JP2010021684A - Rfid system, rfid reader-writer, rfid tag, and rfid communication method - Google Patents

Abstract

An object of the present invention is to suppress deterioration in communication quality even when there is an interference signal at the frequency of a response signal.
An RFID system includes an RFID reader / writer that transmits an interrogation signal obtained by modulating a carrier wave having a first frequency with an interrogation data signal, and an interrogation signal transmitted from the RFID reader / writer. The RFID tag 3 returns a response signal obtained by modulating the response data signal to the signal by the mirror subcarrier method to the RFID reader / writer 4, and the RFID reader / writer 4 interferes with the frequency of the response signal modulated by the mirror subcarrier method. An interference determination unit 50 that determines the presence or absence of a signal, and frequency switching that switches the frequency of the carrier wave of the transmission unit 45 to a second frequency different from the first frequency when the interference determination unit 50 determines that there is an interference signal Part 51.
[Selection] Figure 7

Description

  The present invention relates to an RFID system, an RFID reader / writer, an RFID tag, and an RFID communication method.

  In recent years, an RFID (Radio Frequency IDentification) system has been used in order to improve the management of physical distribution, merchandise, etc., and further expansion of the application range is desired. The RFID system includes an RFID reader / writer and an RFID tag, and transmits an interrogation signal from the RFID reader / writer to the RFID tag by radio waves, and returns a response signal from the RFID tag to the RFID reader / writer by radio waves.

The conventional RFID system employs a baseband system that transmits and receives an interrogation signal and a response signal at the same frequency. Therefore, if multiple RFID readers / writers with overlapping communication areas issue interrogation signals at the same channel frequency at the same time, they interfere. It was. In order to eliminate this interference, in the conventional RFID system, an LBT (Listen Before) that receives and confirms whether or not the frequency of the channel to be used is previously used by another reader / writer before transmitting the interrogation signal. (Talk) method was used (see, for example, Patent Document 1).
JP 2007-193772 A

  In the conventional RFID system, since the RFID reader / writer performs LBT every time an inquiry signal is transmitted, the communication time is long. Therefore, a mirror subcarrier (Miller-Modulated Subcarrier) method has been proposed as a method for eliminating this LBT. In this mirror subcarrier method, three channels having continuous frequencies are allocated to the RFID reader / writer, the RFID reader / writer transmits a query signal to the RFID tag using the channel of the middle frequency, and the response signal from the RFID tag is The interrogation signal was received using two other channels having different frequencies. As a result, the RFID reader / writer can transmit an interrogation signal to the RFID tag without performing LBT, so that high-speed communication is performed with the RFID tag.

  However, when the RFID reader / writer performs transmission / reception by the mirror subcarrier method, there is a problem that if there is an interference signal by another RFID reader / writer in the frequency of the response signal, the RFID reader / writer is disturbed and communication quality is lowered.

  Accordingly, an object of the present invention is to suppress a reduction in communication quality even when there is an interference signal at the frequency of the response signal.

  In order to achieve this object, an RFID system of the present invention receives an interrogation signal transmitted from an RFID reader / writer, and an RFID reader / writer that transmits an interrogation signal obtained by modulating a carrier wave of a first frequency with an interrogation data signal. An RFID system including an RFID tag that returns a response signal modulated by a mirror subcarrier method to a response data signal to an interrogation data signal to the RFID reader / writer, wherein the RFID reader / writer is modulated by a mirror subcarrier method An interference determination unit that determines the presence or absence of an interference signal at the frequency of the response signal, and a frequency switch that switches the carrier frequency to a second frequency different from the first frequency when the interference determination unit determines that there is an interference signal It has the part. With such a configuration, the intended purpose is achieved.

  The RFID reader / writer according to the present invention includes a modulation unit that modulates a carrier wave having a first frequency with an interrogation data signal to generate an interrogation signal, and a transmission unit that transmits the interrogation signal generated by the modulation unit to the RFID tag. A reception unit that receives a response signal returned from the RFID tag by modulating a carrier wave of the first frequency by the response data signal by the mirror subcarrier method, and an interference signal at the frequency of the response signal received by the reception unit. An interference determination unit that determines presence / absence, and a frequency switching unit that switches the carrier frequency of the transmission unit to a second frequency different from the first frequency when the interference determination unit determines that there is an interference signal. It is characterized by that. With such a configuration, the intended purpose is achieved.

