U.S. patent application number 11/897100 was filed with the patent office on 2008-10-02 for system and method for simulated dosimetry using a real time locating system.
This patent application is currently assigned to Q-Track Corporation. Invention is credited to Hans Gregory Schantz.
Application Number | 20080241805 11/897100 |
Document ID | / |
Family ID | 39136974 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080241805 |
Kind Code |
A1 |
Schantz; Hans Gregory |
October 2, 2008 |
System and method for simulated dosimetry using a real time
locating system
Abstract
A system for providing a simulated total dose exposure
measurement during a nuclear facility training exercise by locating
participants using a real time location system, modeling
incremental exposure as a function of location and summing
incremental exposure to produce a total dose for each of the
participants. Total dose may be displayed via a wireless link to a
simulated dosimiter worn by each participant. Radiation sources may
also have location tags and the exposure model may be modified in
real time according to the tracked location of the radiation
source. In one embodiment, the locating technology comprises near
field locating technology based on comparing near field signal
characteristics. Alternative locating technologies may be used.
Inventors: |
Schantz; Hans Gregory;
(Huntsville, AL) |
Correspondence
Address: |
JAMES RICHARDS
58 BONING RD
FAYETTEVILLE
TN
37334
US
|
Assignee: |
Q-Track Corporation
Huntsville
AL
|
Family ID: |
39136974 |
Appl. No.: |
11/897100 |
Filed: |
August 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60841589 |
Aug 31, 2006 |
|
|
|
Current U.S.
Class: |
434/218 |
Current CPC
Class: |
C23C 16/08 20130101;
C23C 16/30 20130101; C23C 16/45525 20130101; C23C 16/4481 20130101;
C23C 16/16 20130101; C23C 16/4402 20130101; C23C 16/45544 20130101;
C23C 16/18 20130101; C23C 14/48 20130101 |
Class at
Publication: |
434/218 |
International
Class: |
G09B 19/00 20060101
G09B019/00 |
Claims
1. A system for determining a simulated radiation dose for a
participant comprising: a real time location system, said real time
location system comprising: a first locator tag to be worn by said
participant, and a locator system for determining a plurality of
positions for said first locator tag during a training period; a
radiation field model for determining a dose rate for a position
within a training area during said training period; and a computer,
said computer determining a dose rate for each position of said
plurality of positions of said first locator tag based on said
radiation field model, said computer calculating a total received
dose for said participant based on said dose rate for each position
of said plurality of positions of said first locator tag during
said training period.
2. The system of claim 1, wherein the real time location system
comprises a near field location system.
3. The system of claim 2, wherein said first locator tag comprises
a transmitter tag.
4. The system of claim 1, further including: a dosimeter worn by
said participant, said dosimeter displaying said total received
dose for said participant.
5. The system of claim 1, further including an input from a trainer
to modify said radiation field model during said training
period.
6. The system of claim 1, further including an input from said
participant to modify said radiation field model during said
training period.
7. The system of claim 1, further including a second locator tag,
said second locator tag associated with an item in said training
area, wherein said radiation field model is modified by location
information from said second locator tag.
8. The system of claim 7, wherein the item is a radiation
source.
9. The system of claim 1, wherein the radiation model comprises a
pre-calculated lookup table of dose rate values for a plurality of
locations within said training area.
10. A method for determining a simulated radiation dose for a
participant comprising: associating a radio frequency locating tag
with said participant for locating said participant's movements
within a training facility; generating a plurality of position
measurements of said participant based on said radio frequency
locating tag; producing a simulated dose rate for each position of
said plurality of position measurements for said participant based
on a simulated dose rate model; and generating a total dose for
said participant based on said plurality of position measurements
and said simulated dose rate for each position of said plurality of
position measurements for said participant.
11. The method of claim 10, further including the step of:
displaying said total dose for viewing by said participant by a
simulated dosimetry display to be worn by said participant.
12. The method of claim 10, further including the step of:
modifying the simulated dose rate model in real time based on an
input from a trainer.
