Distance measurement system, communication station, and distance measurement method

Abstract

Provided are: a distance measurement system that is configured so that a measurement frequency can be set in accordance with a measured distance, thereby enabling precise distance measurement; a communication station; and a distance measurement method.　The distance measurement system includes a first communication station and a second communication station, and the second communication station has a distance measurement unit that performs distance measurement processing for measuring the distance to the first communication station on the basis of a result of the second communication station having bidirectionally transmitted a signal between the second communication station and the first communication station, and a frequency setting unit that sets the frequency with which the distance measurement unit performs the distance measurement processing, in accordance with the distance measured by the distance measurement unit.

Description

Ranging system, communication station, and ranging method

[0001] The present disclosure relates to a ranging system, a communication station, and a ranging method.

[0002] Conventionally, there has been a positioning time interval control device that controls the time interval for measuring a position. The positioning time interval control device includes an acquisition unit that acquires the moving state and moving speed of a mobile terminal device, and a positioning time interval setting unit that sets the time interval for measuring the position (distance) of the mobile terminal device and the time interval for outputting the position information obtained by the measurement based on the moving state and moving speed of the mobile terminal device acquired by the acquisition unit. The positioning time interval setting unit changes the time interval when the moving state and / or moving speed of the mobile terminal device change. The mobile terminal device acquires and outputs the position information of the mobile terminal device at the time interval set by the positioning time interval setting unit. The higher the moving speed of the mobile terminal device, the longer the positioning time interval setting unit sets the time interval for measuring the position of the mobile terminal device and the time interval for outputting the position information obtained by the measurement (see, for example, Patent Document 1).

[0003] International Publication No. 2011 / 102151

[0004] However, conventional positioning time interval control devices did not change the frequency of measuring (ranging) the distance to the mobile terminal device depending on the distance to the mobile terminal device, so they were unable to measure the distance to the mobile terminal device with high accuracy.

[0005] Therefore, an object of the present invention is to provide a distance measurement system, a communication station, and a distance measurement method that are capable of measuring distances with high accuracy by making it possible to set the measurement frequency according to the measured distance.

[0006] A ranging system according to an embodiment of the present disclosure includes a first communication station and a second communication station, and the second communication station has a ranging unit that performs ranging processing to measure the distance between the second communication station and the first communication station based on the results of bidirectional transmission of signals between the second communication station and the first communication station, and a frequency setting unit that sets the frequency at which the ranging unit performs the ranging processing in accordance with the distance measured by the ranging unit.

[0007] By making it possible to set the measurement frequency according to the measured distance, it is possible to provide a distance measuring system, a communication station, and a distance measuring method that are capable of measuring distances with high accuracy.

[0008] 1 is a diagram showing an example of the configuration of a vehicle 10 and a smartphone 20 equipped with ranging devices 100 and 200 according to a first embodiment, respectively. FIG. 2 is a diagram showing an example of the configuration of the ranging devices 100 and 200 according to the first embodiment. FIG. 3 is a diagram explaining an example of an overview of the overall processing of the ranging devices 100 and 200. FIG. 4 is a diagram explaining an example of the frequency of ranging processing. FIG. 5 is a flowchart showing an example of processing executed by the ranging devices 100 and 200. FIG. 6 is a flowchart showing an example of processing executed by the ranging devices 100 and 200. FIG. 7 is a diagram showing an example of a configuration in which a ranging system 300M according to a modified example of the first embodiment is applied to a speaker system. FIG. 8 is a diagram showing an example of the configuration of the ranging devices 100 and 200 according to a second embodiment. FIG. 9 is a diagram showing an example of a position where ranging information is stored in an advertising signal. FIG. 10 is a diagram showing an example of received information and ranging information received by the ranging device 100. FIG. 11 is a diagram showing an example of a calculation result of an evaluation point. FIG. 11 is a sequence diagram showing an example of processing executed by the ranging devices 100 and 200. FIG. 12 is a flowchart showing an example of specific processing content of processing 1. Processing 1 is executed by the ranging device 100. FIG. 10 is a flowchart showing an example of specific processing content of process 2; FIG. 11 is a diagram showing an example of calculation of a predicted position;

[0009] Hereinafter, embodiments to which the distance measuring system, communication station, and distance measuring method of the present disclosure are applied will be described.

[0010] <Embodiment 1> Fig. 1 is a diagram showing an example of a vehicle 10 and a smartphone 20 equipped with distance measuring devices 100 and 200, respectively, according to embodiment 1. Fig. 2 is a diagram showing an example of the configuration of the distance measuring devices 100 and 200 according to embodiment 1. A system including the distance measuring devices 100 and 200 is a distance measuring system 300.

[0011] Here, as an example, a case will be described in which the distance measuring device 100 is implemented in a smart entry system mounted on a vehicle 10, and the distance measuring device 200 is implemented in a smartphone 20. The smartphone 20 functions as a smart key for the smart entry system of the vehicle 10. The distance measuring devices 100 and 200 perform packet communication using BLE (Bluetooth (registered trademark) Low Energy), as an example.

[0012] The ranging device 100 is an example of a first communication station, and the ranging device 200 is an example of a second communication station. Here, as an example, a configuration will be described in which the ranging device 100 is a fixed station that does not move because the vehicle 10 is parked and not moving, and the ranging device 200 is a mobile station that can move as the owner of the smartphone 20 moves. The fixed station is not limited to the parked vehicle 10, and may be, for example, a building or the like. However, the ranging device 100 is not limited to a fixed station and may be mobile.

[0013] As another example, the vehicle 10 is equipped with an automatic parking assistance system, and the distance measuring device 100 is included in the automatic parking assistance system. The automatic parking assistance system is a system that autonomously parks the vehicle 10 in a parking position or autonomously causes the vehicle 10 to leave the parking position by remotely transmitting a command to the vehicle 10 from the smartphone 20 via wireless communication.

[0014] At least one of the ranging device 100 of the vehicle 10 and the ranging device 200 of the smartphone 20 measures the distance between the vehicle 10 and the smartphone 20, and the locks on the doors, trunk, etc. of the vehicle 10 are unlocked when the distance measured by the ranging device 100 or 200 is an appropriate distance.

[0015] Here, as an example, it is assumed that the distance measuring device 200 of the smartphone 20 performs a distance measurement process to measure the distance, and notifies the distance measurement result to the distance measuring device 100 of the vehicle 10. The distance measuring devices 100 and 200 have, as an example, the same configuration.

[0016] <Configuration of Distance Measuring Device 100> The distance measuring device 100 includes three antennas 110, a communication unit 120, and an MCU (Micro Controller Unit) 130.

[0017] <Antenna 110> The antenna 110 is connected to the communication unit 120 and receives a signal transmitted from the ranging device 200 of the smartphone 20. Although Fig. 1 illustrates a configuration in which the ranging device 100 includes three antennas 110, the ranging device 100 may include four or more antennas 110. Of the three antennas 110, two are arranged on a first axis of two mutually orthogonal axes, two are arranged on a second axis of the two mutually orthogonal axes, and one of the antennas is arranged on both the first axis and the second axis.

[0018] <Communication Unit 120> The communication unit 120 includes an AFE (Analog Front End), an AD (Analog to Digital) converter, etc., and performs signal processing such as AD conversion on the signal received by the antenna 110 from the distance measuring device 200 and outputs the signal to the MCU 130.

[0019] <MCU 130> The MCU 130 includes a main control unit 131, a signal strength measurement unit 132, a permission determination unit 133, a transmission / reception processing unit 134, a distance measurement unit 135, an angle measurement unit 136, a frequency setting unit 137, and a memory 138. The MCU 130 is realized, for example, by a microcomputer including a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), an internal bus, etc. The main control unit 131, the signal strength measurement unit 132, the permission determination unit 133, the transmission / reception processing unit 134, the distance measurement unit 135, the angle measurement unit 136, and the frequency setting unit 137 are functional blocks representing the functions of a program executed by the MCU 130. The memory 138 is a functional representation of the memory of the MCU 130.

[0020] <Main control unit 131> The main control unit 131 is a processing unit that controls the entire MCU 130, and performs processing other than the processing performed by the signal strength measurement unit 132, the permission determination unit 133, the transmission / reception processing unit 134, the distance measurement unit 135, the angle measurement unit 136, and the frequency setting unit 137.

[0021] <Signal Strength Measurement Unit 132> The signal strength measurement unit 132 measures a received signal strength indicator (RSSI) that indicates the signal strength of an advertising signal received from the ranging device 200 via the communication unit 120, and outputs the RSSI to the permission determination unit 133. Since the RSSI of the advertising signal output by the ranging device 200 and the distance between the ranging devices 100 and 200 are proportional to each other, if the RSSI of the advertising signal output by the ranging device 200 is measured in advance at a plurality of distances, the distance between the ranging devices 100 and 200 can be estimated based on the RSSI measured by the signal strength measurement unit 132 by interpolation processing or the like.

[0022] <Permission Determination Unit 133> The permission determination unit 133 determines whether to permit the ranging device 100 to communicate with the ranging device 200 via BLE, based on the RSSI of the advertising signal measured by the signal strength measurement unit 132, and if permission is granted, performs permission determination processing to generate a permission signal. More specifically, if the signal strength measured by the signal strength measurement unit 132 is equal to or greater than a predetermined strength, the permission determination unit 133 permits the ranging unit 235 of the ranging device 200 to perform ranging processing. The permission signal is transmitted to the ranging device 200 by the main control unit 131.

[0023] <Transmission and Reception Processing Unit 134> The transmission and reception processing unit 134 transmits and receives signals to and from the transmission and reception processing unit 234 of the ranging device 200 in order to acquire data such as the round-trip time, phase difference, and frequency components of the signal required for the ranging unit 135 of the ranging device 100 or the ranging unit 235 of the ranging device 200 to perform ranging. In the first embodiment, as an example, the ranging process for calculating the distance between the ranging devices 100 and 200 is performed by the ranging unit 235 of the ranging device 200, and not by the ranging unit 135 of the ranging device 100. For this reason, the transmission and reception processing unit 134 performs the following auxiliary processing in accordance with the processing of the transmission and reception processing unit 234 when the ranging unit 235 of the ranging device 200 performs ranging.

[0024] When the ranging unit 235 of the ranging device 200 performs ranging in the RTT (Round Trip Time) format, the transmission / reception processing unit 134 receives an RTT signal from the transmission / reception processing unit 234 of the ranging device 200 via the antenna 110, and then sends the RTT signal back from the antenna 110 to the transmission / reception processing unit 234 of the ranging device 200. In this case, the transmission / reception processing unit 134 only needs to use one of the three antennas 110 to receive and transmit signals.

[0025] The transmission / reception processing unit 134 transmits and receives signals to and from the transmission / reception processing unit 234 of the ranging device 200 when the ranging unit 235 of the ranging device 200 performs ranging using the TOA (Time of Arrival) method. In this case, the transmission / reception processing unit 134 may transmit and receive signals using one of the three antennas 110. The transmission / reception processing unit 134 measures the phase of the signal received from the ranging device 200 and transmits data indicating the measured phase to the ranging device 200.

[0026] In addition, when the angle measurement unit 236 of the ranging device 200 performs angle measurement using the AOA (Angle of Arrival) format, the transmission / reception processing unit 134 receives the signal from the ranging device 200 using the three antennas 110, measures the phase difference when the three antennas 110 receive the signal, and transmits data representing the measured phase difference to the ranging device 200.

[0027] <Range measurement unit 135> The range measurement unit 135 can perform ranging processing using the RTT method and ranging processing using the TOA method. In the first embodiment, the range measurement unit 235 of the range measurement device 200 performs ranging processing (processing for calculating distance), and therefore the range measurement unit 135 does not perform ranging processing. The ranging processing using the RTT method and the TOA method will be described later for the range measurement unit 235 of the range measurement device 200. Here, as an example, in order to describe a configuration in which the range measurement devices 100 and 200 have the same configuration, the MCU 130 of the range measurement device 100 has the range measurement unit 135, but the MCU 130 of the range measurement device 100 does not have to have the range measurement unit 135.

[0028] <Angle measurement unit 136> The angle measurement unit 136 can perform angle measurement processing using the three antennas 110 to measure the elevation angle and azimuth angle in a polar coordinate system of the position of the ranging device 200 relative to the ranging device 100 in the AOA format. However, in the first embodiment, as an example, the angle measurement unit 136 of the ranging device 100 does not perform angle measurement processing, and the angle measurement unit 236 of the ranging device 200 performs angle measurement processing, so the angle measurement unit 136 does not perform angle measurement processing. Note that the MCU 130 of the ranging device 100 does not need to have the angle measurement unit 136.

