Radio communication device and radio communication method

An embodiment of the present invention relates to a wireless communication device and a wireless communication method for transmitting an inquiry signal to a wireless tag and receiving a response signal.

By providing an antenna and performing wireless communication using radio waves with a wireless tag existing in the communication area of this antenna, it is possible to read data from the memory mounted on the wireless tag and write data to the memory. Wireless communication devices have been developed and put into practical use. Such wireless tags are called RFID (Radio Frequency Identification) and the like. Further, the wireless communication device is called an RFID reader or the like.

As an example of a wireless communication device, a carrier wave of a predetermined frequency is transmitted to a wireless tag to activate the wireless tag, an inquiry signal is transmitted to the activated wireless tag, and a response signal from the wireless tag is received to form the wireless tag. Those configured to read are known. The wireless tag that communicates with this type of wireless communication device returns a response signal having the same frequency as the carrier wave from the wireless communication device by so-called backscatter modulation.

Wireless tags and wireless communication devices having such functions are used in various fields such as goods management in the logistics industry. In recent years, in stores that sell various products, a wireless tag is attached to the products in the store, and the payment process can be performed by reading the wireless tag attached to the product at the time of payment at the cash register. There is also an example of introducing a product sales system.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2000-20651</text></patcit></p>

<p> In a system in which a plurality of wireless communication devices are arranged, a wireless tag that should be read by only one wireless communication device may be read by the plurality of wireless communication devices at the same time.</p><p> In such a case, each wireless communication device performs processing using the information read from the wireless tag, which causes a problem. For example, in the above-mentioned product sales system, when the wireless tag attached to the product carried to a certain cash register is read not only by the wireless communication device arranged at the cash register but also by the wireless communication device of the adjacent cash register, both of them. One item may be sold at the cash register.</p><p> From the above circumstances, when a plurality of wireless communication devices are arranged close to each other and used, it is necessary to take measures to prevent the same wireless tag from being read by the plurality of wireless communication devices at the same time.</p>

<p> In order to solve the above problems, the wireless communication device according to the embodiment includes a transmission / reception means for transmitting an inquiry signal to the wireless tag and a response signal returned from the wireless tag, and an inquiry signal transmitted by the transmission / reception means. A preamble detecting means that detects a preamble included in a response signal returned by a radio tag that has received the inquiry signal within a time range set with reference to the transmission timing, and a preamble detecting means that detects the preamble of the response signal. The data detection means for detecting the data indicated by the response signal and the response time from when the transmission / reception means receives the response signal from the radio tag until the next inquiry signal is transmitted to the radio tag are set as parameters unique to the device. It is provided with a response time setting means for setting according to the situation.</p><p> Further, the wireless communication method in one embodiment is a method of communicating with the wireless tag by a wireless communication device having a transmitting / receiving means for transmitting an inquiry signal to the wireless tag and receiving a response signal returned from the wireless tag. Using the step of setting the response time from when the means receives the response signal from the wireless tag to the transmission of the next inquiry signal to the wireless tag according to the parameter peculiar to the device, and the set response time. A step of transmitting an inquiry signal and receiving a response signal by the transmission / reception means, a step of detecting a preamble included in the response signal received by the transmission / reception means within a time range set based on the transmission timing of the inquiry signal, and a preamble. When this is done, it includes a step of detecting the data indicated by the response signal.</p>

