Wireless tag, communication terminal, communication system, and communication method

Abstract

Provided are a wireless tag, a communication terminal, a communication system, and a communication method capable of performing stable data communication. This communication terminal identifies the cycle of a clock signal generated by a wireless tag, on the basis of a falling period of the signal level in a prefix included in tag transmission data obtained as terminal reception data. The communication terminal acquires tag information from the tag transmission data on the basis of the cycle of the clock signal detected from the tag transmission data by means of a terminal controller, without independently setting the clock signal by itself.

Description

Wireless tag, communication terminal, communication system, and communication method

[0001] The present invention relates to a wireless tag, a communication terminal, a communication system, and a communication method.

[0002] In recent years, wireless tags have been developed that transmit individual identification information by radio signals such as RF (Radio Frequency) signals, and the identification information of the wireless tags is read by a communication terminal such as a wireless tag reader or a wireless tag reader / writer.

[0003] Asynchronous communication is known as a communication method for reading identification information from a wireless tag using a communication terminal (see, for example, Patent Document 1). Asynchronous communication operates using a clock signal synchronized between the transmitter and receiver. The transmitter generates transmission data using transmission information represented in bits, and generates a transmission wave by modulating a predetermined carrier wave using the transmission data. The generated transmission wave contains bit information that changes according to the cycle of the clock signal. Therefore, the receiver can obtain bit information from the received transmission wave after synchronizing the clock signal.

[0004] In an example of start-stop synchronization, the data length of information transmitted at one time is predetermined (e.g., 8 bits), and the transmitting side continuously transmits "1" (rising signal level) while not transmitting information. When transmitting information, the transmitting side generates transmission data in which "0" (falling signal level) indicating the start of transmission is followed by transmission information of a predetermined data length.

[0005] The receiving side demodulates the received transmission wave to obtain the received data, and then analyzes the obtained received data to obtain the identification information, etc. In this way, the receiving side can obtain the information transmitted from the transmitting side.

[0006] Japanese Patent Application Publication No. 11-355277

[0007] In Patent Document 1, the transmitter and receiver must generate clock signals with the same period to achieve start-stop synchronization. However, when a wireless tag is powered by radio waves transmitted from a communication terminal, if the radio waves from the communication terminal are weak, the period of the clock signal generated based on the power supply may be unstable. Furthermore, for some reason, the period of the clock signal generated by a wireless tag may differ from the period of the clock signals of other wireless tags. In such cases, stable data communication between the wireless tag and the communication terminal may not be possible.

[0008] The present invention has been made to solve the above problems, and has an object to provide a wireless tag, a communication terminal, a communication system, and a communication method that are capable of performing stable data communication.

[0009] The wireless tag of the present invention is a wireless tag that modulates tag transmission data including tag information of a predetermined data length and transmits it as a tag transmission wave to a communication terminal, and is equipped with a clock signal generation circuit that generates a clock signal of a predetermined period, a tag controller that assigns a prefix of a fixed signal pattern indicating the start of the tag information to the tag information and generates the tag transmission data including the prefix and the tag information, whose signal level changes according to the period of the clock signal, a modulation circuit that modulates the tag transmission data generated by the tag controller to generate the tag transmission wave, and a tag antenna that transmits the tag transmission wave to the communication terminal, and by having the communication terminal receive the tag transmission wave, the communication terminal is made to identify the period of the clock signal generated by the clock signal generation circuit based on the rise period and / or fall period of the signal level in the prefix, and acquires the tag information based on the identified period of the clock signal.

[0010] The communication terminal of the present invention is a communication terminal that receives tag transmission waves transmitted from a wireless tag by modulating tag transmission data including tag information of a predetermined data length, and acquires the tag information by demodulating the tag transmission waves, and is equipped with a terminal antenna that receives from the wireless tag the tag transmission waves generated by modulating the tag transmission data including the prefix and tag information, the signal level of which has changed according to a clock signal of a predetermined period generated by the wireless tag, a signal processing unit that demodulates the tag transmission waves and generates the tag transmission data, and a terminal controller that identifies the period of the clock signal generated by the wireless tag based on the rise period and / or fall period of the signal level of the prefix included in the tag transmission data, and acquires the tag information based on the identified period of the clock signal.

[0011] The communication system according to the present invention is a communication system having a radio tag that modulates tag transmission data including tag information of a predetermined data length and transmits the modulated tag transmission data as a tag transmission wave, and a communication terminal that receives the tag transmission wave transmitted from the radio tag and demodulates the tag transmission wave to acquire the tag information, wherein the radio tag has a clock signal generation circuit that generates a clock signal of a predetermined period, a tag controller that assigns a prefix of a fixed signal pattern indicating the start of the tag information to the tag information, and generates the tag transmission data including the prefix and the tag information, the signal level of which changes according to the period of the clock signal, and The communication terminal comprises a modulation circuit that modulates the tag transmission data generated by a tag controller to generate the tag transmission wave, and a tag antenna that transmits the tag transmission wave to the communication terminal, and the communication terminal comprises a terminal antenna that receives the tag transmission wave transmitted from the wireless tag, a signal processing unit that demodulates the tag transmission wave to generate the tag transmission data, and a terminal controller that identifies the period of the clock signal generated by the wireless tag based on the rise period and / or fall period of the signal level in the prefix included in the tag transmission data, and acquires the tag information based on the identified period of the clock signal.

[0012] A communication method according to the present invention is a communication method carried out between a wireless tag that modulates tag transmission data including tag information of a predetermined data length and transmits the modulated tag transmission data as a tag transmission wave, and a communication terminal that receives the tag transmission wave transmitted from the wireless tag and demodulates the tag transmission wave to acquire the tag information, the method comprising the steps of: a clock signal generation step in which the wireless tag generates a clock signal of a predetermined period using a clock signal generation circuit; a tag transmission data generation step in which the wireless tag adds a prefix of a fixed signal pattern indicating the start of the tag information to the tag information, and generates the tag transmission data including the prefix and the tag information, the signal level of which has changed in accordance with the period of the clock signal; and a transmitting step of transmitting the tag transmission wave from a tag antenna to the communication terminal, and the communication terminal performs a receiving step of receiving the tag transmission wave transmitted from the wireless tag with a terminal antenna, a demodulating step of demodulating the tag transmission wave to generate the tag transmission data with a signal processing unit, and an acquiring step of specifying, by a terminal controller, the period of the clock signal generated by the wireless tag based on the rise period and / or fall period of the signal level in the prefix included in the tag transmission data, and acquiring the tag information based on the specified period of the clock signal.

[0013] According to the present invention, the communication terminal detects the period of the clock signal generated by the clock signal generation circuit of the RF tag based on the prefix added to the tag information, and the communication terminal acquires the tag information based on the period of the detected clock signal, so that even if there is variation in the period of the clock signal generated by the RF tag, the communication terminal can acquire the tag information, thereby achieving stable data communication.

