JP2013061151A - Radio tag reader and monitor system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio tag reader which has good precision of direction detection of a radio tag.SOLUTION: Correlation errors between electric power intensity patterns and a reference pattern are calculated respectively from radio waves from respective antennas 412, 414, and 416 of a radio tag 400 (S108). The reference pattern is an electric power intensity pattern when a vertical polarized wave is received in an ideal environment on sequential switching of directivity by an antenna part 1. Correlation errors Γ between the reference pattern and received electric power intensity patterns of the radio waves received from the respective antennas 412, 414, and 416 have large values when the received radio waves principally comprise horizontal polarized waves. An electric power intensity pattern having a minimum correlation error Γ is selected as a pattern for direction estimation, so the selected pattern may be a pattern when the radio wave principally comprising the vertical polarized waves are received with high possibility. Direction detection of the radio tag 400 can be therefore performed with high precision.

Description

  The present invention relates to a wireless tag reader capable of estimating the direction of a wireless tag and a monitoring system using the wireless tag reader.

  A wireless tag system that reads information from a wireless tag using radio waves is being used in various applications, and the wireless tag reader that is the main element of this system is required to have high functionality so that it can be applied to a wide range of applications. Yes. As an example of high functionality, for example, it is possible not only to simply read information on a wireless tag, but also to specify in which direction the wireless tag can exist, and to use it for searching for a wireless tag holder, It is being considered to use the tag holder to determine whether or not the tag holder is present in an appropriate direction.

  As a technique related to specifying the direction of the wireless tag, for example, a technique as disclosed in Patent Document 1 has been proposed. This Patent Document 1 discloses a radio wave arrival direction detection method using an array antenna that includes a plurality of antenna elements and can change directivity characteristics. In this radio wave arrival direction detection method, an omnidirectional angle of 360 degrees is disclosed. The direction of arrival of radio waves is estimated by beam switching that is divided into 12 parts.

  Further, in Patent Document 2, as a system for semi-moving and mobile station antenna control, a gyrocompass, an acceleration sensor, or the like is used to detect the position, orientation, and orientation of a moving body, and the antenna is based on these. It is disclosed that a technique for controlling the posture of the camera is known.

Japanese Patent No. 3836080 Japanese Patent No. 3002612

  The array antenna of Patent Document 1 is usually installed so as to perform horizontal scanning, and in this case, has good sensitivity to vertical polarization (linear polarization). Therefore, accurate direction detection can be performed when the radio wave to be direction detected is vertically polarized.

  However, when the wireless tag is carried by a person, the wireless tag is in various directions. Therefore, if there is only one antenna from the wireless tag, the radio wave from the wireless tag may be horizontally polarized. However, the array antenna of Patent Document 1 has low sensitivity to horizontal polarization and is not sharp in directivity, so that the direction detection accuracy decreases when the radio wave from the wireless tag is horizontal polarization. There is a problem of end up.

  Therefore, the wireless tag includes a plurality of transmission antennas and transmits radio waves from the respective transmission antennas, and the wireless tag reader selects an antenna transmitting vertical polarization from the radio waves transmitted from the respective transmission antennas (that is, It is conceivable to perform antenna selection diversity (selecting radio waves that are vertically polarized).

  As described above, the array antenna of Patent Document 1 has good sensitivity to vertical polarization. Therefore, as the antenna selection diversity, radio waves transmitted by the wireless tag while switching the transmission antenna are received by a wireless tag reader equipped with an array antenna, and the strongest power intensity among the plurality of transmission antennas of the wireless tag can be obtained. It is conceivable to specify the transmitting antenna as an antenna transmitting vertically polarized waves.

  However, there is a case where the polarization is not coincident when the power intensity is strongest. For example, when a wireless tag is placed in the rear pocket, due to the influence of the human body, the vertical polarization is deteriorated forward of the human body, and the horizontal polarization is relatively emphasized. In such a case, even with horizontal polarization, the power intensity may be stronger than with vertical polarization, so there is a possibility of selecting horizontal polarization. When the horizontal polarization is selected, the direction detection accuracy is lowered as described above.

  The technique described in Patent Document 2, that is, the technique of detecting the attitude of a moving body using a sensor such as a gyrocompass or an acceleration sensor and controlling the attitude of the antenna based on this, controls the sensor and the attitude. Since the device to be used is necessary, the entire device becomes expensive. Therefore, it is not realistic to apply it to the wireless tag.

  The present invention has been made based on this situation, and an object of the present invention is to provide a wireless tag reader with good direction detection accuracy of a wireless tag and a monitoring system using the wireless tag reader.

In order to achieve the object, the invention according to claim 1
An array antenna configured to switch the directivity in the horizontal plane with respect to the vertical polarization to a plurality of set angles;
Directivity switching means for sequentially switching the directivity of the array antenna to a plurality of set angles;
Radio waves received from radio tags that transmit radio waves from a plurality of tag antennas whose polarization planes are orthogonal to each other are received by the array antenna while the directivity is switched by the directivity switching means. A wireless tag reader that estimates the arrival direction of
Reception intensity measuring means for measuring the power intensity received by the array antenna;
For each tag antenna that is the power intensity for one period of the set angle received from each tag antenna from the power intensity measured by the reception intensity measuring means while the directivity switching means sequentially switches the directivity of the array antenna. Power intensity pattern determining means for determining the power intensity pattern of
Reference pattern storage means for storing a reference pattern that is a standard power intensity pattern when the array antenna receives vertical polarization;
Correlation value calculating means for calculating a pattern correlation value representing the correlation between the power intensity pattern determined by the power intensity pattern determining means and the reference pattern for each tag antenna;
Of the radio waves received from the plurality of tag antennas, the radio wave having the highest correlation among the pattern correlation values for each tag antenna calculated by the correlation value calculation means, Selecting means for selecting.

  As described above, in the present invention, instead of simply using the received power intensity to select the tag antenna, the radio wave intensity acquired continuously is determined, for example, as the interrupt timing associated with establishment of reception of the data frame from the tag to the reader. A power intensity pattern is determined for each tag antenna based on the antenna number information in the data frame, and a pattern correlation value representing the correlation between the power intensity pattern and the reference pattern is calculated.

