JP2013019811A - Transmission position detection apparatus, method, system, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly detect a position of a radio transmission source such as an RFID tag and an RFID reader.SOLUTION: A transmission position detection apparatus according to one embodiment includes at least four reception antennas for receiving signals that are radio transmitted from a radio transmission source, and a measurement unit which measures time differences between timings at which the respective reception antennas receive the signals that are radio transmitted from the radio transmission source and calculates three-dimensional coordinates indicating the position of the radio transmission source on the basis of the respective measured time differences.

Description

  Embodiments described herein relate generally to an apparatus, a method, a transmission position detection system, and a program for detecting the position of a wireless transmission source.

  An RFID (Radio Frequency Identification) tag (also referred to as a wireless tag, a responder, or the like) includes an antenna, a wireless communication unit, and a storage unit, and the identification information that is not duplicated in each tag in the storage unit of each RFID tag. Is remembered. When an RFID reader (also referred to as a reader / writer or an interrogator) transmits an inquiry signal to the RFID tag, the RFID tag performs processing according to the inquiry signal. For example, an RFID tag that returns a response only when the identification information stored in the RFID tag matches the identification information included in the inquiry signal from the RFID reader is known.

  An RFID tag having such a function is used in various fields including goods management in the logistics industry, for example, by attaching to an article. In recent years, a system for selling products and managing inventory by attaching each RFID tag to a product in a store selling various products has been put into practical use.

  By the way, in an industry that handles a large number of articles, there is a demand not only for managing the type and number of articles, but also for easily recognizing where each article is located. In order to detect the position of the RFID tag, a method of detecting the two-dimensional position of the RFID tag from the directivity of the antenna and the phase of the received signal when the RFID reader communicates with the RFID tag can be adopted.

  However, the above method obtains the position of the RFID tag with two-dimensional coordinates. For this reason, for example, when the above method is used to detect the position of an RFID tag attached to an article displayed on a shelf, it is possible to know which shelf the desired article is displayed, but what number of shelves It is impossible to know if it is on display. Further, the directivity can be reduced in the far field of the antenna, but the directivity tends to be poor in the near field. Therefore, when the distance from the RFID reader to the RFID tag is short, the coordinate detection accuracy is lowered.

US Pat. No. 7,873,326

  The problem to be solved by the present invention is that the position of a wireless transmission source such as an RFID tag or an RFID reader can be obtained in three-dimensional coordinates, and the distance between the wireless transmission sources such as the RFID reader and the RFID tag It is an object of the present invention to provide a transmission position detection system and a transmission position detection apparatus used in this system in which the coordinate detection accuracy does not decrease even if the distance is short.

  In one embodiment, the transmission position detection apparatus includes four or more reception antennas that receive signals wirelessly transmitted from a wireless transmission source, and each reception when each reception antenna receives a signal wirelessly transmitted from the wireless transmission source. A measurement unit that measures a time difference between the antennas and calculates a three-dimensional coordinate indicating the position of the wireless transmission source based on each measured time difference.

The schematic perspective view of the transmission position detection system in 1st Embodiment. The schematic block diagram of the transmission position detection apparatus in the embodiment. The schematic block diagram of the measurement part in the embodiment. The signal waveform diagram for demonstrating operation | movement of TDC in the embodiment. The figure for demonstrating the coordinate calculation of the wireless transmission source in the embodiment. The figure for demonstrating communication with the RFID reader and RFID tag in the embodiment. The figure which shows a part of envelope waveform of Query (Q) which the RFID reader in the embodiment transmits. The figure which shows the waveform of the preamble (P) which the RFID tag in the embodiment transmits. The flowchart which shows the operation | movement procedure of the transmission position detection apparatus in the embodiment. The flowchart which shows the operation | movement procedure of the server in the embodiment. 6 is a flowchart showing an operation procedure of the RFID reader according to the embodiment. The schematic diagram of the database with which the server is equipped in the embodiment. The figure which shows the transmission position detection result of a wireless transmission source in the same embodiment as a display example of xz plane. The figure which shows the transmission position detection result of a wireless transmission source in the embodiment as a display example of xy plane. The schematic block diagram of the measurement part in 2nd Embodiment. The input signal waveform figure to each TDC in the embodiment. The output signal waveform figure from each TDC in the embodiment.

Each embodiment will be described below with reference to the drawings.
(First embodiment)
[Main part configuration]
First, the configuration of the main part of the transmission position detection system in the present embodiment will be described.
FIG. 1 is a schematic perspective view of a transmission position detection system, and FIG. 2 is a schematic block diagram of the transmission position detection system. The transmission position detection system obtains the respective positions of the RFID reader 3 as a wireless transmission source and the plurality of RFID tags 4 (4a, 4b, 4c,...) With three-dimensional coordinates (x, y, z). A transmission position detection device 1 and a server 2 are included.

  The transmission position detection device 1 communicates with the server 2 by wire. The server 2 communicates with the RFID reader 3 wirelessly. The wireless communication between the server 2 and the RFID reader 3 uses a packet including the address of the transmitting station (MAC address or Bluetooth address), such as a wireless LAN or Bluetooth (registered trademark).

  The RFID reader 3 communicates with each RFID tag 4 (4a, 4b, 4c...) Wirelessly. Wireless communication between the RFID reader 3 and each RFID tag 4 follows a communication protocol of general RFID technology. In this embodiment, communication is performed in accordance with the EPC global Class 1 Generation 2 standard (hereinafter referred to as the C1G2 standard), which has become widespread in recent years.

  The transmission position detection apparatus 1 has a rectangular parallelepiped housing, for example, as shown in FIG. Then, four receiving antennas 11 (11a, 11b, 11c, 11d) are arranged inside the casing. Further, as shown in FIG. 2, the transmission position detection apparatus 1 includes four demodulation units 12 (12a, 12b, 12c, 12d) and amplification units 13 (13a, 13b, 13c, 13d) corresponding to the respective reception antennas 11 respectively. ) And a measurement unit 14, a control unit 15, and an oscillation unit 16.

