JP5668658B2 - Wireless tag direction detection system - Google Patents

Description

  The present invention relates to a wireless tag direction detection system in which a wireless tag reader detects the direction of a wireless tag, and more particularly to a technique for determining a communication channel through which a wireless tag and a wireless tag reader communicate.

  A variable directivity antenna that can change directivity is known. For example, Patent Document 1 discloses an array antenna that includes an excitation element and a plurality of non-excitation elements arranged around the excitation element, and can control directivity by controlling the reactance value of the non-excitation element. When a variable directivity antenna is used, the direction of arrival of radio waves can be estimated by measuring a signal arriving at the antenna with a plurality of directivity patterns. Therefore, a wireless tag direction detection system has been proposed in which this variable directional antenna is mounted on a wireless tag reader to detect the direction of the wireless tag.

Japanese Patent No. 3836080

  The wireless tag reader in the wireless tag direction detection system includes a communication antenna for exchanging data with the wireless tag, in addition to the variable directivity antenna for performing direction detection.

  In addition, since communication cannot be performed when communication channels are different, the wireless tag and the wireless tag reader need to perform communication through the same communication channel. In addition, if there is only one communication channel, communication may not be possible when there is a lot of noise in the channel, so the wireless tag and wireless tag reader can be switched to a plurality of communication channels. If the channel used for communication is noisy and communication is not possible, the channel is changed to another communication channel with less noise for communication.

  In order to ensure communication using the changed channel, it is necessary to check which channel is a channel with less noise before changing the channel used for communication. For this purpose, the noise intensity must be measured in a plurality of candidate channels before the channel used for communication is changed. Here, the process for this is called a change channel determination process.

  In the change channel determination process, it is necessary to switch to a channel as a change candidate and measure the reception level for a certain period of time. However, in order to perform the change channel determination process, of course, an antenna is required to receive radio waves.

  As the antenna, either a communication antenna or a direction detection antenna (variable directivity antenna) can be used. However, each of these antennas is intended for communication with the wireless tag and determination of the arrival direction of radio waves, and the channel cannot be changed during reception and reception standby for that purpose. It cannot be used as an antenna. In addition, these communication antennas and direction finding antennas are always receiving or waiting for reception for the original purpose of these antennas.

  More specifically, since it is unknown when data is transmitted from the wireless tag, a communication antenna intended to communicate with the wireless tag must always be in a reception standby state. Further, the direction detecting antenna needs to change the directivity when receiving the data of the wireless tag, but as described above, it is not known when the data of the wireless tag is transmitted. Therefore, in preparation for the possibility of data being transmitted from the wireless tag, data reception processing is always performed while changing the directivity.

  For these reasons, in the conventional RFID tag direction detection system, it is necessary to add an antenna for noise detection so that the noise of the channel to be changed can be confirmed before the channel is changed. However, as a matter of course, adding an antenna increases the cost, which is not preferable.

  The present invention has been made based on this situation, and an object of the present invention is to provide a RFID tag direction detection system that can search for a communication channel with less noise without adding an antenna for noise detection. It is to provide.

In order to achieve the object, the invention according to claim 1
(A) a wireless tag that is carried by a person and can be switched to a plurality of communication channels, and that selects one communication channel from the plurality of communication channels and sequentially transmits radio waves;
(B) A communication antenna that transmits and receives data to and from the wireless tag, and a direction detection antenna that receives data transmitted from the wireless tag while changing directivity, and is received by the direction detection antenna. A wireless tag reader that detects the direction of the wireless tag using the recorded data,
A wireless tag direction detection system including:
(A1) The wireless tag periodically transmits trigger data on a preset fixed channel during activation,
(B) The wireless tag reader is
(B1) Communication channels of the communication antenna and the direction detection antenna can be set separately from each other from a plurality of channels that can communicate with the wireless tag,
(B2) The communication antenna is placed in a data reception standby state on the fixed channel until the trigger data is received.
(B3) While the communication antenna is in a data reception standby state, the communication channel of the direction detection antenna is used as a candidate channel that is a candidate of a communication channel that receives data for direction detection. The direction detection channel that is a communication channel for receiving data for direction detection is determined by measuring and comparing the measured noise intensity with the noise tolerance threshold or the noise intensity measured in another candidate channel. Execute direction detection channel decision processing,
(B4) When the trigger data is received by the communication antenna, channel designation data for designating a direction detection channel determined by the direction detection channel determination process is transmitted from the communication antenna through the fixed channel, and then The communication channel of the communication antenna is also in the data reception standby state as the direction detection channel,
(B5) A communication channel of the direction detection antenna is also used as the direction detection channel, and direction detection data acquisition processing for performing data reception while sequentially switching the directivity of the direction detection antenna is performed.
(A2) When the wireless tag receives the channel designation data from the wireless tag reader, the wireless tag transmits direction detection data that the wireless tag reader can perform direction detection using the communication channel designated by the channel designation data,
(B6) The wireless tag reader, after determining the end of reception of the direction detection data using the radio wave received by the communication antenna, ends the direction detection data acquisition process using the direction detection antenna, The direction detection channel determination process is resumed.

  Conventionally, as described above, since the direction detection data is not transmitted from the wireless tag, the wireless tag reader always performs the direction detection data acquisition process using the direction detection antenna and performs communication. The antenna was in a data reception standby state.

  On the other hand, in the present invention, the wireless tag transmits the direction detection data when the channel designation data is received, and the channel designation data is transmitted by the wireless tag reader. In other words, in the present invention, the wireless tag does not transmit the direction detection data unless the wireless tag reader transmits the channel designation data.

  In the present invention, since the wireless tag reader transmits the channel designation data when the trigger data is received from the wireless tag, the wireless tag reader is in a reception standby state in which the wireless tag reader can receive the trigger data transmitted by the wireless tag. It is necessary to keep. In order to enable direction detection decision processing even in this reception standby state, the communication channel of the communication antenna and the communication channel of the direction detection antenna can be set separately, and only the communication antenna can be used for transmitting trigger data. A fixed channel set as a channel to be used is set in a reception standby state. Thus, the direction detecting antenna does not need to be in a reception standby state in order to receive data from the wireless tag. Therefore, while the communication antenna is in the reception standby state, the direction detection channel determination process is performed in which the direction detection channel is determined by measuring the noise intensity with the direction detection channel candidate channel using the direction detection antenna. Can do.

  Since the direction detection channel determined in this direction detection channel determination process is specified in the channel specification data transmitted to the wireless tag after receiving the trigger data, the direction detection data transmission / reception has been performed until immediately before. This can be performed using the direction detection channel determined by the detection channel determination process. Therefore, transmission / reception of direction finding data can be performed using a communication channel suitable for transmission / reception of direction finding data without adding an antenna separately.

