JP2020149445A - Communication system and communication method employed by the same - Google Patents

Abstract

To provide a communication system which enables communication with wireless tags with priority levels assigned to reader/writers without complicating the system.SOLUTION: When radio waves of other reader/writers are detected before communicating with an RFID tag (4), each reader/writer performs a process for delaying the start of the communication by a predetermined standby time period. An average standby time period for gate reader/writers (2) is set to be shorter than that for shelf management reader/writers (3).SELECTED DRAWING: Figure 1

Description

The present invention relates to a communication system that prevents interference between readers and writers that transmit and receive information with a wireless tag.

Conventionally, the use of wireless tags has become widespread for the purpose of identifying articles and the like. Regarding a reader / writer that transmits / receives information to / from a wireless tag, there is an LBT (Listen Before Talk) function as an example of means for preventing interference caused by a plurality of reader / writers being active at the same time. However, since the right to communicate is equally given to the reader / writer only by the LBT function, it is not possible to meet the need to raise the priority of a specific reader / writer.

On the other hand, Patent Document 1 discloses a technique in which a management server controls the start / end of carrier sense and the transmission / stop of a radio signal by a query device (corresponding to a reader / writer). In addition, the worker gives priority to each interrogator, and when granting the right to perform wireless communication, the management server grants the right to perform wireless communication to the interrogator with high priority first. The method is disclosed.

JP-A-2007-317174

However, in the above-mentioned conventional technology, since the priority of the reader / writer is controlled by the management server which is a higher-level system, there is a problem that the system becomes complicated, and the cost increases and the management becomes complicated. In addition, since the management server mediates the communication rights of the reader / writer, there will be a waiting time for processing and communication associated with the mediation. Therefore, for example, there is a problem that sufficient measures may not be provided in situations where real-time performance is required, such as passing a wireless tag through a gate.

One aspect of the present invention is to provide a communication system capable of setting a priority for a reader / writer and performing communication with a wireless tag without inviting complication of the system.

In order to solve the above problems, the communication system according to one aspect of the present invention is a communication system including a plurality of reader / writers that read and write data to a plurality of RFID tags. When each reader / writer detects a radio wave emitted when another reader / writer communicates with the RFID tag, and detects the radio wave of the other reader / writer before communicating with the RFID tag to be communicated, the above-mentioned Performs at least one of a process of waiting for the start of communication with the RFID tag to be communicated with a predetermined waiting time and a process of waiting with a predetermined waiting time after the communication process with the RFID tag to be communicated is completed. A standby unit is provided, and among the plurality of reader / writers, the average value of the standby time of the first reader / writer is set shorter than the average value of the standby time of the second reader / writer.

Further, the communication method of the communication system according to one aspect of the present invention is a communication method in a communication system including a plurality of readers / writers that read and write data to a plurality of RFID tags. When each reader / writer detects a radio wave emitted when another reader / writer communicates with the RFID tag, and detects the radio wave of the other reader / writer before communicating with the RFID tag to be communicated, the communication is performed. Waiting to perform at least one of a process of waiting for the start of communication with the target RFID tag in a predetermined waiting time and a process of waiting in a predetermined waiting time after the communication process with the communication target RFID tag is completed. Among the plurality of reader / writers including the step, the average value of the standby time of the first reader / writer is set shorter than the average value of the standby time of the second reader / writer.

According to the above configuration or method, the average value of the standby time of the first reader / writer is set shorter than the average value of the standby time of the second reader / writer, so that the first reader / writer acquires the communication right. The possibility can be increased. Therefore, the priority of communication can be set higher for the first reader / writer than for the second reader / writer.

Further, since the priority can be set by setting the standby time in each reader / writer, the control by the host system is unnecessary, and the priority can be set without inviting the complexity of the system.

In the above configuration, the communication system according to one aspect of the present invention may have a configuration in which the standby unit of the first reader / writer has a standby time of zero.

According to the above configuration, the first reader / writer has the highest priority, and the communication process can be started quickly without waiting time.

In the above configuration, the communication system according to one aspect of the present invention may have a configuration in which the standby unit of the first reader / writer randomly determines a standby time from a range of T3 or more and T4 or less each time it waits. ..

According to the above configuration, for example, when a specific leader / writer communicates in a predetermined communication cycle, the communication cycle and the standby time become equal, so that the first reader / writer completely loses the opportunity to acquire the communication right. It is possible to prevent such a situation.

