U.S. patent application number 12/969627 was filed with the patent office on 2011-04-14 for rfid interrogator device.
This patent application is currently assigned to TOSHIBA TEC KABUSHIKI KAISHA. Invention is credited to Takahiro SHIMURA.
Application Number | 20110084812 12/969627 |
Document ID | / |
Family ID | 38556365 |
Filed Date | 2011-04-14 |
United States Patent
Application |
20110084812 |
Kind Code |
A1 |
SHIMURA; Takahiro |
April 14, 2011 |
RFID INTERROGATOR DEVICE
Abstract
An RFID interrogator device has a transmission section for
transmitting a command to an RFID tag and a reception section for
receiving an RF signal from the RFID tag and is configured to
perform backscatter radio communication with the RFID tag. The RFID
interrogator device comprises a time window setting section
configured to set a time window at timing of receiving preamble
data added to a head of response data transmitted from the RFID tag
in response to the command, and an identifying data storage section
storing preamble identifying data. The RFID interrogator device
compares the data received within the time window, with preamble
identifying data stored in the identifying data storage section,
thereby determining whether the data received is identical to the
preamble data transmitted from the RFID tag.
Inventors: |
SHIMURA; Takahiro;
(Gotemba-shi, JP) |
Assignee: |
TOSHIBA TEC KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
38556365 |
Appl. No.: |
12/969627 |
Filed: |
December 16, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11879971 |
Jul 19, 2007 |
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12969627 |
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Current U.S.
Class: |
340/10.3 |
Current CPC
Class: |
G06K 7/10039 20130101;
G06K 7/0008 20130101 |
Class at
Publication: |
340/10.3 |
International
Class: |
G06K 7/01 20060101
G06K007/01 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2006 |
JP |
2006-208834 |
Claims
1. An RFID interrogator device, transmitting query data to an RFID
tag and receiving response data from the RFID tag after lapse of
predetermined time, comprising: a time window setting section
configured to set a time window at timing of receiving
predetermined lower bits of preamble data added to a head of
response data transmitted from the RFID tag; an identifying data
setting section configured to set the predetermined lower bits of
preamble data as preamble identifying data; and decision means for
comparing data received within a range of the time window set by
the time window setting section, with preamble identifying data set
by the identifying data setting section, thereby determining
whether the data received is identical to the preamble data
transmitted from the RFID tag.
2. The RFID interrogator device according to claim 1, wherein the
time window setting section sets the time window to start at a sum
of a time that elapses until the preamble data is received from the
RFID tag after the query data has been transmitted to the RFID tag
and a time obtained by multiplying the sampling cycle by a
difference between the number of preamble data bits and the number
of preamble identifying data bits.
3. The RFID interrogator device according to claim 1 or 2, wherein
the time window setting section sets the time window based on the
number of bits constituting the preamble identifying data and the
sampling cycle.
4. The RFID interrogator device according to claim 3, wherein the
time window is assigned with a time equivalent to a difference
between maximum and minimum values preset for a predetermined
response time of the RFID tag.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/879,971 filed on Jul. 19, 2007. This
application claims the benefit of Japanese Patent Application No.
2006-208834 filed Jul. 31, 2006. The disclosures of the above
applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an RFID interrogator device
that performs backscatter radio communication with RFID tags by
using absorption and reflection of radio waves.
[0004] 2. Description of the Related Art
[0005] Any RFID tag transmits, at a predetermined bit rate, a
signal composed of a sync part, a response data part and an error
detecting part. The sync part contains preamble data. U.S. Pat. No.
6,501,807 discloses an RFID interrogator device which compares
preamble data preset in the device, with the preamble data of a
signal the device has received and which determines that the signal
received is a signal from an RFID tag if the preamble data of the
signal is identical to the preset preamble data.
[0006] In the conventional RFID interrogator device, the preset
preamble data is compared with the preamble data of any signal
received. The signal the device has received inevitably contains
noise. A part of the noise may be identical to the preset preamble
data. In this case, the signal received will be mistaken for a
signal from an RFID tag.
BRIEF SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide an RFID
interrogation device that can prevent the detection of erroneous
preamble data, due to noise, thereby increasing the precision of
recognizing RFID tags.
