JP2009225371A - Radio receiver, distance determining device, position determining device and radio receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique can easily measure a distance between a transmitter and a receiver. <P>SOLUTION: The radio receiver includes: a receiving means for receiving predetermined data to be transmitted from a predetermined radio transmitter at predetermined times one time; a sensitivity changing means for decreasing or increasing the reception sensitivity in the receiving means each time the receiving means receives data; and a control means for receiving the data each time by the receiving means (step 72) while decreasing or increasing the reception sensitivity by the sensitivity changing means (step 76), and outputting information corresponding to the minimum reception sensitivity at which the data have been received in order to provide the information for determining the distance between this radio transmitter and the radio receiver (step 79). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radio reception apparatus and a radio reception method for receiving predetermined data from a radio transmission apparatus and outputting the data for use in determining the distance between itself and the radio transmission apparatus, and distance determination for determining the distance The present invention relates to an apparatus and a position determination apparatus that determines the position of the wireless reception apparatus.

  Conventionally, as a technique for measuring the distance between a transmitter and a receiver, measurement is mainly based on the arrival time of radio waves from the transmitter to the receiver, and radio waves from the transmitter are received by the receiver. What performs measurement based on the received electric field strength is used. According to the technique that performs measurement based on the arrival time of radio waves, the distance from the transmitter to the receiver can be measured with an accuracy of several centimeters of error. In the technique of measuring based on the received electric field strength, the distance is measured based on the RSSI value representing the received electric field strength. According to this, however, binary (whether close or far) or multi-value ( Near, middle, far, etc.) distance measurements can be made.

  FIG. 12 shows the configuration of the receiver when measuring the distance based on the RSSI value. As shown in the figure, the signal from the transmitter is received by the high frequency processing unit 91 and converted to an intermediate frequency by the local oscillation signal, and then the unnecessary component is removed by the intermediate frequency processing unit 92 and the detection processing unit 93. Is demodulated and supplied to the low-frequency processing unit 94. At that time, the RSSI signal is detected by the detection processing unit 93, converted into a digital value by the AD converter 95, and supplied to the microcomputer 96. The microcomputer 96 can determine the distance to the transmitter based on the supplied RSSI value.

  As a technique for measuring the distance based on the arrival time of radio waves, for example, a technique described in Patent Document 1 is known. In this technique, the base station transmits the first data, the mobile station transmits the second data in response to receiving the first data, and the base station determines the time until the base station receives the second data. By measuring, the distance between the base station and the mobile station is calculated.

Japanese Patent Application Laid-Open No. 07-226976

  However, according to the above-described conventional technique for measuring distance based on the arrival time of radio waves, it is possible to expect a measurement accuracy of an error of several centimeters, but at least in the transmitter or in both the transmitter and the receiver Need to implement an accurate and synchronized clock. Alternatively, all transmitters must have an accurate clock that can be synchronized or a network for synchronization.

  Further, according to the technique for performing measurement based on the RSSI value, a measurement accuracy with an error of about 1 meter can be expected, but a comparator or an A / D converter is required. In addition, distance measurement based on the RSSI value cannot be performed under a strong electric field where the distance between the transmitter and the receiver is close. As shown in FIG. 13, when the transmitter and the receiver are separated to some extent and the received electric field strength is relatively weak below Th, the RSSI voltage is almost proportional to the electric field strength, but the distance is close, This is because when the electric field strength is equal to or greater than Th, the RSSI voltage is saturated and the electric field strength cannot be expressed.

  An object of the present invention is to provide a technique capable of more easily determining the distance between a transmitter and a receiver in view of such problems of the prior art.

  To achieve this object, a wireless receiving device according to a first aspect of the present invention includes a receiving unit that receives predetermined data that is wirelessly transmitted a predetermined number of times at a time from a predetermined wireless transmitting device, and data received each time by the receiving unit. Each time reception is performed, the sensitivity change means for reducing the reception sensitivity in the reception means by a predetermined amount, and the reception sensitivity is reduced by the sensitivity change means while receiving the data each time by the reception means, And control means for outputting information corresponding to the minimum reception sensitivity capable of receiving data for use in determining the distance between the wireless transmission device and the wireless reception device. .