[0029] <Frequency setting unit 137> When the ranging unit 135 executes a ranging process, the frequency setting unit 137 sets the frequency at which the ranging unit 135 executes the ranging process, depending on the distance measured by the ranging process executed by the ranging unit 135. However, in the first embodiment, as an example, the ranging unit 135 of the ranging device 100 does not execute the ranging process, and the ranging unit 235 of the ranging device 200 executes the ranging process, and therefore the frequency setting unit 137 does not execute the process of setting the frequency. Note that the MCU 130 of the ranging device 100 does not need to have the frequency setting unit 137.

[0030] <Memory 138> The memory 138 stores programs, data, etc. required when the main control unit 131, signal strength measurement unit 132, permission determination unit 133, transmission / reception processing unit 134, distance measurement unit 135, angle measurement unit 136, and frequency setting unit 137 execute processing.

[0031] <Configuration of Distance Measuring Device 200> The distance measuring device 200 includes three antennas 210, a communication unit 220, and an MCU 230. Each antenna 210 is connected to the communication unit 220 and receives a signal transmitted from the distance measuring device 100. Although Fig. 1 illustrates a configuration in which the distance measuring device 200 includes three antennas 210, the distance measuring device 200 may include four or more antennas 210. Of the three antennas 210, two are arranged on a first axis of two mutually orthogonal axes, two are arranged on a second axis of the two mutually orthogonal axes, and one of the antennas is arranged on both the first axis and the second axis.

[0032] The ranging device 200 has, as an example, the same configuration as the ranging device 100. That is, the antenna 210, the communication unit 220, and the MCU 230 are the same as the antenna 110, the communication unit 120, and the MCU 130 of the ranging device 100, respectively. However, in the first embodiment, the ranging device 200 does not measure RSSI or determine whether to permit connection, but instead performs ranging processing, angle measurement processing, and frequency setting processing. Therefore, in the first embodiment, the operations of the ranging devices 100 and 200 are different. The MCU 230 will be described below.

[0033] <MCU 230> The MCU 130 has a main control unit 231, a signal strength measurement unit 232, a permission determination unit 233, a transmission / reception processing unit 234, a distance measurement unit 235, an angle measurement unit 236, a frequency setting unit 237, and a memory 238. The main control unit 231, the signal strength measurement unit 232, the permission determination unit 233, the transmission / reception processing unit 234, the distance measurement unit 235, the angle measurement unit 236, the frequency setting unit 237, and the memory 238 are the same as the main control unit 131, the signal strength measurement unit 132, the permission determination unit 133, the transmission / reception processing unit 134, the distance measurement unit 135, the angle measurement unit 136, the frequency setting unit 137, and the memory 138 of the MCU 130 of the distance measuring device 100, respectively.

[0034] The main control unit 231, signal strength measurement unit 232, permission determination unit 233, transmission / reception processing unit 234, distance measurement unit 235, angle measurement unit 236, and frequency setting unit 237 are functional blocks showing the functions of the program executed by the MCU 230. Also, memory 238 is a functional representation of the memory of the MCU 230.

[0035] <Main control unit 231> The main control unit 231 is a processing unit that controls the entire MCU 230, and performs processing other than the processing performed by the signal strength measurement unit 232, the permission determination unit 233, the transmission / reception processing unit 234, the distance measurement unit 235, the angle measurement unit 236, and the frequency setting unit 237.

[0036] <Signal Strength Measurement Unit 232> Like the signal strength measurement unit 132 of the ranging device 100, the signal strength measurement unit 232 can measure the RSSI of the advertising signal received from the ranging device 100 via the communication unit 220. However, in the first embodiment, since the signal strength measurement unit 132 of the ranging device 100 measures the RSSI, the MCU 230 of the ranging device 200 does not need to have the signal strength measurement unit 232.

[0037] <Permission Determination Unit 233> Similar to the permission determination unit 133 of the ranging device 100, the permission determination unit 233 determines whether to permit the ranging device 200 to communicate with the ranging device 200 via BLE, based on the RSSI of the advertising signal measured by the signal strength measurement unit 232, and is capable of generating a permission signal if permission is permitted. However, in the first embodiment, the permission determination unit 133 of the ranging device 100 performs the permission determination process, and therefore the MCU 230 of the ranging device 200 does not need to have the permission determination unit 233.

[0038] <Transmission / reception processing unit 234> The transmission / reception processing unit 234 transmits and receives signals to and from the ranging device 100 in order to acquire data such as phase difference and frequency components necessary for the ranging unit 235 and angle measuring unit 236 to perform ranging and angle measurement.

[0039] The transmission and reception processing unit 234 transmits and receives signals to and from the transmission and reception processing unit 134 of the ranging device 100 in order to acquire data such as the round-trip time, phase difference, and frequency components of the signal that are necessary for the ranging unit 235 to perform the ranging process. That is, the ranging unit 235 performs the ranging process together with the transmission and reception processing unit 134 of the ranging device 100. In this way, the ranging unit 235 performing the ranging process together with the transmission and reception processing unit 134 of the ranging device 100 is equivalent to the ranging device 200 performing the ranging process together with the ranging device 100. Also, the transmission and reception processing unit 234 transmits and receives signals to and from the transmission and reception processing unit 134 of the ranging device 100 in order to acquire signals and the like that the angle measurement unit 236 requires to perform the angle measurement process. That is, the angle measurement unit 236 performs the angle measurement process together with the transmission and reception processing unit 134 of the ranging device 100. In this way, the angle measurement unit 236 performing the angle measurement process together with the transmission and reception processing unit 134 is equivalent to the ranging device 200 performing the angle measurement process together with the ranging device 100.

[0040] The distance measurement process for calculating the distance between the distance measuring devices 100 and 200 is performed by the distance measuring unit 235 of the distance measuring device 200, but not by the distance measuring unit 135 of the distance measuring device 100. Furthermore, the angle measurement process is performed by the angle measurement unit 236 of the distance measuring device 200, but not by the angle measurement unit 136 of the distance measuring device 100. For this reason, when the distance measuring unit 235 and the angle measurement unit 236 perform the distance measurement process and the angle measurement process, respectively, the transmission / reception processing unit 234 performs the following auxiliary processes in accordance with the processes of the distance measuring unit 235 and the angle measurement unit 236.

[0041] When the ranging unit 235 performs ranging in the RTT format, the transmission / reception processing unit 234 transmits an RTT signal to the ranging device 100 via the antenna 210, and upon receiving the RTT signal from the ranging device 100, measures the round-trip time, which is the time required from transmission to reception, and outputs it to the ranging unit 235. The transmission / reception processing unit 234 may use one of the three antennas 110 to receive and transmit the RTT signal.

[0042] When the ranging unit 235 performs distance measurement using the TOA method, the transmission / reception processing unit 234 transmits TOA signals of multiple frequencies bidirectionally to and from the transmission / reception processing unit 134 of the ranging device 100. In this case, the transmission / reception processing unit 234 only needs to transmit the TOA signal using one of the three antennas 110. The transmission / reception processing unit 234 measures the phase of the TOA signal received from the ranging device 100, calculates the phase difference between the round trip of the TOA signal of each frequency using data representing the phase received from the ranging device 200, and outputs data representing the phase difference for each of the multiple frequencies to the ranging unit 235.

[0043] In addition, when the angle measurement unit 236 performs angle measurement using the AOA format, when the distance measurement unit 235 performs distance measurement using the TOA format, data representing the phase difference when the three antennas 210 receive from the distance measurement device 100 is output to the angle measurement unit 236.

[0044] The ranging unit 235 can perform ranging processing in the RTT format and ranging processing in the TOA format. When performing ranging processing in the RTT format, the ranging unit 235 calculates the distance between the ranging devices 100 and 200 based on data indicating the round-trip time acquired from the transmission / reception processing unit 234.

[0045] When performing distance measurement processing using the TOA method, the distance measurement unit 235 acquires data representing the phase difference for each of multiple frequencies from the transmission / reception processing unit 234, and calculates the distance between the distance measuring devices 100 and 200 based on the relationship between the multiple phase differences and the frequencies. The distance calculated using the TOA method has much higher accuracy than the distance calculated using the RTT method.

[0046] <Angle measurement unit 236> The angle measurement unit 236 measures the elevation angle and azimuth angle in a polar coordinate system of the position of the ranging device 100 relative to the ranging device 200 in the AOA format using the three antennas 210. The angle measurement unit 236 measures the elevation angle and azimuth angle in the AOA format based on the phase difference when the three antennas 210 receive the signal transmitted from the ranging device 100. The phase difference when the three antennas 210 receive the signal is a first phase difference when the two antennas 210 located on the first axis receive the signal, and a second phase difference when the two antennas 210 located on the second axis receive the signal. The angle measurement unit 236 calculates the azimuth angle representing the position of the ranging device 100 relative to the ranging device 200 from the ratio between the first phase difference and the second phase difference. Furthermore, the angle measurement unit 236 calculates an elevation angle that indicates the position of the ranging device 100 relative to the ranging device 200, based on the azimuth angle and the first phase difference or the second phase difference. In the AOA type angle measurement process, the elevation angle and azimuth angle in the polar coordinate system of the position of the ranging device 100 relative to the ranging device 200 can be measured.

[0047] <Frequency setting unit 237> The frequency setting unit 237 sets the frequency at which the distance measurement unit 235 performs the distance measurement process, depending on the distance measured by the distance measurement process executed by the distance measurement unit 235. The frequency at which the distance measurement process is performed represents the number of times the distance measurement process is performed within a predetermined unit time (e.g., 60 seconds), or the time interval at which the distance measurement process is performed. A high frequency of the distance measurement process represents a large number of times the distance measurement process is performed within a predetermined unit time, or in other words, a short time interval at which the distance measurement process is performed.

[0048] When the distance between the distance measuring devices 100 and 200 is far, the frequency of the distance measurement process may be low. This is because the smartphone 20 equipped with the distance measuring device 200 is far away from the vehicle 10 equipped with the distance measuring device 100, and it is unlikely that the owner of the smartphone 20 will immediately unlock the doors or trunk of the vehicle 10. On the other hand, when the distance between the distance measuring devices 100 and 200 is close, the frequency of the distance measurement process is increased. This is because the smartphone 20 is close to the vehicle 10, and there is a possibility that the owner of the smartphone 20 will immediately unlock the doors or trunk of the vehicle 10. For this reason, the frequency setting unit 237 increases the frequency as the distance measured by the distance measuring unit 235 becomes shorter. How the frequency setting unit 237 sets the frequency of measurement by the distance measuring unit 235 according to the distance will be described later using the flowcharts of FIGS. 4A and 4B .

[0049] <Memory 238> The memory 238 stores programs, data, etc. required when the main control unit 231, signal strength measurement unit 232, permission determination unit 233, transmission / reception processing unit 234, distance measurement unit 235, angle measurement unit 236, and frequency setting unit 237 execute processing.

[0050] The main control unit 231 determines the position of the distance measuring device 100 relative to the distance measuring device 200 based on the distance determined by the distance measuring unit 235 and the angle (elevation angle and azimuth angle) determined by the angle measuring unit 236 .

[0051] <Overview of Overall Processing> Fig. 3A is a diagram illustrating an example of an overview of the overall processing of the ranging devices 100 and 200. Fig. 3B is a diagram illustrating an example of the frequency of ranging processing. Fig. 3A shows a state in which a person carrying a smartphone 20 is walking toward a vehicle 10. Fig. 3B shows the frequency of ranging processing performed by the ranging devices 100 and 200 in chronological order. In Fig. 3B, the ranging device 100 is an Anchor (fixed station), the ranging device 200 is a Tag (mobile station), and the horizontal axis is the time axis.

[0052] 3A, as an example, threshold values ​​of 60 m (an example of distance 3), 30 m (an example of distance 2), and 10 m (an example of distance 1) are set for the distance between distance measuring device 100 mounted on vehicle 10 and distance measuring device 200. Distance 2 is an example of a first predetermined distance, and distance 1 is an example of a second predetermined distance.

[0053] In addition, the frequency (time interval) of the RSSI measurement process by the signal strength measurement unit 132 or the distance measurement process by the distance measurement unit 135 using the RTT or TOA method is set according to the distance between the distance measuring devices 100 and 200. In the following, time interval 1, time interval 2, and time interval 3 are used. Time interval 1 is the shortest and time interval 3 is the longest. In other words, the relationship of time interval 1 < time interval 2 < time interval 3 holds. Time interval 1, time interval 2, and time interval 3 are expressed in terms of frequency as high frequency, medium frequency, and low frequency, respectively.

