Distancing system, communication station, and distance measuring 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

Technical Field

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

Background Art

[0002] Conventionally, there is 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 movement state and movement speed of a mobile terminal device, and a positioning time interval setting unit that sets, based on the movement state and movement speed of the mobile terminal device acquired by the acquisition unit, the time interval at which the position (distance) of the mobile terminal device should be measured and the time interval at which the position information obtained by the measurement should be output. When the movement state and / or movement speed of the mobile terminal device changes, the positioning time interval setting unit changes the time interval. The mobile terminal device acquires the position information of the mobile terminal device at the time interval set by the positioning time interval setting unit and outputs the position information. The positioning time interval setting unit sets a longer time for the time interval at which the position of the mobile terminal device should be measured and the time interval at which the position information obtained by the measurement should be output as the movement speed of the mobile terminal device is higher (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, since the conventional positioning time interval control device did not change the frequency of measuring (distance measurement) the distance of the mobile terminal device according to the distance from the mobile terminal device, accurate distance measurement of the mobile terminal device could not be performed.

[0005] Therefore, the objective is to provide a distance measuring system, communication station, and distance measuring method that enable accurate distance measurement by allowing the measurement frequency to be set according to the measured distance. [Means for solving the problem]

[0006] The ranging system of the embodiment of the present disclosure includes a first communication station and a second communication station, the second communication station having a ranging unit that performs ranging processing to measure the distance to the first communication station based on the result of the second communication station transmitting signals bidirectionally to and from the first communication station, and a frequency setting unit that sets the frequency at which the ranging unit performs ranging processing according to the distance measured by the ranging unit. [Effects of the Invention]

[0007] By allowing the measurement frequency to be set according to the measured distance, it is possible to provide a distance measuring system, communication station, and distance measuring method that enable highly accurate distance measurement. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of the configuration of a vehicle 10 and a smartphone 20, each equipped with the distance measuring devices 100 and 200 of Embodiment 1. [Figure 2] This figure shows an example of the configuration of the distance measuring devices 100 and 200 of Embodiment 1. [Figure 3A] This diagram illustrates an example of the overall processing overview of the distance measuring devices 100 and 200. [Figure 3B] This diagram illustrates an example of the frequency of distance measurement processing. [Figure 4A] This flowchart shows an example of the processes performed by the distance measuring devices 100 and 200. [Figure 4B] This flowchart shows an example of the processes performed by the distance measuring devices 100 and 200. [Figure 5] This figure shows an example of a configuration in which the distance measuring system 300M, a modified example of Embodiment 1, is applied to a speaker system. [Figure 6]This figure shows an example of the configuration of the distance measuring devices 100 and 200 of Embodiment 2. [Figure 7] This figure shows an example of a location where distance measurement information is stored in the advertisement signal. [Figure 8] This figure shows an example of the received information and distance measurement information received by the distance measuring device 100. [Figure 9] This figure shows an example of the calculation results for the evaluation score. [Figure 10] This is a sequence diagram illustrating an example of the processing performed by the distance measuring devices 100 and 200. [Figure 11] This flowchart shows an example of the specific processing details for Process 1. Process 1 is performed by the distance measuring device 100. [Figure 12] A flowchart illustrating an example of the specific processing details for Process 2. [Figure 13] This figure shows an example of how to calculate a predicted position. [Modes for carrying out the invention]

[0009] The following describes embodiments to which the ranging system, communication station, and ranging method of this disclosure are applied.

[0010] <Embodiment 1> Figure 1 shows an example of a vehicle 10 and a smartphone 20, each equipped with the distance measuring devices 100 and 200 of Embodiment 1, respectively. Figure 2 shows an example of the configuration of the distance measuring devices 100 and 200 of Embodiment 1. The system including the distance measuring devices 100 and 200 is a distance measuring system 300.

[0011] Here, as an example, we will describe a configuration 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 communicate via packet data using BLE (Bluetooth® 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, since the vehicle 10 is parked and not moving, the ranging device 100 is a fixed station that does not move, and the ranging device 200 is a mobile station that can move along with the movement of the owner of the smartphone 20. 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 move.

[0013] Also, as an example, the vehicle 10 is equipped with an automatic parking assistance system, and the ranging device 100 is included in the automatic parking assistance system. The automatic parking assistance system is a system that remotely transmits commands to the vehicle 10 by wireless communication from the smartphone 20 to automatically park the vehicle 10 at a parking position or to automatically move the vehicle 10 out of the parking position.