<figref num="1">The figure for demonstrating the command sequence of wireless tag reading in C1G2 (Class 1 Generation 2).</figref><figref num="2">The block diagram which shows the main part structure of the reader in one Embodiment.</figref><figref num="3">The block diagram for demonstrating the detection of the preamble in one embodiment.</figref><figref num="4">The figure for demonstrating the response time in C1G2.</figref><figref num="5">The figure which shows the preamble which is added to the beginning of the Query command in C1G2.</figref><figref num="6">The figure which shows the relationship between FT (Frequency Tolerance) and other parameters in C1G2.</figref><figref num="7">The figure for demonstrating the comparison start time Ts and the comparison end time Te in one Embodiment.</figref><figref num="8">The schematic diagram which shows the data structure of the conversion table in one Embodiment.</figref><figref num="9">The figure which shows an example of the conversion table in one Embodiment.</figref><figref num="10">The flowchart which shows the operation of the response time setting part in one Embodiment.</figref><figref num="11">The figure for demonstrating the operation in the same embodiment.</figref><figref num="12">The figure for demonstrating the operation in the same embodiment.</figref><figref num="13">The figure which shows the communication sequence in the state shown in FIG.</figref><figref num="14">The figure which shows the communication sequence in the state shown in FIG.</figref>

Hereinafter, one embodiment will be described. In the embodiment described below, the C1G2 (Class 1 Generation 2) type, which is a standard protocol for UHF band (950MHz band) RFID proposed by EPC (Electronic Product Code) Global, which is an RFID tag standardization organization, is used. An example of a wireless communication device that communicates with a wireless tag using a communication method.

[Communication in C1G2] First, the outline of communication in C1G2 will be described. In C1G2, reading of wireless tags is realized by a command sequence called Inventory Tags. Inventory Tags consists of a Select command that selects communication tags, a Query, Query Rep, Query Adjust command that performs anti-collision (collision avoidance) processing, and an ACK command that acquires (requests) tag data after anti-collision processing. Realize a command sequence to acquire tag data by combining the commands of.

Figure 1 shows how tag data is acquired by the Inventory Tags command sequence. The tag data acquired here is called an EPC code. The wireless communication device transmits an unmodulated carrier (CW) from the antenna, and receives the unmodulated carrier to activate the wireless tag. When the wireless tag to be communicated is specified after the activation, the Select command is transmitted from the wireless communication device. However, in this embodiment, the Select command is not used.

That is, the wireless communication device first transmits a Query command. Upon receiving this Query command, the wireless tag backscatter-modulates the unmodulated carrier when a predetermined response time T1 elapses from the completion of receiving the command, and returns a random number called RN16. The wireless communication device that has received this RN16 transmits an ACK command with the RN16 as an argument after the response time T2 has elapsed from the completion of the reception of the RN16. If the RN16 transmitted by itself matches the RN16 of the ACK command, the radio tag that received this ACK command backscatter-modulates the unmodulated carrier when the response time T1 elapses from the completion of receiving the command to the PC. It returns header information called (Protocol Control), which indicates the length of data, an EPC code, and CRC16 (Cyclic Redundancy Check 16) for detecting communication errors. If the PC + EPC + CRC16 returned in this way is received and the CRC check result is normal, the wireless communication device queries when the response time T2 has elapsed from the completion of receiving the PC + EPC + CRC16. Send the Rep command. On the other hand, if the EPC code cannot be obtained normally, such as when the CRC check result is abnormal, the NAK command is sent when the response time T2 has elapsed since the reception of PC + EPC + CRC16 was completed.

[leader] Next, a reader 1 that functions as a wireless communication device in this embodiment will be described. The reader 1 and the wireless tags read by the reader 1 communicate with each other according to C1G2.

FIG. 2 is a block diagram showing a main configuration of the reader 1. The reader 1 is a control unit 2 composed of a CPU (Central Processing Unit), a memory, a timer 2a, etc., a directional coupler 3, a low-pass filter (LPF) 4, an antenna 5, and a command for a wireless tag ( It includes a transmission system circuit used for transmitting an inquiry signal) and an unmodulated carrier, and a reception system circuit used for receiving a response signal from a wireless tag. Further, the control unit 2 includes, for example, a frequency setting unit 2b realized by information processing using software. The frequency setting unit 2b sets the frequency channel used by the reader 1 for communication with the wireless tag based on the information input by the operation of the operation means (not shown) or the information input from the host device. The frequency channel of the reader 1 is set to a frequency channel different from the frequency channel used by other wireless communication devices operating in the surroundings.

