JP2014070923A - Rfid tag positioning system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an RFID tag positioning system capable of accurately determining two-dimensional coordinates of an RFID tag.SOLUTION: A radial movement distance (measured distance Dm) being a distance for which an RFID tag 200 has moved in a radial direction of an RFID tag reader 100 is measured (S2). Radial movement distances (calculated distances Dc) are calculated for pairs of points before and after movement wherein points before movement are area apexes generated by dividing a positioning range 400 into a plurality of small areas and points after movement are remaining area apexes other than the points before movement, and distance differences e between the measured distance Dm and the calculated distances Dc are calculated for all the pairs of points before and after movement with respect to each of four RFID tag readers 100 (S4), and a total of four distance differences e (total distance difference E) is calculated also (S5). Two-dimensional coordinates o the RFID tag 200 are determined in accordance with a minimum value (minimum total distance difference Emin) of the total distance differences E.

Description

  The present invention relates to a wireless tag positioning system that measures the absolute position of a wireless tag.

  As a technique for measuring the absolute position of a wireless tag (hereinafter referred to as absolute positioning), many techniques using radio waves such as a TOA method, a TDOA method, and an RSSI method have been proposed. Further, Non-Patent Document 1 summarizes techniques for performing absolute positioning in an environment where multipaths such as indoors occur using these methods.

Liu, H., H. Darabi, P. Banerjee, and J. Liu, "Survey of wireless indoor positioning techniques and systems," IEEE Transactions on Systems, Man, and Cybernetics, Part C: Applications and Reviews, Vol. 37, No. 6, 1067-1080, 2007.

  All of the various conventionally known methods for performing absolute positioning using radio waves are based on the premise that the absolute distance from the base station to the wireless tag can be measured using radio waves. However, in a multipath environment such as a room, it is often difficult to accurately measure the absolute distance using radio waves. Therefore, it is difficult to perform absolute positioning with high accuracy by the method using the absolute distance.

  If two-dimensional coordinates are determined as absolute positions in a multipath environment using a conventional method, a map of radio wave intensity that can be received when a wireless tag exists at predetermined intervals of the two-dimensional coordinates is created in advance. It is not realistic because a huge amount of preparation is required in advance.

  The present invention has been made based on this situation, and an object thereof is to provide a wireless tag positioning system capable of accurately determining the two-dimensional coordinates of the wireless tag.

In order to achieve the object, the invention according to claim 1 is a transmission / reception unit that sequentially transmits a signal wave for distance measurement and receives a response wave coming from a wireless tag based on the signal wave for distance measurement A wireless tag positioning system that sequentially determines the two-dimensional coordinates of the wireless tag present in a positioning range, comprising at least four wireless tag readers comprising:
Radial distance measuring means for measuring a radial movement distance, which is a distance that the wireless tag has moved in the radial direction of the wireless tag reader at a predetermined time, based on a transmission / reception result of each wireless tag reader, and for each wireless tag reader;
The area vertices generated by dividing the positioning range into a plurality of small areas are the points before the movement, and the remaining area vertices excluding the points before the movement are the points after the movement. The distance difference between the calculated radial movement distance that is the radial movement distance calculated for the combination and each radial movement distance measured by the radial distance measuring means is calculated for each wireless tag reader, and these First total distance difference calculating means for calculating a total distance difference obtained by summing the distance differences for all the combinations of the points before and after the movement;
A minimum total distance difference, which is a minimum value among the total distance differences calculated by the first total distance difference calculation means, is determined, and after the movement determined by the calculated radial movement distance used for calculating the minimum total distance difference First candidate determining means for determining a point as a candidate for a two-dimensional coordinate of the wireless tag;
And position determining means for determining the two-dimensional coordinates of the wireless tag based on the two-dimensional coordinate candidates determined by the first candidate determining means.

  In the present invention, the absolute distance to the wireless tag is not measured, the radial movement distance that is the distance that the wireless tag has moved in the radial direction of the wireless tag reader at a predetermined time is measured, and the wireless tag is used by using this radial movement distance. The two-dimensional coordinates are determined.

  First, the reason why the two-dimensional coordinates of the wireless tag can be determined by the radial movement distance will be described. In the present invention, not only the radial movement distance is measured but also the calculated radial movement distance which is the calculated radial movement distance is used. In order to obtain the calculated radial movement distance, the positioning range is divided into a plurality of small areas. Then, a combination of pre- and post-movement points is created in which the area vertices before the movement are the respective area vertices of the small area and the remaining area vertices excluding the area vertices before the movement are the points after movement. The radial travel distance for all these combinations can be calculated geometrically.

  In the first total distance difference calculating means, the distance difference between the calculated radial movement distance obtained by the geometric calculation and the measured radial movement distance is calculated for each wireless tag reader, and these distance differences are summed up. The total distance difference. This total distance difference is calculated for all combinations of points before and after movement.

  Since the radial movement distance measured by the radial distance measuring means is obtained from the transmission / reception result for the actually moved wireless tag, the calculated radial movement distance is a movement close to the position where the wireless tag existed before and after the movement. When using what was obtained from the combination of front and back points, the total distance difference is likely to be minimized.

  This wireless tag positioning system includes at least four wireless tag readers, and the distance difference is calculated for the radial movement distances respectively corresponding to the at least four wireless tag readers. That is, at least four distance differences are calculated. Since the two-dimensional coordinates before and after the movement can be expressed by a total of four parameters, a combination of the points before and after the movement that minimizes at least four distance differences can be determined as one.

Minimizing at least four distance differences means minimizing the total distance difference. Therefore, the first candidate determining means determines the minimum total distance difference that is the minimum value of the total distance differences.
Then, the point after movement determined by the calculated radial movement distance used for calculating the minimum total distance difference is determined as a candidate for the two-dimensional coordinates of the wireless tag. The position determining means determines the two-dimensional coordinates of the wireless tag based on the two-dimensional coordinate candidates. In this way, the two-dimensional coordinates of the wireless tag can be determined from the radial movement distance.

