JP2012208716A - Rfid reader/writer device and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for determining a channel optimal for communication in a reader/writer.SOLUTION: In a reader/writer 2 including a transmitting/receiving section 6 capable of transmitting/receiving signals with an RFID tag by utilizing the same channel as an adjacent reader/writer 2, a transmitting/receiving processing section 5 processes signals to be transmitted/received with the tag. A carrier sense processing section 9 detects reception levels of a plurality of channels. A random time generator 8 generates the timing to detect the reception levels in the carrier sense processing section 9. In accordance with the timing generated by the random time generator 8, a control section 3 switches a connection to the transmitting/receiving section 6 from the transmitting/receiving processing section 5 to the carrier sense processing section 9 and sets a channel with a lowest reception level among the detected reception levels to a channel to be used. The transmitting/receiving section 6 transmits/receives signals processed in the transmitting/receiving processing section 5 by using the channel set in the control section 3.

Description

  The present invention relates to an RFID reader / writer device that can use a plurality of transmission / reception channels with an RFID (Radio Frequency IDentification) tag and a control method thereof.

  Conventionally, in an RFID system, an RFID reader / writer device (hereinafter abbreviated as a reader / writer) can use a plurality of channels for communication with an RFID tag (hereinafter abbreviated as a tag). A process for determining a channel suitable for communication is widely and generally performed. The reader / writer performs communication using the determined channel, thereby preventing interference with other reader / writers.

Conventional channel determination methods include a method of manually setting a channel in the system and a method of determining an optimum channel in the system.
A method for determining a channel in the system will be described with reference to a configuration diagram of a conventional reader / writer shown in FIG. The reader / writer 102 in the prior art performs a test or the like before starting communication with the tag to determine a channel to be set in each reader / writer 102 in the system. At this time, the channel of each reader / writer 102 in the system is determined by, for example, the server 101 which is a host device of the reader / writer 102. The reader / writer 102 stores the channel notified from the server 102 in the used channel storage unit 104 in its own apparatus. When the transmission / reception processing unit 105 in the reader / writer 102 executes processing related to transmission / reception of signals with the tag, the transmission / reception processing unit 105 transmits and receives signals using the channel stored in the used channel storage unit 104.

  As for the channels used in the RFID system, there is a technique in which the used frequencies are separated by the number of channels so as not to cause interference between readers. For example, there is a technique in which a reader transmits a command signal of a single sideband to a tag, shifts the frequency band of the single sideband, and receives a response signal of a double sideband whose frequency band is shifted from the tag. Known (for example, Patent Document 1).

  In addition, in the system, a technique including a synchronization device that transmits a signal for controlling the timing at which a plurality of tag readers communicating with a tag respectively communicate with the tag is also known (for example, Patent Document 2). According to this, when receiving the carrier transmitted from the tag reader, the synchronization device returns a synchronization request signal by the same backscatter method as the tag. When detecting the synchronization request signal, the plurality of tag readers shift to the synchronization start mode and continuously distribute the unmodulated carrier. After returning the synchronization request signal, the synchronization device gives a trigger for starting control to the plurality of tag readers, and the plurality of tag readers start control for communicating with the tag when the trigger is given. As described above, a technique is known in which control is performed by the synchronization device so that the control timing for communicating with the tag by each tag reader does not overlap.

  In recent years, a technique has also been realized in which a reader / writer communicates with a tag using the same channel as another reader / writer adjacent thereto. In this regard, for example, the reader / writer determines the presence or absence of an interference signal at the frequency of the response signal from the tag modulated by the mirror subcarrier method, and if it is determined that there is an interference signal, the frequency of the carrier wave of the transmission unit is determined. A technique for switching is known (for example, Patent Document 3).