The transmission system circuit sets the response time from the PLL (Phase Locked Loop) section 11, the response time setting section 12, the conversion table 13, and the control section 2 that output the local carrier signal of the frequency set by the frequency setting section 2b. The coding unit 14 that encodes the transmission signal output through the unit 12, the amplitude modulator 15 that performs the amplitude modulation of the encoded transmission signal, and the unnecessary components are removed from the modulated transmission signal. It is composed of a bandpass filter (BPF) 16 and a power amplifier (PA) 17 that amplifies the transmission signal that has passed through the bandpass filter 16 and supplies it to the directional coupler 3.

When the unmodulated carrier is transmitted to the wireless tag by this transmission system circuit, the local carrier signal output from the PLL section 11 is encoded to a high level by the coding section 14, and the amplitude is set to the maximum level by the amplitude modulator 15. Then, after removing unnecessary components with the bandpass filter 16, the power amplifier 17 amplifies the components. The output of the power amplifier 17 is supplied to the low-pass filter 4 via the directional coupler 3, is supplied to the antenna 5 after removing unnecessary high-frequency components, and is transmitted as an unmodulated carrier.

When a command such as Query or ACK is transmitted to the wireless tag by the transmission circuit, the control unit 2 outputs the bit data of the command with the local carrier signal output from the PLL unit 11, and the coding unit. Encode with FM0 code at 14. The coded signal is amplified to a predetermined amplitude by the amplitude modulator 15, unnecessary components are removed by the bandpass filter 16, and then amplified by the power amplifier 17. The output of the power amplifier 17 is supplied to the low-pass filter 4 via the directional coupler 3, is supplied to the antenna 5 after removing unnecessary high-frequency components, and is transmitted as a command. The FM0 sign inverts the level from "H" to "L" or "L" to "H" at the center of 1 bit when representing "0", and sets the level within 1 bit when representing "1". It is a method that keeps it constant, does not change it, and inverts the level when switching from one bit to the next. However, other coding methods such as Manchester code may be adopted instead of the FM0 symbol. The response time setting unit 12 sets the response time T2 using the parameters unique to the reader 1, and the details will be described later.

The receiving system circuit is binarized with a 90-degree phase shifter 21 that shifts the phase of the local carrier signal from the PLL section 11 by 90 degrees, a mixer 22 (22I, 23Q), and a low-pass filter 23 (23I, 23Q). It is composed of a circuit 24 (24I, 24Q) and a signal processing unit 25 (25I, 25Q), and performs reception processing by a direct conversion system that directly removes carrier components. Further, each signal processing unit 25 includes a sampling unit 31 (31I, 31Q), a detection time setting unit 32 (32I, 32Q), a preamble detection unit 33 (33I, 33Q), and a decoding unit 34 (34I, 34Q). And an error detection unit 35 (35I, 35Q).

The local carrier signal from the PLL section 11 is supplied to the mixer 22I as it is, and the local carrier signal after the phase is shifted by 90 degrees by the 90-degree phase shifter 21 is supplied to the mixer 22Q.

The reception process by the reception system circuit will be described. When the wireless tag receives the command transmitted by the transmission system circuit, it backscatter-modulates the unmodulated carrier and returns a response signal. When this response signal is received by the antenna 5, the received signal corresponding to the response signal is output from the antenna 5. This received signal is supplied to the low-pass filter 4, and after removing unnecessary high-frequency components contained in the signal, it is supplied to the mixers 22I and 22Q via the directional coupler 3.

In the mixer 22I, the local carrier signal supplied from the PLL section 11 and the received signal supplied from the directional coupler 3 are mixed to generate an I signal having a common mode component with the local carrier signal. This I signal is supplied to the low-pass filter 23I, and after removing unnecessary high-frequency components, it is binarized by the binarization circuit 24I and supplied to the signal processing unit 25I.

