Wireless tag communication device

Abstract

To secure a situation in which communication with a wireless tag where a data rate of a data signal wirelessly transmitted is reduced with a reduction in reception power can be appropriately performed.SOLUTION: A wireless tag communication device of an embodiment includes an extraction unit, an acquisition unit, a measurement unit, and an output unit. The extraction unit extracts a data signal obtained by encoding data, from a wireless signal transmitted from a wireless tag. The acquisition unit acquires an identifier of the wireless tag which transmits the wireless signal, from the data signal extracted by the extraction unit. The measurement unit measures a bit length in the data signal extracted by the extraction unit. The output unit outputs discrimination information capable of discriminating whether or not the bit length measured by the measurement unit is in a predetermined excessive state, together with the identifier acquired by the acquisition unit.SELECTED DRAWING: Figure 7

Description

Technical Field

[0005] , ,

[0001] Embodiments of the present invention relate to a wireless tag communication device.

Background Art

[0002] Among wireless tags that operate using received power to perform wireless transmission, there are some in which the data rate of the data signal to be wirelessly transmitted changes according to the magnitude of the received power. And it has been desired to ensure a situation where a wireless tag communication device can properly communicate with a wireless tag having such characteristics.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the present invention is to provide a wireless tag communication device capable of ensuring a situation where communication with a wireless tag in which the data rate of a data signal to be wirelessly transmitted changes according to the magnitude of the received power can be properly performed.

Means for Solving the Problems

[0005] The wireless tag communication device according to the embodiment includes an extraction unit, an acquisition unit, a measurement unit, and an output unit. The extraction unit extracts a data signal obtained by encoding data from a wireless signal transmitted from a wireless tag. The acquisition unit acquires an identifier of the wireless tag that transmitted the wireless signal from the data signal extracted by the extraction unit. The measurement unit measures the bit length in the data signal extracted by the extraction unit. The output unit outputs determination information that enables determination as to whether the bit length measured by the measurement unit is in a predetermined excessive state, together with the identifier acquired by the acquisition unit.

Brief Description of the Drawings

[0006] [Figure 1] A block diagram showing the main circuit configuration of a tag reader according to one embodiment. [Figure 2] A schematic diagram representing one of the data structures of a data record included in the read table in Figure 1. [Figure 3] A flowchart of the reading process in the first embodiment. [Figure 4] A diagram illustrating an example of tag data structure. [Figure 5] This figure shows an example of the waveform of the data signal output from the demodulation circuit in Figure 1. [Figure 6] A diagram illustrating the concept of bit length measurement. [Figure 7] A diagram showing an example of a results screen. [Figure 8] This diagram shows an example of the results screen after editing. [Figure 9] Flowchart of the reading process in the second embodiment. [Figure 10] A diagram showing an example of a confirmation screen. [Modes for carrying out the invention]

[0007] The following describes two embodiments, the first and second, with reference to the drawings. In the following description, a tag reader that reads data from a wireless tag will be used as an example. Wireless tags are also broadly referred to as RFID (radio frequency identification) tags, so in the following description, they will be referred to as RFID tags. The tag reader reads data by communicating with the RFID tag and is an example of a wireless tag communication device. The tag reader described below is envisioned to be a handheld device used by workers for purposes such as locating items in warehouses. However, it is not limited to this, and can be implemented as a communication device in any form or for any purpose.

[0008] Figure 1 is a block diagram showing the main circuit configuration of the tag reader 1 according to this embodiment. The configuration shown in Figure 1 is common to both the first and second embodiments. The tag reader 1 includes an oscillator 11, a digital-to-analog (DA) converter 12, a modulator 13, a power amplifier 14, an antenna sharer 15, an antenna 16, a quadrature detector 17, an amplifier 18, an analog-to-digital (AD) converter 19, a baseband processing unit 20, a processor 21, a storage unit 22, a display unit 23, an input unit 24, and a communication unit 25. Note that some elements, such as the antenna 16, the display unit 23, and the input unit 24, may not be included in the tag reader 1 but may be externally attached to it.

