JP2011070606A - Radio tag communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the reliability of information transmission and reception, by suppressing interference between a plurality of pieces of radio tag communication equipment or interference at a radio tag side. <P>SOLUTION: A reader 1 is provided with a reader antenna unit 3, capable of executing radio communication to a radio tag 1 within a prescribed frequency range and an RSSI(received signal strength indicator) circuit 226 for detecting the reception signal strength of a received radio wave. The usage situations for all a plurality of channels are determined based on detected reception signal strength Vs, and a communication operation is determined according to whether it is determined that all the channels are not used, or it is determined that any of the plurality of channels is used. Then, the channel to be used is selected from among the plurality of channels, and information transmission/reception is performed by the use of a radio tag T by a communicating operation determined by using the selected channel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wireless tag communication system, and more particularly to suppression of mutual interference in a wireless tag communication apparatus.

  A wireless tag communication device that performs wireless communication with a wireless tag is already known. As a prior art regarding interference suppression when a plurality of RFID tag communication apparatuses perform communication, for example, there is an RFID tag communication system described in Patent Document 1.

  The RFID tag communication apparatus provided in this conventional RFID tag communication system determines the level of the received interference signal, and determines the channel and polarization direction that make the level of the interference signal equal to or less than the threshold value. Then, the wireless tag communication device executes communication with the wireless tag using the determined channel and polarization direction. As a result, when one RFID tag communication apparatus tries to start communication, it increases the possibility that an unused channel that is not used by another RFID tag communication apparatus can be detected, and suppresses interference among a plurality of RFID tag communication apparatuses. To do.

International Publication No. 2006/082612

  In the above prior art, when one RFID tag communication apparatus tries to start communication, if there is an unused channel among a plurality of channels, information transmission / reception is performed using the channel. However, in this case, although interference between a plurality of RFID tag communication devices operating simultaneously can be suppressed, interference may occur on the RFID tag side capable of receiving radio waves from the plurality of RFID tag communication devices. there were. As a result, it has been difficult to improve the reliability of information transmission / reception between the wireless tag communication device and the wireless tag communication.

  An object of the present invention is to provide a wireless tag communication device that can suppress interference between a plurality of wireless tag communication devices and interference on the wireless tag side and improve the reliability of information transmission / reception.

  To achieve the above object, according to a first aspect of the present invention, there is provided antenna means capable of performing wireless communication with a wireless tag within a predetermined frequency range including a plurality of channels, and reception of radio waves received by the antenna means. An intensity detector that detects a signal intensity; a first determiner that determines a use situation for all of the plurality of channels based on a received signal intensity detected by the intensity detector; and A communication operation determining means for determining a communication operation according to whether it is determined that all of the plurality of channels are not used or one of the plurality of channels is used; and Channel selecting means for selecting a channel to be used among a plurality of channels, and the channel selected by the channel selecting means Using Yan'neru, said by the antenna means, characterized by having a transmission and reception control means for performing radio tag information transmitted and received in a communication operation by the communication operation determining means has determined.

  In the wireless tag communication device according to the first aspect of the present invention, when performing wireless communication, the first determination means determines the usage status for all the plurality of channels based on the received signal strength detected by the strength detection means. The communication operation determining means performs the communication operation according to whether the first determination means determines that all of the plurality of channels are not used, or whether any of the plurality of channels is used. decide. Then, using the selected channel, the transmission / reception control means transmits / receives information to / from the wireless tag by the communication operation determined by the communication operation determination means.

  As described above, in the first invention of the present application, after confirming the non-use of all the plurality of channels included in the predetermined frequency range, information transmission / reception is executed, or at least some of the channels are used. In this state, it is possible to reduce the transmission output and execute communication. Thereby, it is possible to suppress the occurrence of interference on the wireless tag side having no frequency selection function. As a result, the reliability of communication can be improved as compared with the conventional technique in which an unused channel is confirmed among a plurality of channels and information is transmitted and received using the channel. Therefore, the reliability of information transmission / reception can be improved as a whole communication system including a plurality of RFID tag communication apparatuses.

  In a second aspect based on the first aspect, the communication operation determining means performs communication by the transmission / reception control means when the first determination means determines that all of the plurality of channels are not used. It is characterized by determining.

  When it is determined that all channels are not used, it is possible to prevent the other readers from communicating with the tag by performing communication.

  According to a third aspect of the present invention, in the first or second aspect of the invention, when the communication operation determining unit determines that any one of the plurality of channels is being used by the first determining unit, the intensity detecting unit The transmission output of the transmission / reception control means is determined on the basis of the result.

  Even when it is determined that at least some of the channels are being used, the influence of other readers communicating with the tag can be reduced by executing communication with a reduced transmission output.

  A fourth invention includes any one of the first to third inventions, further comprising prohibition control means for prohibiting wireless communication by the antenna means for a predetermined time, and when information transmission / reception by the transmission / reception control means is completed, The prohibition control means prohibits wireless communication by the antenna means.