  Thus, in the present invention, the two-dimensional coordinates of the wireless tag are determined from the radial movement distance. Since the influence of the multipath before and after the movement of the wireless tag can be considered to be almost the same, the radial movement distance measured by the radial distance measuring means is less affected by the multipath. Therefore, by determining the two-dimensional coordinates of the wireless tag from the radial movement distance, the two-dimensional coordinates of the wireless tag can be determined with high accuracy.

The invention according to claim 2 is configured to repeatedly execute the radial distance measuring means for each distance measurement period,
A storage unit for sequentially storing past radial movement distances measured by the radial distance measuring means;
By adding the radial movement distance for the latest one time or the past multiple times sequentially measured in order from the newest measurement time stored in the storage unit and the radial movement distance measured this time, multiple consecutive times A total movement distance calculation means for calculating a total radial movement distance, which is a distance that the wireless tag has moved in the radial direction of the wireless tag reader during the distance measurement cycle, for each wireless tag reader;
The distance difference between the calculated radial movement distance and the total radial movement distance calculated by the total movement distance calculation means is calculated for each wireless tag reader, and the total distance difference obtained by summing those distance differences A second total distance difference calculating means for calculating a combination of points before and after movement;
The minimum total distance difference, which is the minimum value of the total distance differences calculated by the second total distance difference calculation means, is determined, and the post-movement determined by the calculated radial movement distance used for the calculation of the minimum total distance difference. A second candidate determining means for setting a point as a candidate for a two-dimensional coordinate of the wireless tag,
The position determining means determines the two-dimensional coordinates of the wireless tag based on the two-dimensional coordinate candidates determined by the first candidate determining means and the two-dimensional coordinate candidates determined by the second candidate determining means. It is characterized by doing.

  In this invention, the past radial movement distances measured by the radial distance measuring means are sequentially stored, and a plurality of continuous radial movement distances and the past radial movement distances are added to obtain a plurality of continuous movement distances. At least one total radial movement distance is calculated for each wireless tag reader, which is the distance that the wireless tag has moved in the radial direction of the wireless tag reader during each distance measurement cycle.

  This total radial movement distance is the same as the one-time radial movement distance except that the time required for movement is different. Therefore, using this total radial movement distance, the total distance difference is calculated for all combinations of front and rear movement points in the same manner as the one-time radial movement distance (second total distance difference calculation means), Further, the minimum total distance difference is determined to determine a candidate for the two-dimensional coordinates of the wireless tag (second candidate determination means).

  By doing so, it is possible to obtain the two-dimensional coordinate candidates determined by the first candidate determining means and the two-dimensional coordinate candidates determined by the second candidate determining means. Since the position determining means determines the two-dimensional coordinates of the wireless tag based on the plurality of two-dimensional coordinate candidates, the two-dimensional coordinates of the wireless tag can be determined with higher accuracy.

According to a third aspect of the present invention, the radial movement distance measured by the radial distance measuring means is changed into a plurality of values within a preset measurement error range, and the plurality of values are measured in the radial distance measurement. A first plurality of candidate determinations for determining a plurality of candidates for the two-dimensional coordinates by executing the first total distance difference calculating means and the first candidate determining means, respectively, instead of using the radial movement distance measured by the means. Means,
Movement from a point before movement determined by the minimum total distance difference determined by the first candidate determination means so that the smaller the variation of the plurality of two-dimensional coordinate candidates determined by the first plurality of candidate determination means, the higher the value. First reliability determination means for determining the reliability of movement to a later point;
The total radial movement distance calculated by the total movement distance calculation means is changed to a plurality of values within a preset measurement error range, and the plurality of values are used in place of the total radial movement distance, respectively. A second plurality of candidate determining means for determining a plurality of candidates for the two-dimensional coordinates by executing the second total distance difference calculating means and the second candidate determining means;
Move from the point before movement determined by the minimum total distance difference determined by the second candidate determining means so that the smaller the variation of the plurality of two-dimensional coordinate candidates determined by the second multiple candidate determining means, the higher the value. Second reliability determining means for determining the reliability of movement to a later point;
The position determining means determines the two-dimensional coordinate candidates determined by the first candidate determining means and the two-dimensional coordinate candidates determined by the second candidate determining means as the first reliability determining means and the second reliability determining The two-dimensional coordinates of the wireless tag are determined based on the reliability determined by each means.

  The radial movement distance measured by the radial distance measuring means naturally includes a certain amount of measurement error. Since there is a measurement error of the radial movement distance measured by the radial distance measuring means, the two-dimensional coordinate candidates determined based on the radial movement distance are also affected by the measurement error. However, the influence of the measurement error on the two-dimensional coordinate candidates differs depending on the specific coordinates of the points before and after the movement. That is, the reliability of two-dimensional coordinate candidates varies depending on the specific coordinates of the points before and after the movement. The reason for this is that the closer the movement of the wireless tag is to a circular movement around a certain wireless tag reader, the smaller the radial movement distance measured by the wireless tag reader is compared to the actual movement distance of the wireless tag. This is because, as a result, the influence of the ranging error on the radial movement distance becomes large.

  Therefore, in the present invention, the reliability is determined for each of the two-dimensional coordinate candidate determined from the radial movement distance measured by the radial distance measuring means and the two-dimensional coordinate candidate determined from the total radial movement distance. To do.