13. The method of claim 10, further including the step of:
modifying the simulated dose rate model in real time based on an
input from said participant.
14. The method of claim 10, further including the step of:
modifying the simulated dose rate model in real time based on a
position measurement of an item within said training facility.
15. The method of claim 10, wherein the simulated dose rate model
includes a pre-calculated lookup table of dose rate values for a
plurality of positions within said training facility.
16. The method of claim 10, wherein the radio frequency locating
tag comprises a near field locating tag.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit under 35 USC 119(e) of
provisional application Ser. No. 60/841,598, titled: "System and
Method of Simulated Dosimetry Using a Real Time Locating System,"
filed Aug. 31, 2006, by Schantz, which is hereby incorporated
herein by reference in its entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention pertains generally to the field of
real time simulation based training systems, more particularly to
training systems for workers in nuclear or other hazardous
environments.
[0004] 2. Background of the Invention
[0005] Radiation exposure of workers in the nuclear industry poses
a significant safety and health hazard to the workers, and imposes
significant costs to the utilities that employ them. Training is
essential to help workers avoid unnecessary exposure to radiation
hazards and minimize total dosage.
[0006] Existing training techniques involve equipping workers with
simulated dosimeters during training exercises. A trainer
supervising the exercise may remotely control the readouts on these
simulated dosimeters.
[0007] This approach leaves much to be desired. Since the simulated
dosimetry is left to the subjective judgment of a trainer, the
simulated dose is subject to considerable variation. Further, in
complicated simulated radiation environments, it may be difficult
for a trainer to accurately estimate the simulated dose. Similarly,
in a complex exercise involving multiple workers, an individual
trainer may not be capable of realistically modifying several
dosimetry readings.
[0008] Thus, there is a need for a system and method of simulated
dosimetry in which simulated dosimetry can be acquired
automatically, without the direct intervention or input of a
trainer.
BRIEF DESCRIPTION OF THE INVENTION
[0009] Briefly, the present invention pertains to a system for
providing a simulated total dose exposure measurement during a
nuclear facility training exercise by locating participants using a
real time location system, modeling incremental exposure as a
function of location and summing incremental exposure to produce a
total dose for each of the participants. Total dose may be
displayed via a wireless link to a simulated dosimeter worn by each
participant. Radiation sources may also have location tags, and the
exposure model may be modified in real time according to the
tracked location of the radiation source.
[0010] In one embodiment, the locating technology comprises near
field locating technology based on comparing near field signal
characteristics. Alternative locating technologies may be used.
[0011] These and further benefits and features of the present
invention are herein described in detail with reference to
exemplary embodiments in accordance with the invention.
BRIEF DESCRIPTION OF THE FIGURES
[0012] The present invention is described with reference to the
accompanying drawings. In the drawings, like reference numbers
indicate identical or functionally similar elements. Additionally,
the left-most digit(s) of a reference number identifies the drawing
in which the reference number first appears.
[0013] FIG. 1 illustrates an exemplary simulated dosimetry system
in accordance with the present invention.
[0014] FIG. 2 illustrates an exemplary simulated dosimetry process
in accordance with the present invention.
[0015] FIG. 3 illustrates an exemplary flow loop training
facility.
[0016] FIG. 4 shows a flow section of the flow facility of FIG. 3,
which may be displayed to a trainer in a virtual radiation
environment (VRE) display.
[0017] FIG. 5 shows the flow section of FIG. 4 with radiation
sources placed in the VRE.
[0018] FIG. 6 illustrates the training facility of FIG. 3 with a
system for simulated dosimetry installed in accordance with the
present invention.
[0019] FIG. 7 shows a flow section of FIG. 6 with the VRE setup of
FIG. 5 and including trainees 602, one of which is wearing a
locating tag and a simulated dosimeter display.
[0020] FIG. 8 illustrates a method for simulated dosimetry for
multiple trainees using real time calculation of radiation for each
point.