  Note that the direction detection data may be data for the purpose of only direction detection. However, the data content is not particularly limited in direction detection, and therefore data necessary for control is transmitted as the direction detection data. You may do it.

  In the above-described direction detection channel determination processing, for example, the direction detection channel can be determined by comparing noise intensities measured in a plurality of candidate channels.

In the invention according to claim 2, the wireless tag reader is
When it can be determined that the wireless tag does not exist within the communication range of the wireless tag reader, the candidate channels for measuring the noise intensity in the direction detection channel determination process are all settable communication channels, and for each candidate channel , Performing an all-channel omnidirectional measurement process for measuring noise intensity in all set azimuths within the direction detection range, and determining the direction detection channel based on a comparison of noise intensity in all candidate channels,
When the wireless tag can be determined to be within the communication range of the wireless tag reader, the direction detection channel determination process executed when the communication antenna enters the data reception standby state limits the candidate channels for measuring the noise intensity. The direction detection channel is determined by executing the limited channel noise measurement process,
In this limited channel noise measurement process, for the direction detection channel determined in the previous direction detection channel determination process, the noise intensity is measured in all setting directions within the direction detection range, and the measured noise intensity in all setting directions is the noise level. If the allowable threshold is not exceeded, the previous direction detection channel is determined as the current direction detection channel,
If there is an azimuth that exceeds the noise tolerance threshold among the noise intensities measured in all settings, only the communication channel adjacent to the communication channel that measured the noise intensity in all settings and this time, The noise intensity is measured only for the setting direction with the highest noise intensity in the communication channel for which the noise intensity is measured. The noise intensity measured in the communication channel is compared, and the communication channel with the lowest noise intensity is updated as the direction detection channel.

  When the wireless tag does not exist within the communication range of the wireless tag reader, the wireless tag reader does not need to perform the direction detection of the wireless tag, so that there is sufficient time for determining the direction detection channel. Therefore, when it can be determined that the wireless tag does not exist within the communication range of the wireless tag reader, an all-channel omnidirectional measurement process is executed. In this all-channel omnidirectional measurement processing, candidate channels for measuring noise intensity are set as all communication channels that can be set, and the noise intensity is measured for all candidate channels in all setting azimuths within the direction detection range. Therefore, the direction detection channel determined by this all-channel omnidirectional measurement process has high reliability.

  On the other hand, when the wireless tag is within the communication range of the wireless tag reader, the wireless tag reader periodically receives trigger data from the wireless tag. Therefore, when the wireless tag exists in the communication range of the wireless tag reader, direction detection of the wireless tag is frequently performed. Further, the noise intensity may change depending on time. Therefore, even when the wireless tag exists in the communication range of the wireless tag reader, it is necessary to repeat the direction detection channel determination process.

  However, since the direction detection data acquisition process uses a direction detection antenna, the direction detection channel determination process using the same direction detection antenna is performed in a short time between the frequent direction detection data acquisition processes. It must be made.

  Therefore, when it can be determined that the wireless tag is present in the communication range of the wireless tag reader, the direction detection channel is determined by executing limited channel noise measurement processing in which candidate channels for measuring noise intensity are limited. In this limited channel noise measurement process, first, only the direction detection channel determined in the previous direction detection channel determination process measures the noise intensity in all the set orientations within the direction detection range. If the measured noise intensities in all the setting directions do not exceed the allowable noise threshold, the previous direction detection channel is determined as the next direction detection channel at this time. Therefore, in this case, since the channel for measuring the noise intensity is only one channel, the direction detection channel can be determined in a short time.

  In addition, even if there is an azimuth exceeding the noise tolerance threshold among the noise intensities measured in all settings, the noise intensity is additionally measured by the communication adjacent to the communication channel in which the noise intensity in all settings is measured. This is only for the setting direction having the highest noise intensity in the communication channel for which only the channel and the noise intensity of all setting directions has been measured this time. Therefore, also in this case, the direction detection channel can be determined in a short time.

  In addition, the noise intensity is measured in the adjacent communication channel only for the setting direction in which the noise intensity is the highest in the communication channel for which the noise intensity of all setting directions is measured this time. However, the suitability of this communication channel can be determined with a certain degree of accuracy. The reason is as follows.

  Although each channel is separated by a certain frequency range, the frequency range is continuous with the adjacent communication channel. For this reason, it is considered that noise measured in a certain communication channel often affects adjacent channels in which the frequency range is continuous. For this reason, when the change of the noise intensity with respect to the set orientation is graphed, a certain communication channel and a communication channel adjacent thereto have similar graph shapes. Therefore, in the limited channel noise measurement process this time, the setting direction with the highest noise intensity in the channel that measured the noise intensity in all setting directions is the direction with the highest noise intensity in the communication channel adjacent to that channel. I can guess. Therefore, the noise intensity is measured in the adjacent communication channel only for the setting direction in which the noise intensity is the highest in the communication channel in which the noise intensity of all setting directions is measured this time.

  In addition, the direction detection channel determination process can determine the direction detection channel by comparing the noise intensity of the candidate channel with a noise allowable threshold as in the third aspect.

In the invention according to claim 3, the direction detection channel determination process includes:
The communication channel of the direction detection antenna is set as one candidate channel, the noise intensity is sequentially measured in the candidate channel, the measured noise intensity is compared with the noise allowable threshold, and the measured noise intensity is the noise While the allowable threshold is not exceeded, the candidate channel is determined as the direction detection channel,
If the measured noise intensity exceeds the noise tolerance threshold, change the communication channel of the direction detection antenna to another candidate channel, measure the noise intensity, compare with the noise tolerance threshold, and move the candidate channel to the direction. It is a process that repeats the determination of whether or not to determine a detection channel.