  In order to determine the reliability, in the present invention, the radial movement distance measured by the radial distance measuring means and the total radial movement distance are changed to a plurality of values within a preset measurement error range. Let Then, a plurality of two-dimensional coordinate candidates are determined by using the plurality of values instead of the radial movement distance measured by the radial distance measuring means and the total radial movement distance. The movement from the point before movement determined by the minimum total distance difference determined by the first candidate determination means to the point after movement from the variation of the two-dimensional coordinate candidates for each radial movement distance and total radial movement distance. The reliability of the movement from the point before the movement determined by the reliability and the minimum total distance difference determined by the second candidate determination means to the point after the movement is determined.

  In determining the two-dimensional coordinates of the wireless tag, a plurality of two-dimensional coordinate candidates are used based on the reliability. Therefore, the two-dimensional coordinates of the wireless tag can be determined with higher accuracy.

It is a conceptual diagram of the system configuration | structure of the RFID tag positioning system 1 used as embodiment of this invention. It is a figure which shows the structure of the wireless tag reader 100 of FIG. It is a figure which shows the structure of the radio | wireless tag 200 of FIG. 4 is a flowchart illustrating processing performed by the controller 300 to determine the two-dimensional coordinates of the wireless tag 200 in the first embodiment. It is a figure which shows the cell (small area | region) for calculating the calculation distance Dc. FIG. 6 is a diagram showing that the wireless tag 200 has moved from a position P _t-1 (0,0) at time t _-1 to P _t (0,1) at time t. FIG. 3 is a diagram showing that the wireless tag 200 has moved from a position P _t-1 (3,5) at time t _-1 to P _t (1,3) at time t. 10 is a flowchart illustrating processing performed by the controller 300 to determine the two-dimensional coordinates of the wireless tag 200 in the second embodiment. It is a flowchart which shows in detail the reliability calculation process of S24 of FIG. It is a figure explaining the total distance Ds calculated by step S14 of FIG. 6 is an example of a change in position of the wireless tag 200. In the example of FIG. 11, the two-dimensional position before and after the movement determined from only one measurement distance Dm or one total distance Ds is illustrated. It is a figure which shows the dispersion | variation in the candidate of the solution determined by performing step S241-S246 of FIG.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram of a system configuration of a wireless tag positioning system 1 according to an embodiment of the present invention. The wireless tag positioning system 1 of the present embodiment includes four wireless tag readers 100A to 100D. Since the four RFID tag readers 100A to 100D have the same configuration, they are simply referred to as the RFID tag reader 100 when they are not distinguished.

  In addition to the wireless tag reader 100, the wireless tag positioning system 1 also includes a controller 300 (see FIG. 2) that manages the four wireless tag readers 100, thereby performing absolute positioning of the wireless tag 200. The wireless tag 200 is carried by a person, and by performing absolute positioning of the wireless tag 200, the position of the person carrying the wireless tag 200 can be grasped.

  In the present embodiment, the positioning range 400 in which the absolute positioning of the wireless tag 200 needs to be performed is a quadrangle, and the wireless tag readers 100 </ b> A to 100 </ b> D are disposed at each corner of the positioning range 400. The positioning range is, for example, one room or one site. The communication range of each wireless tag reader 100 is a range that includes the entire positioning range 400.

  FIG. 2 is a diagram illustrating a configuration of the wireless tag reader 100. As shown in FIG. 2, the wireless tag reader 100 includes a control unit 110, a transmission unit 120, a reception unit 130, a distance measurement communication unit 140, and an antenna 150.

  The control unit 110 transmits data to be wirelessly transmitted to the outside to the transmission unit 120 and acquires data received by the antenna 150 and demodulated / decoded by the reception unit 130 from the reception unit 130. In addition, the control unit 110 controls the distance measurement communication unit 140 to transmit a distance measurement radio wave from the antenna 150 to the wireless tag 200 and acquires a signal demodulated by the distance measurement communication unit 140.

  The control unit 110 includes a memory 111 and a timer 112 inside. The memory 111 stores the ID of the wireless tag reader 100, installation coordinates, and the like. The timer 112 is used for measuring a transmission cycle.

  The transmission unit 120 and the reception unit 130 are parts that transmit and receive data to and from the wireless tag 200. The transmission unit 120 includes a coding unit 121, a modulation unit 122, and an amplification unit 123. The encoding unit 121 encodes the data supplied from the control unit 110. The encoding unit 121 outputs the encoded signal to the modulation unit 122. The modulation unit 122 converts the signal encoded by the encoding unit 121 into an electrical digital signal, and then uses a predetermined communication channel to perform a predetermined modulation method such as phase shift keying or frequency shift keying. Modulate with The amplification unit 123 amplifies the signal modulated by the modulation unit 122. The amplified signal is transmitted from the antenna 150 as a radio wave.

  The antenna 150 receives a radio wave transmitted from the wireless tag 200. The received radio wave is demodulated by the demodulator 131. The demodulated signal is encoded by the decoding unit 132, and the encoded signal is sent to the control unit 110.

  When the control unit 110 detects that the wireless tag 200 has entered the communication range of the wireless tag reader 100 based on the signal supplied from the receiving unit 130, the distance to the wireless tag 200 is determined by distance measurement communication. Measurement is performed using the unit 140.

  The distance measurement communication unit 140 transmits radio waves having a predetermined frequency for distance measurement different from the frequency for data communication using the transmission unit 120 and the reception unit 130 to the wireless tag 200 in accordance with an instruction from the control unit 110. As the frequency for distance measurement, various high frequencies described in Patent Document 1 can be used. Further, a frequency that is about the reciprocal distance of radio waves between the wireless tag reader 100 and the wireless tag 200 existing near the boundary of the communication range of the wireless tag reader 100 may be used. For example, when the distance from the wireless tag reader 100 to the boundary of the communication range of the wireless tag reader 100 is 15 m, a radio wave having a frequency of 10 MHz (wavelength 30 m) may be used.

