JP2010048748A - Radio frequency tag distance measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid interference of response signals transmitted from a plurality of radio frequency tags and to improve distance measuring precision in a radio frequency tag distance measuring system. <P>SOLUTION: A radio frequency tag distance measuring device 10 generates PN signals changing values in response to inherent assignment PN codes of the radio frequency tag of a distance measuring object, and further generates sine wave PN signals multiplying reference sine wave signals to the PN signals, and transmits a diffusion pulse modulation signal converting the sine wave PN signal into a radio signal. The radio frequency tag distance measuring device 10 receives a compression pulse modulation signal executing time compression processing to the diffusion pulse modulation signal with the radio frequency tag. The radio frequency tag distance measuring device 10 calculates a distance up to the radio frequency tag based on a phase difference between the reference sine wave signal being an origin generating the sine wave PN signal and the reference sine wave signal included in a received compression pulse modulation signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless tag distance measuring device that measures a distance to a 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, the RFID tag distance measurement system is widely 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 wireless tag that has received the pulse signal modulates the received pulse signal with a uniquely assigned code and transmits it as a response pulse signal. The distance measuring device that has received the response pulse signal identifies the wireless tag that has transmitted the response pulse signal by identifying the original code that modulated the response pulse signal. Then, the distance to the specified wireless tag is measured 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-described wireless tag distance measuring system, when there are a plurality of wireless tags having the same distance from the distance measuring device, 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. In addition, when the response pulse signal detected by the RFID tag distance measuring device contains noise, there is a problem that an error in the measured distance increases.

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

  The present invention provides a wireless transmission unit that transmits a distance measurement signal for measuring a target distance, a wireless reception unit that receives an incoming signal that has arrived after transmission of the distance measurement signal, and a wireless tag as a target. A distance calculation unit that calculates a distance, and generates a PN signal having a value corresponding to a unique assigned PN code of the wireless tag, and a signal obtained by multiplying the PN signal by a sine wave signal A distance measurement signal generation unit that generates the distance measurement signal based on the received signal, and the wireless reception unit receives, as the incoming signal, a time compressed signal obtained by performing time compression processing on the distance measurement signal by the wireless tag. The distance calculation unit is based on the phase difference between the sine wave signal that is the source for generating the distance measurement signal and the sine wave signal included in the incoming signal received by the wireless reception unit, And calculates the distance to the serial radio tag.

  Further, in the wireless tag distance measuring device according to the present invention, the distance calculating unit is based on a difference between a rising time of the distance measuring signal and a rising time of the incoming signal received by the wireless receiving unit. It is preferable to calculate the distance to the wireless tag.

  Further, in the RFID tag distance measuring device according to the present invention, the distance measurement signal generation unit converts a signal obtained by multiplying the PN signal by a sine wave signal into a signal in which a carrier wave is modulated, and measures a previous distance. Generating a signal, and the distance calculation unit calculates a distance to the wireless tag based on a phase difference between the carrier wave of the incoming signal received by the wireless reception unit and the carrier wave of the distance measurement signal. Is preferred.

  According to the wireless tag distance measuring apparatus of the present invention, it is possible to avoid interference of response signals transmitted from a plurality of wireless tags, and to measure the distance to each wireless tag. Further, the distance measurement accuracy can be improved.

  FIG. 1 shows the configuration of the RFID tag distance measuring system according to the first 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. A unique PN code (PN is an abbreviation of Pseudo Noise) is assigned to the wireless tags 12-1 to 12-4. In FIG. 1, “01001...”, “10011...”, “01111...”, And “10001. "Is assigned. The wireless tag distance measuring device 10 specifies a wireless tag as a distance measurement target by a PN code.

  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 value changes with the pattern of the PN code.

  When a convolution operation is performed between two PN signals based on the same PN code, a time compressed signal having a time length of one code 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 if another signal is added to the PN signal. The RFID tag distance measurement system according to the embodiment of the present invention utilizes such orthogonality of the PN code.

  When measuring the distance to the wireless tag as the distance measurement target, the wireless tag distance measurement device 10 generates a PN signal by using the uniquely assigned PN code of the wireless tag as the distance measurement target. Then, a spread pulse modulation signal obtained by converting a signal obtained by multiplying the PN signal by the reference sine wave 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.