On the other hand, in the mixer 22Q, the local carrier signal supplied from the 90-degree phase shifter 21 and the received signal supplied from the directional coupler 3 are mixed to generate a local carrier signal and a Q signal having an orthogonal component. This Q signal is supplied to the low-pass filter 23Q, and after removing unnecessary high-frequency components, it is binarized by the binarization circuit 24Q and supplied to the signal processing unit 25Q.

The sampling unit 31I samples the received signal with a clock synchronized with the I signal supplied from the binarization circuit 24I to generate bit data. The detection time setting unit 32I is set with a time window based on the transmission timing of the command transmitted immediately before. The preamble detection unit 33I detects the preamble added to the beginning of the response signal from the wireless tag from the bit data generated by the sampling unit 31I within the time window range set in the detection time setting unit 32I. The decoding unit 34I decodes the portion of the bit data generated by the sampling unit 31I following the preamble in response to the detection of the preamble by the preamble detection unit 33I, and shows the final digital response signal from the wireless tag. Generates data and outputs it to control unit 2 and error detection unit 35I. In this decoding, when the continuous bit data is "0,0" or "1,1", it is decoded as data "1", and when the continuous bit data is "1,0" or "0,1". Decrypt as data "0". If the preamble detection unit 33I does not detect the preamble, the error detection unit 35I notifies the control unit 2 of the preamble detection error.

The detection of the preamble by the preamble detection unit 33I will be described with reference to the block diagram of FIG. The preamble detection unit 33I stores in the determination data setting unit 330 that stores the preamble pattern defined by C1G2, the shift register 331 that sequentially stores the bit data sampled by the sampling unit 31I, and the determination data setting unit 330. It is equipped with a comparator 332 that compares the preamble pattern and the bit data stored in the shift register 331. Further, the detection time setting unit 32I stores the comparison start time Ts and the comparison end time Te. The comparison start time Ts is the time from when the last bit of a command such as Query or ACK is output from the control unit 2 to the transmission system circuit until the comparison by the comparator is started. Further, the comparison end time Te is the time from when the last bit of the command such as Query or ACK is output from the control unit 2 to the transmission system circuit until the comparison by the comparator is completed. That is, the difference between the comparison end time Te and the comparison start time Ts is the time window.

The control unit 2 outputs the last bit of a command such as Query or ACK to the transmission system circuit, then starts the time measurement by the timer 2a, and starts the comparison in which the measurement time of the timer 2a is set in the detection time setting unit 32I. When the time Ts is reached, the comparison start signal is output to the comparator 332, and then when the measurement time of the timer 2a reaches the comparison end time Te set in the detection time setting unit 32I, the comparison end signal is output to the comparator 332. To do. The comparator 332 has, for example, the same number of bits as the preamble pattern stored in the determination data setting unit 330 in response to the input of the comparison start signal and the bit data stored in the shift register 331 from the beginning. The comparison with the data is started, and the comparison is ended when the comparison start signal is input. Further, when the comparator 332 detects a pattern in which the preamble matches the preamble pattern stored in the determination data setting unit 330 during the comparison, the comparator 332 outputs the preamble detection signal to the decoding unit 34I. The decoding unit 34I decodes the bit data following the preamble as described above in response to the input of this preamble detection signal. The decoded bit data is output to the control unit 2.

On the other hand, if the preamble is not detected when the comparison end time Te has elapsed, the error detection unit 35I notifies the control unit 2 of the preamble detection error as described above.

Since the processing by the signal processing unit 25Q using the Q signal is the same as the processing by the signal processing unit 25I using the I signal, the description thereof will be omitted. The control unit 2 performs processing such as outputting one of the data output from the signal processing units 25I and 25Q with good accuracy to a higher-level device (not shown).

[Response time T1, T2] Next, the response times T1 and T2 will be described. In C1G2, response times T1 and T2 are defined as shown in Fig. 4.