It is a figure explaining the system configuration | structure of the RFID tag direction detection system of embodiment of this invention. 1 is a diagram illustrating a configuration of a wireless tag reader 100. FIG. 2 is a diagram showing a configuration of a wireless tag 200. FIG. 4 is a flowchart illustrating a main part of control contents executed by the control unit 110 of the wireless tag reader 100. FIG. 3 is a diagram showing a time flow of data transmission / reception between the wireless tag reader 100 and the wireless tag 200. FIG. 5 is a flowchart showing a direction detection channel determination process started in step S1 of FIG. 4. FIG. It is a figure which shows the time flow of the data transmission / reception with the wireless tag reader and wireless tag in the conventional wireless tag direction detection system. FIG. 5 is a diagram showing processing performed by the wireless tag reader 100 using a direction detecting antenna 150. It is a flowchart which shows the processing content of the noise scan. It is a flowchart which shows the processing content of the omnidirectional noise scan of S22 of FIG. 10 is a flowchart showing details of a direction detection channel determination process in S24 of FIG. It is a flowchart which shows the processing content of the noise scan 2. FIG. It is a flowchart which shows the detail of the specific orientation noise scan of S35 of FIG. It is a flowchart which shows the specific process of the change detection process of the direction detection channel of S37 of FIG. It is the figure which illustrated the noise level with respect to a frequency. It is a graph which shows the change of the noise level with respect to a setting direction.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a system configuration of a wireless tag direction detection system according to an embodiment of the present invention. As shown in FIG. 1, the wireless tag direction detection system of this embodiment includes a wireless tag reader 100 and a wireless tag 200, and also includes a controller 300 shown in FIG.

  The wireless tag 200 is carried by a person and communicates with the wireless tag reader 100. The wireless tag reader 100 receives the radio wave from the radio tag 200 and estimates the arrival direction of the radio wave as the direction of the radio tag 200.

  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 channel control unit 115, a transmission unit 120, a reception unit 130, a communication antenna 140, a direction detection antenna 150, and a direction detection unit 160.

  The control unit 110 transmits a signal to be wirelessly transmitted to the outside to the transmission unit 120 and obtains a signal received by the communication antenna 140 and demodulated / decoded by the reception unit 130 from the reception unit 130. The control unit 110 includes a memory 111 and a timer 112 inside. The memory 111 stores a program executed by the control unit 110, a default channel described later, and the like.

  The channel control unit 115 is connected to the control unit 110, and when the communication channel is designated by the control unit 110, the transmission unit 120 and the reception unit 130 communicate with each other through the designated communication channel. The modulation unit 122 of the receiver and the demodulation unit 131 of the reception unit 130 are controlled. Note that a plurality of channels (for example, 16 channels) can be set as the communication channel.

  The transmission unit 120 includes a coding unit 121, a modulation unit 122, and an amplification unit 123. The encoding unit 121 encodes the command supplied from the control unit 110. As this command, for example, there is a channel transmission instruction command for instructing transmission of a direction detection channel to the wireless tag 200. The direction detection channel is a communication channel for transmitting / receiving data for performing direction detection, and this direction detection channel is determined by a direction detection channel determination process described later. The encoding unit 121 outputs the encoded command to the modulation unit 122. The modulation unit 122 converts the command encoded by the encoding unit 121 into an electrical digital signal, and then performs predetermined modulation such as phase shift keying and frequency shift keying on the communication channel set by the channel control unit 115. Modulate according to the method. The amplification unit 123 amplifies the signal modulated by the modulation unit 122. The amplified signal is transmitted as radio waves from the communication antenna 140.

  The communication antenna 140 is an antenna used for communication (data transmission / reception) with the wireless tag 200, and the radio wave received by the communication antenna 140 is demodulated by the demodulation unit 131. The demodulator 131 also performs demodulation on the communication channel set by the channel controller 115. The demodulated signal is encoded by the decoding unit 132, and the encoded signal is sent to the control unit 110.

  The direction detection antenna 150 is an electronic scanning waveguide array antenna device, and includes one excitation element 151 and six non-excitation elements provided at equal intervals on a circumference centered on the excitation element 151. 152. Both the excitation element 151 and the non-excitation element 152 are arranged vertically on the ground conductor 153. In addition, the excitation element 151 is connected to the power receiving unit 162.

  Furthermore, although not shown, each variable reactance circuit having a variable reactance element is connected to each non-excitation element 152 of the direction detecting antenna 150, and this variable reactance element is controlled by the directivity control unit 161. The reactance value is changed.

  The directivity control unit 161 sets the reactance value of the variable reactance element to a value determined based on the directivity in order to set the directivity of the direction detection antenna 150 to the directivity instructed by the control unit 110.

  The power receiving unit 162 is a circuit that detects the power intensity (reception power intensity) of the received signal received by the excitation element 151 of the direction detecting antenna 150, and various known circuits that detect the power of the radio signal, such as diodes. The circuit configuration includes a detector. The power receiving unit 162 can also be set to the same channel as the transmitting unit 120 and the receiving unit 130. The power receiving unit 162 supplies a signal indicating the detected received power intensity to the control unit 110 via an AD conversion circuit (not shown). The channel control unit 163 is connected to the control unit 110. When a reception channel is designated by the control unit 110, the channel control unit 163 sets the reception channel of the power reception unit 162 to the designated channel.

  The above-described control unit 110 further outputs a signal for instructing directivity to the directivity control unit 161. The directivity control unit 161 changes the directivity of the direction detection antenna 150 by a preset detection range in accordance with a signal from the control unit 110. The detection range is, for example, from 0 to 330 °, and the change in directivity is every predetermined angle, for example, every 30 °.

  Next, the configuration of the wireless tag 200 will be described with reference to FIG. FIG. 3 is a diagram illustrating a configuration of the wireless tag 200. The wireless tag 200 is an active wireless tag and includes a built-in power supply 210. In addition to the built-in power supply 210, the wireless tag 200 includes a channel control unit 215, a transmission unit 220, a reception unit 230, an antenna unit 240, a changeover switch 250, and a control unit 260. Supply.

  The channel control unit 215 is connected to the control unit 260. The channel control unit 215 has the same function as the channel control unit 115 of the wireless tag reader 100. When a communication channel is designated by the control unit 260, the transmission unit 220 and the reception unit 230 communicate with each other through the designated communication channel. The modulation unit 222 of the transmission unit 220 and the demodulation unit 231 of the reception unit 230 are controlled so as to be performed.

  The transmission unit 220 includes a coding unit 221 and a modulation unit 222. The encoding unit 221 encodes data supplied from the control unit 260 and sends the encoded data to the modulation unit 222. The modulation unit 222 modulates the code from the coding unit 221 with a modulation scheme such as amplitude displacement modulation, for example, on the communication channel set by the channel control unit 215. The modulated signal is amplified by an amplifying unit (not shown) and then output to the antenna unit 240.

  The antenna unit 240 includes a first antenna 241 and a second antenna 242, and the first antenna 241 and the second antenna 242 have different antenna angles. Is different. For example, a chip antenna or a pattern antenna is used for each of the first antenna 241 and the second antenna 242, and the angles are different from each other by 90 °.

  A changeover switch 250 is disposed between the antenna unit 240 and the transmission unit 220. The changeover switch 250 is a switch that switches between a state in which the transmission unit 220 or the reception unit 230 is connected to the first antenna 241 and a state in which the transmission unit 220 or the reception unit 230 is connected to the second antenna 242, and the connection state is switched by the control unit 260.