  The RFID tag according to the present invention receives a query signal transmitted from an RFID reader / writer after a carrier wave having a first frequency is modulated by a query data signal, and uses a mirror subcarrier system for the carrier wave with a response data signal to the query signal. The RFID tag is modulated by the RFID reader / writer and returned as a response signal to the RFID reader / writer, and the RFID reader / writer determines that there is an interference signal at the frequency of the response signal modulated by the mirror subcarrier method. When the frequency of the carrier wave is switched to a second frequency different from the first frequency, a response signal is returned using the carrier wave of the second frequency. With such a configuration, the intended purpose is achieved.

  The RFID communication method according to the present invention also includes an interrogation step in which an interrogation signal obtained by modulating a carrier wave having a first frequency with an interrogation data signal is transmitted from the RFID reader / writer, and an interrogation signal transmitted from the RFID reader / writer is transmitted using an RFID tag. An RFID communication method comprising: a response step of receiving and returning a response signal obtained by modulating a response data signal in response to an interrogation data signal from the RFID tag to the RFID reader / writer, and modulated by the mirror subcarrier method An interference determination step for determining the presence or absence of an interference signal at the frequency of the response signal, and a second carrier frequency of the RFID reader / writer different from the first frequency when the interference determination step determines that there is an interference signal. Having a frequency switching step for switching to a frequency And features. By such a method, the intended purpose is achieved.

  An RFID system according to the present invention transmits an interrogation signal obtained by modulating a carrier wave of a first frequency with an interrogation data signal, receives an interrogation signal transmitted from the RFID reader / writer, and responds to the interrogation data signal. An RFID tag for returning a response signal obtained by modulating the signal by the mirror subcarrier method to the RFID reader / writer, and determining whether there is an interference signal at the frequency of the response signal modulated by the mirror subcarrier method in the RFID reader / writer And a frequency switching unit that switches the frequency of the carrier wave of the transmission unit to a second frequency different from the first frequency when the interference determination unit determines that there is an interference signal. In some cases, it is possible to quickly move to the second frequency for communication and suppress deterioration in communication quality. It is possible.

  The RFID reader / writer of the present invention includes a modulation unit that modulates a carrier wave having a first frequency with an interrogation data signal, a transmission unit that transmits an interrogation signal modulated by the modulation unit, and a response data signal that has a first frequency. A receiving unit that receives a response signal returned from the RFID tag after the carrier wave is mirror-subcarrier modulated, an interference determining unit that determines the presence or absence of an interference signal at the frequency of the response signal received by the receiving unit, and an interference determining unit The frequency switching unit that switches the carrier frequency of the transmission unit to a second frequency different from the first frequency when it is determined that there is an interference signal is quickly provided when there is an interference signal. Communication can be performed by moving to the second frequency, and deterioration in communication quality can be suppressed.

  In the RFID tag of the present invention, the RFID reader / writer determines that there is an interference signal at the frequency of the response signal modulated by the mirror subcarrier method, and the frequency of the carrier wave output by the RFID reader / writer is the first. When switching to a second frequency different from the frequency, a response signal is returned using a carrier wave of the second frequency, so that if there is an interference signal, the second frequency is quickly transferred to communicate with the RFID reader / writer. It is possible to suppress a decrease in communication quality.

  The RFID communication method of the present invention also includes an interference determination step for determining the presence or absence of an interference signal at the frequency of the response signal modulated by the mirror subcarrier method, and an RFID when the interference determination step determines that there is an interference signal. Since there is a frequency switching step for switching the frequency of the carrier wave of the reader / writer to a second frequency different from the first frequency, if there is an interference signal, the communication is quickly moved to the second frequency and communicated And the deterioration of communication quality can be suppressed.

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

(Embodiment)
First, an RFID system 1 using an RFID communication method according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic block diagram for explaining a usage pattern of an RFID system 1 according to an embodiment of the present invention. FIG. 2 shows signals transmitted and received between the RFID reader / writer 4 and the RFID tag 3 of the RFID system 1. FIG. 3 is an explanatory diagram showing a frequency allocation state of signals used in the RFID system 1, FIG. 4 is a waveform diagram showing a state when interference occurs in the RFID system 1, and FIG. FIG. 6 is a spectrum diagram showing a state when interference is avoided in the RFID system 1.

  FIG. 1 shows an example in which the RFID system 1 of the present embodiment is used in the manufacturing process of an article 2. The RFID system 1 includes an RFID tag 3 attached to an article 2 and an RFID reader / writer 4 that reads tag information of the RFID tag 3. An RFID tag 3 that stores and holds a management number and the like is attached to the article 2. An RFID reader / writer 4 is installed at a predetermined position in the manufacturing process.

