Abstract:
A method of measuring a range from a reader unit to a non-contacted IC medium, includes: transmitting an inquiry signal at a first frequency from the reader unit to the non-contacted IC medium; causing the non-contacted IC medium to perform modulation to modulate the first frequency by using a second frequency to obtain a modulated frequency, and causing the non-contacted IC medium to respond to a response signal at the modulated frequency; causing the reader unit to receive the response signal to acquire a plurality of frequency components; calculating a phase difference between signals of at least two of the acquired plurality of frequency components; and measuring the range by using the phase difference.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a range measuring method, a range measuring apparatus, a non-contacted IC medium and a range measuring system, which measures a range, for example, from a reader unit to a non-contacted IC medium. 
         [0002]    There is a range measuring apparatus that measures the range to a non-contacted IC medium using multiple frequencies (refer to International Publication WO 2006/095463). The range measuring apparatus controls an RFID tag (non-contacted IC medium) to transmit two times a R/W request signal that requests transmission of a tag response signal. At this time, a frequency controller controls a PLL portion to transmit respective R/W request signals by transfer frequencies differing from each other. A phase information acquisition portion detects fluctuation amounts in phase of tag response signals transmitted by the transfer frequencies differing from each other, respectively, and calculates the range between a reader/writer and the RFID tag based on the fluctuation amounts in the phase. Therefore, the range between the reader/writer and the RFID tag can be accurately calculated. 
         [0003]    However, it cannot be necessarily said that the non-contacted IC medium always stops at a fixed position. And, there is a case where the range to a non-contacted IC medium in motion is requested to be obtained. In such a case, since the above-described range measuring apparatus carries out transmission and receiving of different frequencies at different timings, a deviation occurs at the receiving timing. Therefore, where the non-contacted IC medium is conveyed at a high speed, it is difficult to accurately calculate the range. 
       SUMMARY 
       [0004]    It is therefore an object of the invention to provide a range measuring method, a range measuring apparatus, a non-contacted IC medium and a range measuring system, which are capable of carrying out highly accurate range measurements even if a non-contacted IC medium is in motion. 
         [0005]    In order to achieve the object, according to the invention, there is provided a method of measuring a range from a reader unit to a non-contacted IC medium, the method comprising: transmitting an inquiry signal at a first frequency from the reader unit to the non-contacted IC medium; causing the non-contacted IC medium to perform modulation to modulate the first frequency by using a second frequency to obtain a modulated frequency, and causing the non-contacted IC medium to respond to a response signal at the modulated frequency; causing the reader unit to receive the response signal to acquire a plurality of frequency components; calculating a phase difference between signals of at least two of the acquired plurality of frequency components; and measuring the range by using the phase difference. 
         [0006]    Phase shift keying may be used for the modulation. 
         [0007]    Frequency shift keying may be used for the modulation. 
         [0008]    The modulation may be digital modulation, and the plurality of frequency components may be high frequency components generated in the digital modulation. 
         [0009]    The response signal may be separated into an upper side band and a lower side band in order to acquire the plurality of frequency components. 
         [0010]    According to the invention, there is also provided an apparatus, operable to measure a range from a reader unit to a non-contacted IC medium, the apparatus comprising: a communication unit, transmitting an inquiry signal at a first frequency from the reader unit to the non-contacted IC medium, and receiving a response signal from the non-contacted IC medium; a frequency component acquiring unit, acquiring a plurality of frequency components from the response signal; and a range measuring unit, calculating a phase difference between signals of at least two of the acquired plurality of frequency components, and measuring the range by using the phase difference. 
         [0011]    According to the invention, there is also provided a non-contact IC medium, comprising: a communication unit, receiving an inquiry signal at a first frequency from a reader unit, and responding to a response signal to the reader unit; and a modulation unit, performing modulation to modulate the first frequency by using a second frequency to obtain a modulated frequency, wherein the communication unit responds to the response signal at the modulated frequency. 
