U.S. patent application number 16/364062 was filed with the patent office on 2019-10-10 for rfid systems using distributed exciter network.
This patent application is currently assigned to Mojix, Inc.. The applicant listed for this patent is Mojix, Inc.. Invention is credited to Michael Collender, John Gevargiz, Christopher Jones, Robert Lee, Majid Manteghi, Gordon Oliver, Ramin Sadr, Syed Hassan Yousaf.
Application Number | 20190311163 16/364062 |
Document ID | / |
Family ID | 39788982 |
Filed Date | 2019-10-10 |
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United States Patent
Application |
20190311163 |
Kind Code |
A1 |
Sadr; Ramin ; et
al. |
October 10, 2019 |
RFID Systems Using Distributed Exciter Network
Abstract
RFID systems are disclosed that include at least one RFID
receiver system and a distributed exciter architecture. Exciters
can be connected via wired and/or wireless connections to the RFID
receiver system, which can control activation of the exciters to
detect the presence of RFID tags within interrogation spaces
defined by the exciter topology. One embodiment includes an RFID
receiver system configured to detect information from RFID tags
within a receive coverage area, and a plurality of exciters
defining a plurality of interrogation spaces within the receive
coverage area of the receiver system. The receiver system is
configured to transmit a control signal that identifies one of the
exciters and includes information indicative of an RFID tag
interrogation signal, the exciters are configured to receive the
control signal, and the exciter identified in the control signal is
configured to illuminate an interrogation space with the RFID tag
interrogation signal.
Inventors: |
Sadr; Ramin; (Los Angeles,
CA) ; Gevargiz; John; (Los Angeles, CA) ; Lee;
Robert; (Los Angeles, CA) ; Manteghi; Majid;
(Blackburg, VA) ; Oliver; Gordon; (Los Angeles,
CA) ; Collender; Michael; (Los Angeles, CA) ;
Jones; Christopher; (Pacific Palisades, CA) ; Yousaf;
Syed Hassan; (Los Angeles, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mojix, Inc. |
Los Angeles |
CA |
US |
|
|
Assignee: |
Mojix, Inc.
Los Angeles
CA
|
Family ID: |
39788982 |
Appl. No.: |
16/364062 |
Filed: |
March 25, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15904027 |
Feb 23, 2018 |
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16364062 |
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15633623 |
Jun 26, 2017 |
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15904027 |
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14213851 |
Mar 14, 2014 |
9690957 |
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15633623 |
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13757688 |
Feb 1, 2013 |
8680970 |
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14213851 |
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12054331 |
Mar 24, 2008 |
8395482 |
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13757688 |
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60896864 |
Mar 23, 2007 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06K 7/10158 20130101;
G06Q 10/087 20130101; G06K 7/01 20130101; G06K 7/10475 20130101;
G06K 7/10188 20130101 |
International
Class: |
G06K 7/10 20060101
G06K007/10; G06K 7/01 20060101 G06K007/01; G06Q 10/08 20060101
G06Q010/08 |
Claims
1. An RFID system configured to manipulate RFID tags, comprising:
an RFID receiver system configured to read RFID tag information
from activated RFID tags within a receive coverage area; and a
plurality of exciters defining a plurality of interrogation spaces
within the receive coverage area of the RFID receiver system, where
at least one of the plurality of exciters is able to activate an
RFID tag within the plurality of interrogation spaces and the
plurality of interrogation spaces are contained within the receive
coverage area of the RFID receiver system; wherein the RFID
receiver system is configured to transmit a control signal that
identifies one of the plurality of exciters and includes
information indicative of an RFID tag interrogation signal; wherein
the plurality of exciters are configured to receive the control
signal; wherein the exciter identified in the control signal is
configured to illuminate an interrogation space with the RFID tag
interrogation signal and activate an RFID tag within the
interrogation space; and wherein the RFID receiver system is
configured to read RFID tag information from an RFID tag activated
by an RFID tag interrogation signal generated by one of the
plurality of exciters.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/904,027 filed Feb. 23, 2018, which is a
continuation of U.S. patent application Ser. No. 15/633,623 filed
Jun. 26, 2017, which is a continuation of U.S. patent application
Ser. No. 14/213,851 filed Mar. 14, 2014 and issued as U.S. Pat. No.
9,690,957 on Jun. 27, 2017, which is a continuation of U.S. patent
application Ser. No. 13/757,688 filed Feb. 1, 2013 and issued as
U.S. Pat. No. 8,680,970 on Mar. 25, 2014, which is a continuation
of U.S. patent application Ser. No. 12/054,331 filed Mar. 24, 2008
and issued as U.S. Pat. No. 8,395,482 on Mar. 12, 2013, which
claims priority to U.S. Provisional Patent Application No.
60/896,864 filed Mar. 23, 2007, the disclosures of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to RFID systems and more
specifically to an RFID system that incorporates at least one RFID
receiver system and a distributed exciter architecture that defines
a plurality of interrogation spaces.
[0003] The detection of signals in difficult environments, such as
where the signal to noise ratio is very low and/or the interference
from other signals is very high, has always been a challenging
problem.
[0004] In RFID systems such as the RFID systems described in U.S.
patent application Ser. No. 11/971678, entitled "RFID System with
Low Complexity Implementation and Pallet Coding Error Correction,"
filed Jan. 9, 2008, the disclosure of which is incorporated by
reference herein in its entirety, RFID receiver subsystems rely on
an enhanced RF front end as well as processing capabilities, for
detecting very low power signals in the presence of additive white
Gaussian noise with further channel distortions in in-door or
out-door wireless propagation channels. These techniques are
particularly applicable to Radio Frequency Identification (RFID)
based systems. FIG. 12 illustrates a transmit and receive RFID
reader similar to the transmit and receive readers described in
U.S. patent application Ser. No. 11/971,678 and the specifics of
the RF front end. The reader (12-9) follows an RFID tag protocol to
communicate with tags (12-5) using the same transmit and receive
frequencies. The time-line showing this communication is shown in
FIG. 13. The protocol governs the reader transmission of (12-4)
data (13-2) and a continuous waveform (CW) (13-4) to the tag, and
reception (12-2) of the tag's data (13-10). From FIG. 13, during
the period that the tag is backscattering a packet to the reader,
the reader is transmitting CW signal (13-4). That is the received
signal is a composite of transmitted CW and received tag signal
(12-7). The receiver subsystem (12-9) performs baseband down
conversion (12-12, 12-14), filtering (12-16, 12-18), and
amplification (12-20, 12-22). At the output of the baseband
amplifiers the signal from the tag is present, as well as a strong
DC component. This DC component is canceled by using DC block
capacitors (12-27, 12-29). To further improve the performance of
the DC cancellation, the input to the DC block capacitors (12-27,
12-29) is controlled through a switch (12-24, 12-26) which is only
closed during the period that the system is receiving data from the
tag, as depicted in FIG. 13 (13-10). The digital processor (12-46),
which maintains the system timing control of the switch control,
opens the switch during the reader transmit periods (13-2, 13-6,
13-14, 13-18), and closes the switches during the expected receive
periods (13-4, 13-10, 13-16). The output of the DC cancellation
capacitors is followed by the AGC loops (12-32, 12-34), analog to
digital converters (12-36, 12-38), and digital processor (12-40),
which includes the control algorithms.