[0008] According to an aspect of the present invention, there is
provided an RFID interrogation device that has a reader function
and performs backscatter radio communication with RFID tags by
using absorption and reflection of radio waves. The RFID
interrogation device comprises: a transmission section configured
to transmit a command to the RFID tag; a reception section
configured to receive an RF signal from the RFID tag; a time window
setting section configured to set a time window at timing of
receiving preamble data added to a head of response data
transmitted from the RFID tag in response to the command: and an
identifying data storage section storing preamble identifying data.
The RFID interrogator device compares the data received within the
time window, with preamble identifying data stored in the
identifying data storage section, thereby determining whether the
data received is identical to the preamble data transmitted from
the RFID tag.
[0009] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0010] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention, and together with the general description given
above and the detailed description of the embodiments given below,
serve to explain the principles of the invention.
[0011] FIG. 1 is a block diagram showing the configuration of an
RFID interrogator device according to a first embodiment of the
present invention;
[0012] FIG. 2 is a block diagram showing the I-signal preamble
detecting section and the decoding section, both provided in the
first embodiment;
[0013] FIG. 3A is a diagram showing a pattern that the preamble
data may have if the identifying data used is 12-bit data in the
first embodiment;
[0014] FIG. 3B is a diagram showing the 12-bit identifying data as
applied to the preamble data shown in FIG. 3A in the first
embodiment;
[0015] FIG. 3C is a diagram showing a pattern that the preamble
data may have if it is set within a time window in the first
embodiment;
[0016] FIG. 3D is a diagram showing a pattern that data received
and containing noise may have in the first embodiment;
[0017] FIG. 3E is a diagram showing a pattern that the data
received may have if no time window is set in the first
embodiment;
[0018] FIG. 4A is a diagram showing a pattern that the preamble
data may have if the identifying data used is 18-bit data in the
first embodiment;
[0019] FIG. 4B is a diagram showing the 18-bit identifying data as
applied to the preamble data shown in FIG. 4A in the first
embodiment;
[0020] FIG. 4C is a diagram showing a pattern that 18-bit preamble
data may have if it is set within a time window in the first
embodiment;
[0021] FIG. 5 is a chart illustrating the data communication
between an RFID tag and the RFID interrogator device according to
the first embodiment, with respect to the time windows TW that have
been preset; and
[0022] FIG. 6 is a flowchart explaining the preamble detecting
process performed in the control section provided in a second
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0023] FIG. 1 is a block diagram showing the configuration of an
RFID interrogator device that includes an orthogonal demodulator.
The RFID interrogator device comprises a control section 1, a
transmission section 2, a reception section 3, a received data
processing section 4, an external interface section 5, a circulator
6, a low-pass filter (LPF) 7, and an antenna 8. The RFID
interrogator device receives data from, and transmits data to, an
external host apparatus via the external interface section 5.
[0024] The transmission section 2 is composed of an encoding
section 21, an amplitude modulator 22, a phase-locked loop device
(PLL) 23, a band-pass filter 24, and a power amplifier 25.
[0025] The transmission section 2 receives a transmission signal
from the control section 1. In the transmission section 2, this
signal is input to the encoding section 21. The encoding section 21
encodes the transmission signal output from the control section
1.
[0026] The encoding section 21 encodes the transmission signal
into, for example, a Manchester code or an FM0 code. A Manchester
code is acquired by an encoding system, wherein data rises at the
center of the bit if it is 0 and falls at the center of the bit if
it is 1. In other words, the code changes from 0 to 1 if the data
is 0, and from 1 to 0 when the data is 1. An FM0 code is acquired
by an encoding system, wherein the code is inverted at every bit
border and even at the center of the bit if the data is 0.
[0027] The PLL 23 supplies a local carrier signal to the amplitude
modulator 22. The amplitude modulator 22 modulates the amplitude of
the local carrier signal with the transmission signal supplied from
the encoding section 21. The band-pass filter 24 filters out
unnecessary frequency components from the transmission signal whose
amplitude has been modulated by the amplitude modulator 22. The
power amplifier 25 amplifies the transmission signal that has
passed through the band-pass filter 24.
[0028] The transmission section 2 is connected to the circulator 6.
The signal amplified in the power amplifier 25 is supplied from the
circulator 6 to the antenna 8 via the low-pass filter 7. The
antenna 8 radiates the signal in the form of radio waves.
[0029] The reception section 3 is connected to the circulator 6.
The reception section 3 is composed of first and second mixers 31
and 32, two low-pass filters 33 and 34, two binary coding circuits
35 and 36, a 90.degree. phase shifter 37, and the above-mentioned
PLL 23.