[0054] <When the distance between the ranging devices 100 and 200 is longer than 60 m> As an example, when the distance between the ranging devices 100 and 200 is longer than 60 m, the ranging unit 235 of the ranging device 200 does not perform ranging processing, and the signal strength measurement unit 132 of the ranging device 100 simply measures the RSSI of the advertising signal output by the ranging device 200. The RSSI measurement is performed at the longest time interval 3. Because the distance between the ranging devices 100 and 200 is sufficiently far, it is unlikely that the owner of the smartphone 20 will immediately unlock the doors or trunk of the vehicle 10. In such a situation, not performing ranging processing can reduce the power consumption of the ranging devices 100 and 200.

[0055] Furthermore, since the signal strength measurement unit 132 of the ranging device 100 simply measures the RSSI of the advertising signal, the processing load on the ranging devices 100 and 200 is small, which can improve the responsiveness of the ranging devices 100 and 200. In particular, when there are multiple ranging devices 200, high responsiveness of the ranging device 100 is useful.

[0056] <When the distance between the ranging devices 100 and 200 is 60 m or less but greater than 30 m> Also, as an example, when the distance between the ranging devices 100 and 200 is 60 m or less but greater than 30 m, the ranging unit 235 of the ranging device 200 performs ranging processing in the RTT format at time interval 3 (low frequency). Ranging at the longest time interval 3 is low frequency ranging. For example, low frequency ranging processing is performed at a very long time interval, as shown in the upper part of FIG. 3B . For example, time interval 3 is 100 seconds.

[0057] In the RTT ranging process, the ranging device 200 transmits an RTT signal to the ranging device 100 once, and the ranging device 100, having received the RTT signal, transmits the RTT signal back to the ranging device 200 once, thereby determining the distance between the ranging devices 100 and 200 based on the round-trip time of the RTT signal between the ranging devices 100 and 200. Because the ranging devices 100 and 200 only transmit the RTT signal once each, the processing load on the ranging devices 100 and 200 is small, and ranging process can be performed in a short time. However, the ranging accuracy is lower than that of the TOA ranging method.

[0058] The distance between the distance measuring devices 100 and 200 is relatively long, and it is unlikely that the owner of the smartphone 20 will immediately unlock the doors or trunk of the vehicle 10. Therefore, when the distance measured in the RTT format is 60 m or less but longer than 30 m, the power consumption of the distance measuring devices 100 and 200 can be reduced by performing the distance measuring process in the RTT format, which has a small processing load on the distance measuring devices 100 and 200, without performing the distance measuring process using TOA as part of the authentication process. Furthermore, it is unlikely that the owner of the smartphone 20 will immediately unlock the doors or trunk of the vehicle 10, and the need for authentication process is low, so the power consumption of the distance measuring devices 100 and 200 is reduced by not performing the authentication process including TOA.

[0059] Furthermore, since the processing load of the distance measuring devices 100 and 200 is small, it is possible to improve the responsiveness of the distance measuring devices 100 and 200. In particular, when there are multiple distance measuring devices 200, it is useful that the distance measuring device 100 has high responsiveness.

[0060] <When the distance between the ranging devices 100 and 200 is 30 m or less but greater than 10 m> Also, as an example, when the distance between the ranging devices 100 and 200 is 30 m or less but greater than 10 m, the ranging unit 235 of the ranging device 200 performs TOA-type ranging processing at time interval 2 (medium frequency). Ranging at time interval 2 is medium-frequency ranging. As an example, as shown in the middle part of Figure 3B, the time interval 2 for performing medium-frequency ranging processing is shorter than the low-frequency time interval 3 shown in the upper part of Figure 3B and longer than the high-frequency time interval 1 shown in the lower part of Figure 3B. As an example, time interval 2 is 10 seconds.

[0061] In addition, when the distance between the ranging devices 100 and 200 is 30 m or less but greater than 10 m, the angle measurement unit 236 measures the elevation angle and azimuth angle in AOA format at time intervals of 2 (medium frequency) based on the phase difference when the signal transmitted from the ranging device 100 is received by the three antennas 210.

[0062] If the distance determined by TOA ranging is 30 m or less but longer than 10 m, it is still unlikely that the owner of the smartphone 20 will immediately unlock the doors or trunk of the vehicle 10. Considering that a human moving speed is approximately 1 m / s to 4 m / s, if the distance is longer than 10 m, it is likely that it will take several seconds for the owner of the smartphone 20 to reach the vehicle 10. Because TOA ranging involves bidirectional transmission of signals at multiple frequencies between the ranging devices 100 and 200, the processing load on the ranging devices 100 and 200 is relatively large. However, by reducing the frequency of ranging processing, it is possible to reduce the power consumption of the ranging devices 100 and 200 and improve responsiveness. Furthermore, high responsiveness of the ranging device 100 is particularly useful when multiple ranging devices 200 are used. Furthermore, if the distance determined by TOA ranging is 30 m or less but longer than 10 m, elevation and azimuth angles are measured using the AOA method at a moderate frequency.

[0063] <When the distance between the ranging devices 100 and 200 is 10 m or less> Also, as an example, when the distance between the ranging devices 100 and 200 is 10 m or less, the ranging unit 235 of the ranging device 200 performs TOA ranging processing at time interval 1 (high frequency). Ranging at time interval 1 is high frequency ranging. For example, as shown in the bottom row of Figure 3B, the time interval for performing ranging processing is shorter than the low frequency and medium frequency shown in the top and middle rows of Figure 3B, and the ranging processing is repeatedly performed with almost no waiting. For example, time interval 1 is 0.1 seconds.

[0064] In addition, when the distance between the ranging devices 100 and 200 is 10 m or less, the angle measurement unit 236 measures the elevation angle and azimuth angle in AOA format at time interval 1 (high frequency) based on the phase difference when the signal transmitted from the ranging device 100 is received by the three antennas 210.

[0065] If the distance obtained by TOA distance measurement is 10 m or less, there is a possibility that the owner of the smartphone 20 will immediately unlock the doors or trunk of the vehicle 10. For this reason, the frequency of TOA distance measurement processing is increased, authentication processing is performed frequently, and elevation angles and azimuth angles are measured frequently using AOA.

[0066] 4A and 4B are flowcharts showing an example of processing executed by the distance measuring devices 100 and 200. In Fig. 4A and 4B, the left half shows processing of the distance measuring device 100, and the right half shows processing of the distance measuring device 200, thereby explaining the relationship between the processing of the distance measuring devices 100 and 200.

[0067] When the process starts, first, the ranging device 200, which is the Tag, transmits an advertising signal (step S201). Note that the process of the ranging devices 100 and 200 starts, for example, when the ranging device 200 transmits a start notification to the ranging device 100 and the ranging device 100 receives the start notification.

[0068] The ranging device 200, which is the anchor, receives the advertising signal and measures the RSSI (step S101). The RSSI measurement is performed by the signal strength measurement unit 132.

[0069] The ranging device 100 estimates the distance between the ranging devices 100 and 200 based on the measured RSSI, and determines whether the estimated distance is equal to or less than distance 3 (step S102). This process is executed by the permission determination unit 133. Distance 3 is, for example, 60 m.

[0070] If the distance measuring device 100 determines that the estimated distance is equal to or less than distance 3 (S102: YES), it generates a permission signal and transmits it to the distance measuring device 200 (step S103). The permission determination unit 133 generates the permission signal.

[0071] If the ranging device 100 determines in step S102 that the estimated distance is not equal to or less than distance 3 (S102: NO), the flow returns to step S101. This is to receive the advertising signal again and measure the RSSI again.

[0072] After transmitting the permission signal to the ranging device 200, the ranging device 100 transmits a measurement start notification of the RTT-type ranging process to the ranging device 200 (step S104). The measurement start notification of the RTT-type ranging process is a notification indicating that the ranging process will be performed in the RTT format. The process of step S104 is executed, for example, by the transmission / reception processing unit 134 of the ranging device 100.

[0073] When the ranging device 100 transmits the measurement start notification of the RTT-type ranging process, the ranging device 100 executes the RTT-type ranging process together with the ranging device 200 (step S105). The process of step S105 is executed by the transmission / reception processing unit 134 of the ranging device 100, for example.

[0074] The ranging device 200 determines whether or not an authorization signal is received within a predetermined time after transmitting the advertising signal (step S202). The predetermined time is, for example, 0.01 seconds. If the authorization signal is not received within the predetermined time, a timeout occurs. The processing of step S202 is, for example, executed by the main control unit 231 of the ranging device 200.

[0075] If the ranging device 200 determines that it has received the permission signal within the predetermined time (S202: YES), it receives a measurement start notification for the RTT ranging process (step S203). The process of step S203 is executed by the main control unit 231 of the ranging device 200, for example.

[0076] If the ranging device 200 determines in step S202 that it has not received the permission signal within the predetermined time (S202: NO), it returns the flow to step S201 to retransmit the advertising signal and start the process again.

[0077] When the ranging device 200 receives the measurement start notification of the RTT-type ranging process, it executes the ranging process in the RTT type together with the ranging device 100 (step S204). The process of step S204 is performed integrally with the process of step S105 executed by the ranging device 100, and is executed by the transmission / reception processing unit 134 of the ranging device 100 and the transmission / reception processing unit 234 and the ranging unit 235 of the ranging device 200. Specifically, the transmission / reception processing unit 234 transmits an RTT signal, the transmission / reception processing unit 134 transmits a return RTT signal, and the ranging unit 235 measures the distance between the ranging devices 100 and 200 in the RTT type based on the round-trip time acquired by the transmission / reception processing unit 234. In the process of step S204, the distance between the ranging devices 100 and 200 is calculated by the RTT-type ranging process.

[0078] When the ranging process in the RTT format in steps S105 and S204 is completed, the ranging device 200 determines whether the measured distance is equal to or less than distance 2 (step S205). The process of step S205 is executed by the frequency setting unit 237 of the ranging device 200, for example.

[0079] If the distance measuring device 200 determines that the measured distance is not equal to or less than distance 2 (S205: NO), it sets the time interval for measuring distance to time interval 3 (step S206A). If the measured distance is not equal to or less than distance 2, the measured distance is distance 3, and therefore the time interval is set to time interval 3, which corresponds to distance 3. The processing of step S206A is executed by the frequency setting unit 237 of the distance measuring device 200, for example.

[0080] Furthermore, if the distance measuring device 200 determines in step S205 that the measured distance is equal to or less than distance 2 (S205: YES), it sets the time interval for measuring distance to time interval 2 (step S206B). If the measured distance is equal to or less than distance 2, the measured distance is distance 2 or distance 1, and therefore the time interval is provisionally set to time interval 2, which corresponds to distance 2. The processing of step S206B is executed by the frequency setting unit 237 of the distance measuring device 200, for example.

[0081] After completing the process of step S206A or S206B, the distance measuring device 200 transmits interval data indicating the time interval set in step S206A or S206B to the distance measuring device 100 (step S207). The process of step S207 is executed by the main control unit 231 of the distance measuring device 200, for example.

[0082] The distance measuring device 100 receives the interval data from the distance measuring device 200 (step S106). The process of step S106 is executed by the main control unit 131 of the distance measuring device 100, for example.

[0083] The distance measuring device 100 determines whether the time interval represented by the interval data received in step S106 is time interval 2 (step S107). The process of step S107 is executed by the main control unit 131 of the distance measuring device 100, for example.

[0084] If the ranging device 100 determines that the time interval represented by the received interval data is not time interval 2 (S107: NO), it sets the standby time in the ranging device 100 to time interval 3 (step S108A). The process of step S108A is executed, for example, by the main control unit 131. After completing the process of step S108A, the ranging device 100 returns the flow to step S101. This is to start over from measuring the RSSI.

[0085] Furthermore, if the ranging device 100 determines in step S107 that the time interval represented by the received interval data is time interval 2 (S107: YES), it sets the standby time in the ranging device 100 to time interval 2 (step S108B). After completing the process of step S108B, the ranging device 100 proceeds to step S109. The process of step S108B is executed by the main control unit 131, for example.

[0086] The ranging device 100 transmits a measurement start notification for the TOA ranging process and the AOA angle measuring process to the ranging device 200 (step S109). The measurement start notification for the TOA ranging process and the AOA angle measuring process is a notification indicating that the TOA ranging process and the AOA angle measuring process will be performed. The processing of step S109 is executed, for example, by the transmission / reception processing unit 134 of the ranging device 100.