         [0012]    According to the invention, there is also provided a range measuring system, comprising: a non-contacted IC medium; and a range measuring apparatus, operable to measure a range from a reader unit to the non-contacted IC medium, the apparatus comprising: a first communication unit, transmitting an inquiry signal at a first frequency from the reader unit to the non-contacted IC medium, and receiving a response signal from the non-contacted IC medium; a frequency component acquiring unit, acquiring a plurality of frequency components from the response signal; and a range measuring unit, calculating a phase difference between signals of at least two of the acquired plurality of frequency components, and measuring the range by using the phase difference, wherein the non-contacted IC medium comprises: a second communication unit, receiving the inquiry signal at the first frequency from the reader unit, and responding to the response signal to the reader unit; and 
         [0013]    a modulation unit, performing modulation to modulate the first frequency by using a second frequency to obtain a modulated frequency, and the second communication unit responds to the response signal at the modulated frequency. 
         [0014]    The inquiry signal may be made into a signal for which the reader unit causes the non-contacted IC medium to respond, and for example, may be made into a signal including a command to send an ID. 
         [0015]    The response signal may be made into a signal for which the non-contacted IC medium responds to the reader unit, and for example, may be made into a signal to send an ID. 
         [0016]    The upper side band may be made into a USB (Upper Side Band), and the lower side band may be made into an LSB (Lower Side Band). 
         [0017]    The frequency component acquiring unit may be a unit for acquiring, for example, frequency components while separating the same into USB components and LSB components, and may be composed as a unit for acquiring frequencies with the same separated as per component. 
         [0018]    The range measuring unit may be composed of a unit for measuring a range by per-component frequencies, and may be composed of a unit for calculating appropriately using numerical expressions. 
         [0019]    The range measuring apparatus may be made into a reader unit that can communicate with a non-contacted IC medium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a system configuration view of a range measuring system. 
           [0021]      FIGS. 2A ,  2 B and  2 C are schematic views describing a configuration of an RFID tag. 
           [0022]      FIGS. 3A and 3B  are schematic views describing a configuration of a reader/writer. 
           [0023]      FIGS. 4A ,  4 B and  4 C are schematic views describing a detailed configuration of a reader/writer. 
           [0024]      FIGS. 5A ,  5 B and  5 C are schematic views describing a PSK system. 
           [0025]      FIGS. 6A and 6B  are schematic views describing an FSK system. 
           [0026]      FIG. 7  is a flowchart showing actions of the range measuring system. 
           [0027]      FIG. 8  is a schematic view describing a system utilizing high frequency components. 
           [0028]      FIG. 9  is a configurational view of a frequency component separating portion that carries out complex FFT operations. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0029]    A description is given of one embodiment of the invention with reference to the following drawings. 
         [0030]      FIG. 1  is a configuration view of a range measuring system  1 ,  FIGS. 2A to 2C  are schematic views of a configuration of an REID tag (Radio Frequency Identification Tag)  20 , and  FIGS. 3A and 3B  are schematic views of a configuration of reader/writer  10 . 
         [0031]    The range measuring system  1  is composed of a reader/writer  10  and an RFID tag  20 . 
         [0032]    The REID tag  20  is provided with a sub carrier generation portion  22 , a modulation portion  23 , a communications controller  24  and a memory portion  25  in addition to an antenna  21  as shown in  FIG. 2A . 
         [0033]    The antenna  21  communicates with the reader/writer  10  in a non-contacted state. The antenna may be composed of an appropriate antenna such as a UHF antenna or a loop antenna. 
         [0034]    The sub carrier generation portion  22  generates a sub carrier (sub carrier wave) whose frequency is different from the first frequency (frequency fc) used by the reader/writer  10  as a carrier wave. In the embodiment, phase shift keying (PSK) or frequency shift keying (FSK) may be selectively used as the modulation system of the sub carrier. Also, a lower frequency than the first frequency is adopted for the sub carrier. 
         [0035]    The memory portion  25  stores ID being identification information of the RFID tag  20  and other data. 
         [0036]    The communications controller  24  carries out communications control by which it receives a command from the reader/writer  10 , modulates digital data in the memory portion  25  and responds to the reader/writer  10 . The communications controller  24  is composed of digital circuits (logic) to execute parallel processing such as sub carrier generation. 