The response time T1 is the time from when the wireless tag receives the command from the reader 1 to when the wireless tag returns the response signal as described above. Specifically, it is the time from the rise of the last bit of the command when the above command is received to the rise of the first bit when the response signal is returned to the command, and the value is given by the following equation (1). Determined within the range shown.

T1min T1 T1 max ... (1) Here, the minimum value T1min and the maximum value T1max of the response time T1 are defined by the following equations (2) and (3).

T1min = MAX (RTcal, 10Tpri) × (1-FT)-2μsec ... (2) T1max = MAX (RTcal, 10Tpri) × (1 + FT) + 2μsec ... (3) Here, RTcal (Interrogator-to-Tag calibration symbol) is a value that determines the communication speed from the wireless tag to reader 1, and is included in the preamble added to the beginning of the Query command as shown in Fig. 5. Defined. The illustrated preamble is bit data indicating a command-to-command delimiter, bit data indicating the time interval Tari (Type a reference interval) of the data symbol 0, and a wireless tag to reader 1. It is composed of bit data indicating the above RTcal, which is a value for determining the communication speed, and bit data indicating TRcal (Tag-to-Interrogator calibration symbol), which is a value for determining the communication speed from the wireless tag to the reader 1. .. Also, FT (Frequency) Tolerance) is the fluctuation (frequency tolerance) of the backscatter modulation of the radio tag, and is determined based on the correspondence shown in FIG. 6 defined by C1G2. The illustrated table shows the division ratio DR (Divide Ratio), TRcal, radio tag response frequency LF (Link Frequency), the frequency tolerance FT at the rated temperature (nominal temp), and the frequency at the extended temp. Correspondence between tolerance FT and frequency variation during backscatter modulation is defined. The division ratio DR is the ratio of the above TRcal to the response period Tpri (Backscatter-link pulse-repetition interval) indicating the response time of 1 bit (DR = TRcal / Tpri), which is 64/3 and 8. Set to either. The response frequency LF is the reciprocal of the response period Tpri (LF = 1 / Tpri). Normally, FT at the rated temperature may be used for the calculation of equations (2) and (3).

In this embodiment, it is assumed that RTcal and Tpri are predetermined as fixed values. That is, the values of T1min and T1max represented by the equations (2) and (3) are known.

[Comparison start time Ts, comparison end time Te] Next, the comparison start time Ts and the comparison end time Te will be described with reference to FIG. 7. In the present embodiment, the preamble added to the beginning of the response signal from the wireless tag shall be represented by 18 symbols of "0000000000001010V1". The top 12 "0" s are pilot tones, and the "1010V1" following this pilot tone is bit data for preamble detection. Note that "V" is a bit that does not follow the FM0 sign rule and is used only in the preamble. When this preamble is encoded with the FM0 code, it becomes the bit data of "101010101010101010101010110100100011". Of this bit data, "110100100011" corresponding to the bit data for preamble detection is stored in the determination data setting unit 330. Further, in the sampling units 31I and 31Q, the binarized I signal and Q signal are sampled at 0.5 Tpri, bit data is generated, and the bit data is sequentially stored in the shift register 331 of the preamble detection units 33I and 33Q, respectively. To.

In this case, if the radio tag returns a response signal with the shortest response time T1 in the range of equation (1), that is, T1min, after the last bit of the command requesting the response signal is output to the transmission system circuit. , The preamble of the response signal starts to be stored in the shift register 331 of the preamble detection units 33I and 33Q when the response time T1min elapses, and then when 18 × Tpri elapses, the bit data of the preamble to each shift register 331. Will be stored. If the radio tag returns a response signal with the longest response time T1 in the range of equation (1), that is, T1max, after the last bit of the command requesting the response signal is output to the transmission system circuit, The preamble of the response signal starts to be stored in the shift register 331 of the preamble detectors 33I and 33Q when the response time T1max elapses, and when 18 × Tpri elapses thereafter, the bit data of the preamble to each shift register 331 is stored. The storage will be completed.