[0014] 4 is a block diagram showing the circuit configuration of a wireless tag. It is a block diagram showing the circuit configuration of a communication terminal. 1001 is a schematic diagram showing the waveform of a terminal transmission wave received by a wireless tag, 1002 is a schematic diagram showing the output of a rectifier circuit of the wireless tag, 1003 is a schematic diagram showing the waveform of a clock signal generated by the wireless tag, 1004 is an explanatory diagram for explaining tag information of the wireless tag, 1005 is a schematic diagram showing the waveform of tag transmission data generated by the wireless tag, and 1006 is a schematic diagram showing the waveform of a tag transmission wave generated by the wireless tag. 1011 is a schematic diagram showing the waveform of a clock signal, and 1012 is a schematic diagram for explaining tag transmission data generated according to the cycle of the clock signal 1011. 1021 is a schematic diagram showing the waveform of a clock signal, and 1022 is tag transmission data generated according to the cycle of the clock signal 1021, and is an enlarged view of the area of ​​the information transmission period shown in 1012 in FIG. 4. It is a flowchart showing a data transmission processing procedure in a wireless tag. It is a flowchart showing a data reception processing procedure in a communication terminal. 1 is a flowchart showing a tag information acquisition process procedure. 1031 is a schematic diagram showing the waveform of tag transmission data when the width TA of one cycle of the clock signal is small, and 1032 is a schematic diagram showing the waveform of tag transmission data when one cycle of the clock signal has a width TB larger than the width TA. 1041 is a schematic diagram showing the waveform of the clock signal, and 1042 is a schematic diagram for explaining tag transmission data (1) according to another embodiment, which is generated according to the cycle of the clock signal of 1041. 1051 is a schematic diagram showing the waveform of the clock signal, and 1052 is a schematic diagram for explaining tag transmission data (2) according to another embodiment, which is generated according to the cycle of the clock signal of 1051. 1061 is a schematic diagram showing the waveform of the clock signal, and 1062 is a schematic diagram for explaining tag transmission data (3) according to another embodiment, which is generated according to the cycle of the clock signal of 1061. 1071 is a schematic diagram showing the waveform of a clock signal, 1072 is a schematic diagram showing the waveform of tag transmission data, and 1073 is a schematic diagram showing the waveform of terminal received data (1) in which the timing of the falling and rising edges of the signal level is shifted.1081 is a schematic diagram showing the waveform of a clock signal, 1082 is a schematic diagram showing the waveform of tag transmission data, and 1083 is a schematic diagram showing the waveform of terminal received data (2) in which the timing of the falling and rising edges of the signal level is shifted.

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] <Overview of Communication System> Fig. 1 is a block diagram showing the circuit configuration of a wireless tag 1 according to this embodiment, and Fig. 2 is a block diagram showing the circuit configuration of a communication terminal 2 according to this embodiment. The communication system is composed of the wireless tag 1 shown in Fig. 1 and the communication terminal 2 shown in Fig. 2. In the communication system, for example, a plurality of wireless tags 1 are pre-installed on devices, products, etc., and when a user who owns a communication terminal 2 moves to each installation location of the wireless tags 1, the user holds the communication terminal 2 over the wireless tags 1, thereby enabling data communication between the wireless tags 1 and the communication terminal 2.

[0017] The data communication between the wireless tag 1 and the communication terminal 2 is carried out in accordance with a predetermined communication standard, using, for example, a shortwave band (13.56 MHz) to which the wireless tag 1 can supply power by electromagnetic induction, a UHF band (860 to 960 MHz), a microwave band (2400 to 2483.5 MHz), etc.

[0018] In this case, the communication system transmits a carrier wave (hereinafter referred to as a terminal transmission wave) from the communication terminal 2 to the wireless tag 1, and when the wireless tag 1 receives the terminal transmission wave from the communication terminal 2, the wireless tag 1 is powered by the radio wave energy of the terminal transmission wave. The wireless tag 1 is started up by being powered by the radio wave energy of the terminal transmission wave and generates a clock signal. The wireless tag 1 also operates the tag controller 15 with the clock signal and generates tag transmission data from a prefix, which is a fixed signal pattern, and tag information, which is identification information unique to the wireless tag 1. In this way, the wireless tag 1 generates the prefix and tag information in the tag controller 15, modulates the obtained tag transmission data to generate a carrier wave (hereinafter referred to as a tag transmission wave), and transmits the tag transmission wave to the communication terminal 2.

[0019] When the communication terminal 2 receives a tag transmission wave from the wireless tag 1, it demodulates the tag transmission wave and detects the prefix included in the tag transmission data. The communication terminal 2 then identifies the period of the clock signal generated by the wireless tag 1 based on the rise and fall changes in the signal level of the prefix, which is a fixed signal pattern. This allows the communication terminal 2 to identify the period of the clock signal used in the wireless tag 1 when the wireless tag 1 generated the tag transmission data, and to obtain tag information included in the tag transmission data based on the identified period of the clock signal, without having to generate a clock signal by itself.

[0020] In this way, the communication system of this embodiment allows the communication terminal 2 to identify the period of the clock signal generated by the wireless tag 1 based on the prefix assigned to the tag information in the wireless tag 1. Therefore, even if the period of the clock signal generated by the wireless tag 1 is deviated from the period of the clock signal generated by another wireless tag (not shown) for some reason, the tag information can be obtained based on the period of the clock signal of the wireless tag 1 identified by the communication terminal 2.

[0021] <Configuration of Wireless Tag> Next, the wireless tag 1 will be described in detail. As shown in Fig. 1 , the wireless tag 1 includes a tag antenna 11, such as an RF (Radio Frequency) antenna, a rectifier circuit 12, a clock signal generation circuit 13, an ID data recording unit 14, a tag controller 15, and a modulation circuit 16. The tag antenna 11 can transmit and receive radio waves capable of data communication with the communication terminal 2, such as radio waves in the short wave band (13.56 MHz) used in electromagnetic induction systems, radio waves in the UHF band (860-960 MHz), and radio waves in the microwave band (2400-2483.5 MHz). In this case, the tag antenna 11 receives terminal transmission waves transmitted from the communication terminal 2 and transmits tag transmission waves generated in response to the reception of the terminal transmission waves to the communication terminal 2.

[0022] 3 indicates an example of a waveform of a terminal transmission wave received by the wireless tag 1. The wireless tag 1 according to this embodiment does not have a power source, and power is supplied to each circuit based on the terminal transmission wave received from the communication terminal 2. The tag antenna 11 tunes to the frequency band of the terminal transmission wave transmitted from the communication terminal 2 and excites AC power based on the received terminal transmission wave. The tag antenna 11 generates a current according to the intensity of the received terminal transmission wave, and because the terminal transmission wave is an AC signal, positive and negative currents are generated alternately.

[0023] The rectifier circuit 12 has a function of converting AC to DC, and rectifies the AC power excited by the tag antenna 11 into DC power. The rectifier circuit 12 generates a constant DC power as shown by 1002 in Fig. 3, and outputs the obtained DC power to the clock signal generation circuit 13, etc. In this case, the rectifier circuit 12 is, for example, a bridge full-wave rectifier circuit using a plurality of rectifier elements (for example, point-contact semiconductor diodes), and generates DC power that serves as drive power for the wireless tag 1 from positive power of a predetermined strength.

[0024] The rectifier circuit 12 may rectify AC power to DC power and may also boost the DC power, or may output the resulting DC voltage to a battery (not shown) to charge the battery with the DC power. Here, a case will be described in which the wireless tag 1 operates using DC power generated by the rectifier circuit 12, but the present invention is not limited to this, and the wireless tag 1 may also operate using power supplied from a battery provided in advance.

