Wireless tag system

Abstract

To provide a wireless tag system that can expand the reading areas of wireless tags and reduce the number of missed readings of moving wireless tags.SOLUTION: A wireless tag system is composed of a plurality of transceivers (10A, 10B, 10C) each including a transmitting unit (11A) and a receiving unit (21A). The transceiver (10A) includes a frequency generation unit (20A) that generates a carrier, a modulation unit (14A), and a demodulation unit (24A). In the wireless tag system, communication lines (30A, 30B) are provided to notify demodulation units (24B, 24C) of other transceivers (10B, 10C) of a frequency of the carrier used in the modulation unit (14A) of one transceiver (11A) that has transmitted, and the demodulation units (24B, 24C) of the other transceivers (10B, 10C) receive RFID tag information at a frequency synchronized with the notified carrier.SELECTED DRAWING: Figure 1

Description

Technical Field

[0004]

[0001] The present invention relates to a wireless tag system composed of a transceiver including a transmitter and a receiver for reading information of an RFID tag.

Background Art

[0002] <0​​​​​​​​​​​​​​​​​​​​​​​​​​​Reading the response wave with a different transceiver than the one used for transmission can reduce the chances of missed readings due to changes in the radio wave path during transmission and reception, as described above. However, this can cause a shift in the transmission frequency, resulting in a beat (a phenomenon in which two waves with slightly different frequencies interfere, producing a composite wave whose amplitude changes slowly and periodically), making demodulation impossible. This is because the frequency (carrier frequency) of the transmitted wave generated by the transceiver is affected by the precision of its components, temperature changes, etc.

[0006] Figure 10 is a diagram illustrating the generation of a beat. In Figure 10, the horizontal axis represents time, and the vertical axis represents the received signal strength (gain). If there is a 20Hz deviation at a given carrier frequency, beats will occur at 50ms intervals. Figure 10 also shows the received sensitivity at the time when the beats occur. Between approximately 13ms and 18ms, and between approximately 45ms and 50ms, the signal voltage is halved, meaning the reception sensitivity drops by approximately -6dB. Between approximately 29ms and 34ms, the reception sensitivity is at its maximum, and the beat effect is negligible. Between approximately 53ms and 58ms, the signal voltage drops to less than 1 / 10, meaning the reception sensitivity drops by approximately -20dB or more, making reception impossible.

[0007] The present invention was made to solve the above-mentioned problems, and its objective is to provide a wireless tag system that can expand the reading area of ​​wireless tags and reduce the chance of missing readings of moving wireless tags. [Means for solving the problem]

[0008] To achieve the above objective, the invention described in claim 1 is a wireless tag system comprising a plurality of transceivers (10A, 10B, 10C) each having a transmitting unit (11A) and a receiving unit (21A) for reading information of an RFID tag, wherein the transceiver (10A) comprises a frequency generating unit (20A) for generating a carrier, a modulation unit (14A) constituting the transmitting unit, a demodulation unit (24A) constituting the receiving unit, and a control unit (12A) for controlling each of the units, and has notification means (30A, 30B) for notifying the demodulation units (24B, 24C) of the other transceivers (10B, 10C) of the carrier frequency used by the modulation unit (14A) of one transceiver (11A) that performed the transmission, and the technical feature is that the demodulation units (24B, 24C) of the other transceivers (10B, 10C) receive the RFID tag information at a frequency synchronized with the carrier.

[0009] To achieve the above objective, the invention described in claim 6 is a wireless tag system comprising a transceiver (10) having one transmitting unit (11) for reading information on an RFID tag and a plurality of receiving units (21a, 21b, 21c), wherein the transceiver (21a, 21b, 21c) comprises a frequency generating unit (20) for generating a carrier, a modulation unit (14) constituting the transmitting unit (11), demodulation units (24a, 24b, 24c) constituting the receiving units, and a control unit (12) for controlling each of the units, and has notification means (30a, 30b, 30c) for notifying the plurality of demodulation units of the carrier frequency used by the modulation unit, and the plurality of demodulation units (24a, 24b, 24c) are technically characterized in that they receive information on an RFID tag at a frequency synchronized with the carrier frequency. The symbols within the parentheses above indicate the correspondence with the specific means described in the embodiments described later. [Effects of the Invention]

[0010] In the invention of claim 1, since the demodulation units of multiple transceivers can demodulate with synchronized carrier frequencies, no beats are generated, and tag information can be read by multiple transceivers. The tag reading area can be expanded, and the chances of missing moving tags can be reduced.

[0011] In the invention of claim 2, since the notification means consists of a signal line connecting the frequency generation unit of one transceiver and the frequency generation unit of another transceiver, demodulation can be reliably performed at a synchronized carrier frequency by the demodulation units of multiple transceivers. This makes it possible to read tag information with multiple transceivers.