That is, when the response time T1 fluctuates within the range of the equation (1), in order to reliably detect the preamble of the response signal from the radio tag, the comparison start time Ts and the comparison end time Te are set to the following equation (4). ) Must be set to the value shown in (5).

Ts = T1min + 18 × Tpri ... (4) Te = T1max + 18 × Tpri ... (5) From equations (4) and (5), the difference between the comparison end time Te and the comparison start time Ts, that is, the time window Δt for comparing the preambles is expressed by the following equation (6). Δt = T1max-T1min ... (6) The time window Δt represented by the equation (6) is used to set the response time T2, the details of which will be described later.

[Response time T2 setting] Next, the setting of the response time T2 performed by the response time setting unit 12 will be described. In this embodiment, a case where the frequency channel set by the frequency setting unit 2b is used as a parameter peculiar to the reader 1 is illustrated.

The response time T2 is set within the range of the following equation (7).

T2min T2 T2max ... (7) Here, as can be seen from FIG. 4, the minimum value T2min and the maximum value T2max of the response time T2 in C1G2 are expressed by the following equations (8) and (9). T2min = 3 × Tpri ... (8) T2max = 20 × Tpri ... (9) The response time T2 is set within the range represented by these equations (7) to (9).

Further, the response time setting unit 12 in the present embodiment changes the response time T2 according to the frequency set by the frequency setting unit 2b.

The correspondence between the frequency set by the frequency setting unit 2b and the response time T2 to be set by the response time setting unit 12 is described in the conversion table 13. FIG. 8 is a schematic diagram showing the data structure of the conversion table 13. As can be seen from equations (7) to (9), the permissible range of the response time T2 changes depending on the value of the response period Tpri. Therefore, in the present embodiment, the conversion table 13 is prepared for each value of the response cycle Tpri. In this way, the response time T2 can be selected so as not to deviate from the permissible range defined by C1G2 even when the response cycle Tpri is changed.

Each conversion table 13 is configured by describing the center frequency and response time T2 of each channel for each frequency channel (No. 1 to n) set by the frequency setting unit 2b. The center frequency is a reference value of the frequency used in each frequency channel. Further, the response time T2 is described as a unique value in each conversion table 13 within the range satisfying the equations (7) to (9).

Here, the difference between each response time T2 described in each conversion table 13 and other response times T2 described in the same table (hereinafter referred to as discrete intervals) is at least the time represented by the equation (6). Set larger than the window Δt (discrete interval&gt; Δt).

FIG. 9 shows an example of the conversion table 13 in which specific numerical values are described. In this conversion table 13, RTcal = 75 μsec, the response cycle of the wireless tag Tpri = 25 μsec, and all 9 channels defined at 0.2 MHz intervals between the UHF band frequencies 952.2 MHz and 953.8 MHz as the frequency channels used by the reader 1 are included. This is an example when it is prepared. In this case, the permissible range of the response time T2 is 75 μsec to 500 μsec according to the equations (7) to (9), and the time window Δt is 24 μsec according to the equation (6). In consideration of this, the response time T2 corresponding to each frequency channel is set in the range of 75 μsec to 500 μsec with the discrete interval set to 25 μsec, which is larger than 24 μsec.

Next, the operation of the response time setting unit 12 will be described. The response time setting unit 12 operates according to the flowchart shown in FIG. 10 and sets the response time T2. This operation is started, for example, when the frequency used by the reader 1 for communication is changed by the frequency setting unit 2b.

At the initial stage of starting the response time T2 setting process, the response time setting unit 12 first accesses the memory of the control unit 2 to acquire information indicating the frequency channel set by the frequency setting unit 2b (step S1). Further, the response time setting unit 12 accesses and acquires the information indicating the response cycle Tpri currently used by the reader 1 by accessing the memory of the control unit 2 (step S2).