[0021] FIG. 9 illustrates a method for simulated dosimetry for
multiple trainees using pre-calculated radiation for each point
retrieved from a lookup table.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention offers a solution to the problem of
providing accurate simulated dosimetry to nuclear facility training
programs by using a real-time-location-systems (RTLS) in
combination with a radiation exposure model. The RTLS may employ
near-field electromagnetic ranging (NFER) technology, ultrawideband
(UWB), time difference of arrival (TDOA), time-of-flight (ToF) or
any other RTLS technology known by practitioners of the RF
arts.
[0023] FIG. 1 illustrates an exemplary simulated dosimetry system
100 in accordance with the present invention. Referring to FIG. 1,
a training facility 108 may include any number of different types
of hardware as are necessary to provide the necessary training.
Included in the training may be exercises directed to handling
fault conditions including leaks or spills of radioactive
materials. Such fault conditions may be modeled by computer 124 as
set up by a trainer/operator. Multiple functions are shown
performed by computer 124; however, the functional partitions and
number of computers is for convenience of illustration and may be
implemented many different ways according to the preference of the
implementer. Each participant (also referred to as a
worker/trainee) may wear a simulated dosimeter 106 comprising a
locator tag 102a, for reporting the trainee's position, and a
display 104, for displaying computed simulated total dose. The
locator tag 102a and display 104 may be housed in the same package
106 or may be separate, as desired. The locator tag 102a
communicates with an array of locator receivers 126 for determining
the location of the tag 102a. Receiver output signals are processed
by a location computer 127 to determine the location coordinates of
each trainee. Location tags 102b may also be placed on items, such
as radiation sources 110 within the environment 108. Location
coordinates for such items 110 as well as control inputs 112 which
may be operated by the trainees may be used to vary the radiation
dose rate model 114 for the environment 108. The dose rate model
may also be configured by a system operator through operator inputs
116. Trainee location coordinates together with the current real
time radiation model 114 output are used to generate a dose rate
118 for the trainee at the measured location at the given time.
Dose rate values are summed 120 over the time of the training
exercise to provide a total dose value 120. The total dose value
122 may be displayed to the operator 116 and may be delivered to
the trainee via a wireless link or network 128. Thus, the trainee
may wear a simulated dosimeter device 104 similar in appearance to
an actual radiation dosimeter that provides a display during
simulation training showing simulated exposure to radiation based
on the trainee's actual proximity and path through the simulated
environment 108. The system further allows for the real time
varying of the environment by the trainees and trainer as the
training event unfolds. Real time, within this disclosure, refers
to measurements or other events that occur and are acted upon
during the original progress of the training event.
[0024] FIG. 2 illustrates an exemplary simulated dosimetry process
200 in accordance with the present invention. Referring to FIG. 2,
the process 200 starts by setting initial conditions in the
radiation model 202 and associating a locating tag/dosimeter with
each participant 204. The training event starts, and during the
event, participants are tracked and coordinates for the
participants are mapped 206. At each mapped point, the received
dose rate from the radiation model is used to determine an
incremental dose for the associated time interval at the mapped
point of the participant 208. Dose increments are accumulated for
each participant 210. As the training event progresses, continuous
updates of total dose may be displayed to each participant via an
RF link or network to a simulated dosimeter display worn by each
participant 212.
[0025] The process 200 may be further understood by considering an
exemplary training process at an exemplary flow-loop training
facility.
[0026] FIG. 3 illustrates an exemplary flow loop training facility.
Referring to FIG. 3, the flow-loop training facility 302 contains a
variety of pumps 308, pipes 304, valves 310, tanks 306, and other
mechanical equipment similar to those used in actual nuclear
facilities. Although the present invention is described in terms of
a flow-loop raining facility, the teachings of the present
invention apply to any industrial, operational, simulation, or
other environment in which one might chose to operate a simulated
dosimetry system.
[0027] FIG. 4 shows a flow section of the flow facility of FIG. 3
which may be displayed to a trainer in a virtual radiation
environment (VRE) display. FIG. 3 shows various pumps 308, pipes
304, valves 310, and a tank 306.