  The distance measurement communication unit 140 and the distance measurement communication unit 240 of the wireless tag 200 constitute a phase synchronization circuit (phase locked loop (PLL)). As the ranging communication unit 240, the one shown in the transmitter / receiver described in Patent Document 1 can be used.

  Upon receiving the distance measurement radio wave from the radio tag reader 100, the radio tag 200 transmits (replies) the radio wave to the radio tag reader 100 that has transmitted the distance measurement radio wave. The ranging communication unit 140 acquires the radio wave transmitted by the wireless tag reader 100 via the antenna 150. The phase difference between the phase of the acquired radio wave and the phase of the transmitted distance measurement radio wave is output to the control unit 110. Further, the phase of the ranging radio wave is controlled so that the phase of the ranging radio wave is synchronized with the phase of the received radio wave, and the transmission of the ranging radio wave is continued. The controller 110 sends the phase difference to the controller 300.

  The ranging communication unit 140 only needs to be able to transmit and receive radio waves that can determine the phase difference. Therefore, the ranging communication unit 140 may include an amplification unit and a modulation unit as a transmission function, and a demodulation unit as a reception function. No part is required.

  The controller 300 is a computer that includes a CPU, a ROM, a RAM, and the like, and executes various processes when the CPU executes a program stored in the ROM. In addition, a storage unit that stores the processing results is also provided.

  As a process executed by the controller 300, there is a process of measuring a radial change distance of the wireless tag 200 with respect to each wireless tag reader 100 in a certain time using the phase difference output from the wireless tag reader 100. Further, the controller 300 further calculates the two-dimensional coordinates of the wireless tag 200 from the four radial direction change distances at a constant period. These processes performed by the controller 300 will be described later.

  FIG. 3 is a diagram illustrating a configuration of the wireless tag 200. The wireless tag 200 is carried by a person. The wireless tag 200 is an active wireless tag and includes a battery 210. In addition to the battery 210, the wireless tag 200 includes a transmission unit 220, a reception unit 230, a distance measurement communication unit 240, an antenna 250, and a control unit 280, and the battery 210 supplies power to them.

  The transmission unit 220 includes a coding unit 221, a modulation unit 222, and an amplification unit 223. The encoding unit 221 encodes data transmitted from the control unit 280 and sends the encoded data to the modulation unit 222. The modulation unit 222 modulates the code from the code unit 221 by a modulation method such as amplitude displacement modulation, for example. The amplification unit 223 amplifies the signal modulated by the modulation unit 222 and transmits the amplified signal from the antenna 250.

  The receiving unit 230 includes a demodulating unit 231 that demodulates radio waves received by the antenna 250 and a decoding unit 232 that decodes a signal demodulated by the demodulating unit 231. The decoding unit 232 supplies the decoded signal to the control unit 280.

  The distance measurement communication unit 240 has a function of acquiring a distance measurement radio wave transmitted by the wireless tag reader 100 via the antenna 250 and returning the distance measurement radio wave to the wireless tag reader 100. As a simple configuration, a local oscillator and a mixer may be provided, and a distance measurement radio wave transmitted from the wireless tag reader 100 and a signal generated by the local oscillator may be mixed by the mixer. Moreover, the structure of the transmitter / receiver of patent document 1 is also employable.

  The control unit 280 controls the transmission unit 220, the reception unit 230, and the ranging communication unit 240. The control unit 280 includes a timer 281 and a memory 282. The timer 281 measures time by counting clocks of a clock oscillator (not shown).

  Next, processing of the controller 300 that determines the two-dimensional coordinates of the wireless tag 200 will be described. FIG. 4 is a flowchart illustrating a process performed by the controller 300 to determine the two-dimensional coordinates of the wireless tag 200 in the first embodiment. The controller 300 executes the process shown in FIG. 4 at a constant distance measurement cycle.

  First, the controller 300 measures a radial movement distance (hereinafter referred to as measurement distance) Dm (step S2). This process corresponds to radial distance measuring means. In step S <b> 2, the distance obtained by multiplying the phase difference sequentially acquired from each wireless tag reader 100 by the wavelength of the distance measuring radio wave and moving the wireless tag 200 in the radial direction of the wireless tag reader 100 during the distance measurement period. The radial movement distance (that is, the measurement distance Dm) is calculated. The measurement distance Dm is measured for each wireless tag reader 100 by obtaining a phase difference from each wireless tag reader 100. Hereinafter, the measurement distance Dm for the wireless tag reader 100A is Dm (A), the measurement distance Dm for the wireless tag reader 100B is Dm (B), the measurement distance Dm for the wireless tag reader 100C is Dm (C), and the measurement distance Dm for the wireless tag reader 100D is Dm. (D).

  In the subsequent step S4, a distance difference e between the measurement distance Dm and the calculation distance Dc is calculated. The calculation distance Dc is a radial movement distance obtained by calculation. In order to obtain the radial movement distance by calculation, in this embodiment, the positioning range 400 is divided into small grid-shaped regions as shown in FIG. The size of this cell is appropriately determined in consideration of the calculation load.

Then, consider the case where each of the intersections of vertical and horizontal lines forming the grid (that is, the region vertex) is a point before the movement, and the point before the movement is moved to each of the remaining intersections. In this case, the radial movement distance can be calculated geometrically. If the coordinates of the point before movement are (x _t-1 , y _t-1 ) and the coordinates of the point after movement are (x _t , y _t ), Specifically, the radial movement distance is calculated by subtracting the distance from the distance to the point after the movement to the point before the movement using the wireless tag reader 100 as the origin. In FIG. 5, the point P _t-1 before the movement, but not on the intersection with the point P _t after the movement, it is because of the omitted part of the line with the vertical and horizontal lines for convenience of illustration. In Expression 1, L is a distance between the wireless tag readers 100.

