JP4321490B2 - Non-contact communication system - Google Patents

Description

  The present invention relates to a non-contact communication system including a reader and a wireless tag that communicate on one frequency channel among a plurality of frequency channels.

For example, in physical distribution management, sorting information is stored in a wireless tag attached to an article, and the sorting information stored in the wireless tag is read by a reader to automatically sort the article.
JP 2003-78459 A JP 2003-188765 A

By the way, the operable distance of the wireless tag is affected by the use environment of the wireless tag. For example, when a wireless tag is sandwiched between books, or when there are a plurality of wireless tags, the resonance frequency shifts and the received power received by the wireless tag from the reader decreases. The possible distance is shortened.
Therefore, in order to secure the operable distance of the wireless tag, a specific environment is assumed, and for example, the resonance frequency is shifted in advance by adjusting the antenna pattern of the wireless tag (Patent Document 1). , 2).
However, even if the resonance frequency is adjusted in this way, there is still a problem that the operable distance is shortened if the actual usage environment changes from the assumed specific environment.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a contactless communication system that can prevent the operable distance of the wireless tag from being reduced with respect to the reader regardless of the use environment. is there.

According to the first aspect of the present invention, the frequency channel at which the reception power received by the wireless tag from the reader is maximized by the reception power monitor is set as the frequency channel of the reader. Communication is possible with the maximum frequency channel.
According to the second aspect of the present invention, since the wireless tag detects the reception power at the timing when the transmission frequency channel change completion code is received, the reception power can be detected at the timing when the frequency channel is reliably switched. .
According to the invention of claim 3, since how many times the frequency channel is changed is transmitted from the reader to the wireless tag, monitoring of received power by the wireless tag can be executed in cooperation with each other.

According to the fourth aspect of the present invention, when the switching of all frequency channels is completed, the slot number from which the maximum received power is obtained is transmitted as a received power monitor result response from the wireless tag to the reader. It is possible to notify the reader of the detection result at the timing when the monitoring is completed.
According to the invention of claim 5, since the wireless tag can detect the maximum received power by using the power regeneration circuit, it can be implemented without using a special circuit for detecting the received power. .

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 2 is a schematic diagram showing the entire system. In FIG. 2, a reader / writer (corresponding to a reader) 1 is composed of a controller 2 and an antenna 3. The controller 2 reads data read from an RFID tag (corresponding to a wireless tag) 4 through the antenna 3 with a host device. The data is output to a certain computer 5.

  FIG. 1 is a functional block diagram showing an electrical configuration of the reader / writer 1. In FIG. 1, a reader / writer 1 is composed mainly of a CPU (corresponding to frequency channel switching means and frequency setting means) 6. As will be described later, the CPU 6 has a function of generating a command to be transmitted to the RFID tag 4, processing a response received from the RFID tag 4, and controlling a frequency channel of high-frequency oscillation. Further, the CPU 6 is configured to execute a received power monitor described later when the power is turned on.

  On the transmission circuit side, the data encoding circuit 7 converts the data sent from the CPU 6 into a modulation signal (baseband signal). The modulator 8 multiplies the carrier wave (953 MHz in the UHF band) output from the high-frequency oscillation circuit 9 on the receiving circuit side by the baseband signal output from the data encoding circuit 7 to thereby perform ASK (Amplitude Shift Keying) modulation. Then, the modulated transmission signal is output. The high frequency amplifier circuit 10 amplifies the transmission signal from the modulator 8 and outputs the amplified signal to the filter 11. The filter 11 passes only a signal having a necessary frequency among signals from the high-frequency amplifier circuit 10, and attenuates a signal having an unnecessary frequency. The circulator 12 prevents the high-frequency signal from the filter 11 from flowing in the reverse direction. That is, the high-frequency signal input from the transmission circuit side is output to the antenna 3, and the high-frequency signal input from the antenna 3 is output to the reception circuit side. And the antenna 3 transmits a high frequency signal as a radio signal.