  In this manufacturing process, the article 2 to which the RFID tag 3 is attached is conveyed in the direction of the arrow by a conveying device (not shown) such as a belt conveyor. A central control device 5 for controlling the entire manufacturing process is provided to control the RFID reader / writer 4 via the communication line 6, and the RFID reader / writer 4 communicates with the RFID tag 3, thereby managing the management number of the article 2. The manufacturing process is managed by reading

  The RFID reader / writer 4 transmits an interrogation signal to the RFID tag 3 by radio waves by the transmission antenna 7 and receives a response signal returned from the RFID tag 3 by the reception antenna 8. A region 9 indicated by a broken line in FIG. 1 indicates a range in which each RFID reader / writer 4 can communicate. When a plurality of RFID reader / writers 4 are installed close to each other, the areas 9 that can be communicated with each other may overlap (details will be described later).

  The RFID reader / writer 4 receives the response signal returned from the RFID tag 3 and identifies the management number of the article 2. In accordance with the identified management number, the central controller 5 controls a manufacturing apparatus (not shown) during the manufacturing process to perform predetermined processing and assembly on the article 2.

  As shown in FIG. 2, when the article 2 is conveyed to a predetermined position, the RFID reader / writer 4 transmits a question signal Q for inquiring a management number to the RFID tag 3. This interrogation signal Q is obtained by subjecting a carrier wave of a predetermined channel to ASK (Amplitude Shift Keying) modulation by an interrogation code signal encoded by PIE (Phase-Interval Encoding).

  Thereafter, for a certain period, the RFID reader / writer 4 transmits an unmodulated continuous carrier wave C to supply power to the RFID tag 3.

  The RFID tag 3 receives the question signal Q, demodulates the question code signal, and returns a response signal R such as a management number of the article 2 in response to the question. The RFID tag 3 controls whether or not the radio wave of the continuous carrier wave C transmitted from the RFID reader / writer 4 is reflected by a tag antenna section (to be described later) of the RFID tag 3 according to the response code signal (in this way, radio wave reflection). Is also referred to as backscatter control), and a response signal R is returned.

  In the RFID system 1, there are two types, a baseband method and a mirror subcarrier method, depending on a method in which the RFID tag 3 returns a response signal to the RFID reader / writer 4. The standard used in the RFID system 1 is defined in, for example, EPCglobal Class-1 Generation-2.

  In the baseband system, a response signal is generated by modulating a carrier wave at the same data rate as the interrogation signal transmitted from the RFID reader / writer 4. Therefore, a response signal is returned on the same channel as the question signal.

  On the other hand, in the mirror subcarrier method used in the RFID reader / writer 4 of the present embodiment, a subcarrier component is created by the RFID tag 3 and a response signal is created by modulating the subcarrier (subcarrier) with a response data signal. . Therefore, in the mirror subcarrier system, the RFID tag 3 returns a response signal at a frequency different from that of the interrogation signal, that is, a different channel.

  In order to create this subcarrier, the RFID tag 3 first doubles (M = 2), 4 (M = 4), or 8 times the baseband clock signal created from the received / demodulated question code signal. Multiply to double (M = 8) frequency. Since the baseband question code signal is usually created at a data rate of 40 KHz, 80 KHz, or 120 KHz, the subcarrier for mirror subcarrier modulation is 80 KHz (= 40 KHz × 2) to 960 KHz (= 120 KHz × 8). Create

  The response code signal is mirror-encoded with the clock having the frequency of the subcarrier. Further, a backscatter control is performed on a tag antenna section (to be described later) of the RFID tag 3 with the mirror-encoded signal. As a result, the RFID tag 3 can send back a response signal R based on the mirror subcarrier method, centering on the position of the frequency separated from the original continuous carrier frequency by the subcarrier frequency.

  Next, an example of a usage state of a frequency used in the RFID system 1 will be described with reference to FIG. Here, 942 MHz to 944 MHz are allocated for RFID, and nine channels (hereinafter also referred to as “CH”) from channel 1 to channel 9 are set at intervals of 200 kHz. Of these, 2CH and 8CH are allocated for the mirror subcarrier system. The baseband RFID reader / writer 4 can be used in any channel of 1CH to 9CH.

  When a plurality of RFID reader / writers 4 are provided close to each other and their communicable areas overlap, signals of different channels are used for each RFID reader / writer 4 so that signals do not interfere with each other. The For example, the first RFID reader / writer 4 uses 5CH, and the adjacent second RFID reader / writer 4 uses 6CH. The channel to be used can be controlled by the central controller 5.

