JP2010101737A - Radio frequency tag set, radio frequency tag, and distance measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a means for identifying a larger number of radio frequency tags and to avoid interference of response signals transmitted respectively from the radio frequency tags in a plurality, in a radio frequency tag distance measuring system. <P>SOLUTION: A radio frequency tag distance measuring device 10 forms a diffusion pulse modulation signal, based on a peculiar assignment PN code of the radio frequency tag of a distance measuring object, and transmits the signal. The radio frequency tag of which the peculiar assignment PN code coincides with the PN code used for formation of the diffusion pulse modulation signal transmits a compression pulse modulation signal subjected to time compression processing, for the diffusion pulse modulation signal which it receives. In each radio frequency tag, an internal time delay from reception of the diffusion pulse modulation signal to transmission of the compression pulse modulation signal is set. In the radio frequency tag distance measuring system, the internal time delays different from each other are set in the radio frequency tags which belong to a radio frequency tag group having the same peculiar assignment PN codes. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless tag set including a plurality of wireless tags, each wireless tag being a measurement target of a distance measuring device, a wireless tag constituting the wireless tag set, and a distance measuring device for measuring a distance to the wireless tag. .

  In a mass production factory or the like, in many cases, a storage position is determined for each production process or product type, and product management is performed. In order to perform such product management, a wireless tag distance measurement system is used. In the wireless tag distance measurement system, the distance measurement device measures the distance to the wireless tag by wireless transmission and reception between the wireless tag attached to the managed product and the distance measurement device.

  When measuring the distance to the wireless tag, the distance measuring device transmits a pulse signal. The pulse signal includes a unique assignment code of a wireless tag to be measured for distance. The wireless tag transmits a response pulse signal when a code uniquely assigned to the wireless tag is included in the received pulse signal. The distance measuring device that has received the response pulse signal measures the distance to the wireless tag based on the time from when the pulse signal is transmitted until the response pulse signal is received.

  According to such processing, it is possible to measure the distance to a specific wireless tag among a plurality of wireless tags, and to measure the distance from the distance measuring device to the product to which the specific wireless tag is attached. .

  The wireless tag distance measurement system can be used for product management in factories, retail stores that sell daily necessities, accessories, etc., event venues that need to manage the location of event participants, and the like.

JP-T-2006-505018 JP-T-2005-513629

In the above wireless tag distance measurement system, if the number of unique assigned codes of each wireless tag is limited due to restrictions on the hardware design of the wireless tag, the number of unique assigned codes cannot be secured sufficiently. There was a problem.
Further, in the above-described wireless tag distance measurement system, when there are a plurality of wireless tags having the same unique assignment code, response pulse signals transmitted from these wireless tags are temporally overlapped and received by the distance measuring device. . At this time, there is a problem that it becomes difficult to measure the distance to each wireless tag because a plurality of response pulse signals interfere with each other.

  The present invention has been made for such a problem. That is, an object of the wireless tag distance measurement system is to secure a means for identifying more wireless tags and to avoid interference of response signals respectively transmitted from a plurality of wireless tags.

The present invention includes a plurality of wireless tags that receive wireless signals and wirelessly transmit the received signals, and each wireless tag is a measurement target of a distance measuring device that measures a distance to an object by transmitting and receiving wireless signals. In the wireless tag set, each wireless tag includes delay means for setting a delay time from reception of a signal to wireless transmission, the delay means being uniquely determined for each wireless tag, The received signal is delayed with a delay time that differs between them.
The present invention also includes a plurality of wireless tags that wirelessly transmit the received signal when the wireless signal is received and the code included in the received wireless signal matches the unique code assigned to the wireless signal. Each wireless tag is a measurement target of a distance measuring device that measures the distance to an object by transmitting and receiving wireless signals. In the wireless tag set, each wireless tag has a delay from receiving a signal to transmitting wirelessly. A delay unit configured to set a time, and the delay unit delays a received signal with a delay time that is uniquely determined for each wireless tag and is different between wireless tags to which a common unique code is assigned. It is characterized by.

  The wireless tag according to the present invention is a measurement target of the distance measuring device and constitutes the wireless tag set.