JP 2007-151132 A JP 2009-021848 A JP 2010-021684 A

  For example, according to the method of manually determining the channel, it is necessary for the RFID specialist to determine the most efficient channel allocation according to the arrangement of the reader / writer for each system, and set it for each reader / writer or for the system. . Specifically, it is necessary to set the channels of adjacent reader / writers that are close to each other as far as possible. For this reason, RFID specialists have to be involved in channel setting for each system. Further, when the arrangement of the reader / writer and the surrounding conditions are changed, there is a drawback that the channel needs to be reset depending on the surrounding conditions of the site.

  Further, according to the method for determining a channel in the above-described system, other devices are provided in the system in order to shift the timing of communication between a plurality of reader / writers, as in the technique described in Patent Document 2, for example. There was a need.

  The present invention enables an RFID reader / writer device to determine the optimum channel for communication when the RFID reader / writer device can communicate using the same channel as another adjacent RFID reader / writer device. The purpose is to provide the technology.

  According to one aspect of the present invention, an RFID system having a transmission / reception unit capable of transmitting / receiving a signal to / from an RFID tag using the same channel as an adjacent RFID reader / writer device among a plurality of channels. In the RFID reader / writer device, a transmission / reception processing unit that processes signals transmitted to and received from the RFID tag, a carrier sense processing unit that detects reception levels of the plurality of channels, and the carrier sense processing unit A carrier sense start timing generation unit that generates timing for detecting a reception level, and a connection to the transmission / reception unit from the transmission / reception processing unit to the carrier sense process according to the timing generated in the carrier sense start timing generation unit The reception level detected by the carrier sense processing unit. A control unit configured to set a channel having the lowest reception level among the channels, wherein the transmission / reception unit uses the channel set in the control unit to process a signal processed in the transmission / reception processing unit Send and receive.

  According to another aspect of the present invention, a transceiver unit capable of transmitting and receiving signals to and from an RFID tag using the same channel as an adjacent RFID reader / writer device among a plurality of channels. A method for controlling an RFID reader / writer device in an RFID system having a timing for detecting reception levels of the plurality of channels, and connecting to the transmission / reception unit according to the generated timing, Switching from a transmission / reception processing unit that processes signals to / from the RFID tag to a carrier sense processing unit that detects reception levels of the plurality of channels, and the lowest reception level among the detected reception levels Of the signal to be transmitted to and received from the RFID tag using the set channel. Performing the receiving.

  According to the present invention, when an RFID reader / writer device can communicate using the same channel as another adjacent RFID reader / writer device, the RFID reader / writer device determines an optimum channel for communication. Is possible.

It is a figure which shows the structural example of a RFID system. 1 is a configuration diagram of a reader / writer according to a first embodiment. FIG. It is a figure explaining the combination of a channel. It is a figure explaining the carrier sense timing of the reader / writer concerning a 1st embodiment. It is a figure explaining the transition of the channel of the reader / writer concerning a 1st embodiment. It is a flowchart which shows operation | movement of the control part of the reader / writer based on 1st Embodiment. It is a block diagram of the reader / writer which concerns on 2nd Embodiment. It is a block diagram of a carrier sense timing generator. It is a figure explaining the carrier sense timing of the reader / writer which concerns on 2nd Embodiment. It is a flowchart which shows operation | movement of the control part of the reader / writer which concerns on 2nd Embodiment. It is a block diagram of a conventional reader / writer.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<First Embodiment>
FIG. 1 is a diagram illustrating a configuration example of an RFID system including a reader / writer according to the present embodiment.

  The reader / writer 2 includes an antenna 7, sends a signal to the tag 10 through the antenna 7, and receives a response signal from the tag 10 to the information to write information to the tag 10. The information is read from the tag 10.

  The server 1 is an upper device of the reader / writer 2 and manages information necessary for the RFID system 100. The tag 10 holds information in the memory, and executes processing such as updating the information held in the memory according to the signal received from the reader / writer 2 and transmitting the held information in the response signal. . In the embodiment, the tag 10 is a UHF (Ultra-High Frequency) band RFID tag.

  One or more reader / writers 2 are installed in the RFID system 100. In the following, in order to describe a method in which the reader / writer 2 according to the present embodiment determines a channel so that interference does not occur with other reader / writers 2, in FIG. A configuration including a single reader / writer 2 is illustrated.