  After the information transmission / reception is completed, the prohibition control means prevents the wireless communication from being performed for a predetermined time, so that it is possible to prevent other wireless tag communication devices from being unable to communicate.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the apparatus further includes channel switching means for switching the channel used in wireless communication by the antenna means, and the first determination means is the channel switching means. For each channel switched by the above, it is determined whether or not the received signal strength detected by the strength detecting means is greater than a usage confirmation threshold.

  By making a determination for each channel while switching a plurality of channels, the configuration of the circuit on the receiving side can be simplified, and a general-purpose carrier sense circuit that has been conventionally used can also be used.

  In a sixth aspect based on any one of the first to fourth aspects, the first determination means determines whether or not the received signal strength detected by the strength detection means is larger than a usage condition confirmation threshold value. It is characterized in that a plurality of channels are collectively determined.

  By performing the determination for all the channels collectively, it is possible to perform the determination more quickly than when performing the determination for each channel while switching a plurality of channels.

  According to a seventh invention, in the fifth or sixth invention, the received signal strength detected by the strength detecting means using the channel selection threshold value smaller than the usage status confirmation threshold value is the channel. And a second determination unit configured to determine whether the received signal strength is greater than the threshold value for selection. The channel selection unit is configured to select the channel selection signal by the second determination unit among the plurality of channels. The channel determined to be equal to or less than the threshold for use is selected as a channel to be used.

  The channel selection threshold value that is normally used is often set to a relatively low value, assuming that a plurality of RFID tag communication apparatuses are spaced apart and interfere with each other. Assuming the occurrence of interference in the wireless tag, a stronger radio wave is required between the wireless tag communication device and the wireless tag. It is preferable to use a large value.

  In the seventh invention of the present application, based on the above, the first determination means and the second determination means are obtained by using both threshold values such that the threshold value for channel selection <the threshold value for checking the usage status. Reasonable and effective judgment can be made in

  In an eighth aspect of the present invention, in any one of the first to seventh aspects, the antenna attribute of the antenna unit is determined when the first determination unit determines that any one of the plurality of channels is used. Antenna switching means for switching the antenna, the strength detection means detects the received signal strength at the antenna means after the antenna attribute has been switched by the antenna switching means, and the first determination means includes the antenna Based on the received signal strength detected by the strength detection unit after the antenna attribute is switched by the switching unit, the usage status for all of the plurality of channels is determined.

  When the antenna attribute of the antenna means can be switched to a plurality of modes, it is preferable to check the usage state for each mode because the communication range and the wireless tag to be communicated differ for each mode. Therefore, in the eighth invention of the present application, when the first determination unit determines that any one of the plurality of channels is used, the antenna switching unit switches the antenna attribute. Then, the strength detection means detects the received signal strength of the antenna means after the switching, and the first determination means determines the usage status of all the plurality of channels based on the detected strength. As a result, it is possible to find an antenna mode that can suppress the occurrence of interference between a plurality of RFID tag communication devices and the occurrence of interference on the RFID tag side, and perform highly reliable information transmission / reception in the antenna mode.

  According to a ninth invention, in any one of the first to fourth inventions, a reader communication means for communicating with another RFID tag communication apparatus, and the other RFID tag communication apparatus using the reader communication means A stop request transmission means for transmitting a stop request signal for requesting stop of wireless communication, and a communication status signal from the other RFID tag communication means corresponding to the stop request signal from the stop request means A communication status receiving means for receiving, wherein the first determination means is based on the received signal strength detected by the strength detecting means when the communication status receiving means has not received the communication status signal. The use status of all the plurality of channels is determined.

  In the ninth invention of the present application, a plurality of RFID tag communication apparatuses communicate with each other using a reader communication means to perform a cooperative operation. By performing such a cooperative operation, when one RFID tag communication apparatus executes wireless communication, the other RFID tag communication apparatuses that cooperate with each other stop the wireless communication, so that all channels can be used quickly and reliably. Confirmation and transmission / reception of information can be started. As a result, information transmission efficiency can be improved. In addition, it is not necessary to provide a host controller for controlling the plurality of RFID tag communication devices by performing a cooperative operation by communicating with each other.

  According to the present invention, it is possible to suppress interference between a plurality of RFID tag communication apparatuses and interference on the RFID tag side, and improve the reliability of information transmission / reception.

It is a figure showing an example at the time of applying the reader of one embodiment of the present invention to management of many books to which a wireless tag is stuck. It is a functional block diagram showing schematic structure of a reader. It is a functional block diagram showing the detailed structure of the RF communication control part and reader antenna unit in a reader. It is a flowchart showing the control procedure of CPU. It is a functional block diagram showing the detailed structure of RF communication control part and a reader antenna unit in the modification which judges collectively about a some channel. It is a flowchart showing the control procedure of CPU. It is a functional block diagram showing the schematic structure of the reader in the modification which communicates and cooperates between several readers. It is explanatory drawing explaining the operation | movement cooperated with a some reader | leader. It is a flowchart showing the control procedure of CPU.

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

  With reference to FIG. 1, an example of how the reader 1 is used as a wireless tag communication apparatus according to an embodiment of the present invention will be described.