[0025] 3, the clock signal generation circuit 13 generates a clock signal in which the duration of the rising edge (also referred to as the rising period) and the duration of the falling edge (also referred to as the falling period) of the signal level are constant and the rising period and the falling period change alternately and repeatedly in a cyclical manner, as shown by 1003 in Fig. 3, based on the DC power output from the rectifier circuit 12. The clock signal generation circuit 13 outputs the obtained clock signal to the tag controller 15, which will be described later.

[0026] The ID data recording unit 14 records a unique identifier that has been individually set in advance for each wireless tag 1 as tag information. The tag information according to this embodiment is, for example, identification information used to allow the communication terminal 2 to identify the wireless tag 1, and is a binary signal consisting of a predetermined number of bits (data length) expressed in binary notation of "0" and "1", as shown by 1004 in Fig. 3. The tag information according to this embodiment will be described below assuming, for example, that the identification information identifying the wireless tag 1 is expressed as a binary signal of "10110101".

[0027] In this embodiment, a case will be described in which identification information for identifying the wireless tag 1 is used as tag information possessed by the wireless tag, but the present invention is not limited to this. For example, in a wireless tag equipped with a sensor, an arithmetic circuit, etc., the tag information may include, in addition to identification information for identifying the wireless tag, temperature information measured by the sensor, various detection information detected by the sensor, and calculation information calculated by the arithmetic circuit. In this case, the communication terminal 2 can not only identify the wireless tag but also acquire the temperature information, detection information, and calculation information obtained by the wireless tag. In the following, for simplicity of explanation, a case will be described in which identification information for identifying the wireless tag 1 is used as tag information.

[0028] The tag controller 15 reads the tag information recorded in the ID data recording unit 14, and adds a prefix (described later) to the tag information, thereby including the wait information, the prefix, and the tag information. As a result, the tag controller 15 generates tag transmission data (1005 in FIG. 3) in which the wait information is followed by the prefix and the tag information.

[0029] Here, 1011 in Fig. 4 is a schematic diagram showing the waveform of a clock signal, and 1012 in Fig. 4 is a schematic diagram showing the waveform of tag transmission data generated from the wait information, prefix, and tag information of the clock signal of 1011 in Fig. 4. As shown in 1012 in Fig. 4, the tag transmission data has a wait period and an information transmission period. In the tag transmission data according to this embodiment, a wait period with a continuous rising signal level exists before the prefix period of the information transmission period, and the wait period and the information transmission period are arranged alternately.

[0030] The standby period is a period during which standby information is generated that has a data length (bit length) longer than the data length (bit length) of the tag information and that has a continuous signal level different from the signal level at the beginning of the prefix. Here, the data length of the tag information is 8 bits, so the standby period is set to a data length of 9 bits, which is one bit longer than the data length of the tag information. Also, here, the beginning of the prefix is ​​set to a falling signal level, so during the standby period, a signal is generated that has a continuous rising signal level different from the signal level of the prefix.

[0031] The tag controller 15 generates, as the standby information, a rising signal level having a predetermined data length represented by, for example, a binary "1," thereby generating a signal in which the falling timing of the "1" of the standby information and the falling timing of the "1" are varied in accordance with the rising and falling timing of the clock signal, as shown in 1012 of FIG. 4. In 1012 of FIG. 4, the data length from the start time (also referred to as the start time) t1 of the standby period to the end time (also referred to as the end time) t2 of the standby period is 9 bits, and a rising signal level continues continuously from time t1 to t2. Here, the start time t1 of the standby period is the time when a predetermined rising edge occurs, and the end time t2 of the standby period is the time when a falling edge occurs after the rising signal level has continued continuously for the predetermined data length from the start time t1.

[0032] The information transmission period following the waiting period is composed of a period in which a signal related to a prefix is ​​generated (hereinafter also referred to as a prefix period) and a period in which a signal related to tag information is generated (hereinafter referred to as a tag information period), and the prefix period occurs immediately before the tag information period.

[0033] The prefix is ​​also called SOF (Start Of Frame) and is set in advance in, for example, the tag controller 15. The prefix indicates the start of tag information in tag transmission data and is a binary signal with a fixed signal pattern expressed in binary numbers of "0" and "1." In this embodiment, the following description will be given taking as an example a case where the prefix is ​​a signal pattern of "010" in which the signal level changes in the order of falling, rising, and falling immediately after a standby period.

[0034] The tag controller 15 according to this embodiment adds prefixes and tag information expressed in binary numbers "0" and "1" after the standby information, and generates a signal in which the falling timing of "0" and the rising timing of "1" of the prefix and tag information are changed according to the rising and falling timing of the clock signal (1012 in FIG. 4 shows the case where only the rising timing is shown), for example, with "0" of the prefix and tag information being a falling edge and "1" being a rising edge, as shown in 1011 in FIG. 4.

[0035] As a result, in the tag transmission data, standby information with a rising signal level whose data length is longer than the data length of the tag information is generated during the standby period. Also, in the tag transmission data, a prefix of a binary signal (here, "010") with a fixed signal pattern whose leading edge has a falling signal level different from the rising signal level of the standby information, and tag information represented by a predetermined binary signal (here, "10110101") are generated during the information transmission period. The tag controller 15 outputs the generated tag transmission data to the modulation circuit 16 (FIG. 1).

[0036] The modulation circuit 16 generates a tag transmission wave as shown by 1006 in Fig. 3 by modulating the tag transmission data based on the terminal transmission wave received from the communication terminal 2. As a result, the tag antenna 11 transmits the tag transmission wave generated by the modulation circuit 16 to the communication terminal 2 as a reflected wave of the terminal transmission wave. Note that in this embodiment, a case will be described in which the tag transmission data is modulated based on the terminal transmission wave received from the communication terminal 2 and the tag transmission wave is transmitted from the wireless tag 1 to the communication terminal 2 as a reflected wave (radio wave) of the terminal transmission wave, but the present invention is not limited to this. For example, the wireless tag 1 may be configured to have a transmission wave generation unit, and the tag transmission wave may be generated by modulating the tag transmission data using a carrier wave generated by the transmission wave generation unit.

[0037] <Configuration of Communication Terminal> Next, a detailed description will be given of the communication terminal 2. The communication terminal 2 according to this embodiment is a reader, reader / writer, or the like, and as shown in Fig. 2, includes, for example, a terminal antenna 21 such as an RF antenna, a signal processing unit 22, a carrier wave generating unit 23, a terminal controller 24, a communication module 25, and a battery 26. The battery 26 is a power source that supplies power to various circuits within the communication terminal 2.

[0038] The terminal antenna 21 can transmit and receive radio waves capable of data communication with the wireless tag 1, such as radio waves in the short wave band (13.56 MHz) used in the electromagnetic induction system, radio waves in the UHF band (860 to 960 MHz), and radio waves in the microwave band (2400 to 2483.5 MHz). In this case, the terminal antenna 21 transmits terminal transmission waves toward the wireless tag 1, and receives tag transmission waves transmitted from the wireless tag 1 in response to the wireless tag 1 receiving the terminal transmission waves.