[0087] When the ranging device 100 transmits the measurement start notification for the TOA ranging process and the AOA angle measuring process, the ranging device 100 executes the TOA ranging process together with the ranging device 200 (step S110). The process of step S110 is executed by the transmission / reception processing unit 134 of the ranging device 100, for example.

[0088] The distance measuring device 200 receives the notification of the start of the TOA distance measuring process and the AOA angle measuring process (step S208). The process of step S208 is executed by the main control unit 231 of the distance measuring device 200, for example.

[0089] When the ranging device 200 receives the measurement start notification of the TOA ranging process and the AOA angle measuring process, it performs the TOA ranging process together with the ranging device 100, and also performs the AOA angle measuring process when receiving a signal from the ranging device 100 (step S209). The ranging process in step S209 is performed integrally with the process of step S110 performed by the ranging device 100, and is executed by the transmission / reception processing unit 134 of the ranging device 100, and the transmission / reception processing unit 234 and the ranging unit 235 of the ranging device 200. Specifically, the transmission / reception processing unit 234 sequentially transmits TOA signals of multiple frequencies, and the transmission / reception processing unit 134 sequentially returns TOA signals of the same frequencies, and transmits phase data indicating the phase when the transmission / reception processing unit 134 received the signal to the ranging device 200. In addition, the AOA type angle measurement processing in step S209 is a process in which the ranging device 200 measures the first phase difference and the second phase difference when it receives a TOA signal from the ranging device 100, and measures the azimuth angle and elevation angle representing the position of the ranging device 100 relative to the ranging device 200 based on the first phase difference and the second phase difference.

[0090] Furthermore, the distance measuring device 200 transmits data indicating the distance and angle obtained in the distance measurement process and angle measurement process in step S209 to the distance measuring device 100. Such data transmission may be performed by the transmission / reception processing unit 234, for example.

[0091] The ranging unit 235 of the ranging device 200 acquires a round-trip phase difference for each frequency, which is obtained by adding the phase when the transmission / reception processing unit 234 receives a signal from the ranging device 100 and the phase represented by the phase data received from the ranging device 100. The ranging unit 235 measures the distance between the ranging devices 100 and 200 using the TOA method based on the relationship between multiple frequencies and the round-trip phase difference at each frequency. In the process of step S209, the distance between the ranging devices 100 and 200 is calculated using the TOA method. The accuracy of ranging using the TOA method is much higher than the accuracy of ranging using the RTT method. In the process of step S209, the angle measurement unit 236 of the ranging device 200 measures the elevation angle and azimuth angle using the AOA method at time interval 1 (high frequency) based on the phase difference when the TOA signal transmitted from the ranging device 100 is received by the three antennas 210.

[0092] When the distance measurement process in the TOA format and the angle measurement process in the AOA format in steps S110 and S209 are completed, the distance measuring device 200 determines whether the measured distance is equal to or less than distance 1 (step S210). The process of step S210 is executed by the frequency setting unit 237 of the distance measuring device 200, for example.

[0093] If the distance measuring device 200 determines that the measured distance is not equal to or less than distance 1 (S210: NO), it sets the time interval for measuring distance to time interval 2 (step S211A). If the measured distance is not equal to or less than distance 1, the measured distance is longer than distance 1 and equal to or less than distance 2, so the time interval is set to time interval 2. The process of step S211A is executed by the frequency setting unit 237 of the distance measuring device 200, for example.

[0094] Furthermore, if the distance measuring device 200 determines in step S210 that the measured distance is equal to or shorter than distance 1 (S210: YES), it sets the time interval for measuring distance to time interval 1 (step S211B). If the measured distance is equal to or shorter than distance 1, the time interval is set to time interval 1. The process of step S211B is executed by the frequency setting unit 237 of the distance measuring device 200, for example.

[0095] After completing the process of step S211A or S211B, the distance measuring device 200 transmits interval data indicating the time interval set in step S211A or S211B to the distance measuring device 100 (step S212). The process of step S212 is executed by the main control unit 231 of the distance measuring device 200, for example.

[0096] The distance measuring device 100 receives the interval data from the distance measuring device 200 (step S111). The process of step S111 is executed by the main control unit 131 of the distance measuring device 100, for example.

[0097] The distance measuring device 100 determines whether the time interval represented by the interval data received in step S111 is time interval 1 (step S112). The process of step S112 is executed by the main control unit 131 of the distance measuring device 100, for example.

[0098] If the ranging device 100 determines that the time interval represented by the received interval data is not time interval 1 (S112: NO), it sets the standby time in the ranging device 100 to time interval 2 (step S113A). The process of step S113A is executed by the main control unit 131. After completing the process of step S113A, the ranging device 100 returns the flow to step S104. This is to restart the ranging process in the RTT format.

[0099] Furthermore, if the distance measuring device 100 determines in step S112 that the time interval represented by the received interval data is time interval 1 (S112: YES), it sets the standby time in the distance measuring device 100 to time interval 1 (step S113B). The processing of step S113B is executed by the main control unit 131.

[0100] After completing the process of step S113B, the ranging device 100 determines whether to end the process (step S114). The process ends when, for example, the authentication process is successful. The process of step S114 is executed by the main control unit 131. The authentication process uses the distance and angle data obtained by the ranging device 200 in the ranging process and angle measurement process of step S209 and transmitted to the ranging device 100.

[0101] If the ranging device 100 determines not to end the process (S114: NO), the flow returns to step S109 in order to perform the TOA ranging process and the AOA angle measuring process at a high frequency of time interval 1.

[0102] Furthermore, when the distance measuring device 100 determines to end the process (S114: YES), it transmits a notification of end to the distance measuring device 200 (step S115). After transmitting the notification of end to the distance measuring device 200, the distance measuring device 100 ends the process (END).

[0103] When the distance measuring device 200 receives the notification of completion from the distance measuring device 100, the series of processes ends (END).

[0104] <Effects> The ranging system 300 of the first embodiment includes the ranging device 100 and the ranging device 200, and the ranging device 200 has a ranging unit 235 that performs ranging processing to measure the distance between the ranging device 200 and the ranging device 100 based on the results of signals transmitted in both directions between the ranging device 200 and the ranging device 100, and a frequency setting unit 237 that sets the frequency at which the ranging unit 235 performs the ranging processing in accordance with the distance measured by the ranging unit 235. Therefore, the frequency at which the ranging unit 235 performs the ranging processing can be set in accordance with the distance measured by the ranging unit 235.

[0105] Therefore, by making it possible to set the measurement frequency according to the measured distance, it is possible to provide a distance measuring system 300 that is capable of measuring distances with high accuracy. Furthermore, since the measurement frequency is set according to the measured distance, it is possible to reduce the power consumption of the distance measuring devices 100 and 200 according to the measured distance.

[0106] Furthermore, the distance measuring device 200 is movable relative to the distance measuring device 100. Therefore, when the distance between the distance measuring devices 100 and 200 changes due to the movement of the distance measuring device 200 relative to the distance measuring device 100, the measurement frequency can be set according to the measured distance, thereby providing a distance measuring system 300 capable of measuring distances with high accuracy.

[0107] Furthermore, the frequency setting unit 237 increases the frequency as the distance measured by the distance measuring unit 235 becomes shorter, and therefore, the shorter the distance between the distance measuring devices 100 and 200, the more frequently distance measurement processing can be performed. Therefore, it is possible to provide a distance measuring system 300 that can measure distances more frequently as the distance between the distance measuring devices 100 and 200 becomes shorter. Furthermore, by setting the measurement frequency lower as the measured distance becomes longer, the power consumption of the distance measuring devices 100 and 200 can be reduced as the measured distance becomes longer.

[0108] The ranging device 100 also has a signal strength measurement unit 132 that performs a signal strength measurement process that measures the signal strength (RSSI) of a signal received from the ranging device 200, and a permission determination unit 133 that permits the ranging unit 235 of the ranging device 200 to perform the ranging process when the signal strength measured by the signal strength measurement unit 132 is equal to or greater than a predetermined strength. Therefore, the ranging unit 235 can perform the ranging process when the RSSI of the signal transmitted by the ranging device 200 is equal to or greater than a predetermined value and the ranging device 200 is somewhat close to the ranging device 100, and can prevent the ranging process from being performed when the RSSI of the signal transmitted by the ranging device 200 is less than the predetermined value. When the ranging devices 100 and 200 are sufficiently far apart, it is unlikely that a person carrying a device (for example, a smartphone 20) equipped with the ranging device 200 will immediately come into contact with a device (for example, a vehicle 10) equipped with the ranging device 100. In such a situation, the power consumption of the distance measuring devices 100 and 200 can be reduced by not performing distance measuring processing as part of the authentication processing of the distance measuring device 200.

[0109] Furthermore, when the distance between the ranging device 100 and the ranging device 200 becomes equal to or less than a first predetermined distance (distance 2), the ranging unit 235 measures the distance between the ranging device 100 using the TOA method based on the relationship between the round-trip phase difference and the multiple frequencies, which is obtained when the ranging devices 100 and 200 transmit signals at multiple frequencies in both directions. Therefore, when the distance between the ranging devices 100 and 200 becomes relatively short (distance 2 or less), the ranging device 235 can measure the distance with high accuracy using the TOA method. Furthermore, the ranging process using the TOA method requires many processing steps to determine the relationship between the round-trip phase difference and the multiple frequencies, which increases the power consumption of the ranging devices 100 and 200. By limiting the ranging process, which consumes a lot of power, to when the distance between the ranging devices 100 and 200 becomes equal to or less than distance 2, the power consumption of the ranging devices 100 and 200 can be reduced.

[0110] Furthermore, when the distance to the ranging device 100 is not equal to or less than the first predetermined distance (distance 2), the ranging unit 235 measures the distance to the ranging device 100 in the RTT format based on the round-trip time required for the ranging devices 100 and 200 to send a signal back and forth. Therefore, when the distance between the ranging devices 100 and 200 is moderately short, the distance between the ranging devices 100 and 200 can be roughly measured in the RTT format. Furthermore, the ranging process in the RTT format requires only one round-trip signal between the ranging devices 100 and 200, and can be performed with less power consumption than the ranging process in the TOA format. Therefore, when the distance to the ranging device 100 is not equal to or less than the first predetermined distance (distance 2), the power consumption of the ranging devices 100 and 200 can be reduced by using the ranging process in the RTT format.

[0111] Furthermore, when the distance to the ranging device 100 becomes equal to or shorter than a first predetermined distance (distance 2), the frequency setting unit 237 sets the frequency at which the ranging unit 235 performs ranging processing higher than when the distance to the ranging device 100 is not equal to or shorter than the first predetermined distance. Therefore, when the distance between the ranging devices 100 and 200 is not equal to or shorter than the first predetermined distance, ranging can be performed less frequently using RTT-type ranging processing, and when the distance between the ranging devices 100 and 200 is equal to or shorter than the first predetermined distance (distance 2), ranging can be performed more frequently using TOA-type ranging processing. When the distance between the ranging devices 100 and 200 is not equal to or shorter than the first predetermined distance, there is little need for ranging, so by using RTT-type ranging processing, which consumes less power, and reducing the frequency of ranging processing, further reduction in power consumption can be achieved. Furthermore, when the distance between the ranging devices 100 and 200 is less than the first predetermined distance (distance 2), there is a high need for ranging, so by performing ranging frequently using a TOA-type ranging process, which has high ranging accuracy, it is possible to achieve frequent and highly accurate ranging.

[0112] Furthermore, when the distance to the ranging device 100 becomes equal to or shorter than a second predetermined distance (distance 1) that is shorter than the first predetermined distance, the frequency setting unit 237 sets the frequency at which the ranging unit 235 performs ranging processing higher than when the distance to the ranging device 100 is not equal to or shorter than the second predetermined distance. Therefore, when the distance between the ranging devices 100 and 200 is equal to or shorter than the first predetermined distance (distance 2), the frequency at which the TOA-type ranging processing is performed can be changed depending on whether the distance is equal to or shorter than distance 1, and when the ranging device 200 approaches the ranging device 100 to within distance 1, the distance between the ranging devices 100 and 200 can be measured with high frequency and high accuracy using the TOA-type. Furthermore, when the distance between the ranging devices 100 and 200 is equal to or shorter than the first predetermined distance (distance 2), changing the frequency at which the ranging processing is performed depending on whether the distance is equal to or shorter than distance 1 allows low power consumption of the ranging devices 100 and 200 when the distance is greater than distance 1.

[0113] The ranging device 200 also includes an angle measurement unit 236 that has multiple antennas 210 and performs angle measurement processing to measure the angle representing the position of the ranging device 100 relative to the ranging device 200 based on the phase difference when the multiple antennas 210 of the ranging device 200 receive signals from the ranging device 100 when the ranging device 100 and the ranging device 200 transmit signals of multiple frequencies in both directions. This makes it possible to determine the angle (azimuth angle and elevation angle) of the ranging device 100 relative to the ranging device 200.