In the above configuration, the communication system according to one aspect of the present invention may have a configuration in which the standby unit of the second reader / writer randomly determines the standby time from the range of T5 or more and T6 or less each time it waits. ..

According to the above configuration, for example, when a specific leader / writer communicates in a predetermined communication cycle, the communication cycle and the standby time become equal, so that the second reader / writer completely loses the opportunity to acquire the communication right. It is possible to prevent such a situation.

In the communication system according to one aspect of the present invention, in the above configuration, the standby unit of the second reader / writer randomly determines the standby time from the range of T5 or more and T6 or less each time the standby unit waits. It may be configured to have a value smaller than T5.

According to the above configuration, the standby time of the first reader / writer is always shorter than the standby time of the second reader / writer, so that the priority of the first reader / writer can be surely increased.

In the communication system according to one aspect of the present invention, in the above configuration, the standby unit of the second reader / writer randomly determines the standby time from the range of T5 or more and T6 or less each time the standby unit waits. The configuration may be such that the value is equal to T5.

According to the above configuration, the standby time of the first reader / writer and the standby time of the second reader / writer may be equal depending on the situation. In this case, the first reader / writer and the second reader / writer have priority. The degrees can be equal.

In the communication system according to one aspect of the present invention, in the above configuration, the standby unit of the second reader / writer randomly determines the standby time from the range of T5 or more and T6 or less each time the standby unit waits. The value may be larger than T5.

According to the above configuration, depending on the situation, the standby time of the first reader / writer may be longer than the standby time of the second reader / writer. In this case, the priority of the first reader / writer is the second reader. It may be lower than the writer's priority. That is, the priority of the first reader / writer can be set weakly.

In the communication system according to one aspect of the present invention, in the above configuration, the first reader / writer has a fixed position of itself and communicates with an RFID tag passing through a communication area. The second reader / writer may be configured to communicate with an RFID tag that has not moved by moving itself.

In the above configuration, the first reader / writer needs to communicate with the moving RFID tag within a limited time. On the other hand, the second reader / writer only needs to communicate with the RFID tag that is not moving, and there is no time limit. Therefore, in such a system, it is possible to appropriately set a high priority for the first reader / writer, and it is possible to realize the granting of the communication right in a preferable state.

According to one aspect of the present invention, it is possible to set a priority for the reader / writer and perform communication with the wireless tag without inviting complication of the system.

It is a block diagram which shows the structure of the communication system 100 which concerns on this embodiment. It is a flowchart which shows the flow of communication processing with RFID tag 4 in R / W2 for gate and R / W3 for shelf management. When the standby time is set by the fixed method, the gate R / W2 and the shelf management R / W3 receive the communication instruction at the same timing, and the radio wave from another reader / writer is detected at that time. It is a timing chart which shows the communication sequence example. It is a timing chart which shows the example of the communication sequence when the radio wave is not emitted from the other reader / writer when the standby time is set by the fixed method. It is a timing chart which shows the example of another communication sequence when the radio wave is not emitted from another reader / writer when the standby time is set by the fixed method. When the standby time is set by a fixed method in which the standby time of the gate R / W2 is 0, the gate R / W2 and the shelf management R / W3 receive the communication instruction at the same timing, and at that time, the other It is a timing chart which shows the example of the communication sequence when the radio wave from the reader / writer of is detected. It is a timing chart which shows the example of the communication sequence in the case where the standby time is set by the fixed method which set the standby time of R / W2 for a gate to 0, and the radio wave is not emitted from another reader / writer. It is a timing chart which shows the other communication sequence example when the radio wave is not emitted from another reader / writer when the standby time is set by the fixed method. It is a timing chart which shows the example of the communication sequence in the case where the waiting time is set by a random method, and the radio wave is not emitted from another reader / writer. It is a figure which shows the waiting time setting example by variation of the waiting time setting method by a random method. It is a flowchart which shows the flow of the communication process with the RFID tag 4 in the gate R / W2 and the shelf management R / W3 when the standby process is performed after communication. This is a timing chart showing an example of a communication sequence when radio waves are not emitted from another reader / writer in the case of performing standby processing after communication.

Hereinafter, embodiments according to one aspect of the present invention (hereinafter, also referred to as “the present embodiment”) will be described with reference to the drawings. However, the embodiments described below are merely examples of the present invention in all respects. Needless to say, various improvements and modifications can be made without departing from the scope of the present invention.