Further, the present invention provides a distance measurement device that measures a distance to a wireless tag, a transmission unit that wirelessly transmits a distance measurement signal, and a reception that receives a response wireless signal transmitted from a wireless tag that has received the distance measurement signal. A wireless tag identification unit that identifies a wireless tag that has transmitted the response wireless signal based on a response time from when the distance measurement signal is transmitted to when the response wireless signal is received, A distance measuring unit that obtains a distance to the wireless tag based on the response time.
In the distance measuring device according to the present invention, it is preferable that the transmitting unit transmits a distance measuring signal including a unique code assigned to a wireless tag to be measured for distance.

  According to the present invention, in the RFID tag distance measuring system, it is possible to avoid interference of response signals respectively transmitted from a plurality of RFID tags.

  FIG. 1 shows a configuration of a wireless tag distance measuring system according to an embodiment of the present invention. In this system, the wireless tag distance measuring device 10 measures the distance to a wireless tag as a distance measurement target by transmitting and receiving wireless signals.

  The wireless tags are classified into wireless tag groups to which the same unique PN code (PN is an abbreviation for Pseudo Noise) is assigned. In FIG. 1, wireless tags to which PN codes “01001...”, “10011...”, “01111...”, And “10001. It is classified into groups 12-1, 12-2, 12-3, and 12-4. The wireless tags belonging to the wireless tag groups 12-1 to 12-4 are distinguished from each other by numbers “−1−” to “−4−” added next to the code “12”.

  Further, an integer of 1 or more is assigned as an in-group number to each wireless tag belonging to the same wireless tag group. For example, the wireless tags 12-2-1 to 12-2-3 belonging to the wireless tag group 12-2 are assigned 1 to 3 as group numbers, respectively. In the following description, the end of the code attached to the wireless tag indicates the in-group number.

  In FIG. 1, for the description related to the classification of the wireless tag by the unique PN code, the wireless tags belonging to the same wireless tag group are shown in close proximity, but the wireless tag belongs to the wireless tag group to which it belongs. Regardless, it may be randomly distributed.

  When measuring the distance to the wireless tag to be measured, the wireless tag distance measuring device 10 identifies the wireless tag to be measured by the PN code and the in-group number.

  In general, a PN code indicates a pseudo-noise pattern due to 1 and 0. By associating the signal values “1” and “−1” with the values “1” and “0” of the PN code, respectively, it is possible to generate a PN signal whose polarity changes according to the pattern of the PN code.

  When a convolution operation is performed between two PN signals based on the same PN code having two or more code lengths, it has a time length of one code, and a signal value is cumulatively added to the time length of one code. A time-compressed signal is obtained. Here, the convolution operation is also referred to as correlation operation or convolution, and is an operation for obtaining the degree of approximation of the waveforms of two signals. On the other hand, even if a convolution operation is performed between two PN signals based on different PN codes, the time length of the obtained signal remains unchanged. Such a property relating to time compression can be maintained even for a signal in which another signal is multiplied by the PN signal and the sign changes in the same manner as the PN signal. The RFID tag distance measurement system according to the embodiment of the present invention uses such orthogonality of the PN code.

  The wireless tag distance measuring device 10 generates a PN signal using a unique assignment PN code of a wireless tag to be measured for distance. Then, a spread pulse modulation signal obtained by converting the PN signal into a radio signal is generated and transmitted.

  Among the plurality of wireless tags that have received the spread pulse modulation signal, the wireless tag in which the PN code used to generate the spread pulse modulation signal and its own uniquely assigned PN code match the received spread pulse modulation signal. A compressed pulse modulation signal subjected to time compression processing is transmitted. As a result, the wireless tag belonging to the same wireless tag group as the wireless tag of the distance measurement target transmits the compressed pulse modulation signal.

  Each wireless tag is set with an internal delay time from reception of the spread pulse modulation signal to transmission of the compressed pulse modulation signal. In the wireless tag distance measurement system according to the present embodiment, different internal delay times are set for wireless tags belonging to the same wireless tag group. As a result, each wireless tag belonging to the same wireless tag group as the wireless tag of the distance measurement target transmits a compressed pulse modulated signal at a different timing. The relationship between the maximum measurement distance of the wireless tag distance measuring device 10 and the internal delay time set for each wireless tag is given by the wireless tag distance measuring device 10 by giving the following restrictions. According to the reception timing of a plurality of compressed pulse modulated signals, it is possible to specify the compressed pulse modulated signal to be measured for distance.