[0009] The oscillator 11 generates sine and cosine waves of predetermined frequencies as carrier waves. The DA converter 12 converts the data signal for transmission, which is output digitally from the baseband processing unit 20, into an analog signal. The modulator 13 uses the data signal, which has been converted to analog by the DA converter 12, as a modulated signal, modulates the carrier wave generated by the oscillator 11, and obtains a transmission signal. The power amplifier 14 amplifies the transmission signal output from the modulator 13 to a level suitable for wireless transmission.

[0010] The antenna sharer 15 has a power amplifier 14 connected to its input terminal. The antenna sharer 15 has an antenna 16 connected to its input / output terminal. The antenna sharer 15 has a quadrature detector 17 connected to its output terminal. When the transmit signal, amplified by the power amplifier 14, is input to the input terminal of the antenna sharer 15, this transmit signal is supplied from the input / output terminal to the antenna 16. The antenna sharer 15 receives the received signal output from the antenna 16 from its input / output terminal and outputs it from its output terminal.

[0011] Antenna 16 radiates radio waves corresponding to the transmission signal supplied from antenna multiplexer 15. Antenna 16 generates an electrical signal corresponding to the radio waves transmitted from and arriving at RFID tag 2 as a reception signal. Note that the reception signal generated in antenna 16 in response to the radio waves transmitted from and arriving at RFID tag 2 includes a signal modulated by a data signal obtained by the RFID tag 2 backscattering the radio waves radiated from antenna 16 and encoding the data (hereinafter referred to as tag data) stored in RFID tag 2. For example, an NRZ (non-return to zero) code is used for the above encoding.

[0012] Quadrature detector 17 performs quadrature detection on the reception signal output from the output terminal of antenna multiplexer 15 using the carrier wave generated by oscillator 11. Quadrature detector 17 outputs an analog state data signal obtained by detection. Amplifier 18 amplifies the data signal output from quadrature detector 17 to a level that can be demodulated by demodulation circuit 202 described later. In order to prevent saturation due to the influence of the DC component, amplifier 18 blocks the DC component through a capacitor prior to amplification. AD converter 19 digitizes the data signal after being amplified by amplifier 18.

[0013] Baseband processing unit 20 includes encoding circuit 201, demodulation circuit 202, measurement circuit 203, decoding circuit 204, and control circuit 205. For example, an FPGA (field-programmable gate array) is used as baseband processing unit 20, and encoding circuit 201, demodulation circuit 202, measurement circuit 203, decoding circuit 204, and control circuit 205 are respectively formed as its internal circuits.

[0014] Encoding circuit 201 encodes the transmission data output from control circuit 205 for transmission to RFID tag 2 using a predetermined encoding method to obtain a data signal for transmission, and outputs it to DA converter 12. The demodulation circuit 202 obtains a demodulated signal corresponding to a data signal having a waveform according to the original NRZ code from the data signal that has become a differential waveform due to passing through the capacitor in the amplifier 18.

[0015] Thus, each process in the control circuit 205, the encoding circuit 201, the DA converter 12, the modulator 13, and the power amplifier 14 is a process for wireless transmission from the antenna 16, and the functions as a transmission unit are realized by the cooperation of these control circuit 205, encoding circuit 201, DA converter 12, modulator 13, and power amplifier 14. Also, a data signal is extracted from the wireless signal received by the antenna 16 by a series of processes by the quadrature detector 17, the amplifier 18, the AD converter 19, and the demodulation circuit 202, and the functions as an extraction unit are realized by the cooperation of these quadrature detector 17, amplifier 18, AD converter 19, and demodulation circuit 202.

[0016] The measurement circuit 203 measures the bit length of the demodulated signal output from the demodulation circuit 202. That is, the measurement circuit 203 is an example of a measurement unit. The decoding circuit 204 decodes the tag data included in the demodulated signal output from the demodulation circuit 202. The decoding circuit 204 changes the operation timing as described later based on the bit length measured by the measurement circuit 203 in order to decode the tag data. The control circuit 205 outputs transmission data to read tag data from the plurality of RFID tags 2 in a predetermined reading sequence, and notifies the processor 21 of the tag data output from the decoding circuit 204 together with the bit length measured by the measurement circuit 203 with respect to the demodulated signal that is the original of the decoded tag data.

