U.S. patent application number 12/463411 was filed with the patent office on 2009-09-03 for wireless tracking system and method with multipath error mitigation.
This patent application is currently assigned to AWAREPOINT CORPORATION. Invention is credited to Dyami Caliri, Derek Smith.
Application Number | 20090219210 12/463411 |
Document ID | / |
Family ID | 39708336 |
Filed Date | 2009-09-03 |
United States Patent
Application |
20090219210 |
Kind Code |
A1 |
Caliri; Dyami ; et
al. |
September 3, 2009 |
Wireless Tracking System And Method With Multipath Error
Mitigation
Abstract
A system (50) and method (300) for providing multipath error
mitigation for real-time wireless tracking of an object (100) is
disclosed herein. A plurality of sensor readings are obtained from
a tag (60) attached to an object (100) within an indoor facility
(70). A plurality of reading sets are generated and sorted by
zones. A zone with the highest average reading is preferably
selected and the location of the object (100) is calculated based
on the selected zone readings. In this manner, faulty position
readings are eliminated from the location calculation thereby
allowing for more accurate tracking of the object (100) within the
indoor facility (70).
Inventors: |
Caliri; Dyami; (Encinitas,
CA) ; Smith; Derek; (San Diego, CA) |
Correspondence
Address: |
Clause Eight Intellectual Property Services
P.O Box 131270
CARLSBAD
CA
92013
US
|
Assignee: |
AWAREPOINT CORPORATION
San Diego
CA
|
Family ID: |
39708336 |
Appl. No.: |
12/463411 |
Filed: |
May 10, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11672047 |
Feb 7, 2007 |
7545326 |
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12463411 |
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10968814 |
Oct 18, 2004 |
7312752 |
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11672047 |
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60513784 |
Oct 22, 2003 |
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60528052 |
Dec 9, 2003 |
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60572690 |
May 19, 2004 |
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Current U.S.
Class: |
342/451 |
Current CPC
Class: |
H04W 64/00 20130101;
G01S 5/0252 20130101; Y02D 30/70 20200801; G01S 5/021 20130101 |
Class at
Publication: |
342/451 |
International
Class: |
G01S 3/02 20060101
G01S003/02 |
Claims
1. A method for determining a location of an object within a
predetermined environment, the method comprising: transmitting a
plurality of radiofrequency signals for a wireless tracking device
to a positioning engine, each of the plurality of radiofrequency
signals corresponding to a signal transmitter within the
environment; processing each of the plurality of radiofrequency
signals to determine the location of the signal transmitter for
each of the plurality of radiofrequency signals; determining a
probable region of the object based on the location of a of the
signal transmitter for each of the plurality of radiofrequency
signals; weighting any of the plurality of radiofrequency signals
corresponding from a fixed signal transmitter located outside of
the probable region of the object; and calculating the position of
the object within the predetermined environment using only the
plurality of radiofrequency signals corresponding to a fixed signal
transmitter within the probable region of the object.
2. The method according to claim 1 wherein the predetermined
environment is a hospital and the probable region of the object is
a room in the hospital.
3. The method according to claim 1 wherein transmitting a plurality
of radio frequency signals for a wireless tracking device to a
positioning engine comprises: transmitting radio frequency signals
from the wireless tracking device comprising signal strength, link
quality, time of transmission and identification of the wireless
tracking device; receiving the radio frequency signals at a
plurality of stationary sensors positioned within the predetermined
environment; and transmitting the signal strength, the link
quality, the time of transmission and the identification of the
wireless tracking device from each of the plurality of stationary
sensors to a server for processing.
4. The method according to claim 1 further comprising displaying
the real-time location of the object on a graphical user
interface.
5. The method according to claim 1 further comprising comparing the
calculated location of the object within the predetermined
environment to a previously calculated location for the object.
6. The method according to claim 5 further comprising monitoring
the motion state of the object to confirm movement of the object
from the previously calculated location to the location of the
object within the predetermined environment.