  The signal output from the transmission unit 220 is transmitted to the outside from the antennas 241 and 242 determined according to the conduction state of the changeover switch 250. In addition, radio waves received by the antennas 241 and 242 on the side connected to the receiving unit 230 by the changeover switch 250 are supplied to the receiving unit 230 as electrical signals.

  The receiving unit 230 includes a demodulating unit 231 that demodulates radio waves received by the antenna unit 240 and a decoding unit 232 that decodes a signal demodulated by the demodulating unit 231. The demodulator 231 performs demodulation on the communication channel set by the channel controller 215. The decoding unit 232 supplies the decoded signal to the control unit 260.

  The control unit 260 controls the channel control unit 215, the transmission unit 220, and the reception unit 230. In addition, the control unit 260 includes a timer 261 and a memory 262. The timer 261 measures time by counting clocks of a clock oscillator (not shown). The memory 262 stores ID data of the wireless tag 200 and the like.

  The control unit 260 is periodically activated. And during starting, trigger data is transmitted with a fixed period. This trigger data is always transmitted on a preset default channel (corresponding to a fixed channel in claims). The data content of the trigger data may be any data content as long as the wireless tag reader 100 that has received the trigger data can start the direction detection data acquisition process. For example, it may be a short data including the ID of the wireless tag 200, a command for instructing the start of the direction detection data acquisition process, and a header and a checksum.

  When data transmitted by the wireless tag reader 100 in response to the trigger data is received, the control unit 260 causes the direction detection data to be transmitted instead of periodically transmitting the trigger data. The direction detection data may be any transmission time that is longer than the time required for the direction detection antenna 150 of the wireless tag reader 100 to change the directivity by a preset detection range, and the data content is not particularly limited. Therefore, for example, data necessary for control is transmitted as direction detection data. In the case where the wireless tag 200 includes a vibration sensor, the periodic activation may be limited while the vibration is detected by the vibration sensor.

  FIG. 4 is a flowchart showing a main part of the control content executed by the control unit 110 of the wireless tag reader 100. FIG. 5 is a diagram showing a temporal flow of data transmission / reception between the wireless tag reader 100 and the wireless tag 200. The control contents of the control unit 110 of the wireless tag reader 100 will be described with reference to FIGS. 4 and 5.

  As shown in FIG. 4, the control unit 110 of the wireless tag reader 100 first starts a direction detection channel determination process in step S1. 4 is started by an instruction from the controller 300, and the controller 300 issues a start instruction in FIG. 4 to the wireless tag reader 100 when the power is turned on.

  Although details of the direction detection channel determination processing will be described later, in the direction detection channel determination processing in the present embodiment, the communication channel of the direction detection antenna 150 is set to a candidate channel, and the noise intensity is sequentially measured using the candidate channel. Then, the measured noise intensity is compared with the noise allowable threshold value, and the candidate channel is set as a direction detection channel while the measured noise intensity does not exceed the noise allowable threshold value. On the other hand, when the measured noise intensity exceeds the noise tolerance threshold, the reception channel of the direction detecting antenna 150 is changed to another candidate channel, and the process after the measurement of the noise intensity is repeated.

  In the following step S2, the reception channel of the communication antenna 140 is set as a data communication channel and a data reception waiting state is set. This data communication channel is fixed to a certain channel and is shown as a default channel in FIG. 5 and is the same channel as the channel through which the wireless tag 200 transmits trigger data.

  In a succeeding step S3, it is determined whether or not the trigger data is received by the communication antenna 140. This trigger data is transmitted by the wireless tag 200 at a constant cycle. Therefore, while this determination is a negative determination, it can be determined that the wireless tag 200 does not exist within the communication range of the wireless tag reader 100. In this case, the determination in step S3 is repeated. On the other hand, if the determination is affirmative, it can be determined that the wireless tag 200 has entered the communication range of the wireless tag reader 100. In this case, since it is necessary to detect the direction of the wireless tag 200, if the determination in step S3 is affirmative, the process proceeds to step S4, and the direction detection channel determination process started in step S1 is stopped. In FIG. 5, the wireless tag 200 transmits trigger data from t1 to t2, and the communication antenna 140 receives the trigger data. Therefore, at the time t2, the direction detection antenna 150 stops the direction detection channel determination process.

  Although details will be described later in the direction detection channel determination processing, a communication channel is determined as the direction detection channel regardless of the time when this processing is stopped. Therefore, in step S5, the communication channel of the direction detection antenna 150 is set to the direction detection channel determined by the direction detection determination process.

  In subsequent step S6, the direction detection data acquisition process is started using the direction detection antenna 150 set in the direction detection channel in step S5. In FIG. 5, steps S5 and S6 are executed at time t3.

  In step S7, channel designation data for designating a direction detection channel is transmitted from the communication antenna 140 as a communication channel for transmitting direction detection data (t3 to t4 in FIG. 5). At this time, since the communication antenna 140 is still a default channel and the wireless tag 200 is also a default channel, the communication channels of both are the same. Therefore, transmission / reception of channel designation data usually succeeds.

  In step S8, the reception channel of the communication antenna 140 is also a direction detection channel. In addition, the wireless tag 200 is configured to transmit direction detection data when channel designation data is received. In FIG. 5, the direction detection data is transmitted from t5 to t6. The wireless tag 200 transmits the direction detection data through the direction detection channel designated by the channel designation data.

  In step S9, the direction detection data transmitted by the wireless tag 200 is received. The direction detection data is received by both the communication antenna 140 and the direction detection antenna 150.

  Reception using the direction detection antenna 150 can only measure the received power intensity. However, since the communication antenna 140 is connected to the reception unit 130 (the demodulation unit 131 and the decoding unit 132), the control unit 110 receives the direction detection data also by the communication antenna 140, so that the control unit 110 is used for direction detection. The end of data reception can be determined.

  When it is determined that the reception of direction detection data has been completed (t6 in FIG. 5), a response signal is transmitted from the communication antenna 140 in step S10 (t7 to t8 in FIG. 5). At this time, the communication channel of the communication antenna 140 is still a direction detection channel, and the wireless tag 200 is still a direction detection channel.