Next, the response time setting unit 12 refers to the conversion table 13 corresponding to the response cycle Tpri indicated by the information acquired in step S2, and sets the response time T2 associated with the frequency channel acquired in step S1. Get (step S3).

Then, the response time setting unit 12 sets the response time T2 acquired in step S3 as the response time T2 to be used in the subsequent communication (step S4). Specifically, the response time T2 acquired in step S3 is stored in the storage area for setting the response time T2 provided in the memory of the control unit 2.

Step S4 completes a series of processes related to the setting of response time T2. After this series of processing is performed, the control unit 2 communicates with the wireless tag using the response time T2 set in step S4. That is, when the last bit of RN16 or PC + RPC + CRC16 is received from the wireless tag, the set response time T2 is measured by the timer 2a, and then the first bit of the command such as ACK or Query Rep is transmitted. Output to the circuit.

In this way, the response time setting unit 12 selects one corresponding to the frequency channel currently used by the reader 1 from the plurality of time widths described in the conversion table 13, and selects the selected time width. Set as the response time T2 used for subsequent communication.

[Action] The operation of the above configuration will be described. Here, as shown in FIGS. 11 and 12, the case where the two readers 1A and 1B are arranged close to each other will be illustrated. In the figure, 100A indicates the range reached by the Query command and ACK command transmitted from the antenna 5A of the reader 1A, and 100B indicates the range reached by the Query command and the ACK command transmitted from the antenna 5B of the reader 1B. .. The placement positions of the antennas 5A and 5B are adjusted so that these ranges 100A and 100B do not overlap. The frequency channels used by the readers 1A and 1B are set to have center frequencies of 952.2 MHz and 952.4 MHz, respectively, and are fixed at RTcal = 75 μsec and Tpri = 25 μsec.

Figure 11 shows the case where only reader 1A is operating. At this time, since the Query command and the ACK command transmitted from the antenna 5A do not reach the wireless tag 200 located outside the range 100A, the reader 1A does not read the wireless tag 200.

On the other hand, FIG. 12 illustrates a case where both readers 1A and 1B are in operation. At this time, if the wireless tag 200 is located within the range 100B, the query command and the ACK command transmitted from the antenna 5B reach the wireless tag 200, so that the reader 1B can read the wireless tag 200.

However, since the unmodulated carrier amplifies the amplitude to the maximum level and transmits it as described above, the unmodulated carrier from the reader 1A may reach the wireless tag 200 in the state of FIG. In this case, when the wireless tag 200 receives a command from the reader 1B, it backscatter-modulates the unmodulated carriers of both the readers 1A and 1B and transmits a 952.2 MHz response signal and a 952.4 MHz response signal. Become. At this time, as shown in FIG. 13, when the timing when the reader 1A outputs the bit of the Query command to its own transmission system circuit and the timing when the reader 1B outputs the bit of the Query command to its own transmission system circuit coincide with each other. , The RN16 (952.4MHz) returned by the wireless tag 200 can be received by the reader 1B, and the RN16 (952.2MHz) can also be received by the reader 1A.

Here, assuming that the response times T2 are the same for both readers 1A and 1B for 100 μsec, the readers 1A and 1B transmit the ACK command when 100 μsec has elapsed from the time when RN16 has been received. Of these, only the ACK command transmitted from the reader 1B reaches the wireless tag 200. When the wireless tag 200 receives the ACK command from the reader 1B, it backscatter-modulates the unmodulated carriers of both the readers 1A and 1B and returns the tag data of the EPC or the like. In this way, the tag data (952.4 MHz) returned by the wireless tag 200 can be received by the reader 1B, and the tag data (952.2 MHz) can also be received by the reader 1A. That is, the wireless tag 200, which should not be read by the reader 1A, may be read by the reader 1A.