  Here, the reduction in reception sensitivity is performed, for example, by adjusting the gain in the receiving means with an attenuator. The information corresponding to the minimum reception sensitivity that could receive data includes, for example, the value of the reception sensitivity when the data was received and the number of times the data was received. Applicable data.

  In this configuration, when wireless transmission is performed a predetermined number of times at a time from a predetermined wireless transmission device, the reception unit attempts to receive the wireless transmission. At that time, each time data is received by the receiving means, the sensitivity changing means decreases the receiving sensitivity of the receiving means by a predetermined amount. Accordingly, the data is received when the reception sensitivity is higher than the level at which the data can be received, and the data is not received when the reception sensitivity is lower. On the other hand, when the reception sensitivity is constant, the data receivability varies depending on the distance between the wireless transmission device and the wireless reception device. Therefore, the minimum receiving sensitivity with which the data can be received corresponds to the distance, and the control means can output information corresponding to the receiving sensitivity for use in determining the distance.

  In the wireless receiver according to a second aspect of the present invention, in the first aspect, each piece of data transmitted a predetermined number of times includes number-of-times identifying information for identifying how many times the data relates to transmission, As the information corresponding to the reception sensitivity, the number-of-times specifying information included in the last data that can be received by receiving the data each time accompanied by a decrease in the reception sensitivity is output.

  According to a third aspect of the present invention, in the first or second aspect, the predetermined data includes identification information of the wireless transmission device, and the information output from the control means includes the identification information. It is included.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, in the third aspect, the transmission of the predetermined number of data is to grasp the position of the wireless reception apparatus based on a position previously associated with the identification information. The beacon transmission is performed periodically.

  A distance determination device according to a fifth invention is a device for determining a distance between the wireless transmission device and the wireless reception device according to any one of the first to fourth inventions, wherein the reception sensitivity output by the wireless reception device is obtained. The distance is determined based on corresponding information.

  A position determination apparatus according to a sixth aspect of the present invention is a position determination apparatus for determining the position of the wireless reception apparatus according to the third or fourth aspect, wherein the reception sensitivity included in the information output from the control means of the wireless reception apparatus The position of the wireless receiving device is determined based on information corresponding to the information and identification information, and a position associated with the identification information in advance.

  According to a seventh aspect of the present invention, there is provided a wireless communication method in which a receiving unit receives predetermined data wirelessly transmitted a predetermined number of times at a time from a predetermined wireless transmitting device, and a sensitivity changing unit includes: Each time data is received, a sensitivity changing step for reducing the receiving sensitivity in the receiving means by a predetermined amount, and the control means, while reducing the receiving sensitivity by the sensitivity changing means, A control step of receiving data and outputting information corresponding to the minimum reception sensitivity with which the data could be received for use in determining the distance between the wireless transmission device and the receiving means. It is characterized by that.

  According to the present invention, the data is received each time while the reception sensitivity is reduced, and the information corresponding to the minimum reception sensitivity with which the data can be received is transmitted between the wireless transmission device and the wireless reception device. Therefore, the distance can be determined with a simple configuration without using GPS or RSSI values.

  FIG. 1 shows the configuration of a location management system according to an embodiment of the present invention. As shown in the figure, this system includes a beacon transmitter 1 that transmits a beacon of weak radio (short range radio), a beacon receiver 2 that receives this beacon, and a mobile station radio that is connected to the beacon receiver 2. 3. A base station 4 that communicates with the mobile station radio 3 and a terminal management system PC (hereinafter simply referred to as “PC”) that is connected to the base station 4 and manages the position of the beacon receiver 2 .) 5 is provided.

  FIG. 2 is a block diagram showing the configuration of the beacon transmitter 1. As shown in the figure, the beacon transmitter 1 generates a carrier wave, modulates with beacon data, an oscillation unit 11, amplifies the modulated carrier wave from the oscillation unit 11, and outputs from the antenna, A central control processing unit 13 that controls the oscillation unit 11 and the power amplification unit 12 and a control information storage unit 14 that stores control information used for control by the central control processing unit 13 are provided. The beacon data includes a beacon ID unique to the beacon transmitter 1.

  The control information storage unit 14 stores control information such as a transmission frequency, a transmission output level, a transmission timing, and transmission contents when transmitting a beacon. Based on the control information stored in the control information storage unit 14, the central control processing unit 13 controls the frequency and modulation of the carrier wave in the oscillation unit 11 and the output level in the power amplification unit 12.