[0017] The processor 21 performs information processing for the user interface using the display unit 23 and input unit 24, or information processing for data exchange with external devices connected to the communication unit 25. For example, an MPU (microprocessing unit) is used as the processor 21. The processor 21 executes various information processing tasks according to the application program stored in the memory unit 22.

[0018] The memory unit 22 stores the above-mentioned application program. The memory unit 22 also stores data necessary for the processor 21 to perform various information processing, or data generated by the processor 21 after performing various information processing. One of the data stored in the memory unit 22 is the read table TAA for recording read results. Details of the read table TAA will be described later. The memory unit 22 can use various well-known storage devices, such as ROM (read-only memory), RAM (random-access memory), EEPROM (electric erasable programmable read-only memory), HDD (hard disk drive), SSD (solid state drive), or other storage devices, either individually or in combination.

[0019] The display unit 23 includes a display device that performs display operations to present various information to the operator. The display device is, for example, a liquid crystal display that displays any screen. The display device is a lamp that emits light for alarms. The display unit 23 may also include various other types of display devices.

[0020] The input unit 24 is equipped with input devices for receiving various instructions from the operator. These input devices include, for example, a transparent touch sensor superimposed on the display surface of the liquid crystal display of the display unit 23. Alternatively, they may be hard keys. The input unit 24 may also be equipped with various other types of input devices.

[0021] The communication unit 25 performs processing for data communication with the connected external device. The communication unit 25 can use, either alone or in combination with, devices that communicate directly with the external device, such as an interface device compliant with the USB (universal serial bus) standard, or devices that communicate with the external device via a communication network, such as a communication device compliant with the LAN (local area network) standard.

[0022] Figure 2 schematically represents one data structure of a data record REA contained in the read table TAA. The read table TAA contains data records REA associated with each RFID tag 2 whose tag data has been read. Therefore, if only one RFID tag 2 has had its tag data read, only the data record REA associated with that single RFID tag 2 will be included in the read table TAA. If the tag data of multiple RFID tags 2 has been read, the read table TAA will be a collection of multiple data records REA associated with each of those multiple RFID tags 2.

[0023] The data record REA includes fields FEA, FEB, and FEC. Field FEA contains the reading number assigned to each reading sequence of the tag data of the associated RFID tag 2. Field FEB contains the tag data read from the associated RFID tag 2. Field FEC contains the bit length notified by the control circuit 205 along with the tag data set in field FEB.

[0024] [First Embodiment] Next, the operation of the tag reader 1 in the first embodiment configured as described above will be explained. Note that many of the operations for reading the RFID tag 2 are the same as those already known. Here, we will focus on the operations characteristic of the tag reader 1. Furthermore, the content of the various processes described below is merely an example, and it is possible to change the order of some processes, omit some processes, or add other processes as appropriate. For example, when the input unit 24 is instructed to start reading by a predetermined operation, the processor 21 starts information processing for reading the tag data (hereinafter referred to as the reading process) according to the application program stored in the storage unit 22.

[0025] Figure 3 is a flowchart of the reading process in the first embodiment. As ACT11, the processor 21 instructs the control circuit 205 to start a read transmission to read tag data from the RFID tag 2, which is in a state where it can communicate with the tag reader 1. The read transmission is an operation to cause the antenna 16 to emit radio waves in order to operate the RFID tag 2. During the transmission operation, the control circuit 205 outputs transmission data in a well-known sequence so that the RFID tags 2, which are capable of receiving the radio waves emitted from the antenna 16, sequentially perform the operation of backscattering the radio waves emitted from the antenna 16 and generating reflected waves modulated with the tag data.

[0026] The transmitted data is sequentially processed by the encoding circuit 201, the DA converter 12, the modulator 13, and the power amplifier 14, and the resulting transmitted signal is supplied to the antenna 16 via the antenna sharer 15, causing the above-mentioned radio waves to be emitted from the antenna 16. In this way, the RFID tag 2, upon receiving radio waves emitted from antenna 16, operates using the power obtained from these radio waves and generates a reflected wave modulated with the tag data. Note that the RFID tag 2 generates a reflected wave modulated with the preamble and start bit prior to the tag data.

