JP2009253839A - Rfid reader/writer - Google Patents

Abstract

An RFID reader / writer capable of satisfying the spurious standard without using an expensive oscillator and reducing the cost is provided.
A reader / writer includes a processing control unit, a transmission unit, a reception unit, a local oscillator, and a circulator. The processing control unit 13 operates in accordance with a control command from the PC 10 and switches the oscillation frequency of the local oscillator 16 to set the communication channels ch1 to ch9 of the transmission unit 14 and the reception unit 15. The processing control unit 13 includes a carrier sense function and a transmission power setting function, and when transmitting an interrogation wave to the IC tag, performs a carrier sense and sets a vacant channel as a transmission channel. When channels ch2 to ch8 are selected, the transmission power is set to a large value, and when channels ch1 and ch9 at both ends of the band are selected, the value is set to a value smaller than ch2 to ch8 to reduce the occurrence of spurious.
[Selection] Figure 1

Description

  The present invention relates to an RFID (Radio Frequency IDentification) reader / writer of a non-contact IC tag.

  Conventionally, by attaching a non-contact IC tag to goods, articles, etc., transmitting an interrogation wave by radio wave from the antenna of the RFID reader / writer to the IC tag, receiving a response wave from the IC tag, and reading specific data A non-contact IC tag system that manages products and articles is generally known (see, for example, Patent Document 1).

In the RFID reader / writer, the antenna power (transmission power) at the antenna connection end is determined by the Radio Law, and the spurious level at that time is also determined. The UHF band RFID reader / writer can use a maximum of 9 channels, but in the case of the high output type 1Wmax with particularly severe spurious standards, the spurious standard (allowable intensity of unwanted radiation near the carrier wave) is shown in FIG. As shown 945MHz to 950MHz or less: -61dBm / 100kHz
Over 950 MHz and below 952 MHz: -39 dBm / 100 kHz
954 MHz and 956 MHz or less: -39 dBm / 100 kHz
Over 956 MHz and below 956 MHz: -61 dBm / 100 kHz
It has become. FIG. 4 shows the frequency (MHz) on the horizontal axis and the intensity of unwanted radiation (dBm / 100 kHz) on the vertical axis.

As described above, the UHF band RFID reader / writer can use a maximum of nine channels. However, in the conventional RFID reader / writer, the transmission power of each channel (ch1 to ch9) is substantially constant as shown in FIG. Is set to In FIG. 5, the frequencies 952.2, 952.4,..., 953.8 MHz indicate the center frequency (carrier wave carrier) of each channel ch1 to ch9, and each channel width is 200 kHz.
JP 2004-350140 A

  In the UHF band RFID reader / writer in which the transmission power of each channel is set to a substantially constant level as described above, it is necessary to generate a carrier wave with good phase noise characteristics in order to satisfy strict spurious standards. Therefore, an expensive oscillator must be used, and there is a problem that the cost of the entire apparatus becomes high.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an RFID reader / writer that can satisfy the spurious standard and can reduce the cost without using an expensive oscillator.

  An RFID reader / writer according to a first aspect of the present invention includes a transmitter that transmits an interrogation wave to an IC tag using an empty channel among a plurality of transmission channels set in a predetermined frequency band, and a response wave from the IC tag. And a processing control unit that includes a carrier sense function, sets a communication channel of the transmission unit and the reception unit and sets transmission power of the transmission unit, and the processing control unit includes: The carrier sense is executed when the interrogation wave is transmitted, and an empty channel is set as a communication channel, and the transmission power of channels at both ends of the band is set to a value smaller than the transmission power of other inner channels.

  According to a second aspect of the present invention, in the RFID reader / writer according to the first aspect, when the processing control unit performs carrier sense and sets a communication channel and transmission power, each channel inside the channel at both ends of the band is set. The transmission power is set to substantially the same value.

  According to a third aspect of the present invention, in the RFID reader / writer according to the first aspect, when the processing control unit performs carrier sense and sets a communication channel and transmission power, the transmission power of the channel at the center of the band is the largest. The transmission power of the channels in both end directions is set so as to sequentially become a low value.