[0028] FIG. 5 shows the flow section of FIG. 4 with radiation
sources placed in the VRE. Referring to FIG. 5, a point source 502
is shown at the valve 310. A line source 506 is shown at pipe 304,
and a volume source 504 is shown near pump 308a.
System for Simulated Dosimetry Using RTLS
[0029] FIG. 6 illustrates the training facility of FIG. 3 with a
system for simulated dosimetry installed in accordance with the
present invention. Referring to FIG. 6, four locator receivers 126
are placed at the corners of the area or in other suitable
locations to measure the position of a locating tag 102 on a
trainee 602. Positioning signals 125 from the exemplary locating
tag 102 are shown being received by all four receivers 126.
Position information from the receivers 126 is sent to a computer
124 for processing via communication signals 129, which may be a
wireless network. Alternatively, a wired network may be used.
[0030] FIG. 7 shows a flow section of FIG. 6 with the VRE setup of
FIG. 5 and including trainees 602, one of which is wearing a
locating tag 102 and a simulated dosimeter display 104.
[0031] Before each exercise, a trainer sets up one or more virtual
radiation environment (VRE) configurations by defining simulated
point, line, area, volume, and other sources of radiation
throughout the training facility (see FIG. 5). The trainer inputs
the location, intensity, and geometry of the radiation sources. In
a preferred embodiment, a software application records the
simulated sources defined by a trainer and calculates the radiation
exposure (or dose rate) for the VRE at a suitable resolution for
each location throughout the training facility.
[0032] The trainer may create multiple VRE's to capture time
varying radiation characteristics. For instance during a training
exercise, a trainer may switch to an alternate VRE to model
changing plant characteristics, like opening or closing of valves,
turning on or off pumps, variations of flow, or other operations
that might impact radiation characteristics.
[0033] A worker-trainee 602 undergoes training in the training
facility. The worker-trainee 602 carries a locator tag 102 that
enables a real-time locating system (RTLS) 126 and 127 to determine
the worker-trainee's location. A variety of RTLS technologies are
known in the RF arts by which one may accomplish this localization.
In a preferred embodiment, the tag 102 radiates localizing signals
125 that are picked up by a plurality of locator-receivers 126. The
plurality of locator-receivers 126 then send data signals 129 to a
computer 127 (part of 124). The data signals 129 may be wireless
data signals (e.g. 802.11b, 802.11g, &c.), hardwired Ethernet
data signals, or any other convenient form of data signaling. The
computer 127 receives the data signals 129 and determines the
location of the worker-trainee 602 (see FIG. 6). The computer 124
updates the location of the worker-trainee 602 on a time scale
appropriate to create a suitable simulation of the worker-trainee's
radiation exposure.
[0034] The computer 124 uses the actual location of the
worker-trainee 602 and the locations of the plurality of simulated
radiation sources 502, 504, 506, to calculate an instantaneous
simulated dose rate based on the distance between the simulated
source and the actual location of the worker-trainee (see FIG.
7).
[0035] The computer 124 monitors and records the instantaneous
simulated dose rate. The instantaneous simulated dose rate may be
integrated over time to determine a cumulative simulated dose. The
computer 124 may also send signals to a simulated dosimeter 104 to
cause the simulated dosimeter 104 to display a simulated dose rate
and a cumulative simulated dose. The simulated dosimeter 104 may
flash, alarm, or otherwise convey information to a worker-trainee
602 in analogous fashion to the alerts of a real dosimeter in a
real environment. In a preferred embodiment, a simulated dosimeter
may be a PDA or other device with a software application to enable
the PDA to provide simulated dose and simulated dose rate and
otherwise behave as a simulated dosimeter 104.