  The receiving circuit side is configured to execute the IQ detection method. The reason is that in order to avoid that the signal reflected from the RFID tag 4 cannot be detected due to the phase difference between the signal reflected from the RFID tag 4 and the carrier wave output to the RFID tag 4, This is because detection is performed using signals whose phases are shifted by 90 °.

  The signal from the circulator 12 is output to the mixers 14 and 15 after frequency discrimination by the filter 13. The high-frequency oscillation circuit 9 generates a carrier wave signal (reference signal) and outputs it to the mixers 14 and 15 on the reception circuit side in addition to the modulator 8 on the transmission circuit side. In the present embodiment, the high-frequency oscillation circuit 9 is set to be able to output by switching seven channels at every 1 MHz from 950 MHz to 956 MHz. The mixers 14 and 15 extract the difference between the received signal and the carrier wave signal in order to demodulate the signal of the RFID tag 4 from the high frequency signal. The demodulated signals from the mixers 14 and 15 are output to the A / D conversion circuits 18 and 19 after frequency discrimination by the filters 16 and 17. The A / D conversion circuits 18 and 19 convert the demodulated signal from the RFID tag 4 into a digital signal. The data restoration circuit 20 restores the response of the RFID tag 4 based on the digital data from the A / D conversion circuits 18 and 19. In this case, when the data restoration circuit 20 restores the response of the RFID tag 4 based on the digital data from the two A / D conversion circuits 18 and 19, the digital data that has been correctly restored is adopted. It has become.

  FIG. 3 is a functional block diagram showing an electrical configuration of the RFID tag 4. In FIG. 3, the RFID tag 4 includes an antenna 21, a power regeneration circuit 22, a regulator 23, a CPU / logic circuit (corresponding to reception power detection means and notification means) 24, a demodulation modulation circuit 25, and a reception power monitor circuit 26. Has been. The power regeneration circuit 22 rectifies the carrier signal received by the antenna 21 to generate power power. The regulator 23 outputs the power supplied from the power regeneration circuit 22 to the CPU / logic circuit 24, the demodulation / modulation circuit 25, and the received power monitor circuit 26 in a state where the power is stabilized. The demodulation modulation circuit 25 demodulates the transmission data from the reader / writer 1 superimposed on the carrier wave signal received by the antenna 21 and outputs it to the CPU / logic circuit 24. The received power monitor circuit 26 A / D converts the power supply voltage generated by the power supply regeneration circuit 22 and outputs it to the CPU / logic circuit 24. When transmitting data to the reader / writer 1, the CPU / logic circuit 24 reads out data stored in a memory (not shown) and outputs the data to the demodulation and modulation circuit 25. When a write command is transmitted from the reader / writer 1, the data transmitted together with the command is written in the memory. The demodulation modulation circuit 25 performs modulation by changing the reflectance of the antenna according to the data read by the CPU / logic circuit 24. Therefore, the reader / writer 1 can read the data stored in the RFID tag 4 when the carrier signal is ASK modulated.

  Here, the reception frequency of the RFID tag 4 is set to a 950 to 956 MHz band centering on 953 MHz (actually, a wider frequency band is set to be receivable, but the operation guarantee frequency is 950 to 956 MH. Is set).

Next, the operation of the above configuration will be described.
The reader / writer 1 starts the received power monitoring operation when the power is turned on.
FIG. 4 shows a flowchart of the received power monitoring operation of the reader / writer 1. In FIG. 4, the reader / writer 1 sets an initial value as a transmission frequency channel (a1). This initial value is a frequency channel output first in the reception power mode, and is set to 953 MHz which is the center frequency of the reader / writer 1. This is because the reception frequency band of the RFID tag 4 is set to 950 to 956 MHz, and is set to 953 MHz, which is a frequency that is most likely to be transmitted and received stably. Next, a reception power monitor start command is transmitted as transmission data (a2). This reception power monitor start command is for instructing the RFID tag 4 to start reception power monitoring, and includes the number N of slots indicating how many times the frequency channel is changed in the command frame. In this embodiment, the number of slots is set to 7 corresponding to 7 frequency channels for 1 MHz from 950 to 956 MHz.