[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 of the doors, trunks, 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, the ranging device 200 of the smartphone 20 performs a ranging process for measuring the distance and notifies the ranging device 100 of the vehicle 10 of the result of the ranging. The ranging devices 100 and 200 have the same configuration as an example.

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

[0017] <Antenna 110> Antenna 110 is connected to the communication unit 120 and receives signals transmitted from the distance measuring device 200 of the smartphone 20. Although Figure 1 describes a configuration in which the distance measuring device 100 includes three antennas 110, the distance measuring device 100 may include four or more antennas 110. The three antennas 110 are configured such that two are positioned on the first axis of two mutually orthogonal axes, two are positioned on the second axis of two mutually orthogonal axes, and one of these antennas is positioned in common on both the first and second axes.

[0018] <Communications Section 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 rangefinder 200 and outputs it to the MCU 130.

[0019] <mcu130> The MCU130 comprises 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 MCU130 is implemented, for example, by a microcomputer including a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and an internal bus. 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 represent the functions of the program executed by the MCU130 as functional blocks. The memory 138 functionally represents the memory of the MCU130.

[0020] <Main Control Unit 131> The main control unit 131 is the processing unit that oversees the entire MCU 130 and performs processing other than that performed by the 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.

[0021] <Signal strength measurement unit 132> The signal strength measurement unit 132 measures the RSSI (Received Signal Strength Indicator), which represents the signal strength of the advertisement signal received from the distance measuring device 200 via the communication unit 120, and outputs it to the permission determination unit 133. Since the RSSI of the advertisement signal output by the distance measuring device 200 and the distance between the distance measuring devices 100 and 200 are proportional, if the RSSI of the advertisement signal output by the distance measuring device 200 is measured in advance at multiple distances, the distance between the distance measuring devices 100 and 200 can be estimated based on the RSSI measured by the signal strength measurement unit 132 through interpolation processing or the like.

[0022] <Permission determination unit 133> The authorization determination unit 133 determines whether to allow the distance measuring device 100 to connect the distance measuring device 200 to BLE communication based on the RSSI of the advertised signal measured by the signal strength measurement unit 132, and if it does, it performs authorization determination processing to generate an authorization signal. More specifically, the authorization determination unit 133 authorizes the distance measuring unit 235 of the distance measuring device 200 to perform distance measuring processing if the signal strength measured by the signal strength measurement unit 132 is equal to or greater than a predetermined strength. The authorization signal is transmitted to the distance measuring device 200 by the main control unit 131.

[0023] <Transmit / receive processing unit 134> The transmitting and receiving processing unit 134 transmits and receives signals with the transmitting and receiving processing unit 234 of the distance measuring device 200 in order to acquire data such as the round-trip time, phase difference, and frequency components of the signals necessary for the distance measuring unit 135 of the distance measuring device 100 or the distance measuring unit 235 of the distance measuring device 200 to perform distance measurement. In Embodiment 1, as an example, the distance measurement process to calculate the distance between the distance measuring devices 100 and 200 is performed by the distance measuring unit 235 of the distance measuring device 200, and not by the distance measuring unit 135 of the distance measuring device 100. For this reason, when the distance measuring unit 235 of the distance measuring device 200 performs distance measurement, the transmitting and receiving processing unit 134 performs the following auxiliary processing in accordance with the processing of the transmitting and receiving processing unit 234.

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

[0025] The transmitting / receiving processing unit 134 transmits and receives signals with the transmitting / receiving processing unit 234 of the distance measuring device 200 when the distance measuring unit 235 of the distance measuring device 200 performs distance measurement in the TOA (Time of Arrival) format. In this case, the transmitting / receiving processing unit 134 only needs to use one of the three antennas 110 to transmit and receive signals. The transmitting / receiving processing unit 134 measures the phase of the signal received from the distance measuring device 200 and transmits data representing the measured phase to the distance measuring device 200.

[0026] Furthermore, when the angle measuring unit 236 of the distance measuring device 200 performs angle measurement in the AOA (Angle of Arrival) format, the transmission / reception processing unit 134 receives the signal received from the distance measuring device 200 with 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 distance measuring device 200.

[0027] <Distance measurement section 135> The distance measuring unit 135 is capable of performing distance measurement processing in RTT format and distance measurement processing in TOA format. In Embodiment 1, the distance measuring unit 235 of the distance measuring device 200 performs distance measurement processing (processing to calculate distance), so the distance measuring unit 135 does not perform distance measurement processing. Distance measurement in RTT format and distance measurement processing in TOA format will be described later for the distance measuring unit 235 of the distance measuring device 200. Here, as an example, a configuration in which distance measuring devices 100 and 200 have the same configuration is described, so the MCU 130 of the distance measuring device 100 has a distance measuring unit 135, but the MCU 130 of the distance measuring device 100 does not have to have a distance measuring unit 135.