Method for Simulated Dosimetry Using RTLS
[0036] FIG. 8 illustrates a method for simulated dosimetry for
multiple trainees using real time calculation of radiation for each
point. Referring to FIG. 8, the method, referred to as a first
method, begins at a start block 802. The first method continues
with a training supervisor, health physicist, or other appropriate
individual defining the VRE 804. The definition of a VRE includes
defining appropriate point, line, area, or other sources of
radiation. The definition must include location and source
strength. Distributed sources like line or area sources must
further include the geometry of the source distribution and the
variation of source strength or concentration along, across or
throughout the simulated source. The VRE may also be defined so as
to vary according to any appropriate health physics model
including, for instance, the variation or distribution of airborne
radiation sources in a plume, or radiation sources dissolved in a
liquid spill. The VRE may evolve in time, may vary in accord with
activities in a training exercise or may change in accord with
simulated changes in plant operations or other factors. The VRE is
captured, encompassed, and stored in particular source data.
[0037] The first method continues by determining a location of a
worker-trainee 808. In preferred embodiments, this step may be
accomplished through use of an RTLS. The first method recalls the
source data for the first source 810. Then the first method
determines the distance between the simulated radiation source and
the actual location of the worker-trainee 812. In the case of a
point simulated radiation source, this is the distance between the
simulated point source and the actual location of the
worker-trainee. In the case of a line source, this may be the
effective distance integrating along the line (accounting for any
variation in source distribution along the line source). In the
case of an area source, this may be the effective distance
integrating across the area (accounting for any variation in source
distribution across the source area).
[0038] The first method continues by determining the dose due to
this source 814. If the source in question is a point source, then
dose (D) follows from point source strength (P) and distance (a)
according to the formula:
D = P d 2 ( 1 ) ##EQU00001##
If the source in question is a line source, then dose follows from
line source strength (L in source strength per unit length)
according to the formula:
D = .intg. e 1 e 2 L ( l ) d ( l ) 2 l ( 2 ) ##EQU00002##
Note that both the line source strength and the distance d between
the source point and the worker-trainee location depend upon the
location (l) along the line. The line integral is evaluated from
one end of the line (e1) to the other (e2).
[0039] If the source in question is an area source, then dose
follows from area source density (a in source strength per unit
area) according to the formula:
D = .intg. .intg. A .sigma. ( x , y ) d 2 ( x , y ) x y ( 3 )
##EQU00003##
Note that both the area source density and the distance between the
source point and the worker-trainee location depend upon the
location (x, y) within the area. The area integral is evaluated for
all locations within the area A.
[0040] If the source in question is a volume source, then dose
follows from volume source density (.rho. in source strength per
unit volume) according to the formula:
D = .intg. .intg. .intg. V .rho. ( x , y , z ) d 2 ( x , y , z ) x
y z ( 4 ) ##EQU00004##
Note that both the volume source density and the distance between
the source point and the worker-trainee location depend upon the
location (x, y, z) within the volume. The volume integral is
evaluated for all locations within the volume V.
[0041] The first method continues with the instantaneous dose for
the first source being added to the total instantaneous dose for
the first worker-trainee 816. Total instantaneous dose is initially
set to zero until the contribution of the first source is
determined.
[0042] The first method continues with a decision block 818. If all
sources have not been accounted for, the first method continues by
determining distance to the next source. Thus the first method
loops through and accounts for dose contributions due to all
simulated sources in the VRE. If all sources have been accounted
for, then the first method continues by storing 820 the total
simulated instantaneous dose for the first worker-trainee in a
simulated dose data database 822. In alternate embodiments, the
first method may send the total simulated instantaneous dose to a
simulated dosimeter or may add the total simulated instantaneous
dose to a total simulated cumulative dose. In still further
alternate embodiments the first method may send the total simulated
cumulative dose to a simulated dosimeter.
[0043] The first method continues with a decision block 824. If all
worker-trainees have not been accounted for, the first method
continues by finding the actual location of the next
worker-trainee. Thus the first method loops through and determines
the instantaneous simulated dose for every worker-trainee in the
training exercise.
[0044] If all worker-trainees have been accounted for, then the
first method continues with a decision block 826. If the exercise
is over, then the first method terminates in an end block 830.