SUMMARY OF THE INVENTION
[0005] RFID systems in accordance with many embodiment of the
invention include one or more RFID receiver systems that are
associated with a number of distributed transmitters, referred to
as RFID tag exciters (or just "exciter"). The exciters can act as
signal repeaters from the RFID receiver system that enable
transmission of a tag signal to a distant exciter, which in turn
filters, amplifies and re-transmits the signal to the intended
collection of RFD tags within the line-of-sight view of the
exciter. The logical interconnect and communications topology
scales from a centralized point of control up to a fully connected
graph. Physically, the communications network can be either wired
lines or wireless.
[0006] Each exciter may or may not embed active re-generation of
the transmitted signal to the RFID tag; however, in many
embodiments each exciter emits sufficient power and a waveform
compatible with the requirements of a standard such as set forth by
Electronic Product Code Global (EPC Global) or International
Standard Organizations (ISO). The transmission from the RFID
receiver system to an exciter may be compatible with these
standards and/or utilize other waveforms compatible with regulatory
requirements such as set forth by US Federal Communication
Commission (FCC) or other international regulatory agencies.
[0007] One embodiment of the invention includes an RFID receiver
system configured to detect information from RFID tags within a
receive coverage area, and a plurality of exciters defining a
plurality of interrogation spaces within the receive coverage area
of the RFID receiver system. In addition, the RFID receiver system
is configured to transmit a control signal that identifies one of
the plurality of exciters and includes information indicative of an
RFID tag interrogation signal, the plurality of exciters are
configured to receive the control signal, and the exciter
identified in the control signal is configured to illuminate an
interrogation space with the RFID tag interrogation signal.
[0008] In a further embodiment of the invention, the RFID receiver
system communicates to at least one of the plurality of exciters
via a wired connection.
[0009] In another embodiment of the invention, the wired connection
directly connects the exciter to the RFID receiver system.
[0010] In a still further embodiment of the invention, the wired
connection connects the exciter to another of the plurality of
exciters, which is configured to relay control signals from the
RFID receiver system via the wired connection.
[0011] In still another embodiment of the invention, the wired
connection is a coaxial cable, and the control signal is modulated
at a first RF frequency.
[0012] In a yet further embodiment of the invention, the exciter is
configured to down convert the control signal to extract at least
the identity of the exciter identified by the control signal, and
the exciter is configured to up convert and transmit the RFID tag
interrogation signal at a second RF frequency, when the exciter is
the exciter identified by the control signal.
[0013] In yet another embodiment of the invention, the control
signal specifies the frequency of the second RF frequency.
[0014] In a further embodiment of the invention again, the second
RF frequency is the same as the first RF frequency.
[0015] In another embodiment of the invention again, the wired
connection is a twisted pair cable, and the control signal is a
baseband signal.
[0016] In a further additional embodiment of the invention, the
exciter is configured to extract at least the identity of the
exciter identified by the control signal, and the exciter is
configured to up convert and transmit the RFID tag interrogation
signal at a transmit RF frequency, when the exciter is the exciter
identified by the control signal.
[0017] In another additional embodiment of the invention, the
control signal specifies the transmit RF frequency.
[0018] In a still yet further embodiment of the invention, the RFID
receiver system communicates with at least one of the plurality of
exciters via a wireless connection.
[0019] In still yet another embodiment of the invention, the
wireless connection is a direct connection between the RFID
receiver system and the exciter.
[0020] In a still further embodiment of the invention again, the
wireless connection is between the exciter and a second of the
plurality of exciters.
[0021] In still another embodiment of the invention again, the
second of the plurality of exciters is configured to relay control
signals from the RFID receiver system via the wireless
connection.
[0022] In a still further additional embodiment of the invention,
the control signal is modulated at a first RF frequency, and the
exciter is configured to down convert the control signal to extract
at least the identity of the exciter identified by the control
signal.
[0023] In still another additional embodiment of the invention, the
exciter is configured to up convert and transmit the RFID tag
interrogation signal at a second RF frequency when the exciter is
the exciter identified by the control signal.
[0024] In a yet further embodiment of the invention again, the
control signal specifies the frequency of the second RF
frequency.
[0025] In yet another embodiment of the invention again, the
exciter is configured to generate an RFID tag interrogation signal
and modulate the RFID tag interrogation signal onto a second RF
frequency.
[0026] In a yet further additional embodiment of the invention, the
control signal specifies the frequency of the second RF
frequency.
[0027] In yet another additional embodiment of the invention, the
RFID receiver system is configured to transmit a status signal at a
first RF frequency that identifies one of the plurality of
exciters, the exciter is configured to extract at least the
identity of the exciter identified by the status signal, and the
exciter is configured to generate a response signal and transmits
the response signal at a second RF frequency.
[0028] In a further additional embodiment of the invention again,
the waveform of the response signal is similar to the waveform
generated by an illuminated RFID tag.
[0029] In another additional embodiment of the invention again, the
status signal specifies the frequency of the second RF
frequency.
[0030] In another further embodiment of the invention, the RFID
receiver system is configured to transmit control signals that
activate a plurality of the exciters to transmit RFID tag
interrogation signals at different frequencies.
[0031] In still another further embodiment of the invention, the
control signals transmitted by the RFID receiver system cause the
plurality of activated exciters to transmit in accordance with a
frequency hopping protocol.
[0032] In yet another further embodiment of the invention, the RFID
receiver system is configured to allocate frequencies to exciters
randomly.
[0033] In another further additional embodiment of the invention,
the RFID receiver system possesses information concerning the
exciter distribution topology, and the RFID receiver system uses
the topology information when allocating frequencies to activated
exciters.
[0034] In another further embodiment of the invention again, the
control signal includes an n-bit address.
[0035] In still yet another further embodiment of the invention,
the control signal includes all the necessary signal
characteristics and parameters to generate the desired waveform
output from the exciter.
[0036] In still another further additional embodiment of the
invention, the control signal includes information that can be used
by an exciter to perform transmit power calibration.
[0037] In still another further embodiment of the invention again,
the control signal includes information indicative of a
transmission frequency selection.
[0038] Yet another further additional embodiment of the invention
also includes a second RFID receiver system configured to detect
information from RFID tags within a second receive coverage area,
and a plurality of exciters defining a plurality of interrogation
spaces within the receive coverage area of the second RFID receiver
system. In addition, the second RFID receiver system is configured
to transmit a control signal that identifies one of the plurality
of exciters and includes information indicative of an RFID tag
interrogation signal, the plurality of exciters within the coverage
area of the second RFID receiver system are configured to receive
the control signal from the second RFID receiver system, and the
exciter identified in the control signal is configured to
illuminate an interrogation space within the coverage area of the
second RFID receiver system with the RFID tag interrogation
signal.
[0039] In yet another further embodiment of the invention again,
the RFID receiver system is configured to detect RFID tag
information when an exciter illuminates an interrogation space with
an RFID tag interrogation signal, and the RFID receiver system is
configured to determine whether the detected information is from an
RFID tag located within the interrogation space illuminated by the
exciter.
[0040] Another further additional embodiment of the invention again
includes a sensor located within the illuminated interrogation
space configured to detect changes within the interrogation space.
In addition, the sensor is configured to communicate sensor output
to the RFID receiver system, and the RFID receiver system is
configured to determine whether the detected information is from an
RFID tag located within the interrogation space illuminated by the
exciter using information including the sensor output.