  When receiving the compressed pulse modulation signal, the wireless tag distance measuring device 10 determines the distance to the wireless tag to be measured based on the time from when the spread pulse modulated signal is transmitted until the compressed pulse modulated signal is received. calculate.

  FIG. 2 shows the configuration of the RFID tag distance measuring apparatus 10 for executing such processing. The wireless tag distance measuring device 10 converts a sine wave PN signal obtained by multiplying a PN signal by a reference sine wave signal into a wireless signal, and transmits it as a spread pulse modulation signal. By using the sine wave PN signal, the compressed pulse modulation signal transmitted from the wireless tag becomes a signal modulated by the reference sine wave signal. The wireless tag distance measuring device 10 performs distance measurement with high accuracy using the phase of the reference sine wave signal included in the compressed pulse modulation signal.

  The PN code storage unit 14 stores a unique assignment PN code of a wireless tag used in the wireless tag distance measurement system. When a wireless tag to be measured for distance is specified by a user operation or a device provided separately, the code selection unit 16 reads a specific assigned PN code of the specified wireless tag from the PN code storage unit 14. 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 and the sine wave distance calculation unit 36. 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 rising distance calculation unit 34.

  FIGS. 3A, 3B, and 3C show the PN signal, the reference sine wave signal, and the sine wave PN signal output from the code selection unit 16, 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 setting of the frequency of the reference sine wave signal will be described later.

  The wireless transmission unit 22 converts the sine wave PN signal into a wireless signal by the local signal output from the local signal generator 24, and generates a spread pulse modulation signal. The spread pulse modulation signal is a signal obtained by modulating a local signal with a sine wave PN signal, and has the same pulse time length as that of the original PN signal. The wireless transmission unit 22 outputs the spread pulse modulation signal to the carrier phase difference detection unit 40 and transmits the spread pulse modulation signal via the measurement device antenna 26.

  Through such processing, a sine wave PN signal based on the PN code designated by the code selection unit 16 is generated, and a spread pulse modulation signal obtained by converting the sine wave PN signal into a radio signal is transmitted from the radio tag distance measuring device 10. Is done.

  The reference sine wave signal output from the sine wave signal generation unit 18 to the sine wave distance calculation unit 36, the sine wave PN signal output from the multiplication unit 20 to the rising distance calculation unit 34, and the carrier wave level from the wireless transmission unit 22. The spread pulse modulation signal output to the phase difference detection unit 40 is used for measuring 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 44 is input to the duplexer 46. The duplexer 46 outputs the pulse modulated signal to the correlation processing device 48. The duplexer 46 can be configured using a circulator, a directional coupler, or the like.

  As the correlation processing device 48 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 48A is used is shown. When using a SAW convolver, the digital matched filter 48A may be replaced with a SAW convolver. The wireless tag 12 includes a PN code storage unit 52 that stores a PN code and a PN code setting circuit 50. The PN code storage unit 52 stores a plurality of different PN codes in advance. The PN code setting circuit 50 reads the PN code from the PN code storage unit 52, and sets the operation state of the digital matched filter 48A so that the digital matched filter 48A executes processing based on the PN code. Further, instead of providing the PN code storage unit 52 and the PN code setting circuit 50, a configuration may be adopted in which a PN code is set in the digital matched filter 48A by a device external to the wireless tag 12. According to the configuration of the wireless tag 12 using the digital matched filter 48A, it is possible to share hardware for a plurality of wireless tags 12 to which different PN codes are given.

  The correlation processing device 48 performs a convolution operation on the signal output from the duplexer 46 using the unique assignment PN code of the wireless tag 12 and outputs the result to the duplexer 46. The duplexer 46 outputs the signal output from the correlation processing device 48 to the wireless tag antenna 44. The signal output from the duplexer 46 is transmitted from the wireless tag antenna 44.

  When the signal input to the correlation processing device 48 is a signal multiplied by the uniquely assigned PN code, the correlation processing device 48 outputs a signal obtained by performing time compression processing on the input signal. On the other hand, when the signal input to the correlation processing device 48 is a signal multiplied by a code different from the uniquely assigned PN code, the correlation processing device 48 performs time compression processing on the input signal. No signal is output.