[0012] In the invention of claim 3, the notification means consists of a communication unit that sends and receives carrier frequency information and information used for frequency correction to other transceivers, so that a simple configuration can be used to demodulate at a synchronized carrier frequency by the demodulation units of multiple transceivers. This makes it possible to read tag information with multiple transceivers.

[0013] In the invention of claim 4, the carrier from the frequency generation unit used in the modulation unit of one transmitting transceiver is used for demodulation in the demodulation unit of another transceiver, so that the demodulation units of multiple transceivers can reliably demodulate with synchronized carrier frequencies. This makes it possible to read tag information with multiple transceivers.

[0014] In the invention of claim 5, the control unit of one transceiver that performed the transmission performs a cyclic redundancy check on the data demodulated by the modulation unit of that transceiver, and the control unit of the other transceiver performs a cyclic redundancy check on the data demodulated by the demodulation unit of the other transceiver, and determines that they are correct, so that the information on the RFID tag can be read without error.

[0015] In the invention of claim 6, since the multiple demodulation units of the transceiver can demodulate at synchronized carrier frequencies, no beats are generated, and tag information can be read by multiple demodulation units. The tag reading area can be expanded, and the chances of missing moving tags can be reduced.

[0016] The invention of claim 7 includes a plurality of transceivers and a second notification means that notifies the demodulation units of the other transceivers of the carrier frequency used by the modulation unit of one transceiver that performed the transmission. Since the multiple demodulation units of the multiple transceivers can demodulate with synchronized carrier frequencies, tag information can be read by a large number of demodulation units. The tag reading area can be expanded and the chances of missing moving tags can be reduced.

Brief Description of the Drawings

[0017] [Figure 1] It is a block diagram showing the electrical configuration of the wireless tag system according to the first embodiment. [Figure 2] It is a block diagram showing the electrical configuration of the wireless tag system according to the first modification example of the first embodiment. [Figure 3] It is a block diagram showing the electrical configuration of the wireless tag system according to the second modification example of the first embodiment. [Figure 4] It is a flowchart showing the processing in the wireless tag system according to the second modification example of the first embodiment. [Figure 5] It is a block diagram showing the electrical configuration of the wireless tag system according to the second embodiment. [Figure 6] It is a block diagram showing the electrical configuration of the wireless tag system according to the first modification example of the second embodiment. [Figure 7] It is a block diagram schematically showing the electrical configuration of the wireless tag. [Figure 8] FIG. 8(A) is an explanatory diagram of tag reading in a prior art wireless tag system, and FIG. 8(B) is an explanatory diagram of tag reading in a wireless tag system according to an embodiment. [Figure 9] FIG. 9(A) is an explanatory diagram of reading a moving tag in a prior art wireless tag system, FIG. 9(B) is an explanatory diagram of reading a moving tag in a wireless tag system for comparison, and FIG. 9(C) is an explanatory diagram of reading a moving tag in a wireless tag system of an embodiment. [Figure 10] It is a waveform diagram showing the beats generated in a prior art wireless tag system.

Modes for Carrying Out the Invention

[0018] [First Embodiment] Hereinafter, the wireless tag system according to the first embodiment of the present invention will be described with reference to the drawings. The wireless tag system shown in Figure 1 consists of three transceivers: a first transceiver 10A, a second transceiver 10B, and a third transceiver 10C. The first transceiver 10A comprises a transmitter (1) [transmitting unit] 11A and a receiver (1) [receiving unit] 21A. The second transceiver 10B comprises a transmitter (2) 11B and a receiver (2) 21B. The third transceiver 10C comprises a transmitter (3) 11C and a receiver (3) 21C. The first transceiver 10A, the second transceiver 10B, and the third transceiver 10C have substantially similar configurations, and their basic parts are composed of known RF tag readers.

[0019] The first transceiver 10A includes a control unit 12A. The control unit 12A includes a memory unit, a communication processing unit, and an external interface, etc. The control unit 12A is mainly composed of a microcontroller and has a CPU, a system bus, an input / output interface, etc., and together with a memory unit consisting of semiconductor memory, etc., it constitutes an information processing device.