  The wireless tag distance measuring device 10 identifies a signal transmitted from the wireless tag to be measured among a plurality of received compressed pulse modulated signals based on the reception timing. Then, the distance to the wireless tag to be measured is calculated based on the reception timing of the specified compressed pulse modulation signal and the propagation speed of the wireless signal.

  FIG. 2 shows the configuration of the RFID tag distance measuring apparatus 10 for executing such processing. The PN code storage unit 14 stores a unique assignment PN code of a wireless tag used in the wireless tag distance measurement system. The wireless tag designation control unit 16 reads a specific assigned PN code of the designated wireless tag from the PN code storage unit 14 when a wireless tag to be measured for distance is designated by a user operation or a device provided separately. Then, a PN signal is generated based on the read PN code and output to the multiplication unit 20.

  The sine wave signal generation unit 18 outputs the reference sine wave signal to the multiplication unit 20. The multiplication unit 20 outputs a sine wave PN signal obtained by multiplying the PN signal by the reference sine wave signal to the wireless transmission unit 22 and the distance calculation unit 28.

  3A, 3B, and 3C show the PN signal, the reference sine wave signal, and the sine wave PN signal, respectively. However, the time waveform shown in these figures is an example for explanation. The vertical axis in FIG. 3 indicates the signal value, and the horizontal axis indicates time. The PN signal is a rectangular signal whose polarity changes according to the code change of the PN code. The sine wave PN signal is a sine wave signal whose polarity changes according to the value of the PN signal.

  The wireless transmission unit 22 converts the sine wave PN signal into a wireless signal, and generates a spread pulse modulated signal. The wireless transmission unit 22 transmits the spread pulse modulated signal via the measurement device antenna 24.

  According to such processing, a sine wave PN signal based on the PN code designated by the wireless tag designation control unit 16 is generated, and a spread pulse modulation signal obtained by converting the sine wave PN signal into a wireless signal is used to measure the wireless tag distance. Sent from the device 10. Note that the sine wave PN signal output from the multiplication unit 20 to the distance calculation unit 28 is used to measure the distance to the wireless tag, as will be described later.

  The spread pulse modulation signal is received by each wireless tag. FIG. 4A shows the configuration of the wireless tag 12. The spread pulse modulated signal received by the wireless tag antenna 34 is input to the duplexer 36. The duplexer 36 outputs the pulse modulated signal to the correlation processing device 38. The duplexer 36 can be configured using a circulator, a directional coupler, or the like.

  As the correlation processing device 38 of the wireless tag 12, a device that performs a convolution operation on an input signal and outputs it by a PN code uniquely assigned to the wireless tag 12 is used. As such a device, a SAW device, a CCD (Charge Coupled Device) matched filter, a digital matched filter, or the like can be used. Some SAW devices require supply power (such as SAW convolvers) and others do not require supply power. When a SAW device that does not need to supply power is used, it is not necessary to mount a power supply source on the wireless tag 12.

  In addition, a digital matched filter, a SAW convolver, and the like can arbitrarily set a PN code when performing a convolution operation. The configuration in this case is shown in FIG. Here, the case where the digital matched filter 38A is used is shown. When using a SAW convolver, the digital matched filter 38A may be replaced with a SAW convolver. The wireless tag 12 includes a PN code storage unit 42 that stores a PN code and a PN code setting circuit 40. The PN code storage unit 42 stores a plurality of different PN codes in advance. The PN code setting circuit 40 reads the PN code from the PN code storage unit 42, and sets the operation state of the digital matched filter 38A so that the digital matched filter 38A executes processing based on the PN code. Further, instead of providing the PN code storage unit 42 and the PN code setting circuit 40, a configuration may be adopted in which a PN code is set in the digital matched filter 38A by a device external to the wireless tag 12. According to the configuration of the wireless tag 12 using the digital matched filter 38A, it is possible to share hardware for a plurality of wireless tags 12 to which different PN codes are given.