  Specific numerical values are determined for the right sides of (1) to (4) in Equation 1 above. Therefore, the calculation distance Dc can be calculated. It seems that the coordinates of the points before and after the movement can be obtained by substituting the measurement distance Dm measured in step S2 for the left side of Equation 1. However, in this case, since it is a simultaneous equation having irrational numbers, it cannot generally be solved algebraically. Therefore, in the present embodiment, as described above, the combination of the points before and after the movement is covered and the value of the right side of Equation 1 is obtained, and then the two-dimensional coordinates of the point Pt after the movement are obtained by the method described below. decide.

  In step S4, a distance difference e between the measurement distance Dm and the calculation distance Dc is calculated for each wireless tag reader 100. In the subsequent step S6, a total distance difference E obtained by summing the distance differences e calculated in step S4 is calculated for all combinations of the points before and after the movement.

An example will be described. For example, it is assumed that L = 10 m and P _t−1 (0,0) and P _t (0,1) as shown in FIG. The calculation distances Dc (A), Dc (B), Dc (C), and Dc (D) can be calculated as shown in the following equation 2.

Further, it is assumed that the measurement distance Dm is a value shown in Equation 3.

The total distance difference E may be calculated by adding the absolute value of the distance difference e as in Expression 4, or may be the sum of squares of the distance difference e as in Expression 5. In Formulas 4 and 5, i is A to D.

If the calculation distance Dc and the measurement distance Dm are values shown in Expressions 2 and 3, respectively, the total distance difference E according to Expression 4 is calculated as shown in Expression 6 below and becomes 21.574.

Further, as shown in FIG. 7, if P _t-1 (3,5) and P _t (1,3), the calculation distances Dc (A), Dc (B), Dc (C), Dc ( D) The total distance difference E can be calculated as in Equation 7 and Equation 8, respectively.

In step S8, the minimum total distance difference Emin which is the minimum value among the total distance differences E for all combinations of the movement front and rear points calculated in step S6 is determined. If the measured distance Dm is the value shown in Equation 3 above, the calculation distance Dc is calculated as the point P _t-1 (2,2) before movement and the point P _t (7,4) after movement. The total distance difference E calculated from the calculated distance Dc using Expression 4 or Expression 5 becomes the minimum total distance difference Emin.

Here, the total distance difference E is a total value of the distance differences e between the four measurement distances Dm and the corresponding four calculation distances Dc, and each distance difference e is expressed by (1) to (4) in Equation 1. Is the difference between the right and left sides of the expression. Therefore, determining the points before and after the movement at which the total distance difference E is the minimum is that the four unknowns P _t−1 (x _t−1 , y _t-1 ) and P _t (x _t , y _t ) are solved.

Therefore, in step S10, the calculation distance Dc used to calculate the minimum total distance difference Emin is determined, and the moved point corresponding to the determined calculation distance Dc is determined as the two-dimensional coordinates of the wireless tag 200. As in the specific example above, the calculated distance Dc that is the minimum total distance difference Emin is calculated from the point P _t-1 (2,2) before movement and the point P _t (7,4) after movement. In this case, the current coordinates of the wireless tag 200 are determined to be (7, 4).

As described above, in the first embodiment described above, the radial movement distance (measurement distance Dm) that is the distance that the wireless tag 200 has moved in the radial direction of the wireless tag reader 100 is measured. Then, and it determines the two-dimensional coordinates P _t of the radio tag 200 from the measured distance Dm. Since the influence of multipath on the transmission / reception of radio waves between the wireless tag 200 and the wireless tag reader 100 before and after the movement of the wireless tag 200 can be considered to be almost the same, the measurement distance Dm is less affected by the multipath. Thus, from the measured distance Dm to determine the two-dimensional coordinates P _t of the radio tag 200 can be determined accurately dimensional coordinates P _t of the radio tag 200.

In addition, the processing in steps S4 and S6, that is, the distance difference e is calculated for each wireless tag reader 100, and the total distance difference E, which is the sum of the distance differences e for each wireless tag reader 100, is calculated for all combinations of points before and after the movement. The calculation process is independent for each combination of the points before and after the movement. Therefore, by performing parallel computations, it is also possible to determine the two-dimensional coordinate P _t at a high speed.

(Second Embodiment)
Next, a second embodiment will be described. In the following description of the second embodiment, elements having the same reference numerals as those used so far are the same as the elements having the same reference numerals in the previous embodiments unless otherwise specified. In addition, when only a part of the configuration is described, the embodiment described above can be applied to other parts of the configuration.

  FIG. 8 is a flowchart illustrating processing performed by the controller 300 to determine the two-dimensional coordinates of the wireless tag 200 in the second embodiment. As in FIG. 4, the controller 300 executes the processing shown in FIG. 8 at a constant distance measurement cycle.

  In step S2, as in FIG. 4, four measurement distances Dm (A), Dm (B), Dm (C), and Dm (D) are measured. In step S3, the measurement distance Dm is stored in a predetermined storage unit. Steps S4, S6, and S8 are the same as those in FIG. In step S4, a distance difference e between the measurement distance Dm and the calculation distance Dc is calculated for each wireless tag reader 100. That is, four distance differences e are calculated. In the second embodiment, in order to distinguish from the distance difference calculated in step S16, the distance difference in step S4 is set to e (m).

  In step S6, a total distance difference (E (m)) obtained by adding up the four distance differences e (m) calculated in step S4 is calculated for all combinations of the points before and after the movement. In step S8, the minimum value of the total distance difference E (m), that is, the minimum total distance difference E (m) min is determined.