[0045] If the exercise is not over, then the first method continues
back by determining the actual location of the first worker-trainee
828.
[0046] FIG. 9 illustrates a method for simulated dosimetry for
multiple trainees using pre-calculated radiation for each point
retrieved from a lookup table. Referring to FIG. 9, the lookup
table method, referred to as a second method, begins at a start
block 902. The second method continues with a training supervisor,
health physicist, or other appropriate individual defining a VRE
904 as in the first method. In the second method, the VRE is used
to create a dose rate look-up table for each location of interest
within the training environment 906-916.
[0047] Once the VRE is defined, the second method continues by
determining the instantaneous dose rate at a first location due to
a first source 906. The second method continues by adding the
instantaneous dose rate due to a source to the total instantaneous
dose rate at a location 908. The second method continues with a
decision block 910. If all sources have not yet been accounted for,
then the second method continues by looping back to consider the
contribution of the next source. Thus, the second method loops over
all sources to determine the total instantaneous does rate due to
all sources at a particular location. If all sources have been
accounted for, then the second method continues by storing 912 the
total dose rate at a particular location to a dose rate look-up
table 914.
[0048] The second method continues with a decision block 916. If
all locations have not yet been considered, then the second method
continues by evaluating the dose rate due to the first source at
the next location. If all locations have been accounted for, then
the dose rate look-up table is completed, and the second method is
ready to begin simulated dosimetry.
[0049] The second method continues by determining worker-trainee
actual location 918. Then, the second method continues by using the
dose rate look-up table to look-up the dose rate at the
worker-trainee's actual location 920. Depending on the resolution
of the dose rate look-up table, the second method may select the
dose rate at the location closest to the worker-trainee's actual
location or the second method may interpolate between a few of the
closest locations in the dose rate look-up table.
[0050] The second method continues by storing 922 the total
simulated instantaneous dose for the first worker-trainee in a
simulated dose data database 924. In addition or in alternate
embodiments, the second method may send the total simulated
instantaneous dose to a simulated dosimeter or may add the total
simulated instantaneous dose to a total simulated cumulative dose.
In still further alternate embodiments the second method may send
the total simulated cumulative dose to a simulated dosimeter.
[0051] The second method continues with a decision block 926. If
all worker-trainees have not been accounted for, the second method
continues by determining actual location of the next
worker-trainee. Thus the second method loops through and determines
the instantaneous simulated dose for every worker-trainee in the
training exercise.
[0052] If all worker-trainees have been accounted for, then the
second method continues with a decision block 928. If the exercise
is over, then the second method terminates in an end block 932. If
the exercise is not over, then the second method continues back by
determining the actual location of the first worker-trainee
930.
[0053] Both the first method and the second method may be augmented
by providing real-time feedback to worker-trainees and to a
training supervisor. Both the first method and the second method
may be further augmented by integrating real-time simulated dose
data with video or other telemetry captured during the
exercise.
Near-Field Location System
[0054] In a preferred embodiment, the active location tag and
locating receiver of the present invention are based on
transmitting and receiving near field signals. Location by near
field signals is fully described in the US patents and patent
applications incorporated by reference below. In summary, near
field signals are signals received within a near field of the
transmitter. The near field is best within 1/6 wavelength, but the
effects may be utilized out to one wavelength or so. Near field
signals show unique amplitude and phase changes with distance from
the transmitter. In particular E field and H field antennas couple
in different ways to the signal with different amplitude decay
profiles and different signal phase changes with distance. These
amplitude and phase profiles may be used to measure distance. In
particular, by comparing E field and H field phase or E field and H
field amplitude, distance may be determined by referring to the
theoretical predictions for the measured property as a function of
distance. Alternatively, the signal properties may be pre-measured
for a particular site to account for site specific disturbances and
the range measurement compared with previously measured data. An E
field antenna is typically a whip antenna and may be on the order
of a meter in length for a 1 MHz signal. An H field antenna is
typically a coil and may include a ferrite core. The H field
antenna may be on the order of a few centimeters in length, width,
and height. Thus, it can be advantageous to utilize magnetic
antennas for mobile units because of the compact size and to use
both E field and H field antennas for the fixed units because of
the size of the whip antenna. In some situations however, the
reverse may be desired. Numerous variations are disclosed in the
applications incorporated by reference below.