  According to a fourth aspect of the present invention, in the RFID reader / writer according to the first, second, or third aspect of the invention, the processing control unit sets carrier channels higher in priority than channels at both ends of the band and performs carrier sense. The communication channel and the transmission power are set.

  According to the present invention, it is possible to suppress the occurrence of spurious in the channels at both ends of the band, and it is possible to sufficiently satisfy the spurious standards in the channels at both ends of the band, which are the strictest in electrical characteristics. For this reason, the spurious standard can be sufficiently satisfied without using an expensive local oscillator for generating a carrier wave with good phase noise characteristics, and the cost can be reduced.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram of a UHF band RFID reader / writer according to an embodiment of the present invention.

  In FIG. 1, 11 is a reader / writer, and this reader / writer 11 is connected to, for example, a personal computer (hereinafter abbreviated as PC) 10 that manages a non-contact IC tag system via an I / F (interface) 12. ing.

The reader / writer 11 is provided with a processing control unit 13 that operates in accordance with a control command sent from the PC 10, and a transmission unit 14 and a receiving unit 15 connected to the processing control unit 13. The transmitter 14 and the receiver 15 are provided with a common local oscillator 16. The oscillation frequency of the local oscillator 16 is switched by the processing control unit 13. The processing control unit 13 switches and sets the communication channels ch1 to ch9 of the transmission unit 14 and the reception unit 15 by switching the oscillation frequency of the local oscillator 16. The center frequency (carrier wave carrier) of each channel ch1 to ch9 is, for example, ch1: 952.2 MHz
ch2: 952.4MHz
ch3: 952.6MHz
ch4: 952.8MHz
ch5: 953.0MHz
ch6: 953.2MHz
ch7: 953.4MHz
ch8: 953.6MHz
ch9: 953.8MHz
Each channel width is 200 kHz.

  Further, the processing control unit 13 has a carrier sense function for checking whether or not the channel is free for each channel before transmitting the interrogation wave, that is, whether or not the channel is being used by another RFID reader / writer. And a function of setting the transmission power of the transmission unit 14. The processing control unit 13 executes the carrier sense according to the control of the PC 10, sets the communication channel of the transmission unit 14 and the reception unit 15, and sets the transmission power in the channel.

  The transmission unit 14 operates according to a control command from the processing control unit 13 and generates an interrogation wave of a designated channel. This interrogation wave passes through terminals 1 → 2 of circulator 17 and is sent to antenna port P.

  An antenna 19 such as a patch antenna is connected to the antenna port P via a coaxial cable 18. For example, the antenna 19 is installed at a passing gate of a belt conveyor that moves goods, articles, and the like, and transmits and receives radio waves to and from an IC tag attached to the goods, articles, and the like.

  The antenna 19 transmits an interrogation wave transmitted from the transmission unit 14 via the circulator 17 toward an IC tag (not shown), and receives a response wave from the IC tag. The response wave of the IC tag received by the antenna 19 is input to the antenna port P of the reader / writer 11 and sent to the receiving unit 15 through the terminal 2-3 of the circulator 17 to be detected. The detected IC tag data is decoded by the processing control unit 13 and sent to the PC 10.

  When the processing control unit 13 performs carrier sense according to the control of the PC 10 and sets the communication channels of the transmission unit 14 and the reception unit 15, the processing control unit 13 sets transmission power in the channel as shown in FIG. FIG. 2 shows the relationship between the transmission power of each channel ch1 to ch9. When using the channels ch1 and ch9 at both ends of the band, the processing control unit 13 sets the transmission power to be 2 dB or more lower in terms of decibels than when using the other channels ch2 to ch8, for example, transmitting when using the channels ch2 to ch8 When the power is 900 mW and the channels ch1 and ch9 are used, the transmission power is set to 200 mW.

  In the above configuration, when the interrogation wave is transmitted from the reader / writer 11 to the IC tag, the processing control unit 13 performs signal reception processing for each channel ch1 to ch9, and indicates whether the channel is free for each channel. Perform sense. In this case, the processing control unit 13 sets the carrier sense level to “−74 dBm” or less and the carrier sense determination time to “5 msec”. Note that the continuous transmission time of the reader / writer 11 is defined as “4 sec” or less, and the pause time is defined as “50 msec”.