  Three reader / writers 2 are referred to as reader / writers 2A, 2B, and 2C, respectively. The tags 10 in the radio wave output ranges 11A, 11B, and 11C of the reader / writers 2A, 2B, and 2C are assumed to be 10A, 10B, and 10C, respectively. In the following description, when it is necessary to distinguish the three reader / writers 2, the radio wave output range 11, and the tag 10, they are denoted by reference numerals A, B, and C. When there is no need to distinguish between these, these symbols are omitted and expressed as “Reader / Writer 2” or the like.

  FIG. 1 shows a configuration in which three reader / writers 2 </ b> A to 2 </ b> C are arranged in a straight line for easy explanation. That is, the reader / writer 2 adjacent to the reader / writer 2A is the reader / writer 2B, the reader / writer 2 adjacent to the reader / writer 2B is the reader / writer 2A and the reader / writer 2C, and the reader / writer 2 adjacent to the reader / writer 2C is the reader / writer 2C. Writer 2B.

  In the following description, each of the reader / writers 2A to 2C in FIG. 1 can use two channels, and can transmit / receive a signal to / from the tag 10 using the same channel as the adjacent reader / writer 2. Is assumed. In the embodiment, this is realized by adopting a mirror subcarrier system in the RFID system 100.

  FIG. 2 is a configuration diagram of the reader / writer 2 according to the present embodiment. The reader / writer 2 shown in FIG. 2 includes a control unit 3, an antenna 7, a used channel storage unit 4, a transmission / reception processing unit 5, a transmission / reception unit 6, a carrier sense processing unit 9, and a random time generator 8. FIG. 2 shows only the configuration related to the channel determination method according to the present embodiment.

  The transmission / reception unit 6 transmits signals received from the transmission / reception processing unit 5 and the carrier sense processing unit 9 via the antenna 7 and receives a response signal from the tag 10 via the antenna 7.

The transmission / reception processing unit 5 executes processing related to transmission / reception of signals with the tag 10. Specifically, processing such as generation of a signal to be transmitted and analysis of a received response signal is performed.
The used channel storage unit 4 stores a channel used for transmission / reception of a signal with the tag 10 in the transmission / reception unit 6.

  The carrier sense processing unit 9 performs carrier sense. Specifically, the carrier sense processing unit 9 detects a reception level of a channel that can be used by the reader / writer 2 before executing processing related to signal transmission / reception with the tag 10. For example, FIG. 1 shows a configuration example in which three reader / writers 2A to 2C are arranged in a straight line. Actually, however, the distance between the reader / writer 2 and the nearest reader / writer 2 is determined by carrier sense. Control is performed so that the channel is not covered.

  The random time generator 8 generates a timing at which the carrier sense processing unit 9 detects the reception level. Specifically, the random time generator 8 generates a “random time” that indicates a period during which a signal is transmitted to and received from the tag 10. When the random time has elapsed, the carrier sense processing unit 9 starts carrier sense. In order to keep the period during which carrier sense is not performed within a predetermined range, the random time is generated within the predetermined time.

The control unit 3 controls each unit of the reader / writer 2 to determine a channel used for transmission / reception of a signal with the tag 10.
A method for determining a channel to be used when the reader / writer 2 according to the present embodiment transmits / receives a signal to / from the tag 10 by carrier sense will be specifically described below.

  FIG. 3 is a diagram illustrating channel combinations. As described above, each of the three reader / writers 2A to 2C can use two channels (channel 1 and channel 2). FIG. 3 shows possible channel patterns when each reader / writer 2A to 2C determines a channel to be used from two channels. In FIG. 3, “1” of the reader / writer channel indicates that channel 1 is determined, and “2” indicates that channel 2 is determined as the use channel. A pattern in which the transmission / reception efficiency with the tag 10 in each channel pattern is the best is represented by “◯”, a pattern having a moderate transmission / reception efficiency is represented by “Δ”, and a pattern having the lowest transmission / reception efficiency is represented by “×”.