  In FIG. 1, in this example, a large number of books B are stored in a bookcase S of a library. A radio tag T is affixed to the spine of each book B. The wireless tag T stores book information such as a book name and an author name. In this example, the two readers 1 and 1 search for the wireless tag T attached to the book B, respectively, within a predetermined vicinity. The reader 1 transmits / receives information to / from the wireless tag T existing in the area A where wireless communication is possible, and acquires the book information.

  In this example, the reader 1 is a portable or so-called handheld type wireless communication device, and has a substantially rectangular parallelepiped housing 2a. The housing 2 a is provided with a reader antenna unit 3 whose polarization plane can be switched between the vertical direction and the horizontal direction, and an operation unit 7 and a display unit 8.

  A schematic system configuration of the reader 1 will be described with reference to FIG.

  The system of the reader 1 includes a main body control unit 2 provided inside the housing 2a and a reader antenna unit 3 as antenna means.

  The reader antenna unit 3 transmits and receives radio waves for performing wireless communication with the wireless tag T (details will be described later) within a predetermined frequency range including a plurality of channels, for example, all bands permitted by laws and regulations. In this example, the reader antenna unit 3 includes a microstrip antenna 11 and a changeover switch circuit 12 for switching the polarization plane of the microstrip antenna 11.

  The main body control unit 2 includes a CPU 4, a nonvolatile storage device 5, a memory 6, the operation unit 7, the display unit 8, and an RF communication control unit 9.

  The wireless tag T includes a wireless tag circuit unit To including a tag antenna 151 and an IC circuit unit 150. The wireless tag T is configured such that the wireless tag circuit portion To is provided on a base material (not shown) or the like and can be attached to the book B. In FIG. 1 described above, the wireless tag T is affixed to each book B in a posture in which the longitudinal direction of the tag antenna 151 is oriented in either the vertical direction or the horizontal direction. In this example, the surface including the longitudinal direction of the tag antenna 151 that is a dipole antenna has higher sensitivity to the electric field of the radio wave. This plane is called the polarization plane.

  The RF communication control unit 9 accesses the information including the tag ID stored in the IC circuit unit 150 of the RFID tag circuit unit To via the reader antenna unit 3.

  The nonvolatile storage device 5 includes a hard disk device and a flash memory, and stores various information such as the management status of the book B. The memory 6 is composed of, for example, a RAM or a ROM. The operation unit 7 receives instructions and information from the user. The display unit 8 displays various information and messages.

  The CPU 4 performs signal processing according to a program stored in advance in the nonvolatile storage device 5 while utilizing the temporary storage function of the RAM in the memory 6, thereby performing various controls of the entire reader 1. Further, the CPU 4 processes the signal read from the IC circuit unit 150 of the RFID tag circuit unit To to read out information, and generates various commands for accessing the IC circuit unit 150 of the RFID tag circuit unit To. .

  Detailed configurations of the RF communication control unit 9 and the reader antenna unit 3 will be described with reference to FIG.

  The RF communication control unit 9 includes a transmission unit 212, a reception unit 213, and a transmission / reception separator 214.

  The transmission unit 212 is a block that generates a query wave for accessing the wireless tag information of the IC circuit unit 150 of the wireless tag circuit unit To via the reader antenna unit 3. The transmission unit 212 includes a crystal resonator 215 </ b> A, a Phase Locked Loop (PLL) 215 </ b> B, a Voltage Controlled Oscillator (VCO) 215 </ b> C, a transmission multiplication circuit 216, and a variable transmission amplifier 217.

  The crystal resonator 215A generates a reference frequency. The PLL 215B controls the frequency of the carrier wave output from the VCO 215C based on a command from the CPU 4 based on the frequency generated by the crystal resonator 215A. The VCO 215C outputs a carrier wave having a frequency determined based on the control voltage generated by the PLL 215B. For example, a UHF band, a microwave band, or a short wave band is used as the frequency of the generated carrier wave.

  The transmission multiplication circuit 216 modulates the generated carrier wave based on the signal supplied from the CPU 4. In this example, the transmission multiplication circuit 216 performs amplitude modulation based on the “TX_ASK” signal from the CPU 4. In the case of such amplitude modulation, a variable amplification factor amplifier or the like may be used instead of the transmission multiplication circuit 216.

  The variable transmission amplifier 217 amplifies the modulated wave modulated by the transmission multiplication circuit 216. In this example, the variable transmission amplifier 217 performs amplification at an amplification factor determined by the “TX_PWR” signal from the CPU 4. The output of the transmission amplifier 217 is transmitted to the microstrip antenna 11 via the transmission / reception separator 214, is radiated from the microstrip antenna 11 as an interrogation wave, and is supplied to the IC circuit unit 150 of the RFID circuit unit To. . The interrogation wave is not limited to the signal modulated as described above, that is, the modulation wave, and may be only a simple carrier wave.

  The receiving unit 213 inputs a response wave from the RFID tag circuit unit To received by the reader antenna unit 3. The receiving unit 213 includes a transmission / reception separator 214, a band pass filter 227, an I phase reception multiplication circuit 218, an I phase low pass filter 219, an I phase reception amplifier 221, an I phase limiter 220, and a phase shifter 227. , A Q-phase reception multiplication circuit 222, a Q-phase low-pass filter 223, a Q-phase reception amplifier 225, a Q-phase limiter 224, and a received signal strength indicator (RSSI) circuit 226 as intensity detection means.