7. A system for providing real-time location information for a
plurality of non-stationary objects within an indoor facility, the
system comprising: a mapped space of a physical environment of the
indoor facility; and a processor comprising means for updating the
mapped space in response to received measurements of the physical
environment from one or more stationary sensors located within the
indoor facility, means for generating a plurality of location
hypotheses for a non-stationary object within the physical
environment, at least one of the location hypotheses computed in
response to measurement received from the non-stationary object and
the mapped space, and means for generating a location estimate
based on one or more of the plurality of location hypotheses,
wherein one or more of the plurality of location hypotheses are
selected based on a probability associated respectively therewith,
and wherein a probability is computed in association with a
plurality of known barriers in the physical space.
8. The system according to claim 7 wherein the indoor facility is a
hospital.
9. The system according to claim 7 wherein the measurement from the
object is generated from a radiofrequency signal from a tag.
10. The system according to claim 9 wherein the radiofrequency
signal from a tag comprises signal strength, link quality, time and
identification of the tag.
11. The system according to claim 10 wherein the processor is
located at a remote server in communication with the plurality of
stationary sensors through at least one bridge device.
12. The system according to claim 9 wherein the tag transmits a
radiofrequency signal of approximately 2.48 GigaHertz, and each of
the plurality of stationary sensors communicates utilizing a
802.15.4 protocol.
13. A system for providing real-time location information for a
plurality of non-stationary objects within an indoor facility, the
system comprising: a plurality of stationary sensors, each of the
plurality of stationary sensors positioned within the indoor
facility; a plurality of tags, each of the plurality of tags
attached to one of the plurality of non-stationary objects, each of
the plurality of tags having means for wirelessly transmitting to
each of the plurality of stationary sensors tag specific data; a
mapped space of a physical environment of the indoor facility; a
processor comprising means for updating the mapped space in
response to received measurements of the physical environment from
one or more stationary sensors located within the indoor facility,
means for generating a plurality of location hypotheses for each of
the plurality of non-stationary objects located within the physical
environment, at least one of the location hypotheses computed in
response to measurement received from a non-stationary object of
the plurality of non-stationary objects and the mapped space, and
means for generating a location estimate based on one or more of
the plurality of location hypotheses, wherein one or more of the
plurality of location hypotheses are selected based on a
probability associated respectively therewith, and wherein a
probability is computed in association with a plurality of known
barriers in the physical space.
14. The system according to claim 13 wherein the indoor facility is
a hospital.
15. The system according to claim 13 wherein the measurement from
the object is generated from a radiofrequency signal from the
tag.
16. The system according to claim 15 wherein the radiofrequency
signal from a tag comprises signal strength, link quality, time and
identification of the tag.
17. The system according to claim 13 wherein the processor is
located at a remote server in communication with the plurality of
stationary sensors through at least one bridge device.
18. The system according to claim 15 wherein the tag transmits a
radiofrequency signal of approximately 2.48 GigaHertz, and each of
the plurality of stationary sensors communicates utilizing a
802.15.4 protocol.
19. The system according to claim 13 wherein a radial basis
function is utilized by the processor in generating a location
estimate.
20. The system according to claim 13 wherein the processor further
comprises means for determining if the calculated location is
consistent with a previous location.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The Present Application is a divisional application of U.S.
patent application Ser. No. 11/672,047, filed on Feb. 7, 2007,
which is a Continuation-In-Part Application of U.S. patent
application Ser. No. 10/968,814, filed on Oct. 18, 2004, now U.S.
Pat. No. 7,312,752, which claims priority to U.S. Provisional
Application No. 60/572,690, filed on May 19, 2004, now abandoned,
U.S. Provisional Application No. 60/528,052, filed on Dec. 9, 2003,
now abandoned, and U.S. Provisional Application No. 60/513,784,
filed on Oct. 22, 2003, now abandoned.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention is related to wireless tracking
systems and methods. More specifically, the present invention
relates to a system and method for mitigating multipath errors
associated with the wireless tracking of objects.
[0005] 2. Description of Related Art
[0006] The ability to quickly determine the location of objects
located within a facility is becoming a necessity of life. To the
uninformed observer, the placement of transponders, also known as
tags, on numerous non-stationary objects whether in an office or
home would appear to be an unnecessary use of resources. However,
the uninformed observer fails to appreciate the complexity of
modern life and the desire for efficiency, whether at the office or
home.