§1 Application example (Communication system configuration)
First, an example of a situation in which the present invention is applied will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of a communication system 100 according to the present embodiment. As shown in the figure, the communication system 100 has a gate R / W (first reader / writer) 2 that reads and writes data to a plurality of RFID tags 4 and a shelf management R / W. It is equipped with W (second reader / writer) 3.

The gate R / W2 has a detection unit 27 that detects radio waves emitted when another reader / writer communicates with the RFID tag 4, and detects radio waves of the other reader / writer before communicating with the RFID tag 4 to be communicated with. Then, a standby unit 26 that waits for the start of communication with the RFID tag 4 for a predetermined standby time is provided.

Similarly, the shelf management R / W3 has a detection unit 37 that detects radio waves emitted when another reader / writer communicates with the RFID tag 4, and another reader / writer before communicating with the RFID tag 4 to be communicated with. When the radio wave is detected, the RFID tag 4 is provided with a standby unit 36 that waits for the start of communication with the RFID tag 4 within a predetermined standby time.

Here, the average value of the waiting time of the gate R / W2 is set shorter than the average value of the waiting time of the shelf management R / W3. As a result, it is possible to perform communication in a state where the priority of the gate R / W2 is higher than that of the shelf management R / W3.

The communication system 100 may be provided with three or more reader / writers whose priorities should be set, and the length of each standby time may be set to be shorter as the priority is higher.

§2 Configuration example The configuration of the communication system 100 will be described in more detail below. As shown in FIG. 1, the communication system 100 includes a gate R / W2, a shelf management R / W3, a PLC (Programmable Logic Controller) 1, which is a higher-level system that collectively manages a plurality of reader / writers, and a reader / writer. And an RFID (Radio Frequency Identifier) tag 4 on a carrier 5 and a shelf 6 for transmitting and receiving data. The PLC1 and the gate R / W2 and the shelf management R / W3 are communicated and connected via a communication network. Although not shown, the communication system 100 may include a reader / writer in addition to the gate R / W2 and the shelf management R / W3.

When the transport vehicle 5 passes through the gate, the gate R / W2 communicates with the RFID tag 4 attached to the product loaded on the transport vehicle 5. That is, the gate R / W2 has its own arrangement position fixed and communicates with the RFID tag 4 passing through the communication area. This makes it possible to recognize the products loaded on the automatic guided vehicle 5 that has passed through the gate.

The gate R / W2 includes an upper communication unit 21, an RF (Radio Frequency) communication unit 22, and an antenna 23. The upper communication unit 21 controls communication with the PLC 1, transmits an instruction from the PLC 1 to the RF communication unit 22, and transmits an output from the RF communication unit 22 to the PLC 1. The RF communication unit 22 controls communication of radio waves transmitted and received by the antenna 23. Here, since it is assumed that the RFID tag 4 as the communication target of the gate R / W2 is moving, real-time performance is required for wireless communication with the gate R / W2.

The standby unit 26 included in the RF communication unit 22 holds standby time information indicating the standby time. This waiting time information can be changed by an instruction from the outside. For example, the standby time information may be rewritten by an instruction from the PLC 1, or the standby time information may be rewritten by a PC or the like directly connected to the gate R / W2 by USB (Universal Serial Bus) or the like. Further, the gate R / W2 may include an input unit that receives input from the user, and the standby time information may be rewritten by this input unit (button, switch, touch panel, etc.).

The shelf management R / W 3 communicates with the RFID tag 4 attached to the product mounted on the shelf 6. That is, the shelf management R / W3 communicates with the RFID tag 4 that has not moved by moving itself by being transported by the user. This makes it possible to recognize what kind of product is placed on the shelf 6.

The shelf management R / W3 includes an upper communication unit 31, an RF communication unit 32, an antenna 33, and a trigger switch 34. The upper communication unit 31, the RF communication unit 32, and the antenna 33 have the same functions as the upper communication unit 21, the RF communication unit 22, and the antenna 23 described above. The trigger switch 34 accepts an operation by the user, and transmits an instruction to start communication with the ID tag 4 to the RF communication unit 32 at the timing operated by the user. The instruction to start the communication with the ID tag 4 may be received from the PLC1.