[0027] Figure 4 shows an example of the structure of tag data. Tag data includes a preamble, a start bit, and actual data. The preamble is 2 bytes of data where "1" and "0" appear alternately. The start bit is 1 byte of data, "11001100". The actual data is 4 bytes of data that differs for each RFID tag 2. The actual data can be any data, but it must include at least a tag ID as an identifier to identify each RFID tag 2. Often, tag data consists only of the tag ID. However, in addition to the tag ID, the tag data may include arbitrary data other than the tag ID. For example, check data such as a CRC (cyclic redundancy check) code may be included in the actual data. The preamble and start bit are common to all RFID tags 2. The reflected waves emitted from the RFID tag 2 reach the antenna 16, and the received signal generated at the antenna 16 is sequentially processed by the quadrature detector 17, amplifier 18, AD converter 19, and demodulation circuit 202 to form a data signal, which is then input to the measurement circuit 203 and decoding circuit 204.

[0028] Figure 5 shows an example of the waveform of the data signal output from the demodulation circuit 202. In the data signal output from the demodulation circuit 202, high levels and low levels alternate during the preamble period with a 1-bit interval. In the data signal output from the demodulation circuit 202, high levels and low levels alternate during the start bit period with a 2-bit interval. In the data signal output from the demodulation circuit 202, high levels and low levels appear during the actual data period according to the content of the actual data.

[0029] Figure 6 is a diagram illustrating the concept of bit length measurement. The measurement circuit 203 measures the bit length as the length of the period from the rising edge to the falling edge of the demodulated signal, for example, during the preamble period. More specifically, the measurement circuit 203 counts the number of clock cycles of a reference clock with a period PA that is sufficiently shorter than the bit length during the period from the rising edge to the falling edge of the demodulated signal, and the bit length measurement result is obtained by multiplying the count value N by the period PA of the reference clock.

[0030] The decoding circuit 204 starts detecting the preamble when it detects the rising edge of the demodulated signal. The decoding circuit 204 then determines that the preamble has been detected when it has detected a certain number of rising and falling edges of the demodulated signal at regular intervals. Furthermore, the decoding circuit 204 then determines that the start bit has been detected when the demodulated signal shows repeated rising and falling edges with a period of twice the bit length notified by the measurement circuit 203. After detecting the start bit, the decoding circuit 204 decodes the actual data by sampling the demodulated signal at a sampling timing with the same period as the bit length notified by the measurement circuit 203. Once the control circuit 205 has finished decoding the actual data for one RFID tag 2, it notifies the processor 21 of the actual data along with the latest bit length measured by the measurement circuit 203. This notification will be referred to as the read notification below.

[0031] After starting the read transmission at ACT11 in Figure 3, the processor 21 proceeds to ACT12. As ACT12, processor 21 checks whether the above read notification has been made. If processor 21 cannot confirm the event, it determines NO and proceeds to ACT13. As ACT13, processor 21 checks whether the completion notification described later has been issued. If processor 21 cannot confirm the relevant event, it determines NO and returns to ACT12. Thus, the processor 21 waits for a read notification or a completion notification as ACT12 and ACT13. If the processor 21 confirms that the read notification has been made, it determines YES in ACT12 and proceeds to ACT14.

[0032] As ACT14, processor 21 updates the read table TAA. For example, processor 21 adds a new data record REA to the read table TAA, associated with the RFID tag 2 that transmitted the actual data notified by the current read notification. Processor 21 sets the field FEA of the new data record REA to a number one greater than the maximum value of the read number set in the field FEA of the data record REA already included in the read table TAA. Processor 21 sets the actual data notified by the current read notification in the field FEB of the new data record REA. Processor 21 sets the bit length notified by the current read notification in the field FEC of the new data record REA. Since the actual data includes the tag ID, the process by which processor 21 stores the actual data in the storage unit 22 in this way means that the tag ID has been acquired, and processor 21 functions as an acquisition unit.