  The correlation processing device 38 performs a convolution operation on the signal output from the duplexer 36 using the unique assignment PN code of the wireless tag 12 and outputs the result to the duplexer 36. The duplexer 36 outputs the signal output from the correlation processing device 38 to the RFID tag antenna 34. A signal output from the duplexer 36 is transmitted from the wireless tag antenna 34.

  When the signal input to the correlation processing device 38 is a signal based on the uniquely assigned PN code, the time length is reduced from the total time length of the PN code to the time length of one code from the correlation processing device 38. Then, a signal in which the signal value is accumulated and added to the time length of one code, that is, a signal subjected to time compression processing is output. On the other hand, when the signal input to the correlation processing device 38 is a signal based on a code different from the uniquely assigned PN code, the correlation processing device 38 receives a signal obtained by performing time compression processing on the input signal. Not output.

  Therefore, when the spread pulse modulated signal received by the RFID tag antenna 34 is a signal whose polarity changes according to the uniquely assigned PN code, the correlation processing device 38 performs time compression processing on the spread pulse modulated signal. The applied signal is output. As a result, among the plurality of wireless tags, the wireless tag in which the original PN code that generated the received spread pulse modulated signal and its own uniquely assigned PN code match each other is time-compressed with respect to the spread pulse modulated signal. The processed signal is transmitted as a compressed pulse modulated signal.

  In the wireless tag, an internal delay time from reception of the spread pulse modulation signal to transmission of the compressed pulse modulation signal is set. Different internal delay times are set for a plurality of wireless tags belonging to the same wireless tag group.

  The setting of the internal delay time of the wireless tag will be described. Between wireless tags belonging to the same wireless tag group, a difference equal to or greater than the allocated time difference Ts is provided for the set internal delay time. In this embodiment, the internal delay time Te of the wireless tags belonging to the same wireless tag group is set as shown in (Equation 1).

  (Equation 1) Te = Tm + (n−1) · Ts

  Here, Tm is the minimum value of the internal delay time determined by the configuration of the correlation processing device 38. n is an in-group number of the wireless tag. For example, the internal delay times to be set for the wireless tags 12-2-1, 12-2-2, and 12-2-3 belonging to the wireless tag group 12-2 are Tm, Tm + Ts, and Tm + 2Ts, respectively.

  The allocation time difference Ts is longer than the maximum round-trip propagation time Tx. Here, the maximum round-trip propagation time Tx is defined as twice the time required for the wireless signal to propagate the predetermined maximum measurement distance in the wireless tag distance measuring apparatus 10.

  The setting of the internal delay time when a SAW device is used as the correlation processing device 38 will be described. FIG. 5 shows the configuration of the SAW device. The SAW device includes a substrate 44 through which surface acoustic waves propagate, and an input electrode 46 and an output electrode 48 provided on the substrate 44. The input electrode 46 is composed of a pair of input comb electrodes 50 arranged so that the other comb tooth enters between one comb tooth. The output electrode 48 is constituted by a pair of output comb-shaped electrodes 52 arranged so that the other comb tooth enters between one comb tooth. The output comb electrode 52 is arranged at a predetermined distance from the input comb electrode 50 so that the comb teeth and the comb teeth of the input comb electrode 50 are parallel to each other.

  The comb teeth of the output comb electrode 52 are arranged with a change in density between the teeth. The modulation region where the comb electrodes are densely arranged modulates the surface acoustic wave with a one-digit code. In the SAW device of FIG. 5, six modulation regions are arranged, and the surface acoustic wave is modulated with the signs “1”, “−1”, “1”, “−1”, “−1”, and “1” in order from the left in FIG. . Whether the sign is positive or negative can be determined according to the positional relationship between the upper and lower comb teeth in FIG. 5 in the modulation region.

  The internal delay time can be adjusted by changing the distance between the input comb electrode 50 and the output comb electrode 52. The longer the distance, the longer the internal delay time, and the shorter the distance, the shorter the internal delay time.

  When a device other than the SAW device is adopted as the correlation processing device 38, for example, a delay transmission line is provided inside the correlation processing device 38, and the internal delay time is set by changing the length of the delay transmission line. Can be adjusted.

  By setting the internal delay time of the wireless tag as described above, the spread pulse modulated signal transmitted from the wireless tag distance measuring device 10 and the wireless tag distance measuring device 10 transmitted from the wireless tag belonging to the same wireless tag group are used. The timing with the compressed pulse modulated signal received at is as shown in FIG.