[0007] For example, in a typical hospital there are numerous shifts
of employees utilizing the same equipment. When a new shift arrives
the ability to quickly locate medical equipment not only results in
a more efficient use of resources, but also can result in averting
a medical emergency. Thus, the tracking of medical equipment in a
hospital is becoming a standard practice.
[0008] The tracking of objects in other facilities is rapidly
becoming a means of achieving greater efficiency. A typical radio
frequency identification system includes at least multiple tagged
objects, each of which transmits a signal, multiple receivers for
receiving the transmissions from the tagged objects, and a
processing means for analyzing the transmissions to determine the
locations of the tagged objects within a predetermined environment.
One exemplary method triangulates the strongest received signals to
determine the location of a tagged object. This method is based on
the assumption that the receivers with the strongest received
signals are the ones located closest to the tagged object. However,
such an assumption is sometimes erroneous due to common
environmental obstacles. Multipath effects can result in a further
located receiver having a stronger signal from a tagged object than
a more proximate receiver to the tagged object, which result in a
mistaken location determination.
[0009] Tekinay, U.S. Pat. No. 6,259,894 for a Method For Improved
Line-Of-Sight Signal Detection Using RF Model Parameters, discloses
a method for reducing time-shift due to multipathing for a RF
signal in an RF environment.
[0010] Close, U.S. Pat. No. 3,869,673 for a Method And Apparatus
For Measuring Multipath Distortion, discloses a method for
indicating multipath distortion in a received signal.
[0011] Lennen, U.S. Pat. No. 5,402,450 for a Signal Timing
Synchronizer, discloses a method and apparatus for reducing the
effects of multipath induced distortions on the accuracy of
detecting the time of arrival of a received signal.
[0012] Fortune et al., U.S. Pat. No. 5,450,615 for a Prediction Of
Indoor Electromagnetic Wave Propagation For Wireless Indoor
Systems, discloses techniques for predicting RF propagation within
a structure.
[0013] The prior art has yet to resolve mistaken location
calculations based on multipath effects.
BRIEF SUMMARY OF THE INVENTION
[0014] One aspect of the present invention is a method for
determining a real-time location of an object within an indoor
facility. The method begins with obtaining a plurality of sensor
readings from a transponder attached to the object. Next, a reading
set is generated from the plurality of sensor readings. The reading
set is then sorted by a plurality of physical regions. Then, a
first physical region is selected from the plurality of physical
regions. The first physical region is composed of a first plurality
of sensor readings that have the highest average signal strength.
Next, the first plurality of sensor readings is sorted into a
second plurality of sensor readings. Each of the second plurality
of sensor readings corresponds to sensor located in a zone within
the first physical region. A selected zone having the highest
average reading is then selected. Next, a real-time location of the
object is calculated using only the second plurality of sensor
readings that correspond to the selected zone.
[0015] Each sensor reading preferably comprises a signal strength,
link quality, time and identification of the transponder. The
method may further comprise displaying the real-time location of
the object on a graphical user interface. The method may also
include comparing the calculated real-time location of the object
to a previously calculated location for the object. The method may
include monitoring the motion state of the object to confirm
movement of the object from the previously calculated location to
the real-time location. In a preferred embodiment, the indoor
facility is a hospital, with each of the plurality of physical
regions being a floor of the hospital, and the selected zone being
a room on a floor of the hospital. The plurality of sensor readings
of the reading set preferably comprises from eight to thirty sensor
readings for the transponder, and each sensor reading originates
from a single stationary sensor positioned within the indoor
facility. Each sensor reading is preferably a radio frequency
transmission from the transponder. The step of obtaining a
plurality of sensor readings from the transponder attached to the
object preferably comprises, transmitting a radio frequency
transmission from the transponder, the radio frequency transmission
comprising a signal strength, link quality, time of transmission
and identification of the transponder, receiving the radio
frequency transmission at a plurality of stationary sensors
positioned within the indoor facility, and transmitting the signal
strength, the link quality, the time of transmission and the
identification of the transponder from each of the plurality of
stationary sensors to a server for processing.