[0020] The first transceiver 10A includes a frequency generation unit 20A that generates a carrier (carrier frequency signal) and a frequency control unit 22A that controls the frequency generation unit 20A. The transmitter (1) 11A of the first transceiver 10A includes a modulation unit 14A that modulates the carrier, an amplifier 16A, and a transmitting antenna 18A. The amplifier 16A amplifies the input signal (the modulated signal modulated by the modulation unit 14A) at a set amplification factor, and the amplified signal is output to the transmitting antenna 18A as a transmission signal. The modulation unit 14A has a built-in encoding unit. The frequency generation unit 20A outputs a carrier (carrier wave) of a predetermined frequency, and the encoding unit encodes the transmission data output from the control unit 12A and outputs it to the modulation unit. The modulation unit 14A receives the carrier wave from the frequency generation unit 20A and the transmission data from the coding unit. It generates a modulated signal that is ASK (Amplitude Shift Keying) modulated with the carrier wave output from the frequency generation unit 20A by the encoded transmission code (modulation signal) output from the coding unit when a command is sent to the communication target, and outputs this to the amplifier 16A.

[0021] The receiver (receiving unit) 21A of the first transceiver 10A includes a demodulation unit 24A and a receiving antenna 28A. The input terminal of the demodulation unit 24A is connected to the receiving antenna 28A, and the radio signal (received signal) corresponding to the response wave from the radio tag received by the receiving antenna 28A is input to the demodulation unit 24A. The demodulation unit 24A is composed of, for example, an amplifier and a demodulation unit, and amplifies the received signal received by the receiving antenna 28 with the amplifier, and demodulates the amplified signal with the demodulation unit. Furthermore, it outputs a signal corresponding to the demodulated signal waveform as received data to the control unit 12A.

[0022] The modulation section 14A of the transmitter (1) 11A of the first transceiver 10A and the demodulation section 24A of the receiver (1) 21A both output the same carrier from the frequency generation section 20A. When an unmodulated carrier is transmitted from the transmitter (1) 11A, and a radio signal (received signal) corresponding to the response wave from the wireless tag, i.e., a carrier reflected wave with superimposed information, is transmitted, the demodulation section 24A performs demodulation using the same carrier as the transmitter side.

[0023] The frequency generation unit 20A of the first transceiver 10A and the frequency generation unit 20B of the second transceiver 10B are connected by a signal line 30A, which constitutes a notification means for notifying the demodulation unit of the other transceiver of the frequency of the carrier used in the modulation unit. The frequency generation unit 20A of the first transceiver 10A and the frequency generation unit 20B of the second transceiver 10B synchronize via the signal line 30A and generate a carrier of the same frequency. Similarly, the frequency generation unit 20B of the second transceiver 10B and the frequency generation unit 20C of the third transceiver 10C are connected by a signal line 30B. The frequency generation unit 20B of the second transceiver 10B and the frequency generation unit 20C of the third transceiver 10C synchronize via the signal line 30B and generate a carrier of the same frequency. Furthermore, unless the frequency generation units 20B of the first transceiver 10A, the second transceiver 10B, and the third transceiver 10C are synchronized, the carrier frequencies will be shifted by several Hz due to the effects of component precision, etc. Therefore, when the carrier transmitted from another transceiver is demodulated by the demodulation unit, the beat described above will occur as shown in Figure 10.

[0024] In the wireless tag system of the first embodiment: (1) When a transmission signal is sent from the transmitter (1) 11A of the first transceiver 10A, the received signal is demodulated in the demodulator (1) 24A of the receiver (1) 21A using the same carrier as the transmitted signal used in the modulation unit 14A. Simultaneously, the received signal is demodulated in the demodulator (2) 24B of the receiver (2) 21B of the second transceiver 10B using a carrier of the same frequency synchronized with the demodulator (1) 24A via the signal line 30A. Furthermore, the received signal is demodulated in the demodulator (3) 24C of the receiver (3) 21C of the third transceiver 10C using a carrier of the same frequency synchronized with the demodulator (2) 24B via the signal line 30B. In the wireless tag system of the first embodiment, the demodulation unit (1) 24A of the first transceiver 10A, the demodulation unit (2) 24B of the second transceiver 10B, and the demodulation unit (3) 24C of the third transceiver 10C perform demodulation on the same frequency carrier, so no beats are generated, and tag information can be read by the first transceiver 10A, the second transceiver 10B, and the third transceiver 10C, respectively.

[0025] (2) When a transmission signal is sent from the transmitter (2) 11B of the second transceiver 10B, the received signal is demodulated in the demodulator (2) 24B of the receiver (2) 21B using the same carrier as the transmitted signal used in the modulation unit 14B. At the same time, the received signal is demodulated in the demodulator (1) 24A of the receiver (1) 24A of the first transceiver 10A using a carrier of the same frequency synchronized with the demodulator (2) 24B via the signal line 30A. Furthermore, the received signal is demodulated in the demodulator (3) 24C of the receiver (3) 21C of the third transceiver 10C using a carrier of the same frequency synchronized with the demodulator (2) 24B via the signal line 30B. In the wireless tag system of the first embodiment, the demodulation unit (2) 24B of the second transceiver 10B, the demodulation unit (1) 24A of the first transceiver 10A, and the demodulation unit (3) 24C of the third transceiver 10C perform demodulation on the same frequency carrier, so no beats are generated, and tag information can be read by the second transceiver 10B, the first transceiver 10A, and the third transceiver 10C, respectively.