  There is a limitation on the arrangement of the receiving antennas 11a to 11d. For example, it is assumed that four receiving antennas 11a to 11d are arranged on the xy plane which is the same plane, and each receiving antenna 11a to 11d has a shape having a rectangular apex. In this case, the receiving antennas 11a to 11d are equidistant from any point on a line in the z-axis direction that passes through the intersection of diagonal lines of the rectangle and is perpendicular to the surface of the rectangle. For this reason, since there is no difference in arrival time between the receiving antennas 11a to 11d, the distance in the z-axis direction cannot be obtained.

  In order to avoid such a problem, when the receiving antennas 11a to 11d are arranged on the same plane, they are arranged under the following conditions. That is, when each receiving antenna 11a to 11d is a quadrangle having apexes, it is arranged so that the sum of the opposite angles does not become 180 degrees and the center of the two diagonal lines does not become the same point. Note that the receiving antennas 11a to 11d may not be arranged on the same plane. When the receiving antennas 11a to 11d are not arranged on the same plane, the receiving antennas 11a to 11d are arranged so as not to be the vertices of a regular tetrahedron.

  Each receiving antenna 11a to 11d is ideally a point from the viewpoint of position detection accuracy. However, in reality, a size that depends on the wavelength of the received radio wave is required. However, it is not necessary to use a high-gain directional antenna. Rather, it is preferable to use a miniaturized antenna that is shortened in wavelength using a material having a high dielectric constant.

The radio waves radiated from the RFID reader 3 and the RFID tag 4 pass through the space and reach the receiving antennas 11a to 11d. Since the receiving antennas 11a to 11d are arranged under the above-described conditions, the distance from the position of the wireless transmission source (RFID reader 3 or RFID tag 4) that radiates radio waves to the receiving antennas 11a to 11d Different for each. For this reason, the time until the radio wave reaches each of the receiving antennas 11a to 12d is also different for each antenna. The speed of radio waves propagating in free space is about 3 × 10 ⁸ m / s. Therefore, for example, when the difference between the distance from the radio transmission source to the reception antenna 11a and the distance from the radio transmission source to the reception antenna 11b is 1 m, an arrival time difference of about 3.3 ns (3300 ps) occurs, When the difference is 10 cm, an arrival time difference of about 0.33 ns (330 ps) occurs.

  Each of the receiving antennas 11a to 11d converts the received radio wave into a high-frequency signal and outputs the high-frequency signal to the corresponding demodulating units 12a to 12d. The demodulator 12a combines the high-frequency signal output from the receiving antenna 11a and the output of the oscillator 16 to convert it into a baseband signal, and outputs this baseband signal to the amplifier 13a. Similarly, the other demodulating units 12b to 12d combine the high-frequency signals output from the receiving antennas 11b to 11d and the output of the oscillating unit 16 to convert them into baseband signals. To 13d. The baseband signals output from the demodulating units 12a to 12d include amplitude information for measuring received signal strength, generally called RSSI (Received Signal Strength Indication).

  The amplifying unit 13a amplifies and saturates the signal output from the demodulating unit 12a, and outputs it as binary information represented by “H (High)” or “L (Low)”. Similarly, the other amplifying units 13b to 13d amplify the baseband signals output from the demodulating units 12b to 12d, respectively, and output them as binary information. Note that a comparator may be used instead of each of the amplifying units 13a to 13d.

  The binary information signal output from the amplifying unit 13 a is input to the measuring unit 14 and the control unit 15. The binary information signals output from the other amplifying units 13 b to 13 d are input only to the measuring unit 14 and are not input to the control unit 15. The control unit 15 decodes the signal output from the amplification unit 13a and performs processing according to the decoded data. Specifically, the amplitude of the signal transmitted by the RFID reader 3 is large, and the amplitude of the backscatter signal transmitted by the RFID tag 4 is small. For this reason, the control unit 15 controls the gains of the amplification units 13a to 13d so that the gain when receiving the signal of the RFID reader 3 is small and the gain when receiving the signal of the RFID tag 4 is large. To do. Although only the output of the amplification unit 13a is input to the control unit 15, a signal output from the amplification unit 13b, 13c, or 13d may be input to the control unit 15.

  As described above, signals transmitted from the RFID reader 3 and the RFID tag 4 which are wireless transmission sources become binary information at the output stage of each of the amplification units 13a to 13d. The timing at which the output of the binary information changes from “L” to “H” is determined by the time when the radio wave from the RFID reader 3 or the RFID tag 4 reaches the receiving antennas 11a to 11d.

  The measurement unit 14 detects a time difference between signals input from the amplification units 13a to 13d. And the measurement part 14 calculates the position of the wireless transmission source which transmitted the received signal as a three-dimensional coordinate based on each time difference and the coordinate data of receiving antenna 11a-11d. The three-dimensional coordinates calculated here are coordinates based on the transmission position detection apparatus 1. The measurement unit 14 outputs the calculated three-dimensional coordinate value to the control unit 15.

  The control unit 15 includes a CPU (Central Processing Unit) and a storage unit (not shown). The control unit 15 operates according to a program stored in the storage unit, and controls the amplification unit 13 (13a, 13b, 13c, 14d), the measurement unit 14, and the oscillation unit 16. The control unit 15 associates the signal output from the amplification unit 13 a with the three-dimensional coordinate value output from the measurement unit 14, and transmits the associated value to the server 2. Further, the control unit 15 receives frequency information used by the RFID reader 3 from the server 2.

  The oscillation unit 16 generates a high frequency signal and outputs the high frequency signal to each of the demodulation units 12a to 12d. The oscillation frequency of the oscillating unit 16 is a frequency necessary for demodulating the radio wave transmitted by the RFID reader 3. For example, when the demodulator 12 employs the direct conversion method, the oscillation frequency is the same as the carrier wave transmitted by the RFID reader 3. On the other hand, when the demodulator 12 employs a method that uses an intermediate frequency, the oscillation frequency is a frequency obtained by subtracting the intermediate frequency from the carrier frequency transmitted by the RFID reader 3. Such an oscillation frequency can be changed according to a signal from the control unit 15.

[Time measurement]
FIG. 3 shows a schematic block diagram of the measuring unit 14. The measurement unit 14 includes four TDCs (Time to Digital Converter) 21 (21a, 21b, 21c, 21d) and a calculation unit 22.