  The I-phase reception multiplication circuit 218 multiplies the response wave from the RFID tag circuit section To received by the microstrip antenna 11 and input via the transmission / reception separator 214 and the bandpass filter 227 and the generated carrier wave. Then demodulate.

  The I-phase low-pass filter 219 extracts only a necessary band signal from the output of the I-phase reception multiplication circuit 218. The I-phase reception amplifier 221 amplifies the output of the I-phase low-pass filter 219. The I-phase limiter 220 further amplifies the output of the I-phase receiving amplifier 221 and converts it into a digital signal.

  The phase shifter 227 delays the phase of the carrier wave generated as described above by 90 °. The Q-phase reception multiplication circuit 222 multiplies the response wave received from the RFID tag circuit unit To by the reader antenna unit 3 and the carrier wave whose phase is delayed by 90 ° by the phase shifter 227. The Q-phase low-pass filter 223 extracts only a necessary band signal from the output of the Q-phase reception multiplication circuit 222. The Q-phase reception amplifier 225 amplifies the output of the Q-phase low-pass filter 223. The Q-phase limiter 224 further amplifies the output of the Q-phase receiving amplifier 225 and converts it into a digital signal.

  The signal “RXS-I” output from the I-phase limiter 220 and the signal “RXS-Q” output from the Q-phase limiter 224 are input to the CPU 4 and processed. The outputs of the I-phase reception amplifier 221 and the Q-phase reception amplifier 225 are also input to the RSSI circuit 226, and a signal “RSSI” indicating the strength of these signals is input to the CPU 4. As described above, the reader 1 demodulates the response wave from the RFID tag circuit unit To by IQ orthogonal demodulation.

  As described above, the reader antenna unit 3 includes the microstrip antenna 11 and the changeover switch circuit 12 for switching the polarization plane of the microstrip antenna 11. The changeover switch circuit 12 is, for example, a switch circuit using a known high-frequency FET or diode. The changeover switch circuit 12 selects one of two feeding points provided in the microstrip antenna 11 according to a control signal from the CPU 4 and connects it to the transmission / reception separator 214. By the connection switching operation by the selector switch circuit 12, the microstrip antenna 11 is switched between two directions whose polarization planes are orthogonal to each other, for example, the vertical direction and the horizontal direction indicated by broken lines in FIGS.

  As described above, the feature of the present embodiment is that the CPU 4 determines the usage status for all of the plurality of channels based on the received signal strength detected by the RSSI circuit 226. When it is determined that all the plurality of channels are not used, the CPU 4 selects a channel to be used from among the plurality of channels. Then, information transmission / reception with the wireless tag T is performed using the selected channel.

  Control executed by the CPU 4 of the reader 1 to realize the above contents will be described with reference to FIG.

  First, in step S <b> 10, the CPU 4 executes appropriate initial antenna settings for various parameters of the reader antenna unit 3. At this time, the CPU 4 outputs a control signal to the changeover switch circuit 12, and the polarization plane of the microstrip antenna 11 as an antenna attribute is initially set to one of the two orthogonal planes.

  Thereafter, the process proceeds to step S11, in which the variable CH (hereinafter, simply referred to as “channel variable CH”) representing the channel numbers included in a plurality of channels set in advance in a predetermined frequency range permitted by law, for example, is set to 1. Initialize to. In addition, a channel number TX_Ch (hereinafter simply referred to as “channel TX_Ch”) representing a channel to be used is initialized to zero.

  Then, the process proceeds to step S <b> 12, and the CPU 4 acquires the received signal strength Vs detected by the RSSI circuit 226.

  Thereafter, the process proceeds to step S13, in which the CPU 4 determines whether or not the received signal strength Vs acquired in step S12 is larger than a predetermined use state confirmation threshold value V_t1. This procedure functions as first determination means described in each claim.

  For example, when another reader 1 in communication is in the vicinity, the received signal strength Vs is larger than the usage status confirmation threshold value V_t1, so the determination in step S13 is satisfied, and the process proceeds to step S14. In step S <b> 14, the CPU 4 outputs a control signal to the changeover switch circuit 12 and switches the polarization plane of the microstrip antenna 11 to a plane orthogonal to the currently used plane among the planes described above. This procedure functions as the antenna switching means described in each claim. Instead of switching the polarization plane of the same antenna as described above, a plurality of antennas having different antenna attributes may be provided in advance, and the antenna switching unit may be switched to another antenna. Then, it returns to step S11 and repeats the same procedure.

  On the other hand, in step S13, when the received signal strength Vs is equal to or less than the usage status confirmation threshold value V_t1, the determination in step S14 is not satisfied, and the process proceeds to step S15.

  In step S15, the CPU 4 determines whether or not the channel Tx_ch at this time is set to 0. If Tx_ch = 0, the determination is satisfied, and the routine goes to Step S16. In step S16, the CPU 4 determines whether or not the received signal strength Vs acquired in step S12 is smaller than a channel selection threshold value V_t2 (predetermined smaller than the usage status confirmation threshold value V_t1). . This procedure functions as the second determination means described in each claim.