  In addition to the UHF band (for example, 942 MHz to 945 MHz) as described above, the frequency of the microwave band (for example, 2.35 GHz) and the HF band (for example, 13.46 MHz) can also be used as the predetermined carrier wave. .

  FIG. 3 shows the state of the frequency distribution of the interrogation signal Q and the response signal R in the mirror subcarrier system. Assuming that the carrier wave of the interrogation signal Q transmitted from the RFID reader / writer 4 is 2CH, the response signal R returned from the RFID tag 3 is a frequency separated from the 2CH by a subcarrier frequency (also referred to as “SC frequency”) up and down. Signal. In this example, the subcarrier frequency is set to 160 KHz (40 KHz × 4 or 80 KHz × 2) so that the frequency of the response signal falls within the adjacent 1CH and 3CH frequency bands. The frequency is 2CH ± 160 KHz. The subcarrier frequency used by the RFID tag 3 is specified by an instruction signal included in the interrogation signal Q from the RFID reader / writer 4.

  As described above, the frequency of the response signal R returned from the RFID tag 3 to the RFID reader / writer 4 is separated from the interrogation signal Q transmitted from the RFID reader / writer 4 or the unmodulated continuous carrier C by the subcarrier frequency. Become a frequency. For this reason, the RFID reader / writer 4 can receive a single response signal at a distant frequency instead of receiving a response signal buried in a carrier signal transmitted by itself as in the baseband method. Therefore, even if the response signal R from the RFID tag 3 is weak, it can be received with high quality. In addition, since the LBT is not required, the communication time can be shortened and the speed can be increased, and the data can be demodulated more accurately because of the mirror coding.

  As described above, if the mirror subcarrier method is used, the weak response signal of the RFID tag 3 located away from the RFID reader / writer 4 can be received, so that the use range can be expanded. Furthermore, since the RFID reader / writer 4 does not require an LBT, the communication time with the RFID tag 3 can be shortened.

  Thus, although the mirror subcarrier system is a system with great effect, an interference signal such as an interrogation signal from another RFID reader / writer 4 at the frequency of the response signal R from the RFID tag 3, that is, a frequency having a subcarrier component. If there is, there is a problem that the communication quality deteriorates due to interference.

  A state when interference occurs in the RFID system 1 will be specifically described with reference to FIGS. 4 and 5.

  FIG. 4 shows the passage of time when communicating with the RFID tag 3 using 2CH as the interrogation signal Q of the RFID reader / writer 4.

  After the RFID reader / writer 4 transmits the inquiry signal Q on 2CH from time t1, the response signal R from the RFID tag 3 is received on 1CH and 3CH from time t2. At this time, since there is no interference signal in 1CH and 3CH, the response signal R can be received well.

  Next, when the RFID reader / writer 4 transmits another interrogation signal Q from time t3 and then attempts to receive the response signal R at 1CH and 3CH from time t4, the other RFID reader / writer 4 in the vicinity 3CH Assume that an interference signal D such as an interrogation signal is generated. At this time, since the response signal R from the RFID tag 3 is a weak signal, it is interfered by the strong interference signal D and cannot be normally received by the RFID reader / writer 4. As described above, the RFID reader / writer 4 transmits a question signal without determining in advance whether or not there is an interference signal when communication is started by the mirror subcarrier method.

  FIG. 5 shows a spectrum in a state where radio wave interference occurs in the RFID system 1. A strong interference signal D such as an interrogation signal using 3CH is output from another RFID reader / writer 4 to the subcarrier frequency (2CH + 160 KHz) of the response signal R from the RFID tag 3. In this way, the interrogation signal output from the RFID reader / writer 4 that performs communication by the baseband method becomes the interference signal D.

  The case where the RFID reader / writer 4 cannot normally receive the response signal R from the RFID tag 3 includes the case where it is obstructed by the strong interference signal D as described above, and the RFID tag within the communicable range of the RFID reader / writer 4. There is a case where the response signal R itself does not exist because 3 does not exist. In the latter case, it is sufficient to wait until the article 2 is conveyed and the RFID tag 3 enters the communication range of the RFID reader / writer 4. However, in the former case, although the response signal R is returned from the RFID tag 3 to the RFID reader / writer 4, the response signal R is not normally received by the RFID reader / writer 4. There is a possibility that the article 2 will pass through without being processed as necessary. In such a case, the RFID reader / writer 4 must establish communication with the RFID tag 3 while avoiding interference by the interference signal D.