[0041] In still yet another further additional embodiment of the
invention, the RFID receiver system is configured to detect RFID
tag information when other exciters illuminate other interrogation
spaces with RFID tag interrogation signals, and the RFID receiver
system is configured to determine whether the detected information
is from an RFID tag located within the interrogation space
illuminated by the exciter using information including the RFID tag
information detected when other exciters illuminated other
interrogation spaces.
[0042] In still yet another further embodiment of the invention
again, the RFID tag information is an RF signal, the RFID receiver
system is configured to collect information concerning features of
the RFID tag information RF signal, and the RFID receiver system is
configured to determine whether the detected information is from an
RFID tag located within the interrogation space illuminated by the
exciter using information including the features of the RFID tag
information RF signal.
[0043] In yet another further additional embodiment of the
invention again, the collected features of the RFID tag information
RF signal include signal strength, signal-to-noise ratio, and
direction of arrival.
[0044] In a still yet further additional embodiment of the
invention, the RFID receiver system repeatedly causes a plurality
of exciters to sequentially illuminate a plurality of interrogation
spaces and records the detection of RFID tag information, and the
RFID receiver system is configured to determine whether detected
information is from an RFID tag located within an interrogation
space illuminated by one of the plurality of exciters using
information including the rate at which the RFID tag information is
detected when the interrogation space is illuminated.
[0045] In still yet another additional embodiment of the invention,
the RFID receiver system possesses information concerning the
exciter topography, the RFID receiver system is configured to
estimate expected detection rates for RFID tags in different
interrogation spaces, and the RFID receiver system is configured to
determine whether detected information is from an RFID tag located
within an interrogation space illuminated by one of the plurality
of exciters using information including the rate at which the RFID
tag information is detected when the interrogation space is
illuminated and the expected detection rates for RFID tags in
different interrogation spaces.
[0046] In a yet further additional embodiment of the invention
again, the RFID receiver system is configured to determine movement
of an RFID tag from one interrogation space to another
interrogation space using information including the rate at which
the information is detected when interrogation spaces are
illuminated and the expected detection rates for RFID tags in
different interrogation spaces.
[0047] An exciter configured to illuminate an interrogation space
in accordance with an embodiment of the invention includes, an
input configured to receive a control signal including an exciter
address and information indicative of an RFID tag interrogation
signal, and a transmitter configured to transmit an RFID tag
interrogation signal, a decode module configured to control the
transmitter to transmit the RFID tag interrogation signal indicated
by a control signal, when the exciter is addressed by the exciter
address in the control signal.
[0048] In a further embodiment of the invention, the input includes
a coaxial cable connector, the control signal is modulated on a
first RF frequency, and the transmitter is configured to modulate
the RFID tag interrogation signal onto a second RF frequency.
[0049] In another embodiment of the invention, the frequency of the
second RF frequency is specified by the control signal.
[0050] In a still further embodiment of the invention, the
frequency of the second RF frequency is the same as the frequency
of the first RF frequency.
[0051] Still another embodiment of the invention also includes an
output, where the output includes a coaxial cable connector, and a
coupler connected to the input, the decode module, and the output,
where the coupler is configured to split the input signal between
the decode module and the output.
[0052] In a yet further embodiment of the invention, the input
includes a twisted pair connector, the control signal is a baseband
signal, and the transmitter is configured to modulate the RFID tag
interrogation signal onto an RF frequency.
[0053] In yet another embodiment of the invention, the frequency of
the RF frequency is specified by the control signal.
[0054] A further additional embodiment of the invention includes an
output, where the output includes a twisted pair connector, and a
coupler connected to the input, the decode module, and the output,
where the coupler is configured to split the input signal between
the decode module and the output.
[0055] In another additional embodiment of the invention, the input
is connected to a receive antenna, the control signal is a wireless
signal transmitted at a first RF frequency, and the transmitter is
configured to modulate the RFID tag interrogation signal onto a
second RF frequency.
[0056] In a further embodiment of the invention again, the
frequency of the second RF frequency is specified by the control
signal.
[0057] In another embodiment of the invention again, the decode
module is configured to control the transmitter to retransmit the
control signal, when the exciter is not addressed by the exciter
address in the control signal.
[0058] In a still yet further embodiment of the invention, the
transmitter includes a power amplifier, and a level control loop
configured to monitor the output of the power amplifier to adjust
the gain of the power amplifier to maintain the output signal below
a predetermined threshold.
[0059] In still yet another embodiment of the invention the
transmitter includes a power amplifier, and a level control loop
configured to detect the power of input signals to the power
amplifier and the output of the power amplifier and to adjust the
gain of the power amplifier to maintain the output signal below a
predetermined threshold.
[0060] An embodiment of the method of the invention includes
generating a control signal including an exciter address and an
RFID tag interrogation signal, transmitting the control signal to
at least one of the plurality of distributed exciters, illuminating
an interrogation space with the RFID tag interrogation signal using
the exciter addressed by the control signal, and receiving an RFID
tag information signal.
[0061] In a further embodiment of the method of the invention,
generating a control signal includes identifying an n-bit address
associated with an exciter located within an interrogation
space.
[0062] In another embodiment of the method of the invention,
generating a control signal includes determining signal
characteristics and parameters of an RFID tag interrogation signal
to be generated by an exciter.
[0063] In a still further embodiment of the method of the
invention, generating a control signal includes generating
information that can be used by an exciter to perform transmit
power calibration.
[0064] In still another embodiment of the method of the invention,
generating a control signal includes generating information
indicative of a transmission frequency selection.
[0065] In a yet further embodiment of the method of the invention,
transmitting the control signal includes transmitting the control
signal to a first exciter that relays the signal to a second
exciter.
[0066] In yet another embodiment of the method of the invention,
illuminating the interrogation space includes extracting the RFID
tag interrogation signal from the control signal, modulating the
RFID tag interrogation signal onto a transmission frequency, and
transmitting the modulated RFID tag interrogation signal.
[0067] In a further additional embodiment of the method of the
invention, extracting the RFID tag interrogation signal further
comprises down converting the control signal.
[0068] In another additional embodiment of the method of the
invention, modulating the RFID tag interrogation signal onto a
transmission frequency further comprises modulating the RFID tag
interrogation signal onto a transmission frequency specified by the
control signal.
[0069] In a further embodiment again of the method of the
invention, receiving an RFID tag information signal includes
determining whether received RFID tag information is from an RFID
tag located within the illuminated interrogation space.
[0070] In another embodiment again of the method of the invention,
determining whether received RFID tag information is from an RFID
tag located within the illuminated interrogation space includes
detecting changes in the interrogation space using at least one
sensor.
[0071] In a still yet further embodiment of the method of the
invention, determining whether received RFID tag information is
from an RFID tag located within the illuminated interrogation space
includes detecting RFID tag information when other interrogation
spaces are illuminated.
[0072] In still yet another embodiment of the method of the
invention, determining whether received RFID tag information is
from an RFID tag located within the illuminated interrogation space
includes collecting information concerning features of the RFID tag
information signal.
[0073] In a still further additional embodiment of the method of
the invention, the collected information concerning features of the
RFID tag information includes signal strength, signal-to-noise
ratio, and direction of arrival.
[0074] In still another additional embodiment of the method of the
invention, determining whether received RFID tag information is
from an RFID tag located within the illuminated interrogation space
includes repeatedly illuminating a plurality of interrogation
spaces, recording the detection of RFID tag information, and
determining the rate at which RFID tag information is detected when
each interrogation space is illuminated.