[0016] Another object of the present invention is a system for
providing real-time location information for a plurality of
non-stationary objects within an indoor facility. The system
includes a plurality of sensors, a plurality of transponders and a
processing means. Each of the stationary sensors is positioned
within the indoor facility. Each of the transponders is attached to
one of the non-stationary objects. Each of the transponders has
means for wirelessly transmitting to each of the stationary sensors
transponder-specific data. The processing means processes the
transponder-specific data to obtain a real-time reading set for the
transponder. The processing means also processes the real-time
reading set to determine a first plurality of sensor readings. The
first plurality of sensor readings corresponds to a physical region
within the indoor facility having the highest average reading. The
processor means then processes the first plurality of sensor
readings, which are associated with the selected physical region,
to select a zone within the physical region having the highest
average reading. The processing means then calculates the position
of the non-stationary object using the sensor readings from the
stationary sensors positioned within the selected zone of the
selected physical region.
[0017] The transponder-specific data preferably comprises a signal
strength, link quality, time and identification of the transponder.
In a preferred embodiment, the indoor facility is a hospital with
the physical region preferably a floor of the hospital, and the
selected zone is a room on a floor of the hospital. The processing
means is preferably a server in communication with the plurality of
stationary sensors through a network. Each transponder preferably
transmits a radio frequency transmission of approximately 2.48
gigahertz, and each stationary sensor preferably communicates
utilizing a 802.15.4 protocol. The system may further comprise
means for eliminating those sensor readings not associated with
(i.e., located within) the selected zone.
[0018] Another aspect of the present invention is a method for
determining a location of an object within a predetermined
environment. The method begins with transmitting a plurality of
radio frequency signals for a wireless tracking device to a
positioning engine. The wireless tracking device is attached to the
object and each of the radio frequency signals corresponds to a
fixed signal transmitter within the environment. Each radio
frequency signal is processed to determine the location of the
respective fixed signal transmitter. A probable region of the
object is determined based on the location of a majority of the
fixed signal transmitters for the plurality of radio frequency
signals. The radio frequency signals that correspond to fixed
signal transmitters located outside of the probable region of the
object are eliminated from the location determination. The position
of the object within the predetermined environment is calculated
using only the radio frequency signals that correspond to fixed
signal transmitters located within the probable region of the
object.
[0019] The predetermined environment is preferably a hospital, and
the probable region of the object is preferably a room in the
hospital. The step of transmitting a plurality of radio frequency
signals for a wireless tracking device to a positioning engine
preferably comprises transmitting radio frequency signals from the
wireless tracking device, each radio frequency signal comprising a
signal strength, link quality, time of transmission and
identification of the transponder, receiving the radio frequency
signals at a plurality of stationary sensors positioned within the
predetermined environment, and transmitting the signal strength,
the link quality, the time of transmission and the identification
of the wireless tracking device from each of the plurality of
stationary sensors to a server for processing.
[0020] Yet another aspect of the present invention is a system for
providing real-time location information for a plurality of
non-stationary objects within an indoor facility. The system
includes a mapped space and a processor. The mapped space is of a
physical environment of the indoor facility. The processor includes
means for updating the mapped space in response to received
measurements of the physical environment from one or more
stationary sensors located within the indoor facility, means for
generating a plurality of location hypotheses for a non-stationary
object within the physical environment, at least one of the
location hypotheses computed in response to measurement received
from the non-stationary object and the mapped space, and means for
generating a location estimate based on one or more of the
plurality of location hypotheses, wherein one or more of the
plurality of location hypotheses are selected based on a
probability associated respectively therewith. The probability is
computed in association with known barriers in the physical
space.
[0021] Having briefly described the present invention, the above
and further objects, features and advantages thereof will be
recognized by those skilled in the pertinent art from the following
detailed description of the invention when taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0022] FIG. 1 is schematic view of a system of the present
invention.
[0023] FIG. 2 is a multi-floor view of a facility employing the
system of the present invention.
[0024] FIG. 3 is a floor plan view of a single floor in a facility
employing the system of the present invention.
[0025] FIG. 4 is a two-floor view of a facility including a tagged
object and sensors of the system of the present invention.
[0026] FIG. 5 is a flow chart of a general method of the present
invention.
[0027] FIG. 6 is a flow chart of a specific method of the present
invention.
[0028] FIG. 7 is a flow chart of a specific method of the present
invention.
[0029] FIG. 8 is a flow chart of a single sensor reading input.
DETAILED DESCRIPTION OF THE INVENTION
[0030] As shown in FIGS. 1-4, a system is generally designated 50.