  Therefore, in the RFID system 1 according to the present embodiment, the RFID reader / writer 4 determines the presence or absence of the interference signal D at the frequency of the response signal R, and when it determines that there is the interference signal D, the channel in use is switched. To avoid interference. As a result, in the RFID system 1, when there is an interference signal, it is possible to quickly move to another channel frequency for communication, thereby suppressing a decrease in communication quality.

  That is, as shown in FIG. 4, the RFID reader / writer 4 determines a predetermined threshold value Lv and monitors the magnitude of the received signal at the frequency of the response signal R during the response period from the RFID tag 3. Since the strength of the response signal R is very weak, if the magnitude of the received signal during the response period is smaller than the predetermined threshold Lv, the reception is continued as it is. However, when the strong interference signal D is generated and the reception signal received during the response period is larger than the predetermined threshold Lv, it is determined that there is the interference signal D. Note that the predetermined threshold Lv may be set larger than the value of carrier sense for detecting the response signal of the RFID tag 3. Furthermore, the predetermined threshold Lv may be adjusted according to the magnitude of the output (air power) from the peripheral RFID reader / writer 4 using another baseband method. For example, when the output from the transmission antenna 7 of the RFID reader / writer 4 is 10 mW, it is set to −54 (dBm). Further, for example, when the output of the RFID reader / writer 4 is 1 W, it is set to −44 (dBm).

  When the RFID reader / writer 4 determines that the interference signal D is present in the frequency of the response signal R, the carrier frequency used for the question is changed from the first frequency 2CH to another one as shown in FIG. Switch to 8CH, which is the permitted second frequency. Along with this, the frequency of the response signal R returned by the RFID tag 3 is also automatically switched to 8CH ± subcarrier frequency.

  As described above, the RFID reader / writer 4 determines the presence or absence of the interference signal D at the frequency of the response signal R, and when it is determined that there is an interference signal, the frequency of the carrier wave is set to the second frequency (which is different from the first frequency). Since there is an interference signal, it is possible to quickly move to the second frequency and perform communication, and it is possible to suppress a decrease in communication quality.

  In addition, although the example which switches from 2CH in use to 8CH which is another channel was demonstrated here, it is not limited to this example. Even if there are three or more assigned channels instead of two, it is possible to switch to that channel. For example, it is assumed that a third frequency and a fourth frequency are further allocated in addition to the first frequency and the second frequency. In this case, similarly, the RFID reader / writer 4 sequentially changes the carrier frequency from the first frequency to the second frequency, from the second frequency to the third frequency, and from the third frequency to the fourth frequency. Can be switched. Similarly, the RFID reader / writer 4 can also switch from the first frequency to the third frequency and from the first frequency to the fourth frequency. As described above, the RFID reader / writer 4 determines the presence or absence of the interference signal D at the frequency of the response signal R. When it is determined that there is an interference signal, the frequency of the carrier wave in use (this is set as the first frequency). Is switched to another frequency (this is the second frequency), so that if there is an interfering signal, it is possible to quickly move to another frequency (second frequency) and communicate, The decrease can be suppressed.

  Next, the configuration and operation of the RFID system 1 according to the present embodiment will be described with reference to FIGS. FIG. 7 is a block diagram showing the configuration of the RFID system 1 in the embodiment of the present invention, and FIG. 8 is a flowchart for explaining the operation of the RFID system 1.

  First, the RFID system 1 will be described from the state in which the RFID reader / writer 4 starts to communicate with the RFID tag 3.

  The RFID reader / writer 4 is controlled by the central controller 5 and is installed at a predetermined location in the manufacturing process. The central control device 5 transmits a control signal for the RFID reader / writer 4 to the control unit 42 via the communication line 6 and the interface (I / F) 41.

  When the operation starts, the RFID reader / writer 4 first transmits a question signal such as “Reply management number” to the RFID tag 3. At this time, the control unit 42 reads out data necessary for the question from the memory unit 43, and ASK-modulates a predetermined channel, here, 2CH carrier wave by the modulation unit 44 based on the query data signal, and amplifies it by the transmission unit 45. Then, the radio wave is transmitted as an interrogation signal to the RFID tag 3 via the transmission antenna 7 (S100).

  Next, when the RFID reader / writer 4 ends the transmission of the interrogation signal (S102), subsequently, the unmodulated continuous carrier wave is transmitted using 2CH through the modulation unit 44 and the transmission unit 45 under the control of the control unit 42 ( S104), a state of waiting for a response from the RFID tag 3 is entered.