[0033] Once the processor 21 has finished updating the reading table TAA, it returns to the waiting state for ACT12 and ACT13. Thus, the processor 21 repeatedly performs ACT14 when reflected waves are sequentially emitted from multiple RFID tags 2 that are in a state where communication with the tag reader 1 is possible, and reading notifications are repeatedly made, and adds the data record REA associated with each of the multiple RFID tags 2 to the reading table TAA.

[0034] Now, when the control circuit 205 determines that all RFID tags 2 that are in a state where they can communicate with the tag reader 1 have finished emitting reflected waves, and that the decoding circuit 204 can no longer decode new actual data, it notifies the processor 21 that the reading is complete. Upon receiving this notification, the processor 21 determines that a completion notification has been made, and in ACT 13 it determines YES and proceeds to ACT 15. As ACT15, processor 21 stops read transmission. As ACT16, processor 21 generates a results screen. The results screen is a screen that shows the reading results.

[0035] Figure 7 shows an example of the SCA results screen. The result screen SCA shown in Figure 7 includes an image IMA representing a list based on the read table TAA. The processor 21 generates the result screen SCA by representing the read number set in field FEA of the data record REA included in the read table TAA, the tag ID from the actual data set in field FEB, and the bit length set in field FEC, as shown in Figure 7. Note that in Figure 7, the tag ID is represented as "AAAAAAAA" and the bit length as "WA", but in reality, the tag ID is a string in a different form, and the bit length is a numerical value.

[0036] As ACT17, the processor 21 checks whether an oversized state is occurring. An oversized state occurs when the bit length of any one of the RFID tags 2 being read is excessive. For example, if the bit lengths set in each field FEC of all data records REA included in the reading table TAA are all below a predetermined threshold value, the processor 21 determines that none of the RFID tags 2 being read are in an oversized state. In this case, the processor 21 determines NO and proceeds to ACT18. As ACT18, processor 21 displays the result screen SCA generated in ACT16. For example, processor 21 displays the result screen SCA generated in ACT16 on display unit 23. After this, processor 21 terminates the reading process.

[0037] On the other hand, if the processor 21 determines that there is an overloaded RFID tag 2 if, for example, one of the bit lengths set in each field FEC of all data records REA included in the reading table TAA is greater than or equal to a reference value, it determines YES in ACT17 and proceeds to ACT19. Thus, the processor 21 functions as a determination unit that determines whether or not an overloaded state exists.

[0038] As ACT19, the processor 21 updates the result screen SCA generated in ACT19 so that it can identify the RFID tag 2 that caused the determination of an overload state. For example, the processor 21 edits the result screen SCA so that it can identify which of the RFID tags 2 that were read caused the determination of an overload state. Highlighting may be achieved by changing the text color, background color, font type, or other similar methods. Alternatively, the two can be easily distinguished by displaying separate lists of reading results for RFID tag 2 that is not in an overloaded state and RFID tag 2 that is in an overloaded state.

[0039] Figure 8 shows an example of the SCA results screen after editing. Figure 8 shows the case where the bit length WB is determined to be in an over-excess state because it exceeds the specified value. The result screen SCA shown in Figure 8 is the same as the result screen SCA shown in Figure 7, but with the image IMA replaced by image IMB. Image IMB is an image in which the bit length WB and the tag ID "BBBBBBBB" of the RFID tag 2 that was read when this bit length WB was measured are highlighted in italics. Note that Figure 8 is an example where only one RFID tag 2 is in an over-excess state, but if multiple RFID tags 2 are in an over-excess state, the tag ID and bit length for each of the relevant RFID tags 2 will be highlighted.

[0040] As ACT20, processor 21 displays the result screen SCA updated in ACT19. For example, processor 21 displays the result screen SCA updated in ACT19 on display unit 23. As ACT21, the processor 21 executes an alarm operation. The alarm operation is a predetermined action to notify the operator of an excessive condition. The alarm operation is, for example, the illumination or flashing of a lamp included in the display unit. Thus, the function as an alarm unit is realized through the cooperation of the processor 21 and the display unit 23. The processor 21 then terminates the reading process.