In subsequent step S12, in order to determine the current two-dimensional coordinate candidate of the wireless tag 200, first, the calculation distance Dc used to calculate the minimum total distance difference E (m) min determined in step S8 is determined. In the first embodiment, the point after movement corresponding to the calculated distance Dc were determined in a two-dimensional coordinate P _t of the wireless tag 200, in the second embodiment, after the movement corresponding to the calculated distance Dc Let a point be a candidate for its two-dimensional coordinates.

  In step S14, the total distance Ds is calculated. The total distance Ds corresponds to the total radial movement distance in the claims, and step S14 corresponds to the total movement distance calculation means. FIG. 10 is a diagram for explaining the total distance Ds. In FIG. 10, Dm (t), Dm (t-1), and Dm (t-2) are measured distances Dm measured at time t, time t-1, and time t-2, respectively. It is stored in the storage unit in step S3.

  The total distance Ds is a value obtained by summing a plurality of measurement distances Dm in order from the latest, and Ds (2) in FIG. 10 is two measurement distances Dm, that is, the latest measurement distance Dm and the previous one. Is the total of the measured distances Dm (t-1). Ds (3) is the total of the three measurement distances Dm, that is, the latest measurement distance Dm, the previous measurement distance Dm (t-1), and the two previous measurement distances Dm (t-2). It is.

  FIG. 10 also shows the position P (t) at the present time (time t) of the wireless tag 200, the position P (t−1) at the previous measurement time, the position P (t− at the previous measurement time, 2) The position P (t-3) at the measurement time three times before is also shown. Thus, although the wireless tag 200 moves also in the circumferential direction of the wireless tag reader 100, the measurement distance Dm is the distance that the wireless tag 200 has moved in the radial direction of the wireless tag reader 100. Therefore, the total distances Ds (2) and Ds (3) are also represented by the position P (t-2) at the measurement time two times before or the position P (t at the measurement time three times before, as shown in FIG. It is the radial movement distance from -3) to the present time.

  FIG. 10 shows two types of total distances Ds (2) and Ds (3) with different summing periods, but it is sufficient to calculate at least one type of total distance Ds. Whether to calculate Ds is preset. Further, for each type of total distance Ds, all four RFID tag readers 100, that is, four total distances Ds are calculated.

  The total distance Ds is the same as the measurement distance Dm for one time except that the time required for movement is different. Therefore, a candidate for the two-dimensional coordinates of the wireless tag 200 is determined using the total distance Ds in the same manner as the measurement distance Dm.

  In step S16, a distance difference e (s) between each of the four total distances Ds calculated in step S14 and the previously calculated calculation distance Dc is calculated. The calculation method is the same as step S4 except that the total distance Ds is used instead of the measurement distance Dm. If a plurality of types of total distances Ds (n) (n = 1, 2,...) Are calculated in step S14, four distance differences e (s) are calculated for each of the plurality of types. To do.

  In step S18, a total distance difference (referred to as E (s)) obtained by adding up the four distance differences e (s) calculated in step S16 is calculated for all combinations of the points before and after the movement. When a plurality of types of distance differences e (s) are calculated, a total distance difference E (s) for all combinations of points before and after the movement is calculated for each type of distance difference e (s).

  In step S20, the minimum value of the total distance difference E (s) for all combinations of the movement front and rear points calculated in step S18, that is, the minimum total distance difference E (s) min is determined. When a plurality of types of total distance difference E (s) are calculated, the minimum total distance difference E (s) min is determined for each type of total distance difference E (s).

  In step S22, the calculation distance Dc used to calculate the minimum total distance difference E (s) min determined in step S20 is determined. Then, the point after movement corresponding to the calculated distance Dc is set as a candidate for the two-dimensional coordinates of the wireless tag 200. If a plurality of minimum total distance differences E (s) min are determined in step S20, two-dimensional coordinate candidates are determined for each minimum total distance difference E (s) min.

  In step S24, the reliability of the two-dimensional coordinate candidate determined in steps S12 and S22 is calculated. Details of the processing in step S24 are shown in FIG.

  In FIG. 9, first, in step S241, a plurality of four measurement distances Dm (A), Dm (B), Dm (C), and Dm (D) measured in step S2 of FIG. Change to the value of. This measurement error er is set in advance when the wireless tag reader 100 is installed. Since the measurement error er is greatly affected by the device configuration of the wireless tag reader 100, the measurement error er may be set at the time of manufacture. Moreover, in order to consider an installation environment, you may make it set at the time of installation. The number for changing the value is set in advance as a number necessary for accurately determining the variance (step S246) described later. A value to be added to or subtracted from the measurement distance Dm may be set in advance or may be randomly generated. Further, the value to be added or subtracted may be different for each wireless tag reader 100 or may be the same.

  In step S242, the total distance Ds calculated in step S14 of FIG. 8 is changed to a plurality of values within the range of the measurement error er. The measurement error er is the same as in step S241, and the value to be added to or subtracted from the total distance Ds is also the same as in step S241.

  In step S243, the value changed in steps S241 and S242 (hereinafter referred to as the changed value) is used in place of the measurement distance Dm and the total distance Ds in the same manner as in step S4 and step S16. The distance difference e is calculated for each wireless tag reader 100 (that is, four). In step S244, for each change value, the total distance difference E, which is the sum of the four distance differences e calculated in step S243, is calculated for all combinations of the points before and after the movement in the same manner as in steps S6 and S18. . In step S245, the minimum value (minimum total distance Emin) of the total distance differences E calculated for all combinations of the points before and after the movement in step S244 is determined for each change value.

In step S246, the calculation distance Dc used for calculating the minimum total distance difference Emin determined in step S245 is determined for each change value. Then, the points before and after the movement corresponding to the calculation distance Dc are determined as the solution candidates of (x _t−1 , y _t−1 ) and (x _t , y _t ) in Equation 1. Since the calculation distance Dc used to calculate the minimum total distance difference Emin is determined for each change value, solution candidates are determined by the number of change values. In step S247, the variance (= σ ² ) of the solution candidates determined in step S246 is calculated for each measurement distance Dm or total distance Ds that is the reference for the change value.

