Systems and methods of location and tracking
A position location system is described for determining position of mobile Tags attached to assets or people. Zone Tags are installed in the venue to assist in position location estimation of mobile Tags. Time is divided into intervals, each interval comprising at least one range measurement sub-interval, and an idle sub-interval where zone Tags and mobile Tags go to sleep to save power. A zone Tag or mobile Tag is designated as the anchor network element. The anchor network element contends and seizes the communications channel at the beginning of each interval to start the range measurement phase. Mobile Tag position location estimates are made periodically. Between the periodic range measurement based position estimates, mobile Tag sensor readings are used to update the mobile Tag's position location. The period between range measurement based position updates is adjusted based on the statistics of the differences between the range measurements based position estimate and the sensor based position updated.
1. A position location determination system comprising:
a first network comprising at least one Access Point (AP) network element, each AP creating a coverage area referred to as a Basic Service Set (BSS), configuring other network elements in its BSS, and providing access to the internet to network elements in its BSS;
a second network of zone tags underlying the first network capable of making range measurements with mobile tags;
time being divided into range-measurement-period intervals, each interval comprising a measurement period when zone tags make range measurements, followed by a sleep period wherein zone tags, mobile tags or both, sleep to save power;
said zone tags and mobile tags waking up at the beginning of range-measurement-period, and an anchor network element contends for the channel and seizes the channel;
mobile tags and zone tags making range measurements according to a schedule; and
the range measurements are used by triangulation algorithms to estimate the position of the mobile tags.
2. The system of claim 1 , whereby a zone tag is the anchor network element further comprising:
the anchor zone tag sending a Data frame to each mobile tag, the mobile tags responding with an Acknowledgement frame, and the anchor zone tag estimating the Round Trip Delay (RTD) using Time Of Departure (TOD) of the Data frame and Time Of Arrival (TOA) of the Acknowledgement frame; and
the anchor zone tag designating a second zone tag as the anchor zone tag.
3. The system of claim 2 , whereby:
the network elements are IEEE 802.11 enabled devices; and
consecutive Data and Acknowledgement frames are spaced by a short enough inter-frame time interval to prevent other IEEE 802.11 enabled devices from seizing the channel.
4. The system of claim 1 , whereby:
a first zone tag is the anchor network element, said anchor network element sending a Data frame to each mobile tag, the mobile tags responding with an Acknowledgement frame, and all zone tags and said anchor network element simultaneously measuring Time Of Arrival (TOA) of the Acknowledgement frame.
5. The system of claim 4 , whereby:
the at least one Access Point (AP) network element, the zone tags, and the mobile tags are IEEE 802.11 enabled devices; and consecutive transmitted Data and Acknowledgement frames are spaced by a short enough inter-frame time interval to prevent other IEEE 802.11 enabled devices from seizing the channel.
6. The system of claim 1 , whereby a first mobile tag is the anchor network element, the anchor network element sending a Data frame, all zone tags and said anchor network element measuring the Time Of Arrival (TOA) of the Data frame; and
a second mobile tag taking the role of the anchor network element.
7. The system of claim 6 , whereby:
the at least one Access Point (AP) network element, the zone tags, and the mobile tags are IEEE 802.11 enabled devices; and consecutive Data frames sent by first and second mobile tags forming first and second anchor network elements are spaced by a short enough inter-frame time interval to prevent other IEEE 802.11 enabled devices from seizing the channel.
8. The system of claim 1 , whereby:
the mobile tag position location is periodically estimated by triangulating range measurements between mobile tags and zone tags;
mobile tags contain sensors and apparatus to update the mobile tag position location; and
between periodic range measurement based mobile tag position location estimates, the mobile tag sensor readings are used to update the mobile tags' position location.
9. The system of claim 8 , whereby:
statistics of the difference of the periodic range measurement based position estimates and the sensor based position updates is computed; and
the time between range measurement based position estimate updates is changed based on the computed statistics.
10. The system of claim 9 , whereby:
the time between range measurement based position estimate updates is increased if the average, or some other metric, of the differences is below a threshold; and
the time between range measurement based position estimate updates is decreased if the average, or some other metric, of the differences is above a threshold.