  As mentioned above, even if the horizontal polarization is relatively strong due to the influence of the human body, etc., the directivity switched by the array antenna is the directivity of the vertical polarization. In this case, the power intensity pattern determined based on the received radio wave is not a pattern reflecting the directivity switching. On the other hand, the reference pattern is a power intensity pattern serving as a reference when the array antenna receives vertical polarization when the directivity with respect to vertical polarization is sequentially switched. Therefore, the pattern correlation value is a value indicating that the correlation with the reference pattern is low when the received radio wave is horizontally polarized. Therefore, if the radio wave showing the highest correlation value among the pattern correlation values for each tag antenna is selected as the radio wave to be used for estimating the direction of arrival, selection of horizontally polarized radio waves can be suppressed. Is done. That is, the possibility of selecting vertically polarized waves is improved. Therefore, the direction detection accuracy of the wireless tag is improved.

The invention according to claim 2 is a weight determined for each set angle based on the surrounding environment where the wireless tag reader is installed, and the reflection from the radio wave reflector is large for the angle where the radio wave reflector exists. A weight setting means for setting a weight that becomes smaller,
Pattern correction means for correcting the power intensity in the power intensity pattern of each tag antenna determined by the power intensity pattern determination means using the weight set by the weight setting means,
The correlation value determining unit calculates the pattern correlation value using the power intensity pattern corrected by the pattern correcting unit and the reference pattern.

  Regarding the angle at which the radio wave reflector exists around the wireless tag reader, the received power intensity may increase due to reflection from the radio wave reflector. However, in the present invention, for the angle at which the reflecting object exists, a weight that is smaller as the reflection from the radio wave reflecting object is larger is set. And the power intensity in the power intensity pattern of the tag antenna is corrected by this weight. Therefore, the power intensity pattern after correction by the weight is a pattern in which the influence of reflection from the radio wave reflector is reduced. The pattern correlation value is calculated using the power intensity pattern after correction by weight. Therefore, this pattern correlation value is also a value in which the influence of the reflection from the radio wave reflector is reduced, and as a result, it is a value that well reflects the difference in polarization. Therefore, selection of horizontally polarized radio waves can be further suppressed.

In the invention according to claim 3, the correlation value determining means calculates the pattern correlation value using the power intensity pattern determined by the power intensity pattern determining means and the reference pattern,
A weight that is determined for each set angle based on the surrounding environment where the RFID tag reader is installed, and for the angle at which the radio wave reflector is present, a weight that sets a smaller weight as the reflection from the radio wave reflector increases. Setting means;
Correlation value correcting means for correcting the pattern correlation value of each tag antenna determined by the correlation value determining means using the weight set by the weight setting means,
The selection unit selects a radio wave to be used for estimating an arrival direction based on a pattern correlation value of each tag antenna after correction by the correlation value correction unit.

  As described above, regarding the angle at which the radio wave reflector exists around the wireless tag reader, the received power intensity may increase due to reflection from the radio wave reflector. However, in the present invention, for the angle at which the reflecting object exists, a weight that is smaller as the reflection from the radio wave reflecting object is larger is set. Then, the pattern correlation value is corrected with this weight. Therefore, the pattern correlation value after the correction by the weight is a value in which the influence of the reflection from the radio wave reflector is reduced, and as a result, it is a value that well reflects the difference in polarization. Therefore, selection of horizontally polarized radio waves can be further suppressed.

  The weight set by the weight setting means is a value correlated with at least one of the distance between the array antenna and the radio wave reflector and the radio wave reflectivity of the radio wave reflector. It is characterized by becoming.

  The magnitude of reflection from the radio wave reflector varies depending on the distance between the array antenna and the radio wave reflector. Further, the magnitude of reflection from the radio wave reflector also varies depending on the radio wave reflectivity of the radio wave reflector. Therefore, according to the fourth aspect, it is possible to set a weight that decreases as the reflection from the radio wave reflector increases.

  According to a fifth aspect of the present invention, the weight set by the weight setting means is a value correlated with the distance between the array antenna and the radio wave reflector, and is set to a smaller value as the distance is shorter. It is characterized by that.

  In this way, if the weight is set to be smaller as the distance to the radio wave reflector is shorter, the power intensity that has become stronger due to the presence of the radio wave reflector can be reduced to an intensity that reduces the influence of the radio wave reflector. it can.

A sixth aspect of the present invention is a monitoring system comprising: a laser sensor that sequentially measures the distance and direction of an object in a monitoring area; and the wireless tag reader according to claim 5 that includes the monitoring area as a communication range. A system,
The wireless tag reader is
The distance and direction of the object detected by the laser sensor can be obtained sequentially,
The weight set by the weight setting means is a value corresponding to the distance of the object sequentially acquired from the laser sensor with respect to a set angle determined based on the direction of the object sequentially acquired from the laser sensor. It is characterized by.

  In this way, since the weight is set based on the distance and direction of the object sequentially measured by the laser sensor, even when there is a moving object, the weight that reflects the presence of the moving object is set. can do.

1 is a schematic diagram of a monitoring system according to a first embodiment of the present invention. It is a flowchart which shows the process which the controller 300 performs in 1st Embodiment. 1 is a configuration diagram of a wireless tag reader / writer 100 used in a monitoring system. 2 is a block diagram illustrating a detailed configuration of a transmission unit 4 and a reception unit 5 of the wireless tag reader / writer 100. FIG. 2 is a configuration diagram of a wireless tag 400. FIG. 4 is a diagram conceptually showing an arrangement of three tag antennas 412, 414, and 416 in a wireless tag 400. FIG. It is a figure which shows the structure of the direction detection part 7 in detail. It is a figure which shows an example of a reference pattern. It is the schematic of the directivity pattern of the radio | wireless tag reader / writer 100 formed sequentially by changing a directivity angle sequentially. It is a figure which shows an example of the power intensity pattern produced | generated by the received power intensity detected changing a directivity angle. It is a figure explaining the reflection of an electromagnetic wave in case the wireless tag reader / writer 100 is installed adjacent to a house. 12 is an example of a weight coefficient list in the arrangement environment of FIG. It is a flowchart which shows the direction detection process which the direction detection part 7 performs. It is a flowchart which shows the direction detection process which the direction detection part 7 performs, Comprising: It is a part performed following FIG. It is a data frame used with the monitoring system of 1st Embodiment. 15 is a detailed flowchart of a correlation error calculation process in step S100 of FIG. It is a figure which illustrates the electric power detection value of the radio wave which the 1st tag antenna, the 2nd tag antenna, and the 3rd tag antenna transmitted, and the wireless tag reader / writer 100 received in the state where there is no radio wave shielding by a human body. FIG. 6 is a diagram illustrating a power detection value of a radio wave transmitted by the first tag antenna, the second tag antenna, and the third tag antenna and received by the wireless tag reader / writer 100 in a state where there is radio wave shielding by a human body. It is a figure which illustrates the gain when the radio | wireless tag reader / writer 100 receives the electromagnetic wave which each tag antenna 412, 414, 416 transmitted in the state with a human body shield. 3 is a diagram illustrating the directivity of the antenna unit 1 of the wireless tag reader / writer 100. FIG. It is explanatory drawing when the wireless tag reader / writer 100 of 2nd Embodiment detects the direction of the wireless tag 400 of an intruder. It is a weighting coefficient list in the second embodiment. It is explanatory drawing in case the wireless tag reader / writer 100 of 3rd Embodiment detects the direction of the wireless tag 400 of an intruder. It is a flowchart which shows the process which the controller 300 which concerns on 3rd Embodiment sets weighting coefficient W ((theta)) automatically. It is a weighting coefficient list in the third embodiment. It is a part of detailed flowchart of the calculation process of the correlation error performed in 4th Embodiment.