  Therefore, when the spread pulse modulated signal received by the RFID tag antenna 44 is a signal multiplied by the uniquely assigned PN code, the correlation processing device 48 outputs a signal obtained by performing time compression processing on the spread pulse modulated signal. Is output. As a result, among the plurality of wireless tags, the wireless tag in which the original PN code multiplied by the received spread pulse modulation signal and its own uniquely assigned PN code match each other with respect to the spread pulse modulation signal. A signal subjected to time compression processing is transmitted as a compressed pulse modulated signal.

  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 receiver 28 receives the compressed pulse modulated signal via the measurement device antenna 26. The reception amplification unit 30 amplifies the received signal until it reaches a predetermined signal level, and outputs the amplified signal to the frequency conversion unit 32 and the carrier phase difference detection unit 40. The frequency conversion unit 32 performs frequency conversion for shifting the frequency of the compressed pulse modulated signal to the low frequency side by the local signal output from the local signal generator 24, and the signal after the frequency conversion is used as the rising distance calculation unit 34 and the sine It outputs to the wave distance calculation part 36.

  The rising distance calculation unit 34 obtains the envelope of the compressed pulse modulation signal as a reception envelope signal. Further, the rising distance calculation unit 34 obtains the envelope of the sine wave PN signal output from the multiplication unit 20 as a transmission envelope signal.

  The rising distance calculation unit 34 measures the difference between the rising time of the transmission envelope signal and the rising time of the reception envelope signal. Then, based on the measured time difference, a round-trip propagation time when the wireless signal reciprocates between the wireless tag distance measuring device 10 and the wireless tag is obtained. The rising distance calculation unit 34 calculates a round trip distance between the wireless tag (twice the distance to the wireless tag) as a round trip rising distance D0 based on the round trip propagation time and the propagation speed of the wireless signal, and a sine wave distance. It outputs to the calculation part 36.

  When the rising distance calculation unit 34 calculates the round-trip propagation time, the delay time from when the signal is output from the multiplication unit 20 to the measurement device antenna 26, the reception / transmission response time of the wireless tag, and the signal are measured. The delay time from reception by the apparatus antenna 26 to the rise distance calculation unit 34 is subtracted from the difference between the transmission envelope signal rise time and the reception envelope signal rise time. As a result, the reciprocating rising distance D0 can be calculated with reference to the position of the measuring device antenna 26. These delay times are times unique to the RFID tag distance measuring device 10 and the RFID tag, and can be obtained in advance in the design or calibration stage.

The round-trip rising distance D0 obtained in this way includes a resolution error corresponding to the measurement resolution. That is, the true reciprocal distance is between the distance obtained by subtracting the resolution error from the reciprocal rise distance D0 and the distance obtained by adding the resolution error to the reciprocal rise distance D0. This resolution error δR is a value determined by the signal-to-noise ratio SNR of the compressed pulse modulation signal, the time length τ per PN code, the waveform of the signal to be transmitted / received, and the like, and is given by the following (Equation 1) It has been known.
(Equation 1) δR≈ (1/2) · k · c · τ / √SNR

Here, c is a radio signal propagation speed (3 × 10 ⁸ ), k is a coefficient determined based on the waveform of the signal to be transmitted / received, etc., and a sine wave PN signal as shown in FIG. 3C is used. May be 1. The resolution error δR can be obtained at the design stage.

  According to such processing, it is possible to obtain a round trip distance in which an error of the resolution error δR is expected on the plus side and the minus side with the round trip rising distance D0 as the center.

  Here, the rising distance calculation unit 34 may output the round-trip rising distance D0 to the display unit 42, and may cause the display unit 42 to display half of the round-trip rising distance D0 as a measurement distance.

In the RFID tag distance measuring apparatus 10 according to the present embodiment, the distance is obtained by using the phase difference between the reference sine wave signal output from the sine wave signal generation unit 18 and the response sine wave signal included in the compressed pulse modulation signal. Improve measurement accuracy. The measurement accuracy improvement process using the phase difference of the sine wave signal is a wireless tag distance measurement so that twice the resolution error δR is shorter than the propagation wavelength λ = c / f of the electromagnetic wave having the frequency f of the reference sine wave signal. High effect can be obtained when the system is designed. That is, it is preferable that the system is designed so that the following relationship (Equation 2) is established.
(Expression 2) 2δR <c / f

When the resolution error δR is determined in advance, the frequency f of the reference sine wave signal generated by the sine wave signal generation unit 18 is smaller than c / (2δR), that is, the reference sine wave signal The wavelength λ may be determined to be longer than 2δR. That is, the following relationship (Equation 3) can be obtained by using (Equation 1).
(Expression 3) f <c / (2δR) = √SNR / (k · τ)

  Here, for example, if SNR = 20 dB = 100, k = 1, and τ = 100 ns, the design condition that the frequency f of the reference sine wave signal is less than 100 MHz, that is, the design condition that the wavelength λ is longer than 3 m. Can be obtained.