  When the response signal is transmitted, in step S11, the communication channels of the communication antenna 140 and the direction detection antenna 150 are both set as default channels (t9 in FIG. 5). Then, it returns to step S1. As a result, the communication antenna 140 continues to be in a reception standby state with the default channel, and the direction detection antenna 150 performs the direction detection channel determination process in order to determine the direction detection channel used in the next direction detection data acquisition process. Resume. The wireless tag 200 also returns the communication channel to the default channel when receiving the response signal. Note that the control unit 110 determines the direction of the wireless tag 200 using the received power intensity acquired using the direction detection antenna 150 in the direction detection data acquisition process. Various known methods can be used as the direction determination method. For example, the directivity direction when the received power intensity reaches the maximum value is estimated as the direction in which the wireless tag 200 exists. As shown in FIG. 5, the received power intensity actually used for direction determination is the intensity while the direction detection data is being received.

  Next, the direction detection channel determination process started in step S1 of FIG. 4 will be described. FIG. 6 is a flowchart showing this direction detection channel determination processing. As shown in FIG. 5, the direction detection channel determination process is performed using the direction detection antenna 150 while the communication antenna 140 is waiting for reception on the default channel.

  First, in step S101, a default channel is set as a change candidate channel. In the subsequent step S102, the change candidate channel set in step S101 (that is, the default channel) is set as a reception channel for actual reception. In step S103, reception processing is performed on the reception channel. This reception process is a process of measuring the reception level (noise level) of the reception channel, and is a process of measuring the reception intensity while sequentially switching the directivity of the direction detection antenna 150 within the detection range.

  In subsequent step S104, it is determined whether or not the reception level obtained as a result of the reception process in step S103 is larger than the change threshold. Here, the reception level may be an average value in all directions in the reception process of step S103 or may be a maximum value. The change threshold value corresponds to the noise allowable threshold value in the claims. When the reception level does not exceed the change threshold (S104 is NO), it can be determined that the noise level of the current reception channel, that is, the current change candidate channel, is within an allowable range. Therefore, in step S105, the current reception channel is set as a direction detection channel.

  On the other hand, when the reception level exceeds the change threshold, the current noise level of the reception channel exceeds the allowable value. Then, it progresses to step S106 and another channel is selected as a change candidate channel. In step S107, the change candidate channel selected in step S106 is set as a reception channel for actual reception. After that, the above-described step S103 and subsequent steps are executed.

  Therefore, in the direction detection channel determination process of FIG. 6, when the reception level of the change candidate channel exceeds the change threshold, the process of searching for a channel whose reception level does not exceed the change threshold is continued by switching to another channel. It will be. When a change candidate channel whose reception level does not exceed the change threshold is found, the channel is set as a direction detection channel. As long as the reception level of the change candidate channel does not exceed the change threshold, the change candidate channel is set as a direction detection channel, and the reception level of the channel is continuously monitored.

  The effects of the RFID tag direction detection system of the present embodiment described above compared to the conventional direction detection system will be described. FIG. 7 is a diagram showing a temporal flow of data transmission / reception between the wireless tag reader and the wireless tag in the conventional wireless tag direction detection system. In the conventional system, the wireless tag transmits the ID and the direction detection data in one data transmission. Although this data is transmitted during the period from t1 to t3 in the figure, since the wireless tag reader cannot determine when the data from the wireless tag is transmitted, the direction detection antenna is always used for the direction. Detecting data acquisition processing was performed. Similarly, the communication antenna is always waiting for reception or in a data transmission / reception state. Therefore, the noise level of another channel cannot be measured using these antennas.

  On the other hand, in the RFID tag direction detection system according to the present embodiment, as shown in FIG. 5, the RFID tag 200 transmits the direction detection data when channel designation data is received. The designated data is transmitted by the wireless tag reader 100. That is, in the present embodiment, unless the wireless tag reader 100 transmits channel designation data, the wireless tag 200 does not transmit direction detection data.

  However, in the present embodiment, the wireless tag reader 100 transmits the channel designation data when the trigger data is received from the wireless tag 200. Therefore, the wireless tag reader 100 receives the trigger data transmitted by the wireless tag 200. It is necessary to be ready for reception. In order to perform the direction detection channel determination process even in this reception standby state, the communication channel of the communication antenna 140 and the communication channel of the direction detection antenna 150 can be set separately, and only the communication antenna 140 is triggered. It is in a reception standby state with a default channel used for data transmission. Thus, the direction detecting antenna 150 does not need to be in a reception standby state in order to receive data from the wireless tag 200. Therefore, until the time t2 when the communication antenna 140 finishes receiving the trigger data, the direction detection channel is determined by measuring the noise intensity using the direction detection channel candidate channel and determining the direction detection channel using the direction detection antenna 150. Processing can be performed.

  Then, since the direction detection channel determined in this direction detection channel determination process is specified for the channel designation data transmitted to the wireless tag 200 after receiving the trigger data, transmission / reception of the direction detection data has been performed just before. This can be performed using the direction detection channel determined by the direction detection channel determination processing. Therefore, the direction detection data can be transmitted / received through a communication channel suitable for transmission / reception of the direction detection data without adding an antenna separately. As a result, the direction detection accuracy of the wireless tag 200 is improved.

  Furthermore, by dividing the data transmitted by the wireless tag 200 into trigger data and direction detection data, the following effects can be obtained. In other words, in this embodiment, the wireless tag 200 does not transmit direction detection data having a transmission time longer than that of the trigger data unless it receives channel designation data after transmitting short trigger data. Therefore, battery consumption due to data transmission can be suppressed as compared with the wireless tag of the conventional system that transmits the direction detection data even when the wireless tag reader 100 does not exist within the communication range.

  In addition, in this embodiment, the direction detection data can be transmitted on a channel with less noise, but the trigger data cannot be changed on the channel, but the trigger data is transmitted once by the wireless tag of the conventional system. The data transmission time is much shorter than the data to be transmitted. Therefore, the possibility that suddenly generated noise is superimposed on the trigger data is reduced. Therefore, the communication success rate is higher than when the ID and the direction detection data are transmitted at a time as in the conventional system.

(Second Embodiment)
Next, a second embodiment will be described. In the first embodiment, the direction detection channel determination process continuously measures the reception level of the communication channel determined as the direction detection channel, and performs reception when the reception level exceeds the change threshold. Switch the channel to another change candidate channel and measure the reception level. If the reception level of the changed candidate channel also exceeds the change threshold, switch to another change candidate channel and measure the reception level. I was doing the process. The direction detection channel determination processing is the same processing regardless of whether the wireless tag 200 is within the communication range of the wireless tag reader 100 or outside the communication range.

  On the other hand, in the second embodiment, the contents of the direction detection channel determination process are different depending on whether the wireless tag 200 is outside the communication range of the wireless tag reader 100 or the communication range. When it can be determined that 200 does not exist within the communication range of the wireless tag reader 100, the noise detection 1 (corresponding to the all-channel omnidirectional measurement process in the claims) is executed to determine the direction detection channel. On the other hand, when it can be determined that the wireless tag 200 is within the communication range of the wireless tag reader 100, noise scanning 2 (corresponding to the limited channel noise measurement process in the claims) is executed to determine the direction detection channel. In the second embodiment, other processes and apparatus configurations are the same as those in the first embodiment.