         [0037]    The modulation portion  23  modulates the sub carrier based on digital data transmitted from the communications controller  24 . It is composed so that the modulation is selectively carried out based on two types of PSK and FSK. 
         [0038]    First, a detailed description is given of the PSK. As shown in  FIG. 2B , the calculator  26  obtains an exclusive logic sum (XOR: exclusive or) of the sub carrier  28  (sub carrier wave shown at [ 1 ] in  FIG. 2C ) and digital data (data shown at [ 2 ] in  FIG. 2C ) that is framed by adding a preamble and CRC (Cyclic Redundancy Check), etc., in a framing portion  29 , and an after-calculated signal (signal shown at [ 3 ] in  FIG. 2C ) is generated. And, reflected signals of the first frequency fc, which are from the reader/writer  10 , by the antenna  21  are controlled by changing the impedance of the antenna  21  based on the signals. The reflected signals by the antenna  21  become a response to the reader/writer  10 . 
         [0039]    A detailed description is given of FSK. As shown in  FIG. 3A , output signals (signals shown at [ 4 ] in  FIG. 3B ) are generated by changing a sub carrier  28   a  and a sub carrier  28   b  by a multiplexer  27  (MUX) using the sub carrier  28   a  (sub carrier wave shown at [ 1 ] in  FIG. 3B ), sub carrier  28   b  (sub carrier wave shown at [ 2 ] in  FIG. 3B ) and digital data (data shown at [ 3 ] in  FIG. 3B ) framed by adding a preamble and a CRC thereto at the framing portion  29 . And, the signals are sent back from the antenna  21  to the reader/writer  10 . 
         [0040]    Also, the RFID tag  20  is provided with a demodulator and a decoder (illustration of which is omitted). The demodulator demodulates signals received by the antenna  21  and acquires command signals transmitted from the reader/writer  10 . The decoder decodes demodulated command signals, and takes out coded command data, wherein processes of reading (transmitting a designated area of the memory portion  25 ) and writing (writing data following the command in the designated area of the memory portion  25 ) are carried out. 
         [0041]    In addition, for the RFID tag  20 , there are two types, one of which is a passive type that does not have any power source and responds to actuation by an electric field or magnetic field and the other of which is a semi-passive type that internally includes a power source and responds when receiving a response request from the reader/writer  10 . Therefore, the RFID tag  20  can synchronize with carrier waves transmitted from the reader/writer  10 . 
         [0042]    The reader/writer  10  is provided with the antenna  11 , and is also provided with a controller and a memory portion, illustration of which is omitted. The memory portion stores various types of data and also stores a range measuring program to measure the range. In addition, the reader/writer  10  includes a range calculating portion  13 , a frequency component separating portion  14  and a frequency converting portion  15  as shown in  FIG. 4A . 
         [0043]    The frequency converting portion  15  carries out frequency conversion in regard to signals received from the antenna  11 , and sends the frequency component (±fs) of a sub carrier to the frequency component separating portion  14 . 
         [0044]    The frequency component separating portion  14  separates the received frequency component (±fs) into USB and LSB. 
         [0045]    Herein, the LSB can be picked up by the configuration shown in  FIG. 4B . That is, first, I components and Q components are extracted from input frequencies by means of an orthogonal mixer  14   a , wherein the phase of the Q components is changed by +90° by a phase converter  14   b . And, the after-phase changed Q component and I components for which the phase has not been changed are synthesized by a synthesizer  14   c , thereby extracting the LSB. 
         [0046]    In addition, USB can be picked up by the configuration shown in  FIG. 4C . That is, first, I components and Q components are extracted from input frequencies by an orthogonal mixer  14   a , wherein the phase of the Q components is changed by −90° by a phase converter  14   d . And, the after-phase changed Q component and I components for which the phase has not been changed are synthesized by a synthesizer  14   c , thereby extracting the USB. 
         [0047]    The range calculating portion  13  shown in  FIG. 4A  calculates the range using the USB and LSB that are extracted by the frequency component separating portion  14 . The range calculation is carried out as follows. 