  For example, when the received signal strength Vs is smaller than the channel selection threshold V_t2, the determination in step S16 is satisfied, and the process proceeds to step S17. In step S17, the CPU 4 sets the channel TX_ch used for communication to the value of the variable CH at this time. This procedure functions as channel selection means described in each claim. Thereafter, the process proceeds to step S18.

  On the other hand, for example, when the received signal strength Vs is equal to or higher than the channel selection threshold V_t2, the determination in step S16 is not satisfied, and the process proceeds to step S18 described later.

  In step S18, the CPU 4 determines whether or not the channel variable CH at this time has reached CH_max corresponding to the maximum value of the channel number among the preset number of channels in the predetermined frequency range. If the channel variable CH has not reached CH_max, the determination at step S18 is not satisfied, and the routine goes to step S19.

  In step S19, 1 is added to the channel variable CH in order to switch the channel used in wireless communication. This procedure functions as channel switching means described in each claim. Thereafter, the process returns to step S12, and the same procedure is repeated for the next channel.

On the other hand, if the channel variable CH is equal to CH_max at step S18, the determination at step S18 is satisfied, and the routine goes to step S20.
In step S20, using the channel Tx_ch set to be used at this time, wireless communication is performed with the wireless tag T via the reader antenna unit 3, and information transmission / reception is performed. This procedure functions as a communication operation determining unit and a transmission / reception control unit described in each claim.

  Then, it moves to step S21 and CPU4 determines whether the predetermined | prescribed waiting time passed. Until the waiting time elapses, the determination is not satisfied and the loop waits. When the waiting time elapses, the determination in step S21 is satisfied, and this flow ends. In other words, before this flow is started again next time, wireless communication by the reader antenna unit 3 is prohibited for the waiting time. As a result, other readers 1 existing in the vicinity repeat the same flow (step S10 to step S19). As a result, it is determined that radio waves can be emitted, and communication can be started. That is, step S21 functions as prohibition control means described in each claim.

  As described above, in the reader 1 of this embodiment, when performing wireless communication in step S20, based on the received signal strength detected by the RSSI circuit 226, step S13, step S16, step S18, step S19, and the like. To determine the usage status for all of the plurality of channels. If it is determined that all of the plurality of channels are not used, information is transmitted / received to / from the wireless tag T in step S20 using the channel selected in step S17.

  As a result, it is possible not only to suppress interference between the plurality of readers 1 but also to prevent interference from occurring on the wireless tag T side having no frequency selection function. That is, it is possible to prevent other readers 1 from communicating with the wireless tag T. As a result, the reliability of communication can be improved as compared with the conventional technique in which an unused channel is confirmed among a plurality of channels and information is transmitted and received using the channel. Therefore, the reliability of information transmission / reception can be improved as a whole communication system including a plurality of readers 1.

  Note that it is not always necessary to perform the method of transmitting / receiving information to / from the wireless tag T after confirming that all the plurality of channels are not used as described above. That is, when the use of any one channel is confirmed, in step S20, the CPU 4 controls the variable transmission amplifier 217 to limit the transmission output to an appropriate small value according to the reception power in that channel. Communication with the wireless tag T may be performed. In this case, since it is possible to adjust the degree of overlap between the communication range of the reader 1 and the communication range of other readers 1 in the vicinity, it is possible to suppress the occurrence of interference between the plurality of readers 1 in substantially the same manner as described above. It is possible to reduce the influence exerted on other readers 1 communicating with the wireless tag T.

  In the present embodiment, in particular, after completion of information transmission / reception in step S20, wireless communication is not performed for a predetermined time in step S21. As a result, other readers 1 in the vicinity that have not been able to start communication by communication of the reader 1 until this predetermined time can start communication, so that it is possible to prevent other readers 1 from being unable to communicate. Can do.

  In this embodiment, in particular, in step S18 and step S19, for each channel to be switched, it is determined whether or not the received signal strength Vs detected by the RSSI circuit 226 in step S13 is larger than the usage status confirmation threshold V_t1. Determined. As described above, by performing the determination for each channel while switching a plurality of channels, the configuration of the circuit on the receiving side can be simplified as shown in FIG. As a result, a general-purpose carrier sense circuit that has been conventionally used can also be used.

  In this embodiment, in particular, after it is determined in step S1 whether or not the received signal strength Vs is larger than the usage confirmation threshold value V_t1, further in step S16, the received signal strength Vs is changed to the channel selection threshold value. It is determined whether it is smaller than V_t2. This has the following significance. That is, the channel selection threshold value V_t2 that is normally used is often set to a relatively low value assuming that the readers 1 are spaced apart from each other and interfere with each other. Assuming the occurrence of interference in the wireless tag T, a stronger radio wave is required between the reader 1 and the wireless tag T. Therefore, the threshold value for use status confirmation V_t1 is the channel selection threshold value. It is preferable to use a value larger than V_t2. Therefore, in the present embodiment, based on the above, both threshold values that satisfy the relationship of channel selection threshold value V_t2 <usage status confirmation threshold value V_t1 are used. Thereby, in step S13 and step S16 described above, it is possible to make a reasonable and effective determination in accordance with the above purpose.