[0026] (3) When a transmission signal is sent from the transmitter (3)11C of the third transceiver 10C, the received signal is demodulated in the demodulation unit (3)24C of the receiver (3)21C using the same carrier as the transmitted signal used in the modulation unit 14C. Simultaneously, the received signal is demodulated in the demodulation unit (2)24B of the receiver (2)21B of the second transceiver 10B using a carrier of the same frequency synchronized with the demodulation unit (3)24C via the signal line 30B. Furthermore, the received signal is demodulated in the demodulation unit (1)24A of the receiver (1)24A of the first transceiver 10A using a carrier of the same frequency synchronized with the demodulation unit (2)24B via the signal line 30A. In the wireless tag system of the first embodiment, the demodulation unit (3) 24C of the third transceiver 10C, the demodulation unit (2) 24B of the second transceiver 10B, and the demodulation unit (3) 24C of the third transceiver 10C perform demodulation on the same frequency carrier, so no beats are generated, and tag information can be read by the second transceiver 10B, the third transceiver 10C, and the first transceiver 10A, respectively.

[0027] Here, the electrical configuration of the wireless tag 40 to be read by the first transceiver 10A, second transceiver 10B, and third transceiver 10C of the wireless tag system will be explained with reference to Figure 7. As shown in Figure 7, the wireless tag 40 is composed of an antenna 41, a power supply circuit 42, a demodulation circuit 43, a control circuit 44, a memory 45, a modulation circuit 46, and the like. The power supply circuit 42 rectifies and smooths the transmission signal (carrier signal) from the transceiver 10 received via the antenna 41 to generate an operating power supply, which is then supplied to the control circuit 44 and other components.

[0028] Furthermore, the demodulation circuit 43 demodulates the data superimposed on the transmission signal (carrier signal) and outputs it to the control circuit 44. The memory 45 is composed of various semiconductor memories such as ROM and EEPROM, and stores the control program, identification information (tag ID) for identifying the wireless tag 40, or data according to the application of the wireless tag 40. The control circuit 44 is configured to read the above information and data from the memory 45 and output it as transmission data to the modulation circuit 46. The modulation circuit 46 is configured to load-modulate the response signal (carrier signal) with the transmission data and transmit it as a response wave from the antenna 41. Although Figure 7 shows an example of the electrical configuration of the wireless tag 40, other known electrical configurations may be used as long as they enable wireless communication via electromagnetic waves.

[0029] In the first embodiment described above, the wireless tag system was composed of three transceivers: a first transceiver 10A, a second transceiver 10B, and a third transceiver 10C. However, the wireless tag system of the first embodiment can be composed of two or more transceivers.

[0030] Figure 8(B) shows a wireless tag system consisting of two transceivers (reader / writers) according to the first embodiment. Referring to Figure 8(A), the conventional wireless tag system described above shows a configuration in which the reader / writer (1) and reader / writer (2) read the respective tags at intervals. In contrast, in the first embodiment, whether the transmission is made from reader / writer (1) or reader / writer (2), reading is performed simultaneously by both reader / writer (1) and reader / writer (2).

[0031] Figure 9(C) shows a wireless tag system consisting of two transceivers (reader / writers) according to the first embodiment. Referring to Figure 9(A), in the conventional wireless tag system described above, when reading a moving wireless tag, the radio wave path during transmission and the radio wave path during reception change. For example, in the transmission path, radio waves from the transceiver are reflected and reach the wireless tag, while in the reception path, the reflected waves from the wireless tag are shifted by several tens of centimeters from the reflection point in the transmission path to reach the transceiver, sometimes entering a null point and causing the wireless tag response to be missed. Referring to Figure 9(B), in the comparative wireless tag system described above, in a configuration where reader / writer (1) and reader / writer (2) read each tag at different times, when reading a moving tag, cases of missed readings occur, similar to the case in Figure 9(A).

[0032] In contrast, in the wireless tag system according to the first embodiment shown in Figure 9(C), reception is performed by two transceivers (reader / writer (1), reader / writer (1)). Therefore, when a tag is in motion, reader / writer (1) transmits, and reader / writer (1) cannot receive a response from the tag, reader / writer (2) may be able to receive the response from the tag. In the wireless tag system according to the first embodiment, the tag reading area can be expanded, and the chances of missing a tag response can be reduced.