  FIG. 3 is a block diagram showing the configuration of the beacon receiver 2. As shown in the figure, the beacon receiver 2 includes a band filter 21 that extracts a predetermined band from a reception signal input from an antenna, a high-frequency amplification unit 22 that amplifies the extracted reception signal of the predetermined band, and a high-frequency amplification unit. 22 converts the high frequency from 22 into an intermediate frequency and processes the signal from the local oscillation / detection unit 23 that performs detection, the low frequency amplification unit 24 that amplifies the low frequency signal obtained by the detection, and the low frequency amplification unit 24 A central control processing unit 25 that obtains beacon data and controls the amplification factor in the high-frequency amplification unit 22 and the local oscillation frequency in the local oscillation / detection unit 23. The central control processing unit 25 can control the reception sensitivity by changing the amplification factor in the high frequency amplification unit 22 by an attenuator.

  FIG. 4 is a block diagram showing the configuration of the mobile station radio 3. The mobile station radio 3 includes a radio main body 31 and a central control processing unit 32 that controls the radio main body 31 as shown in FIG. The central control processing unit 32 receives beacon data from the beacon receiver 3 and transmits the beacon data to the base station 4 via the radio main unit 31.

  FIG. 5 is a block diagram showing the configuration of the base station 4. As shown in the figure, the base station 4 controls the base station radio 41 that communicates with the mobile station radio 3 and the beacon received by the base station radio 41. A central control processing unit 42 for sending data to the personal computer 5 is provided. In the personal computer 5, the terminal management system which manages the position of each mobile station radio | wireless machine 3 is operating, and the beacon database which matched the beacon ID of each beacon transmitter 1 with the position on the actual map is provided. It has been. The terminal management system updates and maintains the location management database in which the correspondence between the ID unique to each mobile station radio 3 and its current location is registered.

  FIG. 6 shows an image in which beacon data is transmitted from the beacon transmitter 1 to the beacon receivers 2a and 2b. For example, three packets including the beacon ID of the beacon transmitter 1 are transmitted from the beacon transmitter 1 every cycle at a predetermined repetition period. This is also performed in the conventional position management system, and the reason why three packets having the same contents are transmitted in this way is to ensure that the beacon ID is received. However, in this embodiment, sequence numbers are included in the three packets for each cycle. Then, the signals are received with predetermined large, medium, and small reception sensitivities in order.

  FIG. 7 shows a method for determining the distance between the beacon transmitter 1 and the beacon receiver 2. In the figure, the possibility of receiving each packet when the beacon receiver 2 receives a beacon of one cycle is illustrated. In the figure, Pa to Pc are graphs showing the receivability of each packet when the beacon receiver 2 receives one cycle of packets Pa to Pc transmitted from the beacon transmitter 1 at the same transmission output level. It is. A graph graphic packet having a receivability level equal to or higher than Th can be received, and a graph graphic packet lower than Th cannot be received. The packet Pa is received without attenuation by the attenuator, and the packets Pb and Pc are received with the attenuation amount by the attenuator as a predetermined weak level and strong level, respectively. In the figure, an example is shown in which packets Pa and Pb are receivable and packet Pc is not receivable.

  When the attenuation amount by the attenuator is the same, the possibility of receiving each packet Pa to Pc decreases as the distance D between the beacon transmitter 1 and the beacon receiver 2 increases. Therefore, the graph figures Pa to Pc move downward as the distance D increases, and the graph figures Pa to Pc move upward as the distance D decreases. Therefore, the distance D can be determined based on which of the packets Pa to Pc was received. For example, when only the packet Pa can be received, the distance D is a predetermined long distance. When the packets Pa and Pb are received, the distance D is a predetermined medium distance, and all the packets Pa to Pc can be received. In this case, it can be determined that the distance is a predetermined short distance.

  FIG. 8 shows a format of a packet included in a beacon transmitted by the beacon transmitter 1. The beacon is transmitted cyclically at a constant cycle, but as shown in the figure, the period of one cycle is composed of a transmission period T1 and a pause period T2. In the transmission period T1, three packets Pa, Pb, and Pc are transmitted at a constant transmission output level. Each packet has a header in which control information such as a destination address is stored, an ID part in which the beacon ID of the beacon transmitter 1 that transmits the packet is stored, a checksum for performing error detection of the header and the ID part, Each packet is composed of a sequence number in one cycle, a footer for storing communication control information, and a general checksum field. The contents of the ID part in the packets Pa, Pb, and Pc are the same, and for example, “1”, “2”, and “3” are stored in the sequence number field, respectively.

