POSITION DETERMINATION USING TIME OF ARRIVAL MEASUREMENTS IN A WIRELESS LOCAL AREA NETWORK
Ways to determine position or proximity of elements such as tags or mobile devices within a wireless local area network such as an IEEE 802.11 network that includes multiple beacons using time of arrival (TOA) of messages are described. System and methods are described for invoking TOA measurements at the beacons, the systems and methods being compatible with IEEE 802.11 protocols and signaling. Systems and methods are described to estimate the clock offset among beacons in an asynchronous network of IEEE 802.11 enabled Beacons, and to compensate for the clock timing offsets of the measured TOA values when triangulating the TOA values to estimate tag and/or mobile device positionlocation.
1 . A method that determines position using IEEE 802.11 standard components, the method comprising;
transmitting a message from a tag to a network comprising a plurality of beacons, each beacon capable of communicating with the tag;
receiving the message at the plurality of beacons;
measuring, at each beacon in the plurality of beacons, a time of arrival (TOA) of the received message; and
sending the measured TOAs to a position server.
2 . The method of claim 1 further comprising synchronizing the clock timing of each beacon in the plurality of beacons to a reference clock.
3 . The method of claim 2 further comprising, at the position server:
designating a beacon as a reference beacon;
creating a beacon list comprising all beacons excluding the reference beacon;
instructing a second beacon in the beacon list to estimate a clock offset with respect to the clock timing of the reference beacon and to utilize the clock offset to synchronize the second beacon to the reference beacon; and
iteratively:
retrieving a next beacon in the beacon list;
estimating a clock offset of the next beacon with respect to that of a previously processed beacon; and
synchronizing the clock timing of the next beacon to that of the previously processed beacon until all beacons in the beacon list have been processed.
4 . The method of claim 2 , wherein the position server estimates position coordinates of the tag based at least partly on the measured TOAs.
5 . The method of claim 1 , wherein each beacon measures clock offsets with respect to the clock timing of a reference beacon and sends the measure clock offset to the position server.
6 . The method of claim 5 , wherein the position location server uses the estimated clock offsets between beacons to correct the measured TOAs of the beacons to correspond to a synchronous network of beacons.
7 . The method of claim 6 , wherein the position server uses the clock offset estimate among the beacons as well as the measured TOAs at the beacons to estimate tag position coordinates.
8 . The method of claim 5 further comprising, at the position server:
designating a beacon as a reference beacon;
creating a beacon list comprising all beacons excluding the reference beacon;
estimating a clock offset of the next beacon with respect to that of a previously processed beacon; and
iteratively:
retrieving a next beacon in the beacon list;
estimating a clock offset of the next beacon with respect to that of a previously processed beacon; and
recording the estimated clock offset, until all beacons in the beacon list have been processed.
9 . The method of claim 8 , wherein the position server:
designates a beacon as a reference beacon;
creates a beacon list comprising all beacons excluding the reference beacon; and
iteratively:
retrieves a next beacon in the beacon list; and
corrects TOA measurement of the next beacon by adding the clock offset of the next beacon with respect to the reference beacon to the measured TOA, until all beacons in the beacon list have been processed.
10 . The method of claim 8 , wherein the position location server uses the corrected TOA measurements for trilateration to estimate tag position coordinates.
11 . A system that determines position using IEEE 802.11 standard components, the system comprising:
a processor for executing a set of instructions; and
a non-transitory medium that stores the set of instructions, wherein the set of instructions:
transmits a message from a tag to a network comprising a plurality of beacons, each beacon capable of communicating with the tag;
receives the message at the plurality of beacons;
measures, at each beacon in the plurality of beacons, a time of arrival (TOA) of the received message; and
sends the measured TOAs to a position server.
12 . The system of claim 11 , wherein the set of instructions further synchronizes the clock timing of each beacon in the plurality of beacons to a reference clock.
13 . The system of claim 12 , wherein the set of instructions further:
designates a beacon as a reference beacon;
creates a beacon list comprising all beacons excluding the reference beacon;
instructs a second beacon in the beacon list to estimate a clock offset with respect to the clock timing of the reference beacon and to utilize the clock offset to synchronize the second beacon to the reference beacon; and
iteratively:
retrieves a next beacon in the beacon list;
estimates a clock offset of the next beacon with respect to that of a previously processed beacon; and
synchronizes the clock timing of the next beacon to that of the previously processed beacon until all beacons in the beacon list have been processed.
14 . The system of claim 12 , wherein the position server estimates position coordinates of the tag based at least partly on the measured TOAs.
15 . The system of claim 11 , wherein each beacon measures clock offsets with respect to the clock timing of a reference beacon and sends the measure clock offset to the position server, and the set of instructions further:
designates a beacon as a reference beacon;
creates a beacon list comprising all beacons excluding the reference beacon;
estimates a clock offset of the next beacon with respect to that of a previously processed beacon; and
iteratively:
retrieves a next beacon in the beacon list;
estimates a clock offset of the next beacon with respect to that of a previously processed beacon; and
records the estimated clock offset, until all beacons in the beacon list have been processed.
16 . A position server that determines position using IEEE 802.11 standard components, the position server comprising:
a processor for executing a set of instructions; and
a non-transitory medium that stores the set of instructions, wherein the set of instructions:
directs a tag to transmit a message to a network comprising a plurality of beacons, each beacon capable of communicating with the tag;
receives a measured TOA from each beacon in the plurality of beacons.
17 . The position server of claim 16 , wherein:
each beacon measures clock offset with respect to the clock timing of a reference beacon and the measured clock offsets are received at the position server, and
the position server uses the estimated clock offsets between beacons to correct the measured TOAs of the beacons to correspond to a synchronous network of beacons
18 . The position server of claim 17 , wherein the position server uses the clock offset estimate among the beacons as well as the measured TOAs at the beacons to estimate tag position coordinates.
19 . The position server of claim 16 , wherein the set of instructions further:
designates a beacon as a reference beacon;
creates a beacon list comprising all beacons excluding the reference beacon;
estimates a clock offset of the next beacon with respect to that of a previously processed beacon; and
iteratively:
retrieves a next beacon in the beacon list;
estimates a clock offset of the next beacon with respect to that of a previously processed beacon; and
records the estimated clock offset, until all beacons in the beacon list have been processed.
20 . The position server of claim 19 , wherein the set of instructions further:
designates a beacon as a reference beacon;
creates a beacon list comprising all beacons excluding the reference beacon; and
iteratively:
retrieves a next beacon in the beacon list; and
corrects TOA measurement of the next beacon by adding the clock offset of the next beacon with respect to the reference beacon to the measured TOA, until all beacons in the beacon list have been processed.