[0075] In a still further embodiment again of the method of the
invention, determining whether received RFID tag information is
from an RFID tag located within the illuminated interrogation space
includes estimating expected detection rates for RFID tags in
different interrogation spaces using information concerning the
exciter topography, and comparing the rate at which RFID tag
information is detected when an interrogation space is illuminated
with expected detection rates for the interrogation space when an
RFID tag is located within different interrogation spaces.
[0076] A method of estimating the location of an RFID tag within a
plurality of interrogation spaces in accordance with an embodiment
of the method of the invention includes repeatedly illuminating
each of the plurality of interrogation spaces, recording the
illuminated interrogation space when the RFID tag is detected, and
determining the rate at which the RFID tag is detected when each
interrogation space is illuminated, and recording the rate at which
the RFID tag is detected for each interrogation space and for each
exciter.
[0077] A yet further additional embodiment of the method of the
invention includes obtaining information concerning the topology of
the plurality of interrogation spaces, estimating expected
detection rates for RFID tags in different interrogation spaces
using information concerning the interrogation space topography,
and comparing the rate at which RFID tag information is detected
when an interrogation space is illuminated with expected detection
rates for the interrogation space when an RFID tag is located
within different interrogation spaces.
[0078] In yet another additional embodiment of the method of the
invention, comparing the observed detection rate to the estimated
detection rate comprises using the difference between the expected
detection rate and observed detection rate as the argument to a
Gaussian density function to produce a probability of the observed
detection rate in a given interrogation space.
[0079] In a yet further embodiment again of the method of the
invention, recording the rate at which RFID tag information is
detected includes using an exciter ID, a hypothesis region, and an
RFID tag ID.
[0080] Yet another embodiment again of the method of the invention
further includes detecting movement of an RFID tag from a first
interrogation space to a second interrogation space using the
comparison of the rate at which RFID tag information is detected
and the expected detection rates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0081] FIG. 1 is a network diagram of an RFID system including a
distributed exciter architecture, where the exciters are connected
to the RFID system via cables, in accordance with an embodiment of
the invention.
[0082] FIG. 2 is a network diagram of an RFID system including two
RFID receiver systems and a distributed exciter architecture, where
the exciters are connected to the RFID receiver system via cables,
in accordance with an embodiment of the invention.
[0083] FIG. 3 is a network diagram of an RFID system including two
RFID receiver systems and a distributed exciter architecture, where
the exciters communicate with the RFID receiver system wirelessly,
in accordance with an embodiment of the invention.
[0084] FIG. 4 is a semi-schematic circuit diagram of an exciter
configured to be connected to an RFID receiver system via a coaxial
cable in accordance with an embodiment of the invention.
[0085] FIG. 5 is a semi-schematic circuit diagram of an exciter
configured to be connected to an RFID receiver system via a twisted
pair in accordance with an embodiment of the invention.
[0086] FIG. 6 is a semi-schematic circuit diagram of an exciter
configured to wirelessly communicate with an RFID receiver system
in accordance with an embodiment of the invention.
[0087] FIG. 7 is a semi-schematic circuit diagram of a wireless
re-generative exciter in accordance with an embodiment of the
invention.
[0088] FIG. 8 is a plan view of an antenna element in accordance
with an embodiment of the invention.
[0089] FIG. 9 is a cross-sectional view of an antenna assembly in
accordance with an embodiment of the invention.
[0090] FIG. 10 is a plan view of an array of receiver antennas in
accordance with an embodiment of the invention.
[0091] FIG. 11 is a cross-sectional view of an array of receiver
antennas in accordance with an embodiment of the invention that is
similar to the array shown in FIG. 10.
[0092] FIG. 12 is a semi-schematic circuit diagram of a transmit
and receive RFID reader.
[0093] FIG. 13 is a chart conceptually illustrating tag protocol
timing.
[0094] FIG. 14 is a conceptual illustration of software used to
configure an RFID application server in accordance with an
embodiment of the invention.
[0095] FIG. 15 is a flow chart of a process for determining whether
RFID tag information was detected from a tag within a predetermined
interrogation space in accordance with an embodiment of the
invention.
[0096] FIG. 16 is a semi-schematic diagram showing an RFID system
including a distributed exciter architecture in which exciters are
paired to facilitate tag read location discrimination in accordance
with an embodiment of the invention.
[0097] FIGS. 17a and 17b are conceptual diagrams illustrating
frequency assignment and scheduling for a plurality of exciters in
accordance with an embodiment of the invention.
[0098] FIG. 18 is a block diagram illustrating input level
condition measurement and an output level feedback control loop in
accordance with an embodiment of the invention.
[0099] FIG. 19 is a block diagram showing a wireless or wireline
controlled exciter with wireless status information backhaul
enabling the wireless communication of messages from an exciter to
an RFID receiver system in accordance with an embodiment of the
invention.
[0100] FIG. 20 is a conceptual illustration of the movement of an
RFID tag between two hypothesis regions.
[0101] FIG. 21 is a conceptual illustration of the spatial
relationship between an exciter and an RFID tag that can be used to
determine excitation link margin in an exciter/hypothesis topology,
exciter transmit power, exciter radiation pattern, and typical RFID
tag radiation pattern in accordance with embodiments of the
invention.
[0102] FIG. 22 is a chart illustrating a probability mass function
that describes the probability of RFID tag read rates for RFID tags
located within a given hypothesis region under excitation by a
given exciter in accordance with an embodiment of the
invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0103] Turning now to the drawings, RFID systems including at least
one RFID receiver system and a distributed exciter architecture are
shown. In several embodiments, the desired overall interrogation
space is decomposed into a set of interrogation spaces and exciters
are placed in each target interrogation space. The RFID system
obtains information from collections of RFID tags in specific
interrogation spaces by controlling the activation of exciters. An
RFID tag within an interrogation space is manipulated by
illuminating the interrogation space using an RFID tag
interrogation signal provided to the exciter by the RFID receiver
system. The illuminated RFID tag backscatters information, which
can be detected by the RFID receiver system.
[0104] The RFID receiver system can control the size of each
interrogation space by adjusting the total emitter power from the
exciter. In a number of embodiments, the overall performance of the
system is improved by selecting each exciter transmit antenna type
to provide the desired level of directivity, thereby controlling
the beam-width for the target interrogation space. In several
embodiments, the exciters are connected via cables to the RFID
receiver system. In a number of embodiments, the exciters are
wirelessly connected to the RFID receiver system.
[0105] When an interrogation space topology has been defined, RFID
systems in accordance with embodiments of the invention can control
the illumination of individual interrogation spaces to obtain
location information concerning items bearing RFID tags. In many
embodiments, the RFID system polls exciters. In several embodiment,
the RFID system can incorporate additional sensors that detect
changes within an interrogation space (e.g. movement) and the RFID
system can activate the corresponding exciter and/or exciters
associated with adjacent interrogation spaces to obtain information
concerning any items bearing RFID tags moving between interrogation
spaces.
[0106] A problem that can be encountered when using a distributed
exciter architecture is the potential for an RFID tag to be read
from outside of an exciter's interrogation space (a false read). In
several embodiments, information concerning various characteristics
of the RFID system are used to detect the occurrence of false
reads. In a number of embodiments, data from sensors in the
interrogation spaces, RFID tag information detected in other
interrogation spaces and/or the RF features of the detected RFID
tag information can be used to determine whether a false read has
occurred. In many embodiments, statistical analysis is used to
detect false reads based upon predicted read rates for RFID tags
located within the interrogation space. In these embodiments,
repeated illumination of an interrogation space and RFID tag
detection rates are compared to predicted detection rates to
determine the likely location of the RFID tag. In several
embodiments, predicted detection rates are obtained using knowledge
of an RFID system's exciter topology.