Here, since it is assumed that the RFID tag 4 as the communication target of the shelf management R / W3 is stationary, the wireless communication with the shelf management R / W3 is compared with the gate R / W2. Real-time performance is not required.

In FIG. 1, the transport vehicle 5 and the RFID tag 4 on the shelf 6 are shown by two each, but the present invention is not limited to this, and one or more RFID tags 4 may be used.

(Flow of communication processing)
FIG. 2 is a flowchart showing a flow of communication processing with the RFID tag 4 in the gate R / W2 and the shelf management R / W3. Since the basic communication processing flow is the same for the gate R / W2 and the shelf management R / W3, the gate R / W2 will be described here as an example.

First, in step 1 (hereinafter referred to as S1), when the higher-level communication unit 21 receives the signal indicating the reading instruction from the PLC 1, it transmits to that effect to the RF communication unit 22. In the case of the shelf management R / W3, the trigger switch 34 may transmit the operation input by the user as a reading instruction to the RF communication unit 22.

Next, in S2, the detection unit 27 in the RF communication unit 22 confirms whether or not the radio wave from another reader / writer is detected by the antenna 23 by the LBT (Listen Before Talk) function. YES in S2, that is, when the detection unit 27 detects a radio wave from another reader / writer, the standby unit 26 in the RF communication unit 22 performs a process of waiting for RF communication in a predetermined standby time (S3). When the standby process is completed, the process returns from S2.

On the other hand, when NO, that is, no radio wave from another reader / writer is detected in S2, the RF communication unit 22 starts RF communication and performs communication processing with the RFID tag 4 (S4).

In the above description, the case where the read instruction is received in S2 has been described, but the same process is performed in the case where the write instruction is received.

(Variation of waiting time setting)
Next, a variation of the waiting time setting will be described. The waiting time setting method for the gate R / W2 and the shelf management R / W3 can be roughly divided into a fixed method and a random method.

The fixed method is a method in which the standby time is set as a fixed value in each reader / writer. The standby time of the leader / writer with high priority, that is, the gate R / W2 is set to T1 (fixed value), and the standby time of the reader / writer with low priority, that is, the shelf management R / W3 is set to T2 (fixed value). Value), and T1 <T2.

The random method is a method in which each reader / writer sets a waiting time as a random value having a predetermined range each time a standby process occurs. The waiting time of the leader / writer with high priority, that is, the gate R / W2 is set to a random value in the range of T3 to T4, and the waiting time of the reader / writer with low priority, that is, the shelf management R / W3. Is set to a random value in the range of T5 to T6. Further, the average of the random values in the range of T3 to T4 is set to be shorter than the average of the random values in the range of T5 to T6. The above T3 may be 0. Further, either one of the gate R / W2 and the shelf management R / W3 may be a fixed method and the other may be a random method.

(Specific example of communication sequence by fixed method)
A specific example of the communication sequence with the RFID tag 4 in the gate R / W2 and the shelf management R / W3 when the standby time is set by the fixed method will be described below. In FIG. 3, when the standby time is set by the fixed method, the gate R / W2 and the shelf management R / W3 receive the communication instruction at the same timing, and at that time, radio waves from other reader / writers are detected. It is a timing chart which shows the example of the communication sequence when it is done.

In the gate R / W2 and the shelf management R / W3, LBT is performed at the time of receiving the communication instruction. Since radio waves from other reader / writers are detected in this LBT, standby processing is performed. In the gate R / W2, the standby process is performed during the period of T1, and then the LBT is performed again. At this point, radio waves from other reader / writers are not detected, so communication processing is performed after the end of LBT.

On the other hand, in the shelf management R / W3, LBT is performed at the time of receiving the communication instruction. Since radio waves from other reader / writers are detected in this LBT, standby processing is performed. In the shelf management R / W3, the standby process is performed in the period of T2, which is longer than that of T1, and then the LBT is performed again. At this point, since the communication process is being performed on the gate R / W2, the radio wave from the gate R / W2 is detected in the LBT. Therefore, the standby process is subsequently performed during the period of T2. After that, LBT is performed again, and at this point, radio waves from other reader / writers are not detected, so communication processing is performed after the end of LBT.

As described above, since the standby time of the gate R / W2 is set shorter than the standby time of the shelf management R / W3, the communication processing of the gate R / W2 is preferentially executed. I understand.