[0028] <Angle measurement section 136> The angle measuring unit 136 can perform angle measuring processing in AOA format, measuring the elevation angle and azimuth angle of the position of the distance measuring device 200 relative to the distance measuring device 100 in a polar coordinate system, using the three antennas 110. However, in Embodiment 1, as an example, the angle measuring unit 136 of the distance measuring device 100 does not perform angle measuring processing, and the angle measuring unit 236 of the distance measuring device 200 performs angle measuring processing, so the angle measuring unit 136 does not perform angle measuring processing. Note that the MCU 130 of the distance measuring device 100 does not necessarily have an angle measuring unit 136.

[0029] <Frequency setting unit 137> The frequency setting unit 137 sets the frequency at which the distance measuring unit 135 performs distance measuring processing, according to the distance measured by the distance measuring unit 135 when the distance measuring unit 135 performs distance measuring processing. However, in Embodiment 1, for example, the distance measuring unit 135 of the distance measuring device 100 does not perform distance measuring processing, and the distance measuring unit 235 of the distance measuring device 200 performs distance measuring processing, so the frequency setting unit 137 does not perform the processing to set the frequency. Note that the MCU 130 of the distance measuring device 100 does not necessarily have a frequency setting unit 137.

[0030] <Memory 138> The memory 138 stores programs, data, and other information necessary for 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 to perform processing.

[0031] <Configuration of the distance measuring device 200> The rangefinder 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 signals transmitted from the rangefinder 100. Although Figure 1 illustrates a configuration in which the rangefinder 200 includes three antennas 210, the rangefinder 200 may include four or more antennas 210. The three antennas 210 are configured such that two are positioned on the first axis of two mutually orthogonal axes, two are positioned on the second axis of two mutually orthogonal axes, and one of these antennas is positioned in common on both the first and second axes.

[0032] The distance measuring device 200 has, for example, a similar configuration to the distance measuring device 100. That is, the antenna 210, communication unit 220, and MCU 230 are the same as the antenna 110, communication unit 120, and MCU 130 of the distance measuring device 100, respectively. However, in Embodiment 1, the distance measuring device 200 does not perform RSSI measurement or connection permission determination, but rather performs distance measurement processing, angle measurement processing, and frequency setting processing. For this reason, the operation of the distance measuring devices 100 and 200 is different in Embodiment 1. The MCU 230 will be described below.

[0033] <mcu230> The MCU130 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, signal strength measurement unit 232, permission determination unit 233, transmission / reception processing unit 234, distance measurement unit 235, an angle measurement unit 236, a frequency setting unit 237, and a memory 238 are the same as the main control unit 131, signal strength measurement unit 132, permission determination unit 133, transmission / reception processing unit 134, distance measurement unit 135, an angle measurement unit 136, a frequency setting unit 137, and a memory 138 of the MCU130 of the distance measuring device 100.

[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 represent the functions of the program executed by the MCU 230 as functional blocks. The memory 238 functionally represents the memory of the MCU 230.

[0035] <Main Control Unit 231> The main control unit 231 is the processing unit that oversees the entire MCU 230 and performs processing other than that performed by the 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.

[0036] <Signal strength measurement unit 232> The signal strength measurement unit 232, like the signal strength measurement unit 132 of the distance measuring device 100, can measure the RSSI of the advertised signal received from the distance measuring device 100 via the communication unit 220. However, in Embodiment 1, since the signal strength measurement unit 132 of the distance measuring device 100 measures the RSSI, the MCU 230 of the distance measuring device 200 does not need to have a signal strength measurement unit 232.

[0037] <Permission determination unit 233> The authorization determination unit 233, similar to the authorization determination unit 133 of the distance measuring device 100, can determine whether to authorize the distance measuring device 200 to connect to BLE based on the RSSI of the advertised signal measured by the signal strength measurement unit 232, and if authorized, it can generate an authorization signal. However, in Embodiment 1, since the authorization determination unit 133 of the distance measuring device 100 performs the authorization determination process, the MCU 230 of the distance measuring device 200 does not need to have an authorization determination unit 233.