  FIG. 5 shows a flowchart of measurement accuracy improvement processing using the phase difference of the sine wave signal. The sine wave distance calculation unit 36 extracts a component of the frequency f from the compressed pulse modulation signal as a response sine wave signal by using an arithmetic method such as FFT (Fast Fourier Transform) (S101). The sine wave distance calculation unit 36 obtains a phase difference between the reference sine wave signal and the response sine wave signal as a measurement phase difference (S102). The sine wave distance calculation unit 36 further includes a phase change amount from when the signal is output from the multiplying unit 20 to the measurement device antenna 26, a phase change amount based on the reception / transmission response of the wireless tag, and the signal as the measurement device antenna. The distance measurement phase difference P is obtained by subtracting the phase change amount from the reception at 26 to the sine wave distance calculation unit 36 from the measurement phase difference (S103).

  These phase change amounts are specific to the wireless tag distance measuring device 10 and the wireless tag, and can be obtained in advance at the stage of design or calibration.

  The sine wave distance calculation unit 36 obtains a lower limit value d1 obtained by subtracting the resolution error δR from the round trip rise distance D0 and an upper limit value d2 obtained by adding the resolution error δR to the round trip rise distance D0 (S104). Further, the sine wave distance calculating unit 36 obtains a value (integer part) obtained by rounding down the decimal point of the value obtained by dividing the lower limit value d1 by the wavelength λ of the reference sine wave signal as m (S105). A value obtained according to D1 = λ (2mπ + P) / (2π) is set as the first estimated round-trip distance D1 (S106).

  The sine wave distance calculation unit 36 obtains a value obtained by rounding down the decimal point of the value obtained by dividing the upper limit value d2 by the reference sine wave signal wavelength λ as n (S107). A value obtained according to D2 = λ (2nπ + P) / (2π) is set as the second estimated round-trip distance D2 (S108).

  The sine wave distance calculation unit 36 determines whether or not the first estimated round trip distance D1 and the second estimated round trip distance D2 are equal (S109). When these values are equal, the first estimated round trip distance D1 or the second estimated round trip distance D2 is determined as the basic round trip distance E0 (S110), and is output to the detailed distance calculator 38 (S112).

  When the first estimated round trip distance D1 and the second estimated round trip distance D2 are different, the sine wave distance calculation unit 36 selects the round trip distance between the lower limit value d1 and the upper limit value d2. Then, the selected round trip distance is determined as the basic round trip distance E0 (S111), and is output to the detailed distance calculator 38 (S112).

  Here, the sine wave distance calculation unit 36 may output the basic round-trip distance E0 to the display unit 42 and cause the display unit 42 to display half of the basic round-trip distance E0 as a measurement distance.

  According to steps S101 to S103, the difference between the phase of the reference sine wave signal and the phase of the reference sine wave signal included in the compressed pulse modulation signal is obtained as the distance measurement phase difference P with reference to the position of the measurement device antenna 26. It is done. The distance measurement phase difference P takes a value from 0 to 2π. This value represents the propagation phase change amount corresponding to the decimal point when the round-trip distance to the wireless tag is expressed in wavelength units. Therefore, an integer part j is calculated when the round-trip distance to the wireless tag is expressed in wavelength units, and a phase value 2πj + P obtained by adding the distance measurement phase difference P to the phase obtained by multiplying the integer part by 2π is used. The round-trip distance to the wireless tag can be obtained as λ (2πj + P) / (2π).

  Steps S105 and S107 are processes for obtaining integers m and n as integer parts when the lower limit value d1 and the upper limit value d2 of the round-trip distance are expressed in wavelength units, respectively. The integer j is one of the integers m and n, and the round trip distance is one of the estimated round trip distances D1 and D2 obtained in steps S106 and S108, respectively.