FIG. 4 is a timing chart showing an example of a communication sequence when a radio wave is not emitted from another reader / writer when the standby time is set by a fixed method.

In this example, the gate R / W2 first starts LBT. Since radio waves from other reader / writers are not detected in this LBT, the gate R / W2 starts the communication process. On the other hand, the shelf management R / W3 starts the LBT a little later than the gate R / W2, and detects the radio wave from the gate R / W2 in the middle of the LBT. Therefore, in the shelf management R / W3, the standby process is performed in the period of T2.

Then, in the gate R / W2, after the first communication process is completed, LBT is performed to perform the second communication process. Since radio waves from other reader / writers are not detected in this LBT, the gate R / W2 starts the second communication process. On the other hand, the shelf management R / W3 performs LBT again after the standby processing is completed, and detects radio waves from the gate R / W2 again in the middle of the LBT. Therefore, in the shelf management R / W3, the standby process is performed again in the period of T2. After that, LBT is performed again, and at this point, radio waves from other reader / writers are not detected, so communication processing is performed after the end of LBT.

As described above, it can be seen that the communication processing of the gate R / W2 is preferentially executed also in the example shown in FIG.

FIG. 5 is a timing chart showing an example of another communication sequence in the case where the standby time is set by the fixed method and the radio wave is not emitted from another reader / writer.

In this example, the shelf management R / W3 first starts LBT. Since radio waves from other reader / writers are not detected in this LBT, the shelf management R / W3 starts the communication process. On the other hand, the gate R / W2 starts the LBT a little later than the shelf management R / W3, and detects the radio wave from the shelf management R / W3 in the middle of the LBT. Therefore, in the gate R / W2, the standby process is performed during the period of T1.

After that, in the gate R / W2, the LBT is performed again after the standby process, and at this point, radio waves from other reader / writers are not detected, so that the communication process is performed after the end of the LBT.

On the other hand, in the shelf management R / W3, after the first communication process is completed, LBT is performed to perform the second communication process. In the middle of this LBT, the shelf management R / W3 detects radio waves from the gate R / W2. Therefore, in the shelf management R / W3, the standby process is performed in the period of T2. After that, LBT is performed again, and at this point, radio waves from other reader / writers are not detected, so communication processing is performed after the end of LBT.

As described above, in the example shown in FIG. 5, even if the shelf management R / W3 starts LBT first and performs communication processing, the gate R / W2 subsequently acquires the communication right. Communication processing is performed. This is because the standby time of the gate R / W2 is set shorter than the standby time of the shelf management R / W3, so that the probability of acquiring the communication right is increased. That is, even in the example shown in FIG. 5, it can be seen that the communication processing of the gate R / W2 is preferentially executed.

In FIG. 6, when the standby time is set by a fixed method in which the standby time of the gate R / W2 is 0, the gate R / W2 and the shelf management R / W3 receive the communication instruction at the same timing. It is a timing chart which shows the communication sequence example when the radio wave from another reader / writer is detected at that time.

In this example, the standby time of the gate R / W2 is set to 0. In the gate R / W2 and the shelf management R / W3, LBT is performed at the time of receiving the communication instruction. Since radio waves from other reader / writers are detected in this LBT, the LBT is continuously performed because the standby time is 0. At the time of the third LBT, radio waves from other reader / writers are no longer detected, so communication processing is performed after the end of the LBT.

On the other hand, in the shelf management R / W3, LBT is performed at the time of receiving the communication instruction. Since radio waves from other reader / writers are detected in this LBT, standby processing is performed. In the shelf management R / W3, the standby process is performed during the period of T2, and then the LBT is performed again. At this point, since the communication process is being performed on the gate R / W2, the radio wave from the gate R / W2 is detected in the LBT. Therefore, the standby process is subsequently performed during the period of T2. After that, LBT is performed again, and at this point, radio waves from other reader / writers are not detected, so communication processing is performed after the end of LBT.

As described above, it can be seen that even when the standby time of the gate R / W2 is set to 0, the communication processing of the gate R / W2 is preferentially executed.

FIG. 7 is a timing chart showing an example of a communication sequence when the standby time is set by a fixed method in which the standby time of the gate R / W2 is 0 and no radio wave is emitted from another reader / writer. ..