  If the received signal is “−74 dBm” or less, the processing control unit 13 determines that the channel is used by another reader / writer if the received signal is larger than “−74 dBm”. The oscillation frequency of the oscillator 16 is controlled, and a free channel is set as a communication channel. In addition, when the channels ch1 and ch9 are selected as communication channels, the processing control unit 13 adjusts the output of the transmission unit 14 with a variable attenuator or the like to set the transmission power to a small value, for example, 200 mW, and sets the channels ch2 to ch8. When selected, the transmission power is set to a large value, for example, 900 mW.

  The transmission unit 14 operates in accordance with a control command from the processing control unit 13, generates a carrier wave carrier of a designated channel, and generates an interrogation wave having a predetermined power according to the designated channel. This interrogation wave passes through terminals 1 → 2 of the circulator 17 and is sent from the antenna port P to the antenna 19. The antenna 19 transmits the interrogation wave toward the IC tag and receives a response wave from the IC tag. The response wave of the IC tag received by the antenna 19 is input to the antenna port P of the reader / writer 11 and sent to the receiving unit 15 through the terminal 2-3 of the circulator 17 to be detected. The detected IC tag data is decoded by the processing control unit 13 and sent to the PC 10.

  As shown in the above embodiment, when the interrogation wave is transmitted from the reader / writer 11 to the IC tag, carrier sense is executed to determine the communication channel, and if the channel is ch2 to ch8, the transmission power is set to a high output level. In the case of channels ch1 and ch9 at both ends of the band, by setting the transmission power to a low output level, the occurrence of spurious in the channels ch1 and ch9 can be suppressed, and the spurious standards in the channels ch1 and ch9 that are the most severe in electrical characteristics Can be fully satisfied.

  Therefore, the spurious standard can be sufficiently satisfied without using an expensive local oscillator for generating a carrier wave with good phase noise characteristics, and the cost can be reduced. In addition, since the occurrence of spurious in the channels ch1 and ch9 can be suppressed, it is possible to suppress an increase in noise level caused by reducing the transmission power.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.

  The reader / writer in the second embodiment has the same configuration as the reader / writer 11 shown in FIG. 1 of the first embodiment, and will be described with reference to FIG.

  In the first embodiment, when setting the transmission power of each channel ch1 to ch9, the channels ch2 to ch8 are set to a high output level (constant value) of 900 mW, for example, and the channels ch1 and ch9 at both ends of the band are set to 200 mW, for example. Although the low output level is set, in the second embodiment, as shown in FIG. 3, the transmission power of the channel ch5 at the center of the band is set to the largest value, for example, 900 mW, and sequentially decreases in the direction of the band end channels ch1 and ch9. Set in a staircase pattern to achieve an output level. In this case, the transmission power of the channels ch1 and ch9 at both ends is set to a low output level of 200 mW, for example, as in the first embodiment.

  Also in the second embodiment, since the transmission power is set to a low output level for the channels ch1 and ch9 at both ends, the occurrence of spurious can be suppressed and the spurious standards are sufficiently satisfied even under the most severe conditions in terms of electrical characteristics. be able to. Further, even if the transmission power is set larger as it approaches the channel ch5 at the center of the band, the spurious standard can be sufficiently satisfied because the electrical characteristics are relaxed at the center of the band.

(Third embodiment)
Next, a third embodiment of the present invention will be described.

  In the third embodiment, the sequence control operation related to the communication channel setting and the output level setting after the carrier sense in the first embodiment is executed by application software. This application software is set and used in the PC 10 in FIG. The application software set in the PC 10 controls the processing control unit 13 to execute a sequence control operation related to communication channel setting and output level setting after carrier sense.

  The application software preferentially senses the channels ch2 to ch8 whose transmission power is set to a high output level when transmitting the interrogation wave, selects an empty channel, performs transmission processing, and sets the channels ch2 to ch8. When there is no empty channel, carrier sense is performed on the low output level channels ch1 and ch9, and an empty channel is selected to perform transmission processing.

