JP2008293538A - Radio tag reader/writer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform automatic gain control most suitable for communication with a radio tag. <P>SOLUTION: An AGC means 6 sets an AGC value of a variable gain amplifier 32 of a reception par 3 to A and measures an amplitude of a reception signal for a prescribed period after a certain time and then changes the AGC value from A to B on the basis of a measured value after the prescribed period. This change is performed at a timing within a continuous period of 12 '0's in a preamble of a response from the radio tag. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wireless tag reader / writer that performs automatic gain control of a reception level when communicating with a wireless tag by a backscatter method using absorption and reflection of radio waves.

  Conventionally, a backscatter method is used for communication between a wireless tag and a wireless tag reader / writer. In this method, when the wireless tag reader / writer transmits an unmodulated radio wave to the radio tag, the radio tag receives this radio wave, converts it to DC power, and uses it as an operating power source. The wireless tag reflects and absorbs the received radio wave by changing the impedance of the antenna. The wireless tag reader / writer is a system that communicates with the wireless tag by receiving a reflected wave from the wireless tag.

  When the wireless tag reader / writer receives data from the wireless tag, the wireless tag reader / writer transmits radio waves, and thus receives radio waves while transmitting radio waves. Such an operation is unique to communication with the wireless tag. As a modulation method for communication between the wireless tag reader / writer and the wireless tag, ASK modulation or PSK modulation, which is linear modulation, is often used.

On the other hand, wireless LAN systems are widely used as systems for performing linear modulation. In a system that employs linear modulation, it is necessary to amplify a received signal without distortion in order to maintain linearity, and automatic gain control called AGC is used. The AGC is a circuit that functions to keep the reception output constant by reducing the gain of the amplifier when the received electric field strength is high and increasing the gain of the amplifier when the received electric field strength is weak.
A wireless communication terminal device equipped with a receiving device that performs automatic gain control is used in a wireless LAN system, transmits radio waves at the time of transmission, and only receives radio waves at the time of reception by switching. It is known that the AGC is started when the electric field intensity is measured and the received radio wave exceeds a certain RSSI value (see, for example, Patent Document 1).
JP 2003-92561 A

  In a digital wireless communication system such as a wireless LAN, a wireless communication terminal device only operates to transmit a radio wave at the time of transmission and to receive a radio wave at the time of reception. The back scatter method is adopted. That is, when the wireless tag reader / writer performs reception from the wireless tag, the wireless tag reader / writer operates to receive a reflected wave from the wireless tag while transmitting a radio wave to the wireless tag. A radio wave wraps around and a minute reflected wave from the wireless tag is received at the same time.

  The wraparound of the radio wave from the transmission system to the reception system is very large compared to the reflected wave from the wireless tag, so it is impossible to determine when the reflected wave was received from the wireless tag based on the received electric field strength It is. For this reason, the method of detecting the start of reception using the RSSI value as a trigger and starting AGC, which is adopted in the wireless LAN system, cannot be applied to a wireless tag reader / writer that communicates with a wireless tag.

  The present invention has been made to solve such problems, and provides a wireless tag reader / writer capable of performing automatic gain control optimum for communication with a wireless tag.

  The present invention relates to a wireless tag reader / writer that communicates with a wireless tag by a backscatter method using radio wave absorption and reflection, a receiving unit that receives a received signal from the wireless tag, and an amplitude of the received signal received by the receiving unit. When the measuring unit for measuring the signal and the transmitter for transmitting the command to the wireless tag complete the transmission of the command to the wireless tag, the amplitude is measured by the predetermined time measuring unit after a predetermined time Ta has elapsed, and the measurement is performed. The wireless tag reader / writer includes control means for performing automatic gain control of the receiving unit based on the amplitude value.

  According to the present invention, optimal automatic gain control can be performed for communication with a wireless tag.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing a configuration of a wireless tag reader / writer. The wireless tag reader / writer includes an antenna 1, a circulator 2 connected to the antenna 1 and separating a transmission wave and a reception wave, and a receiving unit 3 connected to the circulator 2. And the transmission part 4 is provided. The receiving unit 3 includes an orthogonal demodulator 31, a variable gain amplifier 32, and an A / D converter 33.