[0039] The signal processing unit 22 includes circuits that perform various signal processing required for communication, such as an analog circuit that performs digital-to-analog conversion processing, a matching circuit, and a demodulation circuit. The signal processing unit 22 uses, for example, a matching circuit to match the impedance between the tag antenna 11 and the circuitry in the communication terminal 2, thereby ensuring the communication performance of the terminal antenna 21. The signal processing unit 22 also uses a demodulation circuit to demodulate the tag transmission wave received by the terminal antenna 21, thereby generating a demodulated signal from which the carrier wave (reflected wave) component has been removed. The carrier wave generation unit 23 includes an oscillator and generates a terminal transmission wave of a predetermined frequency.

[0040] The terminal controller 24 performs analog-to-digital conversion processing on the demodulated signal obtained by demodulating the tag transmission wave using the signal processing unit 22, thereby generating the tag transmission data generated by the wireless tag 1 as terminal reception data. The terminal controller 24 analyzes the rise and fall of the signal level of the obtained tag transmission data (terminal reception data), and identifies the cycle of the clock signal used when the tag transmission data was generated in the wireless tag 1 based on the rise and fall of the signal level of the prefix within the information transmission period.

[0041] Specifically, when the terminal controller 24 detects that the signal level has changed to a falling edge after nine consecutive bits of rising signal level in the tag transmission data, as shown by 1012 in Figure 4, it recognizes that the waiting period has transitioned to the information transmission period, and identifies the signal level that has changed in the order of falling, rising, and falling, detected after the waiting period of consecutive rising edges, as a prefix.

[0042] Here, one bit of information represented by one rising edge or one falling edge in the tag transmission data is transmitted during one cycle (one CLC) of the clock signal, which consists of a falling edge and a rising edge, as shown by 1011 and 1012 in Figure 4. Therefore, the terminal controller 24 can identify one cycle of the clock signal by detecting the duration of the falling edge at the beginning of the prefix (the falling period, which is the time from the first falling edge to the next rising edge).The terminal controller 24 can then obtain the data communication speed [bit / sec] by calculating the reciprocal of the identified cycle of the clock signal.

[0043] In this way, the terminal controller 24 detects the duration of the falling edge of the prefix, which corresponds to one cycle (1 CLC) of the clock signal, and thereby can identify the cycle of the clock signal generated on the wireless tag 1 side. The terminal controller 24 sequentially detects the rising and falling signal levels that appear after the last falling edge of the signal level of the prefix, which changes in signal level from falling to rising and falling in that order, based on the identified cycle of the clock signal, and acquires the detected signal level of a predetermined data length (here, 8 bits) as tag information.

[0044] Here, 1021 and 1022 in Figure 5 are enlarged views of the information transmission period indicated by 1011 and 1012 in Figure 4. Below, using 1021 and 1022 in Figure 5, the tag information acquisition process in which the terminal controller 24 acquires tag information will be described in detail. In this case, as described above, the terminal controller 24 measures the time t2 to t3, which is the duration of the falling edge at the beginning of the prefix, and identifies the time from t2 to t3 as one cycle (1 CLC) of the clock signal. The terminal controller 24 sets the time t4 of the last falling edge of the prefix signal level (signal level from times t2 to t5), which changes in the order of falling, rising, and falling, as the reference time t4.

[0045] Here, the terminal controller 24 has preset times tg1 to tg8, at which the signal level is judged in order at predetermined intervals from the set reference time t4. In the terminal controller 24 according to this embodiment, for example, a time tg1 that is 1.5 times the period of one clock signal (denoted as 1.5CLC), a time tg2 that is 2.5 times the period of one clock signal (denoted as 2.5CLC), a time tg3 that is 3.5 times the period of one clock signal (denoted as 3.5CLC), a time tg4 that is 4.5 times the period of one clock signal (denoted as 4.5CLC), a time tg5 that is 5.5 times the period of one clock signal (denoted as 5.5CLC), a time tg6 that is 6.5 times the period of one clock signal (denoted as 6.5CLC), a time tg7 that is 7.5 times the period of one clock signal (denoted as 7.5CLC), and a time tg8 that is 8.5 times the period of one clock signal (denoted as 8.5CLC) are preset as times at which the signal level is determined.

[0046] The terminal controller 24 reads the signal level at time tg1, which is 1.5 CLC after reference time t4, from the terminal reception data (tag transmission data), and acquires the read signal level as the first bit of tag information. Similarly, the terminal controller 24 reads the signal levels at time tg2, which is 2.5 CLC after reference time t4, time tg3, which is 3.5 CLC after reference time t4, time tg4, which is 4.5 CLC after reference time t4, time tg5, which is 5.5 CLC after reference time tg6, time tg7, which is 7.5 CLC after reference time t4, and time tg8, which is 8.5 CLC after reference time t4, from the terminal reception data, and determines whether the read signal level is a rising edge or a falling edge.

[0047] The terminal controller 24 regards the rising signal level as "1" and the falling signal level as "0", obtains the signal level expressed in binary "0" and "1" as information from the first bit to the eighth bit of the tag information, and acquires the tag information represented by a predetermined binary signal ("10110101").

[0048] In this embodiment, the tag information acquired by the terminal controller 24 is output from the terminal controller 24 to the communication module 25. The communication module 25 is, for example, a communication interface capable of sending and receiving data to and from an external device, and transmits the tag information of the wireless tag 1 acquired by the terminal controller 24 to the external device. The external device is, for example, a display device or an information processing device such as a personal computer, and the tag information acquired by the communication terminal 2 can be used for various services such as managing products to which the wireless tag 1 is attached and viewing data.

[0049] In this embodiment, a case will be described in which tag information acquired by the terminal controller 24 is output from the terminal controller 24 to the communication module 25, but the present invention is not limited to this. For example, the communication terminal 2 may be configured to perform determination processing, management processing, etc. using the acquired tag information, and present the processing results to the user via a presentation unit (not shown) for device management, product management, etc.

[0050] <Data Transmission Processing in Wireless Tag> Next, the above-mentioned data transmission processing in the wireless tag 1, which is performed when transmitting and receiving data between the wireless tag 1 and the communication terminal 2, will be described with reference to the flowchart in Fig. 6. As shown in Fig. 6, in step S11, the wireless tag 1 receives the terminal transmission wave transmitted from the communication terminal 2 at the tag antenna 11, and then proceeds to the next step S12.

[0051] In step S12, the wireless tag 1 uses the rectifier circuit 12 to rectify the AC power generated in step S11 as a result of the tag antenna 11 receiving the terminal transmission wave, and supplies the resulting DC power to each circuit in the wireless tag 1 before proceeding to the next step S13. In step S13, the wireless tag 1 activates the clock signal generation circuit 13, which generates a clock signal such as that shown by 1021 in Fig. 4, and then proceeds to the next step S15.

[0052] In step S15, the wireless tag 1 operates the tag controller 15 by the clock signal generated in step S13, reads tag information from the ID data recording unit 14, and adds a prefix to the beginning of the tag information, thereby including wait information, the prefix, and the tag information. As a result, the wireless tag 1 generates tag transmission data (1005 in FIG. 3) in which the wait information is followed by the prefix and the tag information in that order, and proceeds to the next step S16.