  As described above, when a transmission signal is output from the reader / writer 1 to the RFID tag 4, the power supply power is regenerated by the power regeneration circuit 22 of the RFID tag 4, and the regulator 23 includes the CPU / logic circuit 24 inside the RFID tag 4. Power is supplied to each component. Then, the CPU / logic circuit 24 operates to execute the received power monitor.

  FIG. 5 is a flowchart showing the received power monitoring operation of the RFID tag 4. In FIG. 5, when receiving a received power monitor start command from the reader / writer 1 (b1: YES), the RFID tag 4 extracts the number of slots N included in this command (b2). Next, after initializing the slot counter (n = 0) (b3), it waits to receive a transmission frequency setting change completion code from the reader / writer 1 (b4).

  When the slot counter is initialized (a3), the reader / writer 1 increments n (a4), changes to the transmission frequency setting n (= 1) (a5), and then transmits a transmission frequency setting change completion code. (A6). That is, in FIG. 6 showing the communication timing between the reader / writer 1 and the RFID tag 4, a transmission signal in which 950 MHz is set as the frequency channel corresponding to the slot 1 is output, and the transmission frequency setting change completion code is output at the beginning of the slot 1. After is transmitted, an unmodulated transmission signal (carrier wave signal) is output.

  Following initialization of the slot counter (b3), when the RFID tag 4 receives a transmission frequency setting change completion code from the reader / writer 1 (b4: YES), n is incremented (b5), and the slot 1 The received power monitor is executed with the frequency channel (950 MHz) set corresponding to (b6). At this time, as shown in FIG. 6, since an unmodulated transmission signal is transmitted from the reader / writer 1, the RFID tag 4 monitors the received power of the frequency channel (950 MHz), and the monitored received power is Stored in correspondence with the slot number.

  After transmitting the transmission frequency setting change completion code (a6), the reader / writer 1 confirms that the slot counter is smaller than the number of slots N (a7: YES), the slot wait time tw has elapsed. After waiting (a11), the operation is changed to the frequency channel (951 MHz) corresponding to the slot 2 and the transmission frequency setting change completion code is transmitted in the same manner as described above (a4 to a7, a11).

Each time the RFID tag 4 receives the transmission frequency setting change code from the reader / writer 1 (b4: YES), the RFID tag 4 repeats the operation of monitoring the received power for the slot n (b4 to b7).
By the operation as described above, the RFID tag 4 sequentially stores received power corresponding to the frequency channel n.

  When the reader / writer 1 transmits the transmission frequency setting change completion code (a6) and the slot counter n is N (7 in this embodiment) (a7: NO), the received power from the RFID tag 4 Waiting to receive a monitor result response (a8).

  The RFID tag 4 transmits a received power monitor result response to the reader / writer 1 when the received power monitor for the slot is performed (b6), and when the slot n becomes N (= 7) (b7: NO). (B8). That is, as shown in FIG. 6, in the reception state of the transmission signal of the frequency channel (956 MHz) of the slot 7, the slot number X that has the maximum reception power based on the reception power stored in correspondence with the slot number as described above. Is returned to the reader / writer 1. For example, when the maximum received power is reached in slot 2, 2 is returned as slot number X.

  When the reader / writer 1 receives the received power monitor result from the RFID tag 4 (a8: YES), the reader / writer 1 extracts the slot number X indicated by the received power monitor result (a9), and sets the transmission frequency corresponding to this slot number. Change to X (a10). For example, when the slot number X is 2, 951 MHz which is a frequency channel corresponding to the slot 2 is set.

  When the reader / writer 1 changes to the transmission frequency channel corresponding to the slot number X as described above, the reader / writer 1 performs data communication with the RFID tag 4 thereafter using the transmission frequency channel. That is, when a communication start command is transmitted to the RFID tag 4 side and the RFID tag 4 returns a response to the command transmission, the reader / writer 1 next transmits a read command. Then, the RFID tag 4 responds by returning data read from the memory. The reader / writer 1 transmits a write command when writing data to the RFID tag 4. Then, the RFID tag 4 writes the write data transmitted together with the command to the memory, and responds when the writing is completed. As described above, the reader / writer 1 can perform data communication with the RFID tag 4 through the frequency channel in which the RFID tag 4 has the maximum received power.