  The wireless tag reader / writer includes a local oscillator 5 and an AGC (automatic gain control) means 6 for commonly supplying a frequency signal for demodulation and modulation to the quadrature demodulator 31 and the transmission unit 4 of the reception unit 3. Unit 7, a D / A converter 8 that converts the digital output of the AGC means 6 to analog and outputs the analog output to the variable gain amplifier 32, and D / A converts transmission data output from the control unit 7 to perform the transmission A D / A converter 9 for sending to the unit 4 is provided. The AGC means 6 constitutes control means for performing automatic gain control of the variable gain amplifier 32 of the receiving unit 3.

  When receiving a signal backscattered from a wireless tag (not shown) by the antenna 1, the wireless tag reader / writer passes through the circulator 2 and is input to the receiving unit 3. In the receiving unit 3, the signal is taken into the quadrature demodulator 31. The orthogonal demodulator 31 receives a signal having the same frequency as the transmission frequency from the local oscillator 5. Thus, the quadrature demodulator 31 performs quadrature demodulation on the received signal, outputs baseband signal I and Q signals, and supplies them to the variable gain amplifier 32 at the next stage.

  The variable gain amplifier 32 amplifies the input baseband signals I and Q to a desired level, outputs I ′ and Q ′ signals, and supplies them to the A / D converter 33 in the next stage. The A / D converter 33 converts the input I ′ and Q ′ signals into digital I ″ and Q ″ signals and supplies them to the control unit 7.

  The controller 7 performs baseband processing and generates received data from the input digital baseband signals I ″ and Q ″. At the same time, the AGC means 6 outputs a signal for controlling the gain of the variable gain amplifier 32 so as to obtain an optimum gain for reception.

Next, AGC control by the AGC means 6 of the control unit 7 will be described.
FIG. 2 shows the timing of command exchange in communication between the wireless tag reader / writer (R) and the wireless tag (T). R → T indicates a state in which the wireless tag reader / writer (R) sends a command to the wireless tag (T), and T → R indicates a state in which the wireless tag (T) returns a response to the wireless tag reader / writer (R). .

The wireless tag reader / writer (R) transmits an unmodulated wave (CW) to supply power to the wireless tag (T) before transmitting the command. Then, command (1) is sent out. After sending the command (1), the wireless tag reader / writer (R) enters a receiving operation, but continues to send a non-modulated wave (CW) to the wireless tag (T) to supply power.
When the wireless tag (T) receives the command (1), the wireless tag (T) returns a response (1) after elapse of the standard time T1.
When the RFID tag reader / writer (R) continues to send the command (2), the command (2) is sent after the time T2 that is the standard time has elapsed since the response (1) of the RFID tag (T) is completed. When receiving the command (2), the wireless tag (T) returns a response (2) to the command (2) after a lapse of T1 time, as in the case of the command (1).

Here, the standard times T1 and T2 are becoming international standards, and in the EPC global Class-1 Generation-2 (hereinafter referred to as GEN2), when the communication speed is 40 kbps,
T1 = 238 μsec (minimum), 250 μsec (standard), 262 μsec (maximum)
T2 = 75μsec (minimum), 500μsec (maximum)
It is prescribed.

  In this way, since the time T1 from when the wireless tag reader / writer (R) sends a command until the wireless tag (T) returns a response is defined, an AGC specific to the wireless tag reader / writer can be obtained using this rule. Do.

FIG. 3 shows a preamble attached to the head of data when the wireless tag (T) returns a response. GEN2 stipulates that twelve '0' sequences are added before the pattern “1010V1”. Here, encoding by FM0 is adopted. “0” of FM0 is expressed by “10” and “01”, and “1” of FM0 is expressed by “00” and “11”.
In GEN2, the preamble of only the pattern “1010V1” that does not add the sequence of 12 “0” s is also possible, but here, the gain control is performed by AGC, so the sequence of 12 “0” s Using the added preamble, AGC is configured to be implemented with 12 consecutive "0" parts.