  In the present embodiment, particularly, when it is determined in step S13 that the received signal strength Vs is greater than the usage status confirmation threshold value V_t1, the polarization plane of the microstrip antenna 11 is switched in step S14. This has the following significance. That is, when the antenna attributes such as the polarization plane can be switched to a plurality of modes as in the microstrip antenna 11, the communication range and the RFID tag T to be communicated are different for each mode. It is preferable to confirm the usage state. Therefore, in this embodiment, when the determination in step S13 is satisfied and it is determined that any one of a plurality of channels is used, the polarization plane as the antenna attribute is switched in step S14. Then, the received signal strength Vs after the switching is detected, and the use status of all the plurality of channels is determined based on the detected strength. As a result, it is possible to find an antenna mode that can prevent interference between a plurality of readers 1 and interference on the RFID tag T side, and perform highly reliable information transmission / reception in the antenna mode.

  The present invention is not limited to the above, and various modifications can be made without departing from the technical idea. Hereinafter, such modifications will be described in order.

(1) In the case where a plurality of channels are collectively determined In the above embodiment, is the received signal strength Vs detected by the RSSI circuit 226 greater than the usage status confirmation threshold V_t1 in steps S13 and S19? Whether or not was determined individually for a plurality of channels. In this modification, instead of this method, whether or not the received signal strength Vs is larger than the usage status confirmation threshold value V_t1 is collectively determined for a plurality of channels.

  Detailed configurations of the RF communication control unit 9 and the reader antenna unit 3 in this modification are shown in FIG. As shown in FIG. 5, in the RF communication control unit 9 of this embodiment, in addition to the I-phase low-pass filter 219 and the Q-phase reception low-pass filter 223, a band wider than these low-pass filters 219 and 223, ideal Are provided with an I-phase low-pass filter 219A and a Q-phase low-pass filter 223A that can extract signals with a bandwidth that is approximately half of the bandwidth permitted by law. Others are the same as those in FIG.

  Control executed by the CPU 4 of the reader 1 of this modification will be described with reference to FIG.

  First, in step S100, as in step S10 of FIG. 4, the CPU 4 performs initial antenna setting. Thereafter, the process proceeds to step S101.

  In step S <b> 101, the CPU 4 acquires the entire band signal strength Va detected by the RSSI circuit 226 over all bands.

  Thereafter, the process proceeds to step S102, in which the CPU 4 determines whether or not the all-band received signal strength Va acquired in step S101 is larger than a predetermined use state confirmation threshold value V_t1 ′. This procedure functions as first determination means described in each claim.

  For example, when another reader 1 in communication is in the vicinity, the received signal strength Va of the entire band is larger than the use state confirmation threshold value V_t1 ′, so the determination in step S102 is satisfied, and the process proceeds to step S103. In step S103, the CPU 4 outputs a control signal to the changeover switch circuit 12 in the same manner as in step S14 in FIG. 4 described above, and the polarization plane of the microstrip antenna 11 is the plane that is currently used, of the two planes described above. Switch to a plane orthogonal to This procedure functions as the antenna switching means described in each claim. Then, it returns to step S101 and repeats the same procedure.

  On the other hand, if the all-band received signal strength Va is equal to or lower than the use state confirmation threshold value V_t1 ′ in step S102, the determination in step S102 is not satisfied, and the process proceeds to step S104.

  In step S104, as in step S11 of FIG. 4 described above, a channel variable CH representing channel numbers included in a plurality of channels preset in a predetermined frequency range is initialized to 1. Also, channel TX_Ch representing the channel to be used is initialized to zero.

  Thereafter, the process proceeds to step S105, and the CPU 4 acquires the received signal strength Vs detected by the RSSI circuit 226, as in step S12 of FIG.

  Then, the process proceeds to step S106, and similarly to step S16 of FIG. 4, the channel selection threshold is set in advance, in which the received signal strength Vs acquired in step S105 is smaller than the use condition confirmation threshold value V_t1 ′. It is determined whether the value is smaller than V_t2. This procedure functions as the second determination means described in each claim.

  If the received signal strength Vs is smaller than the channel selection threshold V_t2, the determination in step S106 is satisfied, and the process proceeds to step S109 described later.

  On the other hand, if the received signal strength Vs is greater than or equal to the channel selection threshold V_t2, the determination in step S106 is not satisfied, and the routine proceeds to step S107. In step S17, the CPU 4 determines whether or not the channel variable CH at this point has reached CH_max, as in step S18 of FIG. If the channel variable CH has not reached CH_max, the determination at step S107 is not satisfied, and the routine goes to step S108.

  In step S108, 1 is added to the channel variable CH in order to switch the channel used in the wireless communication as in step S19 of FIG. This procedure functions as channel switching means described in each claim. Then, it returns to step S105 and repeats the same procedure.

  On the other hand, if the channel variable CH is equal to CH_max in step S107, the determination is satisfied, the process returns to step S103, and the same procedure is repeated.