[0114] The ranging system 300 also includes a ranging device 100 and a ranging device 200, and the ranging device 100 or the ranging device 200 has a ranging unit (135 or 235) that performs ranging processing to measure the distance between the ranging device 100 and the ranging device 200 based on the results of signals transmitted in both directions by the ranging device 100 and the ranging device 200, and a frequency setting unit (137 or 237) that sets the frequency at which the ranging unit (135 or 235) performs ranging processing according to the distance measured by the ranging processing. Therefore, the frequency at which the ranging unit (135 or 235) performs ranging processing can be set according to the distance measured by the ranging unit (135 or 235).

[0115] Therefore, by making it possible to set the measurement frequency according to the measured distance, it is possible to provide a ranging system 300 that is capable of measuring distances with high accuracy. Furthermore, since the measurement frequency is set according to the measured distance, it is possible to reduce the power consumption of the ranging devices 100 and 200 according to the measured distance. Furthermore, the ranging unit (135 or 235) and the frequency setting unit (137 or 237) may be located in either the ranging device 100 or the ranging device 200.

[0116] The communication station (ranging device 200) of embodiment 1 is a communication station (ranging device 200) as a ranging device 200 capable of communicating with the ranging device 100, and the ranging device 200 has a ranging unit 235 that performs ranging processing to measure the distance to the ranging device 100 based on the results of signals transmitted in both directions between the ranging device 200 and the ranging device 100, and a frequency setting unit 237 that sets the frequency at which the ranging unit 235 performs ranging processing in accordance with the distance measured by the ranging unit 235. Therefore, the frequency at which the ranging unit 235 performs ranging processing can be set in accordance with the distance measured by the ranging unit 235.

[0117] Therefore, by making it possible to set the measurement frequency according to the measured distance, it is possible to provide a distance measuring device 200 that can measure distances with high accuracy.

[0118] The ranging method of the first embodiment is a ranging method in a ranging system 300 including a ranging device 100 and a ranging device 200, in which a ranging process is performed to measure the distance between the ranging device 100 and the ranging device 200 based on the results of signals transmitted in both directions by the ranging device 100 and the ranging device 200, and the frequency of performing the ranging process is set according to the distance measured by the ranging process. Therefore, the frequency of performing the ranging process by the ranging unit 235 can be set according to the distance measured by the ranging unit 235.

[0119] Therefore, by making it possible to set the measurement frequency according to the measured distance, it is possible to provide a distance measuring method that enables accurate distance measurement.

[0120] In the above description, the ranging device 100 measures the RSSI of the advertising signal transmitted by the ranging device 200, and performs ranging processing by the ranging device 200. However, the ranging device 200 may measure the RSSI of the advertising signal transmitted by the ranging device 100, and perform ranging processing by the ranging device 100.

[0121] Also, in the above description, a configuration has been described in which the ranging unit 235 of the ranging device 200 performs ranging processing in the RTT format when the distance between the ranging devices 100 and 200 becomes distance 3 or less. However, the ranging unit 235 may perform ranging processing only in the TOA format without performing ranging processing in the RTT format. In this case, the frequency of performing ranging processing in the TOA format may be changed depending on whether the distance between the ranging devices 100 and 200 is distance 1 or less. Also, in this case, the ranging device 100 may measure the RSSI of the advertising signal until the distance between the ranging devices 100 and 200 becomes distance 2.

[0122] Furthermore, the MUC 230 of the distance measuring device 200 may not include the angle measurement unit 236, and the distance measuring device 200 may not perform angle measurement processing.

[0123] 5 is a diagram showing an example of a configuration in which a distance measuring system 300M according to a modification of Embodiment 1 is applied to a speaker system. The distance measuring system 300M includes a distance measuring device 100M and a distance measuring device 200M.

[0124] 5 shows the arrangement of two speakers A and B that make up a speaker system. Speakers A and B of the speaker system operate depending on their positional relationship with the smartphone 20M. For this reason, FIG. 5 shows the smartphone 20M moving relative to the two speakers A and B. For this reason, the smartphone 20M is shown in five locations according to the position of the smartphone 20M, but one smartphone 20M is provided for the two speakers A and B.

[0125] The speakers A and B include ranging devices 100M1 and 100M2, respectively. The ranging devices 100M1 and 100M2 are similar to the ranging device 100 shown in FIG. 2 and are capable of measuring the RSSI of the advertising signal transmitted by the ranging device 200. When no particular distinction is made between the ranging devices 100M1 and 100M2, they are simply referred to as ranging device 100M. Note that it is sufficient for either one of the speakers A and B to be provided, and the ranging system 300M may include only one ranging device 100M.

[0126] 2, and is capable of performing a distance measurement process for measuring the distance between the distance measuring devices 100 and 200 and an angle measurement process for determining the angle (azimuth angle and elevation angle) of the distance measuring device 100 relative to the distance measuring device 200.

[0127] As an example, when the smartphone 20M moves, the signal strength measurement unit 132 of the ranging device 100M measures the RSSI of the advertising signal transmitted by the ranging device 200M, and if the distance between the ranging devices 100M and 200M is longer than distance 3, only the RSSI is measured, and the ranging device 200M does not perform ranging processing.

[0128] When the distance between the ranging devices 100M and 200M becomes distance 3 or less due to movement of the smartphone 20M, the ranging device 200M performs ranging processing in the RTT format, and when it becomes distance 2 or less, it performs ranging processing in the TOA format. When the distance between the ranging devices 100M and 200M becomes distance 1 or less, the ranging device 200M notifies the ranging device 100M1 or 100M2 that it is distance 1 or less, and the speaker A or B outputs audio. The speaker A or B outputs audio when the distance between the ranging device 100M1 or 100M2 and the ranging device 200M is distance 1 or less, and stops outputting audio when the distance becomes longer than distance 1. The audio may be audio guidance, music, etc.

[0129] In this way, the distance measuring system 300M can be used in a speaker system. The frequency of the distance measuring process is set according to the distance measured by the distance measuring device 200M in the distance measuring process.

[0130] Therefore, by making it possible to set the measurement frequency according to the measured distance, it is possible to provide a distance measuring system 300M that is capable of measuring distances with high accuracy. Furthermore, since the measurement frequency is set according to the measured distance, it is possible to reduce the power consumption of the distance measuring devices 100M and 200M according to the measured distance.

[0131] <Embodiment 2> Embodiment 2 differs from embodiment 1 in that the distance measuring unit 135 and angle measuring unit 136 of the distance measuring device 100 on the vehicle 10 side perform distance measurement processing, angle measurement processing, etc., while the distance measuring unit 235 and angle measuring unit 236 of the distance measuring device 200 on the smartphone 20 side do not perform distance measurement processing, angle measurement processing, etc. Furthermore, the distance measuring devices 100 and 200 of embodiment 2 have additional components compared to the distance measuring devices 100 and 200 of embodiment 1 in order to perform additional processing that is not performed in embodiment 1.

[0132] The ranging device 100 of the second embodiment differs from the ranging device 100 of the first embodiment in that it performs a process of selecting one ranging device 200 that performs both ranging processing and angle measurement processing from among a plurality of ranging devices 200. The ranging device 200 of the second embodiment also differs from the ranging device 200 of the first embodiment in that it transmits an advertising signal that includes ranging information related to ranging processing and angle measurement processing executed by the ranging unit 135 and the angle measurement unit 136 of the ranging device 100.

[0133] In the second embodiment, unlike the first embodiment, the ranging device 100 is an example of a second communication station, and the ranging device 200 is an example of a first communication station. The following describes the second embodiment, focusing on the differences from the first embodiment. Furthermore, redundant descriptions of components similar to those of the ranging devices 100 and 200 of the first embodiment will be omitted.

[0134] Fig. 6 is a diagram showing an example of the configuration of distance measuring devices 100 and 200 according to the second embodiment. A system including the distance measuring devices 100 and 200 is a distance measuring system 300. Here, the distance measuring devices 100 and 200 according to the second embodiment will be described with reference to Fig. 6.

[0135] 6 shows one each of the distance measuring devices 100 and 200, but in the second embodiment, there may be a plurality of distance measuring devices 100 and 200. In an environment where a plurality of distance measuring devices 200 exist, each of the plurality of distance measuring devices 100 in the second embodiment selects one distance measuring device 200 to perform both distance measurement processing and angle measurement processing. The plurality of distance measuring devices 100 are, for example, arranged at intervals of 100 m or more, and each distance measuring device 100 independently performs the processing described below. For this reason, the processing of one distance measuring device 100 will be described below.

[0136] The ranging device 100 performs ranging processing and angle measurement processing together with the selected ranging device 200. In the second embodiment, the ranging processing performed by the ranging unit 235 of the ranging device 200 of the first embodiment is performed by the ranging unit 135 of the ranging device 100 of the second embodiment. The processing performed by the transmission and reception processing unit 234 of the ranging device 200 of the first embodiment is performed by the transmission and reception processing unit 134 of the ranging device 100 of the second embodiment. Furthermore, the processing performed by the transmission and reception processing unit 134 of the ranging device 100 of the first embodiment is performed by the transmission and reception processing unit 234 of the ranging device 200 of the second embodiment. Furthermore, the processing performed by the angle measurement unit 236 of the ranging device 200 of the first embodiment is performed by the angle measurement unit 136 of the ranging device 100 of the second embodiment. Furthermore, just as the main control unit 231 of the ranging device 200 of embodiment 1 determines the position of the ranging device 100 relative to the ranging device 200 based on the distance and angle (elevation angle and azimuth angle), the main control unit 131 of the ranging device 100 of embodiment 1 determines the position of the ranging device 200 relative to the ranging device 100 based on the distance and angle (elevation angle and azimuth angle).

[0137] <Configuration of Distance Measuring Device 200 of Second Embodiment> The distance measuring device 200 includes three antennas 210, a communication unit 220, and an MCU 230. The configurations of the three antennas 210 and the communication unit 220 are the same as the configurations of the three antennas 210 and the communication unit 220 of the first embodiment.

[0138] <MCU 230> The MCU 130 includes a main control unit 231, a signal strength measurement unit 232, a permission determination unit 233, a transmission / reception processing unit 234, a distance measurement unit 235, a distance measurement information acquisition unit 235A, an angle measurement unit 236, a frequency setting unit 237, and a memory 238. The MCU 230 of the second embodiment has a configuration in which the distance measurement information acquisition unit 235A is added to the MCU 230 of the first embodiment.

[0139] <Distance measurement information acquisition unit 235A> The distance measurement information acquisition unit 235A acquires distance measurement information related to distance measurement processing executed by the distance measurement unit 135 of the distance measuring device 100. The distance measurement information includes, for example, identification information of the distance measuring device 100 in the distance measurement processing previously executed by the distance measuring device 200 together with the distance measuring device 100, the time when the distance measuring processing was previously executed (distance measurement time), the position (previous position) of the distance measuring device 200 calculated from the distance calculated in the previous distance measurement processing and the angle calculated in the previous angle measurement processing, and the relative speed with respect to the distance measuring device 200 that executed the distance measuring processing previously together with the distance measuring device 100 (relative speed of the distance measuring devices 100 and 200).

[0140] The previous position is specified by the distance obtained by the distance measuring unit 135 in the previous distance measurement process and the elevation angle and azimuth angle obtained by the angle measuring unit 136 in the previous angle measurement process. The elevation angle and azimuth angle obtained by the angle measuring unit 136 are the elevation angle and azimuth angle in a polar coordinate system of the position of the distance measuring device 200 relative to the distance measuring device 100.

[0141] In addition, the relative velocity is calculated by the transmission / reception processing unit 134 when the transmission / reception processing unit 134 transmits and receives signals with the transmission / reception processing unit 234 of the ranging device 200 in order to obtain data such as the round-trip time, phase difference, and frequency components of the signal necessary for the ranging unit 135 to perform ranging.

[0142] Specifically, the transmission / reception processing unit 134 transmits and receives signals of multiple frequencies f1 to fm (m is an integer greater than or equal to 2) between the transmission / reception processing unit 234 of the ranging device 200, and calculates the round-trip phase (first round-trip phase) of the signal that travels back and forth by being transmitted from the ranging device 100 to the ranging device 200 and then transmitted from the ranging device 200 to the ranging device 100, between the phase when received by the ranging device 200 and the phase when received by the ranging device 100.