FIG. 4 shows an AGC program executed by the AGC means 6 of the control unit 7.
If it is determined in S1 that the state is changed from T to R (the wireless tag reader / writer (R) is in the receiving state), the AGC value of the variable gain amplifier 32 is set to a predetermined value A in S2. . Then, in S3, a certain time Ta is waited. Here, the fixed time Ta is set to a time equal to or less than the minimum value (238 μsec) of the standard time T1, for example, Ta = 220 μsec.

When the Ta time has elapsed, in S4, the amplitude of the received signal is measured for a predetermined time Tb (measuring means). For example, in the case of 40 kbps, the time corresponding to twelve consecutive '0's is (1/40 k) * 12 = 25 μsec * 12 = 300 μsec, so Tb = 300 μsec is set.
It is not essential to set Tb = 300 μsec, and it may be larger or smaller than 300 μsec. In short, it is only necessary that the amplitude measurement of the received signal can be completed during Tb.

  Based on the measured value of the amplitude of the received signal, the received AGC value B is determined in S5, and the AGC value of the variable gain amplifier 32 is changed from the value A to the value B. Naturally, if the amplitude is large, the AGC value B is a small value. Conversely, if the amplitude is small, the AGC value B is a large value. As for the determination method of the AGC value B, for example, a table in which the amplitude value is associated with the setting AGC value A is prepared in advance, and the AGC value B is determined from the maximum value of the amplitude measured at the predetermined time Tb. .

  Then, the AGC value B is held during the state (T → R) in which the wireless tag reader / writer (R) is in the receiving state, and when the state is switched from R → T in S6, it is determined and this AGC processing is performed. finish.

  The AGC value may be held as it is even after the response of the wireless tag (T) is completed. However, for example, if the transmission state from the wireless tag reader / writer (R) to the wireless tag (T) is reached, AGC is unnecessary. Therefore, the AGC value may be set to 0 or the minimum, and the AGC value may be set to the maximum in the carrier sense state.

  FIG. 5 shows an example of a change in the amplitude of the received signal I ′ or Q ′ accompanying the AGC operation. I ′ and Q ′ are baseband signals output from the variable gain amplifier 32. As shown in FIG. 5, the AGC unit 6 sets a preset AGC value A in the variable gain amplifier 32 when the wireless tag (T) is in the state T → R interval in which the response is transmitted. When the predetermined time Ta elapses, the signal amplitude is measured for a predetermined time Tb. When the predetermined time Tb elapses, the AGC value is set to B based on the measured value. That is, the AGC value is changed from the value A to the value B.

As described above, the wireless tag reader / writer (R) can receive the response from the wireless tag (T) in the state T → R, the predetermined time Tb after the elapse of the predetermined time Ta, and the wireless tag (T). By measuring the amplitude of the signal from the radio tag, the amplitude is measured at the time when 12 consecutive “0” s in the preamble attached to the head of the response from the wireless tag continue, and the AGC value B based on the measured value is set. Will be. In the subsequent pattern “1010V1”, since the AGC value is already set correctly, the pattern “1010V1” can be correctly received.
As a result, the wireless tag reader / writer (R) can perform optimum automatic gain control for communication with the wireless tag while simultaneously performing transmission and reception with respect to the wireless tag (T).

(Second Embodiment)
In this embodiment, the hardware configuration is the same as that in FIG. A different point is an AGC program executed by the AGC means 6 of the control unit 7. That is, the AGC means 6 executes the AGC program shown in FIG.

  First, when it is determined in S11 that the state has changed from T to R (the wireless tag reader / writer (R) is in the receiving state), in S12, the AGC value of the variable gain amplifier 32 is set to a predetermined value A1. Set. In S13, a certain time Ta is waited. Here, the fixed time Ta is set to a time equal to or less than the minimum value (238 μsec) of the standard time T1, for example, Ta = 220 μsec.