  As shown in FIG. 3, there are eight channel patterns. Among these, the pattern in which the signal transmission / reception efficiency with the tag 10 is the best is a pattern that does not use the same channel as the adjacent reader / writer 2, and the pattern 3 and the pattern 6 correspond to this pattern. When each reader / writer 2 has a channel different from that of the adjacent reader / writer 2, it can be assumed that the transmission / reception efficiency is approximately the same (O). "Stable state".

  The pattern 2, the pattern 4, the pattern 5 and the pattern 7 are any one of the two reader / writers 2A and 2C adjacent to the reader / writer 2B among the three reader / writers 2A to 2C having the configuration shown in FIG. This is the case where a different channel is selected, while the other channel is selected. For this reason, the transmission / reception efficiency of these four channel patterns is approximately the same (Δ).

  Similarly, in patterns 1 and 8, all three reader / writers 2A to 2C select the same channel. For this reason, the transmission / reception efficiency of these two channel patterns is approximately the same (x).

  According to the reader / writer 2 according to the present embodiment, the random time generated by the random time generator 8 of FIG. 2 is counted, and when the random time has elapsed, the processing by the transmission / reception processing unit 5 is stopped to perform carrier sense. Execute. Each of the three reader / writers 2A to 2C executes carrier sense each time the random time generated by the random time generator 8 of the own device elapses, and determines the channel to be used. The pattern is switched to pattern 3 or pattern 6 with the best transmission / reception efficiency at (the transmission / reception efficiency in FIG. 3 is o), and a stable state is obtained.

  For example, in the pattern 2 in which the transmission / reception efficiency is medium / Δ, in the pattern 2, the reader / writer 2 </ b> A and the reader / writer 2 </ b> B adjacent to each other are set to the same channel 1. When the channel setting of each reader / writer 2 is pattern 2, any one of the three reader / writers 2A to 2C executes carrier sense.

  When the reader / writer 2A performs carrier sense in the state of pattern 2, the reader / writer 2A selects a channel 2 different from the channel 1 of the adjacent reader / writer 2B by carrier sense. Thereby, in the RFID system 100, the channel pattern shifts from the pattern 2 to the pattern 6 in FIG. 3, and the channel is in a stable state.

  When the reader / writer 2B executes the carrier sense in the state of the pattern 2, the reader / writer 2B has a channel different from that of the reader / writer 2 with the shorter distance between the two adjacent reader / writers 2A and 2C due to the carrier sense. Select. When channel 1 is selected closer to the reader / writer 2C, the pattern 2 is maintained. On the other hand, when channel 2 is selected closer to reader / writer 2A, the channel pattern shifts from pattern 2 to pattern 4. Here, the transmission / reception efficiency of the pattern 4 is approximately the same as that of the pattern 2 and remains “Δ”.

  When the reader / writer 2C performs carrier sense in the state of pattern 2, since the reader / writer 2C has a channel different from the channel of the adjacent reader / writer 2B, the channel remains 2 and does not change.

  When all the reader / writers 2A to 2C set the same channel as in the pattern 1 and the pattern 8, the reader / writer 2 that executes carrier sense first is always the same as the other two reader / writers 2. Set a different channel. For this reason, the transmission / reception efficiency of pattern 1 and pattern 8 is not actually set to a low pattern (transmission / reception efficiency in FIG. 3 is x). Further, when the channel is in a stable state as in pattern 3 or pattern 6, the pattern does not shift to another pattern. Therefore, a case where a carrier pattern having a medium transmission / reception efficiency is set may be considered.

FIG. 4 is a diagram illustrating carrier sense timings of the reader / writers 2A to 2C according to the present embodiment.
As described above, the reader / writers 2A to 2C execute carrier sense when the random time generated by the random time generator 8 of their own devices has elapsed. For example, the time required for carrier sense is usually about 5 milliseconds. As the random time, the random time generator 8 is adjusted so as to take a sufficiently long time with respect to the time required for carrier sense. For example, the minimum value of the random time is 200 milliseconds. This is set from the time required for the reader / writer 2 to transmit / receive a signal to / from the tag 10. In this way, by adjusting the random time generator 8 so that the random time is set to about 1 minute, the carrier sense execution timing is duplicated between the reader / writers 2A to 2C in the RFID system 100. To avoid that.