  As described above, the wavelength λ of the reference sine wave signal is set to be longer than twice the resolution error δR. Therefore, the difference (= 2δR) between the upper limit value d2 and the lower limit value d1 is shorter than the wavelength λ, and there are two cases where n = m holds and n = m + 1 holds. Here, since the true reciprocal distance is within the range of the lower limit value d1 to the upper limit value d2, when n = m + 1 holds, λ (2πm + P) / (2π) and λ (2πn + P) / (2π) Of these, those within the range of the lower limit value d1 to the upper limit value d2 may be adopted as the final basic round-trip distance E0. On the other hand, if n = m holds, it goes without saying that λ (2πm + P) / (2π) = λ (2πn + P) / (2π) is the final basic round-trip distance E0.

  Therefore, the basic reciprocating distance E0 is D1 (or D2) when n = m, and is within the range of the lower limit value d1 to the upper limit value d2 of D1 or D2 when n = m + 1. Steps S109 to S111 are to obtain a round-trip distance to the wireless tag based on such a principle.

In the RFID tag distance measuring apparatus 10 according to the present embodiment, the phase difference between the carrier wave of the spread pulse modulation signal output from the wireless transmission unit 22 and the carrier wave of the compressed pulse modulation signal output from the reception amplification unit 30 is used. Thus, the accuracy is further improved than the distance measurement accuracy for the basic reciprocating distance E0. The measurement accuracy improving process using the phase difference of the carrier wave is performed by the RFID tag distance measurement system so that the resolution error 2δr of the basic round-trip distance E0 is shorter than the propagation wavelength λ0 = c / f0 of the electromagnetic wave having the carrier wave frequency f0. When designed, a high effect can be obtained. That is, it is preferable that the system is designed so that the following relationship (Equation 4) is established.
(Expression 4) 2δr <c / f0

When the resolution error 2δr is determined in advance, the carrier frequency f0 may be determined to be smaller than c / (2δr), that is, the carrier wavelength λ0 may be longer than 2δr. That is, the following relationship (Equation 5) can be obtained by using (Equation 4).
(Expression 5) f0 <c / (2δr)

  Here, it has been confirmed that the resolution error 2δr of the basic round-trip distance E0 can be suppressed to 1/50 or less of the wavelength λ of the reference sine wave signal. Therefore, when the frequency of the reference sine wave signal is 10 MHz and the wavelength is 30 m, the resolution error of the basic round-trip distance E0 is 2δr = 60 cm, and the distance measurement error based on the basic round-trip distance E0 is 30 cm (± 30 cm). In this case, the frequency of the carrier wave may be less than 500 MHz based on (Equation 4).

  FIG. 6 shows a flowchart of the measurement accuracy improving process using the phase difference of the carrier wave. This process improves measurement accuracy based on the same principle as the process shown in FIG. The description overlapping with the process shown in FIG. 5 is omitted.

  The carrier phase difference detector 40 obtains the phase difference between the carrier wave of the spread pulse modulation signal and the carrier wave of the compressed pulse modulation signal as a measurement phase difference (S201). The carrier phase difference detection unit 40 includes a phase change amount from when the signal is output from the wireless transmission unit 22 to the measurement device antenna 26, a phase change amount based on the reception / transmission response of the wireless tag, and the signal as the measurement device antenna 26. The distance measurement phase difference Q is obtained by subtracting the phase change amount from the reception to the carrier phase difference detection unit 40 from the measurement phase difference, and is output to the detailed distance calculation unit 38 (S202). This phase change amount is an amount specific to the RFID tag distance measuring device 10 and the RFID tag, and can be obtained in advance at the stage of design or calibration.

  The detailed distance calculation unit 38 obtains a lower limit value e1 obtained by subtracting the resolution error δr from the basic round trip distance E0 output from the sine wave distance calculation unit 36, and an upper limit value e2 obtained by adding the resolution error δr to the basic round trip distance E0 ( S203). Further, the detailed distance calculation unit 38 obtains a value obtained by rounding down the decimal point of the value obtained by dividing the lower limit value e1 by the wavelength λ0 of the carrier wave signal as M (S204). Then, a value obtained according to E1 = λ0 (2Mπ + Q) / (2π) is set as the first estimated round-trip distance E1 (S205).

  The detailed distance calculation unit 38 obtains a value obtained by rounding down the decimal point of the value obtained by dividing the upper limit value e2 by the carrier wavelength λ0 as N (S206). Then, a value obtained according to E2 = λ0 (2Nπ + Q) / (2π) is set as the second estimated round-trip distance E2 (S207).