[0107] An RFID system including a distributed exciter architecture
in accordance with an embodiment of the invention is shown in FIG.
1. The RFID system (1-1) includes an RFID receiver system (1-2)
connected to an array of receiver antennas (1-4) and a plurality of
exciters (1-6, 1-14, 1-18, 1-23, 1-28) that are daisy chained to
the RFID receiver system via cables (1-10, 1-9, 1-16, 1-22, 1-26).
The RFID receiver system (1-2) is also connected to a LAN (1-32)
via connection (1-34). An RFID application server (1-30) is
connected to the LAN via connection (1-36). Although the plurality
of exciters are shown as wired, in many embodiments exciters
communicate wirelessly with the RFID receiver system.
[0108] In operation, the RFID receiver system (1-2) controls the
activation of exciters. The cable segments (1-10, 1-12, 1-16, 1-22,
1-26) carry both direct current (DC) power and control commands
from the RFID receiver system (1-2) to each exciter. The
transmitted "backhaul signal" from the RFID receiver system (1-2)
to the exciters embeds all the necessary signal characteristics and
parameters to generate a desired waveform output from the exciter
module to an RFID tag. In several embodiments, each exciter can be
commanded and addressed by an N-bit address, N-ranging from
16-to-32 bit. The exciters (1-8, 1-14, 1-18, 1-23, 1-28) can be
operated sequentially or concurrently, depending on the number of
possible beams the RFID receiver system can support. In the
illustrated embodiment, the RFID receiver system (1-2) includes a
single antenna array (1-4) and is capable of generating a single
beam. In other embodiments, the RFID receiver system includes
multiple antenna arrays and is capable of generating multiple beams
(see discussion below).
[0109] The interrogation space and transmitted power of each
exciter can be managed and controlled by the RFID receiver system
(1-2). In the illustrated embodiment, the RFID receiver system
(1-2) controls the exciters to create interrogation space (1-8,
1-15, 1-20, 1-24, & 1-28) of different sizes. In addition, the
received coverage area is configurable. The RFID receiver system
can receive signals from the complete coverage area (1-11).
Alternatively, the RFID receiver system can adaptively beam-form to
the specified exciter interrogation spaces (1-12, 1-21).
[0110] The RFID application server (1-30) schedules each exciter to
operate harmoniously in multiple dimensions, which are time,
frequency and space. In a number of embodiments, the RFID
application server (1-30) includes a scheduler for S/T/FDM (Space,
Time and Frequency Division Multiplexing), which utilizes an
optimization algorithm to maximize the probability of successful
manipulation of all the RFID tags within a target interrogation
space. In addition, the controller may utilize frequency hopping in
scheduling the frequency channel for each exciter in order to
satisfy various regulatory constraints.
[0111] An exciter layout and a time line showing frequency channels
assigned by an RFID application server in accordance with an
embodiment of the invention are shown in FIGS. 17a and 17b. The
timeline (17-4), depicts channel selection within the 900 MHz ISM
band (17-10), versus the time line. In the illustrated embodiment
at time exciters 12, 15, 7, 11, 10, 3, 9, 4, 2, 1, 6, 14, 16, 8,
13, and 5 are activated for operation on channels 7, 16, 23, 25,
34, 40, 44, 46, 49, 50, 51, and 52 respectively. Note that more
than one exciter might occupy a given channel and to the extent
that these exciters are topologically co-located (for instance
exciters 7 and 11) collisions can occur. Therefore, better choices
could have been made in the frequency/exciter mapping plan.
However, in the illustrated embodiment, random frequencies were
assigned to the active exciters (17-8), which implies that
co-location frequency collisions are possible (for instance on
channel 23 between exciters 7 and 11 at time instance 1). An
algorithm that can optimize frequency reuse and exciter location
planning (14-12) (S/T/FDM) can be utilized to reduce overall
interference degradation while adhering to regulatory constraints.
An RFID system including two RFID receiver systems and a
distributed exciter architecture in accordance with an embodiment
of the invention is illustrated in FIG. 2. The RFID system includes
two RFID receiver systems (2-2, 2-20), each with a separate array
of receiver antennas (2-4, 2-22), and that are connected to a LAN
(2-21) via connections (2-23, 2-25). A plurality of exciters (2-6,
2-52, 2-58, 2-64, 2-32, 2-28, 2-38, 2-48, 2-44, 2-72, 2-70) are
connected to the two RFID receiver systems to create multiple
interrogation spaces (2-13, 2-54, 2-69, 2-66, 2-34, 2-28, 2-40,
2-46, 2-49, 2-72,). In the illustrated embodiment, the exciters
form two groups, where each group is connected to the RFID receiver
systems by a separate cable (2-24, 2-30, 2-36, 2-42, 2-50 and 2-10,
2-12, 2-56, 2-62, 2-68). The RFID application server (2-51)
interfaces with the RFID receiver systems (2-2, 2-20), through the
LAN (2-21), and manages the operation of the exciters, which
includes control, command, coordination, calibration and
optimization of the exciter interrogation spaces. The functions of
RFID application servers in accordance with embodiments of the
invention are discussed further below.
[0112] As can be seen from the embodiment illustrated in FIG. 2,
each RFID receiver system has a separate receive coverage area
(2-5, 2-29). Therefore, the use of multiple RFID receiver systems
can enable an increase in the coverage area of the system. In
addition, exciters in different coverage areas can be activated
simultaneously. In the illustrated embodiment, several exciters
(2-32, 2-44) occupy locations within the coverage area of both of
the RFID receiver systems. Beam forming at each RFID receiver
system allows a null to be placed in the other RFID receiver
system's interrogation space hence avoiding collisions when two
exciters (and RFID tags) transmit simultaneously in the different
interrogation spaces.
[0113] An RFID system including multiple RFID receiver systems and
a distributed exciter architecture constructed using exciters that
wirelessly communicate with the RFID receiver systems in accordance
with an embodiment of the invention is illustrated in FIG. 3. The
RFID system is similar to the system shown in FIG. 2 with the
exception that the exciters are configured to communicate
wirelessly with the RFID receiver systems. Each RFID receiver
system (2-2', 2-20') has both receive (2-4', 2-22') and transmit
antennas (3-6, 3-8). The transmit antenna radiates the forward link
to the exciter, while the receive antenna array receives the signal
from RFID tags, within the interrogation space of each exciter. The
forward link also carries exciter identification (ID) number,
command, control and management information. In the illustrated
embodiment, the receive coverage areas for the two RFID receiver
systems (2-5', 2-29') is shown. The overlap region between the
coverage areas (2-5', 2-29') is managed through receive array
beam-forming and frequency or time coordination of exciter
operation. The RFID application server (3-7) interfaces with the
two RFID receiver systems (2-2', 2-20') through the LAN (2-21') and
manages the operations of the exciters that includes control,
command, coordination, and calibration of the exciters as well as
optimization of the interrogation spaces.
[0114] Implementations of wired exciters in accordance with
embodiments of the invention are shown in FIGS. 4 and 5. FIG. 4
depicts an exciter in accordance with an embodiment of the
invention that is configured to connect to an RFID system via
coaxial cable. FIG. 5 depicts an exciter in accordance with an
embodiment of the invention that is configured to connect to an
RFID system via universal twisted pair (UTP) in which the exciter
can be connected via CAT-5 or 6 wires.