[0143] In addition, after determining the first round-trip phase, the transmission / reception processing unit 134 transmits and receives signals of multiple frequencies f1 to fm (m is an integer greater than or equal to 2) between the transmission / reception processing unit 234 of the ranging device 200, and determines the round-trip phase (second round-trip phase) of the signal that travels back and forth by being transmitted from the ranging device 100 to the ranging device 200 and then transmitted from the ranging device 200 to the ranging device 100, between the phase when received by the ranging device 200 and the phase when received by the ranging device 100.

[0144] The transmission / reception processing unit 134 then calculates the relative velocity with respect to the distance measuring device 100 from the difference between the first round trip phase and the second round trip phase at frequencies f1 to fm.

[0145] When the smartphone 20 including the ranging device 200 is moving, the ranging device 100 with which the ranging device 200 executed the previous ranging process may be different from the ranging device 100 with which the ranging device 200 will execute the next ranging process. The next ranging process is the ranging process to be executed after the previous ranging process.

[0146] When the ranging device 200 performs ranging processing together with the ranging device 100, the ranging information acquisition unit 235A stores the identification information of the ranging device 100, the ranging time when the ranging processing was performed, the measured position, and the relative velocity as ranging information in the memory 238. The ranging information is acquired by the ranging device 100 when the ranging device 200 next performs angle measurement processing and angle measurement processing together with the ranging device 100. Therefore, when the angle measurement processing and angle measurement processing are next performed, the identification information of the ranging information is the identification information of the ranging device 100 that performed both the previous angle measurement processing and angle measurement processing (hereinafter referred to as previous identification information), the ranging time is the previous ranging time when the previous angle measurement processing was performed, the measured position is the previous position measured in the previous angle measurement processing and angle measurement processing, and the relative velocity is the relative velocity determined in the previous angle measurement processing (hereinafter referred to as previous relative velocity).

[0147] The ranging device 200 stores ranging information including previous identification information, previous ranging time, previous position, and previous relative speed in an advertising signal and transmits the same.

[0148] Here, the location where ranging information is stored in the advertising signal will be described with reference to Fig. 7. Fig. 7 is a diagram showing an example of the location where ranging information is stored in the advertising signal. Fig. 7 also shows an example of the data structure of the advertising signal.

[0149] The ranging information (previous identification information, previous ranging time, previous position, and previous relative speed) may be stored after the mobile ID in the Advertiser's Data in the Protocol Data Unit between the Access Address and CRC of the advertising signal. The mobile ID is identification information of the ranging device 200 that transmits the advertising signal. Note that the ranging information is not limited to this position, and may be placed in other positions in the advertising signal.

[0150] <Configuration of Distance Measuring Device 100 of Second Embodiment> The distance measuring device 100 includes three antennas 110, a communication unit 120, and an MCU 130. The configurations of the three antennas 110 and the communication unit 120 are the same as the configurations of the three antennas 110 and the communication unit 120 of the first embodiment.

[0151] <MCU 130> The MCU 130 includes a main control unit 131, a signal strength measurement unit 132, a first processing unit 132A, a permission determination unit 133, a transmission / reception processing unit 134, a distance measurement unit 135, an angle measurement unit 136, a frequency setting unit 137, and a memory 138. The MCU 130 of the second embodiment has a configuration in which the first processing unit 132A is added to the MCU 130 of the first embodiment. The memory 138 is an example of a storage unit.

[0152] The main control unit 131, the signal strength measurement unit 132, the first processing unit 132A, the permission determination unit 133, the transmission / reception processing unit 134, the distance measurement unit 135, the angle measurement unit 136, and the frequency setting unit 137 are functional blocks showing the functions of the program executed by the MCU 130. The memory 138 is a functional representation of the memory of the MCU 130.

[0153] <First Processing Unit 132A> The first processing unit 132A determines whether the RSSI (signal strength) of the advertising signal measured by the signal strength measurement unit 132 for each of the multiple ranging devices 200 is equal to or greater than a predetermined strength, and extracts the multiple ranging devices 200 whose RSSI is equal to or greater than the predetermined value (predetermined strength). Then, the first processing unit 132A selects one ranging device 200 with which to perform ranging processing together from the multiple ranging devices 200 whose extracted RSSI is equal to or greater than the predetermined value (predetermined strength).

[0154] As an example, the multiple ranging devices 200 whose RSSI measured by the signal strength measurement unit 132 is equal to or greater than a predetermined value are ranging devices 200 whose distance from the ranging device 100 is 100 m or less. Since the RSSI of the advertising signal received by the ranging device 100 from the ranging device 200 is approximately proportional to the distance between the ranging devices 100 and 200, by using the RSSI when the distance between the ranging devices 100 and 200 is 100 m as a predetermined value (predetermined intensity), it is possible to extract ranging devices 200 whose distance from the ranging device 100 is within approximately 100 m.

[0155] If there are multiple ranging devices 200 with RSSIs equal to or greater than a predetermined value (predetermined intensity), the first processing unit 132A stores the multiple RSSIs and multiple ranging information included in the multiple received advertising signals in the memory 138. The ranging information includes previous identification information, ranging time, previous position, and previous relative speed. The previous identification information is identification information of the ranging device 100 with which the ranging device 200 that transmitted the advertising signal performed the previous ranging process. The ranging time is the previous ranging time indicating the time when the ranging device 200 that transmitted the advertising signal performed the previous ranging process. The previous position is the previous position obtained by the ranging device 200 that transmitted the advertising signal from the distance and angle (elevation angle and azimuth angle) obtained in the previous ranging process and the previous angle measurement process. The previous relative speed is the relative speed obtained when the ranging device 200 that transmitted the advertising signal performed the previous ranging process.

[0156] In addition, the first processing unit 132A selects, from among multiple ranging devices 200 whose RSSI is greater than or equal to a predetermined value (predetermined intensity), a ranging device 200 whose ranging device 100 represented by the previous identification information is different from the ranging device 100 itself, as the ranging device 200 with which to perform ranging processing together.

[0157] In addition, if there are multiple ranging devices 200 whose ranging devices 100 represented by the previous identification information are different from the first processing unit 132A's own ranging device 100, the first processing unit 132A selects, from among the multiple ranging devices 200, the ranging device 200 whose receiving time at which the ranging device 100 received the advertising signal is the earliest, as the ranging device 200 with which to perform the ranging process together.

[0158] The first processing unit 132A also performs an evaluation based on the previous ranging time, previous position, and previous relative speed, and selects the ranging device 200 with the highest evaluation score as the ranging device 200 with which to perform ranging processing together. Note that the evaluation score is not limited to being calculated based on all of the previous ranging time, previous position, and previous relative speed, and may be calculated based on information on at least two or more of the previous ranging time, previous position, and previous relative speed.

[0159] Furthermore, when there are multiple ranging devices 200 with the highest evaluation points based on the previous ranging time, previous position, and previous relative speed, the first processing unit 132A predicts the positions of the ranging devices 200 at the time of receiving the signal based on the previous positions, previous ranging time, and previous relative speed for the multiple ranging devices 200. Then, the first processing unit 132A selects the ranging device 200 whose predicted position is closest to the ranging device 100 as the ranging device 200 that will perform ranging processing together.

[0160] 8 is a diagram showing an example of the reception information and distance measurement information received by the distance measuring device 100. The evaluation criteria and evaluation score are also shown for the previous distance measurement time, previous position, and previous relative velocity in the distance measurement information. The evaluation score is shown in parentheses.

[0161] The reception information is the RSSI and the reception time of the advertising signal when the ranging device 100 receives the advertising signal from the ranging device 200. When receiving the advertising signal from the ranging device 200, the ranging device 100 acquires the RSSI and the reception time and stores them in the memory 138 as reception information.

[0162] The ranging information includes the previous identification information, the time of the previous ranging, the previous position, and the previous relative speed, and is included in the advertising signal that the ranging device 100 receives from the ranging device 200. When the ranging device 100 receives the advertising signal, it reads out the ranging information and stores the previous identification information, the time of the previous ranging, the previous position, and the previous relative speed in the memory 138.

[0163] When the first processing unit 132A of the distance measuring device 100 evaluates the distance measuring device 200 based on the previous distance measurement time, previous position, and previous relative velocity, the evaluation points shown in FIG. 8 are used as an example.

[0164] For example, the evaluation criterion for the previous distance measurement time is whether the time is the earliest (oldest). The first processing unit 132A assigns 2 points to the distance measuring device 200 with the oldest previous distance measurement time, and assigns 1 point to the other distance measuring devices 200.

[0165] As an example, the evaluation criterion for the previous position is whether the distance from the ranging device 100 to the ranging device 200 is equal to or less than a threshold. If the distance from the ranging device 100 to the previous position of the ranging device 200 is equal to or less than the threshold, the first processing unit 132A assigns 2 points to the ranging device 200, and if the distance from the ranging device 100 to the previous position of the ranging device 200 is longer than the threshold, the first processing unit 132A assigns 1 point to the ranging device 200.

[0166] For example, the evaluation criterion for the previous relative speed is whether the previous relative speed is equal to or greater than a threshold value. If the previous relative speed is equal to or greater than the threshold value, the first processing unit 132A assigns 2 points to the distance measuring device 200. If the previous relative speed is less than the threshold value, the first processing unit 132A assigns 1 point to the distance measuring device 200.

[0167] 9 is a diagram showing an example of the calculation result of the evaluation score. Here, as an example, an example of the result of the calculation of the evaluation score by the first processing unit 132A of the distance measuring device 100 for eight distance measuring devices 200 A to H will be described.

[0168] For example, the first processing unit 132A calculates an evaluation score by multiplying the scores assigned to the previous distance measurement time, the previous position, and the previous relative speed. For the distance measuring device 200 A, the evaluation score obtained by multiplying 2 points for the previous distance measurement time, 2 points for the previous position, and 2 points for the previous relative speed is 8 points. Evaluation scores can be calculated in a similar manner for the distance measuring devices 200 B to H.

[0169] <Sequence> Fig. 10 is a sequence diagram showing an example of processing executed by the ranging devices 100 and 200. In Fig. 10, the left half shows the processing of the ranging device 100, and the right half shows the processing of the four ranging devices 200A to 200D, thereby also explaining the relationship between the processing of the ranging devices 100 and 200A to 200D. Here, to distinguish between the four ranging devices 200, they are referred to as ranging devices 200A to 200D. Furthermore, the ranging device 100 is an Anchor (fixed station), and the ranging devices 200A to 200D are Tags (mobile stations).

[0170] First, the ranging devices 200A to 200D transmit advertising signals in order. Here, as an example, the ranging devices 200A to 200D will be described as transmitting advertising signals in this order.

[0171] The ranging device 100 executes process 1 every time it receives an advertising signal. The ranging device 100 receives advertising signals from the multiple ranging devices 200 in order during the advertising signal reception period of 10 ms (milliseconds). Here, as an example, the ranging device 100 receives advertising signals from the ranging devices 200A to 200D in order during the advertising signal reception period, and executes process 1 every time an advertising signal is received. The advertising signal reception period is, for example, 10 ms. The contents of process 1 will be described later with reference to FIG. 11.

[0172] When the advertising signal reception period ends, the ranging device 100 executes process 2. Process 2 selects the ranging device 200 on which the ranging device 100 will perform both the ranging process and the angle measurement process. Here, as an example, it is assumed that the ranging device 200B is selected.

[0173] After transmitting an advertising signal, each of the ranging devices 200A to 200D waits, for example, 20 ms for a positioning start request to be transmitted. This 20 ms is the positioning start request waiting time. If a positioning start request is not received within the positioning start request waiting time, each ranging device 200 periodically transmits an advertising signal.

[0174] The ranging device 100 transmits a positioning start request to the selected ranging device 200B. Upon receiving the positioning start request, the ranging device 200B transmits a receipt notification. As a result, the ranging device 100 performs ranging and angle measurement together with the ranging device 200B. Thereafter, the ranging devices 100 and 200B perform the processes described in the first embodiment with reference to FIGS. 3A, 3B, 4A, and 4B.

[0175] 11 is a flowchart showing an example of specific processing contents of process 1. Process 1 is executed by the distance measuring device 100.

[0176] The distance measuring device 100 receives an advertising signal (step S251).

[0177] The first processing unit 132A acquires the time when the advertising signal was received (Step S252).