  On the other hand, the RFID tag 3 has a tag antenna unit 31 and a tag IC chip 32, and the tag antenna unit 31 receives a radio wave of a question signal. The RFID tag 3 rectifies the received interrogation signal with the diode 33 to generate a direct voltage (hereinafter referred to as “DC voltage”). The DC voltage is charged in the capacitor 34 and supplied to each part of the tag IC chip 32 as an operation power supply, and the tag IC chip 32 is activated. Thereby, each part of the tag IC chip 32 is activated. As described above, the passive RFID tag 3 can operate the tag IC chip 32 even if a power source such as a battery is not mounted.

  Next, the RFID tag 3 demodulates the question data “Respond management number” from the question signal by the demodulator 36. Then, the control unit 35 reads out the tag information of the management number stored and held from the memory unit 38.

  When the tag information stored in the memory unit 38, that is, the management number of the article 2 is "management number A", the control unit 35 responds to the question with a response data signal "management number A". Create

  On the other hand, the clock unit 39 first reproduces a basic clock signal having a basic period from the baseband interrogation data signal demodulated by the demodulation unit 36. Here, it is assumed that the period of the basic clock signal is 25 μsec (frequency is 40 KHz). Thereafter, the basic clock signal is multiplied by 4 to create a 160 KHz subcarrier clock signal.

  The mirror subcarrier modulation unit 37 uses this subcarrier clock signal to perform M = 4 mirror coding processing on the response code signal. Then, the switching element 37a connected to the tag antenna unit 31 is turned on / off by the mirror-encoded response code signal to perform back scatter control and return a response signal. That is, when the switching element 37a is turned on, the terminal of the tag antenna unit 31 is short-circuited, and when the switching element 37a is turned off, the terminal of the tag antenna unit 31 is opened. Thus, whether or not the unmodulated carrier wave transmitted from the RFID reader / writer 4 is reflected by the tag antenna unit 31 is controlled according to the mirror encoded signal of the response data “management number A”. At this time, since the clock frequency of the mirror-encoded signal is 160 KHz, the backscatter-controlled carrier wave is obtained by modulating a 160 KHz subcarrier with the response code signal, and the response signal of the mirror subcarrier system with M = 4 Can be returned to the RFID reader / writer 4.

  Note that the RFID tag 3 has a capacitor 40 for matching impedance so that no reflection occurs when the terminal of the tag antenna unit 31 is opened.

  Next, the operation of the RFID reader / writer 4 that receives the mirror subcarrier response signal returned from the RFID tag 3 in this way will be described.

  The RFID reader / writer 4 transmits the response signal received by the receiving antenna 8 to the demodulator 47 via the receiver 46 and demodulates the response data. Based on the demodulated response data, the control unit 42 confirms the existence of “management number A”. The RFID reader / writer 4 stores this “management number A” information in the memory unit 43 via the control unit 42.

  At this time, first, the RFID reader / writer 4 waits for and receives a response signal from the RFID tag 3 on the 1CH and 3CH while transmitting an unmodulated carrier wave of 2CH (S106). During the response waiting period, the interference determination unit 50 monitors the magnitudes of the response signals of 1CH and 3CH, and detects whether or not the magnitude of the response signal exceeds a predetermined threshold Lv shown in FIG. Thereby, the presence or absence of an interference signal is determined (S108). If it is determined that there is no interference signal, the process returns to S104 to continue transmission of an unmodulated carrier wave.

  When the response waiting period from the RFID tag 3 ends, transmission of unmodulated carrier waves (S114) is continued, and the magnitudes of the response signals of 1CH and 3CH are monitored by the interference determination unit 50 to determine whether there is an interference signal. Determination is made (S116). If it is determined that there is no interference signal, the control unit 42 decodes the response code obtained by demodulating the response signal, extracts the information of “management number A”, and stores it in the memory unit 43 (S118). When a series of response signal reception processes are repeated and the decoding process is completed (S120), the reading operation of the RFID tag 3 is terminated.

  Then, the information of “management number A” stored in the memory unit 43 is transferred to the central controller 5. The central controller 5 retrieves product information from a database (not shown) stored in the storage unit based on the information of “management number A”, and manages and controls processing, assembly, and the like for the article 2. In the database, various information related to the manufacture of the article 2 is stored as management information.