  In step S109, as in step S17 of FIG. 4, the CPU 4 sets the channel TX_ch used for communication to the value of the variable CH at this point. This procedure functions as channel selection means described in each claim. Thereafter, description of steps S20 and S21 similar to those in FIG. 4 is omitted.

  Also by this modification, the same effect as the above-mentioned embodiment is acquired. In addition, by performing the determination for all the channels collectively in step S101 and step S102, it is possible to perform the determination more quickly than when performing determination for each channel while switching a plurality of channels as in the above embodiment. .

(2) When communicating and cooperating between a plurality of readers In other words, when reducing interference in the plurality of readers 1 as described above, in addition to the technique of the above embodiment and the modified example of (1), the plurality of readers The readers 1 may communicate with each other to cooperate.

  FIG. 7 shows a schematic system configuration of the reader 1 according to this modification. As shown in FIG. 7, the main body control unit 2 of the reader 1 according to this modification includes a short-range communication unit 10 as a reader communication unit for communicating with another reader 1.

  FIG. 8 conceptually shows cooperative control executed between a plurality of readers 1 in this modification. As shown in FIG. 8, the CPU 4 of one reader 1 (shown as “Reader A” in the figure) trying to execute communication with the wireless tag T uses the short-range communication unit 10 to A wave stop request signal for requesting stop of wireless communication is transmitted to the reader 1 (shown as “Reader B” in the figure). When the other reader 1 is currently communicating with the wireless tag T, the other reader 1 transmits a communication flag signal as a communication state signal to one reader 1 and does not respond when it is not communicating. . When one reader 1 receives the in-communication flag signal from the other reader 1 corresponding to the stop request signal, the other reader 1 transmits the stop request signal again to the other reader 1 after a predetermined time. When one reader 1 does not receive a communication flag signal from another reader 1 for a certain period of time after transmitting a stop request signal, the other reader 1 in the vicinity is put into a stop state by the stop request signal. Based on the received signal strength, the usage status for all of the plurality of channels is determined and information is transmitted to and received from the wireless tag T using the method of the above embodiment and the modified example (1).

  When the information transmission / reception of the wireless tag T is completed, one reader 1 transmits a wave stop request release signal for releasing the wireless communication stop request to the other reader 1.

  When the other reader 1 tries to start communication with the wireless tag T, the same procedure as that performed by the one reader 1 is executed. That is, when a stop signal is transmitted using the short-range communication unit 10 and a communication flag signal is not received within a certain time, information is transmitted / received to / from the wireless tag T. Send a request release signal.

  Control executed by the CPU 4 of the reader 1 of this modification will be described with reference to FIG. The same steps as those in FIG. 6 described above are denoted by the same step numbers, and description thereof is omitted or simplified. In the example of FIG. 9, the case where the cooperative control between the readers 1 is applied to the technique of the modified example (1) described above is shown.

  First, in step S199, the CPU 4 determines whether or not it is currently receiving a wave stop request from another reader 1 (the wave is not released). Since communication can be performed in a state where no wave stop request has been received from another reader 1, the determination in step S199 is not satisfied and the process proceeds to step S200 described later. On the other hand, however, in a state where a wave stop request is received from another reader 1, communication cannot be started, so that the determination in step S199 is satisfied, and after waiting for a predetermined time in step S198, the process proceeds to step S197. Move.

  In step S197, the CPU 4 determines whether or not cancellation of wave stop has been received. However, when the stoppage cancellation is not received, the determination in step S197 is not satisfied, and the process returns to step S198 and waits for a predetermined time, and then repeats step S197. If the stoppage cancellation is received, the communication can be started. Therefore, the determination in Step S197 is satisfied, and the routine goes to Step S200.

  In step S <b> 200, the CPU 4 transmits the stop request signal for requesting the other reader 1 to stop the wireless communication by the short-range communication unit 10. This procedure functions as a wave stop request transmission unit described in each claim.

  Thereafter, the process proceeds to step S201, and it is determined whether or not the near field communication unit 10 has received a communication flag signal from another reader 1 corresponding to the wave stop request signal transmitted in step S200 within a predetermined time. This procedure functions as a communication status receiving means described in each claim. When the other reader 1 is not in communication, a communication flag signal is not transmitted from the other reader 1. For this reason, if no communication flag is received within a certain period of time, it is considered that no reader is communicating at the same time, and the determination in step S201 is not satisfied, and the process proceeds to step S101. On the other hand, when the in-communication flag transmitted by another reader 1 is received, the determination in step S201 is satisfied, and after waiting for a predetermined time in step S202, the process returns to step S200 and the same procedure is repeated.

  Steps S101 to S109 and S20 are the same as those in FIG.

  When the communication with the wireless tag T in step S20 is completed, the process proceeds to step S300.

  In step S300, the CPU 4 transmits a wave stop request cancel signal for canceling the wireless communication stop request to the other reader 1 by the short-range communication unit 10, and proceeds to the above-described step S21. Step S21 is the same as described above, and a description thereof will be omitted.