[0033] In the wireless tag system of the first embodiment, demodulation can be performed at a synchronized carrier frequency by the demodulation units of multiple transceivers, so beats are not generated and tag information can be read by multiple transceivers. The tag reading area can be expanded and the chances of missing moving tags can be reduced.

[0034] In the wireless tag system of the first embodiment, the notification means for maintaining synchronization consists of a signal line 30A connecting the frequency generation unit of one transceiver and the frequency generation unit of another transceiver, so that the demodulation units of multiple transceivers can reliably demodulate at a synchronized carrier frequency. This makes it possible to read tag information with multiple transceivers.

[0035] [First Embodiment, First Modification Example] Hereinafter, a wireless tag system according to a first modification example of the first embodiment of the present invention will be described with reference to Figure 2. The wireless tag system shown in Figure 2 consists of two transceivers: a first transceiver 10A and a second transceiver 10B. The first transceiver 10A and the second transceiver 10B in the first modification of the first embodiment are the same as those in the first embodiment. However, in the first modification of the first embodiment, the first transceiver 10A includes a communication unit 26A connected to the control unit 12A, and the second transceiver 10B includes a communication unit 26B connected to the control unit 12B. The communication unit 26A of the first transceiver 10A and the communication unit 26B of the second transceiver 10B are connected via a communication line 29.

[0036] In the first modification of the first embodiment, the first transceiver 10A and the second transceiver 10B communicate by switching between multiple carrier frequencies. The communication unit 26A of the first transceiver 10A and the communication unit 26B of the second transceiver 10B send and receive information used for frequency correction, such as the carrier frequency used for communication and temperature data, to each other via the communication line 29, thereby maintaining synchronization of the carrier frequencies between the frequency generation unit 20A of the first transceiver 10A and the frequency generation unit 20B of the second transceiver 10B.

[0037] In the wireless tag system according to the first modification of the first embodiment: (1) When a transmission signal is sent from the transmitter (1) 11A of the first transceiver 10A, the demodulation unit (1) 24A of the receiver (1) 21A demodulates the received signal using the same carrier as the transmission signal used in the modulation unit 14A. Simultaneously, the demodulation unit (2) 24B of the receiver (2) 21B of the second transceiver 10B demodulates the received signal using the same frequency carrier synchronized with the frequency generation unit 20A via the communication unit 26A - communication line 29 - communication unit 26B. In the wireless tag system according to the first modification of the first embodiment, since the demodulation unit (1) 24A of the first transceiver 10A and the demodulation unit (2) 24B of the second transceiver 10B perform demodulation using the same frequency carrier, no beats are generated, and tag information can be read by the first transceiver 10A and the second transceiver 10B, respectively.

[0038] (2) When a transmission signal is sent from the transmitter (2) 11B of the second transceiver 10B, the demodulation unit (2) 24B of the receiver (2) 21B demodulates the received signal using the same carrier as the transmission signal used in the modulation unit 14B. Simultaneously, the demodulation unit (1) 24A of the receiver (1) 24A of the first transceiver 10A demodulates the received signal using the same frequency carrier synchronized with the frequency generation unit 20B via the communication unit 26B - communication line 29 - communication unit 26A. In the wireless tag system according to the first modification of the first embodiment, since the demodulation unit (2) 24B of the second transceiver 10B and the demodulation unit (1) 24A of the first transceiver 10A perform demodulation using the same frequency carrier, no beats are generated, and tag information can be read by the second transceiver 10B and the first transceiver 10A, respectively.

[0039] In the wireless tag system according to the first modification of the first embodiment, the notification means for maintaining synchronization consists of communication units 26A and 26B and a communication line 29 that send and receive carrier frequency information and information used for frequency correction to other transceivers. Therefore, it is possible to demodulate at a synchronized carrier frequency in the demodulation units of multiple transceivers with a simple configuration that does not use expensive coaxial cables, etc. This makes it possible to read tag information with multiple transceivers. The communication line 29 can be configured as either wired or wireless.

[0040] [Second modification example of the first embodiment] Hereinafter, a wireless tag system according to a second modification of the first embodiment of the present invention will be described with reference to Figure 3. The wireless tag system shown in Figure 3 consists of three transceivers: a first transceiver 10A, a second transceiver 10B, and a third transceiver 10C. The first transceiver 10A comprises a transmitting unit (1) 11A and a receiving unit (1) 21A. The second transceiver 10B comprises a transmitting unit (2) 11B and a receiving unit (2) 21B. The third transceiver 10C comprises a transmitting unit (3) 11C and a receiving unit (3) 21C. The first transceiver 10A, the second transceiver 10B, and the third transceiver 10C have substantially similar configurations, and their basic parts are composed of known RF tag readers.