  Each of the TDCs 21a to 21d has a Start input terminal, a Stop input terminal, and an output terminal. Each of the TDCs 21a to 21d outputs a digital value corresponding to the time until the Stop input changes from “L” to “H” after the Start input changes from “L” to “H”. In recent years, measurement resolution of about 10 ps has been obtained by using 180 nm process CMOS (Complementary Metal Oxide Semiconductor) technology. If the manufacturing process is miniaturized, resolution for measuring a shorter time can be obtained.

  The Start input terminals of the TDCs 21 a to 21 d are connected to the control unit 15. The Stop input terminal of the TDC 21a is connected to the amplifying unit 13a. Similarly, the Stop input terminals of the other TDCs 21b to 21d are also connected to the corresponding amplifying units 13b to 13d, respectively. The output terminals of the TDCs 21 a to 21 d are connected to the calculation unit 22.

The operation of each of the TDCs 21a to 21d will be described with reference to the signal waveforms shown in FIG.
First, the Start input and Stop input to each of the TDCs 21a to 21d are all "L". When the Start input from the control unit 15 becomes “H”, each of the TDCs 21a to 21d starts time measurement. When Stop input to TDC21a becomes "H", TDC21a outputs _{t a} as the measurement time. Next, when the Stop input to the TDC 21c becomes “H”, the TDC 21c outputs t _c as the measurement time. When Stop input to TDC21d becomes "H", TDC21d outputs _{t d} as the measurement time. When Stop input to TDC21b becomes "H", TDC23b outputs _{t b} as measurement time.

  In this way, the control unit 15 causes the measurement unit 14 to start time measurement by setting the Start input to each of the TDCs 21a to 21d to “H”. The timing at which the Start input to each of the TDCs 21a to 23d is set to “H” is determined according to a signal input from the receiving antenna 11a to the control unit 15. The determination method will be described later.

The calculation unit 22 includes a storage unit (not shown). The calculation unit 22 operates according to the program stored in the storage unit, and calculates the arrival time difference of each signal from the input measurement times t _a , t _b , t _c , and t _d . Arrival time difference _{t ba} between the receiving antenna 11a receiving antenna 11b _is obtained in decreasing t b -t _a, arrival time difference _{t ca} receiving antenna 11a and the receiving antenna 11c _is obtained in decreasing t c -t _a, the receiving antenna 11a and the receiving antenna 11d arrival time difference _{t da of,} obtained from t d -t _a.

After calculating the arrival time differences t _ba , t _ca , and t _da in this way, the calculation unit 22 uses the coordinates of the receiving antennas 11a to 11d to determine the coordinates of the wireless transmission source (RFID reader 3 or RFID tag 4). calculate. The coordinates calculated here are coordinates based on the transmission position detection device 1.

[Coordinate calculation]
The coordinate calculation of the wireless transmission source will be described with reference to FIG.

The coordinates of the receiving antenna 11a are (x _a , y _a , z _a ), the coordinates of the receiving antenna 11b are (x _b , y _b , z _b ), and the coordinates of the receiving antenna 11c are (x _c , y _c , z _c ). The coordinates of the receiving antenna 11d are known as (x _d , y _d , z _d ), and are stored in advance in a storage unit or the like included in the calculation unit 22.

The coordinates of one wireless transmission source are P points (x _P , y _P , z _P ), and the radio wave transmission speed is C. Then, the coordinates (x _a , y _a , z _a ), (x _b , y _b , z _b ), (x _c , y _c , z _c ), (x _d , y _d , The following equations [Equation 1], [Equation 2], and [Equation 3] are established using z _d ) and the arrival time differences t _ba , t _ca , and t _da .

Equation [Expression 1], [Formula 2], in [Expression _3], x _P, y P, except _{z P} are known values. Therefore, by solving these three simultaneous equations, the value of the point P (x _P , y _P , z _P ) that is the coordinates of the wireless transmission source can be obtained. The nonlinear simultaneous equations can be solved by using a numerical calculation method such as Newton's method.

However, when the receiving antennas 11a to 11d are arranged on the same plane, there are two solutions. Therefore, in this system, the transmission position detection device 1 is installed on a wall or the like. By doing so, since the back side of the transmission position detecting device 1 (the negative direction of the z-axis) is not radio transmission source is present, to be a solution that value of z _P is positive and the coordinates of the radio transmission source it can. When the receiving antennas 11a to 11d are not arranged on the same plane, there is only one solution, and thus the transmission position detecting device 1 may be installed in any way.

  Here, communication between the RFID reader 3 and the RFID tag 4 will be described with reference to FIG. FIG. 6A shows transmission data of the RFID reader 3, and the hatched portion shows a state in which only a carrier wave is transmitted. FIG. 6B shows transmission data of the RFID tag 4.

  In the C1G2 standard communication, first, the RFID reader 3 transmits a carrier wave. The RFID tag 4 is activated by receiving this carrier wave. Next, the RFID reader 3 transmits a preamble (P), and subsequently transmits a Query (Q) notifying the start of reading.

  When the RFID tag 4 receives the preamble (P), the RFID tag 4 determines a reception speed in order to synchronize so that data following the preamble (P) can be received. When the Query (Q) is received, the RFID tag 4 performs setting according to the contents of the Query (Q). Thereafter, the RFID tag 4 transmits a response in a randomly selected slot. In the present embodiment, for convenience of explanation, the description will be continued assuming that the RFID tag 4 responds immediately.

  After receiving the Query (Q), the RFID tag 4 transmits a preamble (P), and then transmits a 16-bit pseudorandom number (RN16). Since the pseudo random number is used as an encrypted character string, it is retained during the subsequent communication. When the RFID reader 3 receives the preamble (P) and the pseudo-random number (RN16), the RFID reader 3 transmits a Frame-Sync (F) for establishing frame synchronization, and subsequently, a response signal (ACK) notifying that the frame has been correctly received. ).

  When receiving the response signal (ACK), the RFID tag 4 transmits a preamble (P), data (Data), and a data error detection code (CRC: Cyclic Redundancy Check). The data (Data) at this time includes unique identification information for each RFID tag 4, that is, EPC (Electronic Product Code) of the C1G2 standard.