  6A to 6D, the vertical axis represents the signal magnitude, and the horizontal axis represents time. FIG. 6A shows a spread pulse modulated signal transmitted from the RFID tag distance measuring apparatus 10. 6A to 6D, the rising time of the spread pulse modulated signal to be transmitted is set as a transmission reference time t0.

  6 (b) to 6 (d) are respectively transmitted from the wireless tags 12-2-1 to 12-2-3 with respect to the spread pulse modulated signal shown in FIG. 2 shows a compressed pulse modulated signal received at. In these figures, the time required for the wireless signal to propagate through the round-trip distance from the wireless tag distance measuring device 10 to the wireless tags 12-2-1, 12-2-2, and 12-2-3 is indicated by Td1 and Td2, respectively. , And Td3.

  The internal delay time of the wireless tag 12-2-1 is Tm. Therefore, the compressed pulse modulated signal transmitted from the wireless tag 12-2-1 is delayed from the transmission reference time t0 by the time obtained by adding the internal delay time Tm to the round-trip propagation time Td1 for the distance to the wireless tag distance measuring device 10. And received by the RFID tag distance measuring device 10.

  The internal delay time of the wireless tag 12-2-2 is Tm + Ts. Therefore, the compressed pulse modulation signal transmitted from the wireless tag 12-2-2 is delayed from the transmission reference time t0 by a time obtained by adding the internal delay time Tm + Ts to the round-trip propagation time Td2 with respect to the distance to the wireless tag distance measuring device 10. And received by the RFID tag distance measuring device 10.

  The internal delay time of the wireless tag 12-2-3 is Tm + 2Ts. Therefore, the compressed pulse modulated signal transmitted from the wireless tag 12-2-3 is delayed from the transmission reference time t0 by a time obtained by adding the internal delay time Tm + 2Ts to the round-trip propagation time Td3 with respect to the distance to the wireless tag distance measuring device 10. And received by the RFID tag distance measuring device 10.

  When the wireless tags 12-2-1 to 12-2-3 exist in a circle centered on the wireless tag distance measuring device 10 and having a radius of the maximum measurement distance, the times Td1 to Td3 are all based on the maximum round-trip propagation time Tx. Also short. Therefore, the compressed pulse modulated signal transmitted from the wireless tag 12-2-1 is received by the wireless tag distance measuring apparatus 10 until the time Tx + Tm elapses from the transmission reference time t0. Further, the compressed pulse modulated signal transmitted from the wireless tag 12-2-2 is received by the wireless tag distance measuring device 10 until the time Tx + Tm + Ts elapses from the transmission reference time t0. Then, the compressed pulse modulated signal transmitted from the wireless tag 12-2-3 is received by the wireless tag distance measuring device 10 from the transmission reference time t0 until the time Tx + Tm + 2Ts elapses.

  In the present embodiment, the allocation time difference Ts is set to be longer than the maximum round-trip propagation time Tx. Therefore, a time zone in which the compressed pulse modulated signal transmitted from the wireless tag 12-2-1 is received, a time zone in which the compressed pulse modulated signal transmitted from the wireless tag 12-2-2 is received, and the wireless tag 12- The time zones in which the compressed pulse modulated signals transmitted from 2-3 are received do not overlap. In the wireless tag distance measuring device 10, the compressed pulse signal transmitted from the wireless tag 12-2-1, the compressed pulse signal transmitted from the wireless tag 12-2-2, and the wireless tag 12-2-3 are transmitted. The RFID tag distance measuring device 10 receives the compressed pulse signals in the order. As a result, the wireless tag distance measuring device 10 can identify the wireless tag that is the target of distance measurement based on the time zone when the compressed pulse modulation signal is received, as will be described later.

  Here, the wireless tag group 12-2 to which the three wireless tags belong has been described as an example, but the wireless tag group has an arbitrary internal delay time set based on the relationship of (Equation 1). The number of wireless tags may belong.