  The reader / writers 2A to 2C perform carrier sense after a lapse of random time. When the carrier sense is completed, the carrier sense is executed after the lapse of the regenerated random time, and thereafter this is repeated.

  FIG. 5 is a diagram for explaining channel transition of the reader / writers 2A to 2C according to the present embodiment. In FIG. 5, the initial value of the channel shows a case where the transmission / reception efficiency is medium (Δ in FIG. 3) among the eight patterns shown in FIG. Hereinafter, when the channels of the three reader / writers 2A to 2C are the channel 2, the channel 2, and the channel 1, respectively, it is expressed as “channel pattern 2-2-1”. A case where carrier sense is executed in the order shown in FIG. 4 will be described.

  In FIG. 5A, first, the first carrier sense is executed by the reader / writer 2C. Since a channel different from that of the adjacent reader / writer 2B is set, the channel is not switched and the channel pattern remains “2-2-1” and does not change.

  The second carrier sense is executed by the reader / writer 2B. Here, a case is shown in which a channel different from the reader / writer 2A having a shorter distance is set to a channel that is closer to the reader / writer 2A, 2C. As a result, the channel pattern is switched from “2-2-1” to “2-1-1” (pattern 5).

  The third carrier sense is executed by the reader / writer 2A. Since the reader / writer 2A has a channel different from that of the adjacent reader / writer 2B, the channel is not switched and the channel pattern remains “2-1-1” and does not change.

  The fourth carrier sense is executed by the reader / writer 2C. The reader / writer 2C switches the channel to be used to channel 2, which is a channel different from that of the adjacent reader / writer 2B. As a result, the channel pattern is switched to “2-1-2” (pattern 6).

  In the fifth and subsequent carrier senses, each reader / writer 2 has a channel different from that of the adjacent reader / writer 2, so that the pattern 6 set in the fourth carrier sense is maintained, thereby stabilizing the channel. It will change as it is.

  FIG. 5A shows channel pattern transition when the reader / writer 2 closest to the reader / writer 2B is the reader / writer 2A. Therefore, in the second carrier sense, the reader / writer 2B is determined as a channel using a channel 1 different from the channel 1 set in the reader / writer 2A (* 1 in FIG. 5A). On the other hand, FIG. 5B shows channel pattern transition when the reader / writer 2 closest to the reader / writer 2B is the reader / writer 2C.

  As shown in FIG. 5B, when the reader / writer 2C is closer to the reader / writer 2B, the reader / writer 2B has a channel different from the channel of the reader / writer 2C in the second carrier sense. Therefore, channel switching is not performed, and the channel pattern remains “2-2-1” and does not change (* 2 in FIG. 5B).

  In this case, in the third carrier sense, the reader / writer 2A switches the channel to be used to the channel 1 which is a channel different from the adjacent reader / writer 2B. As a result, the channel pattern is switched to “1-2-1” (pattern 3). After the fourth carrier sense, the stable pattern 3 is maintained.

Thus, regardless of which reader / writer 2 is adjacent, the channel pattern finally shifts to a stable state.
If the timing for executing carrier sense is duplicated, even if the channel pattern is switched by a certain reader / writer 2, a situation may occur in which the other reader / writer 2 returns to the original state. However, as previously described in FIG. 4, the reader / writer 2 according to the present embodiment allows the RFID system 100 to have a sufficiently long random time with respect to the carrier sense required time. It is avoided that the timing at which carrier sense is executed among a plurality of reader / writers 2 is duplicated.

  FIG. 6 is a flowchart showing the operation of the control unit 3 of the reader / writer 2 according to the present embodiment. The control unit 3 of the reader / writer 2 starts a series of processes shown in FIG. 6 when the power of the reader / writer 2 is switched from OFF to ON and the reader / writer 2 is activated.