  Upon receiving the preamble (P), data (Data), and data error detection code (CRC), the RFID reader 3 detects the presence or absence of a transmission error using the data error detection code (CRC). As a result, if the RFID reader 3 determines that it has been received correctly, the RFID reader 3 transmits Frame-sync (F), and then transmits QueryRep (QR). On the other hand, when it is determined that the signal could not be received normally, the RFID reader 3 transmits a response signal (NAK) notifying that the signal could not be received normally, instead of QueryRep (QR), and RFID Request retransmission to tag 4. When there is only one RFID tag 4 in the communication area of the RFID reader 3, the communication is completed by the processing so far.

  When there are a plurality of RFID tags 4 in the communication area of the RFID reader 3, another RFID tag 4 transmits a preamble (P) and a pseudorandom number (RN16) after QueryRep (QR). Upon receiving the pseudo-random number (RN16), the RFID reader 3 transmits a Frame-Sync (F) and a normal response signal (ACK), and the RFID tag 4 that has received this transmits a preamble (P) and data (Data). And a data error detection code (CRC). When the RFID reader 3 normally receives data (Data), it transmits Frame-Sync (F). By repeating such processing, the RFID reader 3 acquires identification information of the plurality of RFID tags 4 in the communication area.

  FIG. 7 shows a part of an envelope waveform of Query (Q) transmitted by the RFID reader 3. In the C1G2 standard, PIE (Pulse-interval encoding) that shortens the time representing “0” and lengthens the time representing “1” is used as Query (Q) as an encoding method. PIE has different time lengths for representing “0” and “1”, but the time length for reducing the amplitude is the same. That is, the PIE has a constant time during which the amplitude is small. For this reason, when Query (Q) is received and the amplitude becomes small, anyone can predict the timing when the amplitude becomes large.

  When detecting that the amplitude of the PIE has decreased, the control unit 15 simultaneously sets the Start inputs of the TDCs 21a to 21d to “H” before the amplitude increases. Thereby, each TDC21a-21d starts time measurement. Each amplification unit 13a to 13d outputs "H" when the amplitude of the signal input from the corresponding demodulation unit 12a to 12d is larger than the threshold shown in FIG. 7, and outputs "L" when the amplitude is smaller. . Accordingly, each TDC 21a to 21d has a time ta, tb, a time from when the control unit 15 simultaneously sets the Start inputs to “H” until the outputs of the corresponding amplification units 13a to 13d first become “H”. tc and td are measured.

  FIG. 8 shows the waveform of the preamble (P) transmitted by the RFID tag 4. FIG. 8 shows a preamble (P) when the FM0 code is used in the C1G2 standard. In the FM0 code, when “0” is represented, the level is inverted from “H” to “L” or “L” to “H” at the center of one bit, and when “1” is represented, within one bit. The level is kept constant and does not change, and the level is inverted when switching from one bit to the next. “V” is a bit that does not follow the rule of the FM0 code, and appears only in the preamble (P).

  Normally, the same pattern is repeated at the beginning of the preamble (P) in order to achieve bit synchronization. Thereafter, another predetermined pattern is used so that the boundary between the information following the preamble (P) can be understood. In FIG. 8, a portion where five “0” s appear in succession is used for bit synchronization, and data after “1010V1” after that is data.

  The transmission position detection apparatus 1 receives communication performed in such a procedure. When receiving the preamble (P) after receiving the normal response signal (ACK), the control unit 15 takes bit synchronization. Thus, after bit synchronization is established, the control unit 15 can predict the timing at which the level of the received signal changes.

  Therefore, immediately after detecting “V” with bit synchronization, the control unit 15 simultaneously sets the start inputs of the TDCs 21a to 21d to “H” before the reception signal level first changes from “L” to “H”. To. Thereby, each TDC21a-21d starts time measurement. On the other hand, each of the amplification units 13a to 13d outputs “H” when the reception signal level changes from “L” to “H”. Accordingly, each TDC 21a to 21d has a time ta, tb, a time from when the control unit 15 simultaneously sets the Start inputs to “H” until the outputs of the corresponding amplification units 13a to 13d first become “H”. tc and td are measured.

In the block diagram of FIG. 2, the output of the amplifying unit 13a is input to the control unit 15 to obtain received data. The distance from the wireless transmission source to the reception antenna 11a is not the shortest, and the distance from the wireless transmission source to the other reception antennas 11b to 11d may be short. When the receiving antennas 11a to 11d are arranged as shown in FIG. 5, if the receiving antenna farthest from the receiving antenna 11a is the receiving antenna 11d, the maximum arrival time difference t _m between the receiving antenna 11a and the receiving antenna 11d. Can be expressed by the following equation [Equation 4].

Even when the receiving antenna farthest from the receiving antenna 11a is another antenna, the maximum arrival time difference t _m between the receiving antenna 11a and the farthest antenna can be obtained by the same calculation formula.

Considering these, the Start input to each of the TDCs 21a to 21d is set to “H” at a time before the maximum arrival time difference t _m from the time when the level of the received signal is expected to change from “L” to “H”. That's fine. In other words, the timing for starting the time measurement may be set so that the received signal level of each of the receiving antennas 11a to 11d changes after the time during which the radio wave is transmitted through the maximum distance between the receiving antennas.

  If the measurement time is too long, a change point of the next received signal level appears. Therefore, it is preferable to end the measurement before the next change point appears. The time interval at which the change point of the signal level appears is determined by the transmission rate and the encoding method, so the measurement end time can be determined from this.

  By determining the timing of starting and ending time measurement as described above, the transmission position detection device 1 is related to the arrangement of the reception antennas 11a to 11d and the wireless transmission sources (RFID reader 3 and RFID tag 4). The level change timings of the signals reaching all the receiving antennas 11a to 11d can be captured. And the transmission position detection apparatus 1 can pinpoint the position of a wireless transmission source from the measured time difference.

  In addition, since the transmission position detection device 1 detects the position of the RFID tag 4 using the preamble (P) of the data including the identification information, it can detect the identification information and the position of the RFID tag 4 at a time. Therefore, when the identification information of the plurality of RFID tags 4 is detected, the transmission position detection device 1 can also detect the position corresponding to each identification information.

  In this embodiment, the Start input of each of the TDCs 21a to 21d is set to “H” at the position “V” of the preamble (P). However, any change in the received signal level can be performed after bit synchronization is achieved. The time can be measured similarly in the vicinity of the point.