  Although details of the noise scans 1 and 2 will be described later, the noise scan 2 is a process capable of determining a direction detection channel in a short time. First, when it can be determined that the wireless tag 200 is within the communication range of the wireless tag reader 100, the reason for executing the noise scan 2 that can determine the direction detection channel in a short time will be described.

  FIG. 8 is a diagram illustrating processing performed by the wireless tag reader 100 using the direction detection antenna 150 with the horizontal axis as a time axis. As shown in FIG. 8, the wireless tag reader 100 uses a direction detection antenna 150 to receive direction detection determination data and perform a noise scan (direction detection channel determination process).

  As shown in the figure and as described in the first embodiment, when the wireless tag reader 100 receives trigger data from the wireless tag 200, the wireless tag reader 100 performs a direction detection data acquisition process (after transmitting the channel designation data). . Therefore, when the wireless tag 200 exists in the communication range of the wireless tag reader 100, the direction detection of the wireless tag 200 is frequently performed. In addition, since the direction detection antenna 150 is used for the direction detection data reception process, the noise scan using the direction detection antenna 150 is also performed in a short time between frequent direction detection data acquisition processes. Must be done. Therefore, when it can be determined that the wireless tag 200 is within the communication range of the wireless tag reader 100, the noise scan 2 that can determine the direction detection channel in a short time is executed.

  On the other hand, when the wireless tag 200 does not exist within the communication range of the wireless tag reader 100, the wireless tag reader 100 does not need to detect the direction of the wireless tag 200, and therefore has sufficient time for noise scanning. Therefore, in this case, although it takes time, the noise scan 1 that can reliably set the communication channel most suitable for transmission / reception of the direction detection data as the direction detection channel is executed.

  Note that the direction detection channel determined by the noise scan 1 may be used continuously after the wireless tag 200 enters the communication range of the wireless tag reader 100. However, the noise intensity may change with time. Therefore, even when the wireless tag 200 exists in the communication range of the wireless tag reader 100, it is necessary to repeat the direction detection channel determination process.

  As described above, in the second embodiment, noise scanning 1 or 2 is executed to determine the direction detection channel. These noise scans 1 or 2 are processes in place of FIG. 6 of the first embodiment, and either noise scan 1 or 2 is started in step S1 of FIG.

  Whether to start the noise scan 1 or 2 is determined by whether or not it can be determined that the wireless tag 200 is within the communication range of the wireless tag reader 100. Whether or not the wireless tag 200 is within the communication range of the wireless tag reader 100 is determined based on whether or not trigger data is received, and from the trigger data or the wireless tag 200 for longer than the trigger data transmission cycle. If no other data is received, it is determined that the wireless tag 200 does not exist within the communication range of the wireless tag reader 100.

  When it can be determined that the wireless tag 200 does not exist within the communication range of the wireless tag reader 100, the noise scan 1 is executed. FIG. 9 is a flowchart showing the processing contents of the noise scan 1.

  First, in step S21, one change candidate channel is selected. The change candidate channel selected here is one of the settable communication channels, and which communication channel is selected is determined by the number of repetitions of step S21. Finally, all the settable communication channels are selected by repeating step S21.

  In the subsequent step S22, an omnidirectional noise scan is executed. The details of this omnidirectional noise scan are shown in FIG. In FIG. 10, first, in step S221, channel setting is performed. Specifically, this process is to set the change candidate channel selected in step S21 as the reception channel. In the subsequent step S222, the direction is set. Specifically, the directivity of the direction detection antenna 150 is set to a setting direction determined according to the number of repetitions of step S222 among a plurality of setting directions to be set in the detection range.

  In the subsequent step S223, noise scanning is performed. That is, the noise intensity is measured using the directivity of the direction detecting antenna 150 as the setting direction measured in step S222. The noise intensity is, for example, the average intensity or the maximum intensity of the received signal intensity for a certain time.

  In a succeeding step S224, it is determined whether or not the noise intensity is measured in all the setting directions to be set in the detection range. If this determination is negative, the process returns to step S222. On the other hand, if the determination is affirmative, the omnidirectional noise scan is terminated and the process returns to FIG.

  When the omnidirectional noise scan is completed, it is determined in step S23 whether all settable communication channels have been selected as change candidate channels. If this determination is negative, the process returns to step S21.

  On the other hand, if the determination in step S23 is affirmative, the process proceeds to step S24, and direction detection channel determination processing is executed. Details of this direction detection channel determination processing are shown in FIG. In FIG. 11, first, in step S241, it is checked whether or not there is a change candidate channel in which the noise intensity in all setting directions is equal to or less than the noise allowable threshold as a result of the omnidirectional noise scan performed in step S22.

  In the subsequent step S242, the number of channels satisfying the above condition (that is, the noise intensity in all the setting directions is equal to or less than the noise allowable threshold value) is determined. If the number of channels is 1, the process proceeds to step S243, the channel is determined as a direction detection channel, and FIG.

  On the other hand, when the number of channels satisfying the above condition is other than 1, that is, 0 or 2 or more, the process proceeds to step S244. In step S244, the range of the noise level of each channel is obtained. The range of the noise level is a difference between the maximum value and the minimum value in the omnidirectional noise scan performed in step S22 of FIG. 9 for each channel.

  In the subsequent step S245, the change candidate channel having the smallest noise level range obtained in step S244 is determined as the direction detection channel, and this FIG. 11 is ended.

  The reason why the channel having the smallest noise level range is selected in the case where the number of channels whose noise intensity in all the setting directions is equal to or less than the noise tolerance threshold is 0 or 2 is as follows. That is, the direction detection channel determined in FIG. 11 is a channel used when receiving the direction detection data, and the wireless tag is determined depending on the reception level of the direction detection data received while sequentially changing the set direction. 200 directions are estimated. Therefore, when noise is superimposed on the entire setting azimuth, even if the noise level is large on the whole, there is a low possibility that the azimuth estimation of the wireless tag 200 is erroneous due to noise. On the other hand, if the noise level varies greatly depending on the setting direction even if the noise level of all the setting directions is generally low, it is different from the reception level when directivity is directed to the direction in which the wireless tag 200 exists. This is because the reception level when directivity is directed in the direction of is increased due to the influence of noise, and as a result, there is a high possibility that the orientation of the wireless tag 200 is erroneously estimated.