  In this modification, a plurality of readers 1 communicate with each other using the short-range communication unit 10 to perform a cooperative operation. By performing such a cooperative operation, as described above, when one reader 1 performs wireless communication, the other reader 1 that cooperates stops wireless communication, so that all channels are not used quickly and reliably. Can be confirmed and information transmission / reception can be started. As a result, information transmission efficiency can be improved. In addition, there is an effect that it is not necessary to provide a host controller for controlling the plurality of readers by performing a cooperative operation through communication between the plurality of readers 1.

  It should be noted that the near field communication used for communication between the readers 1 in this modified example is dedicated to using infrared communication, Bluetooth (registered trademark), other broadcast communication, or a specific channel in the predetermined frequency band. May be.

(3) Others In the above, as channel selection means for selecting a channel for communication, it is determined whether or not the received signal strength Vs of each channel is smaller than the channel selection threshold V_t2, and a channel satisfying this determination is communicated. A channel was used (see step S16 and step S106). However, the present invention is not limited to this method, and a method of sequentially switching channels for communication in a pseudo-random manner within a specified time may be used. When this method is used, if a sufficient number of communication channels can be ensured, the probability that the readers 1 will use the same channel decreases, and interference between the readers 1 is less likely to occur. In this case, the second determination means described in the above claims is not necessarily required.

  In addition to those already described above, the methods according to the above-described embodiments and modifications may be used in appropriate combination.

  In addition, although not illustrated one by one, the present invention is implemented with various modifications within a range not departing from the gist thereof.

1 Reader (Radio tag information reader)
3 Reader antenna unit (antenna means)
10 Infrared communication unit (reader communication means)
DESCRIPTION OF SYMBOLS 11 Microstrip antenna 12 Changeover switch circuit 150 IC circuit part 151 Tag antenna 226 RSSI circuit (strength detection means)
T wireless tag To wireless tag circuit part

Claims (9)

Antenna means capable of performing wireless communication with a wireless tag within a predetermined frequency range including a plurality of channels;
Intensity detecting means for detecting the received signal intensity of the radio wave received by the antenna means;
First determination means for determining a use situation for all of the plurality of channels based on the received signal intensity detected by the intensity detection means;
A communication operation is determined according to whether it is determined by the first determination means that all of the plurality of channels are not used or one of the plurality of channels is used. Communication operation determining means for
Channel selection means for selecting a channel to be used from among the plurality of channels;
A wireless tag comprising: a transmission / reception control means for performing transmission / reception of information with a wireless tag in a communication operation determined by the communication operation determination means by the antenna means using the channel selected by the channel selection means. Communication device. The communication operation determining means is
2. The wireless tag communication apparatus according to claim 1, wherein when the first determination unit determines that all of the plurality of channels are not used, the transmission / reception control unit determines to perform communication. The communication operation determining means is
The transmission output of the transmission / reception control unit is determined based on a result of the intensity detection unit when the first determination unit determines that any one of the plurality of channels is used. The wireless tag communication device according to claim 1 or 2. Prohibiting control means for prohibiting wireless communication by the antenna means for a predetermined time,
4. The RFID tag communication apparatus according to claim 1, wherein when the information transmission / reception by the transmission / reception control unit is completed, the prohibition control unit prohibits wireless communication by the antenna unit. Channel switching means for switching the channel used in wireless communication with the antenna means;
The first determination means includes
5. For each channel switched by said channel switching means, it is determined whether or not the received signal strength detected by said strength detecting means is larger than a threshold value for use status confirmation. The wireless tag communication device according to claim 1. The first determination means includes
5. The method according to claim 1, wherein whether or not the received signal intensity detected by the intensity detecting unit is larger than a threshold for use status confirmation is collectively determined for the plurality of channels. The wireless tag communication device described. First, it is determined whether or not the received signal strength detected by the strength detecting means is larger than the channel selection threshold by using a channel selection threshold smaller than the usage confirmation threshold. 2 determination means,
The channel selection means includes
6. The channel determined by the second determination means among the plurality of channels that the received signal strength is determined to be equal to or lower than the channel selection threshold is selected as a channel to be used. Alternatively, the wireless tag communication device according to claim 6. An antenna switching unit that switches antenna attributes of the antenna unit when the first determination unit determines that any one of the plurality of channels is used;
The intensity detection means is
Detecting the received signal strength at the antenna means after the antenna attribute is switched by the antenna switching means;
The first determination means includes
The usage status for all of the plurality of channels is determined based on the received signal strength detected by the strength detection unit after the antenna attribute is switched by the antenna switching unit. 8. The wireless tag communication device according to any one of 7 above. Reader communication means for communicating with another RFID tag communication device;
Corresponding to the stop request signal from the stop request means and a stop request transmitting means for transmitting a stop request signal for requesting the other RFID tag communication device to stop wireless communication using the reader communication means A communication status receiving means for receiving a communication status signal from the other RFID tag communication means,
The first determination means includes
The use status of all of the plurality of channels is determined based on the received signal strength detected by the strength detecting unit when the communication status receiving unit does not receive the communication status signal. Item 5. The wireless tag communication device according to any one of Items 1 to 4.

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