[System Operation]
Next, the operation of the transmission position detection system will be described with reference to FIGS. FIG. 9 is a flowchart showing an operation procedure of the transmission position detection apparatus 1, and FIG. 10 is a flowchart showing an operation procedure of the server 2. FIG. 11 is a flowchart showing the operation procedure of the RFID reader 3.

  In this system, first, the RFID reader 3 transmits transmission setting information to the server 2 before starting reading of the RFID tag 4 (ST31 in FIG. 11). The transmission setting information includes a frequency for reading the RFID tag 4, a transmission rate, and an encoding method.

  The server 2 waits for the transmission setting information of the RFID reader 3 (ST21 in FIG. 10), and receives the transmission setting information from the RFID reader 3 (YES in ST21), the server 2 receives the received transmission setting. The information is transferred to the transmission position detection apparatus 1 (ST22 in FIG. 10).

  The transmission position detection apparatus 1 waits for transmission setting information of the RFID reader 3 (ST1 in FIG. 9). When the transmission setting information is received from the server 2 (YES in ST1), the transmission position detection device 1 sets the reception state of each unit based on the information (ST2 in FIG. 9). For example, the transmission position detection device 1 sets the oscillation unit 16 so that the frequency used for reading the RFID tag 4 can be received. For the control unit 15, a transmission rate and an encoding method used for reception are set.

  Subsequently, the RFID reader 3 starts transmission of an unmodulated wave to activate the RFID tag 4 (ST32 in FIG. 11). The RFID reader 3 transmits Query (Q) after transmitting a non-modulated wave for a predetermined time (ST33 in FIG. 11). A signal transmitted from the RFID reader 3 is received not only by the RFID tag 4 but also by the transmission position detector 1.

In the transmission position detection apparatus 1 that has started receiving the Query (Q), the control unit 15 sets the Start input of each of the TDCs 21a to 21d to “H” at the timing described above (ST3 in FIG. 9). As a result, each of the TDCs 21a to 21d measures the times t _a , t _b , t _c , and t _d from when the Start input becomes “H” to when the Stop input becomes “H”, and the measurement times t _a , t _b , t _c , and t _d are output to the calculation unit 22 (ST4 in FIG. 9). The computing unit 22 calculates arrival time differences t _ba , t _ca , t _da for each of the receiving antennas 11a to 11d based on the input measurement times t _a , t _b , t _c , t _d (ST5 in FIG. 9). . Further, the calculation unit 22 calculates the coordinates of the RFID reader 3 from the calculated arrival time differences t _ba , t _ca , t _da (ST6 in FIG. 9). The transmission position detection apparatus 1 executes the above-described steps ST3, 4, 5, and 6 until the reception of Query (Q) is completed (ST7 in FIG. 9).

  When receiving the Query (Q), the RFID tag 4 transmits a 16-bit pseudo random number (RN16). The pseudo random number (RN16) signal transmitted from the RFID tag 4 is received not only by the RFID reader 3 but also by the transmission position detector 1.

  The RFID reader 3 that has transmitted Query (Q) waits for reception of a pseudo-random number (RN16) (ST34 in FIG. 11). When the pseudo random number (RN16) is received from the RFID tag 4 (YES in ST34), the RFID reader 3 transmits a response signal (ACK) (ST35 in FIG. 11). When receiving the response signal (ACK), the RFID tag 4 transmits unique identification information. The identification information is included in data (Data) following the preamble (P).

Therefore, the transmission position detection apparatus 1 that has completed the reception of Query (Q) first waits for reception of a pseudo random number (RN16) (ST8 in FIG. 11). When the pseudo random number (RN16) is received from the RFID tag 4 (YES in ST8), the transmission position detection device 1 then waits for a response signal (ACK) (ST9 in FIG. 11). When the response signal (ACK) is received from the RFID reader 3 (YES in ST9), the transmission position detection device 1 starts receiving the identification information. In the transmission position detection apparatus 1, the control unit 15 sets the Start input of each of the TDCs 21a to 21d to “H” at the above-described timing during reception of “1010V” included in the preamble (P) (ST10 in FIG. 9). As a result, each of the TDCs 21a to 21d measures the times t _a , t _b , t _c , and t _d from when the Start input becomes “H” to when the Stop input becomes “H”, and the measurement times t _a , t _b , t _c , and t _d are output to the calculation unit 22 (ST11 in FIG. 9). The calculation unit 22 calculates arrival time differences t _ba , t _ca , t _da for each of the receiving antennas 11a to 11d based on the input measurement times t _a , t _b , t _c , t _d (ST12 in FIG. 9). . Further, the computing unit 22 calculates the coordinates of the RFID tag 4 that has transmitted the identification information from the calculated arrival time differences t _ba , t _ca , t _da (ST13 in FIG. 9).

  On the other hand, the RFID reader 3 that has transmitted the response signal (ACK) waits for the identification information of the RFID tag 4 (ST36 in FIG. 11). When the identification information is received from the RFID tag 4 (YES in ST36), the RFID reader 3 transmits QueryRep (QR) (ST37 in FIG. 11). The RFID tag 4 that has transmitted the identification information ends the process when receiving the QueryRep (QR).

  After transmitting the Query Rep (QR), the RFID reader 3 determines whether or not there is communication with another RFID tag (ST38 in FIG. 11). If there is communication (YES in ST38), the RFID reader 3 returns to the pseudo random number (RN16) reception process (ST34 in FIG. 11). When there is no communication (NO in ST38), the RFID reader 3 stops transmission (ST39 in FIG. 11).

  The transmission position detection apparatus 1 waits for completion of reception of data (Data) including identification information (ST14 in FIG. 9). If reception of the identification information is completed (YES in ST14), the transmission position detection apparatus 1 waits for reception of QueryRep (QR) (ST15 in FIG. 9). If QueryRep (QR) is received (YES in ST15), the transmission position detecting device 1 determines whether or not the RFID reader 3 has stopped communication (ST16 in FIG. 9).

  When the next pseudo random number (RN16) is received from the RFID reader 3, the RFID reader 3 has not stopped communication. In this case (NO in ST16), the transmission position detection apparatus 1 returns to the pseudo random number (RN16) reception process (ST8 in FIG. 9).