First, in step S1, the control unit 3 activates the random time generator 8, and reads the state of the timing signal of the random time generator 8 in step S2.
In step S <b> 3, the control unit 3 determines whether or not the state of the timing signal read from the random time generator 8 is a “random time elapsed state”. When the random time generated by the random time generator 8 has elapsed, the state of the read timing signal is “random time elapsed state”. It is assumed that the “elapsed state”.

If it is determined in step S3 that the read timing signal is in a state where the random time has elapsed, the control unit 3 shifts the process to step S4.
In step S4, the control unit 3 stops the operation of the random time generator 8. Specifically, the control unit 3 transmits a stop signal that instructs the random time generator 8 to stop the operation. At the same time, the carrier sense processing unit 9 is connected to the transmission / reception unit 6.

  In step S5, the control unit 3 causes the carrier sense processing unit 9 to execute processing related to carrier sense. In step S6, the control unit 3 determines the channel having the lowest reception level as the channel used by the reader / writer 2 as a result of the carrier sense in step S5. As a technique for avoiding interference by determining a channel having the lowest reception level as a use channel, a well-known technique is used, and thus a detailed description thereof is omitted here. The determined use channel is stored in the use channel storage unit 4, and the process returns to step S1.

On the other hand, in the determination of step S3, when the read timing signal is in a state where the random time has not elapsed, the control unit 3 shifts the process to step S7.
In step S <b> 7, the control unit 3 determines whether there is signal transmission / reception with the tag 10. When there is no signal transmission / reception to / from the tag 10, the control unit 3 returns the process to step S1, and when there is signal transmission / reception to / from the tag 10, the process proceeds to step S8.

  In step S8, the control unit 3 switches the connection to the transmission / reception unit 6 from the carrier sense processing unit 9 to the transmission / reception processing unit 5, sets the channel stored in the use channel storage unit 4 to the use channel, and step S9. Proceed to

When the control unit 3 causes the transmission / reception processing unit 5 to perform transmission / reception processing with the tag 10 in step S9, the process returns to step S1.
Note that the reader / writer 2 executes the processing of step S3 to step S4 after recognizing that the random time has elapsed from the timing signal state read in step S2 until starting carrier sense in step S5. . Since the time required for these processes is negligibly short compared with the time required for random time or carrier sense, it is omitted in the description of FIG.

  As described above, according to the reader / writer 2 according to the present embodiment, each of the plurality of reader / writers 2 in the RFID system 100 starts carrier sense at the timing generated in the own apparatus. Since the carrier sense start timing is different among the plurality of reader / writers 2, each reader / writer 2 that performs carrier sense uses a channel with a low reception level so that the reader / writer 2 does not interfere with other adjacent reader / writers 2. Set the channel to be used. When transmitting / receiving a signal to / from the tag 10, the channel determined in the carrier sense is used. Accordingly, each of the reader / writers 2 can select an optimum channel and set it as a use channel without providing control by the server 1 or other devices for timing control in the RFID system 100. .

<Second Embodiment>
In the above embodiment, the random time is sufficiently longer than the carrier sense time, so that the carrier sense start timing of each reader / writer 2 in the RFID system 100 is prevented from overlapping. On the other hand, the reader / writer 2 according to the present embodiment is different in that the timing not overlapping with other reader / writers 2 is obtained by calculation.

  FIG. 7 is a configuration diagram of the reader / writer 2 according to the present embodiment. The configuration of the RFID system 100 is the same as that of the above embodiment, and is as shown in FIG. Moreover, the same code | symbol is attached | subjected about the structure similar to said embodiment among the structures of the reader / writer 2 shown in FIG. Here, the configuration different from the configuration shown in FIG. 2 will be mainly described.