[0030] The reception section 3 processes a reception signal by a
so-called direct conversion system, in which the carrier component
is removed directly from the reception signal.
[0031] Any RF signal the antenna 8 has received from the RFID tag
is supplied from the antenna 8 to the circulator 6 via the low-pass
filter 7. The RF signal is then supplied from the circulator 6 to
the reception section 3. In the reception section 3, the signal
coming from the circulator 6 is supplied to the first mixer 31 and
the second mixer 32.
[0032] The first mixer 31 receives a local carrier signal from the
PLL 23. The second mixer 32 receives a signal supplied from the PLL
23 and having a phase shifted by 90.degree. by the 90.degree. phase
shifter 37.
[0033] The first mixer 31 mixes the reception signal and the local
carrier signal, generating an in-phase signal (I-signal) that has a
component matching in phase with the local carrier signal. The
second mixer 32 mixes the reception signal and the signal obtained
by phase shifting the local carrier signal by 90.degree.,
generating a quadrature-phase signal (Q-signal) that has a
component orthogonal to the local carrier signal.
[0034] The low-pass filter 33 receives an I-signal from the first
mixer 31, filters out unnecessary high-frequency components from
the I-signal, and outputs encoded data. The low-pass filter 34
receives a Q-signal from the second mixer 32, filters out
unnecessary high-frequency components from the Q-signal, and
outputs encoded data. The binary coding circuits 35 converts the
I-signal coming from the low-pass filter 33, into a binary signal.
The binary coding circuits 36 converts the Q-signal coming from the
low-pass filter 34, into a binary signal.
[0035] The received data processing section 4 has a sync clock
generating section 411, a time window setting section 412, a
preamble detecting section 413, a decoding section 414, and a
response data error detecting section 415, all dedicated to the
I-signal. The received data processing section 4 further has a sync
clock generating section 421, a time window setting section 422, a
preamble detecting section 423, a decoding section 424, and a
response data error detecting section 425, all dedicated to the
Q-signal.
[0036] The I-signal generated by the binary coding circuits 35 is
supplied from the reception section 3 to the sync clock generating
section 411, preamble detecting section 413, decoding section 414
and response data error detecting section 415. The Q-signal
generated by the binary coding circuits 36 is supplied from the
reception section 3 to the sync clock generating section 421,
preamble detecting section 423, decoding section 424 and response
data error detecting section 425.
[0037] The sync clock generating section 411 dedicated to the
I-signal generates, at all times, a clock signal that is
synchronous with the binary signal coming from the binary coding
circuit 35. The clock signal is supplied to the control section 1,
preamble detecting section 413, decoding section 414 and response
data error detecting section 415. The sync clock generating section
421 dedicated to the Q-signal generates, at all times, a clock
signal that is synchronous with the binary signal coming from the
binary coding circuit 36. This clock signal is supplied to the
control section 1, preamble detecting section 423, decoding section
424 and response data error detecting section 425.
[0038] The time window setting section 412 dedicated to the
I-signal sets a time window at the time the preamble detecting
section 413 acquires the preamble data of the I-signal. The time
window setting section 422 dedicated to the Q-signal sets a time
window at the time the preamble detecting section 423 acquires the
preamble data of the Q-signal.
[0039] The preamble detecting section 413 dedicated to the I-signal
compares the preamble data existing at the head of the I-signal,
with the preamble identifying data preset within the time window
set by the time window setting section 412, thereby detecting the
preamble data included in the I-signal. The preamble detecting
section 423 dedicated to the Q-signal compares the preamble data
existing at the head of the Q-signal, with the preamble identifying
data preset within the time window set by the time window setting
section 422, thereby detecting the preamble data included in the
Q-signal. On detecting the preamble data included in the I-signal,
the preamble detecting section 413 outputs a detection signal to
the control section 1. On detecting the preamble data included in
the Q-signal, the preamble detecting section 423 outputs a
detection signal to the control section 1.
[0040] FIG. 2 is a block diagram that shows a reception system that
detects and decodes the preamble data. The reception system shown
in FIG. 2 is configured to receive the I-signal. The reception
system for receiving the Q-signal has the same configuration as the
reception system shown in FIG. 2.
[0041] The sync clock generating section 411 has a digital PLL
circuit 4111. The sync clock generating section 411 generates a
clock signal that is synchronous with the I-signal, which is a
binary signal input from the binary coding circuit 35.