  However, if it is determined in S108 or S116 that there is an interference signal at the frequency of the response signal while receiving the response signal from the RFID tag 3 or in standby, the communication quality with the RFID tag 3 will decrease as it is. Normal communication will not be possible. Therefore, the RFID reader / writer 4 according to the present embodiment stores the channel being used, here 2CH (S110), as shown in FIG. 6, when the interference determination unit 50 determines that there is an interference signal (S110). In addition, the frequency switching unit 51 automatically switches to a channel having a second frequency different from the first frequency, here 8CH (S112). Then, the process returns to S100 and communication with the RFID tag 3 is performed again.

  As described above, the interference determination step (S108, S116) for determining the presence or absence of an interference signal at the frequency of the response signal modulated by the mirror subcarrier method, and the RFID reader when the interference determination step determines that there is an interference signal. Since it has a frequency switching step (S116) for switching the frequency of the carrier wave of the writer 4 to a second frequency different from the first frequency, if there is an interference signal, it quickly moves to the second frequency. Communication can be performed, and deterioration in communication quality can be suppressed.

  The RFID reader / writer 4 also includes a clock unit 35 that generates a clock for performing modulation and synchronization, and a power supply unit 34 for supplying power to each unit.

  As described above, according to the RFID system 1 of the present embodiment, when the RFID reader / writer 4 communicates at the frequency (2CH) of the first carrier wave, the interference signal from the other RFID reader / writer 4 is an interference determination unit. If detected by 50, the frequency switching unit 51 automatically switches the channel to the second carrier frequency (8CH). Thereby, the RFID reader / writer 4 can quickly move to the second frequency for communication when there is an interference signal. Thereby, it is possible to suppress a decrease in communication quality.

  When the RFID reader / writer 4 determines that there is an interference signal by the interference determination unit 50 and the frequency switching unit 51 switches the channel of the question signal, the radio wave of the carrier wave transmitted from the RFID reader / writer 4 is tagged. The RFID tag 3 reflected by the antenna unit 31 also automatically switches the response subcarrier frequency, so that the communication frequency can be switched smoothly. When the RFID tag 3 does not respond by reflection of radio waves from the tag antenna unit 31, the response subcarrier frequency may be switched according to the frequency of the carrier wave of the RFID reader / writer 4. Thus, communication can be performed smoothly by following the communication frequency.

  In this embodiment, the carrier wave used by the RFID reader / writer 4 for the mirror subcarrier communication is 2CH and 8CH. However, other channels may be used.

  Further, the frequency of the subcarrier used in the mirror subcarrier method can be arbitrarily set in consideration of the use frequency of the peripheral RFID reader / writer 4 and the like.

  Further, in the present embodiment, the example in which the RFID system 1 is applied to the manufacturing process has been described. However, in addition to this, the RFID system 1 can be used for various purposes such as storage management at a store and checkout settlement. .

  As described above, the present invention transmits an interrogation signal obtained by modulating a carrier wave of the first frequency with an interrogation data signal by an RFID reader / writer, receives an interrogation signal transmitted from the RFID reader / writer by an RFID tag, and interrogates data. A response signal obtained by modulating the response data signal to the signal by the mirror subcarrier method is returned to the RFID reader / writer. Then, the RFID reader / writer determines the presence or absence of an interference signal at the frequency of the response signal modulated by the mirror subcarrier method. When it is determined that there is an interference signal, the frequency of the carrier wave of the transmission unit is the first frequency. Since switching to a different second frequency is made, if there is an interference signal, it is possible to quickly move to the second frequency for communication.

  Accordingly, the present invention is useful as an RFID system, an RFID reader / writer, an RFID tag, and an RFID communication method that can suppress a decrease in communication quality even when there is an interference signal at the frequency of the response signal.

Schematic block diagram for explaining a usage pattern of an RFID system in an embodiment of the present invention Waveform diagram of signals transmitted and received between the RFID reader / writer and the RFID tag of the RFID system Explanatory drawing which shows the frequency allocation state of the signal used in the RFID system Waveform diagram showing the state when interference occurs in the RFID system Spectrum diagram showing the state when interference occurs in the RFID system Spectrum diagram showing the state when interference is avoided in the RFID system Block diagram showing the configuration of the RFID system Flow chart for explaining the operation of the RFID system

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 RFID system 2 Goods 3 RFID tag 4 RFID reader / writer 5 Central control device 6 Communication line 7 Transmission antenna 8 Reception antenna 31 Tag antenna part 32 Tag IC chip 33 Diode 34, 40 Capacitor 35, 42 Control part 36, 47 Demodulation part 37 Mirror subcarrier modulation unit 37a Switching element 38, 43 Memory unit 39, 48 Clock unit 41 Interface (I / F)
44 Modulating unit 45 Transmitting unit 46 Receiving unit 49 Power source unit 50 Interference determining unit 51 Frequency switching unit