[First embodiment]
FIG. 1 is a schematic diagram of a monitoring system according to the first embodiment of the present invention. This monitoring system uses the wireless tag reader / writer 100 that can estimate the direction (arrival azimuth) of the wireless tag 400 and the laser sensor 200 that measures the distance and direction of an object in the monitoring area, and has entered the monitoring area. The controller 300 determines whether or not a person is carrying the wireless tag 400, and gives a warning when the person is not carrying the wireless tag 400.

  An outline of the processing of the controller 300 in the monitoring system will be described with reference to the flowchart of FIG. First, the laser sensor 200 is controlled to determine whether there is an intruder in the monitoring area (S12). If this determination is negative, S12 is repeated.

  On the other hand, if it is affirmation determination, it will progress to step S14 and will acquire the direction and distance of an intruder. The direction of the intruder is acquired from the scanning direction of the laser sensor 200, and the distance to the intruder is measured from the time from when the laser sensor 200 sends out the laser light until the reflected light of the laser light is received.

  Subsequently, the direction estimation result of the wireless tag 400 is acquired from the wireless tag reader / writer 100 (S16). The direction estimation process performed by the wireless tag reader / writer 100 will be described later. In a succeeding step S18, it is determined whether or not the wireless tag reader / writer 100 can receive a radio wave from the wireless tag 400. The direction estimation processing result of the wireless tag reader / writer 100 also includes information indicating whether or not radio waves from the wireless tag 400 can be received, and the determination in step S18 is performed using the direction estimation processing result.

  If the wireless tag reader / writer 100 has not received the radio wave from the wireless tag 400 (S18: No), it is determined that the intruder is not carrying the wireless tag 400, and an alarm is issued with an alarm sound or the like (S20). . On the other hand, if the wireless tag reader / writer 100 has received a radio wave from the wireless tag 400 (S18: Yes), the direction of the intruder detected by the laser sensor 200 and the wireless tag 400 estimated by the wireless tag reader / writer 100 are also obtained. It is determined whether or not the direction matches (S22). If the direction of the intruder detected by the laser sensor 200 and the direction of the wireless tag 400 estimated by the wireless tag reader / writer 100 do not match (S22: No), the intruder is not carrying the wireless tag 400 and is monitored. It is determined that the wireless tag 400 irrelevant to the intruder exists in any area, and an alarm is issued (S20). If the directions match (S22: Yes), it is determined that the intruder is an intruder authorized to carry the wireless tag 400, and the process ends without issuing an alarm.

  Next, the configuration of the wireless tag reader / writer 100 used in the monitoring system will be described with reference to FIG. The wireless tag reader / writer 100 includes an antenna unit 1, a distributor 3, a transmission unit 4, a reception unit 5, a power detection circuit 6, a direction detection unit 7, and a communication control unit 8.

  The antenna unit 1 is an electronically controlled waveguide array antenna device, and includes one excitation element 10 and six non-excitations provided at equal intervals on the circumference of a radius r centering on the excitation element 10. Elements 11-16 are provided. Each of these has a straight bar shape, and the length thereof is, for example, about λ / 4, and the radius r is also set to λ / 4.

  The exciting element 10 and the non-exciting elements 11 to 16 are provided on the ground conductor 17 so as to be insulated from the ground conductor 17, and these elements are arranged such that the axial direction is the vertical direction. ing. The ground conductor 17 has a sufficiently large area (for example, radius λ / 2) with respect to the excitation element 10 and the non-excitation elements 11 to 16.

  A feeding point of the excitation element 10 is connected to the distributor 3 via the coaxial cable 19, and a reception signal indicating a radio wave transmitted from the wireless tag 400 and received by the excitation element 10 is supplied to the distributor 3.

  Variable reactance circuits 18A to 18F are connected to the non-excitation elements 11 to 16, respectively. The variable reactance circuit 18 is the same circuit as that generally used in an electronically controlled waveguide array antenna apparatus. For example, a variable reactance element (for example, a variable reactance element) whose reactance value changes when a bias voltage is applied. A circuit including a capacitor diode). This circuit is connected to the ground conductor 17 at a high frequency, and a reactance value is electronically changed by a variable reactance control unit 72 (to be described later) of the direction detection computer 6. As the reactance value is changed, the azimuth angle of the antenna unit 1 changes.

  The distributor 3 distributes the reception signal supplied from the excitation element 10 to the reception unit 5 and the power detection circuit 6. The transmission unit 4 encodes and modulates data supplied from the communication control unit 8 and outputs the data to the antenna unit 1. The receiving unit 5 demodulates and decodes the received signal supplied from the distributor 3 and supplies the demodulated signal to the communication control unit 8.

  The power detection circuit 6 is a circuit that detects the power level (power value) of the reception signal supplied from the distributor 3. As the power detection circuit 6, various known circuits for detecting the power of a radio signal can be used. For example, the power detection circuit 6 has a circuit configuration including a diode detector. A power value signal indicating the power value detected by the power detection circuit 6 is supplied to the direction detection unit 7 via an AD conversion circuit (not shown).

  The direction detection unit 7 detects the direction of the wireless tag 400 based on the power value signal supplied from the power detection circuit 6 while controlling the variable reactance circuit 18. The configuration and operation of the direction detection unit 7 will be described in detail later.

  The communication control unit 8 controls the transmission unit 4 and the reception unit 5, transmits data from the transmission unit 4, and acquires data from the wireless tag 400 received by the reception unit 5. FIG. 4 is a block diagram illustrating the detailed configuration of the transmission unit 4 and the reception unit 5. As illustrated in FIG. 4, the transmission unit 4 includes a coding unit 41, a modulation unit 42, and an amplification unit 43.