  FIG. 9 is a flowchart showing the operation of the location management system. As shown in the figure, first, the beacon transmitter 1 transmits a beacon for one cycle (step S1). At the time of transmission, the central control processing unit 13 of the beacon transmitter 1 stores its own beacon ID in the ID part of the packets Pa to Pc constituting the beacon. The sequence numbers “1”, “2”, and “3” are stored in the sequence number fields of the packets Pa to Pc, respectively. The packets Pa to Pc are transmitted in this order.

  In response to this, the beacon receiver 2 receives the possible packets Pa, Pb or Pc (step S2). That is, every time a packet is received, the reception sensitivity is lowered by a predetermined amount, and a packet whose reception possibility in FIG. 7 is Th or higher is received. When receiving the packet Pa, Pb or Pc, the beacon receiver 2 uses the beacon data of the last packet that can be received as data for the wireless device, and sends it to the mobile station wireless device 3 via the serial cable (step S3). . Therefore, the sequence number included in this data corresponds to the reception sensitivity when the data is received, and indicates the distance between the beacon transmitter 1 and the beacon transmitter 2.

  When the wireless device data is received (step S4), the mobile station wireless device 3 generates a data communication message for transmitting the wireless device data (step S5) and transmits it to the base station 4. This message includes a radio ID unique to the mobile station radio 3. When this message is received (step S6), the base station 4 regenerates the data for the wireless device (step S7) and sends it to the personal computer 5 via the serial cable. When the wireless device data is received (step S8), the position management system of the personal computer 5 extracts the beacon ID from the wireless device data (step S9), and determines the distance D between the beacon wireless device 1 and the mobile station wireless device 3. Determine (step S10).

  The determination of the distance D can be made based on the sequence number in the radio data. That is, since this sequence number corresponds to the minimum reception sensitivity with which the packet can be received, depending on whether the sequence number is “3”, “2”, or “1”, the distance D is a predetermined short distance, It can be determined that it is a medium distance or a long distance.

  Based on the determination result, the location management system updates the record for the mobile station radio 3 in the location management database (step S11). That is, the position on the map corresponding to the beacon ID in the radio data is acquired based on the beacon database, the position of the mobile station radio 3 is obtained based on the position and the determination result in step S10, and the mobile station The record corresponding to the wireless device ID of the wireless device 3 is updated.

  FIG. 10 is a flowchart showing processing by the central control processing unit 25 of the beacon receiver 2. This processing corresponds to the processing in steps S2 and S3 in FIG. In this process, the beacon data of each packet transmitted in one cycle is acquired in such a way that the last one that can be received while gradually decreasing the reception sensitivity remains in the beacon buffer. The data is supplied to the mobile station radio 3 as radio data.

  That is, when the process is started, the central processing control unit 25 first sets the beacon receiver 2 in a reception standby state in step 71 and determines in step 72 whether or not a beacon packet has been received. If it is determined that a packet has been received, the process proceeds to step 73, where the beacon buffer is overwritten with the beacon data of the received packet, and in step 74, the transmission standby timer is reset. This transmission waiting timer determines that reception of one cycle has been completed when the packet with the last sequence number cannot be received, and supplies the radio data to the mobile station radio 3 for that cycle. Used to determine when to do.

  Next, in step 75, it is determined whether or not the sequence number of the received beacon data is the last one. If it is determined that the packet is the last one, the transmission of the packet in the current cycle is completed, and the process proceeds to step 79. If it is determined that it is not the last one, the process proceeds to step 76, and the reception sensitivity is changed to a predetermined value lower than the current reception sensitivity. That is, the attenuation amount of the attenuator is increased by a predetermined amount. Thereafter, the process returns to step 71.

  On the other hand, if it is determined in step 72 that a beacon packet has not been received, the process proceeds to step 77 to determine whether or not the beacon buffer is empty. If it is determined to be empty, the process returns to step 71. If it is determined that it is not empty, the process proceeds to step 78 to determine whether or not the transmission standby timer has overflowed. If it is determined that there is no overflow, the process returns to step 71. If it is determined that the packet has overflowed, it is impossible to receive the packet in the current cycle, and it is assumed that the packet has been completed.