         [0048]    First, where it is assumed that the phase of the signal of the first frequency fc transmitted by the reader/writer  10  is the reference phase, the signals of the first frequency fc reach the RFID tag  20  located at a distance r from the reader/writer  10  and is reflected therefrom, and phase of carrier waves returned to the reader/writer  10  becomes Φt. And, the phase Φru of the USB signal, which is generated by modulation with respect to the signal of the first frequency fc at the RFID tag  20  and has reached the reader/writer  10 , for the reference phase and the phase Φrl of the LSB signal for the reference phase may be expressed by the following expression. 
       [Mathematical Expression 1] 
     Phase Φt of Carrier Wave 
       [0049]      Φ t= 2 π·f c·r/c    
         [0050]    *r: Range, C=3×10 8  m/s (Light speed) 
       [Mathematical Expression 2] 
     Phase Delay Φru of USB 
       [0051]      Φ ru =2π·( f c+f s )· r/c    
         [0052]    *r: Range, c=3×10 8  m/s (Light speed) 
       [Mathematical Expression 3] 
     Phase Delay Φrl of LSB 
       [0053]      Φ rl= 2π·( f c−f s )· r/c    
         [0054]    *r: Range, c=3×10 8  m/s (Light speed) 
         [0000]    Therefore, the range from the reader/writer  10  to the RFID tag  20  may be calculated by the following expression. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           
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       [Mathematical Expression 5] 
     Range r 
       [0055]        r =( c ·         Φ)/(2π·2  f s ) 
         [0056]    *ΔΦ (Phase difference)=Φru−Φrl 
         [0057]      FIGS. 5A to 5C  are schematic views describing a carrier wave, a response signal, USB and LSB where PSK is used. 
         [0058]    As shown in  FIG. 5A , an inquiry signal (carrier wave) transmitted by the reader/writer  10  is a signal of the first frequency fc. 
         [0059]    As shown in  FIG. 5B , the response signal (reflected wave) responded by the RFID tag  20  is a signal obtained by synthesizing the first frequency fc and the second frequency fs. For the response signal, data are expressed in the PSK system. 
         [0060]    As shown in  FIG. 5C , the response signal can pick up USB and LSB by separation of frequency components. 
         [0061]      FIGS. 6A and 6B  are schematic views describing a carrier wave, a response signal, USB and LSB where FSK is used. 
         [0062]    As shown in  FIG. 6A , a response signal (reflected wave) that the RFID tag  20  responds to is a signal obtained by synthesizing the first frequency fc and the second frequency fs and the third frequency fs 2 , which are sub carriers. For the response signal, data are expressed in the FSK system. 
         [0063]    As shown in  FIG. 6B , the response signal may obtain a number of components separated into USB and LSB and separated into the second frequency fs 1  component and the third frequency fs 2  component by separation of frequency components. In this case, three or more frequency components may be used, wherein a high-resolution power algorithm based on the MUSIC (Multiple Signal Classification) method disclosed by the International Publication WO2006/095463, etc., may be used. Accordingly, the accuracy under multi-pass environments can be improved with transmission frequency from the reader/writer  10  remaining as one frequency. 
         [0064]      FIG. 7  is a flowchart showing actions when a range from the reader/writer  10  to the RFID tag  20  is obtained by the range measuring system  1 . 
         [0065]    First, the reader/writer  10  carries out command transmission and requests a response for ID from the RFID tag  20  (Step S 1 ). At this time, the command is transmitted by the first frequency fc. Also, the command includes a modulation system code to determine whether the modulation system is based on PSK or FSK. 
         [0066]    The RFID tag  20  analyzes the command from the reader/writer  10  (Step S 2 ) and extracts the modulation system code. 
         [0067]    If the modulation system is based on the PSK (Step S 4 : PSK), the RFID tag  20  changes the modulation portion  23  to the PSK circuit (Step S 5 ). 
         [0068]    If the modulation system is based on the FSK (Step S 4 : FSK), the RFID tag  20  changes the modulation portion  23  to the FSK circuit (Step S 6 ). 