  Next, a process performed by the wireless tag distance measuring device 10 for the compressed pulse modulated signal transmitted from the wireless tag will be described. The wireless reception unit 26 receives the compressed pulse modulated signal transmitted from the wireless tag via the measurement device antenna 24. Then, the received signal is amplified until it reaches a predetermined signal level, the frequency of the signal is converted to the low frequency side, and output to the distance calculation unit 28.

  When a wireless tag to be measured for distance is designated by a user operation or a separately provided device, the wireless tag designation control unit 16 outputs the group number of the designated wireless tag to the distance calculation unit 28.

  The distance calculation unit 28 stores in advance a correspondence relationship between the intra-group number and a time zone during which the compressed pulse modulation signal transmitted from the wireless tag specified by the intra-group number is input to the distance calculation unit 28. .

  The distance calculation unit 28 is a time when the compressed pulse modulation signal to be measured for distance is input to the distance calculation unit 28 based on the stored correspondence and the in-group number output from the wireless tag designation control unit 16. Ask for a belt. Then, the compressed pulse modulation signal input to the distance calculation unit 28 in the obtained time zone is set as a distance measurement target signal. For example, when the wireless tag 12-2-3 is designated as the distance measurement target and the in-group number “3” is output from the wireless tag designation control unit 16 to the distance calculation unit 28, the wireless tag 12-2-3 is shown in FIG. The compressed pulse modulation signal to be measured is used as a distance measurement target signal.

  The distance calculation unit 28 obtains a difference TD between the timing at which the sine wave PN signal is output from the multiplication unit 20 and the timing at which the distance measurement target compressed pulse modulation signal is input. The timing difference TD is the difference between the rise time of the envelope of the sine wave PN signal and the rise time of the envelope of the compressed pulse modulated signal, the reference sine wave multiplied by the sine wave PN signal, and the compressed pulse modulated signal. It can be obtained from the phase difference from the multiplied reference sine wave.

  The distance calculation unit 28 obtains a round-trip propagation time TA between the measurement device antenna 24 and the wireless tag based on the obtained timing difference TD. The round-trip propagation time TA can be obtained by (Equation 2).

  (Expression 2) TA = [TD-D1-Tm-D2] .mod.Ts

  Here, mod is an operator that gives a remainder when [TD-D1-Tm-D2] is divided by Ts. D1 is a delay time from when the signal is output from the multiplication unit 20 until it is transmitted from the measurement device antenna 24, Tm is a minimum delay time in the wireless tag, and D2 is a signal received by the measurement device antenna 24. And the delay time from the wireless reception unit 26 to the output.

  The reason why the round-trip propagation time TA is obtained by (Equation 2) is that the timing difference TD is expressed by (Equation 3) and that the allocation time difference Ts is set to be longer than the round-trip propagation time TA. Is due to.

  (Equation 3) TD = TA + D1 + Tm + D2 + (n-1) .Ts

  The distance calculation unit 28 further calculates the distance to the wireless tag to be measured based on the round-trip propagation time TA and the propagation speed of the wireless signal. When the round-trip propagation time TA is obtained, the delay times D1 and D2 are subtracted from the timing difference TD, so that the obtained distance is based on the position of the measuring device antenna 24.

  The distance calculation unit 28 outputs the distance calculation result to the display unit 30 and the result storage unit 32. The display unit 30 displays the distance calculation result, and the result storage unit 32 stores the distance calculation result. The user can know the distance from the wireless tag distance measuring device 10 to the wireless tag by referring to the display unit 30. In addition, the storage contents of the result storage unit 32 can be acquired by a reading device configured by a personal computer or the like.

  According to such a system configuration, it is possible to measure the distance from the wireless tag distance measuring device 10 to the wireless tag by designating the unique PN code and the intra-group number of the wireless tag to be measured. For example, in the unique PN code assignment and group classification shown in FIG. 1, when the wireless tag 12-2-3 is designated as a distance measurement target, the wireless tag designation control unit 16 sends the wireless tag 12-2-3 to the multiplication unit 20. A PN signal based on the three uniquely assigned PN codes “10011...” Is output. As a result, the wireless tag distance measuring device 10 transmits a spread pulse modulated signal based on the uniquely assigned PN code of the wireless tag 12-2-3. Of the wireless tags that have received the spread pulse modulated signal, the wireless tag belonging to the wireless tag group 12-2 transmits the compressed pulse modulated signal.