The system 50 is capable of determining real-time location of an
object 100 within an indoor facility 70. The system 50 preferably
includes a plurality of sensors 55, a plurality of bridges 56, a
plurality of tags 60 and at least one server 65. One example of the
components of the system 50 is disclosed in U.S. Pat. No. 7,312,752
for a Wireless Position Location And Tracking System, which is
hereby incorporated by reference in its entirety. A more specific
example of the sensors 55 is disclosed in U.S. Pat. No. 7,324,824
for a Plug-In Network Appliance, which is hereby incorporated by
reference in its entirety. Another example of a system 50 is set
forth in U.S. Pat. No. 6,751,455 for a Power-And Bandwidth-Adaptive
In-Home Wireless Communications System With Power-Grid-Powered
Agents And Battery-Powered Clients, which is hereby incorporated by
reference in its entirety.
[0031] The system 50 is preferably employed within an indoor
facility 70 such as a business office, factory, home, hospital
and/or government agency building. The system 50 is utilized to
track and locate various objects positioned throughout the facility
70. The tags 60 continuously transmit signals on a predetermined
time cycle, and these signals are received by sensors 55 positioned
throughout the facility 70. The sensors 55 transmit the data to a
bridge 56 for transmission to a server 65. If a sensor 55 is unable
to transmit to a bridge 56, the sensor may transmit to another
sensor 55 in a mesh network-like system for eventual transmission
to a bridge 56. In a preferred embodiment, a transmission may be
sent from a transmission distance of six sensors 55 from a bridge
56. The server 65 preferably continuously receives transmissions
from the sensors 55 via the bridges 56 concerning the movement of
objects 100 bearing a tag 60 within the facility 70. The server 65
processes the transmissions from the sensors 55 and calculates a
real-time position for each of the objects 100 bearing a tag 60
within the facility 70. The real-time location information for each
of the objects 100 bearing a tag 60 is preferably displayed on an
image of a floor plan of the indoor facility 70, or if the facility
70 has multiple floors, then on the floor plan images of the floors
of the facility 70. The floor plan image may be used with a
graphical user interface so that an individual of the facility 70
is able to quickly locate objects 100 within the facility 70.
[0032] As shown in FIG. 1, the system 50 utilizes sensors 55 to
monitor and identify the real-time position of non-stationary
objects bearing or integrated with tags 60. The sensors 55a-f
preferably wirelessly communicate with each other (shown as double
arrow lines) and with a server 65 through a wired connection 66 via
at least one bridge 56, such as disclosed in the above-mentioned
U.S. Pat. No. 7,324,824 for a Plug-In Network Appliance. The tags
60a-c transmit signals (shown as dashed lines) which are received
by the sensors 55a-e, which then transmit signals to bridges 56 for
eventual transmission to a server 65. The server 65 is preferably
located on-site at the facility 70. However, the system 50 may also
include an off-site server 65, not shown.
[0033] Each tag 60 preferably transmits a radio frequency signal of
approximately 2.48 GigaHertz ("GHz"). The communication format is
preferably IEEE Standard 802.15.4. Those skilled in the pertinent
art will recognize that the tags 60 may operate at various
frequencies without departing from the scope and spirit of the
present invention.
[0034] As shown in FIGS. 2-4, the facility 70 is depicted as a
hospital. The facility 70 has a multitude of floors 75a-c. An
elevator 80 provides access between the various floors 75a, 75b and
75c. Each floor 75a, 75b and 75c has a multitude of rooms 90a-i,
with each room 90 accessible through a door 85. Positioned
throughout the facility 70 are sensors 55a-o for obtaining readings
from tags 60a-d attached to or integrated into non-stationary
objects 100a, 100b (see FIGS. 2 and 4). A bridge 56 is also shown
for receiving transmissions from the sensors 55 for processing by
the server 65.
[0035] As shown in FIG. 4, the tag 60a is attached to movable bed
100a positioned on an upper floor 75c. The tag 60a transmits a
signal which is received by sensors 55a, 55b and 55c. If the signal
to sensor 55c is the strongest, then an analysis of the readings
from the sensors 55a-c may place the tag 60a, and thus the movable
bed 100a, at position 60' on the lower floor 75b. This type of
faulty reading would likely occur with triangulation. To prevent
such a faulty positioning reading, the present invention processes
the readings preferably according to one of the methods illustrated
in FIGS. 5-7, which would eliminate the reading from sensor 55c
from the location calculation for movable bed 100a.