  The encoding unit 41 encodes the signal supplied from the communication control unit 8. The modulation unit 42 converts a signal encoded by the encoding unit 41 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 43 amplifies the signal modulated by the modulation unit 42. The amplified signal is transmitted as a radio wave from the antenna unit 1.

  The reception unit 5 includes a demodulation unit 51, a decoding unit 52, and a carrier sense unit 53. The carrier sense unit 53 detects the reception power level in the communication channel before transmission, and if the reception power level is equal to or greater than the threshold, the carrier sense unit 53 forgoes transmission on the channel and performs carrier sense again. If it is below the threshold value, it is determined that transmission is possible and transmission is started. Note that the wireless tag reader / writer 100 of this embodiment performs communication using radio waves in a frequency band normally used in RFIDs such as 2.45 GHz, 900 MHz, and 433 MHz. The demodulator 51 demodulates the received signal. The demodulated signal is encoded by the decoding unit 52, and the encoded signal is sent to the communication control unit 8.

  Next, the configuration of the wireless tag 400 will be described. FIG. 5 is a diagram illustrating a configuration of the wireless tag 400. As shown in FIG. 5, the wireless tag 400 includes an antenna unit 410, a control unit 420, a transmission unit 430, and a reception unit 440. The wireless tag 400 is an active tag and also includes a built-in power source 460. The control unit 420 includes a memory 422 and a timer 424. The transmission unit 430 includes a code unit 432 that generates a code, a modulation unit 434 that modulates the code, and an amplification unit 436 that amplifies the modulated signal. The receiving unit 440 includes a demodulating unit 444 that demodulates a received signal, a decoding unit 442 that decodes a code from the demodulated received signal, and a carrier sense unit 446 that sets communication when transmission / reception with a wireless tag reader / writer is started.

  The antenna unit 410 includes three first to third tag antennas 412, 414, and 416 whose polarization planes are orthogonal to each other. FIG. 6 is a diagram conceptually illustrating the arrangement of the three tag antennas 412, 414, and 416 in the wireless tag 400. As shown in FIG. 6, the three tag antennas 412, 414, and 416 are all the same linear antennas in this embodiment, and are arranged so as to be orthogonal to the other two tag antennas. .

  Returning to FIG. 5, the control unit 420 of the wireless tag 400 is periodically activated by the timer 424, or when the vibration sensor is provided in the wireless tag 400, the period after the vibration is detected by the vibration sensor. Is activated to determine whether or not data from the wireless tag reader / writer 100 can be received. If it can be received, a response signal is transmitted to the wireless tag reader / writer 100. After communication with the wireless tag reader / writer 100 is established, the wireless tag reader / writer 100 is sequentially connected to the wireless tag reader / writer 100 using the first, second, and third tag antennas 412, 414, and 416 in accordance with instructions from the wireless tag reader / writer 100. Send data. The wireless tag reader / writer 100 detects the direction of the wireless tag 400 using this data transmitted by the wireless tag 400.

  Next, the configuration of the direction detection unit 7 of the wireless tag reader / writer 100 will be described. FIG. 7 is a diagram illustrating the configuration of the direction detection unit 7 in detail. The direction detection unit 7 includes a CPU, a ROM, a RAM, and the like (all not shown), and the CPU executes a program stored in the ROM while using a temporary storage function of the RAM, whereby FIG. It functions as each part 72-77 shown in below.

  The storage device 71 is a nonvolatile storage device and stores a reference pattern. The reference pattern is a reference power intensity pattern for calculating a correlation with a power intensity pattern described later. An example of this reference pattern is shown in FIG. The reference pattern is a power intensity pattern when vertical polarization is received in an ideal environment (an environment where there is no shielding object such as a human body or other objects). In the example of FIG. 8, the antenna unit 1 can take the reference pattern. It consists of the received electric field strength at five consecutive directivity angles α (α = −60 degrees, −30 degrees, 0 degrees, 30 degrees, 60 degrees) of the directivity angles. The storage device 71 also stores a weight coefficient W (θ) described later.

  The variable reactance control unit 72 refers to a digital voltage value stored in a memory (not shown) and converts the digital voltage value into an analog bias voltage value using six built-in DA converters (not shown). The bias voltage value is output as reactance value signals C11 (θ) to C16 (θ) to the variable reactance circuits 18A to 18F. The digital voltage values are stored for a plurality of directional beam patterns that form a beam at a plurality of preset directional angles (in this embodiment, every 30 ° from 0 ° to 330 °). The variable reactance control unit 72 functions as directivity switching means in the claims, and switches the reactance value signals C11 (θ) to C16 (θ) to change the directional beam pattern from 0 ° to 330 °. The directivity angle is sequentially changed by 30 °. FIG. 9 is a diagram schematically showing the directivity patterns sequentially formed by sequentially changing the directivity angles in this way.

  The digital voltage value stored in the memory is a value obtained in advance based on experiments. For example, by reducing the capacitance value of the variable capacitance diode of the variable reactance circuit 18A, the variable reactance circuit 18A having a capacitor property becomes a shortening capacitor, and the electrical length of the non-excitation element 11 becomes shorter than that of the excitation element 10 and is thus introduced. Work as a waver. On the other hand, by increasing the capacitance value of the variable capacitance diode of the variable reactance times 18B to 18F, the variable reactance circuits 18B to 18F have inductance properties, the variable reactance circuits 18B to 18F become extension coils, and the non-exciting elements 12 to 16 Becomes longer than the excitation element 10 and acts as a reflector. In this way, the variable reactance control unit 72 can be adjusted so that the directivity angle of the antenna unit 1 is in the direction of the excitation element 11 in the 0 degree direction.

  The power pattern generation unit 73 is supplied from the power detection circuit 6 at each directivity angle when the variable reactance control unit 72 changes the directivity angle of the antenna unit 1 for one period, that is, from 0 ° to 330 °. A power intensity pattern is generated using the power value. This power intensity pattern is a set of directivity angles from 0 ° to 330 ° and power strengths at these directivity angles. As described above, the wireless tag 400 includes the three tag antennas 412, 414, and 416, and the wireless tag 400 receives signals of the same strength from the three tag antennas 412, 414, and 416, respectively. Send. The power pattern generation unit 73 generates a power intensity pattern for each signal transmitted from each tag antenna 412, 414, 416. FIG. 10 shows an example of the power intensity pattern generated in this way.