  By preferentially using the channels ch2 to ch8 in which the transmission power is set to a high output level as described above, the interrogation wave and the response wave are satisfactorily transmitted and received between the reader / writer 11 and the IC tag. Can do. When channels ch1 and ch9 with low transmission power are used, the communication distance is reduced, but by using channels ch2 to ch8 with high transmission power preferentially as described above, the reader / writer 11 and the IC tag can be connected. The communication state between them can always be kept in a good state.

  In the third embodiment, channels ch2 to ch8 whose transmission power is set to a high output level are preferentially used, and when there are no empty channels in channels ch2 to ch8, channels ch1 and ch9 having a low output level are used. However, only the channels ch2 to ch8 may be used and the channels ch1 and ch9 may not be used.

  The PC 10 may arbitrarily select a sequence that preferentially uses the channels ch2 to ch8 and a sequence that uses only the channels ch2 to ch8.

  In the third embodiment, when setting the transmission power of the channels ch1 to ch9 as shown in the first embodiment, the channels ch2 to ch8 are set to high output levels (constant values), and the channels at both ends are set. The sequence control operation when ch1 and ch9 are set to the low output level has been described. However, as shown in the second embodiment, the transmission power of the channel ch5 at the center of the band is set to the largest value, and the channels ch1 and ch1 at both ends are set. This can also be implemented in the same way when setting the output level to be sequentially lower in the direction of ch9.

  For example, for channels ch1 to ch9, priority is set in the order of ch5 → ch4 or ch6 → ch3 or ch7 → ch2 or ch8 → ch1 or ch9, carrier sense is executed in this priority order, and an empty channel is selected and transmitted. Process.

  In addition, for example, carrier sense may be executed in the above-described priority order, and transmission processing may not be performed when channels ch1 and ch9 are selected.

  Even if the carrier sense is performed by setting the priority order in the order of the channels having the largest transmission power as described above, the communication state between the reader / writer 11 and the IC tag is always maintained even if the transmission process is performed by selecting an empty channel. It can be kept in a good state.

  Further, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.

1 is a configuration diagram of an RFID reader / writer in a contactless IC tag system according to a first embodiment of the present invention. It is a figure which shows the relationship between each channel and transmission power in the embodiment. It is a figure which shows the relationship between each channel and transmission power which concern on 2nd Embodiment of this invention. It is a figure which shows the spurious standard in a high output type RFID reader / writer. It is a figure which shows the relationship between each channel and transmission power in the conventional RFID reader / writer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Personal computer (PC), 11 ... Reader / writer, 13 ... Processing control part, 14 ... Transmission part, 15 ... Reception part, 16 ... Local oscillator, 17 ... Circulator, 18 ... Coaxial cable, 19 ... Antenna.

Claims (4)

A transmission unit that transmits an interrogation wave to an IC tag using an empty channel among a plurality of transmission channels set in a predetermined frequency band; a reception unit that receives a response wave from the IC tag; and a carrier sense function Comprising a processing control unit for setting a communication channel of the transmission unit and the reception unit and setting a transmission power of the transmission unit,
The processing control unit performs carrier sense upon transmission of the interrogation wave, sets an empty channel as a communication channel, and sets transmission power of channels at both ends of the band to a value smaller than transmission power of other inner channels. A featured RFID reader / writer.   2. The processing control unit according to claim 1, wherein when the carrier sense is executed to set the communication channel and the transmission power, the transmission power of each channel inside the channel at both ends of the band is set to substantially the same value. The described RFID reader / writer.   When the carrier control is performed to set the communication channel and transmission power, the processing control unit sets the transmission power of the channel at the center of the band to the largest value, and the transmission power of the channels in both end directions sequentially decreases to a lower value. The RFID reader / writer according to claim 1, wherein the RFID reader / writer is set as follows.   4. The processing control unit according to claim 1, 2, or 3, wherein the processing control unit performs carrier sense by setting a higher priority for channels inside the channels at both ends of the band, and sets a communication channel and transmission power. RFID reader / writer.

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