[0036] A general method 200 of the present invention is illustrated
in FIG. 5. At block 202, the sensors 55 of the system 50 generate
readings from the tags 60. These single sensor reading inputs 600
are illustrated in FIG. 8. As shown in FIG. 8, the inputs
preferably include the tag identification 604, the signal strength
606, the link quality 608 and the time of the reading 610, which
are inputted as a single sensor reading 602. At block 204, a
plurality of readings sets are generated from the sensor readings.
In a preferred embodiment, each of the plurality of readings sets
represents an area of a facility 70. At block 206, the readings are
further sorted by a particular zone of the facility 70 thereby
eliminating readings that may lead to an incorrect location. In a
preferred embodiment, a zone is a subset of an area. At block 208,
the zone with the highest average reading is selected for
calculation of the position of the object 100, again eliminating
readings that may lead to an incorrect reading. At block 210, the
location of the object 100 is calculated based on the readings from
the selected zone.
[0037] A more specific method 300 of the present invention is set
forth in FIG. 6. At block 302, the sensors 55 of the system 50
generate readings from the tags 60. As discussed above, the single
sensor reading inputs 600 are illustrated in FIG. 8. At block 304,
a reading set is generated for readings from a single tag 60. The
generation of the reading set is typically in response to an
inquiry from a user of the system 50 in search of an object 100
bearing tag 60. At decision block 306, the server 65 determines if
there is sufficient data to proceed with the location analysis. If
there is insufficient data, the method is restarted at block 302.
If there is sufficient data, then the method proceeds to block 308.
At block 308, the reading sets are separated by floor 75 of the
facility 70. At block 310, the floor 75 with the highest average
reading set is selected for further processing. At block 312, the
readings for the selected floor are sorted by zones. Each zone may
represent any physical boundary on the selected floor 75 of the
facility 70. Preferably, the zones represent a room 90, station 95
or other easily determined physical location. At block 314, the
zone with the highest average reading is selected. At block 316,
the location of the object 100 is calculated based on the readings
from the selected zone. At block 318, the location is inputted to
the location database for dissemination to users of the system to
locate the object 100.
[0038] An even more specific method 400 of the present invention is
set forth in FIG. 7. At block 402, the sensors 55 of the system 50
generate readings from the tags 60. As discussed above, the single
sensor reading inputs 600 are illustrated in FIG. 8. At block 404,
a reading set is generated for readings from a single tag 60. The
generation of the reading set is typically in response to an
inquiry from a user of the system 50 in search of an object 100
bearing tag 60. At decision block 406, the server 65 determines if
there is sufficient data to proceed with the location analysis. If
there is insufficient data, the method is restarted at block 402.
If there is sufficient data, then the method proceeds to block 408.
At block 408, the reading sets are separated by floor 75 of the
facility 70. At block 410, the floor 75 with the highest average
reading set is selected for further processing. At block 412, the
readings for the selected floor are sorted by zones. Each zone may
represent any physical boundary on the selected floor 75 of the
facility 70. Preferably, the zones represent a room 90, station 95
or other easily determined physical location. At block 414, the
zone with the highest average reading is selected. At block 416,
the location of the object 100 is calculated based on the readings
from the selected zone.
[0039] At decision block 418, the server 65 inquires if the new
calculated location is consistent with available data for the
object 100. The available data includes the motion sensor state of
the object 100 which is tracked at block 424. If the motion sensor
has not detected a motion threshold of the object 100, then that is
one indication that the new calculated location is in error.
However, if the motion sensor has detected movement (a motion
threshold) of the object 100, then that is one indication that the
new calculated location is correct. Additional data for the
decision block 418 includes recently calculated locations for the
object 100 which are available from database 426. Yet further data
available for decision block 418 is data from the possible
hypotheses database 428. The possible hypotheses database includes
data such as the timing between the last calculated location and
the new calculated location. If the object 100 has moved one end of
the facility 70 to another end of the facility 70 within seconds,
then the new calculated location may be in error. If the response
to decision block 418 is yes, then at block 420 the location is
inputted to the location database for dissemination to users of the
system to locate the object 100. If the response to decision block
418 is no, then the new calculated location is held as an unproven
hypothesis at block 422.