[0115] In the embodiment illustrated in FIG. 4, a reader coaxial
interface (4-2, 4-4, 4-6, 4-8, 4-12) and an interface (4-14) for
daisy chaining a plurality of exciters (4-52) are shown. A signal
received from an RFID receiver system typically carries control
signals, which are processed by the demodulate and decode command
and control messages module (4-10) and used to control the self
calibration and automatic level control (ALC) loop (4-18, 4-20,
4-48, 4-34, 4-36, 4-32) or to set the transmit power in response to
a manual setting (4-38, 4-30). Command and control messages for a
wired exciter include messages that cause the exciter to go through
power calibration (described below), to turn the transmit signal on
or off, and to control the reporting of exciter status information
(see description of hybrid wireless/wired exciter provided below
with respect to FIG. 19). The received RF signal is split using a
coupler (4-8) between the next exciter (4-52) and the transmit RF
chain (4-40). The RF chain includes the receive low noise amplifier
(4-16) and the ALC loop (4-22, 4-20, 4-24, 4-48) consisting of the
feedback loop and the power amplifier (PA) (4-24). Output of the PA
is followed by the transmit antenna patch (4-28). The exciter
additionally has interfaces to one or more external alarms (4-58),
which are interfaced to the internal processor (4-47).
[0116] A self calibration and automatic level control loop in
accordance with an embodiment of the invention is shown in FIG. 18.
This block measures both input (18-1) and output (18-4) power
levels. Input power levels between -10 dB Milliwatts and 27 dB
Milliwatts are deemed to be within a tolerable range. If the input
signal is within this range then the Output Power Level Measurement
(18-3) block feeds back a signal to an amplifier module (18-2) to
control the power amplifier's gain such that a total output power
level of 30 dB Milliwatts is achieved. This output level is
compliant with the FCC total radiated power restriction for a
frequency hopped system operating in the 900 MHz band. In other
embodiments, the total output power level of the exciter can be
controlled in accordance with other application constraints. The
embodiment illustrated in FIG. 18 is particularly useful for
applications in which the exciter regenerates a received control
signal. Wireless exciters that synthesize the RFID tag
interrogation waveform in accordance with several embodiments of
the invention can utilize an automatic control loop that simply
monitors the output level and adjusts the transmitter power
accordingly.
[0117] Turning now to FIG. 5, an exciter having a UTP interface,
using CAT-5 or 6 cables (5-4, 5-72) is illustrated. When a UTP
interface is used, the interface between the exciter and the RFID
system (5-4) is at baseband. The exciter detects the baseband
signal and modulates it to the specified RF frequency. When a
coaxial interface is used, the interface is at RF, where the RF
signal is repeated, and baseband carries the control signals. The
raw data, which the RFID receiver system transmits to the exciter
includes the control and command signals as well as the data that
is modulated and transmitted to the RFID tag. Similar to the
coaxial version, UTP exciters can be daisy chained (5-2, 5-4, 5-6,
5-8, 5-10, 5-12, 5-14, 5-72, 5-74) using UTP connectors. The
demodulate and decode command and control messages module (5-18)
decodes the command and control data used for configuring the RF
synthesizer (5-22), the modulator (5-26), the self calibration and
ALC control loop (5-24), and transmit power manual setting
subsystem (5-20). The data decoder and modulator (5-26) detects and
re-modulates transmit data in accordance with the relevant
standard, and is followed by up conversion (5-28, 5-60, 5-58) and
automatic gain control (5-32, 5-34, 5-36, 5-24). The amplified
signal is provided via a connection (5-66) to the transmit antenna
patch (5-40). The exciter additionally has interfaces (5-76) to one
or more external alarms (5-80), which are interfaced to the
internal processor (5-16).
[0118] A wireless exciter in accordance with an embodiment of the
invention is illustrated in FIG. 6. An RFID receiver system
communicates with the wireless exciter on one frequency using the
transmit antenna (6-4), while receiving data from the tags on a
different frequency using its array of receiver antennas. In the
illustrated embodiment, the wireless exciter acts as an RF repeater
utilizing the 900 MHz ISM band. In other embodiments, other
frequency bands can be used. The RF signal is down converted from
the signal transmitted by the RFID receiver system transmit antenna
(6-4), to baseband on the down conversion output connection (6-20),
and then the baseband signal is up converted to a select frequency
on the up conversion output connection (6-30). The specified
frequencies for down and up conversions are communicated to the
exciter using the RF command channel, using the 900 MHz ISM band by
way of example. The same methodology can be employed in other
frequency bands. The exciter patch antenna (6-6) is discussed
further below and includes two feeds for receiving and transmitting
RF signals. The RFID receiver system transmits to the exciters
command, control, and transmit frequency plan information. The
commands are detected by the demodulate and decode command and
control messages module (6-74) and processed to control the dual
synthesizer (6-66), the self-calibration and ALC loop (6-54, 6-36,
6-50, 6-38), and the transmit power manual setting loop (6-56,
6-48).
[0119] Command and control messages for a wireless exciter can
include messages that cause the exciter to go through power
calibration, to turn the transmit signal on or off, to control the
reporting of exciter status information (see discussion of hybrid
wireless/wired exciter below), to select a transmit frequency, and
to set other parameters that define various transmit waveform
characteristics. In other embodiments, the command and control
messages can provide other instructions to an exciter.
[0120] The exciter configures the dual synthesizer (6-66) with the
receive and transmit frequencies in response to instructions
received from the RFID receiver system. The received RF signal is
down converted (6-18) and then up converted (6-28) to the specified
transmit frequency. The transmit power is set and calibrated using
the self calibration and ALC module (6-54) through the control
loops (6-52, 6-62, 6-50), and TX power calibration setting
sub-system (6-56) through the control loops (6-48, 6-58). The RF
path includes the required filters (6-22, 6-32, 6-42) and
amplifiers (6-10, 6-24, 6-38) for maintaining signal integrity and
quality. The output of the last stage (6-42) is followed by the
antenna element (6-46), connected to the exciters transmit feed
(6-46). The exciter additionally has interfaces to one or more
external alarms (6-80), which are interfaced to the internal
processor (6-70).
[0121] A re-generative wireless exciter configured to demodulate,
and detect the data provided by an RFID receiver system at a first
frequency, and then modulate and transmit the RF signal at a
different frequency in accordance with an embodiment of the
invention is illustrated in FIG. 7. The forward link from the RFID
receiver system to the exciter (7-2, 7-5) can carry control and
command signals, as well as raw data. The reader forward link (7-5)
to the exciter can use any modulation format such as spread
spectrum or any simple suppressed carrier modulation. In the
illustrated embodiment, the operating frequency and transmitted
power of this link are configured to meet regulatory requirements.
For example, U.S. Federal Communication Commission (FCC) standards
specified in FCC Part-15 can be satisfied through frequency
hopping.
[0122] The wireless exciter detects and decodes command and control
data using the data demodulator and decoder module (7-70) and the
decode command and control messages module (7-74). The command and
control data is used by the wireless exciter to configure the RF
synthesizer (7-62), the modulator (7-31), the self calibration and
ACL control loop (7-58), and transmit power manual setting
subsystem (7-86). The data encoder and modulator (7-31) detects and
re-modulates transmit data per a standard, followed by up
conversion (7-34) and the automatic gain control loop (7-42, 7-60,
7-44, 7-48) that is managed through the ALC loop control module
(7-58). The amplified signal (7-52) is followed by the transmit
antenna feed and patch (7-54). The exciter additionally has
interfaces to at least one external alarm (7-90), which are
interfaced to the internal processor (7-80).