[0053] In step S16, the wireless tag 1 generates a tag transmission wave by modulating the tag transmission data generated in step S15 using the modulation circuit 16 based on the terminal transmission wave received from the communication terminal 2, and proceeds to the next step S17. In step S17, the wireless tag 1 transmits the tag transmission wave generated in step S16 to the communication terminal 2 using the tag antenna 11, and ends the above-mentioned data transmission processing procedure.

[0054] <Data Reception Processing in Communication Terminal> Next, the above-mentioned data reception processing in the communication terminal 2, which is performed when transmitting and receiving data between the wireless tag 1 and the communication terminal 2, will be described using the flowchart shown in Fig. 7. As shown in Fig. 7, when the communication terminal 2 transmits a terminal transmission wave from the terminal antenna 21, the process proceeds from a start step to step S21, and when the wireless tag 1 receives the terminal transmission wave, the tag transmission wave transmitted from the wireless tag 1 is received via the terminal antenna 21, and the process proceeds to the next step S22.

[0055] In step S22, the communication terminal 2 performs various signal processing such as demodulation processing on the tag transmission wave received in step S21 using the signal processing unit 22 to generate a demodulated signal, outputs the obtained demodulated signal to the terminal controller 24, and proceeds to the next step S23. In step S23, the communication terminal 2 performs tag information acquisition processing on the demodulated signal obtained in step S22 using the terminal controller 24, generates tag transmission data as terminal reception data, acquires tag information from the tag transmission data, and ends the above-mentioned processing.

[0056] The tag information acquisition process performed in step S23 will now be described with reference to the flowchart shown in Fig. 8. As shown in Fig. 8, in step S231, the terminal controller 24 determines whether or not a signal level with consecutive rising edges longer than a preset data length has been detected. If a negative result is obtained in step S231, this indicates that a signal level with consecutive rising edges longer than the preset data length has not been detected, i.e., detection of standby information has not been completed. In this case, the terminal controller 24 waits until a positive result is obtained in step S231.

[0057] On the other hand, if a positive result is obtained in step S231, this indicates that a continuous rising signal level longer than the preset data length has been detected, i.e., detection of standby information has been completed, and the terminal controller 24 then proceeds to the next step S232.

[0058] In step S232, the terminal controller 24 determines whether or not a falling edge has been detected after detecting the standby information. If a negative result is obtained in step S232, this indicates that a falling edge has not been detected, and the terminal controller 24 waits until a falling edge is detected.

[0059] On the other hand, if a positive result is obtained in step S232, this indicates that a falling edge has been detected, and the terminal controller 24 proceeds to the next step S233, assuming that the first bit of the prefix has been detected. In step S233, the terminal controller 24 starts measuring time from the falling edge, and proceeds to the next step S234.

[0060] In step S234, the terminal controller 24 determines whether a rising edge has been detected. If a negative result is obtained in step S234, this indicates that a rising edge has not been detected, that is, the signal level continues to fall from the falling edge, and the terminal controller 24 waits until a rising edge is detected.

[0061] On the other hand, if a positive result is obtained in step S234, this indicates that a rising edge has been detected, i.e., that the signal level has changed from falling to rising, and the terminal controller 24 proceeds to the next step S235. In step S235, the terminal controller 24 ends measurement of the time from the falling edge and determines the period of the clock signal from the duration of the falling edge measured from the falling edge to the rising edge, and proceeds to the next step S236.

[0062] In step S236, the terminal controller 24 again determines whether a falling edge has been detected. If a negative result is obtained in step S236, this indicates that a falling edge has not been detected, that is, the rising signal level continues from the rising edge, and in this case the terminal controller 24 waits until a falling edge is detected.

[0063] On the other hand, if a positive result is obtained in step S236, this indicates that a falling edge has been detected, i.e., that the signal level has changed from rising to falling, and the terminal controller 24 proceeds to the next step S237. In step S237, the terminal controller 24 recognizes that the second detected falling edge is the last falling edge of the prefix, sets the time t4 when the falling edge was detected as the reference time t4, and proceeds to the next step S238.

[0064] In step S238, the terminal controller 24 determines whether the signal level at times tg1 to tg8, which are preset signal level readout times from the reference time t4, is a rising signal level or a falling signal level, in accordance with the period of the clock signal identified in step S235, and acquires tag information of a predetermined data length (8 bits), thereby completing the above-described tag information acquisition processing procedure.

[0065] <Operations and Effects> In the above configuration, the communication system according to this embodiment includes the wireless tag 1 that modulates tag transmission data including tag information of a predetermined data length and transmits the modulated data as a tag transmission wave, and the communication terminal 2 that receives the tag transmission wave transmitted from the wireless tag and demodulates the tag transmission wave to acquire the tag information. When performing data communication with the communication terminal 2, the wireless tag 1 generates a clock signal with a predetermined cycle using the clock signal generation circuit 13.

[0066] The wireless tag 1 then assigns a prefix of a fixed signal pattern indicating the start of the tag information to the tag information, and generates tag transmission data including the prefix and tag information, whose signal level changes in accordance with the cycle of the clock signal, using the tag controller 15. The wireless tag 1 modulates the tag transmission data generated by the tag controller 15 using the modulation circuit 16 to generate a tag transmission wave, and transmits the tag transmission wave from the tag antenna 11 to the communication terminal 2.

[0067] The communication terminal 2 demodulates the tag transmission wave received by the terminal antenna 21 using the signal processing unit 22 to generate tag transmission data as terminal reception data. The communication terminal 2 then identifies the period of the clock signal generated by the wireless tag 1 based on the falling period of the signal level in the prefix included in the tag transmission data obtained as terminal reception data. The communication terminal 2 acquires tag information from the tag transmission data based on the period of the clock signal detected from the tag transmission data by the terminal controller 24, without setting a clock signal on its own.

[0068] Here, since the wireless tag 1 according to this embodiment is powered using terminal transmission waves from the communication terminal 2, the operation of the clock signal generation circuit 13 may become unstable depending on the reception conditions of the terminal transmission waves, and the period of the clock signal in the clock signal generation circuit 13 may become different from the period of the clock signals of other wireless tags. Also, the period of the clock signal generated by the wireless tag 1 may become different from the period of the clock signals of other wireless tags for some reason.

[0069] The communication terminal 2 according to this embodiment can identify the period of the clock signal generated by the wireless tag 1 based on the prefix added to the tag information, and acquire the tag information based on the detected period of the clock signal. As a result, even if the period of the clock signal generated by each wireless tag 1 varies from one wireless tag 1 to another, such as when the width TA of one period of the clock signal generated by the wireless tag 1 is small as shown by 1031 in Fig. 9 , or when the width TB of one period of the clock signal generated by the wireless tag 1 is larger than the width TA as shown by 1032 in Fig. 9 , the communication terminal 2 can acquire the tag information without being affected by the variation in the period of the clock signal. Therefore, stable data communication can be performed between the wireless tag 1 and the communication terminal 2.