The reader / writer 2 according to the present embodiment is different in that it has a carrier sense timing generator 12 instead of the random time generator 8 of FIG.
FIG. 8 is a configuration diagram of the carrier sense timing generator 12. As shown in FIG. 8, the carrier sense timing generator 12 includes a calendar clock 13, a reader / writer unique ID (identification) setting switch (hereinafter abbreviated as setting switch) 14, a carrier sense time 15, and a carrier sense timing signal generation unit (hereinafter referred to as “set”). (Abbreviated as signal generation unit) 16.

  The calendar clock 13 holds time information of the reader / writer 2. The setting switch 14 sets a unique value assigned to each reader / writer 2 in the RFID system 100. The carrier sense time 15 has a predetermined time common between the reader / writers 2 in the RFID system 100. The predetermined time is a time for executing carrier sense in the carrier sense processing unit 9 and is hereinafter referred to as “carrier sense time”.

  The signal creation unit 16 indicates the timing at which carrier sensing is started in the own device using the time information acquired from the calendar clock 13, the eigenvalue set in the setting switch 14, and the carrier sense time held by the carrier sense time 15. Generate a timing signal.

Specifically, the timing (time) at which carrier sense is executed is determined by the following equation. In the following equation (1), a represents time information acquired from the calendar clock 13 at predetermined time intervals.
Carrier sense start timing (time) = a + (carrier sense time × eigen value) (1)
The time at which carrier sense is started is calculated according to equation (1), and when the calculated time is reached, the signal generator 16 generates a timing signal indicating the start timing of carrier sense. When the carrier sense processor 9 detects the timing signal generated by the signal generator 16, the carrier sense processor 9 starts carrier sense.

FIG. 9 is a diagram for explaining carrier sense timings of the reader / writers 2A to 2C according to the present embodiment. “A” in FIG. 9 corresponds to a in equation (1).
Here, it is assumed that the eigenvalues assigned to the reader / writers 2A, 2B, and 2C are 1, 2, and 3, respectively. The time interval for acquiring the time information from the calendar clock 13 is 1 minute. In FIG. 9, the time a is acquired at 12:00:00, 12:12:00, and 12:02:00. The carrier sense timing is shown.

  In this case, the carrier sense timing (time) b of the reader / writer 2A is the time when a time corresponding to carrier sense time × eigen value (= 1) has elapsed from time a. Similarly, for the carrier sense timing (time) c of the reader / writer 2B and the carrier sense timing (time) d of the reader / writer 2C, the eigenvalues 2 and 3 of the reader / writer 2B and 2C are substituted into the equation (1). Is calculated by

  Since the carrier sense time of each reader / writer 2 is calculated using a unique value that differs for each reader / writer 2, the reader / writer 2 does not overlap. This makes it possible to transition the channel to a stable state more reliably.

  FIG. 10 is a flowchart showing the operation of the control unit 3 of the reader / writer 2 according to this embodiment. Here, the operation different from the operation of the control unit of the reader / writer according to the above embodiment will be mainly described. The control unit 3 of the reader / writer 2 starts a series of processes shown in FIG. 10 when the power of the reader / writer 2 is switched from OFF to ON and the reader / writer 2 is activated.

  First, in step S11, the control unit 3 activates the carrier sense timing generator 12, and reads the timing signal state of the carrier sense timing generator 12 in step S12.

  In step S <b> 13, the control unit 3 determines whether or not the state of the read timing signal is a “timing signal generation state”. When the timing signal is output from the carrier sense timing generator 12, the timing signal is generated. When the signal is not output, the timing signal is not generated.

If it is determined in step S13 that the timing signal is generated, the controller 3 shifts the process to step S14.
In step S <b> 14, the control unit 4 connects the carrier sense processing unit 9 to the transmission / reception unit 6 and causes the carrier sense processing unit 9 to perform processing related to carrier sense. In step S15, the control unit 3 determines the channel having the lowest reception level as the channel used by the reader / writer 2 as a result of the carrier sense in step S14. The determined use channel is stored in the use channel storage unit 4, and the process returns to step S12.

On the other hand, if it is determined in step S13 that the timing signal is not generated, the control unit 3 shifts the process to step S16.
About the process of step S16-step S18, it is the same as that of the process of step S7-step S9 of FIG. 6, respectively.