[0123] A hybrid wireless/wireline exciter in accordance with an
embodiment of the invention is illustrated in FIG. 19. In addition
to the features supported by the previously described wired and/or
wireless exciters, this design is able to wirelessly return status
(19-9) or sensor (19-12) information via the same waveform
nominally used by an RFID tag. The hybrid exciter consists of a
wire interface (nominally coaxial cable) (19-1), a receive antenna
interface (19-2), a frequency conversion block (19-5), and a wire
output (daisy chain) interface (19-6). The wireless or wired
interface signal undergoes frequency down conversion using a mixing
frequency created by the receive frequency synthesizer (19-10).
After analog to digital conversion (19-7) a digital processor
(19-8) constructs modulated waveforms for digital to analog
conversion (19-13). These waveforms may describe tag commands
(i.e., signals used to manipulate tags) or exciter status
information (i.e. information transmitted on a return channel to an
RFID receiver system). In many embodiments, exciter status
information includes sensor trigger event data (19-11,12), exciter
calibration information, and/or any other information describing
the present state of the exciter or its surrounding environment.
Low pass filters (19-14, 19-15) precede frequency up conversion
(19-16) per a mix frequency determined by synthesizer block
(19-19). A variable gain block (19-17) calibrates the output power
level to not exceed a given threshold (for instance 30 dBm) prior
to bandpass filtering the output signal (19-18). The final
resulting signal is radiated through the transmit antenna
(19-21).
[0124] The hybrid wireless/wireline exciter shown in FIG. 19 can
generate a waveform similar to that of an illuminated tag to
communicate information to an RFID receiver system. In many
embodiments, the exciter can generate a waveform that emulates an
illuminated RFID tag so that the same RFID receiver system hardware
configuration can be used to both detect illuminated RFID tags and
receive status signals from exciters. In other embodiments, the
return channel from an exciter to an RFID receiver system is a
conventional wireless communication channel and the RFID receiver
utilizes separate receiver configuration/hardware for communicating
with exciters and receiving information from RFID tags.
[0125] An antenna that can be used in the construction of a reader
transmit and receive array, or exciter transmit and receive element
in accordance with an embodiment of the invention is illustrated in
FIG. 8. The antenna is fabricated using a brass, copper or Aluminum
plate (8-2). The plate (8-2) has four slots (8-22, 8-24, 8-28,
8-30), which end with a circular cut through (8-4, 8-6, 8-8, 8-26).
There are two through holes (8-10, 8-12) for connecting the
transmit and receive feeds, and four through holes (8-14, 8-16,
8-18, 8-20) for plastic standoffs.
[0126] An antenna element similar to the antenna shown in FIG. 8
mounted in a housing in accordance with an embodiment of the
invention is shown in FIG. 9. In the antenna assembly (9-2),
bushings (9-10, 9-12) connect the antenna element (9-4) to the
Printed Circuit Board (PCB) (9-18), which also serves as the
antenna ground plane. The connection is through the bushing's pins
(9-14, 9-16) to the PCB and through screws (9-6, 9-8) to the
element. The antenna element is covered using a radome cover (9-11)
at a fixed distance from the element. Plastic pins (9-5, 9-9)
provide the antenna element with additional stability.
[0127] A receive array configuration in accordance with an
embodiment of the invention is depicted in FIGS. 10 and 11. The
array is composed of four elements, similar to the antenna
assemblies (9-2) shown in FIG. 9. The four antenna elements (10-4,
10-6, 10-8, 10-10) are connected to the antenna PCB (10-2). FIG.11
shows the cross-sectional view of the PCB (10-2), bushings (11-8,
11-10,), elements (10-4, 10-6, 10-8, 10-10), and the radome cover
(11-2). In the illustrated embodiment, the element center-to-center
separation is 164 mm (10-5). In other embodiments, the element
center-to-center separation is determined according to the
requirements of the application.
[0128] Although specific antenna configurations are shown in FIGS.
8-11, other antenna configurations capable of transmitting and/or
receiving signals in accordance with a specific application can be
used in embodiments of the invention.
[0129] In a number of embodiments, the operation of exciters in a
distributed architecture is managed and controlled by the RFID
system using command, control and processing algorithms. A series
of processes that are coordinated by the RFID system to control the
operation of distributed exciters in accordance with an embodiment
of the invention is illustrated in FIG. 14. The processes (14-1)
include an exciter network interface and control process (14-2),
which provides the control messages, and manages communication
protocols. In many embodiments, various processes determine the
manner in which the exciters are to be controlled and the exciter
network interface and control process (14-2) is used to communicate
the control information to the exciters. In the illustrated
embodiment, exciter transmit power control process (14-4),
optimizes, controls, manages, and calibrates the transmit power
from each exciter, as specified by the user. In several
embodiments, messages containing transmit power control information
are provided to the exciters using the exciter network interface
and control process (14-2).
[0130] A reader to exciter frequency hopping and management process
(14-6), combines with an exciter management, scheduling and
optimization process (14-10), and RFID frequency reuse, planning
and optimization process (14-8), to optimize the operations of
single and multi-system RFID receiver system deployment. The
exciter frequency hopping and management process (14-6) coordinates
frequency hopping. In several embodiments, the frequency hopping
and management process assigns random frequencies to active
exciters. In other embodiments, the process operates in conjunction
with the RFID frequency reuse, planning and optimization process
(14-8) to employ an algorithm that optimizes frequency reuse based
upon exciter location. In many embodiments, other algorithms
appropriate to the application are employed for the assignment of
frequencies. In several embodiments, the exciter management,
scheduling and optimization process (14-10) coordinates the
activation of exciters. In a number of embodiments, the process
periodically polls exciters. In several embodiments, sensors detect
the likely presence of items bearing RFID tags within an
interrogation zone of an exciter and the sensor information is used
by the process in the controlled activation of individual
exciters.
[0131] An RFID false read discriminator process (14-12), detects
and flags RFID tag's which don't belong to a specified
interrogation space. An RFID false read descriminator process in
accordance with an embodiment of the invention is illustrated in
FIG. 15. The process (15-1) obtains (15-4) sensor data from the
interrogation space, detects (15-06) RFID tag data, which includes
a tag's identification code, and determines (15-8) RF features of
detected tag information, which include signal strength, signal to
noise ratio (SNR) and direction of arrival. The process uses the
collected sensor data, RFID tag data and RF features to determine
whether the RFID tag data was read from a tag located outside of
the interrogation space of the exciter that was activated by the
RFID system. A variety of processes can be used to determine
whether RFID tag data was read from a tag located outside an
interrogation space based upon collected information similar to the
information described above. Specific processes are discussed
further below.
[0132] A deployed RFID system that includes a distributed exciter
architecture in accordance with an embodiment of the invention is
illustrated in FIG. 16. The deployment includes three interrogation
spaces (16-14, 16-16, 16-18). In this deployment each interrogation
space utilizes two exciters (16-2, 16-4 & 16-6, 16-8, &
16-10, 16-12). In many embodiments, the RFID system illuminates
each interrogation space utilizing processes similar to the process
illustrated in FIG. 15 to identify whether RFID tag data was read
from a tag located within an exciter's interrogation space.