[0070] Furthermore, in the communication system, the communication terminal 2 detects the period of the clock signal generated by the wireless tag 1 based on the prefix assigned to the tag information by the wireless tag 1. For this reason, in the communication system according to this embodiment, it is not necessary for the wireless tag 1 to synchronize its own clock signal with the clock signal of the communication terminal 2, or for the communication terminal 2 to synchronize its own clock signal with the clock signal of the wireless tag 1. Therefore, since a synchronization processing circuit for the clock signal is not required, the circuits of the wireless tag 1 and the communication terminal 2 can be made smaller.

[0071] Other Embodiments In the above-described embodiment, the communication terminal 2 determines the period of the clock signal generated by the wireless tag 1 based on the time from the fall to the rise of the signal level in the prefix (fall period), but the present invention is not limited to this. For example, in another embodiment, the communication terminal 2 may determine the period of the clock signal generated by the wireless tag 1 based on the time from the rise to the fall of the signal level in the prefix (rise period).

[0072] Furthermore, in the above-described embodiment, the communication terminal 2 is described as specifying the period of the clock signal generated by the wireless tag 1 based on the time from the falling edge to the rising edge (falling edge period) of the prefix detected after detecting standby information in which a signal level of a rising edge continues in the tag transmission data, but the present invention is not limited to this. For example, as shown by 1041 and 1042 in Fig. 10, the communication terminal 2 may specify the period of the clock signal generated by the wireless tag 1 based on the time from the falling edge to the rising edge of the prefix detected after detecting standby information in which a signal level of a rising edge continues in the tag transmission data, to the falling edge again (falling edge period and rising edge period).

[0073] In this way, the communication terminal 2 may determine the period of the clock signal from two periods A of the clock signal (here, two periods as one unit are represented as A, and A = 2CLC), including not only the duration of the fall (fall period) generated in one period of the clock signal but also the duration of the rise (rise period) generated in the next period of the clock signal, and in such a case, the same effect as in the above-mentioned embodiment can be achieved.

[0074] In the above-described embodiment, one clock signal cycle (1 CLC) is identified based on the prefix of the tag transmission data, and the time t4 at which the trailing edge of the last edge of the prefix is ​​detected is set as the reference time t4. The signal level is determined at 1.5 times one clock signal cycle (1.5 CLC) tg1, 2.5 times one clock signal cycle (2.5 CLC) tg2, and so on, from the reference time t4, to acquire tag information. However, the present invention is not limited to this. In another embodiment, for example, as shown by 1041 and 1042 in FIG. 10 , two clock signal cycles A corresponding to two bits, the trailing edge and the rising edge at the beginning of the prefix, may be identified as one unit, and the times tg1, tg2, and so on, at which the signal level is determined, may be set based on the identified two cycles A.

[0075] In this case, the communication terminal 2 sets the time t4 when the falling edge at the end of the prefix is ​​detected as the reference time t4, and acquires tag information by determining the signal level at a time tg1 that is 0.75 times two cycles A of the clock signal (0.75 A), a time tg2 that is 1.25 times two cycles A, and so on from the reference time t4. Even with this tag information acquisition processing procedure, it is possible to achieve the same effects as in the above-described embodiment.

[0076] In the above-described embodiment, a prefix consisting of a falling edge, a rising edge, and another falling edge is applied, but the present invention is not limited to this. For example, if the standby information has a series of falling edge signals, a prefix consisting of a rising edge, a falling edge, and another rising edge may be applied. In another embodiment, a prefix consisting of two or more consecutive falling edges and rising edges may be applied, as shown by 1051 and 1052 in Fig. 11.

[0077] 11, the prefix 1052 has multiple alternating "0"s indicating a falling edge and "1"s indicating a rising edge, resulting in a configuration of "0101010" where "01" is repeated three times followed by "0". In such a case, the terminal controller 24 may determine the period of the clock signal based on the duration of the falling edges generated in one period of the clock signal (times t2 to t3 (time t3 in 1052 in FIG. 11 is not shown, but is located midway between times t2 and t4)), as in the above-described embodiment, or may further determine the period of the clock signal from two periods of the clock signal, including the duration of the rising edges generated in one period of the clock signal.

[0078] Furthermore, the terminal controller 24 may calculate one cycle (1 CLC) or an average of two cycles A from two cycles A (= 2 CLC) of the clock signal, and identify the cycle of the clock signal from the calculated average. Specifically, as shown in 1052 of FIG. 11 , for example, if there are three two cycles A of the clock signal, the terminal controller 24 calculates the average value of the two cycles A from these three two cycles A. The terminal controller 24 sets the time t8 at which the trailing edge of the prefix is ​​detected as the reference time t8, and acquires tag information by determining the signal level at a time (0.75 A) tg1 that is 0.75 times the average value of two cycles A, a time (1.25 A) tg2 that is 1.25 times the average value of two cycles A, and so on. Even with this tag information acquisition processing procedure, the same effects as those of the above-described embodiment can be achieved.

[0079] Furthermore, in the above-described embodiment, one rising edge and one falling edge of the prefix are generated for each cycle consisting of the rising and falling edges of the clock signal. However, the present invention is not limited to this. In other embodiments, for example, as shown by 1061 and 1062 in FIG. 12 , one falling edge and one rising edge of the prefix may be generated not in one cycle but in half a cycle of the clock signal. Furthermore, the timing of generating the rising and falling edges of the prefix may be different, such as one cycle or half a cycle of the clock signal, for each rising and falling edge of the prefix. Note that 1062 in FIG. 12 shows an example in which the first falling and rising edge of the prefix are generated in synchronization with a half cycle of the clock signal, and the last remaining falling edge of the prefix is ​​generated in synchronization with one cycle of the clock signal. However, all falling and rising edges of the prefix may be generated in half a cycle of the clock signal.

[0080] In this case, the tag controller 15 generates the signal level of the first falling edge of the prefix during the rising edge period of one half cycle of the clock signal (time t2 to t2'), and generates the signal level of the next rising edge of the prefix during the falling edge period of the next half cycle of the clock signal (time t2' to t3).Furthermore, the tag controller 15 generates the signal level of the last falling edge of the prefix during the rising and falling edge periods of the next cycle of the clock signal.

[0081] The terminal controller 24 measures the time from the falling edge to the rising edge of the prefix (times t2 to t3), which corresponds to one cycle of the clock signal, detected after detecting the standby information.The terminal controller 24 then determines the cycle of the clock signal generated by the wireless tag 1 based on the measured time from the falling edge to the rising edge of the prefix, and sets the time t3 at which the falling edge of the prefix is ​​detected as the reference time t3.

[0082] The terminal controller 24 acquires tag information by determining the signal level at each of the following times, starting from the reference time t3: time tg1, which is 1.5 times one cycle B of the clock signal (1.5B), time tg2, which is 2.5 times one cycle B (2.5B), and so on, in accordance with the identified cycle of the clock signal. Even with this tag information acquisition procedure, the same effects as those of the above-described embodiment can be achieved. As shown in 1062 of FIG. 12, when one cycle B of the clock signal is defined as 1 CLC, times tg1 to tg8 correspond to 1.5 CLC to 8.5 CLC.