  In step 79, the contents of the beacon buffer are supplied to the mobile station radio 3 as radio data. The sequence number in the radio data corresponds to the reception sensitivity when it is received. This radio data is reported to the base station 4 as location information indicating the location of the mobile station radio 3. Thereafter, the contents of the beacon buffer are discarded in step 80, the reception sensitivity is reset in step 81, and the process returns to step 71.

  According to this embodiment, the distance between the beacon transmitter 1 and the beacon receiver 2 is received based on how many packets have been received while receiving each packet transmitted in one cycle while reducing the reception sensitivity by a predetermined amount. Therefore, the distance can be determined without using a GPS or RSSI value.

  Therefore, the location of the beacon receiver 2 can be determined without providing an AD converter for converting the RSSI value into digital data in a place where GPS cannot be used, such as indoors or in a mine. In addition, since the RSSI value is not used, even when the distance between the beacon transmitter 1 and the beacon receiver 2 is so close that it cannot be measured due to the saturation of the RSSI value, by appropriately setting the attenuation amount of the reception sensitivity in one cycle. The distance can be determined with a resolution corresponding to the number of packets.

  FIG. 11 is a diagram illustrating the principle of distance measurement in the position management system according to another embodiment of the present invention. As a configuration diagram of this system, FIGS. 1 to 5 can be applied as they are. In this embodiment, the beacon transmitter 1 performs the operation of transmitting the packets Pa, Pb, and Pc in this order three times in one cycle. In FIG. 11, the graphs Pa to Pc indicate the receivability of the packets Pa to Pc when the beacon receiver 2 receives the packets Pa to Pc sequentially transmitted in one cycle. A graph graphic packet having a receivability level equal to or higher than Th can be received, and a graph graphic packet lower than Th cannot be received.

  When transmitting a beacon, the beacon transmitter 1 transmits packets Pa, Pb, and Pc at predetermined large, medium, and small transmission output levels, respectively. The control of the transmission output level is performed by the central control processing unit 13 of the beacon transmitter 1 controlling the power amplification unit 12. The contents of the packets Pa to Pc are the same as those shown in FIG. However, as sequence numbers, serial numbers for nine packets transmitted in one cycle, for example, “1” to “9” are given in the order of transmission. Therefore, the sequence number of each packet Pa to Pc can be used as a value corresponding to the transmission output level of the packet.

  On the other hand, the beacon receiver 2 decreases the attenuation amount of the attenuator by a predetermined amount each time the packets Pa, Pb, and Pc are received once. That is, the first reception is performed without attenuation by the attenuator, and the second and third receptions are performed with the attenuation amount of the attenuator set to a predetermined weak and strong level, respectively. Therefore, by appropriately setting the attenuation amount of the attenuator and the above-described large, medium, and small transmission output levels, the possibility of receiving packets sequentially received in one cycle as shown in FIG. It can be made to go down. That is, nine packets in one cycle are received with nine stages of reception possibility by the three levels of transmission output level in the beacon transmitter 1 and the three levels of reception sensitivity in the beacon receiver 2.

  The nine graph figures Pa to Pc illustrated in FIG. 11 move downward as a unit as the distance between the beacon transmitter 1 and the beacon receiver 2 increases, and move upward as the distance decreases. Therefore, the distance between the beacon transmitter 1 and the beacon receiver 2 can be determined with a resolution of nine stages based on the sequence number of the packet that can be received last in one cycle. The sequence number corresponds to the reception sensitivity and the transmission output level related to the packet including the sequence number.

  Also in this embodiment, the beacon receiver 2 can send information for determining the position of the beacon receiver 2 to the base station 4 by the process of FIG. Further, the position management system can update the position management database by the operation of FIG.

  In addition, this invention is not limited to the above-mentioned embodiment, It can deform | transform and implement suitably. For example, in the embodiment of FIGS. 1 to 10 described above, the number of packets to be transmitted in one cycle has been described as three. However, the present invention is not limited to this, and four or more packets are transmitted and received with four or more different reception sensitivities. You may make it do.