On the other hand, in the present embodiment, the response time T2 is variably set according to the frequency channel. That is, assuming that the conversion table 13 shown in FIG. 9 is used, the response time setting unit 12 of the reader 1A sets the response time T2 of the reader 1A to 100 μsec, and the response time setting unit 12 of the reader 1B sets the response time of the reader 1B. Set T2 to 125 μsec. In this case, the reader 1A waits 100 μsec after receiving the RN16 and sends the ACK command, and the reader 1B waits 125 μsec after receiving the RN16 and sends the ACK command. Then, after the readers 1A and 1B finish transmitting the ACK command, the wireless tag 200 is used from the time when the comparison start time Ts shown by the equation (4) to the time when the comparison end time Te shown by the equation (5) elapses. Performs the preamble detection operation of the tag data returned from. At this time, the reader 1B normally detects the preamble of the tag data (952.4 MHz) returned by the wireless tag 200.

However, in reader 1A, the comparison start time Ts and comparison end time Te arrive 25 μsec earlier than in reader 1B. That is, the comparator 332 finishes the preamble detection before the bit data of the preamble of the tag data (952.2 MHz) actually returned from the wireless tag 200 is completely stored in the shift register 331. Therefore, the reader 1A causes a preamble detection error, and the tag data from the wireless tag 200 is not received.

As described above, in the present embodiment, the response time T2 of the reader 1 is changed according to the frequency channel used by the reader 1. Considering that the frequency channels used by a plurality of readers 1 arranged adjacent to each other are usually carrier-sensed so as not to overlap each other, the response time T2 of each reader 1 is set as in the present embodiment. It can be set to a unique value, and as described with reference to FIGS. 11 to 14, it is possible to prevent the same wireless tag from being read by a plurality of readers 1.

(Modification example) The configurations disclosed in each of the above embodiments can be modified in various ways. Specific examples of modifications include the following.

[1] In the above embodiment, a reader 1 that communicates with a wireless tag using a C1G2 type communication method is illustrated. However, the configuration disclosed in the above embodiment may be applied to a wireless communication device that communicates with a wireless tag using a communication method other than C1G2. In this case, the equations (1) to (9) may be changed according to the communication method to be adopted so that the unique response time T2 is determined for each wireless communication device.

[2] In the above embodiment, the response time setting unit 12 and the conversion table 13 are provided independently of the control unit 2. However, the response time setting unit 12 and the conversion table 13 may be provided in the control unit 2.

[3] In the above embodiment, the case where the response time T2 is set according to the frequency channel has been illustrated. However, a unique response time T2 may be set for each reader 1 using parameters other than the frequency channel. In short, it is sufficient that a unique response time T2 can be set for each of a plurality of readers 1 arranged adjacent to each other. Therefore, for example, a random number can be adopted as a parameter other than the frequency channel. That is, a random number generation unit for generating random numbers is provided in the transmission system circuit or reception system circuit of the reader 1, and the response time T2 is set in the conversion table 13 in association with the numerical values that can be generated by the random number generation unit. Then, the response time setting unit 12 is made to acquire the response time T2 associated with the random number generated by the random number generation unit from the conversion table 13, and the acquired response time T2 is set as the response time T2 used by the reader 1. Let me. Even in this way, the same effect as that of the above embodiment can be obtained.

[4] When digital signal processing is performed when a command is transmitted from reader 1 or a response signal is received from a wireless tag, if a delay time due to the digital signal processing occurs, the response time is taken into consideration. Just set the time T2.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

Ts ... comparison start time, Te ... comparison end time, T1, T2 ... response time, Δt ... time window, 1 ... reader, 2a ... timer, 2 ... control unit , 2b ... Frequency setting section, 12 ... Response time setting section, 13 ... Conversion table, 31I, 31Q ... Sampling section, 33I, 33Q ... Preamble detection section, 34I, 34Q ... Decoding unit, 35I, 35Q ... error detection unit, 330 ... judgment data setting unit, 331 ... shift register, 332 ... comparator