[0083] In the other embodiment described above, as shown by 1061 and 1062 in FIG. 12 , the first falling and rising edges of the prefix are generated in half a cycle of the clock signal rather than in one cycle. However, the present invention is not limited to this. For example, the first falling and rising edges of the prefix may be generated in a predetermined cycle that is an arbitrary multiple of half a cycle (0.5 CLC) of the clock signal.

[0084] In addition, in the communication terminal 2, the timing of the rise and fall of the terminal reception data generated based on the tag transmission wave may be shifted from the timing of the rise and fall of the tag transmission data generated by the wireless tag 1. Such a timing shift occurs for various reasons, such as the modulation processing capability of the wireless tag 1, the surrounding environment in which wireless communication takes place, and the demodulation processing capability of the communication terminal 2.

[0085] Here, 1071 in Fig. 13 is a schematic diagram showing the waveform of a clock signal, 1072 in Fig. 13 is a schematic diagram showing tag transmission data generated in accordance with the cycle of the clock signal, and 1073 in Fig. 13 is a schematic diagram showing terminal reception data generated based on the tag transmission wave. For some reason, the timing at which the signal level falls (times t2", t4", etc.) in the terminal reception data shown in 1073 in Fig. 13 is earlier than the timing at which the signal level falls (times t2, t4, tg1, etc.) in the tag transmission data (1072 in Fig. 13). As a result, in the terminal reception data, for example, the time t2" of the first signal level fall in the prefix appears earlier than the time t2 of the first signal level fall in the prefix of the tag transmission data by |t2-t2"|, resulting in a shift by that amount.

[0086] Furthermore, the timing at which the signal level rises in this terminal reception data (time t3'', etc.) is later than the timing at which the signal level rises in the tag transmission data (times t3, t5, tg2, etc.). As a result, for example, the time t3'' at which the signal level first rises in the prefix in the terminal reception data appears later than the time t3 at which the signal level first rises in the prefix of the tag transmission data by |t3''-t3|, resulting in a shift.

[0087] In this case, it is desirable for the terminal controller 24 to acquire tag information as follows: The terminal controller 24 acquires tag information for a half-cycle period from the first falling edge to the first rising edge of the prefix (the period from the time t2'' when the first falling edge is detected to the time t3'' when the next rising edge is detected) C ＬＯＷ as a half cycle of the clock signal. The terminal controller 24 also determines the period C of one cycle from the first falling edge of the signal level in the prefix to the rising edge and then the next falling edge (the period from the detection time t2'' of the first falling edge to the detection time t4'' of the next falling edge that appears after the rising edge) as one cycle of the clock signal.

[0088] Then, the terminal controller 24 sets the period of the clock signal to a half period C of the signal level of the prefix. ＬＯＷ When the period C of one cycle is specified, the terminal controller 24 sets the detection time t4'' of the falling edge, which is the end time of one cycle of the prefix, as the reference time t4''. ＬＯＷ and one period C, the signal level is determined at the time of the following equation (3) based on the reference time t4''.

[0089] (nC+C ＬＯＷ ) / 2 (3) In the above formula (3), n indicates the number of bits of tag information read from the signal level. Note that in this embodiment, n is 8 because the number of bits of tag information is 8 bits and the number of times reading from the signal level is 8. C in the above formula (3) indicates the period of one cycle. C ＬＯＷ indicates the duration of a half cycle.

[0090] In this case, the terminal controller 24 determines the half-cycle period C as the cycle of the clock signal. ＬＯＷ and the period C of one cycle, from the reference time t4'', {(1C + C ＬＯＷ ) / 2} at time tg1'', {(2C+C ＬＯＷ ) / 2}, time tg2'', {(3C+C ＬＯＷ) / 2} at time tg3'', ..., {(8C+C ＬＯＷ ) / 2}, the signal levels are judged at time tg8''.

[0091] In this way, the terminal controller 24 determines the signal level at each of times tg1'', tg2'', tg3'', ... and acquires tag information of a predetermined data length (here, 8 bits). Even with this tag information acquisition processing procedure, it is possible to achieve the same effects as the above-described embodiment.

[0092] 14 show waveforms when, for some reason, the timing at which the signal level falls in the terminal reception data (time t2'', t4'', etc.) is later than the timing at which the signal level falls in the tag transmission data (1082 in FIG. 14) (time t2, t4, tg1, etc.). Here, 1081 in FIG. 14 is a schematic diagram showing the waveform of a clock signal, 1082 in FIG. 14 is a schematic diagram showing tag transmission data generated in accordance with the cycle of the clock signal, and 1083 in FIG. 14 is a schematic diagram showing terminal reception data generated based on the tag transmission wave.

[0093] In the terminal reception data shown as 1083 in FIG. 14, for example, the time t2'' of the first falling edge of the signal level in the prefix appears later than the time t2 of the first falling edge of the signal level in the prefix of the tag transmission data by |t2-t2''|, resulting in a shift.

[0094] Furthermore, the timing at which the signal level rises in this terminal reception data (time t3'', etc.) is earlier than the timing at which the signal level rises in the tag transmission data (times t3, t5, tg2, etc.). As a result, for example, in the terminal reception data, the time t3'' of the first rise in the signal level in the prefix appears earlier than the time t3 of the first rise in the signal level in the prefix of the tag transmission data by |t3''-t3|, resulting in a shift by that amount.

[0095] Even in this case, the terminal controller 24 determines the half-cycle period from the first falling edge to the first rising edge of the prefix (the period from the time t2'' when the first falling edge is detected to the time t3'' when the next rising edge is detected) C ＬＯＷ as a half cycle of the clock signal. The terminal controller 24 also determines the period C of one cycle from the first falling edge of the signal level in the prefix to the rising edge and then the next falling edge (the period from the detection time t2'' of the first falling edge to the detection time t4'' of the next falling edge that appears after the rising edge) as one cycle of the clock signal.

[0096] Then, the terminal controller 24 sets the period of the clock signal to a half period C of the signal level of the prefix. ＬＯＷ After specifying the half-cycle period C, the terminal controller 24 sets the detection time t4'' of the falling edge, which is the end time of one prefix cycle, as the reference time t4''. ＬＯＷ and the period C of one cycle, based on the above formula (3), from the reference time t4'', {(1C + C ＬＯＷ ) / 2} at time tg1'', {(2C+C ＬＯＷ ) / 2}, time tg2'', {(3C+C ＬＯＷ ) / 2} at time tg3'', ..., {(8C+C ＬＯＷ ) / 2}, the signal levels are judged at times tg8''.

[0097] In this way, the terminal controller 24 determines the signal level at each of the identified times tg1'', tg2'', tg3'', ... and acquires tag information of a predetermined data length (here, 8 bits). Even with this tag information acquisition processing procedure, it is possible to achieve the same effects as the above-described embodiment.

[0098] 13 and 14, the case where a prefix consisting of a falling period, a rising period and a falling period is applied has been described, but the present invention is not limited to this. As a method of acquiring tag information using the above formula (3), for example, a prefix in which the falling and rising edges are arranged in reverse (a prefix consisting of a rising period, a falling period and a rising period) may be used. In this case, the half-cycle period C ＬＯＷ is the period from the first rising edge to the first falling edge of the signal level in the prefix, and the period C of one cycle is the period from the first rising edge of the signal level in the prefix to the first rising edge, followed by a falling edge, and then rising again. A similar effect can be obtained even with such prefixes.