  The reflector processing unit 74 corresponds to the pattern correction unit in the claims, and the power intensity pattern for each tag antenna generated by the power pattern generation unit 73 is used to indicate the presence of a radio wave reflector around the wireless tag reader / writer 100. A correction process is performed according to the situation. Specifically, this correction processing is performed by using the weighting factor W (θ) for each directivity angle determined according to the distance and material of the radio wave reflector around the wireless tag reader / writer 100 to determine the power at each directivity angle θ of the power intensity pattern. It is a process that multiplies strength. Specific weighting factors in the reflector processing unit 74 will be described later.

  The correlation processing unit 75 calculates a correlation error Γ as a value indicating the correlation between the power intensity pattern processed by the reflector processing unit 74 and the reference pattern stored in the storage device 71. This correlation error Γ is calculated for the power intensity patterns of the three tag antennas 412, 414, and 416, respectively. Details of the method for calculating the correlation error Γ will be described later.

  The direction detection signal selection unit 76 determines the minimum value of the correlation errors Γ calculated for the three tag antennas 412, 414, and 416 in the correlation processing unit 75, and the power intensity pattern corresponding to the minimum value is determined. The signal is selected as a signal used for direction finding.

  The direction estimation unit 77 estimates the direction of the wireless tag 400 using the power intensity pattern selected by the direction detection signal selection unit 76. In this embodiment, the maximum power method is used for this direction estimation. That is, the direction in which the signal intensity is maximum in the selected power intensity pattern is estimated as the direction of the wireless tag 400.

  Next, processing in the reflector processing unit 74 will be described in detail. As described above, the reflector processing unit 74 multiplies the power intensity at each directivity angle of the power intensity pattern by the weighting factor for each directivity angle determined according to the distance and material of the radio wave reflector around the wireless tag reader / writer 100. . For example, as shown in FIG. 11, the weighting factor will be described by taking as an example a case where the wireless tag reader / writer 100 is installed adjacent to a house.

  In the example shown in FIG. 11, a house that is a radio wave reflector exists on the back side of the wireless tag reader / writer 100. In this case, as shown in the figure, even if there is an intruder (wireless tag 400) in the 30 degree direction, not only when the directivity angle is set in the 30 degree direction, but also other angles (for example, 330 degrees) When the directivity angle is set to), the received power intensity may be increased. Therefore, in order to reduce the influence of radio wave reflection from the radio wave reflector, a weighting factor that is smaller as the radio wave reflection from the radio wave reflector is larger is set for the direction in which the radio wave reflector is present.

  FIG. 12 is an example of the weighting coefficient list in the arrangement environment of FIG. 11, while the direction where there is no reflection obstacle is set to 1, the weighting coefficient W (θ) is 1, while the direction where there is a reflection obstacle (in this example, 210 degrees). ˜330 degrees) is made smaller than 1. Here, 0.2 is set because the house is a highly reflective object. If the reflector is a large building, a smaller coefficient, for example, 0.15 is set. The weighting factor W (θ) is set by manual operation when the wireless tag reader / writer 100 is installed, for example.

  Next, the direction detection process performed by the direction detection unit 7 will be described with reference to the flowchart shown in FIG. In the description of this flowchart, the processing of the power pattern generation unit 73, the correlation processing unit 75, the direction detection signal selection unit 76, and the direction estimation unit 77 will also be described.

  First, in step S32, a reference pattern P (α) [α = −60, −30, 0, 30, 60] is set. In the subsequent step S34, the direction-specific weighting coefficient W (θ) [θ = 0, 30, 60... 330] is set. These are initial settings, S32 is set in the wireless tag reader / writer 100 at the manufacturing stage, and S34 is set when the wireless tag reader / writer 100, which is a component device of the monitoring system, is installed.

  The wireless tag reader / writer 100 waits in a state where it can receive a signal from the wireless tag 400 while periodically transmitting a command (S36). When receiving a command from the wireless tag reader / writer 100, the wireless tag 400 transmits a communication establishment request frame shown in FIG. If the wireless tag reader / writer 100 receives this transmission, step S36 becomes YES. In this case, in step S38, the measurement angle θ is set to 0 degree. In step S38, the wireless tag reader / writer 100 transmits an ACK frame shown in FIG. 15B to the wireless tag 400.

  In subsequent step S40, the variable reactance control unit 72 switches the directivity of the antenna unit 1 to the measurement angle θ. Subsequently, a command is sent to the wireless tag 400, and processing for receiving data from the wireless tag 400 is performed (S42).

  When the wireless tag 400 receives the command transmitted by the wireless tag reader / writer 100 in step S42, the wireless tag 400 uses the first tag antenna 412, the second tag antenna 414, and the third tag antenna 416 in order, as shown in FIG. Data of the data frame shown in c) is transmitted from each antenna. Note that the data frame shown in FIG. 15C includes an antenna number, and the RFID tag reader / writer 100 can determine which tag antenna the data frame is transmitted from, based on the antenna number included in the data frame. It is like that.

  If step S42 is performed, it will be judged whether the data reception from the wireless tag 400 was received (S44). If there is reception (S44: Yes), the antenna number β is read from the reception data, and the received power Y (θ) measured when the directivity of the antenna unit 1 is set to the azimuth angle θ is obtained. The reception radio wave intensity at the time of data reception is set (S46).

  On the other hand, when there is no reception from the wireless tag 400 (S44: No), a preset minimum value is set as the reception power Y (θ) (S48). Then, the measurement angle θ is increased by 30 degrees (S50), and it is determined whether the measurement angle is 360 degrees or more, that is, whether the measurement of the received radio wave intensity at all angles from 0 degrees to 330 degrees is completed (S52), Until the measurement is completed (S52: No), the process returns to S40. The time required to transmit the data frame shown in FIG. 15C once is received at each azimuth angle θ by repeating steps S40 to S52 and changing the azimuth angle θ from 0 degrees to 330 degrees. The time is set longer than the time required to measure the radio field intensity.

  The determination in step S52 is a determination of completion of measurement of received radio wave intensity for one tag antenna. If YES in step S52, it is determined in step S53 whether the measurement of the received radio wave intensity has been completed for one set of tag antennas, that is, the three tag antennas 412, 414, and 416. Also when this determination is NO, the process returns to step S40. On the other hand, if this determination is YES, a correlation error Γ (θ, β) is calculated in step S100 of FIG. Details of step S100 will be described later.