[0041] As described above, in the first embodiment, the tag reader 1 displays the measured bit length on the result screen SCA. Thus, the operator can recognize from the result screen if any of the RFID tags 2 to be read have an excessive bit length. One of the causes of increased bit length is insufficient power in the RFID tag 2. This power shortage can be improved if the RFID tag 2 can receive the radio waves emitted from the antenna 16 well. Therefore, the operator can take appropriate measures regarding the RFID tag 2 with an excessive bit length, such as adjusting the attachment status to the item, the placement of the item to which it is attached, or removing surrounding radio wave interference objects, in an attempt to improve the reading situation. By properly improving the reading situation, it is possible to ensure that communication with the RFID tag 2 can be properly performed, such that the data rate of the wirelessly transmitted data signal decreases with decreasing received power.

[0042] Furthermore, the result screen SCA shown in Figure 7 or Figure 8 allows for the determination of whether the measured bit length is in a predetermined excessive state; therefore, it is an example of determination information, and the display of the result screen SCA is an example of determination information output. Accordingly, the function as an output unit is realized through the cooperation of the processor 21 and the display unit 23.

[0043] Furthermore, in the first embodiment, the tag reader 1 performs a highlight display as shown in Figure 8, so even an operator who is not aware of what bit length constitutes an excessive state can easily recognize which RFID tag 2 has an excessive bit length.

[0044] [Second Embodiment] Next, the operation of the tag reader 1 configured as described above in the second embodiment will be explained. The operation of the tag reader 1 in the second embodiment is partially the same as the operation in the first embodiment. Therefore, the following description will focus on the operations that differ from those of the first embodiment. The difference in operation between the first embodiment and the second embodiment of the tag reader 1 lies in the content of the reading process performed by the processor 21.

[0045] Figure 9 is a flowchart of the reading process in the second embodiment. In Figure 9, the same reference numerals are used for processes identical to those in Figure 3, and their detailed explanations are omitted. Processor 21 executes ACT11 to ACT15 in the same manner as in the first embodiment. That is, processor 21 reads the RFID tag 2 that is the target of reading in this case in the same manner as in the first embodiment. Processor 21 sets the transmission power for the read transmission that starts in ACT11 to a predetermined reference power. After completing ACT15, processor 21 proceeds to ACT17. The reference power may be determined as appropriate by, for example, the designer or manager of the tag reader 1.

[0046] If processor 21 determines in ACT17 that there is an RFID tag 2 in an overloaded state, it proceeds to ACT31. As ACT31, the processor 21 checks whether the device is set to automatically perform a second reading. For example, the processor 21 sets the operation settings of the tag reader 1 to whether or not to automatically perform a second reading, in accordance with the instructions of the operator or administrator. Then, the processor 21 checks this setting and makes the determination for ACT31. If the device is not set to perform a second reading automatically, the processor 21 determines NO and proceeds to ACT32. As ACT32, processor 21 displays a confirmation screen. The confirmation screen is used to ask the operator whether or not to perform another read operation.

[0047] Figure 10 shows an example of the confirmation screen SCB. The confirmation screen SCB represents the text message MEA and buttons BUA and BUB. The text message MEA is a message prompting the operator to specify whether or not to perform a second read. Button BUA is a soft key for the operator to instruct the operator to perform a second read. Button BUB is a soft key for the operator to instruct the operator not to perform a second read.

[0048] If the operator believes that a second reading is necessary, they will initiate a second reading by performing a predetermined action, such as tapping button BUA. Alternatively, if the operator believes that a second reading is unnecessary, they will initiate a third reading by performing a predetermined action, such as tapping button BUB.

[0049] After completing ACT32 in Figure 9, processor 21 proceeds to ACT33. As ACT33, processor 21 checks whether it has been instructed to perform another read operation. If processor 21 confirms that it has been instructed to perform another read operation as described above, it determines YES and proceeds to ACT34. If processor 21 is configured to automatically perform another read, it will determine YES in ACT31, skip ACT32 and ACT33, and proceed to ACT34.