  On the other hand, when it is determined that there is no reception from the RFID reader 3 and communication is completed (YES in ST16), the transmission position detection device 1 transmits the transmission position information of the wireless transmission source to the server 2. (ST17 in FIG. 9). Thus, the transmission position detection device 1 ends the current process. Here, the transmission position information of the wireless transmission source transmitted to the server 2 includes the coordinates of the RFID reader 3 acquired by the transmission position detector 1 in the current process, and the identification information and coordinates of the RFID tag 4. It is.

  On the other hand, the RFID reader 3 that has stopped communication transmits the identification information read from the RFID tag 4 in the current process to the server 2 (ST40 in FIG. 11). At this time, the RFID reader 3 transmits its own address together with identification information of the RFID tag.

  The server 2 that has transmitted the transmission setting information to the transmission position detection apparatus 1 stands by for the transmission position information of the wireless transmission source (ST23 in FIG. 10). When the transmission position information of the wireless transmission source is received from the transmission position detection device 1 (YES in ST23), the server 2 temporarily stores the transmission position information in the memory (ST24 in FIG. 10). Further, the server 2 acquires the identification information of the RFID tag 4 read by the RFID reader 3 together with the address of the RFID reader 3 (ST25 in FIG. 10). Then, the server 2 collates the identification information of the RFID tag included in the transmission position information with the identification information of the RFID tag 4 read by the RFID reader 3, and determines whether or not they match (ST26 in FIG. 10). ). If they do not match (NO in ST26), the server 2 ends the current process.

  On the other hand, when the identification information of the RFID tag 4 included in the transmission position information matches the identification information of the RFID tag 4 read by the RFID reader 3 (YES in ST26), the server 2 The transmission position information of the wireless transmission source is stored in the database in association with the address of the reading device 3 (ST27 in FIG. 10). Further, the server 2 transmits the transmission position information of the wireless transmission source stored in the database to the RFID reader 3 specified by the address associated with the transmission position information (ST28 in FIG. 10). Thus, the server 2 ends the current process.

  Here, a schematic diagram of a database provided in the server 2 is shown in FIG. The database is associated with the address (AAAAA) of the RFID reader 3, the coordinates (a1, b1, c1) of the RFID reader 3, the identification information of each RFID tag 4 read by the RFID reader 3, and its coordinates And save. For example, the coordinates of the RFID tag 4 of the identification information (BBBBBB) are (a2, b2, c2), the coordinates of the RFID tag 4 of the identification information (CCCCC) are (a3, b3, d3), and the RFID tag of the identification information (DDDDDD) The coordinates of 4 are (a4, b4, d4).

  Although not shown, the database also stores article information associated with the identification information, and the coordinates of the article to which the RFID tag 4 of the identification information is attached can be known from the coordinates of the identification information.

  As described above, the server 2 collates the identification information of the RFID tag 4 received from the RFID reading device 3 with the identification information of the RFID tag 4 received from the transmission position detection device 1, on condition that they are the same. The transmission position information of the wireless transmission source (RFID reader 3 and RFID tag 4) is stored in association with the address of the RFID reader 3. Therefore, the RFID reader 3 and its coordinates are specified even when there is no information for identifying the RFID reader 3 in communication between the RFID reader 3 and the RFID tag 4 as in the C1G2 standard, and there are a plurality of RFID readers 3. can do.

  The RFID reader 3 that has stopped transmitting waits for the transmission position information of the wireless transmission source (ST41 in FIG. 11). When receiving the transmission position information of the wireless transmission source from the server 2 (YES in ST41), the RFID reader 3 displays the transmission position detection result of the wireless transmission source on the display unit (ST42 in FIG. 11). This is the end of the current process.

  13 and 14 are display examples showing the transmission position detection result of the wireless transmission source. 13 and 14, the star 33 represents the detection position of the RFID reader 3, and the black circles 34a, 34b, and 34c represent the detection positions of the RFID tag 4. FIG. 13 is an xz plane display, and FIG. 14 is an xy plane display. By displaying in this way, the operator of the RFID reader 3 can be notified of the positions of the RFID reader 3 and the RFID tag 4 that are wireless transmission sources.

  In addition, identification information may be displayed on the black circles 34a, 34b, and 34c, and article information associated with the identification information may be displayed. Further, by adding a shelf, a passage or the like to this display, the position of the wireless transmission source can be further easily understood. It is also possible to estimate that the RFID reader 3 is facing in the direction of the RFID tag 4 read by the RFID reader 3.

[Correction of coordinate calculation]
In a circuit from each of the receiving antennas 11a to 11d to the measuring unit 14, there may be a variation in circuit delay, a variation in wiring length, or the like. For example, there may be a slight difference between the time when the reception signal is input from the reception antenna 11a and input to the TDC 21a and the time when the reception signal is input from the reception antenna 11b and input to the TDC 21b. If this slight difference is corrected, the deviation between the calculated coordinates and the actual coordinates can be reduced.

Therefore, in order to minimize the above-described deviation, the calculation unit 22 is provided with a function of acquiring correction values of the arrival time differences t _ba , t _ca , t _da , and the arrival time differences t _ba , The coordinates of the transmission point are calculated using t _ca and t _da .

  An example of correcting a difference in arrival time difference occurring between the receiving antennas 11a to 11d will be described.

  The acquisition of the correction value is executed when the transmission position detection apparatus 1 is activated in a mode that is a correction mode, for example. At that time, the RFID reader 3 is arranged in advance at a location equidistant from the receiving antenna 11a and the receiving antenna 11b. In this state, the coordinates are acquired by the method described above.

At this time, the reception for the antenna 11a and the radio wave arrival time to the receiving antenna 11b is the same, transmission delay difference in the circuit appears as an input time difference Delta] t _ba of TDC21a and TDC21b. This time difference Δt _ba is stored as a correction value, for example, in the storage unit of the calculation unit 22. If there is no propagation delay difference in the circuit, Δt _ba = 0. Further, the time differences Δt _ca and Δt _da that are correction values are similarly acquired between the receiving antenna 11 a and the receiving antenna 11 c and between the receiving antenna 11 a and the receiving antenna 11 d.

After acquiring the correction value, when calculating the coordinates of the transmission point in the normal operation mode, the time differences Δt _ba , Δt _ca , Δt are respectively calculated from the arrival time differences t _ba , t _ca , t _da acquired by the calculation unit 22. _da is subtracted and corrected, and the coordinates of the transmission point are calculated using the corrected value.