  After calculating the correlation error Γ (θ, β), in step S54, the power intensity pattern of the tag antenna with the smallest correlation error Γ is selected as a signal used for direction detection. In step S56, the direction in which the signal intensity is maximum in the power intensity pattern selected in step S54 is estimated as the direction of the wireless tag 400, the estimated direction is output to the controller 300, and the process ends.

  Note that the wireless tag reader / writer 100 periodically estimates the direction of the wireless tag 400 even after performing the direction estimation in step S56. At that time, radio waves mainly including vertically polarized waves are acquired by one of the following two methods. The first method designates the tag antenna selected in step S54, and causes the wireless tag 400 to transmit a signal using only the designated tag antenna. The second is a method for determining whether the radio wave is used for direction estimation from the antenna number included in the received data.

  FIG. 16 is a detailed flowchart of the correlation error calculation process in step S100 of FIG. First, in step S102, the measurement angle θ is set to 0 degree, and the antenna number β is set to “1” corresponding to the first tag antenna 412.

  In step S104, the value of the error function Γ (θ, β) is set to 0 (initial value). In the subsequent step S106, the angle α in the reference pattern is set to −60 degrees (initial value). In the subsequent step S108, the correlation error Γ (θ) is updated using the following equation.

Γ (θ, β) = Γ (θ, β) + | P (α) −Y (θ−α, β) × W (θ) |
P (α) is the power intensity Y (θ, β) at the reference pattern angle α, the radio wave 400 is transmitted by the tag antenna β, and the directivity of the antenna unit 1 is set to the azimuth angle θ. Received power intensity at the time of reception In the above equation for calculating the correlation error Γ (θ), the absolute value symbols mean correlation errors at angles θ and α. Further, the received power intensity Y (θ−α, β) is multiplied by a weighting factor W (θ). The weight coefficient W (θ) is set with reference to the weight coefficient list stored in the storage device 71. By multiplying by the weighting factor W (θ), the correction considering the reflection from the radio wave reflector is performed on each received power intensity Y (θ−α, β).

  In the subsequent step S110, 30 degrees is added to the angle α. In step S112, it is determined whether the angle α is greater than 60 degrees. In this determination, all the correlation errors of the angle α = −60 degrees to 60 degrees are added to determine whether the calculation is completed. If step 112 is NO, the process returns to step S108, and if YES, the process proceeds to step S114.

  In step S114, the correlation error Γ (θ, β) is obtained using the following equation.

Γ (θ, β) = Γ (θ, β) × 5 / (Σ (W (θ))
In subsequent step S116, 30 degrees is added to the azimuth angle θ, and in step S118, whether the azimuth angle θ exceeds 330 degrees, that is, whether the calculation of the correlation error Γ (θ) at all angles from 0 degrees to 330 degrees is completed. to decide. If step S118 is NO, the process returns to S104, and the correlation error Γ (θ, β) at the next azimuth angle θ is calculated. On the other hand, if step S118 is YES, 1 is added to β in step S120. In step S122, it is determined whether or not β exceeds 3. If β does not exceed 3 (S122: NO), θ is set to 0 degrees in step 124, and then the process returns to step S104. On the other hand, if β exceeds 3 (S122: YES), the process is terminated.

  The effect of this embodiment configured as described above will be described. FIG. 17 shows the power of the wireless tag reader / writer 100 when the wireless tag 400 transmits data in order by the first tag antenna 412, the second tag antenna 414, and the third tag antenna 416 in a state where there is no radio wave shielding by the human body. The electric power detection value detected by the detection circuit 6 is shown. Note that, during the detection of the power detection value in FIG. 17 and the next FIG. 18, the wireless tag reader / writer 100 sequentially switches the measurement angle θ as described with reference to FIG.

  As shown in FIG. 6, the first to third tag antennas 412, 414, 416 of the wireless tag 400 are arranged in directions orthogonal to each other. Therefore, one of the tag antennas transmits radio waves mainly composed of vertical polarization, and one of the remaining two tag antennas transmits radio waves mainly composed of horizontal polarization. For example, the third tag antenna 416 transmits vertical polarization, and the second tag antenna 414 transmits horizontal polarization. On the other hand, the antenna unit 1 of the wireless tag reader / writer 100 has good reception sensitivity with respect to vertical polarization. Therefore, as shown in FIG. 17, the power detection value is highest when receiving a radio wave from the third tag antenna 416 that transmits a radio wave with vertical polarization, and the radio waves from the first and second tag antennas 412 and 414 are received. The power detection value when receiving is low.

  However, since the wireless tag 400 is carried by a person, radio waves may be shielded by the human body. When the human body is shielded, the vertical polarization is shielded to a greater extent than the horizontal polarization. As a result, when there is a human body shield, as shown in FIG. To be high. In the example of FIG. 18, the third tag antenna 416 transmits radio waves with vertical polarization and the second tag antenna 414 transmits radio waves with horizontal polarization, as in FIG. However, since there is a human body shield, the power detection value of the radio wave received by the RFID tag reader / writer 100 is greater when the radio wave from the second tag antenna 414 is received than when the radio wave from the third tag antenna 416 is received. Even the overall is high.

  FIG. 19 is a diagram illustrating gain when the wireless tag reader / writer 100 receives radio waves transmitted by the tag antennas 412, 414, and 416 in a state where a human body is shielded. As shown in FIG. 19, in the state where the human body is shielded, the horizontal gain of the second tag antenna 414 that transmits the horizontally polarized wave has a relatively high value. As a result, the second tag antenna 414 has the highest combined gain shown in the bottom column of this figure. Therefore, the power detection value detected by the power detection circuit 6 is highest when the radio wave of the second tag antenna 414 is received as shown in FIG.

  In addition, FIG. 20 is a diagram illustrating the directivity of the antenna unit 1 of the wireless tag reader / writer 100. The directivity of the antenna unit 1 is relatively sharp with respect to vertical polarization. (Left figure) Wide directivity with respect to horizontal polarization. Therefore, if a horizontally polarized wave is used as the radio wave transmitted by the wireless tag 400, there is a possibility that accurate direction detection cannot be performed. In addition, since the wireless tag 400 does not know in what direction it is carried by a person, it does not know which tag antennas 412, 414, 416 transmit vertically polarized waves.

  Here, as can be seen from FIG. 18 described above, even when the human body is shielded, the shape of the power intensity pattern is the same as that when no human body is shielded. That is, even when the human body is shielded, the power detection value when receiving the radio wave transmitted by the third tag antenna 416 has a pattern that peaks when the directivity is in the direction in which the wireless tag 400 exists. . On the other hand, the power detection value when the radio wave transmitted by the second tag antenna 414 is received does not have a pattern reflecting directivity switching.