[0178] The first processing unit 132A determines whether the distance from the ranging device 100 to the ranging device 200 is equal to or less than a threshold based on the RSSI (signal strength) of the advertising signal measured by the signal strength measurement unit 132 (step S253). Because the RSSI is approximately proportional to the distance, the first processing unit 132A determines whether the distance from the ranging device 100 to the ranging device 200 is equal to or less than a threshold by determining whether the RSSI is equal to or greater than a predetermined strength. The threshold used in step S253 is 100 m, for example. The threshold in step S253 is set, for example, to a range in which an advertising signal having an RSSI level that allows the ranging device 100 to receive the advertising signal and read out ranging information can be obtained.

[0179] When the first processing unit 132A determines that the distance from the ranging device 100 to the ranging device 200 is equal to or less than the threshold (S253: YES), the first processing unit 132A stores the RSSI, the reception time, and the ranging information in the memory 138 (step S254). The ranging information is read from the received advertising signal.

[0180] The first processing unit 132A calculates an evaluation score based on the previous distance measurement time, previous position, and previous relative speed from the distance measurement information stored in the memory 138 in step S254 (step S255). As described above, the evaluation criterion for the previous distance measurement time is whether the time is the earliest (oldest). The evaluation criterion for the previous position is whether the distance from the distance measuring device 100 to the distance measuring device 200 is equal to or less than a threshold value, and this distance threshold value is, for example, 50 m. The threshold value that serves as the evaluation criterion for the previous relative speed is, for example, 18 km / h.

[0181] The first processing unit 132A determines whether the advertising signal reception period has elapsed (Step S256).

[0182] If the first processing unit 132A determines that the advertising signal reception period has not elapsed (S256: NO), the flow returns to step S251 in order to receive advertising signals from other ranging devices 200 and calculate evaluation points.

[0183] Furthermore, if the first processing unit 132A determines in step S253 that the distance from the ranging device 100 to the ranging device 200 is not equal to or less than the threshold value (S253: NO), the flow returns to step S251. This is because the ranging device 200 is far enough away from the ranging device 100 that it cannot obtain an advertising signal having an RSSI level that allows the ranging device 100 to receive the advertising signal and read the ranging information.

[0184] If the first processing unit 132A determines in step S256 that the advertising signal reception period has elapsed (S256: YES), it ends process 1 and proceeds to process 2.

[0185] By performing the above-described process 1 by the ranging device 100, ranging devices 200 having an RSSI equal to or greater than a predetermined value (predetermined intensity) are extracted. When multiple ranging devices 200 are extracted, process 2 is performed to narrow down the ranging devices 200 that perform both ranging and angle measurement to one.

[0186] 12 is a flowchart showing an example of the specific processing contents of process 2. Process 2 is executed by the distance measuring device 100.

[0187] The first processing unit 132A determines whether or not there is a ranging device 200 (Tag) whose previous identification information differs from the identification information of its own ranging device 100 among the multiple ranging devices 200 (Tags) extracted in process 1 (step S261).

[0188] When the first processing unit 132A determines that there is a ranging device 200 whose previous identification information is different from the identification information of its own ranging device 100 (S261: YES), it selects the ranging device 200 that received the advertising signal earliest among the multiple ranging devices 200 with different identification information as the ranging device 200 that will perform both ranging and angle measurement processing (step S262).

[0189] A ranging device 200 whose previous identification information is different from the identification information of its own ranging device 100 is a ranging device 200 that performed the previous ranging process and angle measurement process with another ranging device 100 different from its own ranging device 100, and is a ranging device 200 that has moved within the threshold (100 m) in step S253 from its own ranging device 100. Such ranging devices 200 are given priority in performing ranging process and angle measurement process.

[0190] If there is one ranging device 200 whose previous identification information is different from the identification information of its own ranging device 100, in step S262, that ranging device 200 is selected as the ranging device 200 that will perform both ranging and angle measurement processing.

[0191] If the first processing unit 132A determines in step S261 that there is no ranging device 200 whose previous identification information differs from the identification information of its own ranging device 100 (S261: NO), it extracts the ranging device 200 with the highest evaluation score (step S263). If there is no ranging device 200 whose previous identification information differs from the identification information of its own ranging device 100, all of the ranging devices 200 extracted in process 1 are ranging devices 200 that performed the previous ranging process and angle measurement process together with its own ranging device 100, so it determines which ranging device 200 should be given priority for the ranging process and angle measurement process based on the evaluation score. The evaluation scores of the ranging devices 200 can be read from the memory 138.

[0192] The first processing unit 132A determines whether there are multiple distance measuring devices 200 with the maximum evaluation points (step S264).

[0193] When the first processing unit 132A determines that there are no multiple ranging devices 200 with the highest evaluation points (S264: NO), it selects the one ranging device 200 with the highest evaluation point as the ranging device 200 that will perform both ranging and angle measurement processing (step S265).

[0194] If the first processing unit 132A determines in step S264 that there are multiple distance measuring devices 200 with the maximum evaluation points (S264: YES), it calculates the predicted positions of each distance measuring device 200 (step S266).

[0195] The predicted position is a predicted position of the ranging device 200 at the time of receiving the advertising signal. The first processing unit 132A calculates a predicted value of the position of the ranging device 200 at the time of receiving the advertising signal by multiplying the time from the previous ranging time included in the ranging information to the time of receiving the advertising signal by the previous relative speed.

[0196] The first processing unit 132A selects the distance measuring device 200 with the smallest difference between the predicted position and the previous position as the distance measuring device 200 that will perform both the distance measurement process and the angle measurement process (step S267).

[0197] After completing the process of step S262, S265, or S267, the first processing unit 132A transmits a positioning start request (see FIG. 10 ) to the selected ranging device 200. As a result, the ranging device 100 executes ranging processing and angle measurement processing together with the selected ranging device 200.

[0198] The distance measuring device 100 transmits the positioning result (the position calculated from the distance and angle) to the distance measuring device 200, and also transmits the interval data to the distance measuring device 200. When the above processing is completed, the distance measuring device 100 returns the flow to processing 1.

[0199] <Calculation example of predicted position> Fig. 13 is a diagram showing a calculation example of a predicted position. Fig. 13 shows a ranging device 100 (Anchor) and three ranging devices 200 (Tags). Cases (1) to (3) will be explained starting from the top. Note that the previous position is indicated by the distance from the ranging device 100 to the ranging device 200. Also, for simplicity of explanation, the elevation angle is set to 0 degrees, and the azimuth angle is an angle representing the left direction with respect to the ranging device 100 in Fig. 13. Also, the previous positioning time and the reception time of the advertising signal are indicated by the elapsed time (seconds) from the reference time.

[0200] In case (1), a user carrying the distance measuring device 200 approaches the distance measuring device 100 by bicycle. The previous position is 50 mm, the previous relative speed is 18 km / h, the previous positioning time is 10.0 seconds, and the advertising signal was received at 15.0 seconds. In this case, the predicted position is 25 m.

[0201] In case (2), the user carrying the distance measuring device 200 is walking toward the distance measuring device 100. The previous position is 30 mm, the previous relative speed is 3 km / h, the previous positioning time is 10.1 seconds, and the advertising signal was received at 15.1 seconds. In this case, the predicted position is 25.8 m.

[0202] In case (3), the user carrying the distance measuring device 200 is moving away from the distance measuring device 100 by bicycle. The previous position is 25 mm, the previous relative speed is -18 km / h (relative speed in the direction away), the time of the previous positioning is 10.0 seconds, and the time of receiving the advertising signal is 10.2 seconds. In this case, the predicted position is 27.5 m.

[0203] When the predicted positions for cases (1) to (3) are calculated in step S266, the first processing unit 132A selects in step S267 the ranging device 200 in case (1) that has the smallest difference between the predicted position and the previous position as the ranging device 200 that will perform both the ranging process and the angle measurement process. The closest ranging device 200 is preferentially selected to perform both the ranging process and the angle measurement process.

[0204] <Effects> The ranging system 300 of the second embodiment includes a ranging device 100 and a ranging device 200. The ranging device 200 has a ranging unit 235 that performs ranging processing to measure the distance between the ranging device 100 and the ranging device 100 based on the results of bidirectional transmission of advertising signals between the ranging device 200 and the ranging device 100, and a frequency setting unit 237 that sets the frequency at which the ranging unit 235 performs the ranging processing according to the distance measured by the ranging unit 235. The ranging device 100 (second communication station) may also have a signal strength measurement unit 132 that performs signal strength measurement processing to measure the RSSI of the advertising signal received from the ranging device 200 (first communication station), and a first processing unit 132A that determines whether the RSSI measured by the signal strength measurement unit 132 for each of the multiple ranging devices 200 is equal to or greater than a predetermined strength, and selects a ranging device 200 with which to perform ranging processing from among the multiple ranging devices 200 with an RSSI equal to or greater than the predetermined strength. Therefore, the frequency with which the distance measuring unit 235 performs the distance measurement process can be set according to the distance measured by the distance measuring unit 235. Furthermore, when there are multiple distance measuring devices 200 with RSSIs of a predetermined strength or higher, one distance measuring device 200 can be selected to perform the distance measurement process together.

[0205] Furthermore, the ranging device 200 may transmit an advertising signal including ranging information related to ranging processing, the ranging device 100 may receive a plurality of advertising signals from a plurality of ranging devices 200, the ranging device 100 may further have a memory 138 (storage unit), and the first processing unit 132A may store a plurality of RSSIs and a plurality of pieces of ranging information included in the received plurality of advertising signals for a plurality of ranging devices 200 whose RSSI is equal to or greater than a predetermined strength in the memory 138. The RSSIs and ranging information for a plurality of ranging devices 200 whose RSSI is equal to or greater than a predetermined strength can be stored in the memory 138 as criteria for selecting one ranging device 200, making it easier to select one ranging device 200.

[0206] Furthermore, there may be a plurality of ranging devices 100, and the ranging information includes previous identification information that identifies a ranging device 100 with which a ranging device 200 among the plurality of ranging devices 100 performed the previous ranging process, and the first processing unit 132A may select a ranging device 200 different from the ranging device 100 represented by the previous identification information as a ranging device 200 with which the ranging device 100 will perform the ranging process from among the plurality of ranging devices 200 with an RSSI of a predetermined strength or higher. The ranging device 200 that performed the previous ranging process with the ranging device 100 different from the ranging device 100 is a ranging device 200 that has moved close to the ranging device 100. Such ranging devices 200 can be preferentially selected.

[0207] When there are multiple ranging devices 200 whose previous identification information is different from the first processing unit 132A's own ranging device 100, the first processing unit 132A may select, among the multiple ranging devices 200, the ranging device 200 whose advertising signal was received at the earliest reception time as the ranging device 200 with which to perform ranging processing together. When there are multiple ranging devices 200 that have moved close to the first processing unit 132A's own ranging device 100, by selecting the ranging device 200 whose advertising signal was received at the earliest reception time, it becomes possible to preferentially select, among the multiple ranging devices 200 that have moved close to the first processing unit 132A's own ranging device 100, the ranging device 200 whose advertising signal was received at the earliest reception time.

[0208] The ranging device 100 further includes a plurality of antennas 110 and an angle measurement unit 136 that performs angle measurement processing to measure an angle representing the position of the ranging device 200 relative to the ranging device 100 based on a phase difference between when the plurality of antennas of the ranging device 100 receive signals from the ranging device 200 when the ranging device 200 and the ranging device 100 transmit signals of multiple frequencies in both directions, and the ranging information includes the previous ranging time when the previous ranging processing was performed, the previous position calculated from the distance measured in the previous ranging processing and the angle measured in the previous angle measurement processing, and the previous relative speed calculated in the previous ranging processing, and the first processing unit 132A may select the ranging device 200 with the highest evaluation score based on at least two or more pieces of information selected from the previous ranging time, the previous position, and the previous relative speed as the ranging device 200 with which to perform the ranging processing together. Using the evaluation score as a judgment index, it is possible to easily determine which ranging device 200 should be prioritized for ranging processing.

[0209] Furthermore, the ranging information includes the time of the previous ranging, the previous position, and the previous relative speed, and when there are multiple ranging devices 200 with the highest evaluation points based on the time of the previous ranging, the previous position, and the previous relative speed, the first processing unit 132A may predict the position of the ranging devices 200 at the time of receiving the advertising signal for the multiple ranging devices 200 based on the previous position, the time of the previous ranging, and the previous relative speed, and select the ranging device 200 whose predicted position is closest to the ranging device 100 as the ranging device 200 that will perform ranging processing together. The closest ranging device 200 can be preferentially selected to perform ranging processing together.