  In the wireless tag distance measuring device 10, the in-group number “3” is output from the wireless tag designation control unit 16 to the distance calculation unit 28. As a result, the distance calculation unit 28 uses a signal transmitted from the wireless tag 12-2-3 among a plurality of compressed pulse modulation signals transmitted from the wireless tags belonging to the wireless tag group 12-2 as a distance measurement target. The distance to the wireless tag 12-2-3 is obtained.

  In the system according to the present embodiment, wireless tags belonging to the same wireless tag group have different internal delay times and transmit compressed pulse modulated signals at different timings. As a result, it is possible to avoid interference of compressed pulse modulated signals transmitted from a plurality of wireless tags.

Further, due to the orthogonality of the PN code, a compressed pulse modulation signal is not transmitted from a wireless tag belonging to a wireless tag group that is not a distance measurement target. Accordingly, it is possible to avoid the transmission of the compressed pulse modulation signal from the RFID tag group that is not the distance measurement target, and it is possible to avoid the interference of the signal received by the RFID tag distance measurement device 10.
Therefore, by assigning the same unique assigned PN code to the wireless tags belonging to the same wireless tag group and assigning different unique assigned PN codes to the wireless tags belonging to different wireless tag groups, the unique assigned PN having a small number of digits. Many wireless tags can be identified by a code.

It is a figure which shows the structure of a radio | wireless tag distance measurement system. It is a figure which shows the structure of a distance measuring device. It is a figure which shows a PN signal, a reference | standard sine wave signal, and a sine wave PN signal. It is a figure which shows the structure of a wireless tag. It is a figure which shows the structure of a SAW device. It is a figure which shows the timing of a spreading | diffusion pulse modulation signal and a compression pulse modulation signal.

Explanation of symbols

  10 wireless tag distance measuring device, 12-1 to 12-4 wireless tag group, 12 wireless tag, 14, 42 PN code storage unit, 16 wireless tag designation control unit, 18 sine wave signal generation unit, 20 multiplication unit, 22 wireless Transmitter, 24 Measuring device antenna, 26 Wireless receiver, 28 Distance calculator, 30 Display, 32 Result storage, 34 RFID tag antenna, 36 Demultiplexer, 38 Correlation processing device, 38A Digital matched filter, 40 PN code Setting circuit, 44 substrate, 46 input electrode, 48 output electrode, 50 input comb electrode, 52 output comb electrode.

Claims (5)

Including a plurality of wireless tags that receive wireless signals and wirelessly transmit the received signals;
Each wireless tag is a measurement target of a distance measurement device that measures the distance to an object by transmitting and receiving wireless signals.
Each wireless tag
Comprising delay means for setting a delay time from when a signal is received until wireless transmission;
The delay means is
A wireless tag set characterized by delaying a received signal with a delay time which is uniquely determined for each wireless tag and is different between wireless tags. Receiving a wireless signal, and when a code included in the received wireless signal matches a unique code assigned to the wireless signal, the wireless signal includes a plurality of wireless tags that wirelessly transmit the received signal;
Each wireless tag is a measurement target of a distance measuring device that measures the distance to an object by transmitting and receiving wireless signals.
Each wireless tag
Comprising delay means for setting a delay time from when a signal is received until wireless transmission;
The delay means is
A wireless tag set, wherein a received signal is delayed by a delay time that is uniquely determined for each wireless tag and is different between wireless tags to which a common unique code is assigned.   A wireless tag that is a measurement target of the distance measuring device and constitutes the wireless tag set according to claim 1 or 2. In a distance measuring device that measures the distance to a wireless tag,
A transmitter for wirelessly transmitting a distance measurement signal;
A receiving unit that receives a response radio signal transmitted from the radio tag that has received the distance measurement signal;
With
A wireless tag identifying unit that identifies a wireless tag that has transmitted the response wireless signal, based on a response time from when the distance measurement signal is transmitted to when the response wireless signal is received;
A distance measuring unit for obtaining a distance to the identified wireless tag based on the response time;
A distance measuring device comprising: The distance measuring device according to claim 4,
The transmitter is
A distance measurement device that transmits a distance measurement signal including a unique code assigned to a wireless tag to be measured.

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