         [0069]    The RFID tag  20  reads memory data stored in the memory  25  (this example includes ID) (Step S 7 ), and frames by adding a preamble and CRC thereto (Step S). 
         [0070]    The RFID tag  20  modulates framed data by the system (PSK or FSK) changed by Steps S 4  through S 6  (Step S 9 ), and sends back a response signal (Response) (Step S 10 ). 
         [0071]    The reader/writer  10  receives a response signal (Response) (Step S 11 ), and detects whether or not there is any error, by a CRC check (redundancy cyclic inspection) (Step S 12 ). 
         [0072]    If any error occurs (Step S 12 : NG), the reader/writer  10  returns the process to Step S 1 , and carries out the process again. 
         [0073]    If there is no error (Step S 12 : OK), the reader/writer  10  carries out a process of FFT (Fast Fourier Transform) of the received signal by the frequency converting portion  15  (Step S 13 ). 
         [0074]    The reader/writer  10  further separates LSB and USB from each other by the frequency component separating portion  14  (Step S 14 ), calculates a phase by the range calculating portion  13  (Step S 15 ), and carries out estimation of the range based on the phase difference (Step S 16 ). 
         [0075]    The reader/writer  10  combines the calculated range with an ID included in the signals received in Step S 11  and outputs the same (Step S 17 ), and then terminates the process. Also, the output may be carried out by an appropriate method such as storing the output in a memory unit of the reader/writer  10 , transmitting the same to another device connected to the reader/writer  10  or displaying the same in a display device secured at the reader/writer  10 . 
         [0076]    Based on the above-described configuration and actions, only by an inquiry signal being transmitted one time at a single frequency from the reader/writer  10 , the reader/writer  10  receives a response signal including multiple frequency components from the RFID tag  20 , and can calculate the range from the reader/writer  10  to the RFID tag  20 . 
         [0077]    Therefore, even if the REID tag  20 , which is the object for range measurement, is moving at a high speed, it is possible to carry out highly accurate range measurements. That is, where a plurality of frequencies are transmitted from the reader/writer  10  one after another, if the RFID tag  20  is moving, accurate range measurements become difficult if the positions of the REID tag  20  differ from each other when transmitting respective frequencies. However, in the above-described embodiment, since an inquiry signal is transmitted one time at a single frequency, no time lag occurs, wherein accurate range measurements are enabled. 
         [0078]    Also, since calculation is carried out by obtaining a phase difference of a sub carrier (the second frequency), it is possible to accurately measure the range by canceling the reflected wave. 
         [0079]    In addition, since the frequency transmitted by the reader/writer  10  is regulated by the radio wave law, it was difficult to change the frequency of transmission waves as in the prior art. However, since the frequency of reflected waves from the RFID tag  20  is not regulated, range measurement can be carried out by frequency separation using frequencies for which differences are sufficiently widened based on the above reason. 
         [0080]    Where the PSK is used, a range can be simply measured. 
         [0081]    Also, where the FSK is used, the RFID tag  20  returns reflected waves (response signals) with respect to a single frequency transmitted from the reader/writer  10 , using frequency components, wherein the measurement accuracy can be improved by using multiple frequencies. 
         [0082]    In addition, since the upper side band (USB) and the lower side band (LSB) are separated from each other, noise in the reflected waves can be separated, wherein highly accurate range measurement can be achieved. 
         [0083]    Further, in the above-described embodiment, although PSK and FSK are used, the frequency separation is not limited thereto, but various methods may be used to separate frequencies to enable range measurement. 
         [0084]    For example, the modulating portion  23  of the RFID tag  20  carries out modulation in the PSK system. The reader/writer  10  extracts high frequency components (odd-number order such as primary, tertiary, quinary, etc.) as shown in  FIG. 8 , and these high frequency components may be used. In this case, since three or more frequency components may be used, a high-resolution power algorithm based on the MUSIC method may be utilized. Therefore, the accuracy under a multiple-pass environment can be improved with the transmission frequency from the reader/writer  10  remaining as one frequency. 