In this example, the shelf management R / W3 first starts LBT. Since radio waves from other reader / writers are not detected in this LBT, the shelf management R / W3 starts the communication process. On the other hand, the gate R / W2 starts the LBT a little later than the shelf management R / W3, and detects the radio wave from the shelf management R / W3 in the middle of the LBT. Therefore, in the gate R / W2, the LBT is continuously performed because the standby time is 0 during the period during which the communication processing by the shelf management R / W3 is performed.

After that, when the communication processing in the shelf management R / W3 is completed, radio waves from other reader / writers are not detected in the LBT in the gate R / W2, so that the communication processing is performed after the LBT is completed.

On the other hand, in the shelf management R / W3, after the first communication process is completed, LBT is performed to perform the second communication process. In the middle of this LBT, the shelf management R / W3 detects radio waves from the gate R / W2. Therefore, in the shelf management R / W3, the standby process is performed in the period of T2. After that, LBT is performed again, and at this point, radio waves from other reader / writers are not detected, so communication processing is performed after the end of LBT.

As described above, it can be seen that the communication processing of the gate R / W2 is preferentially executed also in the example shown in FIG.

When the standby time of the gate R / W2 is set to 0 and the gate R / W2 starts the LBT first as in FIG. 4, the communication sequence is the same as in FIG.

Here, a problem that occurs when the communication cycle TA of the gate R / W2 matches the standby time of the shelf management R / W3 will be described. FIG. 8 is a timing chart showing still another communication sequence example when radio waves are not emitted from other reader / writers when the standby time is set by the fixed method.

In this example, as described above, the communication cycle TA of the gate R / W2 coincides with the standby time of the shelf management R / W3. In this case, depending on the LBT start timing of the shelf management R / W3, the shelf management R / W3 cannot obtain the communication right forever. That is, as shown in FIG. 6, when the shelf management R / W3 performs LBT during the communication processing period of the gate R / W2, the standby processing is T2 by detecting the radio wave from the gate R / W2. It is done in a period. Here, since the standby time T2 coincides with the communication cycle TA, the LBT after the standby processing in the shelf management R / W3 overlaps with the timing of the next communication processing of the gate R / W2 every time. .. It should be noted that this phenomenon may occur when there is a leader / writer having a constant communication cycle regardless of the priority level, and the standby time in the other leader / writers matches the update cycle.

That is, when the standby time is set by the fixed method, there is a problem that the above phenomenon occurs depending on the situation. As a method for solving this problem, an example of setting the waiting time by a random method will be described below.

(Specific example of communication sequence by random method)
A specific example of the communication sequence with the RFID tag 4 in the gate R / W2 and the shelf management R / W3 when the standby time is set by a random method will be described below. FIG. 9 is a timing chart showing an example of a communication sequence when radio waves are not emitted from another reader / writer when the standby time is set by a random method.

In this example, when the shelf management R / W3 performs LBT during the communication processing period of the gate R / W2, the shelf management R / W3 performs standby processing by detecting radio waves from the gate R / W2. The time between T5 and T6 is randomly set as the time for this standby processing.

After that, the gate R / W2 performs a second communication process after the communication cycle TA. At the timing of this communication process, the shelf management R / W3 performs LBT after the standby process, and the standby process is performed again by detecting the radio wave of the gate R / W2. The time between T5 and T6 is randomly set as the time for this standby processing. After this standby process, the shelf management R / W3 performs LBT. At this timing, the gate R / W2 does not perform communication processing, so the shelf management R / W3 performs communication processing after LBT. On the other hand, the gate R / W2 performs LBT after the next communication cycle TA, and the standby process is performed by detecting the radio wave of the shelf management R / W3. The time between T3 and T4 is randomly set as the time for this standby processing.

As described above, when the standby time is set by the random method, the standby time of the shelf management R / W3 does not continue to match the communication cycle of the gate R / W2, so that the shelf management R / W3 is used. There is a possibility that communication rights will be given. That is, according to the random method, when there is a reader / writer with a constant communication cycle, it is possible to eliminate the risk that the communication right is not given to a specific reader / writer.