  When the Ta time has elapsed, in S14, the amplitude of the received signal is measured for a predetermined time Tb '(first measuring means). For example, in the case of 40 kbps, the time corresponding to twelve consecutive '0's is (1 / 40k) * 12 = 25 μsec * 12 = 300 μsec, so Tb ′ is set to 150 μsec, which is half of 300 μsec.

  Then, in S15, it is determined whether or not the measured value of the amplitude of the received signal is equal to or smaller than the predetermined value. If it is equal to or smaller than the predetermined value, in S16, the AGC is performed based on the measured value as in the above-described embodiment. The value B is determined, and the AGC value of the variable gain amplifier 32 is changed from the preset value A1 to the value B. The AGC value B set at this time is naturally a small value if the amplitude is large, and conversely a large value if the amplitude is small. Regarding the determination method of the AGC value B, for example, a table in which the amplitude value and the setting AGC value A1 are associated with each other is prepared in advance, and the AGC value B is determined from the maximum value of the amplitude measured at the predetermined time Tb ′. To do.

  Then, the AGC value B is held during the state (T → R) in which the wireless tag reader / writer (R) is in a receiving state, and when the state is switched from R → T in S17, it is determined and this AGC processing is performed. finish.

  If it is determined in S15 that the measured value of the amplitude of the received signal exceeds the predetermined value, the AGC value preset in the variable gain amplifier 32 is changed from A1 to A2 (<A1) in S18. Thus, the gain of the variable gain amplifier 32 is reduced. In S19, the amplitude of the received signal is measured for a predetermined time Tc (second measuring means). The predetermined time Tc at this time is set to Tc = 150 μsec so that Tb = Tb ′ + Tc.

  In S20, the AGC value C is determined based on the measured value, and the AGC value of the variable gain amplifier 32 is changed from the value A2 to the value C. The AGC value C set at this time is naturally a small value if the amplitude is large, and conversely a large value if the amplitude is small. As for the method for determining the AGC value C, for example, a table in which the amplitude value is associated with the setting AGC value A2 is prepared in advance, and the AGC value C is determined from the maximum value of the amplitude measured at the predetermined time Tc. .

  Then, the AGC value C is held during the state (T → R) in which the wireless tag reader / writer (R) is in the receiving state, and when the state is switched from R → T in S21, it is determined and this AGC processing is performed. finish.

  The AGC value may be held as it is even after the response of the wireless tag (T) is completed. However, for example, if the transmission state from the wireless tag reader / writer (R) to the wireless tag (T) is reached, AGC is unnecessary. Therefore, the AGC value may be set to 0 or the minimum, and the AGC value may be set to the maximum in the carrier sense state.

  FIG. 7 shows an example of a change in the amplitude of the received signal I ′ or Q ′ accompanying the AGC operation. I ′ and Q ′ are baseband signals output from the variable gain amplifier 32. As shown in FIG. 7, the AGC means 6 sets a preset AGC value A 1 in the variable gain amplifier 32 when the wireless tag (T) enters the state T → R in which the response is transmitted. When the predetermined time Ta elapses, the signal amplitude is measured for a predetermined time Tb ′, and it is determined that the measured value exceeds the predetermined value, and the AGC value set in the variable gain amplifier 32 is changed from A1 to A2. . Then, the amplitude of the signal is measured, and when the predetermined time Tc elapses, the AGC value C is set based on the measured value. That is, the AGC value is changed from the value A2 to the value C.

  In this way, the wireless tag reader / writer (R) is able to receive the response from the wireless tag (T), and in the state T → R, the amplitude of the signal from the wireless tag (T) after a certain time Ta has elapsed. Here, when the measured value is large so as to exceed a predetermined value, the AGC value set in the variable gain amplifier 32 is lowered from A1 to A2, and in this state, the amplitude of the signal from the wireless tag (T) is again measured. Measure. Then, an AGC value C is set based on the measured value.