[0050] As ACT34, processor 21 clears the read table TAA. As ACT35, the processor 21 starts a read transmission with increased transmission power compared to the previous read transmission. For example, the processor 21 may use the power increased by a predetermined amount or rate from the transmission power of the previous read transmission as the current transmission power. Alternatively, the processor 21 may determine the maximum bit length set in each field FEC of all data records REA included in the read table TAA before clearing in ACT34, and apply a predetermined amount or rate of increase so that it increases as the maximum value increases. The determination of the amount or rate of increase based on the maximum value may be performed by a predetermined calculation, or by referring to a data table that shows the relationship between the maximum value and the amount or rate of increase. At this time, the processor 21 adjusts the transmission power according to the measured bit length. In other words, the processor 21 functions as an adjustment unit.

[0051] The processor 21 then returns to the standby state for ACT12 and ACT13, and repeats the process as described above. In other words, the processor 21 controls each part to redo the reading of the RFID tag 2 that is the target of this reading, and functions as a control unit. At this time, the amount of power that can be obtained by the RFID tag 2 from the radio waves radiated from the antenna 16 increases, and the bit length of the demodulated signal from the new reflected wave from the RFID tag 2, which had an excessive bit length in the previous reading, is shortened, and the excessive state may be resolved.

[0052] If the processor 21 determines NO in ACT17 because none of the RFID tags 2 targeted for reading are in an overloaded state, it proceeds to ACT16. Also, if the processor 21 determines NO in ACT33 and proceeds to ACT16 based on the display on the confirmation screen SCB, as previously stated, if it is instructed not to perform a reread, the processor 21 proceeds to ACT18. The processor 21 then proceeds to ACT18. In other words, if none of the RFID tags 2 targeted for reading are in an overloaded state, or if it is instructed not to perform a reread, the processor 21 displays a results screen, such as the one shown in Figure 7, to present the reading results to the operator and then terminates the reading process. However, the bit length does not need to be displayed on the results screen shown here.

[0053] As described above, in the second embodiment, the tag reader 1 adjusts the transmission power of the read transmission according to the bit length measured by the measurement circuit 203. This optimizes the bit length in the demodulated signal from the reflected wave of the RFID tag 2, and increases the likelihood of proper data decoding from this demodulated signal. In other words, it is possible to ensure a situation in which communication with the RFID tag 2 can be properly performed, such that the data rate of the wirelessly transmitted data signal decreases with decreasing received power.

[0054] In the second embodiment, if the tag reader 1 is set to perform automatic adjustments, the processor 21 automatically adjusts the transmission power. Therefore, if it is set to perform automatic adjustments, the operator does not need to perform any operation to instruct the adjustment to be executed.

[0055] In the second embodiment, the tag reader 1 can also adjust the transmission power in response to instructions from the operator. In this case, the operator can flexibly decide whether or not to adjust the transmission power.

[0056] In the second embodiment, the tag reader 1 can appropriately change whether the processor 21 automatically adjusts the transmission power or whether it is done in response to instructions from the operator. This allows for flexible operation that can be adapted to the needs of the user.

[0057] In the second embodiment, the tag reader 1 reads again after adjusting the transmission power, making it possible to obtain reading results under favorable conditions.

[0058] This embodiment can be modified in various ways as follows: In the second embodiment, the confirmation screen SCB may display the tag ID and bit length of the RFID tag 2 that is in an overloaded state. Alternatively, the confirmation screen SCB may display a list of reading results as shown in Figure 7 or Figure 8. In this way, the operator can arbitrarily choose to adjust the transmission power or to take the same measures as in the first embodiment without adjusting the transmission power.

[0059] In the first embodiment, instead of displaying the numerical value of the bit length, it may be possible to distinguish whether or not an RFID tag is in an over-extended state by highlighting the string representing the tag ID of an RFID tag that is in an over-extended state compared to the string representing the tag ID of an RFID tag that is not in an over-extended state.

[0060] For example, the output may be provided in a way other than display, such as directly transmitting the read table TAA from the communication unit 25 to an external device.

[0061] The bit length for determining an over-condition may be measured during the start bit or the actual data period. For example, one could find a bit sequence "010" during the actual data period and measure the period corresponding to "1" within that sequence. If RZ (return to zero) coding is used, then the period of "1" that occurs during the actual data period should be measured.

[0062] The bit length may also be measured as the length of the period from the falling edge to the rising edge of the demodulated signal. In this case, one could find a bit sequence of "101" within the duration of the actual data and measure the period corresponding to "0" within that sequence.