[0041] The first transceiver 10A includes a control unit 12A, a frequency generation unit (1) 20A that generates a carrier (carrier frequency signal), and a distributor 35A having a switch SW7 for switching the frequency generation unit (1) 20A. The control unit 12A incorporates a switch WS1 for enabling the transmitter unit (1) 11A and a switch WS2 for enabling the frequency generation unit (1) 20A.

[0042] The transmitter (1) 11A of the first transceiver 10A includes a D / A converter 32A which constitutes the encoding section of the first embodiment, a mixer 34A which constitutes the modulation section of the first embodiment which modulates the carrier, an amplifier 36A, and a low-pass filter 38A. The output of the low-pass filter 38A is connected to a transmitting antenna (not shown).

[0043] The receiver (receiving unit) 21A of the first transceiver 10A includes a low-noise amplifier 39A connected to a receiving antenna (not shown), a mixer 36A which constitutes the demodulation unit of the first embodiment, and an A / D conversion unit 33A which performs A / D conversion on the output of the mixer 36A and outputs it to the control unit 12A.

[0044] Figure 4 is a flowchart showing the processing performed by the wireless tag system according to a second modification of the first embodiment. Inventory is performed by the first transceiver 10A (S12). The control unit 12A of the first transceiver 10A turns on switch SW1 to enable the transmitter (1) 11A. The control unit 12B of the second transceiver 10B turns off switch SW3 to disable the transmitter (2) 11B. The control unit 12C of the third transceiver 10C turns off switch SW5 to disable the transmitter (3) 11C.

[0045] The control unit 12A of the first transceiver 10A turns on switch SW2 and generates a carrier frequency signal in the frequency generation unit (1) 20A. At the same time, the control unit 12B of the second transceiver 10B keeps switch SW4 off, disabling the frequency generation unit (2) 20B, and the control unit 12C of the third transceiver 10C keeps switch SW6 off, disabling the frequency generation unit (3) 20C. The distributor 35A of the first transceiver 10A switches switch SW7 to terminal a, outputting the carrier frequency of the frequency generation unit (1) 20A to the mixer 36A. The distributor 35B of the second transceiver 10B switches switch SW8 to terminal b, outputting the carrier of the frequency generation unit (1) 20A of the first transceiver 10A to the mixer 36B via distributors 35A and 35B. Similarly, the distributor 35C of the third transceiver 10C switches the switch SW9 to the b terminal side and outputs the carrier of the frequency generation unit (1) 20A of the first transceiver 10A to the mixer 36C side via the distributors 35A, 35B, and 35C (S14).

[0046] The transmitting unit (1) of the first transceiver 10A transmits an inventory signal modulated with the carrier frequency of the frequency generation unit (1) 20A (S16).

[0047] The receiving unit (1) 11A of the first transceiver 10A, the receiving unit (2) 11B of the second transceiver 10B, and the receiving unit (3) 11C of the third transceiver 10C, or any or more of them, receive the inventory response signal of the tag, and demodulation processing is performed using the carrier frequency generated by the frequency generation unit (1) 20A of the first transceiver 10A, the receiving unit (2) 11B of the second transceiver 10B, and the receiving unit (3) 11C of the third transceiver 10C (S18).

[0048] Based on the demodulation result, the success or failure of the reading result is determined by a CRC check (Cyclic Redundancy Check) (S20). If the demodulated response signal is deemed valid by the CRC check in the control unit 12A of the first transceiver 10A that transmitted the signal, the RFID tag information is read from that response signal. On the other hand, if the demodulated response signal is deemed invalid by the CRC check in the first transceiver 10A that transmitted the signal, then if the demodulated response signal is deemed valid by the control unit 12B of the second transceiver 10B or the control unit 12C of the third transceiver 10C, the RFID tag information is read from that response signal. Note that, in order to handle the case where the demodulated response signal is deemed valid by both the second transceiver 10B and the third transceiver 10C, a priority order can be predetermined for the second transceiver 10B and the third transceiver 10C. For example, if the received data from both the second transceiver 10B and the third transceiver 10C is deemed valid, the RFID tag information is read from the response signal of the second transceiver 10B.

[0049] When inventory is performed by the second transceiver 10B, demodulation processing is similarly performed by the receiving unit (2) 11B of the second transceiver 10B, the receiving unit (1) 11A of the first transceiver 10A, and the receiving unit (3) 11C of the third transceiver 10C, using the carrier frequency generated by the frequency generation unit (2) 20B of the second transceiver 10B.