  Returning to FIG. 9, when the direction detection channel determination process in step S24 is completed, in step S25, the direction detection channel used in the next direction detection data acquisition process is updated to the direction detection channel determined in step S24. After executing step S25, the process returns to step S21, and noise scan 1 is executed again from the beginning. The noise scan 1 is continued until step S4 in FIG. 4 is executed.

  Next, the noise scan 2 will be described. FIG. 12 is a flowchart showing the processing content of the noise scan 2. First, in step S31, the reception channel of the direction detection antenna 150 is set to the direction detection channel determined by the previous noise scan (the latest noise scan for both noise scans 1 and 2).

  In the subsequent step S32, an omnidirectional noise scan similar to that in step S22 in FIG. 9 is executed on the reception channel set in step S31. In the subsequent step S33, it is determined whether or not there is a set direction exceeding the noise allowable threshold as a result of the omnidirectional noise scan in step S32. If this determination is negative, the processing in FIG. 12 is terminated. Therefore, in this case, the direction detection channel determined by the previous noise scan is maintained as it is.

  On the other hand, if step S33 is affirmative, a communication channel adjacent to the direction detection channel is selected as a change candidate channel in step S34. And it progresses to step S35 and performs a specific orientation noise scan. Details of this specific azimuth noise scan are shown in FIG.

  In FIG. 13, first, in step S351, channel setting is performed. Specifically, this process is to set the change candidate channel (communication channel adjacent to the direction detection channel) selected in step S34 as the reception channel. In the subsequent step S352, the orientation is set. Specifically, the directivity of the direction detection antenna 150 is set to the setting direction in which the noise level is maximized in the omnidirectional noise scan executed in the most recent step S32.

  In step S353, noise scanning is performed. That is, the noise intensity is measured using the directionality of the direction detecting antenna 150 as the setting direction measured in step S353. When this step S353 is executed, the specific azimuth noise scan is completed. Next, step S36 of FIG. 12 is executed.

  In step S36, it is determined whether or not the specific azimuth noise scan has been completed for the two communication channels adjacent to the direction detection channel. If this determination is negative, the process returns to step S324, and this time, a communication channel that has not yet been subjected to the specific direction noise scan is selected from the two communication channels adjacent to the direction detection channel, and the specific direction noise is selected. Run a scan.

  On the other hand, if step S36 is affirmative determination, it will progress to step S37 and will perform the direction detection channel change determination process. Specific processing of this change determination processing is shown in FIG. In FIG. 14, first, in step S371, three communication channels, that is, the direction detection channel that has been subjected to the omnidirectional noise scan in step S32, and noise levels in specific directions of two communication channels adjacent to the direction detection channel are shown. Compare The result of the omnidirectional noise scan in step S322 is used for the direction detection channel, and the result of the specific azimuth noise scan in step S35 is used for two adjacent communication channels. Then, these three noise levels are compared, and the channel with the lowest noise level is set as a new direction detection channel.

  In the following step S372, the direction detection channel used in the next direction detection data acquisition process is changed to the direction detection channel determined in step S371.

  As described above, in the adjacent communication channel, the noise level of only a specific direction is measured, but even if the setting direction for measuring the noise level is limited to only the specific direction, the suitability of this communication channel is limited to some extent. Judgment can be made with accuracy. The reason will be described below.

  Although each channel is separated by a certain frequency range, the frequency range is continuous with the adjacent communication channel. For this reason, it is considered that noise measured in a certain communication channel often affects adjacent channels in which the frequency range is continuous. FIG. 15 is a diagram illustrating a noise level with respect to frequency for a certain noise. For example, when the C channel is a direction detection channel and noise having a peak occurs in the C channel as shown in this figure, this noise often affects the adjacent B channel and D channel. it is conceivable that.

  For this reason, when the change of the noise level with respect to the set direction is graphed, a certain communication channel and a communication channel adjacent thereto have similar graph shapes. The lower part of FIG. 16 illustrates graphs with the horizontal axis as the set direction and the vertical axis as the noise level in several communication channels. In FIG. 16, channel 3 is a direction detection channel, and the noise level exceeds a noise allowable threshold in a certain setting direction due to the occurrence of noise. The 2 channel and 4 channel adjacent to the 3 channel have a graph shape similar to that of the 3 channel, and the same direction as the 3 channel has the highest noise level. On the other hand, the 16 channel, which is a frequency band relatively distant from the 3 channel, has almost no influence of noise generated in the vicinity of the 3 channel, so the graph shape of the 16 channel is not similar to the graph shape of the 3 channel. Note that the upper part of FIG. 16 is a pie chart of the lower line graph.

  As described above, in the processing of the current noise scan 2, the setting direction having the highest noise level in the direction detection channel that has performed the omnidirectional noise scan is the direction in which the noise level is the highest in the communication channel adjacent to this channel ( That is, it can be estimated that the specific orientation). Therefore, even if the direction in which the noise level is measured in the adjacent communication channel is limited to a specific direction, the suitability of this communication channel can be determined with a certain degree of accuracy.

  Further, as shown in FIG. 8, the noise scan 2 needs to be executed after the direction detection data reception process is completed and before the next trigger data is received. Can be fully finished during this time. The reason will be described below using a specific example.

  The time required to execute the noise scan 2 is largely determined by the execution time of the omnidirectional noise scan performed on the direction detection channel and the execution time of the specific azimuth noise scan performed on the two communication channels adjacent to the direction detection channel. The execution time of the omnidirectional noise scan varies depending on how many directions are scanned, and the time required for one scan also affects the execution time. The number of azimuths to be scanned is at most about 24 azimuths. The reason is that the RFID tag direction detection system is intended to detect the direction of the person carrying the RFID tag 200, so it is not necessary to distinguish between 60 ° and 61 °. This is because it is enough. Even if a low-capacity processing apparatus that scans 24 azimuths and takes a relatively long time for one scan is used, the omnidirectional noise scan can be executed in about 700 μs. Further, the specific azimuth noise scan can be executed in about 50 μs. Therefore, it can be said that the noise scan 2 is completed in a time shorter than 1 ms.

  On the other hand, the time from the end of the direction detection data receiving process to the next reception of the trigger data varies depending on the situation, but considering the general home as an example, the time for performing the noise scan 2 most As a situation where the target margin is short, there may be a situation where 4 to 5 family members who carry the wireless tag 200 are present in the communication range at the same time. Since the movement of the person is not so fast, it is sufficient that the interval for detecting the direction of the wireless tag 200 is about 100 ms at the shortest. Therefore, five wireless tags 200 are present in the communication range at the same time. However, on average, communication with any one of the wireless tags 200 is at intervals of 20 ms. Of course, it is not always possible to communicate at an interval of 20 ms, and it is considered that there may be a communication interval shorter than this. However, as described above, the noise scan 2 is completed in a time shorter than 1 ms. Therefore, in most cases, it can be said that the noise scan 2 can be executed after the direction detection data receiving process is completed and before the next trigger data is received.