[0042] An RFID tag has response data and preamble data attached to
the head of the response data. The preamble data is of such a
pattern that it changes every 0.5 T, which is half the cycle T that
corresponds to the transmission rate of the RFID tag. Therefore,
the digital PLL circuit 4111 generates a clock signal whose cycle
is 0.5 T, i.e., half the cycle T corresponding to the transmission
rate of the RFID tag.
[0043] The sync clock generating section 411 supplies from the
clock signal generated by the digital PLL circuit 4111 to the
preamble detecting section 413 and the decoding section 414.
[0044] The preamble detecting section 413 is composed of an
identifying data storage section 4131, a shift register 4132, and a
comparator 4133, all dedicated to preamble data. The data storage
section 4131 stores preamble identifying data that is used to set
preambles. The comparator 4133 is provided as decision means. The
shift register 4132 acquires the I-signal, i.e., the binary signal
input from the binary coding circuit 35, in synchronism with the
clock signal supplied from the digital PLL circuit 4111. The
comparator 4133 compares the bit data acquired in the shift
register 4132 within the time window set by the time window setting
section 412, with the above-mentioned preamble identifying data,
thereby determining whether preamble data exists or not.
[0045] The decoding section 414 is composed of a frequency halving
circuit 4141, a two-input exclusive OR circuit 4142, a D-type
flip-flop 4143, a shift register 4144, a counter 4145, and a data
register 4146. The exclusive OR circuit 4142 has an inverting
output terminal.
[0046] The frequency halving circuit 4141 receives a clock signal
supplied from the digital PLL circuit 4111 and having a cycle of
0.5 T. The circuit 4141 then divides the frequency of this clock
signal by 2, generating a clock signal having cycle T. The
exclusive OR circuit 4142 extracts the bit data shifted in the
shift register 4132, in units of two bits, thus generating an
exclusive logic sum of the signals input to it. The D-type
flip-flop 4143 supplies the output of the exclusive OR circuit 4142
to the D input terminal. The flip-flop 4143 also supplies the clock
signal coming from the frequency halving circuit 4141, to the CLK
terminal. Having this circuit configuration, the D-type flip-flop
4143 decodes every two bits stored in the shift register 4132 into
"1" if the bits are [0,0] or [1,1], and into "0" if the bits are
[1,0] or [0,1].
[0047] The data decoded is supplied from the D-type flip-flop 4143
to the shift register 4144. The counter 4145 counts the digits
constituting the data decoded. The data register 4146 acquires this
data every time data of a predetermined length is input to the
shift register 4144. The data thus acquired is output to the
control section 1.
[0048] The relation between the preamble pattern, the preamble
identifying data and the time window will be described, with
reference to FIGS. 3A to 3E.
[0049] FIG. 3A shows a pattern that preamble data D1 may have. The
preamble data D1 is 20-bit data, "10101010110100100011."
[0050] The data storage section 4131, which is provided to store
preamble identifying data, stores the lower 12 bits of the preamble
data D1, i.e., "110100100011." These 12 bits, or identifying data
P1, will be shown as black dots in FIG. 3B, if they are applied to
the preamble data shown in FIG. 3A.
[0051] The broken lines shown in FIG. 3B indicate a time window TW1
that the time window setting section 412 sets for the preamble data
D1. As seen from FIG. 3B, the pattern corresponding to the
identifying data P1 exists within the time window TW1.
[0052] The higher bits of the preamble data D1 are unstable as the
signal received by the binary coding circuit 35 rises. This is why
the lower bits of the preamble data D1 are used as identifying data
P1.
[0053] The binary signal corresponding to the I-signal extracted
from the signal coming from the RFID tag is input to the shift
register 4132 of the preamble detecting section 413. The shift
register 4132 receives the binary signal, while shifting the signal
bit by bit. At the time the shift register 4132 receives the first
twenty bits, the comparator 4133 compares the data in the shift
register 4132 with the identifying data P1, within the time window
TW1 set by the time window setting section 412. More precisely, the
comparator 4133 compares the lower twelve bits in the shift
register 4132 with the identifying data P1. If these bits are
identical to the bits constituting the comparator 4133, it is
determined that the signal received is the preamble data D1. The
data following the preamble data D1 is then received as response
data from the RFID tag.
[0054] FIG. 3C shows a pattern that the preamble data may have if
received within the time window TW1. As white dots indicate in FIG.