  In the above description, a configuration in which a unique value (ID) is assigned to each reader / writer 2 is described. When the server 1 and each reader / writer 2 are connected to each other by, for example, a USB (Universal Serial Bus) or the like, it is necessary to assign a unique value by the setting switch 14 as described above. However, the reader / writer 2 is not limited to this. For example, if the server 1 and each reader / writer 2 are connected via a LAN (Local Area Network), it is possible to use a MAC address without providing the setting switch 14. The same effect is obtained even when the MAC address is used.

  As described above, according to the reader / writer 2 according to the present embodiment, each reader / writer 2 performs carrier sense in its own device using a unique value (ID) or the like for each reader / writer 2 in the RFID system 100. The execution timing is determined. Since each reader / writer 2 surely executes carrier sense at different timings, it is possible to prevent the channel pattern from returning to the original state and reliably transition the channel to the stable state.

  Needless to say, the present invention is not limited to the configuration exemplified in the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Server 2 Reader / writer 3 Control part 4 Used channel preservation | save part 5 Transmission / reception processing part 6 Transmission / reception part 7 Antenna 8 Random time generator 9 Carrier sense processing part 10 Tag 11 Reader / writer radio wave output range 12 Carrier sense timing generator 13 Calendar clock 14 Reader / writer unique ID setting switch (setting switch)
15 Carrier sense time 16 Carrier sense timing signal generator (signal generator)
100 RFID system

Claims (5)

An RFID reader / writer device in an RFID system having a transmission / reception unit capable of transmitting / receiving a signal to / from an RFID tag using the same channel as an adjacent RFID reader / writer device among a plurality of channels,
A transmission / reception processing unit for processing a signal transmitted to and received from the RFID tag;
A carrier sense processing unit for detecting reception levels of the plurality of channels;
A carrier sense start timing generation unit for generating timing for detecting the reception level in the carrier sense processing unit;
According to the timing generated by the carrier sense start timing generation unit, the connection to the transmission / reception unit is switched from the transmission / reception processing unit to the carrier sense processing unit, and the reception level detected by the carrier sense processing unit is changed. Among them, a control unit that sets a channel using the lowest reception level channel,
With
The RFID reader / writer device, wherein the transmission / reception unit transmits / receives a signal processed in the transmission / reception processing unit using a channel set in the control unit. The carrier sense start timing generator comprises a random time generator that generates a random time within a predetermined time,
The RFID reader / writer device according to claim 1, wherein the control unit switches the connection to the transmission / reception unit from the transmission / reception processing unit to the carrier sense processing unit when the random time has elapsed. The carrier sense start timing generation unit reads time information of the RFID reader / writer device, generates a carrier sense timing signal using the time information and a unique value assigned to each RFID reader / writer device,
The RFID reader / writer device according to claim 1, wherein the control unit switches the connection to the transmission / reception unit from the transmission / reception processing unit to the carrier sense processing unit according to the carrier sense timing signal. The carrier sense start timing generation unit reads the time information every predetermined time, and obtains a value obtained by adding a value obtained by adding the eigenvalue to the predetermined carrier sense time to the predetermined time. The RFID reader / writer device according to claim 3, wherein the carrier sense timing signal is generated. A method for controlling an RFID reader / writer device in an RFID system having a transmission / reception unit capable of transmitting / receiving a signal to / from an RFID tag using the same channel as an adjacent RFID reader / writer device among a plurality of channels. There,
Generating timing for detecting the reception level of the plurality of channels;
According to the generated timing, the connection to the transmission / reception unit is changed from the transmission / reception processing unit that processes the signal transmitted to and received from the RFID tag to the carrier sense processing unit that detects the reception levels of the plurality of channels. And switch
Among the detected reception levels, set the channel using the lowest reception level channel,
A method for controlling an RFID reader / writer device, wherein a signal transmitted / received to / from the RFID tag is transmitted / received using the set channel.