(Random method standby time setting variation)
Here, the range setting of the random value of the waiting time of the gate R / W2 and the shelf management R / W3 will be described. As described above, the waiting time of the gate R / W2 is set to a random value in the range of T3 to T4, and the waiting time of the shelf management R / W3 is set to a random value in the range of T5 to T6. .. In this case, there are three types of variations as a range setting method for both random values. In the random method 1, T4, which is the upper limit of the random value range of the waiting time of the gate R / W2, is smaller than T5, which is the lower limit of the random value range of the waiting time of the shelf management R / W3 (T4 < This is the T5) method. The random method 2 is a method in which T4 and T5 are equal (T4 = T5). The random method 3 is a method in which T4 is larger than T5 (T4> T5).

In the case of the random method 1, the standby time of the gate R / W2 is always shorter than the standby time of the shelf management R / W3, so that the priority of the gate R / W2 can be surely increased. In the case of the random method 2, the waiting time of the gate R / W2 and the waiting time of the shelf management R / W3 may be equal depending on the situation. That is, when the waiting times are the same for both, the priority is the same for the gate R / W2 and the shelf management R / W3. In the case of the random method 3, the waiting time of the gate R / W2 may be longer than the waiting time of the shelf management R / W3 depending on the situation. That is, when the standby time of the gate R / W2 is longer than the standby time of the shelf management R / W3, the priority of the gate R / W2 is lower than the priority of the shelf management R / W3. May become. However, as described above, since the average of the random values in the range of T3 to T4 is set to be shorter than the average of the random values in the range of T5 to T6, any of the random methods 1 to 3 Even so, on average, the gate R / W2 has a higher priority than the shelf management R / W3.

FIG. 10 is a diagram showing an example of waiting time setting according to a variation of the waiting time setting method by the random method. (A) of the figure shows an example in which the standby time of the gate R / W2 is shorter than the standby time of the shelf management R / W3 in the case of the random method 1. (B) of the figure shows an example in which the standby time of the gate R / W2 and the standby time of the shelf management R / W3 are equal in the case of the random method 2. FIG. 3C of the figure shows an example in which the standby time of the gate R / W2 is longer than the standby time of the shelf management R / W3 in the case of the random method 3.

(Example of performing standby processing after communication processing)
Next, an example in which the standby process is performed after the communication process is performed will be described. FIG. 11 is a flowchart showing the flow of communication processing with the RFID tag 4 in the gate R / W2 and the shelf management R / W3 when the standby processing is performed after communication. Since the basic communication processing flow is the same for the gate R / W2 and the shelf management R / W3, the gate R / W2 will be described here as an example.

Since the processing of S11 to S14 is the same as the processing of S1 to S4 in the above-mentioned explanation regarding the flowchart shown in FIG. 2, the description thereof will be omitted. When the communication process in S14 is completed, the standby unit 26 in the RF communication unit 22 performs the post-communication standby process in S15. The standby processing after the communication processing may be started at the end of the communication period secured in the communication processing, or may be at the time when the necessary communication processing is completed before the end of the communication period. Good.

FIG. 12 is a timing chart showing an example of a communication sequence when radio waves are not emitted from another reader / writer in the case of performing standby processing after communication.

In this example, the shelf management R / W3 first starts LBT. Since radio waves from other reader / writers are not detected in this LBT, the shelf management R / W3 starts the communication process. Further, the shelf management R / W3 performs a standby process after the communication process is completed. On the other hand, the gate R / W2 starts the LBT a little later than the shelf management R / W3, and detects the radio wave from the shelf management R / W3 in the middle of the LBT. Therefore, in the gate R / W2, the standby process is performed.

After that, in the gate R / W2, the LBT is performed again after the standby process, and at this point, radio waves from other reader / writers are not detected, so that the communication process is performed after the end of the LBT.

On the other hand, in the shelf management R / W3, after the first communication process is completed and the standby process is completed, LBT is performed to perform the second communication process. In the middle of this LBT, the shelf management R / W3 detects radio waves from the gate R / W2. Therefore, in the shelf management R / W3, the standby process is performed. After that, LBT is performed again, and at this point, radio waves from other reader / writers are not detected, so communication processing is performed after the end of LBT.

As described above, since the standby processing is performed after the communication processing, there is a possibility that another reader / writer may acquire the communication right during this standby processing period. Therefore, it is possible to reduce the possibility that a specific reader / writer keeps securing the communication right.

Further, the waiting time of the standby processing after the communication processing may be set to be shorter as the priority of the reader / writer is higher. Specifically, the average value of the waiting time of the standby processing after the communication processing in the gate R / W2 is set shorter than the average value of the waiting time of the waiting processing after the communication processing in the shelf management R / W3. May be good. In this case, the possibility that the gate R / W2 acquires the communication right can be further increased. Further, similarly to the waiting time after the LBT described above, the waiting time of the waiting processing after the communication processing may be set as a fixed value or a random value.