  As described above, in the second embodiment described above, when it can be determined that the wireless tag 200 does not exist within the communication range of the wireless tag reader 100, the noise scan 1 for performing noise measurement in all setting directions is executed for all communication channels. To do. On the other hand, if it can be determined that the wireless tag 200 is within the communication range of the wireless tag reader 100, the noise scanning 2 is executed to determine the direction detection channel. In this noise scan 2, first, an omnidirectional noise scan is executed only for the direction detection channel determined in the previous noise scan (S31, S32). If the noise levels in all the setting directions do not exceed the noise allowable threshold, the previous direction detection channel is determined as the next direction detection channel at this time. Therefore, in this case, since the channel for measuring the noise level is only one channel, the direction detection channel can be determined in a short time.

  Furthermore, even if there is an azimuth exceeding the noise tolerance threshold among the noise levels of all the set azimuths, the noise level is additionally measured by two communication channels adjacent to the direction detection channel that has performed omnidirectional noise scanning. This is only for the setting direction having the highest noise level in the omnidirectional noise scan. Therefore, also in this case, the direction detection channel can be determined in a short time.

  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, for example, in steps S244 and S245 in the above-described second embodiment, the change candidate channel having the smallest noise level range is determined as the direction detection channel. Instead, the variance of the noise level may be obtained, and the change candidate channel having the smallest variance may be determined as the direction detection channel.

  In the above-described embodiment, the wireless tag 200 includes the two antennas 241 and 242, but only one of them may be used.

100: wireless tag reader 110: control unit 111: memory 112: timer 115: channel control unit 120: transmission unit 121: encoding unit 122: modulation unit 123: amplification unit 130: reception unit 131: demodulation unit 132: decoding unit 140: communication Antenna 150: Direction detection antenna 151: Excitation element 152: Non-excitation element 160: Direction detection unit 161: Directivity control unit 162: Power reception unit 170: Channel control unit 200: Wireless tag 210: Built-in power supply 215: Channel control Unit 220: transmission unit 221: encoding unit 222: modulation unit 230: reception unit 231: demodulation unit 232: decoding unit 240: antenna unit 241: first antenna 242: second antenna 250: Changeover switch 260: Control unit 261: Timer 262: Memory 300: Controller

Claims (3)

A wireless tag that is carried by a person and can be switched to a plurality of communication channels, and that selects one communication channel from a plurality of communication channels and sequentially transmits radio waves;
A communication antenna that transmits and receives data to and from the wireless tag, and a direction detection antenna that receives data transmitted from the wireless tag while changing directivity, and the data received by the direction detection antenna A wireless tag reader for detecting the direction of the wireless tag, and
A wireless tag direction detection system including:
The wireless tag periodically transmits trigger data on a preset fixed channel during startup,
The wireless tag reader is
Communication channels of the communication antenna and the direction detection antenna can be set separately from each other from a plurality of channels capable of communicating with the wireless tag,
The communication antenna is in a data reception standby state on the fixed channel until the trigger data is received,
While the communication antenna is in a data reception standby state, the communication channel of the direction detection antenna is measured as a candidate channel that is a candidate communication channel for receiving data for performing direction detection, and the noise intensity is measured. A direction detection channel that determines a direction detection channel, which is a communication channel for receiving data for direction detection, by comparing the measured noise intensity with a noise tolerance threshold or the noise intensity measured in another candidate channel. Execute the decision process
When the trigger data is received by the communication antenna, channel designation data for designating a direction detection channel determined by the direction detection channel determination process is transmitted from the communication antenna through the fixed channel, and then the communication antenna is transmitted. The communication channel is also in the data reception standby state as the direction detection channel,
The communication channel of the direction detection antenna is also used as the direction detection channel, and direction detection data acquisition processing is performed to receive data while sequentially switching the directivity of the direction detection antenna.
When the wireless tag receives the channel designation data from the wireless tag reader, the wireless tag transmits the direction detection data that can be detected by the wireless tag reader using the communication channel designated by the channel designation data,
The wireless tag reader uses the radio wave received by the communication antenna to determine the end of reception of the direction detection data, and then ends the direction detection data acquisition process using the direction detection antenna, A wireless tag direction detection system characterized by resuming channel determination processing. In claim 1,
The wireless tag reader is
When it can be determined that the wireless tag does not exist within the communication range of the wireless tag reader, the candidate channels for measuring the noise intensity in the direction detection channel determination process are all settable communication channels, and for each candidate channel , Performing an all-channel omnidirectional measurement process for measuring noise intensity in all set azimuths within the direction detection range, and determining the direction detection channel based on a comparison of noise intensity in all candidate channels,
When the wireless tag can be determined to be within the communication range of the wireless tag reader, the direction detection channel determination process executed when the communication antenna enters the data reception standby state limits the candidate channels for measuring the noise intensity. The direction detection channel is determined by executing the limited channel noise measurement process,
In this limited channel noise measurement process, for the direction detection channel determined in the previous direction detection channel determination process, the noise intensity is measured in all setting directions within the direction detection range, and the measured noise intensity in all setting directions is the noise level. If the allowable threshold is not exceeded, the previous direction detection channel is determined as the current direction detection channel,
If there is an azimuth that exceeds the noise tolerance threshold among the noise intensities measured in all settings, only the communication channel adjacent to the communication channel that measured the noise intensity in all settings and this time, Measure the noise intensity only for the setting direction with the highest noise intensity in the communication channel that measured the noise intensity,
This time, the direction of the communication channel with the lowest noise strength is compared by comparing the maximum noise strength of the noise strengths in the communication channels that measure the noise strength in all the setting directions with the noise strength measured in the adjacent communication channel. An RFID tag direction detection system that is updated as a channel. In claim 1,
The direction detection channel determination process includes:
The communication channel of the direction detection antenna is set as one candidate channel, the noise intensity is sequentially measured in the candidate channel, the measured noise intensity is compared with the noise allowable threshold, and the measured noise intensity is the noise While the allowable threshold is not exceeded, the candidate channel is determined as the direction detection channel,
If the measured noise intensity exceeds the noise tolerance threshold, change the communication channel of the direction detection antenna to another candidate channel, measure the noise intensity, compare with the noise tolerance threshold, and move the candidate channel to the direction. A wireless tag direction detection system, characterized in that it is a process of repeatedly determining whether to determine a detection channel.

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