[0055] In particular, an often preferred configuration utilizes a
magnetic antenna (H field antenna) for the mobile beacon
transmitter (active location tag) and a vertically polarized E
field antenna with two orthogonally oriented H field antennas for
each of the fixed receiver locations. The two H field antennas have
the null axes in the horizontal plane. An exemplary signal set from
this arrangement includes:
[0056] E, Electric field strength from the E field antenna
[0057] H1, magnetic field strength from the first H field
antenna
[0058] H2, magnetic field strength from the second H field
antenna
[0059] EH1, phase angle between E and H1 signals
[0060] EH2, phase angle between E and H2 signals
[0061] Thus, multiple determinations of range may be made from this
configuration by making different comparisons between E field and H
field amplitude and phase. Typically, a weighted average of
available determinations is used based on the strongest or most
reliable signals from the set.
[0062] To find a position within an area, as needed for the
exemplary warehouse example, typically multiple receivers are
positioned to allow triangulation based on multiple range
measurements, i.e., to each location receiver from the active
location tag. If height is desired, additional receivers may be
deployed to improve the height resolution. The receivers may be
connected to a central computer for combining the measurements from
all receivers to determine location. The connection may be by wired
or wireless network or other methods as desired.
[0063] In a further alternative embodiment, the area may be
pre-measured to account for specific local propagation disturbances
and to reduce errors from equipment variations. A calibration set
of measurements is made by placing an active location tag at known
locations and measuring the signals and phases at all receivers. A
finer grid, or set of grids, of locations may be generated from
extrapolation and interpolation from the measured locations. In
operation, an unknown location is determined by transmitting from
the unknown location and comparing the set of measured data from
all receivers with the stored calibration data to find a location
having the best match. Best match may be determined by summing
absolute value of the differences between each respective signal
from each receiver, the best match being the lowest sum. In the
sum, amplitudes and phases may be scaled to have similar effect on
the sum. Weak signals may be ignored. Other criteria may be applied
to weight each element. Other matching criteria such as sum of
squared differences or other error criteria may be used. In one
embodiment, a location is determined as the centroid of a region
having an error value above a predetermined threshold. In further
embodiments, motion constraints, such as walls and motion dynamics
including momentum are used to improve position.
[0064] Further details on near field positioning systems can be
found in:
[0065] U.S. patent application Ser. No. 11/272,533 titled: "Near
field location system and method," filed Nov. 10, 2005 by Schantz
et al., now published as Publication US20060132352, Jun. 22,
2006,
[0066] U.S. patent application Ser. No. 11/215,699 titled: "Low
frequency asset tag tracking system and method," filed Aug. 30,
2005 by Schantz et al., now published as Publication US20060192709,
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[0072] All of the above listed US Patent, Patent Applications and
publications are hereby incorporated herein by reference in their
entirety.
CONCLUSION
[0073] The present invention has been described above with the aid
of functional building blocks illustrating the performance of
specified functions and relationships thereof. The boundaries of
these functional building blocks have been arbitrarily defined
herein for the convenience of the description. Alternate boundaries
can be defined so long as the specified functions and relationships
thereof are appropriately performed. Any such alternate boundaries
are thus within the scope and spirit of the claimed invention. One
skilled in the art will recognize that these functional building
blocks can be implemented by discrete components, application
specific integrated circuits, processors executing appropriate
software and the like or any combination thereof.
[0074] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example only, and not limitation. Thus, the
breadth and scope of the present invention should not be limited by
any of the above-described exemplary embodiments, but should be
defined only in accordance with the following claims and their
equivalents.
* * * * *