Claims (13)

An RFID reader / writer for transmitting an interrogation signal obtained by modulating a carrier wave of a first frequency with an interrogation data signal;
An RFID system comprising: an RFID tag that receives the interrogation signal transmitted from the RFID reader / writer and returns a response signal obtained by modulating the response data signal to the interrogation data signal by a mirror subcarrier method to the RFID reader / writer Because
The RFID reader / writer includes an interference determination unit that determines presence / absence of an interference signal at the frequency of the response signal modulated by the mirror subcarrier method;
An RFID system, comprising: a frequency switching unit that switches a frequency of the carrier wave to a second frequency different from the first frequency when the interference determination unit determines that the interference signal is present. The interference determination unit compares the response signal with a predetermined threshold, determines that there is the interference signal when the magnitude of the response signal is greater than the predetermined threshold, and the magnitude of the response signal The RFID system according to claim 1, wherein it is determined that the interference signal is not present when smaller than a predetermined threshold value. 3. The RFID reader / writer transmits the interrogation signal without determining in advance whether or not the interference signal exists when communication is started by the mirror subcarrier method. The described RFID system. The RFID system according to any one of claims 1 to 3, wherein the interference signal is an interrogation signal output by an RFID reader / writer that performs communication by a baseband method. A modulator for generating an interrogation signal obtained by modulating a carrier wave of a first frequency with an interrogation data signal;
A transmitter that transmits the interrogation signal generated by the modulator to an RFID tag;
A receiver for receiving a response signal returned from the RFID tag by modulating a carrier wave of the first frequency by a mirror subcarrier method by a response data signal;
An interference determination unit that determines the presence or absence of an interference signal at the frequency of the response signal received by the reception unit;
A frequency switching unit that switches a frequency of the carrier wave of the transmission unit to a second frequency different from the first frequency when the interference determination unit determines that the interference signal is present; RFID reader / writer. The interference determination unit compares the response signal received by the reception unit with a predetermined threshold, determines that the interference signal is present when the response signal is larger than the predetermined threshold, 6. The RFID reader / writer according to claim 5, wherein when the magnitude of the response signal is smaller than the predetermined threshold, it is determined that there is no interference signal. The RFID reader / writer according to claim 5 or 6, wherein when the communication is started by the mirror subcarrier method, the interrogation signal is transmitted without determining in advance the presence or absence of the interference signal. The RFID reader / writer according to any one of claims 5 to 7, wherein the interference signal is an interrogation signal output by an RFID reader / writer that performs communication by a baseband method. The RFID reader / writer receives the interrogation signal transmitted from the RFID reader / writer after the carrier wave of the first frequency is modulated by the interrogation data signal, modulates the carrier wave by the mirror subcarrier system with the response data signal to the interrogation signal, and An RFID tag that replies as a response signal to
The RFID reader / writer determines that there is an interference signal at the frequency of the response signal modulated by the mirror subcarrier method, and the frequency of the carrier wave output by the RFID reader / writer is the first frequency. An RFID tag which returns the response signal with a carrier wave of the second frequency when switched to a different second frequency. An interrogation step of transmitting an interrogation signal obtained by modulating a carrier wave of a first frequency with an interrogation data signal from the RFID reader / writer;
A response in which the RFID tag receives the interrogation signal transmitted from the RFID reader / writer and returns a response signal obtained by modulating the response data signal to the interrogation data signal by a mirror subcarrier method from the RFID tag to the RFID reader / writer. An RFID communication method comprising steps,
An interference determination step for determining presence or absence of an interference signal at a frequency of the response signal modulated by the mirror subcarrier scheme;
A frequency switching step of switching the frequency of the carrier wave of the RFID reader / writer to a second frequency different from the first frequency when it is determined by the interference determination step that the interference signal is present. RFID communication method. The interference determination step compares the response signal with a predetermined threshold, determines that there is the interference signal when the magnitude of the response signal is greater than the predetermined threshold, and the magnitude of the response signal The RFID communication method according to claim 10, wherein it is determined that the interference signal is not present when smaller than a predetermined threshold value. 12. The interrogation step transmits the interrogation signal without determining in advance the presence or absence of the interference signal when communication is started by the mirror subcarrier method. RFID communication method. The RFID communication method according to any one of claims 10 to 12, wherein the interference signal is an interrogation signal output by an RFID reader / writer that performs communication by a baseband method.

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