These series of measurements are performed within a time period in which twelve consecutive '0's in the preamble attached to the head of the response from the wireless tag continue, and the measured value at the start of the pattern “1010V1” that follows. AGC value C based on the above is set.
As a result, the wireless tag reader / writer (R) can perform optimum automatic gain control for communication with the wireless tag while simultaneously performing transmission and reception with respect to the wireless tag (T). In addition, the dynamic range when receiving a response from the wireless tag (T) can be widened.

In the first embodiment and the second embodiment, the reader / writer has been described as an example, but the present invention may be realized by a reader-dedicated device having no writer function. That is, in a wireless tag reader that communicates with a wireless tag by a backscatter method using radio wave absorption and reflection, a receiving unit that receives a reception signal from the wireless tag, and an amplitude of the received signal received by the receiving unit When the transmission unit that transmits a command to the wireless tag completes the transmission of the command to the wireless tag, the measurement unit measures the amplitude by a predetermined time after a predetermined time Ta has elapsed, You may implement | achieve this invention with the control means which performs the automatic gain control of the said receiving part based on the measured amplitude value, and the wireless tag reader provided.
In the first embodiment and the second embodiment, the maximum value is used in the amplitude measurement, but an average value may be used.

(Third embodiment)
In this embodiment, a read sequence when the wireless tag reader / writer (R) reads data from the wireless tag (T) and a write sequence when the wireless tag reader / writer (R) writes data to the wireless tag (T). The case where both are executed will be described. In this embodiment, the hardware configuration is basically the same as that in FIG. 1, and the difference is that a memory 10 indicated by a dotted line block is provided.

  In GEN2, in addition to the timing chart shown in FIG. 2, the timing shown in FIG. 8 is defined as a write sequence. This is because the response time of the wireless tag (T) to the command W transmitted by the wireless tag reader / writer (R) takes a maximum of 20 msec. Here, the command W is a write command of Write, Kill, Block Write, or Block Erase. The time of 20 msec is much longer than the T1 time in FIG.

  Therefore, the AGC means 6 of the control unit 7 of the wireless tag reader / writer (R) that executes the write command has a determining means for determining whether the command is a read command or a write command, and the wireless tag reader / writer (R) is wireless. It is determined whether the command sent to the tag (T) is a read system or a write system. Then, the AGC value set by measurement at the time of sending the read command is stored in the memory 10, and at the time of sending the write command, the AGC operation is not performed for the response of the wireless tag (T) to this command. The AGC value set when the wireless tag (T) responds to the read command is read from the memory 10 and used when responding to the write command.

  That is, the AGC means 6 of the control unit 7 that executes the write command executes the AGC program shown in FIG. First, when it is determined in S31 that the state of T → R has been reached (the wireless tag reader / writer (R) is in the receiving state), in S32, the wireless tag reader / writer (R) transmits to the wireless tag (T). It is determined whether the received command is a read command or a write command.

  When the command sent to the wireless tag (T) is a read command, a received AGC value calculation process is performed in S33. In this calculation process, any one of the processes from S2 to S4 shown in FIG. 4, the processes from S12 to S15, and the processes from S12 to S15, S18, and S19 shown in FIG. 6 is performed.

  From the result of this calculation process, the received AGC value D is determined in S34, and the AGC value of the variable gain amplifier 32 is changed to D. In S35, the AGC value D at this time is stored in the memory 10. In S36, when the state is switched from R to T, it is determined and the AGC process is terminated.

  In S32, it is determined that the command sent from the wireless tag reader / writer (R) to the wireless tag (T) is a write command, that is, a command of Write, Kill, Block Write, or Block Erase. If so, the AGC value D used at the time of the previous read command stored in the memory 10 is read out and set in the variable gain amplifier 32 in S37. Then, the AGC value D is held during the state (T → R) in which the wireless tag reader / writer (R) is in a receiving state, and when the state is switched from R → T in S38, it is determined and this AGC processing is performed. finish.

