not the mobile tag is inside the zone of a zone tag, and the position location server is configured to compute the coordinates of the mobile tag using the round trip delay measurements between mobile tag and a set of zone tags and the coordinates of the zone tag positions.
9. The system of claim 8 wherein the position location server is configured to filter a sequence of consecutive position location coordinates to determine if the mobile tag's position has changed more than a certain threshold, and to increase the position location update rate if the mobile tag's position has changed by more than a threshold, and to reduce the position update rate if the mobile tag's position has not changed by more than a threshold.