  When the reader / writer 1 is turned on again, the received power monitor is executed again as described above, so that the frequency channel that maximizes the received power of the RFID tag 4 at that time can be set.

  According to such an embodiment, when the reader / writer 1 is powered on, the reception power monitor is executed to set the frequency channel for the RFID tag 4 to receive the maximum reception power. The reader / writer 1 and the RFID tag 4 can perform data communication using a frequency channel with which the RFID tag 4 can obtain the maximum received power. Therefore, unlike the configuration in which the frequency channel between the reader / writer 1 and the RFID tag 4 is fixed, the operable distance of the RFID tag 4 with respect to the reader / writer 1 is short regardless of the usage environment of the reader / writer 1 and the RFID tag 4. Can be prevented.

  In addition, since the reception power monitor having such excellent effects is performed when the power is turned on, even if the optimum frequency channel fluctuates during use, it can be prevented from being affected by the fluctuation. Also, as a result of automatically executing the received power monitor when the power is turned on, the user can carry out the operation without troublesome operations.

The present invention is not limited to the above embodiment, and can be modified or expanded as follows.
The configuration of the system may be a configuration in which a controller and an antenna are integrated as shown in FIG.
The reception power monitor is not limited to when the power is turned on, but may be executed periodically, or may be executed in response to an operation on the reception power monitor switch. Further, it may be executed in response to a request from the host device.

1 is a functional block diagram showing a configuration of a reader / writer in an embodiment of the present invention. Perspective view showing the overall system configuration Functional block diagram showing the configuration of the RFID tag Flowchart showing reception power monitoring operation of reader / writer Flowchart showing received power monitoring operation of RFID tag Diagram showing communication timing between reader / writer and RFID tag FIG. 2 equivalent view showing another embodiment of the present invention.

Explanation of symbols

  In the drawings, 1 is a reader / writer (reader), 4 is an RFID tag (wireless tag), 6 is a CPU (frequency channel switching means, frequency setting means), 22 is a power regeneration circuit, and 24 is a CPU / logic circuit (received power detection). Means, notification means).

Claims (5)

A non-contact communication system comprising a reader having a frequency channel switching means for sequentially switching and transmitting a plurality of frequency channels, and comprising a reader and a wireless tag communicating with one of the plurality of frequency channels. ,
The wireless tag is
Received power detection means for detecting received power in each of the plurality of frequency channels;
Notification means for notifying the reader of the frequency channel where the reception power detected by the reception power detection means is maximized,
The reader is
A non-contact communication system comprising frequency setting means for setting a frequency channel having the maximum received power received from the wireless tag as its own frequency channel. The frequency channel switching means of the reader sequentially changes the plurality of frequency channels in a time division manner, and transmits a change completion code indicating completion of the frequency channel change,
The contactless communication system according to claim 1, wherein the reception power detection unit of the wireless tag detects reception power at a timing when the change completion code is received from the reader.   The frequency channel switching means of the reader transmits a reception power monitor start command indicating the number of slots indicating how many times the plurality of frequency channels are changed in order, and then transmits each command to each time slot of the transmission signal. 3. The contactless communication system according to claim 2, wherein a carrier wave having a frequency assigned to the frequency channel is transmitted without modulation.   When the reception power detection for the number of slots designated by the reader is completed, the notification unit of the wireless tag transmits the slot number from which the maximum reception power is obtained as a reception power monitor result response. The contactless communication system according to claim 3. The wireless tag includes a power regeneration circuit that regenerates a transmission signal from the reader as a power source,
The contactless communication system according to any one of claims 1 to 4, wherein the received power detection means detects a maximum received power based on an output from the power regeneration circuit.

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