[0050] When inventory is performed by the third transceiver 10C, demodulation processing is performed by the receiving unit (3) 11C of the third transceiver 10C, the receiving unit (1) 11A of the first transceiver 10A, and the receiving unit (2) 11C of the second transceiver 10B, using the carrier frequency generated by the frequency generation unit (3) 20C of the third transceiver 10C.

[0051] In the wireless tag system according to the second modification of the first embodiment, the carrier of the frequency generator used in the modulation unit (mixer) of one transmitting transceiver is used for demodulation in the demodulation unit (carrier) of another transceiver, so that the demodulation units of multiple transceivers can reliably demodulate with the same carrier frequency. This makes it possible to read tag information with multiple transceivers.

[0052] In the wireless tag system according to the second modification of the first embodiment, the control unit of one transceiver that transmitted data performs a cyclic redundancy check on the data demodulated by the modulation unit of that transceiver, and the control units of other transceivers perform a cyclic redundancy check on the data demodulated by the demodulation unit of the other transceiver, and determine that the data is correct, so that the RFID tag information can be read without error. Note that the cyclic redundancy check described above is also performed in the wireless tag system of the first embodiment and the wireless tag system according to the first modification of the first embodiment.

[0053] [Second Embodiment] Hereinafter, a wireless tag system according to a second embodiment of the present invention will be described with reference to Figure 5. The wireless tag system shown in Figure 5 consists of one transceiver 10. The transceiver 10 is the same as the first transceiver 10A in the first embodiment. However, the transceiver 10 in the second embodiment includes three receivers: receiver (1) 21a, receiver (2) 21b, and receiver (3). Receiver (1) 21a includes a receiving antenna 28a and a demodulation unit (1) 24a. Receiver (2) 21b includes a receiving antenna 28b and a demodulation unit (2) 24b. Receiver (3) 21c includes a receiving antenna 28c and a demodulation unit (3) 24a. The same carrier frequency signal is input from the frequency generation unit 20 to the demodulation unit (1) 24a via signal line 30a, to the demodulation unit (2) 24b via signal line 30b, and to the demodulation unit (3) 24c via signal line 30c.

[0054] In the transceiver 10 constituting the wireless tag system of the second embodiment, when a transmission signal is sent from the transmitter 11, the demodulation unit (1)24a of receiver (1)21a, the demodulation unit (2)24b of receiver (2)21b, and the demodulation unit (3)24c of receiver (3)21c use the same carrier as the carrier of the transmission signal used in the modulation unit 14 to demodulate the received signal. In the wireless tag system of the second embodiment, since demodulation is performed using the same carrier in the demodulation unit (1)24a of receiver (1)21a, the demodulation unit (2)24b of receiver (2)21b, and the demodulation unit (3)24c of receiver (3)21c, no beats are generated, and tag information can be read by each of the three receivers: receiver (1)21a, receiver (2)21b, and receiver (3)21c.

[0055] In the transceiver 10 constituting the wireless tag system of the second embodiment, multiple demodulation units (1) 24a, (2) 24b, and (3) 24c of the transceiver 10 can demodulate at the same carrier frequency, so beats are not generated and tag information can be read by multiple demodulation units. The tag reading area can be expanded and the chances of missing moving tags can be reduced.

[0056] [Example of the first modification of the second embodiment] Hereinafter, a wireless tag system according to the first modification example of the second embodiment of the present invention will be described with reference to Figure 6. The wireless tag system according to the first modification of the second embodiment shown in Figure 6 is equipped with three transceivers (first transceiver 10A, second transceiver 10B, and third transceiver 10C) of the second embodiment shown in Figure 5. The first transceiver 10A has three receivers: receiver (1) 21Aa, receiver (2) 21Ab, and receiver (3) 21Ac. The second transceiver 10B has three receivers: receiver (4) 21Ba, receiver (5) 21Bb, and receiver (6) 21Bc. The third transceiver 10C has three receivers: receiver (7) 21Ca, receiver (8) 21Cb, and receiver (9) 21Cc.

[0057] The frequency generation unit 20A of the first transceiver 10A and the frequency generation unit 20B of the second transceiver 10B are connected by a second signal line 31A, which constitutes a second notification means for notifying the demodulation unit of the other transceiver of the frequency of the carrier used in the modulation unit. The frequency generation unit 20A of the first transceiver 10A and the frequency generation unit 20B of the second transceiver 10B synchronize via the second signal line 31A and generate a carrier of the same frequency. Similarly, the frequency generation unit 20B of the second transceiver 10B and the frequency generation unit 20C of the third transceiver 10C are connected by a second signal line 31B. The frequency generation unit 20B of the second transceiver 10B and the frequency generation unit 20C of the third transceiver 10C synchronize via the second signal line 31B and generate a carrier of the same frequency.