  The AGC value may be held as it is even after the response of the wireless tag (T) is completed. However, for example, if the transmission state from the wireless tag reader / writer (R) to the wireless tag (T) is reached, AGC is unnecessary. Therefore, the AGC value may be set to 0 or the minimum, and the AGC value may be set to the maximum in the carrier sense state.

  By adopting such a configuration, it is possible to perform optimum automatic gain control for communication with a wireless tag even for a wireless tag reader / writer that uses a write command.

  In each of the embodiments described above, the communication speed is 40 kbps. However, the communication speed is not limited to this. When the communication speed changes, the values of the standard time T1, the constant time Ta, and the predetermined times Tb, Tb ', Tc are naturally different.

1 is a block diagram showing a configuration of a wireless tag reader / writer according to a first embodiment of the present invention. FIG. 5 is a diagram showing command exchange timing in communication between the wireless tag reader / writer and the wireless tag in the embodiment. The figure which shows the preamble pattern attached to the head of data, when the wireless tag in the embodiment returns a response. The flowchart which shows the AGC program which the AGC means of the control part of the RFID tag reader / writer in the embodiment performs. The wave form diagram which shows the change of the AGC value set in the same embodiment, and the change of the amplitude of a received signal. The flowchart which shows the AGC program which the AGC means of the control part of the wireless tag reader / writer concerning the 2nd Embodiment of this invention performs. The wave form diagram which shows the change of the AGC value set in the same embodiment, and the change of the amplitude of a received signal. The figure which shows the timing of the exchange of the write-type command in the communication of the radio | wireless tag reader / writer based on the 3rd Embodiment of this invention, and a radio | wireless tag. The flowchart which shows the AGC program which the AGC means of the control part of the RFID tag reader / writer in the embodiment performs.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 3 ... Reception part, 4 ... Transmission part, 32 ... Variable gain amplifier, 6 ... AGC means, 7 ... Control part.

Claims (5)

In the wireless tag reader / writer that communicates with the wireless tag by the backscatter method using the absorption and reflection of radio waves,
A receiving unit for receiving a received signal from the wireless tag;
Measuring means for measuring the amplitude of the received signal received by the receiving unit;
When the transmission unit that transmits the command to the wireless tag completes the transmission of the command to the wireless tag, the amplitude is measured by the measuring unit for a predetermined time after a predetermined time Ta has elapsed, and the measured amplitude value is set. Control means for performing automatic gain control of the receiving unit based on,
A wireless tag reader / writer characterized by comprising:   The fixed time Ta is set to be equal to or less than the minimum time of the standard time T1 when the time T1 from when the wireless tag receives a command until it returns a response has a range defined by the standard. The wireless tag reader / writer according to 1. The control means
When the measured amplitude value exceeds the predetermined value, the automatic gain control value set in advance is changed, the amplitude is measured again by the measuring means for a predetermined time, and the reception unit is automatically detected based on the measured amplitude value again. 2. The wireless tag reader / writer according to claim 1, wherein gain control is performed. A memory for storing an automatic gain control value set in the receiving unit when a read command is transmitted to the wireless tag;
When transmitting a write command to the wireless tag, the control means sends the automatic gain control value set in the receiving unit when the previous read command is transmitted to the wireless tag to the memory. 4. The wireless tag reader / writer according to claim 1, wherein the wireless tag reader / writer is read out from the receiver and set in the receiving unit again. 5. In the wireless tag reader / writer that communicates with the wireless tag by the backscatter method using the absorption and reflection of radio waves,
A transmission unit for transmitting to the wireless tag;
A receiving unit for receiving the wireless tag;
Measuring means for measuring the amplitude of the received signal received by the receiving unit;
A memory for storing an automatic gain control value set in the receiving unit when a read command is transmitted to the wireless tag;
When transmitting a write command to the wireless tag, the automatic gain control value set in the receiving unit when the previous read command is transmitted to the wireless tag is read from the memory and the receiving unit Control means to set again to
A wireless tag reader / writer characterized by comprising:

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