[0133] For example, when intending to read an RFID tag in a first
interrogation space (16-16) the reader (16-22) can read tag "x"
(16-34), and tag "y" (16-36). Data can be collected from other
exciters, (e.g. tag "x" was read by exciters (16-6 & 16-8),
while tag "y", was read by exciter (16-10, 16-6 & 16-12)), and
the SNR for each signal compared (e.g., the SNR for tag "y" was
lower compared to tag "x" when using exciters (16-6 & 16-8)).
Using the collected information, an RFID application server can
conclude that tag "y" (16-36), does belong to the first
interrogation space (16-16).
[0134] The process used to determine whether RFID tag data is
associated with an RFID tag located within an interrogation space
can depend upon the application. In several embodiments, read rate
information is used to identify relationships between RFID tags and
exciters. Various processes that rely on read rates to draw
conclusions concerning the location of RFID tags in accordance with
embodiments of the invention are discussed below.
[0135] Many processes in accordance with embodiments of the
invention determine the location of RFID tags from which
information has been received by gathering information regarding
RFID tag read rates and combine the read rate information with a
topologic description of exciters and regions in order to determine
tag location. Combining read rates with a topologic description can
enable false read detection when a tag is not located within a
region of interest by approaching the problem of read
discrimination in terms of `event sensing`. In particular the RFID
system is interested in events that involve tags moving from one
`hypothesis region` to another. These events can be called
`transition events`. In several embodiments, probabilities of
transition events (or transition hypotheses) inform the read
discrimination process.
[0136] A transition hypothesis can be determined by defining the
quantity p(x.sub.a|y.sub.{poll,sense}.sup.e.sup.j) as the
posteriori probability that a tag is in hypothesis region x.sub.a
using tag observations y.sub.{poll,sense}.sup.e.sup.j taken due to
exciter e.sub.j, which is in either a polling (poll) or a sensor
(sense) driven mode. An exciter in a polling driven mode is
activated by an RFID receiver system in a way that is strictly
periodic. An exciter in sensor driven mode is enabled when a sensor
event (such as a light beam break or machine vision motion) is
detected. The majority of the time, exciters run in a polling mode
in which access to the RFID receiver system is divided in time
equally between the set of possible exciters. This occurs until a
sensing event is triggered, at which point a subset of exciters is
granted exclusive access to the RIFD receiver system.
[0137] An event associated with a transition hypothesis can be
illustrated pictorially. A series of regions of interest and a
plurality of distributed exciters are shown in FIG. 20. In the
illustrated embodiment, an item bearing an RFID tag (20-1) moves
from a first location x.sub.1 to a second location x.sub.5. The
posteriori probability that a tag has moved from hypothesis region
x.sub.1 or x.sub.3 to region x.sub.5 can be determined by
evaluating the probability:
( p ( y poll e 1 x 1 ) + p ( y sense e 1 x 5 ) ) ( p ( y poll e 2 x
1 ) + p ( y sense e 2 x 5 ) ) ( p ( y poll e 1 x 3 ) + p ( y sense
e 1 x 5 ) ) ( p ( y poll e 2 x 3 ) + p ( y sense e 2 x 5 ) ) C x p
( y ) ##EQU00001##
The normalizing parameters C.sub.x and p(y) can be dropped
(normalization can be handled as a final separate step). The
probability of similar transition events can be described more
generally with the following product of sums:
.PI. a .di-elect cons. A origin .PI. e .di-elect cons. E dest ( p (
y poll e x a ) + p ( y sense e x dest ) ) ##EQU00002##
[0138] A.sub.origin.ident.Set of hypotheses that can transition to
the destination hypothesis
[0139] E.sub.dest.ident.Set of exciters surrounding the destination
hypothesis
[0140] The remainder of this description focuses on the method
through which the system obtains sums of the form
p(y.sub.poll.sup.e|x.sub.a)+p(y.sub.sense.sup.e|x.sub.dest).
[0141] We now refer to FIG. 21 which provides a topological
description of exciter e.sup.j in relation to hypothesis region
x.sub.i. For each such pairing, it is possible to determine the
typical excitation link margin (the amount of power arriving at a
tag above and beyond the absolute minimum power required to
activate the same tag). This link margin is well approximated with
knowledge of excitation power level, P.sub.t, angle from exciter
boresight .theta., mean distance from exciter to hypothesis, d, and
the expected exciter and tag radiation patterns.
[0142] Referring now to FIG. 22, the resulting excitation link
margin from FIG. 21 is used to generate a probability mass function
(pmf) that describes the likelihood that a tag will be read a given
percentage of the time (Read Rate) if it is located within
hypothesis region x.sub.i. Read Rate (RR) is determined empirically
by counting the number of times a tag is read in a fixed time
interval and dividing this quantity by the number of total possible
reads that were possible in the same time duration (note that a
read rate is labeled according to the triplet of exciter ID,
hypothesis region, and tag ID). Read Rates will be indexed by
exciter (e) and hypothesis region (x.sub.j) using notation
RR.sub.e,x.sub.j. The related Read Rates are taken by an exciter
(e) running in polling or sensor driven modes implicitly as
determined by the location of a hypothesis region. Destination
hypothesis regions are typically read using a sensor driven mode.
Given the preceding definitions it is possible to specify the
products of interest as a point on a Gaussian probability mass
function,
p ( y poll e x a ) + p ( y sense e x dest ) = 1 2 .pi..sigma. e , x
a 2 e - ( RR e , x a - .mu. e , x a ) 2 2 .sigma. e , x a 2 + 1 2
.pi..sigma. e , x dest 2 e - ( RR e , x dest - .mu. e , x dest ) 2
2 .sigma. e , x dest 2 ##EQU00003##
which is simply the product of two Gaussians multiplied together.
Note that prior to performing transition probability product of
sums, all probabilities associated with a given exciter, e, are
normalized such that:
a .di-elect cons. H ( p ( y poll e x a ) + p ( y sense e x dest ) )
= 1 ##EQU00004## [0143] H.ident.Set of all hypothesis regions
[0144] The process described above can also include a model for the
probability of reading a tag at a given location relative to the
exciter's beam and tag environment (presence of absorbing material,
etc). Such a model subsumes statistics on the spatial multipath
field, whose large scale structure is somewhat sampled by frequency
hopping. This predicted probability can be used at each read
opportunity to update the Bayesian estimate for each hypothesis,
whether the tag was read or not. Each of these hypotheses has a
particular spatial trajectory versus time; some tags are consider
static (at the same location for all measurements), and some are
moving (usually at constant velocity in a particular direction,
such as through a door or loading area). Since sensors external to
the RFID system are used to align the conjectured moving
trajectories in time, a simplifying approximation can be made to
the every-read-opportunity approach, namely that read fraction
statistics can be kept during key time intervals surrounding the
events. The statistics on these read fraction averages often follow
Poisson statistics, based on the individual probability of a read
and the number of opportunities to read in the interval. (An
exception to this is the case of static tags, where there is a high
correlation between read fraction over time; this correlation can
be taken into account with a spatial correlation function, which
has correlation distance of roughly a wavelength/half-wavelength).
In our preferred embodiment (described above), we approximate
Poisson statistics with a Gaussian distribution on read
fraction.
[0145] While the above description contains many specific
embodiments of the invention, these should not be construed as
limitations on the scope of the invention, but rather as an example
of one embodiment thereof. Accordingly, the scope of the invention
should be determined not by the embodiments illustrated, but by the
appended claims and their equivalents.
* * * * *