  Next, another example of correcting the difference in arrival time difference will be described.

  In this example, the RFID reader 3 is first placed at a position where the coordinates are known in advance. Then, the distance between the RFID reader 3 and each of the receiving antennas 11a to 11d is determined. At this time, a theoretical reception arrival time difference between each of the receiving antennas 11a to 11d can be calculated from the distance between the RFID reader 3 and each of the receiving antennas 11a to 11d and the transmission speed of the radio wave. This time difference may be input to the transmission position detection apparatus 1 from the outside, or may be calculated by the control unit 15.

  Next, the coordinates of the RFID reader are acquired in the correction mode, and the difference in reception arrival time at that time is compared with the theoretical reception arrival time difference to calculate each difference. The calculated difference is stored as a correction value in the storage unit of the calculation unit 22, for example.

Thereafter, when calculating the coordinates of the transmission point in the normal operation mode, the arrival time differences t _ba , t _ca and t _da are corrected using the respective correction values stored in the storage unit.

  As described above, a function for correcting the calculated arrival time differences tba, tca, tda is provided, and the coordinates of the transmission point are detected using the corrected arrival time differences. By doing so, errors due to variations in circuit delay and wiring length are absorbed, and the accuracy of position detection of the transmission point is greatly improved.

(Second Embodiment)
Next, a second embodiment will be described.

  The same components as those in the first embodiment are denoted by the same reference numerals, and redundant description will be given only when necessary. This embodiment is the same except for the configuration of the measurement unit in the above embodiment. Therefore, only the measurement unit will be described in detail.

  FIG. 15 shows a schematic block diagram of the measuring unit in the present embodiment. This block diagram is obtained by replacing the measurement unit 14 shown in FIG. 3 with the measurement unit 114, and realizes a configuration in which a signal from the control unit 15 is not used for the Start input of the TDC.

The measurement unit 114 includes TDCs 123 to 128 and a calculation unit 122. The TDC 123 uses the output of the amplifying unit 13a as the Start input, the output of the amplifying unit 13b as the Stop input, and calculates the time t _{ba +} from when the Start input becomes “H” to when the Stop input becomes “H”. Output to. The TDC 124 uses the output of the amplifying unit 13b as the Start input, the output of the amplifying unit 13a as the Stop input, and calculates the time t _ba− from when the Start input becomes “H” to when the Stop input becomes “H”. It outputs to 122.

The TDC 125 uses the output of the amplifying unit 13a as the Start input, the output of the amplifying unit 13c as the Stop input, and calculates the time t _{ca +} from when the Start input becomes “H” to when the Stop input becomes “H”. Output to. The TDC 126 uses the output of the amplifying unit 13c as the Start input, the output of the amplifying unit 13a as the Stop input, and calculates the time T _ca− from when the Start input becomes “H” to when the Stop input becomes “H”. It outputs to 122.

The TDC 127 uses the output of the amplifying unit 13a as the Start input, the output of the amplifying unit 13d as the Stop input, and calculates the time t _{da +} from when the Start input becomes “H” to when the Stop input becomes “H”. Output to. The TDC 128 uses the output of the amplifying unit 13d as the Start input, the output of the amplifying unit 13a as the Stop input, and calculates the time t _da− from when the Start input becomes “H” to when the Stop input becomes “H”. It outputs to 122.

The order in which the outputs of the amplifying unit 13a and the amplifying unit 13b become “H” differs depending on the arrangement of the transmission position detecting device 1 and the wireless transmission source. When the output of the amplifying unit 13a first becomes “H”, the arrival time difference between the receiving antennas 11a and 11b is measured by the TDC 123. In the TDC 124, after the output of the amplifying unit 13b becomes “H”, the next time until the output of the amplifying unit 13a becomes “H” is measured. Therefore, the time _tba− becomes longer than the time _{tba +} . Conversely, when the output of the amplifying unit 13b first becomes “H”, the arrival time difference between the receiving antennas 11a and 11b is measured by the TDC 124. In the TDC 123, after the output of the amplifying unit 13a becomes “H”, the next time until the output of the amplifying unit 13b becomes “H” is measured. The computing unit 122 employs the shorter one of the times t _{ba +} and t _ba− as the time used for the computation.

Similarly, the calculation unit 122 _{employs one} of the short times t _{ca +} and t _ca− as the time used for the calculation, and _employs the short one of the times t _{da +} and t _da− as the time used for the calculation.

  In order to explain the operation of the measurement unit 114, examples of input / output waveforms of the TDCs 123 to 128 are shown in FIGS. FIG. 16 shows output signals a to d of the amplifying units 13a to 13d, that is, input signal waveforms to the TDCs 123 to 128, respectively. FIG. 17 shows output signal waveforms from the TDCs 123 to 128.

When the output a of the amplifying unit 13a becomes “H”, the Start inputs of the TDC 123, TDC 125, and TDC 127 become “H”, and time measurement is started.
Thereafter, when the output c of the amplifying unit 13c becomes “H”, the Stop input of the TDC 125 becomes “H”, and the Start input of the TDC 126 becomes “H”. Since the Stop input becomes “H”, the TDC 125 outputs the time t _{ca +} .

Next, when the output d of the amplifying unit 13d becomes “H”, the Stop input of the TDC 127 becomes “H”, and the Start input of the TDC 128 becomes “H”. The TDC 127 outputs the time t _{da +} because the Stop input becomes “H”.

Next, when the output b of the amplifying unit 13b becomes “H”, the Stop input of the TDC 123 becomes “H”, and the Start input of the TDC 124 becomes “H”. Since the Stop input becomes “H”, the TDC 123 outputs the time t _{ba +} .

In the example of FIG. 17, TDC 124, TDC 126, and TDC 128 have not finished time measurement. If not finished on time measurable within the maximum time, _t ba- time until the measurement end by TDC124,126,128 the (above maximum time), _{respectively,} t _ca-, and _{t DA-.}

As described above, the calculation unit 122 compares t _{ba +} and t _ba− , t _{ca +} and t _ca− , and t _{da +} and t _da− , and _employs the shorter one for coordinate calculation. The three times adopted are arrival time differences from the wireless transmission source to the respective receiving antennas 11a to 11d. The calculation unit 122 calculates the coordinates of the wireless transmission source using these arrival time differences.