  Focusing on this, in this embodiment, the correlation value (specifically, correlation error Γ) between the power intensity pattern of each tag antenna and the reference pattern is calculated. The reference pattern is a power intensity pattern in a case where vertical polarization is received when the antenna unit 1 sequentially switches the directivity in an ideal environment. Therefore, the correlation error Γ indicating the correlation between the reference pattern and the received power intensity pattern of the radio wave received from each tag antenna 412, 414, 416 is a large value when the received radio wave mainly includes horizontal polarization. . In this embodiment, since the power intensity pattern that minimizes the correlation error Γ is selected as the direction estimation pattern, the selected pattern is a pattern when radio waves mainly including vertical polarization are received. There is a high possibility. Therefore, the direction detection of the wireless tag 400 can be performed with high accuracy.

  In addition, in the present embodiment, for the angle at which the radio wave reflector exists around the RFID tag reader / writer 100, a weighting factor W (θ) that is smaller as the reflection from the radio wave reflector is larger is set. The power coefficient Y (θ) of each power intensity pattern is multiplied by the weighting coefficient W (θ) (S108). Therefore, the power intensity pattern composed of each power intensity Y (θ) after being multiplied by the weight coefficient W (θ) is a pattern in which the influence of reflection from the radio wave reflector is reduced. The correlation error Γ is a correlation error between the power intensity pattern composed of each power intensity Y and the reference pattern after being multiplied by the weighting coefficient W (θ). Therefore, even if there is a radio wave reflector around the wireless tag reader / writer 100, the correlation error Γ is a value that reflects the difference in polarization of the received radio wave because the influence of the reflection from the radio wave reflector is reduced. Become. Therefore, selection of horizontally polarized radio waves can be further suppressed.

[Second Embodiment]
A wireless tag reader / writer 100 according to a second embodiment will be described with reference to FIGS. FIG. 21 is an explanatory diagram when the wireless tag reader / writer 100 according to the second embodiment detects the direction of the wireless tag 400 of the intruder.

  The wireless tag reader / writer 100 of the first embodiment is attached to the front of a house, and only the house is present as a radio wave reflector. On the other hand, in the second embodiment, there is a block wall that reflects radio waves in the monitoring area of the wireless tag reader / writer 100 on the front side of the house. Therefore, in the second embodiment, as in the first embodiment, the weighting factor W (θ) in the direction of the house is set to a small value, and the weighting factor W (θ) in the direction of the block wall is also set to a small value. To do.

  FIG. 22 is a weighting coefficient list in the second embodiment. As in the first embodiment, the weighting factor W (θ) in the direction (210 ° to 330 °) where the house is a radio wave reflector is set to 0.2, and there is a block wall that is a radio wave reflector. The weighting coefficient W (θ) of the direction (30 ° to 150 °) is set to 0.4, 0.6, and 0.8 depending on the reflection angle and distance. Further, the weighting factor W (θ) is set to 1 in the direction where there is no reflection obstacle (0 degrees, 180 degrees). When a hedge is installed instead of the block wall, the radio wave reflectance is smaller than that of the block wall, so the weighting factor W (θ) is set to a large value such as 0.5 to 0.9, for example.

[Third embodiment]
A monitoring system according to a third embodiment will be described with reference to FIGS. In the first and second embodiments, the weighting factor W (θ) for reducing the influence of the radio wave reflector is stored in the storage device 71 by manual operation when the wireless tag reader / writer 100 is installed. On the other hand, in the third embodiment, a radio wave reflector is detected and the weight coefficient W (θ) is automatically determined.

  FIG. 23 is an explanatory diagram when the wireless tag reader / writer 100 according to the third embodiment detects the direction of the wireless tag 400 of the intruder. In the third embodiment, when the truck is stopped in front of the house in the monitoring area, this is detected by the laser sensor 200 (see FIG. 1), and the controller 300 is used to reduce the influence of radio wave reflection by the truck. Automatically sets the weighting coefficient W (θ) to the wireless tag reader / writer 100. Here, the weighting factor W (θ) when the truck is not stopped is the weighting factor W (θ) in the housing direction (210 ° to 330 °) as in the first embodiment described above with reference to FIG. ) Is set to 0.2.

  FIG. 24 is a flowchart showing a process in which the controller 300 according to the third embodiment detects a radio wave reflector in the monitoring area and automatically sets the weighting coefficient W (θ) for the wireless tag reader / writer 100.

  The controller 300 (see FIG. 1) of the monitoring system uses the laser sensor 200 to monitor whether a radio wave reflector is in the monitoring area together with the intruder. Here, intruders and radio wave reflectors such as trucks are sized (for example, detected over an angle of 30 degrees or more), and whether or not they can move (are present in the same place for 10 minutes or more). Identify using.

  When there is a radio wave reflector in the monitoring area (S302: Yes), the controller 300 acquires the angle range and distance in which the radio wave reflector exists from the laser sensor 200 (S304). Then, a weighting factor W (θ) is calculated based on the acquired angle range and distance (S306). Specifically, the angle range and distance of the radio wave reflector with respect to the wireless tag reader 100 are first calculated from the direction and distance acquired from the laser sensor 200. Then, the weighting factor W (θ) of the angle range of the radio wave reflector is determined using the calculated distance and the relational expression in which the weighting factor W decreases as the distance increases. Then, the determined weight coefficient W (θ) is set in the wireless tag reader / writer 100 (S308).

  On the other hand, when the radio wave reflector, for example, the truck moves out of the monitoring area and the radio wave reflector is not present in the radio wave monitoring area (S302: No), the weight coefficient W (θ) for the radio wave reflector is canceled. The wireless tag reader / writer 100 is instructed (S310).

  FIG. 25 is a weighting coefficient list in the third embodiment. Here, the weighting factor W in the direction (120 degrees and 150 degrees) of the radio wave reflector (track) detected by the laser sensor 200 is calculated by the controller 300 according to the distance between the wireless tag reader / writer 100 and the track. A weighting factor W (120 degrees: 0.8, 150 degrees: 0.6) is set.

  The monitoring system of the third embodiment automatically adjusts the weighting factor W (θ) according to the angle range and distance of the object detected by the laser sensor 200. For this reason, for example, even when a truck or the like is temporarily parked in the monitoring area of the wireless tag reader / writer 100, this is detected by the laser sensor 200 to eliminate the influence of radio wave reflection by the truck, and the wireless tag 400 The decrease in direction estimation accuracy can be automatically suppressed. In the above-described example, the house direction weighting factor W (θ) is manually set, but the house direction weighting factor W (θ) is also automatically set according to the configuration of the third embodiment. Setting is possible.