[0210] The ranging system 300 of the second embodiment includes a ranging device 100 and a ranging device 200, and the ranging device 100 (second communication station) has a signal strength measurement unit 132 that performs signal strength measurement processing to measure the RSSI of an advertising signal received from the ranging device 200 (first communication station), and a first processing unit 132A that determines whether the RSSI measured by the signal strength measurement unit 132 for each of the multiple ranging devices 200 is equal to or greater than a predetermined strength, and selects a ranging device 200 with which to perform ranging processing together from the multiple ranging devices 200 with an RSSI of equal to or greater than the predetermined strength. Therefore, when there are multiple ranging devices 200 with an RSSI of equal to or greater than the predetermined strength, it is possible to select one ranging device 200 with which to perform ranging processing together.

[0211] The above describes the ranging system, communication station, and ranging method according to exemplary embodiments of the present disclosure. However, the present disclosure is not limited to the specifically disclosed embodiments, and various modifications and variations are possible without departing from the scope of the claims.

[0212] This international application claims priority based on Japanese Patent Application No. 2022-164644, filed on October 13, 2022, the entire contents of which are incorporated herein by reference.

[0213] 10 Vehicle 20, 20M Smartphone 100, 100M, 100M1, 100M2 Ranging device (an example of a first communication station in the first embodiment, an example of a second communication station in the second embodiment) 110 Antenna 120 Communication unit 131 Main control unit 132 Signal strength measurement unit 132A First processing unit 133 Permission determination unit 134 Transmission / reception processing unit 135 Ranging unit 136 Angle measurement unit 137 Frequency setting unit 138 Memory 200, 200M Ranging device (an example of a second communication station in the first embodiment, an example of a first communication station in the first embodiment) 210 Antenna 220 Communication unit 231 Main control unit 232 Signal strength measurement unit 233 Permission determination unit 234 Transmission / reception processing unit 235 Ranging unit 235A Ranging information acquisition unit 236 Angle measurement unit 237 Frequency setting unit 238 Memory 300, 300M Distance measuring system

Claims

1. A first communication station; The second communication station Including, The second communication station a distance measurement unit that performs a distance measurement process to measure the distance between the second communication station and the first communication station based on a result of bidirectional transmission of a signal between the second communication station and the first communication station; a frequency setting unit that sets a frequency at which the distance measuring unit performs the distance measuring process in accordance with the distance measured by the distance measuring unit; having The second communication station a signal strength measurement unit that performs a signal strength measurement process to measure the signal strength of a signal received from the first communication station; a first processing unit that determines whether or not a signal strength measured by the signal strength measurement unit for each of the plurality of first communication stations is equal to or greater than a predetermined strength, and selects a first communication station that will jointly perform the ranging process from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength; having the first communication station transmits the signal including distance measurement information related to the distance measurement process; the second communication station receives a plurality of the signals from a plurality of the first communication stations; The second communication station further includes a storage unit, the first processing unit stores, in the storage unit, a plurality of the signal strengths and a plurality of the distance measurement information included in the plurality of the received signals for the plurality of the first communication stations whose signal strengths are equal to or greater than the predetermined strength; There are a plurality of second communication stations, the ranging information includes previous identification information for identifying a second communication station with which the first communication station performed the previous ranging process among a plurality of the second communication stations, A ranging system in which the first processing unit selects, from among the multiple first communication stations whose signal strength is equal to or greater than the specified strength, a first communication station whose second communication station represented by the previous identification information is different from its own second communication station, as the first communication station with which to perform the ranging process.

2. The ranging system according to claim 1 , wherein the second communication station is movable relative to the first communication station.

3. The distance measuring system according to claim 1 , wherein the frequency setting unit sets the frequency to be higher as the distance measured by the distance measuring unit becomes shorter.

4. The first communication station a signal strength measurement unit that performs a signal strength measurement process to measure the signal strength of a signal received from the second communication station; a permission determination unit that permits the distance measurement unit of the second communication station to perform the distance measurement process when the signal strength measured by the signal strength measurement unit is equal to or greater than a predetermined strength; The ranging system of claim 1 , further comprising:

5. 2. The ranging system according to claim 1, wherein when the distance to the first communication station becomes equal to or less than a first predetermined distance, the ranging unit measures the distance to the first communication station based on a relationship between a round-trip phase difference and the multiple frequencies obtained by the first communication station and the second communication station transmitting signals of multiple frequencies in both directions.

6. 6. The ranging system according to claim 5, wherein the ranging unit measures the distance to the first communication station based on a round-trip time taken for the first communication station and the second communication station to send a signal back and forth when the distance to the first communication station is not equal to or less than the first predetermined distance.

7. The ranging system of claim 6, wherein the frequency setting unit sets a frequency at which the ranging unit performs the ranging process higher when the distance to the first communication station becomes less than the first specified distance than when the distance to the first communication station is not less than the first specified distance.

8. The ranging system of claim 5, wherein the frequency setting unit sets a frequency at which the ranging unit performs the ranging processing higher when the distance to the first communication station becomes equal to or shorter than a second predetermined distance that is shorter than the first predetermined distance than when the distance to the first communication station is not equal to or shorter than the second predetermined distance.

9. The second communication station A plurality of antennas; an angle measurement unit that performs an angle measurement process for measuring an angle representing a position of the first communication station relative to the second communication station based on a phase difference when the first communication station and the second communication station transmit signals of multiple frequencies in both directions, the phase difference being obtained when the multiple antennas of the second communication station receive signals from the first communication station; The ranging system of claim 5 further comprising:

10. the distance measurement information includes a reception time at which the second communication station received the signal from the first communication station, The ranging system of claim 1, wherein, when there are multiple first communication stations whose second communication stations represented by the previous identification information are different from the first communication station itself, the first processing unit selects, among the multiple first communication stations, the first communication station having the earliest reception time as the first communication station with which to perform the ranging process.

11. The second communication station A plurality of antennas; an angle measurement unit that performs an angle measurement process for measuring an angle representing a position of the first communication station relative to the second communication station based on a phase difference when the first communication station and the second communication station transmit signals of multiple frequencies in both directions, the phase difference being obtained when the multiple antennas of the second communication station receive signals from the first communication station; Further comprising: The distance measurement information is The previous distance measurement time when the previous distance measurement process was performed; a previous position determined by the distance measured in the previous distance measurement process and the angle measured in the previous angle measurement process; The previous relative velocity obtained in the previous distance measurement process, Including, The ranging system of claim 1, wherein the first processing unit selects the first communication station having the largest evaluation point based on at least two or more pieces of information among the previous ranging time, the previous position, and the previous relative velocity as the first communication station with which to perform the ranging process.

12. the distance measurement information includes the previous distance measurement time, the previous position, and the previous relative velocity; the first processing unit, when there are a plurality of the first communication stations having the largest evaluation points based on the previous ranging time, the previous position, and the previous relative speed, predicts the positions of the first communication stations at the time of receiving the signal for the plurality of first communication stations based on the previous position, the previous ranging time, and the previous relative speed; The ranging system according to claim 11 , wherein the first communication station, the predicted position of which is closest to the second communication station, is selected as the first communication station with which the ranging process is performed together.

13. A first communication station; The second communication station Including, The second communication station a signal strength measurement unit that performs a signal strength measurement process to measure the signal strength of a signal received from the first communication station; a first processing unit that determines whether or not a signal strength measured by the signal strength measurement unit for each of the plurality of first communication stations is equal to or greater than a predetermined strength, and selects a first communication station that will perform a distance measurement process together from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength; having The second communication station a signal strength measurement unit that performs a signal strength measurement process to measure the signal strength of a signal received from the first communication station; a first processing unit that determines whether or not a signal strength measured by the signal strength measurement unit for each of the plurality of first communication stations is equal to or greater than a predetermined strength, and selects a first communication station that will jointly perform the ranging process from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength; having the first communication station transmits the signal including distance measurement information related to the distance measurement process; the second communication station receives a plurality of the signals from a plurality of the first communication stations; The second communication station further includes a storage unit, the first processing unit stores, in the storage unit, a plurality of the signal strengths and a plurality of the distance measurement information included in the plurality of the received signals for the plurality of the first communication stations whose signal strengths are equal to or greater than the predetermined strength; There are a plurality of second communication stations, the ranging information includes previous identification information for identifying a second communication station with which the first communication station performed the previous ranging process among a plurality of the second communication stations, A ranging system in which the first processing unit selects, from among the multiple first communication stations whose signal strength is equal to or greater than the specified strength, a first communication station whose second communication station represented by the previous identification information is different from its own second communication station, as the first communication station with which to perform the ranging process.

14. A first communication station; The second communication station Including, The first communication station or the second communication station, a distance measurement unit that performs a distance measurement process to measure a distance between the first communication station and the second communication station based on a result of bidirectional transmission of signals by the first communication station and the second communication station; a frequency setting unit that sets a frequency at which the distance measuring unit performs the distance measuring process in accordance with the distance measured by the distance measuring process; having The second communication station a signal strength measurement unit that performs a signal strength measurement process to measure the signal strength of a signal received from the first communication station; a first processing unit that determines whether or not a signal strength measured by the signal strength measurement unit for each of the plurality of first communication stations is equal to or greater than a predetermined strength, and selects a first communication station that will jointly perform the ranging process from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength; having the first communication station transmits the signal including distance measurement information related to the distance measurement process; the second communication station receives a plurality of the signals from a plurality of the first communication stations; The second communication station further includes a storage unit, the first processing unit stores, in the storage unit, a plurality of the signal strengths and a plurality of the distance measurement information included in the plurality of the received signals for the plurality of the first communication stations whose signal strengths are equal to or greater than the predetermined strength; There are a plurality of second communication stations, the ranging information includes previous identification information for identifying a second communication station with which the first communication station performed the previous ranging process among a plurality of the second communication stations, A ranging system in which the first processing unit selects, from among the multiple first communication stations whose signal strength is equal to or greater than the specified strength, a first communication station whose second communication station represented by the previous identification information is different from its own second communication station, as the first communication station with which to perform the ranging process.

15. A communication station as a second communication station capable of communicating with the first communication station, The second communication station a distance measurement unit that performs a distance measurement process to measure the distance between the second communication station and the first communication station based on a result of bidirectional transmission of a signal between the second communication station and the first communication station; a frequency setting unit that sets a frequency at which the distance measuring unit performs the distance measuring process in accordance with the distance measured by the distance measuring unit; having The second communication station a signal strength measurement unit that performs a signal strength measurement process to measure the signal strength of a signal received from the first communication station; a first processing unit that determines whether or not a signal strength measured by the signal strength measurement unit for each of the plurality of first communication stations is equal to or greater than a predetermined strength, and selects a first communication station that will jointly perform the ranging process from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength; having the first communication station transmits the signal including distance measurement information related to the distance measurement process; the second communication station receives a plurality of the signals from a plurality of the first communication stations; The second communication station further includes a storage unit, the first processing unit stores, in the storage unit, a plurality of the signal strengths and a plurality of the distance measurement information included in the plurality of the received signals for the plurality of the first communication stations whose signal strengths are equal to or greater than the predetermined strength; There are a plurality of second communication stations, the ranging information includes previous identification information for identifying a second communication station with which the first communication station performed the previous ranging process among a plurality of the second communication stations, The first processing unit selects, from among the multiple first communication stations whose signal strength is equal to or greater than the specified strength, a first communication station whose second communication station represented by the previous identification information is different from its own second communication station, as the first communication station with which to perform the ranging process.

16. A first communication station; The second communication station A distance measurement method in a distance measurement system comprising: performing a ranging process for measuring a distance between the first communication station and the second communication station based on a result of bidirectional transmission of signals by the first communication station and the second communication station; setting a frequency of performing the distance measurement process according to a distance measured by the distance measurement process; The second communication station a signal strength measurement unit that performs a signal strength measurement process to measure the signal strength of a signal received from the first communication station; a first processing unit that determines whether or not a signal strength measured by the signal strength measurement unit for each of the plurality of first communication stations is equal to or greater than a predetermined strength, and selects a first communication station that will jointly perform the ranging process from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength; having the first communication station transmits the signal including distance measurement information related to the distance measurement process; the second communication station receives a plurality of the signals from a plurality of the first communication stations; The second communication station further includes a storage unit, the first processing unit stores, in the storage unit, a plurality of the signal strengths and a plurality of the distance measurement information included in the plurality of the received signals for the plurality of the first communication stations whose signal strengths are equal to or greater than the predetermined strength; There are a plurality of second communication stations, the ranging information includes previous identification information for identifying a second communication station with which the first communication station performed the previous ranging process among a plurality of the second communication stations, A ranging method in which the first processing unit selects, from among the multiple first communication stations whose signal strength is equal to or greater than the predetermined strength, a first communication station whose second communication station represented by the previous identification information is different from its own second communication station, as the first communication station with which to perform the ranging process.