[0063] Each function realized by the processor 21 through information processing can also be partially or entirely realized by hardware that performs non-program-based information processing, such as logic circuits. Furthermore, each of the above functions can also be realized by combining the above-mentioned hardware, such as logic circuits, with software control.

[0064] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. The invention described in the original claims of this application is listed below. [Note 1] An extraction unit that extracts a data signal obtained by encoding data from a wireless signal transmitted from a wireless tag, An acquisition unit that acquires the identifier of the wireless tag that transmitted the wireless signal from the data signal extracted by the extraction unit, A measurement unit that measures the bit length of the data signal extracted by the extraction unit, An output unit outputs discrimination information that allows determination whether the bit length measured by the measurement unit is in a predetermined excessive state, together with an identifier acquired by the acquisition unit. A wireless tag communication device equipped with the following features. [Note 2] A determination unit that determines whether the bit length measured by the measurement unit is in a predetermined excessive state, Furthermore, The wireless tag communication device described in Appendix 1, wherein the output unit outputs information representing the determination result by the determination unit as the determination information. [Note 3] If the determination unit determines that the condition is excessive, an alarm unit will issue an alarm. A wireless tag communication device as described in Appendix 2, further comprising the features described in Appendix 2. [Note 4] A transmitting unit that transmits wireless signals, An extraction unit extracts a data signal obtained by encoding data from a wireless tag that operates using power obtained from a wireless signal transmitted from the aforementioned transmitting unit, An acquisition unit that acquires the identifier of the wireless tag that transmitted the wireless signal from the data signal extracted by the extraction unit, A measurement unit that measures the bit length of the data signal extracted by the extraction unit, An adjustment unit adjusts the transmission power of the transmission unit according to the bit length measured by the measurement unit, A wireless tag communication device equipped with the following features. [Note 5] A determination unit that determines whether the bit length measured by the measurement unit is in a predetermined excessive state. Furthermore, The adjustment unit increases the transmission power of the transmission unit when the determination unit determines that the power is excessive. The wireless tag communication device described in Appendix 4. [Explanation of Symbols]

[0065] 1...Tag reader, 2...RFID tag, 11...Oscillator, 12...DA converter, 13...Modulator, 14...Power amplifier, 15...Antenna sharer, 16...Antenna, 17...Quaternary detector, 18...Amplifier, 19...AD converter, 20...Baseband processing unit, 21...Processor, 22...Storage unit, 23...Display unit, 24...Input unit, 25...Communication unit, 201...Encoding circuit, 202...Demodulation circuit, 203...Measurement circuit, 204...Decoding circuit, 205...Control circuit.

Claims

1. An extraction unit that extracts a data signal obtained by encoding data from a wireless signal transmitted from a wireless tag, An acquisition unit that acquires the identifier of the wireless tag that transmitted the wireless signal from the data signal extracted by the extraction unit, A measurement unit that measures the bit length of the data signal extracted by the extraction unit, An output unit outputs discrimination information that allows determination whether the bit length measured by the measurement unit is in a predetermined excessive state, together with an identifier acquired by the acquisition unit. A wireless tag communication device equipped with the following features.

2. A determination unit that determines whether the bit length measured by the measurement unit is in a predetermined excessive state, Furthermore, The wireless tag communication device according to claim 1, wherein the output unit outputs information representing the determination result by the determination unit as the determination information.

3. If the determination unit determines that the condition is excessive, the alarm unit issues an alarm. The wireless tag communication device according to claim 2, further comprising:

4. A transmitting unit that transmits wireless signals, An extraction unit extracts a data signal obtained by encoding data from a wireless tag that operates using power obtained from a wireless signal transmitted from the aforementioned transmitting unit, An acquisition unit that acquires the identifier of the wireless tag that transmitted the wireless signal from the data signal extracted by the extraction unit, A measurement unit that measures the bit length of the data signal extracted by the extraction unit, A determination unit that determines whether the bit length measured by the measurement unit is in a predetermined excessive state, If the determination unit determines that the condition is excessive, the adjustment unit increases the transmission power of the transmission unit. A wireless tag communication device equipped with the following features.

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