[Fourth embodiment]
Next, a fourth embodiment will be described. In the first embodiment, the correction using the weight coefficient W (θ) is performed on the power intensity pattern. On the other hand, in the fourth embodiment, correction using the weighting coefficient W (θ) is performed on the correlation error Γ.

  In this case, step S109 shown in FIG. 26 is executed instead of step S108 in FIG. That is, the correlation error Γ (θ) is updated using the following equation.

Γ (θ, β) = Γ (θ, β) + | {P (α) −Y (θ−α, β)} × W (θ) |
In the above equation, the difference in power intensity is multiplied by a weighting coefficient W (θ), and the difference in power intensity means a correlation error Γ at each (θ, α). Therefore, the above equation corrects the correlation error Γ with the weighting coefficient W (θ). This step S109 corresponds to the correlation value correcting means in the claims.

  As described above, even when the correlation error Γ is corrected by the weighting factor W (θ), the correlation error Γ is reduced in the influence of the reflection from the radio wave reflector, as in the case of correcting the power intensity pattern. The value well reflects the difference in radio wave polarization. Therefore, selection of horizontally polarized radio waves can be further suppressed.

  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 above-described embodiment, the radio waves transmitted and received sequentially from the three tag antennas 412, 414, and 416 are distinguished based on the reception establishment timing of the data frame and the antenna number included in the data frame. However, other than this, the wireless tag reader / writer 100 may instruct a tag antenna to be used for transmission to the wireless tag 400, and the wireless tag 400 may transmit a data frame using the instructed tag antenna. Even in this way, the wireless tag reader / writer 100 can determine which tag antenna has transmitted the received radio wave.

  In the above-described embodiment, the correlation error Γ is calculated as the correlation value. In this case, the larger the value (correlation error Γ), the lower the correlation. However, the present invention is not limited to this, and an index that increases as the correlation increases may be used as the correlation value.

DESCRIPTION OF SYMBOLS 1: Antenna part 3: Divider 4: Transmission part 5: Reception part 6: Power detection circuit 7: Direction detection part 8: Communication control part 10: Excitation element 11-16: Non-excitation element 17: Ground conductor 18: Variable reactance Circuit 19: Coaxial cable 41: Encoding unit 42: Modulating unit 43: Amplifying unit 51: Demodulating unit 52: Decoding unit 53: Carrier sensing unit 71: Storage device 72: Variable reactance control unit 73: Power pattern generation unit 74: Reflector Processing unit (pattern correction means) 75: correlation processing unit 76: direction detection signal selection unit 77: direction estimation unit 100: wireless tag reader / writer 200: laser sensor 300: controller 400: wireless tag 410: antenna unit 412: first tagant 414: Second tag antenna 416: Third tag antenna 420: Control unit 422: Memory 424: Timer 430: Transmission unit 432: Encoding unit 434: Modulation unit 436: Amplification unit 440: Reception unit 442: Decoding unit 444: Demodulation Part 446: career sense part

Claims (6)

An array antenna configured to switch the directivity in the horizontal plane with respect to the vertical polarization to a plurality of set angles;
Directivity switching means for sequentially switching the directivity of the array antenna to a plurality of set angles;
Radio waves received from radio tags that transmit radio waves from a plurality of tag antennas whose polarization planes are orthogonal to each other are received by the array antenna while the directivity is switched by the directivity switching means. A wireless tag reader that estimates the arrival direction of
Reception intensity measuring means for measuring the power intensity received by the array antenna;
For each tag antenna that is the power intensity for one period of the set angle received from each tag antenna from the power intensity measured by the reception intensity measuring means while the directivity switching means sequentially switches the directivity of the array antenna. Power intensity pattern determining means for determining the power intensity pattern of
Reference pattern storage means for storing a reference pattern that is a standard power intensity pattern when the array antenna receives vertical polarization;
Correlation value calculating means for calculating a pattern correlation value representing the correlation between the power intensity pattern determined by the power intensity pattern determining means and the reference pattern for each tag antenna;
Of the radio waves received from the plurality of tag antennas, the radio wave having the highest correlation among the pattern correlation values for each tag antenna calculated by the correlation value calculation means, A wireless tag reader, comprising: selecting means for selecting. In claim 1,
A weight that is determined for each set angle based on the surrounding environment where the RFID tag reader is installed, and for the angle at which the radio wave reflector is present, a weight that sets a smaller weight as the reflection from the radio wave reflector increases. Setting means;
Pattern correction means for correcting the power intensity in the power intensity pattern of each tag antenna determined by the power intensity pattern determination means using the weight set by the weight setting means,
The wireless tag reader, wherein the correlation value determining means calculates the pattern correlation value using the power intensity pattern corrected by the pattern correcting means and the reference pattern. In claim 1,
The correlation value determining means calculates the pattern correlation value using the power intensity pattern determined by the power intensity pattern determining means and the reference pattern,
A weight that is determined for each set angle based on the surrounding environment where the RFID tag reader is installed, and for the angle at which the radio wave reflector is present, a weight that sets a smaller weight as the reflection from the radio wave reflector increases. Setting means;
Correlation value correcting means for correcting the pattern correlation value of each tag antenna determined by the correlation value determining means using the weight set by the weight setting means,
The radio tag reader according to claim 1, wherein the selection unit selects a radio wave to be used for estimating an arrival direction based on a pattern correlation value of each tag antenna corrected by the correlation value correction unit. In claim 2 or 3,
The weight set by the weight setting means is a value correlated with at least one of the distance between the array antenna and the radio wave reflector and the radio wave reflectivity of the radio wave reflector. Wireless tag reader. In claim 4,
The weight set by the weight setting means is a value correlated with the distance between the array antenna and the radio wave reflector, and is set to a smaller value as the distance is shorter. . A monitoring system comprising: a laser sensor that sequentially measures a distance and a direction of an object in a monitoring area; and the wireless tag reader according to claim 5 including the monitoring area as a communication range,
The wireless tag reader is
The distance and direction of the object detected by the laser sensor can be obtained sequentially,
The weight set by the weight setting means is a value corresponding to the distance of the object sequentially acquired from the laser sensor with respect to a set angle determined based on the direction of the object sequentially acquired from the laser sensor. A monitoring system characterized by

Images