  11 to 13 are diagrams for explaining the reason for calculating the variance in step S247. FIG. 11 is an example of a change in the position of the wireless tag 200, and the wireless tag 200 has moved from p1 → p2 → p3 → p4 → p5 → p6.

  FIG. 12 exemplifies two-dimensional coordinates before and after movement determined from only one measurement distance Dm or one total distance Ds in the example of FIG. The straight lines indicated by p5 and p6 are two-dimensional coordinates before and after movement determined from only the measurement distance Dm. The other four straight lines, that is, the straight lines indicated by p1-p6, p2-p6, p3-p6, and p4-p6 are two-dimensional coordinates before and after movement determined from only one total distance Ds. From FIG. 12, it can be seen that the position of p6, which is the current two-dimensional coordinate, varies depending on which is used as the measurement distance Dm or the total distance Ds.

  FIG. 13 is a diagram in which solution candidates determined by executing Steps S241 to S246 of FIG. 9 are plotted according to the measurement distance Dm or the total distance Ds that is the reference for the change value. In FIG. 13, D16, D26, D36, D46, D56 respectively represent the total distance Ds or the measurement distance Dm corresponding to p1-p6, p2-p6, p3-p6, p4-p6, p5-p6 in FIG. This means that steps S241 to S246 are executed to determine a solution candidate.

  From FIG. 13, it can be seen that, even though the distance measurement error er is the same, the dispersion of the solution candidates varies depending on the specific positions before and after the wireless tag 200 moves. This is because the measurement distance Dm is the distance that the wireless tag 200 has moved in the radial direction of the wireless tag reader 100. The closer the movement of the wireless tag 200 is to a movement that draws an arc centering on a certain wireless tag reader 100, the smaller the measured distance Dm that the wireless tag reader 100 measures than the actual movement distance of the wireless tag 200. As a result, the influence of the ranging error er becomes large.

  The smaller the variance, the more reliable the two-dimensional coordinate candidates determined in step S12 or step S22 in FIG. Therefore, in step S248, the inverse of the variance calculated in step S247 is set as the reliability.

  Returning to FIG. 8, in step S26, the current two-dimensional coordinates of the wireless tag 200 are determined using the two-dimensional coordinate candidates determined in step S12 or S22 based on the reliability calculated in step S24.

  As a method of using the reliability, for example, there is the following method. In the first method, the two-dimensional coordinates of the wireless tag 200 are averaged by averaging a plurality of moved points that are candidate solutions with the highest reliability calculated in step S24. In the second method, the two-dimensional coordinates determined from the measurement distance Dm or the total distance Ds with the highest reliability calculated in step S24 are set as the two-dimensional coordinates of the wireless tag 200.

  These first and second methods use only the two-dimensional coordinates obtained from the measurement distance Dm or the total distance Ds with the highest reliability calculated in step S24. The following third and fourth methods are used. As in the method, the two-dimensional coordinates of the wireless tag 200 may be determined using the two-dimensional coordinates obtained from the plurality of measurement distances Dm or the total distance Ds with a weight according to the reliability.

  The third method is a method in which the average value of each solution candidate is weighted and averaged based on the reliability. That is, first, a coefficient is created with the total value of each reliability calculated in step S24 as the denominator and the numerator as each reliability. Also, an average value of solution candidates is calculated. The average value of the solution candidates is obtained by averaging the solution candidates determined in step S246 for each measurement distance Dm or total distance Ds that is the reference for the change value. Then, a value obtained by multiplying the average value of each solution candidate by a coefficient corresponding to the solution candidate is added. As a result, a value obtained by weighting and averaging the average value of each solution candidate by the reliability is obtained. If this is performed separately for the x-coordinate and the y-coordinate, the two-dimensional coordinates of the wireless tag 200 can be determined.

  The fourth method uses the two-dimensional coordinate candidates determined in step S22 in place of the average value of each solution candidate in the third method. Others are the same as the third method.

  As described above, according to the second embodiment described above, the measurement distance Dm measured this time (step S2) and the measurement distance Dm (step S3) measured and stored in the past are added together to be continuous. At least one total distance Ds is calculated for each wireless tag reader 100, which is the distance that the wireless tag 200 has moved in the radial direction of the wireless tag reader 100 during a plurality of distance measurement cycles (step S14). Using this total distance Ds, the total distance difference E (s) is calculated for all combinations of the movement front and rear points in the same manner as the measurement distance Dm (step S18), and further, the minimum total distance difference E (s) ) min is determined (step S20), and two-dimensional coordinate candidates of the wireless tag 200 are determined (step S22). As a result, not only the two-dimensional coordinate candidates determined from the measurement distance Dm but also the two-dimensional coordinate candidates can be obtained from the total distance Ds. The final two-dimensional coordinates are determined based on the plurality of two-dimensional coordinate candidates (step S26). Therefore, the two-dimensional coordinates of the wireless tag 200 can be determined with higher accuracy.

  Further, as described with reference to FIG. 13, even if the measurement error er itself of the wireless tag reader 100 is the same, the two-dimensional coordinate determined in steps S12 and S22 is determined by the specific coordinates before and after the movement of the wireless tag 200. Candidate reliability is different. Therefore, in the second embodiment, the reliability is respectively determined for the two-dimensional coordinate candidate determined from the measurement distance Dm (step S12) and the two-dimensional coordinate candidate determined from the total distance Ds (step S22). It has been determined (step S24). In determining the two-dimensional coordinates of the wireless tag 200, a plurality of two-dimensional coordinate candidates are used based on the reliability (step S24). Thereby, the two-dimensional coordinates of the wireless tag 200 can be determined with higher accuracy.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, The following embodiment is also contained in the technical scope of this invention, and also the summary other than the following is also included. Various modifications can be made without departing from the scope.