3C, data identical to the identifying data P1 exists within the
time window TW1. Therefore, the preamble data coming from the RFID
tag is correctly detected in this case.
[0055] FIG. 3D shows a pattern of the preamble data received and
containing noise. In this case, the pattern existing within the
time window TW1 is different from the pattern that corresponds to
the identifying data P1. The preamble data is therefore determined
to be erroneous.
[0056] FIG. 3E shows a pattern that the signal received may have
when the time window TW1 is not set. This signal contains noise.
The white dots shown in FIG. 3E coincide with the identifying data
P1. These white dots are not detected as preamble data, since the
time window TW1 is not set. Consequently, the signal that follows
the white dots is not detected as response data coming from the
REID tag, either.
[0057] How the preamble data of the I-signal is detected has been
explained above. The preamble data of the Q-signal is detected in
the same manner.
[0058] The signal received may be inverted, depending on its phase.
It is therefore desired that the lower twelve bits in the shift
register 4132 be determined to be preamble data if they are
identical to the inverted pattern of the identifying data P1, or
P1'="001011011100."
[0059] As mentioned above, the lower twelve bits are used as
identifying data. Nevertheless, the identifying data may be
constituted by any other bits.
[0060] FIG. 4A to 4C show the case where the lower eighteen bits of
the preamble data are used as identifying data. That is, the lower
eighteen bits of the preamble data D1 having the pattern shown in
FIG. 4A, i.e., "101010110100100011," are used as identifying data
P2.
[0061] The pattern of this identifying data P2 will be shown as
black dots in FIG. 4B, if they are applied to the preamble data D1
shown in FIG. 4A. In this case, the time window TW2 set for the
preamble data D1 by the time window setting section 412 is broader
than the time window TW1 as indicated by broken lines in FIG. 4B.
That is, the width of the time window varies, depending on the
number of bits used to determine whether the preamble is identical
to the preamble identifying data.
[0062] FIG. 4C shows a pattern the preamble data may have if it is
received within the time window TW2. In this case, data identical
to the identifying data P2 (="101010110100100011") exits within the
time window TW2 as indicated by white dots. Hence, correct preamble
data coming from the RFID tag can be detected.
[0063] The number of bits constituting the identifying data is thus
increased, thereby further decreasing the probability of detecting
a noise-containing signal, erroneously as preamble data. This can
more reliably prevent erroneous detection of the preamble data.
[0064] A method of setting the time window TW in the time window
setting sections 412 and 422 will be explained. More precisely, how
to set a time window for the I-signal will be explained here. Note
that a time window for the Q-signal is set in the same manner.
[0065] FIG. 5 illustrates the data communication between an RFID
tag and the RFID interrogator device, with respect to the time
windows TW that have been preset.
[0066] The present embodiment utilizes a backscatter scheme as a
radio communication scheme. The backscatter scheme uses the
absorption and reflection of radio waves transmitted from the
transmission section 2 of the RFID interrogator device, so that the
RFID interrogator device may accomplish radio communication with
the RFID tag.
[0067] When the RFID interrogator device transmits a Query command
to the RFID tag, the RFID tag responds to this command. In period
A, the RFID tag correctly responds to the command, sending an
appropriate response to the RFID interrogator device. In period B,
a plurality of RFID tags respond at the same time, causing
collision of responses.
[0068] The response time T1' the RFID tag has to the Query command
is known, and the fluctuation of the response time T1' is known,
too. The response time T1' is given as follows:
T1'MIN<T1'<T1'MAX (1)
[0069] In the case of, for example, EPC Global, Class 1, Generation
2, which is now virtually a global standard, the minimum value
T1'MIN for response time T1' is 238 .mu.sec, and the maximum value
T1'MAX for response time T1' is 262 .mu.sec, if the transmission
rate is 40 kbps.
[0070] The preamble detecting section 413 has a delay time TD1 for
the transmission system and a delay time TD2 for the reception
system, both resulting from the processing of digital signals. The
delay time TD1 and the delay time TD2 are known because they are
design values. Hence, the time T1 that the preamble detecting
section 413 requires to receive the preamble data from the RFID tag
after finishing the transmission of the Query command is as
follows:
T1=TD1+T1'MIN+TD2 (2)
[0071] The time window TW is determined as follows:
TW=0.5 T.times.N+(T1'MAX-T1'MIN) (3)
[0072] where N is the number of bits constituting the preamble
identifying data used when the time window TW is applied, and 0.5 T
is the sampling cycle.