  In the above description, each packet in one cycle is transmitted with a sequence number, but the sequence number may be omitted. In this case, step 75 of FIG. 10 is not necessary, but when supplying radio data to the mobile station radio 3 in step 79, data corresponding to the reception sensitivity when a packet related to the data is received, Alternatively, it is necessary to supply data indicating how many times the packet is received in one cycle.

  In the above description, the case where the reception sensitivity and the transmission output level are decreased has been described. Alternatively, the reception sensitivity and the transmission output level may be increased. In that case, the beacon data about the packet that can be received first is supplied for the determination of the distance and the position.

It is a figure showing composition of a position management system concerning one embodiment of the present invention. It is a block diagram which shows the structure of the beacon transmitter in the system of FIG. It is a block diagram which shows the structure of the beacon receiver in the system of FIG. It is a block diagram which shows the structure of the mobile station radio | wireless machine in the system of FIG. It is a block diagram which shows the structure of the base station in the system of FIG. It is a figure which shows the image in which beacon data is transmitted in the system of FIG. FIG. 2 is a diagram illustrating a method for determining a distance between a beacon transmitter and a beacon receiver in the system of FIG. 1. It is a figure which shows the format of the packet of a beacon in the system of FIG. It is a flowchart which shows operation | movement of the system of FIG. It is a flowchart which shows the process in the beacon receiver of the system of FIG. It is a figure which shows the distance measurement principle in the position management system which concerns on other embodiment of this invention. It is a block diagram which shows the structure of the receiver which performs distance measurement based on the conventional RSSI value. It is a graph which shows the relationship between receiving electric field strength and RSSI voltage.

Explanation of symbols

  1: beacon transmitter, 2, 2a, 2b: beacon receiver, 3: mobile station radio, 4: base station, 5: personal computer, 11: oscillator, 12: power amplifier, 13: central control processor, 14: control information storage unit, 21: band filter, 22: high frequency amplification unit, 23: local oscillation / detection unit, 24: low frequency amplification unit, 25: central control processing unit, 31: radio unit, 32: central control Processing unit 41: Base station radio, 42: Central control processing unit, 91: High frequency processing unit, 92: Intermediate frequency processing unit, 93: Detection processing unit, 94: Low frequency processing unit, 95: AD converter, 96: Microcomputer, A, B, C: graph curve, Pa to Pc: packet.

Claims (7)

Receiving means for receiving predetermined data wirelessly transmitted a predetermined number of times at a time from a predetermined wireless transmission device;
Sensitivity changing means for reducing the receiving sensitivity in the receiving means by a predetermined amount each time data is received by the receiving means.
While the reception sensitivity is reduced by the sensitivity changing means, each reception of data by the reception means is performed, and information corresponding to the minimum reception sensitivity that has been able to receive the data is sent to the wireless transmission device and And a control means for outputting the data for use in determining the distance between the wireless reception devices. Each data transmitted the predetermined number of times includes number specifying information for specifying how many times the data relates to transmission,
The control means outputs, as the information corresponding to the reception sensitivity, the number-of-times specifying information included in the last data that can be received by receiving the data each time accompanied by a decrease in the reception sensitivity. The wireless receiver according to claim 1. The predetermined data includes identification information of the wireless transmission device,
The radio reception apparatus according to claim 1 or 2, wherein the information output by the control means includes the identification information.   The wireless reception apparatus according to claim 3, wherein the predetermined number of data transmissions are performed periodically. A device for determining a distance between a wireless transmission device and a wireless reception device according to any one of claims 1 to 4,
The distance determination apparatus, wherein the distance is determined based on information corresponding to reception sensitivity output from the wireless reception apparatus. A position determination device for determining the position of the wireless reception device according to claim 3 or 4,
The position of the wireless reception device is determined based on information and identification information corresponding to reception sensitivity included in information output by the control unit of the wireless reception device, and a position associated with the identification information in advance. A position determination apparatus characterized by that. A receiving step for receiving predetermined data wirelessly transmitted a predetermined number of times at a time from a predetermined wireless transmission device;
A sensitivity changing step for reducing the receiving sensitivity in the receiving unit by a predetermined amount every time data is received each time in the receiving step.
The control means performs the reception of the data each time by the receiving means while reducing the receiving sensitivity by the sensitivity changing means, and the information corresponding to the minimum receiving sensitivity with which the data can be received, And a control step of outputting for use in determining the distance between the wireless transmission device and the receiving means.

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