[0058] In the wireless tag system according to the first modification of the second embodiment, when a transmission signal is sent from the transmitter (1) 11A of the first transceiver 10A, the received signal is demodulated by the demodulation units (1) 24Aa, (2) 24Ab, and (3) 24Ac of the receivers (1) 21Aa, (2) 21Ab, and (3) 21Ac, using the same carrier as the transmitted signal used in the modulation unit 14A. Simultaneously, the received signal is demodulated by the demodulation units (4) 24Ba, (5) 24Bb, and (6) 24Bc of the second transceiver 10B using the carrier of the frequency generation unit 20B, which is synchronized with the frequency generation unit 20A via the second signal line 31A and has the same frequency. In the demodulation units (7) 24Ca, (8) 24Cb, and (9) 24Cc of the third transceiver 10C, the received signal is demodulated using the carrier of the frequency generation unit 20C, which is synchronized with the frequency generation unit 20B via the second signal line 31B. In the wireless tag system according to the first modification example of the second embodiment, demodulation is performed with the same frequency carrier in demodulation units (1) 24Aa, (2) 24Ab, (3) 24Ac, (4) 24Ba, (5) 24Bb, (6) 24Bc, (7) 24Ca, (8) 24Cb, and (9) 24Cc, so no beats are generated, and tag information can be read by each of the nine receivers: receiver (1) 21Aa, receiver (2) 21Ab, receiver (3) 21Ac, receiver (4) 21Ba, receiver (5) 21Bb, receiver (6) 21Bc, receiver (7) 21Ca, receiver (8) 21Cb, and receiver (9) 21Cc.

[0059] The wireless tag system according to the first modification of the second embodiment includes multiple transceivers and a second notification means (second signal line 31A) that notifies the demodulation units of other transceivers of the carrier frequency used by the modulation unit of one transceiver that performed the transmission. Since multiple demodulation units of multiple transceivers can demodulate with synchronized carrier frequencies, tag information can be read by a large number of demodulation units. The tag reading area can be expanded and the chances of missing moving tags can be reduced. [Explanation of symbols]

[0060] 10A...First Transmitter / Receiver 11A...Transmitter (1) 12A...Control Unit 14A...Modulation section 20A…Frequency generation unit 24A... Demodulation unit (1) 30A…Signal line 31A…Second signal line 40... Wireless tags

Claims

1. A wireless tag system comprising multiple transceivers, each having a transmitting unit and a receiving unit for reading information from an RFID tag, The transceiver comprises a frequency generation unit that generates a carrier, a modulation unit that constitutes the transmission unit, a demodulation unit that constitutes the reception unit, and a control unit that controls each of the above units. The system has a notification means for notifying the demodulation unit of another transceiver of the carrier frequency used in the modulation unit of one transceiver that performed the transmission. A wireless tag system characterized in that the demodulation unit of the other transceiver receives RFID tag information at a frequency synchronized with the carrier.

2. A wireless tag system according to claim 1, The notification means is characterized by comprising a signal line connecting the frequency generating unit of one transceiver and the frequency generating unit of the other transceiver, in a wireless tag system.

3. A wireless tag system according to claim 1, The wireless tag system is characterized in that the notification means comprises a communication unit that sends and receives carrier frequency information and information used for frequency correction to the other transceiver.

4. A wireless tag system according to claim 1, A wireless tagging system characterized in that the carrier of the frequency generation unit used in the modulation unit of one transceiver that performed the transmission is used for demodulation in the demodulation unit of the other transceiver.

5. A wireless tag system according to any one of claims 1 to 4, The control unit of one transceiver that performed the transmission performs a cyclic redundancy check on the data demodulated by the modulation unit of that transceiver, and the control unit of the other transceiver performs a cyclic redundancy check on the data demodulated by the demodulation unit of that other transceiver. The data deemed appropriate is then used as the information for the RFID tag.

6. A wireless tag system comprising a transceiver with one transmitting unit and multiple receiving units for reading information from an RFID tag, The transceiver comprises a frequency generation unit that generates a carrier, a modulation unit that constitutes the transmission unit, a demodulation unit that constitutes the reception unit, and a control unit that controls each of the above units. The modulation unit has a notification means for notifying the multiple demodulation units of the frequency of the carrier used in the modulation unit, A wireless tag system characterized in that the plurality of demodulation units receive RFID tag information at a frequency synchronized with the carrier frequency.

7. A wireless tag system according to claim 6, The system comprises multiple of the aforementioned transceivers, A wireless tag system characterized by having a second notification means for notifying the demodulation unit of another transceiver of the carrier frequency used in the modulation unit of one transceiver that performed the transmission.

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