[0040] The following example illustrates the information that is
utilized and eliminated in practicing the present invention.
TABLE-US-00001 TABLE ONE Sensor Signal Strength Link Sensor
Location # dB Quality Time (floor/region) 1 -95 -95 Sep. 14, 2006
5/B 11:22:35 2 -10 -10 Sep. 14, 2006 4/C 11:22:35 3 -20 -20 Sep.
14, 2006 4/C 11:22:36 4 -25 -25 Sep. 14, 2006 4/C 11:22:35 5 -40
-40 Sep. 14, 2006 4/C 11:22:36 6 -50 -50 Sep. 14, 2006 4/C 11:22:36
7 -70 -70 Sep. 14, 2006 4/D 11:22:36 8 -80 -80 Sep. 14, 2006 4/D
11:22:36 9 -90 -90 Sep. 14, 2006 4/E 11:22:37 10 -95 -95 Sep. 14,
2006 4/E 11:22:37
TABLE-US-00002 TABLE TWO Floor Average Reading per Floor 2 N/A 3
-120 4 -30 5 -85
TABLE-US-00003 TABLE THREE Region Peaks Average Reading per Region
C -20 -20 D -10 -70 E -70 -95
[0041] As shown in Table One, the signal strength from each tag 60
is provided dBm with a full strength value of zero, which is a
ratio of power relative to 1 milli-Watt. The Link Quality value is
provided as a similar value as the signal strength. The time is a
date stamp of the time and date that the signal is received by the
sensor 55. The sensor location is preferably a floor and region on
the floor. In a preferred embodiment, the regions on the floors
overlap each other. The regions are preferably determined based on
the facility 70.
[0042] In Table One, ten readings from sensors 55 positioned on
various floors of the facility 70. Each of the readings is
transmitted from a single tag 60 to the sensors 60. The sensors 60
transmit the data from the tag 60 to the server 65 via bridges 56.
The server 65 uses the data to calculate the location of the object
100 as discussed. The sensor location may also be provided in terms
of a X-Y position which is based on a floor plan image of each
floor of the facility 70. The X-Y position may be based on the
pixel location on the image of the floor plan.
[0043] The average reading from all of the sensors 55 on each floor
is provided in Table Two. More specifically, if the fifth floor has
ten sensors 55 that each received a signal from a specific tag 60,
then the readings from those ten sensors 55 are averaged to obtain
the average reading per floor value provided in Table Two. The
readings from the floor with the highest value are then further
processed to determine the location of the object 100. The readings
from the sensors 55 on the other floors are eliminated from the
calculation for the location of the object 100.
[0044] The average reading from all of the sensors 55 in each
region on the selected floor is provided in Table Three. As
mentioned above, the regions preferably overlap so that a single
sensor 55 may be in two or more regions, and used in the average
reading for both regions. The peak reading for each region is also
set forth in Table Three. In an alternative embodiment, if the peak
reading exceeds a threshold, then that region is selected even if
the average readings for that region are less than another region.
In calculating the location of the object 100, the highest readings
within a selected region are used for the calculation. The number
of readings used preferably ranges from 2 to 10, and is most
preferably 3 to 5. The more readings used in the calculation, the
longer the processing time for the calculation. Thus, using 10
readings may provide a more accurate location, however, the
processing time will be longer than using 3 readings. In a
preferred embodiment, a radial basis function is utilized in
calculating the location of the object 100. The location of the
object 100 is preferably conveyed as an XY coordinate on an floor
plan image of the facility 70.
[0045] From the foregoing it is believed that those skilled in the
pertinent art will recognize the meritorious advancement of this
invention and will readily understand that while the present
invention has been described in association with a preferred
embodiment thereof, and other embodiments illustrated in the
accompanying drawings, numerous changes modification and
substitutions of equivalents may be made therein without departing
from the spirit and scope of this invention which is intended to be
unlimited by the foregoing except as may appear in the following
appended claim. Therefore, the embodiments of the invention in
which an exclusive property or privilege is claimed are defined in
the following appended claims.
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