[0073] That is, the time based on the minimum value T1'MIN and
maximum value T1'MAX for the response time preset for the RFID tag
has been added to the time window TW. More specifically, the time
equivalent to the difference between the maximum and minimum values
T1'MAX and T1'MIN for the response time is added to the time window
TW.
[0074] Therefore, the time window TW1 is given as follows, if the
lower twelve bits of the preamble data D1 shown in FIG. 3A (that
is, N=12) are used as identifying data P1:
TW1=0.5 T.times.12+(T1'MAX-T1'MIN)
[0075] The time window TW2 for the case where the lower eighteen
bits of the preamble data D2 shown in FIG. 4A (that is, N=18) are
used as identifying data P2 is given as follows:
TW1=0.5 T.times.18+(T1'MAX-T1'MIN)
[0076] The time window TW need not absolutely accord with the
equation (3). It may be larger than is defined in the equation (3).
If it is excessively large, however, the probability of detecting
noise as preamble data will increase. It is therefore undesirable
to expand more than necessary.
[0077] The time window TW is opened upon lapse of the sum of time
T1 and time t1 after the RFID interrogator device has transmitted
the Query command. Time T1 is the time the device needs in order to
receive the preamble data from the RFID tag. Time t1 is obtained by
multiplying the sampling cycle 0.5 T by the difference between the
number of preamble data bits and the number of preamble identifying
data bits (N). If the preamble data consists of 20 bits, time t1
is:
t1=(20-N).times.0.5 T
[0078] The time at which the RFID interrogator device detects the
preamble data is the sum of the time (T1+t1) and the time window
TW. That is, the device detects the preamble data upon lapse of
(T1+t1+TW) after it has transmitted the Query command.
[0079] In period A, the RFID interrogator device detects the
preamble data coming from the RFID tag upon lapse of (T1+t1+TW)
after the transmission of the Query command, and then outputs a
preamble detection signal to the control section 1. In period B,
the signals from a plurality of RFID tags collide with one another,
generating noise, and the preamble data is determined to be
erroneous in the time window TW.
[0080] In the RFID interrogator device so configured as described
above, the control section 1 inputs the Query command to the
transmission section 2. The transmission section 2 supplies the
Query command via the circulator 6 and low-pass filter 7 to the
antenna 8. The antenna 8 transmits the Query command. There is a
time delay TD1 between the time the control section 1 inputs the
Query command and the time the antenna 8 transmits the Query
command.
[0081] If any RFID tag should respond to the RFID interrogator
device at this time, it receives the Query command coming from the
RFID interrogator device. Upon lapse of time T1', the RFID tag
transmits response data to the RFID interrogator device.
[0082] When the RFID interrogator device receives the response data
from the RFID tag at the antenna 8, the reception section 3
receives the response data via the low-pass filter 7 and circulator
6. In the reception section 3, the response data is input to the
first and second mixers 31 and 32.
[0083] The first mixer 31 outputs an I-signal. The I-signal is
supplied via the low-pass filter 33 to the binary coding circuit
35. The binary coding circuit 35 converts the I-signal to a binary
I-signal. The binary I-signal is input to the sync clock generating
section 411, preamble detecting section 413, decoding section 414
and response data error detecting section 415, all dedicated to the
I-signal.
[0084] The second mixer 32 outputs a Q-signal. The Q-signal is
supplied via the low-pass filter 34 to the binary coding circuit
36. The binary coding circuit 36 converts the Q-signal to a binary
Q-signal. The binary Q-signal is input to the sync clock generating
section 421, preamble detecting section 423, decoding section 424
and response data error detecting section 425, all dedicated to the
Q-signal.
[0085] The preamble detecting section 413 dedicated to the I-signal
detects the preamble data added to the head of the response data
received within the time window TW set by the time window setting
sections 412 that is dedicated to the I-signal. Then, the preamble
detecting section 413 compares the preamble data, thus detected,
with the preamble identifying data that has been already
stored.
[0086] The preamble detecting section 423 dedicated to the Q-signal
detects the preamble data added to the head of the response data
received within the time window TW set by the time window setting
sections 422 that is dedicated to the Q-signal. Then, the preamble
detecting section 423 compares the preamble data, thus detected,
with the preamble identifying data that has been already
stored.