  For example, in the second embodiment, a plurality of two-dimensional coordinate candidates are used based on the reliability. However, the reliability may not be calculated, and only a plurality of two-dimensional coordinate candidate positions that are close to each other may be used, and a value obtained by averaging them may be used as the two-dimensional coordinates of the wireless tag 200. A value obtained by simply averaging the coordinate candidates may be used as the two-dimensional coordinates of the wireless tag 200.

  In the above-described embodiment, the controller 300 executes the processes in FIG. 4 or FIGS. 8 and 9. However, any one of the wireless tag readers 100 may execute these processes.

  In the above-described embodiment, the measurement distance Dm is measured from the phase difference between the radio waves using a radio wave as the signal wave. However, the measurement distance Dm may be measured by a Doppler radar using a sound wave as the signal wave.

  In addition, the positioning range does not have to be a quadrangle, and can be any various shape.

1 wireless tag positioning system 100 wireless tag reader 200 wireless tag 300 controller 400 positioning range S2 radial distance measuring means S4, S6 first total distance difference calculating means S8 first candidate determining means S10 position determining means S14 total moving distance calculating means S18 first 2 Total distance difference calculating means S20, S22 Second candidate determining means S24 Position determining means S246 First plural candidate determining means, second plural candidate determining means S248 First reliability determining means, second reliability determining means

Claims (3)

At least four wireless tag readers with transmission / reception units that sequentially transmit distance measurement signal waves and receive response waves coming from wireless tags based on the distance measurement signal waves, and exist within the positioning range A wireless tag positioning system that sequentially determines two-dimensional coordinates of the wireless tag,
Radial distance measuring means for measuring a radial movement distance, which is a distance that the wireless tag has moved in the radial direction of the wireless tag reader at a predetermined time, based on a transmission / reception result of each wireless tag reader, and for each wireless tag reader;
The area vertices generated by dividing the positioning range into a plurality of small areas are the points before the movement, and the remaining area vertices excluding the points before the movement are the points after the movement. The distance difference between the calculated radial movement distance that is the radial movement distance calculated for the combination and each radial movement distance measured by the radial distance measuring means is calculated for each wireless tag reader, and these First total distance difference calculating means for calculating a total distance difference obtained by summing the distance differences for all the combinations of the points before and after the movement;
A minimum total distance difference, which is a minimum value among the total distance differences calculated by the first total distance difference calculation means, is determined, and after the movement determined by the calculated radial movement distance used for calculating the minimum total distance difference First candidate determining means for determining a point as a candidate for a two-dimensional coordinate of the wireless tag;
A wireless tag positioning system comprising: position determining means for determining the two-dimensional coordinates of the wireless tag based on the two-dimensional coordinate candidates determined by the first candidate determining means. In claim 1,
The radial direction distance measuring means is repeatedly executed every distance measurement period,
A storage unit for sequentially storing past radial movement distances measured by the radial distance measuring means;
By adding the radial movement distance for the latest one time or the past multiple times sequentially measured in order from the newest measurement time stored in the storage unit and the radial movement distance measured this time, multiple consecutive times A total movement distance calculation means for calculating a total radial movement distance, which is a distance that the wireless tag has moved in the radial direction of the wireless tag reader during the distance measurement cycle, for each wireless tag reader;
The distance difference between the calculated radial movement distance and the total radial movement distance calculated by the total movement distance calculation means is calculated for each wireless tag reader, and the total distance difference obtained by summing those distance differences A second total distance difference calculating means for calculating a combination of points before and after movement;
The minimum total distance difference, which is the minimum value of the total distance differences calculated by the second total distance difference calculation means, is determined, and the post-movement determined by the calculated radial movement distance used for the calculation of the minimum total distance difference. A second candidate determining means for setting a point as a candidate for a two-dimensional coordinate of the wireless tag,
The position determining means determines the two-dimensional coordinates of the wireless tag based on the two-dimensional coordinate candidates determined by the first candidate determining means and the two-dimensional coordinate candidates determined by the second candidate determining means. A wireless tag positioning system characterized by: In claim 2,
The radial movement distance measured by the radial distance measuring means is changed to a plurality of values within a preset measurement error range, and the radial movement distance measured by the radial distance measuring means is measured. A first plurality of candidate determining means for determining a plurality of candidates for the two-dimensional coordinates by executing the first total distance difference calculating means and the first candidate determining means, respectively.
Movement from a point before movement determined by the minimum total distance difference determined by the first candidate determination means so that the smaller the variation of the plurality of two-dimensional coordinate candidates determined by the first plurality of candidate determination means, the higher the value. First reliability determination means for determining the reliability of movement to a later point;
The total radial movement distance calculated by the total movement distance calculation means is changed to a plurality of values within a preset measurement error range, and the plurality of values are used in place of the total radial movement distance, respectively. A second plurality of candidate determining means for determining a plurality of candidates for the two-dimensional coordinates by executing the second total distance difference calculating means and the second candidate determining means;
Move from the point before movement determined by the minimum total distance difference determined by the second candidate determining means so that the smaller the variation of the plurality of two-dimensional coordinate candidates determined by the second multiple candidate determining means, the higher the value. Second reliability determining means for determining the reliability of movement to a later point;
The position determining means determines the two-dimensional coordinate candidates determined by the first candidate determining means and the two-dimensional coordinate candidates determined by the second candidate determining means as the first reliability determining means and the second reliability determining The RFID tag positioning system, wherein the two-dimensional coordinates of the RFID tag are determined based on the reliability determined by each means.

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