The standby processing time after LBT may be set equally for each reader / writer, while the standby processing time after communication processing may be set to be shorter as the priority of the reader / writer is higher. This also increases the possibility that the leader / writer with high priority acquires the communication right.

[Example of realization by software]
The control blocks of the gate R / W2 and the shelf management R / W3 (particularly, the upper communication unit 21, the RF communication unit 22, the upper communication unit 31, and the RF communication unit 32) are formed in an integrated circuit (IC chip) or the like. It may be realized by a logic circuit (hardware) or by software.

In the latter case, the gate R / W2 and the shelf management R / W3 include a computer that executes program instructions that are software that realizes each function. The computer includes, for example, one or more processors and a computer-readable recording medium that stores the program. Then, in the computer, the object of the present invention is achieved by the processor reading the program from the recording medium and executing the program. As the processor, for example, a CPU (Central Processing Unit) can be used. As the recording medium, in addition to a “non-temporary tangible medium” such as a ROM (Read Only Memory), a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like can be used. Further, a RAM (Random Access Memory) or the like for expanding the program may be further provided. Further, the program may be supplied to the computer via an arbitrary transmission medium (communication network, broadcast wave, etc.) capable of transmitting the program. It should be noted that one aspect of the present invention can also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

1 PLC
R / W for 2 gates (1st reader / writer)
3 R / W for shelf management (second reader / writer)
4 RFID tag 5 Transport vehicle 21, 31 Upper communication unit 22, 32 RF communication unit 23, 33 Antenna 26, 36 Standby unit 27, 37 Detection unit 34 Trigger switch 100 Communication system

Claims (9)

A communication system including a plurality of readers / writers that read or write data to a plurality of RFID tags.
Each leader / writer
A detector that detects radio waves emitted when other reader / writers communicate with RFID tags,
When the radio wave of another reader / writer is detected before communicating with the RFID tag to be communicated, the process of waiting for the start of communication with the RFID tag to be communicated with a predetermined standby time, and
It is provided with a standby unit that performs at least one of the processes of waiting for a predetermined standby time after the communication process with the RFID tag to be communicated is completed.
A communication system in which the average value of the standby time of the first reader / writer is set shorter than the average value of the standby time of the second reader / writer among the plurality of reader / writers. The communication system according to claim 1, wherein the standby unit of the first reader / writer has a standby time of 0. The communication system according to claim 1, wherein the standby unit of the first reader / writer randomly determines a standby time from a range of T3 or more and T4 or less each time it waits. The communication system according to any one of claims 1 to 3, wherein the standby unit of the second reader / writer randomly determines a standby time from a range of T5 or more and T6 or less each time it waits. The communication according to claim 3, wherein the standby unit of the second reader / writer randomly determines a standby time from a range of T5 or more and T6 or less each time the standby unit waits, and the T4 is a value smaller than the T5. system. The communication system according to claim 3, wherein the standby unit of the second reader / writer randomly determines a standby time from a range of T5 or more and T6 or less each time it waits, and the T4 is a value equal to the T5. .. The communication according to claim 3, wherein the standby unit of the second reader / writer randomly determines a standby time from a range of T5 or more and T6 or less each time the standby unit waits, and the T4 is a value larger than the T5. system. The first reader / writer has a fixed position of itself and communicates with an RFID tag passing through a communication area.
The communication system according to any one of claims 1 to 7, wherein the second reader / writer communicates with an RFID tag that has not moved by moving itself. A communication method in a communication system including a plurality of readers / writers that read or write data to a plurality of RFID tags.
Each leader / writer
A detection step that detects radio waves emitted when other reader / writers communicate with RFID tags,
When the radio wave of another reader / writer is detected before communicating with the RFID tag to be communicated, the process of waiting for the start of communication with the RFID tag to be communicated with a predetermined standby time, and
Includes a standby step of performing at least one of the processes of waiting for a predetermined standby time after the communication process with the RFID tag to be communicated is completed.
A communication method in a communication system in which the average value of the standby time of the first reader / writer is set shorter than the average value of the standby time of the second reader / writer among the plurality of reader / writers.

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