[0087] The time window TW starts when the RFID interrogator device
finishes transmitting the Query command to the RFID tag and ends
when the period (T1+t1) elapses thereafter. If the preamble
identifying data is consist of the lower twelve bits of the
preamble data, the lower twelve bits of the preamble data added to
the response data received will fall within the time window TW.
[0088] The data existing in the time window TW are compared with
the preamble identifying data. If the response data received from
the RFID tag is correct data, the data within the time window TW
will be identical to the preamble identifying data. In this case,
the RFID interrogator device determines that the response data has
been received from the RFID tag.
[0089] If the response data received from the RFID tag contains
noise and is therefore incorrect data, however, the data within the
time window TW will not be identical to the preamble identifying
data, at high probability. In this case, the RFID interrogator
device does not determine that the response data has been received
from the RFID tag.
[0090] Erroneous detections of the preamble data, due to noise, can
thus be avoided in the present embodiment. This can enhance the
precision of recognizing RFID tags.
Second Embodiment
[0091] A second embodiment of the present invention will be
described, in which the received data processing section 4 used in
the first embodiment is incorporated in the form of software and a
program is executed to determine whether the preamble data exists
or not. The second embodiment is identical to the first embodiment,
except that the received data processing section 4 is incorporated
in the control section 1. Thus, no block diagrams of the second
embodiment are attached hereto, and the configuration of the second
embodiment will not be described.
[0092] The control section 1 executes the program, detecting the
preamble as illustrated in the flowchart of FIG. 6. First, the
control section 1 sets the count of the counter n to "1" in Step
S1. Then, a timer starts measuring time T in Step S2. In Step S3,
the control section 1 determines whether T.ltoreq.(T1+t1+TW) or
not.
[0093] If T.ltoreq.(T1+t1+TW), the control section 1 stores the
received data into a memory in Step S4. In Step S5, the control
section 1 determines whether the data in the memory is identical to
the preset preamble identifying data.
[0094] If the data is not identical to the preset preamble
identifying data, the process returns to Step S3. Thereafter, Steps
S3 to S5 are repeated.
[0095] The control section 1 may determine in Step S5 that the data
in the memory is identical to the preset preamble identifying data.
If this is the case, the control section 1 determines in Step S6
whether T.gtoreq.(T1+t1).
[0096] If T.gtoreq.(T1+t1) in Step S6, the control section 1
determines that the data is identical to the preamble identifying
data within the time window TW and then terminates the process of
detecting the preamble. In other words, the data received is found
to contain the preamble data coming from the RFID tag. The control
section 1 then performs a process of acquiring the response data
that follows the preamble data. This process will not be explained
here.
[0097] Even if the data in the memory is found to be identical to
the preamble identifying data, the control section 1 determines
that the preamble data has not been detected, unless
T.gtoreq.(T1+t1). That is, the control section 1 determines that
the data is outside the time window TW and does not recognize the
data as preamble data. The process then returns to Step S3.
[0098] If the time T measured by the timer increases over
(T1+t1+TW) while no preamble data is being detected, the control
section 1 determines that the preamble data has not been detected.
In this case, the control section 1 determines in Step S7 whether
the count of the counter n has reached a predetermined value N.
Unless n=N, the control section 1 increases the count of the
counter n by one in Step S8. Then, in Step S9, the control circuit
1 resets time T in the timer. The process then returns to Step S2.
Steps S2 to S5 and Step S6 are repeated.
[0099] No preamble data may be detected even if the count of the
counter n reached the value N. In this case, the control section 1
determines that there exists no preamble data to detect and
terminates the process of detecting the preamble.
[0100] To detect preamble data by using software, too, a time
window TW is set and it is determined whether the data in the
memory is identical to the preamble identifying data within the
time window TW. Thus, no preamble data is detected at high
probability if the reception signal is not correct response data
coming from the RFID tag, but data that contains noise. Erroneous
detection of preambles, due to noise, can therefore be avoided.
This can enhance the precision of recognizing RFID tags.
[0101] To detect preamble data, whether the data in the memory is
identical to the preamble identifying data within the time window
TW is determined not only once, but several times. A preamble can
therefore be eventually detected even if it has not been detected
because the response data coming from a RFID tag contains temporary
noise. Thus, the RFID interrogator device can reliably receive the
response data transmitted from the RFID tag.
[0102] In the embodiments described above, the transmission section
2 and the received data processing section 4 are components that
work independently of each other. Nonetheless, the received data
processing section 4 may be incorporated into the transmission
section 2, so that a larger transmission section may be
provided.
[0103] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
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