(Modification)
Various modifications can be made to the configurations disclosed in the above embodiments. Specific examples of modifications are as follows.

(1) In each of the above embodiments, the case where four reception antennas, four demodulation units, and four amplification units are used has been exemplified. However, the number of reception antennas, demodulation units, and amplification units may be five or more.

  When there are five or more receiving antennas or the like, the coordinates of the transmission point can be obtained by using a calculation method in which the Newton method is combined with the least square method. As the number of reception arrival time differences increases, the calculated coordinates tend to approach the actual coordinates. Therefore, by using five or more reception antennas, demodulation units, and amplification units, the position detection of the transmission position detection device can be performed. Accuracy can be increased.

(2) In each of the above-described embodiments, the description has been given on the assumption that the coordinates are obtained before the completion of the query reception of the transmission position detecting device 1 and before the reception of the identification information. Good.

(3) In each of the above embodiments, the processing program has been described as being stored in advance in the storage unit of the control unit 15 or the calculation units 22 and 122. However, the present invention is not limited to this, and each program may be downloaded from a server, or a program in which similar functions are stored in a recording medium may be installed in the transmission position detection device. As the recording medium, any form may be used as long as it can use a CD-ROM or the like and can be read by the transmission position detecting device. In addition, the function obtained by installing or downloading in advance may be realized in cooperation with an OS (Operating System) or the like inside the transmission position detecting apparatus.

  In addition, although several embodiment was described for this invention, these embodiment was shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Transmission position detection apparatus, 2 ... Server, 3 ... RFID reader, 4 ... RFID tag, 11 (11a, 11b, 11c, 11d) ... Reception antenna, 12 (12a, 12b, 12c, 12d) ... Demodulation part, 13 (13a, 13b, 13c, 13d) ... amplification unit, 14,114 ... measurement unit, 15 ... control unit, 16 ... oscillation unit, 21 (21a, 21b, 21c, 21d), 123, 124, 125, 126, 127, 128... TDC, 22, 122.

Claims (13)

Four or more receiving antennas for receiving signals wirelessly transmitted from a wireless transmission source;
Measure the time difference between the receiving antennas when each receiving antenna receives a signal wirelessly transmitted from the wireless transmitting source, and based on each measured time difference, the three-dimensional coordinates indicating the position of the wireless transmitting source A measurement unit to calculate,
A transmission position detecting device comprising: A control unit that inputs a signal output from the reception antenna that has received a signal wirelessly transmitted from the wireless transmission source, and controls the start of time measurement of the measurement unit according to the input signal;
The transmission position detecting apparatus according to claim 1, further comprising:   The control unit controls time measurement start of the measurement unit when a signal input from the receiving antenna is a Query signal included in transmission data of an RFID reader that reads data of an RFID tag. The transmission position detection apparatus according to claim 2.   The control unit starts time measurement of the measurement unit when the signal input from the reception antenna is a preamble signal of data including identification information unique to the RFID tag transmitted from the RFID tag to the RFID reader. The transmission position detecting device according to claim 2, wherein the transmission position detecting device is controlled.   The transmission position detecting device according to claim 1, wherein the measuring unit measures a time difference between the receiving antennas when receiving a signal modulated by an RFID reader that reads data of the RFID tag.   The measurement unit measures a time difference between the reception antennas when receiving a signal including identification information unique to the RFID tag transmitted from the RFID tag to the RFID reader, and calculates a three-dimensional coordinate calculated from each time difference and 2. The transmission position detecting apparatus according to claim 1, wherein identification information received at the time of measuring each time difference used for calculation of three-dimensional coordinates or information specified based on the identification information is output in association with each other. .   When the four receiving antennas are arranged on the same plane, the shape of the quadrangle with each antenna as the apex is such that the sum of the opposing faces does not become 180 degrees, and the centers of the two diagonal lines do not become the same point. The transmission position detection apparatus according to claim 1, wherein the transmission position detection apparatus is arranged in a position. The signal transmitted wirelessly from the wireless transmission source is received by four or more receiving antennas,
The measurement unit measures a time difference between the reception antennas when the reception antennas receive a signal wirelessly transmitted from the wireless transmission source, and indicates the position of the wireless transmission source based on the measured time differences. A transmission position detection method characterized by calculating three-dimensional coordinates. A server that communicates with an RFID reader that performs wireless communication with an RFID tag that stores unique identification information and reads the identification information from the RFID tag, and a communication method other than the wireless communication;
Each reception when the wireless communication between the RFID reader and the RFID tag is received by four or more receiving antennas, and each receiving antenna receives a signal wirelessly transmitted from the RFID reader or the RFID tag. A transmission position detecting device that measures a time difference between antennas, calculates three-dimensional coordinates indicating the positions of the RFID reader and the RFID tag based on the measured time differences, and transmits the calculated result to the server; ,
A transmission position detection system comprising: When the server receives the transmission setting information for reading the RFID tag from the RFID reader, the server transfers the transmission setting information to the transmission position detection device,
The said transmission position detection apparatus sets a receiving state so that the electromagnetic wave from the said RFID tag can be received based on this transmission setting information, if the said transmission setting information is received from the said server. The described transmission position detection system. The transmission position detection device transmits the identification information of the RFID tag to the server together with the RFID reader and the three-dimensional coordinates of the RFID tag as a result of the calculation,
The server fetches identification information of the RFID tag read by the RFID reader from the RFID reader, and receives the RFID tag identification information taken from the RFID reader and the RFID received from the transmission position detecting device. The coordinate of the RFID reader and the coordinates of the RFID tag read by the RFID reader are stored in association with the address of the RFID reader when the identification information of the tag matches. 9. The transmission position detection system according to 9.   The server transmits the coordinates of the RFID reader stored in association with the address of the RFID reader and the coordinates of the RFID tag read by the RFID reader to the RFID reader identified by the address. The transmission position detection system according to claim 11. In a computer having a casing in which four or more receiving antennas for receiving signals wirelessly transmitted from a wireless transmission source are arranged.
A measurement function for measuring a time difference between the reception antennas when the reception antennas receive a signal wirelessly transmitted from the wireless transmission source;
A calculation function for calculating a three-dimensional coordinate indicating the position of the wireless transmission source based on each time difference measured by the measurement function;
A transmission position detection program for realizing the above.

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