  The detailed distance calculation unit 38 determines whether or not the first estimated round trip distance E1 and the second estimated round trip distance E2 are equal (S208). When these values are equal, half of the first estimated round trip distance E1 or the second estimated round trip distance E2 is determined as the measurement distance to the wireless tag (S209), and the measurement distance information is output to the display unit 42 ( S211). The display unit 42 displays the measurement distance.

  When the first estimated round trip distance E1 and the second estimated round trip distance E2 are different, the detailed distance calculation unit 38 selects the round trip distance between the lower limit value e1 and the upper limit value e2. Then, half of the selected round-trip distance is determined as the measurement distance to the wireless tag (S210), and the measurement distance information is output to the display unit 42 (S211). The display unit 42 displays the measurement distance.

  According to such a configuration and processing, it is possible to specify a wireless tag as a distance measurement target and measure the distance from the wireless tag distance measuring device 10 to the wireless tag. For example, in the code assignment shown in FIG. 1, when the wireless tag 12-2 is specified as the distance measurement target, the multiplication unit 20 has a PN signal based on the unique assignment PN code “10011. Is output. As a result, a spread pulse modulated signal based on the PN code “10011...” Of the wireless tag 12-2 is transmitted from the wireless tag distance measuring device 10. Among the wireless tags 12-1 to 12-4 that have received the spread pulse modulation signal, the wireless tag 12-2 to which the same uniquely assigned PN code as the uniquely assigned PN code “10011. Transmit a pulse modulated signal. Therefore, the wireless tag distance measuring device 10 can calculate the distance to the wireless tag 12-2.

  According to the wireless tag distance measurement system according to the present embodiment, only the wireless tag as a distance measurement target performs time compression processing and transmits a compressed pulse modulation signal due to the orthogonality of the PN code described above. A compressed pulse modulated signal is not transmitted from a wireless tag that is not a distance measurement target. Therefore, even when there are a plurality of wireless tags having a small difference in distance from the wireless tag distance measuring apparatus 10, signals transmitted from the plurality of wireless tags do not interfere with each other, and the wireless tag to be measured Can be calculated.

  Further, in the RFID tag distance measuring system according to the present embodiment, the round-trip rising distance obtained based on the difference between the rising time of the transmission signal and the rising time of the reception signal is obtained, and further, a reference sine used for generation of the transmission signal The round trip distance to the wireless tag is determined as the basic round trip distance based on the phase difference between the wave signal and the response sine wave signal included in the received signal. The distance measurement accuracy is further improved based on the basic round-trip distance and the phase difference between the transmission carrier and the reception carrier. Thereby, the distance measurement accuracy can be improved as compared with the case where the distance measurement is performed based only on the rise time of the signal.

  Furthermore, in the RFID tag distance measuring system according to the present embodiment, the RFID tag distance measuring device 10 transmits a spread pulse modulated signal. In the spread pulse modulation signal, energy is spread over the time length of the PN signal as compared with a pulse signal having a time length corresponding to one code of the PN code.

  The wireless transmission unit 22 of the wireless tag distance measuring device 10 cannot transmit a signal exceeding the saturation level or a value defined in the standard. However, in the present embodiment, since the pulse signal to be transmitted is time-spread, the total power that can be transmitted can be increased without increasing the level of the signal to be transmitted.

  In this embodiment, a signal transmitted from the wireless tag to the wireless tag distance measuring device 10 is subjected to time compression processing by the wireless tag. The level of the signal obtained by performing the time compression process increases as the total power amount of the signal before the time compression process increases. Therefore, the level of the signal received by the RFID tag distance measuring device 10 can be increased and the maximum measurable distance can be increased as compared with a positioning system that does not perform time spreading processing and time compression processing. .

Next, with reference to FIG. 7 will be described wireless tag positioning system which applies the radio tag distance measuring system. The wireless tag positioning system measures the position of the wireless tag by arranging a plurality of wireless tag distance measuring devices 10. FIG. 7 shows an example in which four RFID tag distance measuring devices 10 are arranged.

  The information processing device 54 outputs designation information for designating the distance measurement target wireless tag to the code selection unit 16 of each wireless tag distance measurement device 10. The code selection unit 16 of each wireless tag distance measuring device 10 reads from the PN code storage unit 14 the uniquely assigned PN code of the wireless tag designated by the designation information. Then, distance measurement is performed based on the read PN code. Thereby, each wireless tag distance measuring device 10 calculates the distance to the wireless tag designated by the information processing device 54 and outputs the calculated distance to the information processing device 54.