[0099] REFERENCE SIGNS LIST 1 wireless tag 2 communication terminal 11 tag antenna 13 clock signal generating circuit 15 tag controller 16 modulation circuit 21 terminal antenna 22 signal processing unit 24 terminal controller

Claims

1. A wireless tag that modulates tag transmission data including tag information of a predetermined data length and transmits it as a tag transmission wave to a communication terminal, comprising: a clock signal generation circuit that generates a clock signal of a predetermined period; a tag controller that assigns a prefix of a fixed signal pattern indicating the start of the tag information to the tag information and generates the tag transmission data including the prefix and tag information, the signal level of which changes according to the period of the clock signal; a modulation circuit that modulates the tag transmission data generated by the tag controller to generate the tag transmission wave; and a tag antenna that transmits the tag transmission wave to the communication terminal, wherein by having the communication terminal receive the tag transmission wave, the communication terminal is able to determine the period of the clock signal generated by the clock signal generation circuit based on the rise and / or fall periods of the signal level in the prefix, and obtain the tag information based on the determined period of the clock signal.

2. The wireless tag according to claim 1, wherein the prefix is ​​added before the tag information.

3. The radio tag according to claim 1, wherein the prefix includes at least one of a configuration in which the signal level changes in the order of falling, rising and falling, and a configuration in which the signal level changes in the order of rising, falling and rising.

4. The radio tag of claim 1, wherein the tag transmission data includes a waiting period before the prefix and the tag information, which is longer than the data length of the tag information and in which a rising or falling signal level continues continuously.

5. A radio tag as described in claim 1, which, upon receiving a terminal transmission wave transmitted from the communication terminal, generates driving power based on the terminal transmission wave and operates the clock signal generation circuit, the tag controller, and the modulation circuit using the driving power.

6. A wireless tag as described in claim 1, which, when receiving a terminal transmission wave transmitted from the communication terminal by the tag antenna, generates a tag transmission wave based on the terminal transmission wave and transmits the tag transmission wave to the communication terminal.

7. The wireless tag according to claim 1, wherein the communication terminal that receives the tag transmission wave is caused to: identify a falling period or a rising period of the signal level in the prefix as a half-cycle period based on the tag transmission wave; identify either a period from a falling edge of the signal level in the prefix to a rising edge and then falling again, or a period from a rising edge of the signal level to a falling edge and then rising again, as a one-cycle period; and acquire the tag information by determining the signal level at a time according to the following formula (1) using the half-cycle period and one-cycle period that have been identified as the period of the clock signal, with the end time of one cycle as a reference time and the reference time as a reference. (nC+C ＬＯＷ ) / 2 (1) where n indicates the number of bits of the tag information read from the signal level. C indicates the period of one cycle. ＬＯＷ denotes the duration of said half cycle.

8. A communications terminal that receives tag transmission waves transmitted from a wireless tag by modulating tag transmission data including tag information of a predetermined data length, and demodulates the tag transmission waves to acquire the tag information, comprising: a terminal antenna that receives from the wireless tag the tag transmission waves generated by modulating the tag transmission data including the prefix and tag information, the tag information being assigned a prefix of a fixed signal pattern indicating the start of the tag information, and the tag transmission data having a changed signal level in accordance with a clock signal of a predetermined period generated by the wireless tag; a signal processing unit that demodulates the tag transmission waves to generate the tag transmission data; and a terminal controller that identifies the period of the clock signal generated by the wireless tag based on the rise period and / or fall period of the signal level of the prefix included in the tag transmission data, and acquires the tag information based on the identified period of the clock signal.

9. The communication terminal according to claim 8, wherein the prefix includes either a configuration in which the signal level changes in the order of falling, rising and falling again, or a configuration in which the signal level changes in the order of rising, falling and rising again.

10. The communication terminal according to claim 8, wherein the terminal controller calculates the average value of the rising or falling periods of the signal level that appears two or more times in the prefix, and determines the period of the clock signal generated by the wireless tag based on the calculated average value.

11. The communication terminal according to claim 8, wherein the terminal controller detects, as the tag information, rising and falling signal levels following the signal level at the end of the prefix in accordance with the period of the clock signal detected based on the prefix.

12. The communications terminal according to claim 8, wherein the terminal controller: specifies a falling period or a rising period of the signal level in the prefix as a half-cycle period; specifies either a period from a falling edge of the signal level in the prefix to a rising edge and then a falling edge again, or a period from a rising edge of the signal level to a falling edge and then a rising ... a rising edge and then a rising edge and a rising edge and then a rising edge and a rising edge and then a rising edge and a rising edge and then a rising edge and a rising edge and then a rising edge and a rising edge and then a rising edge and a rising edge and then ＬＯＷ ) / 2 (2) where n indicates the number of bits of the tag information read from the signal level. C indicates the period of one cycle. ＬＯＷ denotes the duration of said half cycle.

13. A communication system having a radio tag that modulates tag transmission data including tag information of a predetermined data length and transmits it as a tag transmission wave, and a communication terminal that receives the tag transmission wave transmitted from the radio tag and demodulates the tag transmission wave to acquire the tag information, wherein the radio tag comprises: a clock signal generation circuit that generates a clock signal of a predetermined period; a tag controller that assigns a prefix of a fixed signal pattern indicating the start of the tag information to the tag information and generates the tag transmission data including the prefix and the tag information, the signal level of which changes according to the period of the clock signal; a modulation circuit that modulates the tag transmission data generated by the tag controller to generate the tag transmission wave; and a tag antenna that transmits the tag transmission wave to the communication terminal, and wherein the communication terminal comprises: a terminal antenna that receives the tag transmission wave transmitted from the radio tag; and a signal processing unit that demodulates the tag transmission wave to generate the tag transmission data. a terminal controller that identifies the period of the clock signal generated by the wireless tag based on the rise period and / or fall period of the signal level in the prefix included in the tag transmission data, and acquires the tag information based on the identified period of the clock signal.

14. A communication method carried out between a wireless tag that modulates tag transmission data including tag information of a predetermined data length and transmits it as a tag transmission wave, and a communication terminal that receives the tag transmission wave transmitted from the wireless tag and demodulates the tag transmission wave to acquire the tag information, wherein the wireless tag executes: a clock signal generation step of generating a clock signal of a predetermined period using a clock signal generation circuit; a tag transmission data generation step of adding a prefix of a fixed signal pattern indicating the start of the tag information to the tag information and generating, by a tag controller, the tag transmission data including the prefix and the tag information, the signal level of which has changed according to the period of the clock signal; a modulation step of modulating, by a modulation circuit, the tag transmission data generated by the tag controller to generate the tag transmission wave; and a transmission step of transmitting the tag transmission wave from a tag antenna to the communication terminal, and wherein the communication terminal executes: a reception step of receiving, by a terminal antenna, the tag transmission wave transmitted from the wireless tag; and a demodulation step of demodulating the tag transmission wave to generate the tag transmission data by a signal processing unit. and an acquisition step in which a terminal controller identifies the period of the clock signal generated by the wireless tag based on the rise period and / or fall period of the signal level in the prefix included in the tag transmission data, and acquires the tag information based on the identified period of the clock signal.

Images