         [0085]    Furthermore, where such high frequency components are used, it is preferable that the RFID tag  20  is of a semi-passive type having a power source. Accordingly, power necessary to pick up high frequencies can be secured, and can be effectively utilized. 
         [0086]    Also, as shown in  FIG. 9 , it may be composed that the frequency component separating portion  14  uses a complex FFT operation. In this case, received signals are separated into I signals and Q signals by the orthogonal mixer  14   a , and the respective signals may be separated into real parts and imaginary parts by complex FFT operations  14   e  and  14   f . And, USB components and LSB components for which addition and subtraction are further carried out are extracted, and phases of USB and LSB may be calculated from the respective I components and Q components. 
         [0087]    In this case, the respective phases of USB and LSB may be obtained by the following mathematical expressions. 
       [Mathematical Expression 6] 
     Phase Delay of USB 
       [0088]      Φ ru =Arctan( FFT ( I ) Re   +FFT ( Q ) Im )/( FFT ( I ) Im   −FFT ( Q ) Re ) 
         [0000]    *FFT (I) Re : Real part separated from 1 signals by complex FFT operation 
         [0089]    FFT(I) Im : Imaginary part separated from 1 signals by complex FFT operation 
         [0090]    FFT(Q) Re : Real part separated from Q signals by complex FFT operation 
         [0091]    FET(Q) Im : Imaginary part separated from Q signals by complex FFT operation 
         [0092]    Arctan(X): Function for calculation of arc-tangent of X 
       [Mathematical Expression 7] 
     Phase Delay of LSB 
       [0093]      Φ rl =Arctan( FFT ( I ) Re   −FFT ( Q ) Im )/( FFT ( I ) Im   +FFT ( Q ) Re ) 
         [0000]    FFT(I) Re : Real part separated from 1 signals by complex FFT operation 
         [0094]    FFT(I) Im : Imaginary part separated from 1 signals by complex FFT operation 
         [0095]    FFT(Q) Re : Real part separated from Q signals by complex FFT operation 
         [0096]    FFT(Q) Im : Imaginary part separated from Q signals by complex FFT operation 
         [0097]    Arctan(X): Function for calculation of arc-tangent of X 
         [0098]    In this case, only by an inquiry signal being transmitted from the reader/writer  10  one time at a single frequency, the reader/writer  10  receives a response signal from the RFID tag  20  corresponding thereto, and can calculate the range from the reader/writer  10  to the RFID tag  20 . 
         [0099]    In addition, the RFID tag  20  may be composed so as to function as a sensing device. In this case, the RFID tag  20  may be equipped with an appropriate sensor such as a temperature sensor, a humidity sensor, etc., instead of the memory portion  25  or connecting thereto. And, it may be composed that the RFID tag  20  frames a measurement value of the corresponding sensor as data, modulates the same and responds to the reader/writer. 
         [0100]    Therefore, the reader/writer  10  can acquire sensing information in a non-contacted state, and is able to recognize by range calculation at which position (range) the sensing information has been obtained. 
         [0101]    The composition of the invention matches or corresponds to the above-described embodiment as shown below; 
         [0102]    The range measuring system according to the invention matches or corresponds to a range measuring system  1  according to the embodiment. 
         [0103]    Similarly, the reader unit and range measuring apparatus match or correspond to the reader/writer  10 , 
         [0104]    the communication unit matches or corresponds to the antenna  11 , 
         [0105]    the range measuring unit matches or corresponds to the range calculating portion  13 , 
         [0106]    the frequency component acquiring unit matches or corresponds to the frequency component separating portion  14 , 
         [0107]    the non-contacted IC medium matches or corresponds to the RFID tag  20 , 
         [0108]    the communications unit matches or corresponds to the antenna  21 , and 
         [0109]    the modulating unit matches or corresponds to the modulating portion  23 . 
         [0110]    However, the invention is not limited to only the composition of the above-described embodiment, but may be subjected to various embodiments. 
         [0111]    According to an aspect of the invention, it is possible to provide a range measuring method, a range measuring apparatus, a non-contacted IC medium and a range measuring system, which are capable of executing highly accurate range measurements even if the non-contacted IC medium is in motion.