  The information processing device 54 stores installation position information indicating the position where each wireless tag distance measuring device 10 is installed. The information processing device 54 obtains the position of the designated wireless tag based on the distance calculation result output from each wireless tag distance measuring device 10 and the installation position information of each wireless tag distance measuring device 10.

  The position of the wireless tag 12 can be obtained as follows. For each RFID tag distance measuring device 10, the information processing device 54 obtains an expression representing a calculated distance spherical surface 56 with the calculated distance as the length of the radius centered on the position of the RFID tag distance measuring device 10. The information processing device 54 calculates the position of the intersection 58 where the calculated distance spherical surface 56 obtained for each wireless tag distance measuring device 10 intersects as the position of the wireless tag 12.

  When the RFID tag distance measuring device 10 is arranged on a plane and the position of the RFID tag on the plane is measured, if three or more RFID tag distance measuring devices 10 that are not on the same straight line are arranged, 1 An intersection 58 of the points can be obtained, and this can be obtained as the position of the wireless tag. When measuring the position of the wireless tag in a three-dimensional space, four or more wireless tag distance measuring devices 10 that are not on the same plane may be arranged.

  An RFID tag positioning system using an RFID tag distance measurement system according to an embodiment of the present invention is a product management in a factory, a retail store that sells daily necessities, accessories, etc., and an event venue that needs to manage the location of event participants Etc. can be used.

It is a figure which shows the structure of the RFID tag distance measurement system which concerns on embodiment. It is a figure which shows the structure of the wireless tag distance measuring apparatus which concerns on embodiment. 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 flowchart of the measurement accuracy improvement process using the phase difference of a sine wave signal. It is a flowchart of the measurement accuracy improvement process using the phase difference of a carrier wave. It is a figure which shows the structure of a wireless tag positioning system.

Explanation of symbols

  10 wireless tag distance measuring device, 12, 12-1 to 12-4 wireless tag, 14, 52 PN code storage unit, 16 code selection unit, 18 sine wave signal generation unit, 20 multiplication unit, 22 wireless transmission unit, 24 local Signal generator, 26 measuring device antenna, 28 wireless receiver, 30 reception amplifier, 32 frequency converter, 34 rise distance calculator, 36 sine wave distance calculator, 38 detailed distance calculator, 40 carrier phase difference detector, 42 Display unit, 44 RFID tag antenna, 46 duplexer, 48 correlation processing device, 48A digital matched filter, 50 PN code setting circuit, 54 information processing device, 56 calculation distance spherical surface, 58 intersection.

Claims (3)

A wireless transmitter for transmitting a distance measurement signal for measuring a target distance;
A radio reception unit for receiving an incoming signal that has arrived after transmission of the distance measurement signal;
A distance calculation unit that calculates the distance to the target wireless tag;
In a wireless tag distance measuring device comprising:
A distance measurement signal generation unit that generates a PN signal having a value corresponding to a PN code uniquely assigned to the wireless tag and generates the distance measurement signal based on a signal obtained by multiplying the PN signal by a sine wave signal;
With
The wireless receiver is
A time-compressed signal that is time-compressed with respect to the distance measurement signal by the wireless tag is received as the incoming signal;
The distance calculation unit
Calculating a distance to the wireless tag based on a phase difference between a sine wave signal that is a source for generating the distance measurement signal and a sine wave signal included in an incoming signal received by the wireless reception unit; A wireless tag distance measuring device. The wireless tag distance measuring device according to claim 1,
The distance calculation unit
The wireless tag distance measuring apparatus, wherein a distance to the wireless tag is calculated based on a difference between a rising time of the distance measurement signal and a rising time of an incoming signal received by the wireless reception unit. In the wireless tag distance measuring device according to claim 1 or 2,
The distance measurement signal generator is
A signal obtained by multiplying the PN signal by a sine wave signal is converted into a signal modulated on a carrier wave to generate the distance measurement signal,
The distance calculation unit
A wireless tag distance measuring device that calculates a distance to the wireless tag based on a phase difference between a carrier wave of an incoming signal received by the wireless reception unit and a carrier wave of the distance measurement signal.

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