Assisted passive geo-location of a wireless local area network device
First Claim
Patent Images
1. A method of determining a location of a wireless device, the method comprising:
- identifying a departure time difference between a first Time of Departure (TODn) of a first beacon transmitted from the wireless device according to a clock associated with the wireless device, and a second TODm of a second beacon transmitted from the wireless device to the measuring station according to the clock associated with the wireless device;
identifying an arrival time difference between a first Time of Arrival (TOAn) of the first beacon according to a clock associated with the measuring station and a second TOAm of the second beacon at the measuring station according to the clock associated with the measuring station;
determining a first propagation time δ
n represented by a time interval between sending, by the measuring station, a first ranging packet to the wireless device and receiving, by the wireless device, the first ranging packet;
determining a second propagation time δ
m represented by a time interval between sending, by the measuring station, a second ranging packet to the wireless device and receiving, by the wireless device, the second ranging packet;
the first propagation time and the second propagation time δ
according to the clock associated with the measuring station being determined according to δ
=(Th−
Tc−
TSIFS−
tr)/2, where;
Tc is a time when the measuring station finishes sending the first ranging packet to the wireless device;
Th is a time when the measuring station receives a complete first response packet from the wireless device;
TSIFS is an interval between a time when the wireless device receives a complete first ranging packet and a time when the wireless device starts transmission of a first response packet to the measuring station; and
tr is a duration of the first response packet; and
determining a relative drift between the clock associated with the wireless device and the clock associated with the measuring station, the relative drift based at least upon the departure time difference, the arrival time difference, the first propagation time δ
n and the second propagation time δ
m, the relative drift β
being determined according to β
=[(TOAn−
TOAm)−
(δ
n−
δ
m)]/(TODn−
TODm);
revising a previously determined relative drift to arrive at an adjusted relative drift by averaging the previously determined relative drift and the determined relative drift; and
determining the location of the wireless device based at least in part on the adjusted relative drift.
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Abstract
An assisted passive geo-location method and system for determining the location of a wireless device. The method includes passive location techniques in order to assist in determining the location of the wireless device and active techniques in order to assist in the calculation of the relative drift between the clock associated with the wireless device and the clock associated with the measuring station.
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Citations
12 Claims
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1. A method of determining a location of a wireless device, the method comprising:
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identifying a departure time difference between a first Time of Departure (TODn) of a first beacon transmitted from the wireless device according to a clock associated with the wireless device, and a second TODm of a second beacon transmitted from the wireless device to the measuring station according to the clock associated with the wireless device; identifying an arrival time difference between a first Time of Arrival (TOAn) of the first beacon according to a clock associated with the measuring station and a second TOAm of the second beacon at the measuring station according to the clock associated with the measuring station; determining a first propagation time δ
n represented by a time interval between sending, by the measuring station, a first ranging packet to the wireless device and receiving, by the wireless device, the first ranging packet;determining a second propagation time δ
m represented by a time interval between sending, by the measuring station, a second ranging packet to the wireless device and receiving, by the wireless device, the second ranging packet;the first propagation time and the second propagation time δ
according to the clock associated with the measuring station being determined according to δ
=(Th−
Tc−
TSIFS−
tr)/2, where;Tc is a time when the measuring station finishes sending the first ranging packet to the wireless device; Th is a time when the measuring station receives a complete first response packet from the wireless device; TSIFS is an interval between a time when the wireless device receives a complete first ranging packet and a time when the wireless device starts transmission of a first response packet to the measuring station; and tr is a duration of the first response packet; and determining a relative drift between the clock associated with the wireless device and the clock associated with the measuring station, the relative drift based at least upon the departure time difference, the arrival time difference, the first propagation time δ
n and the second propagation time δ
m, the relative drift β
being determined according to β
=[(TOAn−
TOAm)−
(δ
n−
δ
m)]/(TODn−
TODm);revising a previously determined relative drift to arrive at an adjusted relative drift by averaging the previously determined relative drift and the determined relative drift; and determining the location of the wireless device based at least in part on the adjusted relative drift. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A measuring station for determining a location of a wireless device, the measuring station comprising:
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an interface configured to; transmit, to the wireless device, a first and second ranging packets; receive, from the wireless device, first and second beacons; a processor; and a memory storing instructions that, when executed, configure the processor to; identify a departure time difference between a first Time of Departure (TODn) of the first beacon transmitted from the wireless device according to a clock associated with the wireless device, and a second TODm of a second beacon transmitted from the wireless device according to the clock associated with the wireless device; identify an arrival time difference between a first Time of Arrival (TOAn) of the first beacon at the measuring station according to a clock associated with the measuring station and a second TOAm of the second beacon at the measuring station according to the clock associated with the measuring station; determine a first propagation time δ
n represented by a time interval between sending the first ranging packet to the wireless device and receipt of the first ranging packet by the wireless device;determine a second propagation time δ
m represented by a time interval between sending the second ranging packet to the wireless device and receipt of the second ranging packet by the wireless device;the first propagation time and the second propagation time δ
according to the clock associated with the measuring station being determined according to δ
=(Th−
Tc−
TSIFS−
tr)/2, where;Tc is a time when the measuring station finishes sending the first ranging packet to the wireless device; Th is a time when the measuring station receives a complete first response packet from the wireless device; TSIFS is an interval between a time when the wireless device receives a complete first ranging packet and a time when the wireless device starts transmission of a first response packet to the measuring station; and tr is a duration of the first response packet; and determine a relative drift between the clock associated with the wireless device and the clock associated with the measuring station, the relative drift based at least upon the departure time difference, the arrival time difference, the first propagation time δ
n and the second propagation time δ
m, the relative drift β
being determined according to β
=[(TOAn−
TOAm)−
(δ
n−
δ
m)]/(TODn−
TODm);revise a previously determined relative drift to arrive at an adjusted relative drift by averaging the previously determined relative drift and the determined relative drift; and determine the location of the wireless device based at least in part on the adjusted relative drift. - View Dependent Claims (9, 10, 11, 12)
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Specification