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

[0039] The transmitting / receiving processing unit 234 transmits and receives signals with the transmitting / receiving processing unit 134 of the distance measuring device 100 in order to acquire data such as the round-trip time, phase difference, and frequency components of the signal necessary for the distance measuring unit 235 to perform distance measuring. In other words, the distance measuring unit 235 performs distance measuring together with the transmitting / receiving processing unit 134 of the distance measuring device 100. Thus, the fact that the distance measuring unit 235 performs distance measuring together with the transmitting / receiving processing unit 134 of the distance measuring device 100 is equivalent to the distance measuring device 200 performing distance measuring together with the distance measuring device 100. Furthermore, the transmitting / receiving processing unit 234 transmits and receives signals with the transmitting / receiving processing unit 134 of the distance measuring device 100 in order to acquire signals such as the signal necessary for the angle measuring unit 236 to perform angle measuring. In other words, the angle measuring unit 236 performs angle measuring together with the transmitting / receiving processing unit 134 of the distance measuring device 100. Thus, the fact that the angle measuring unit 236 performs angle measuring together with the transmitting / receiving processing unit 134 is equivalent to the distance measuring device 200 performing angle measuring together with the distance measuring device 100.

[0040] The distance measurement process, which calculates the distance between distance measuring devices 100 and 200, is performed by the distance measuring unit 235 of distance measuring device 200, and not by the distance measuring unit 135 of distance measuring device 100. Similarly, the angle measurement process is performed by the angle measuring unit 236 of distance measuring device 200, and not by the angle measuring unit 136 of distance measuring device 100. Therefore, when the distance measuring unit 235 and the angle measuring unit 236 perform the distance measurement process and the angle measurement process, respectively, the transmission / reception processing unit 234 performs the following auxiliary processing in accordance with the processing performed by the distance measuring unit 235 and the angle measuring unit 236.

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

[0042] When the distance measuring unit 235 performs distance measurement using the TOA format, the transmit / receive processing unit 234 transmits TOA signals of multiple frequencies bidirectionally to the transmit / receive processing unit 134 of the distance measuring device 100. In this case, the transmit / receive processing unit 234 only needs to use one of the three antennas 110 to transmit the TOA signals. The transmit / receive processing unit 234 measures the phase of the TOA signals received from the distance measuring device 100, uses the phase data received from the distance measuring device 200 to determine the round-trip phase difference of the TOA signals of each frequency, and outputs data representing the phase difference for each of the multiple frequencies to the distance measuring unit 235.

[0043] Furthermore, when the angle measuring unit 236 performs angle measurement in AOA format, the distance measuring unit 235 outputs data representing the phase difference when the three antennas 210 receive data from the distance measuring device 100 when performing distance measurement in TOA format to the angle measuring unit 236.

[0044] <Distance measurement section 235> The distance measuring unit 235 is capable of performing distance measurement processing in RTT format and distance measurement processing in TOA format. When performing distance measurement processing in RTT format, the distance measuring unit 235 calculates the distance between the distance measuring devices 100 and 200 based on data representing the round-trip time obtained from the transmission / reception processing unit 234.

[0045] When the distance measuring unit 235 performs distance measuring processing in TOA format, it obtains data representing the phase difference for each of the 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 frequencies. The distance calculated in TOA format is much more accurate than the distance calculated in RTT format.

[0046] <Angle measurement section 236> The angle measuring unit 236 uses three antennas 210 to measure the elevation angle and azimuth angle in polar coordinates of the position of the distance measuring device 100 relative to the distance measuring device 200 in AOA format. The angle measuring unit 236 measures the elevation angle and azimuth angle in AOA format based on the phase difference when the three antennas 210 receive the signal transmitted from the distance measuring device 100. The phase difference when the three antennas 210 receive the signal is the first phase difference when the two antennas 210 located on the first axis receive the signal, and the second phase difference when the two antennas 210 located on the second axis receive the signal. The angle measuring unit 236 calculates the azimuth angle representing the position of the distance measuring device 100 relative to the distance measuring device 200 from the ratio of the first phase difference and the second phase difference. The angle measuring unit 236 also calculates the elevation angle representing the position of the distance measuring device 100 relative to the distance measuring device 200 based on the azimuth angle and the first or second phase difference. In AOA-type angle measurement processing, the elevation angle and azimuth angle of the position of the distance measuring device 100 relative to the distance measuring device 200 can be measured in a polar coordinate system.

[0047] <Frequency setting unit 237> The frequency setting unit 237 sets the frequency at which the distance measuring unit 235 performs distance measuring operations, according to the distance measured by the distance measuring operations performed by the distance measuring unit 235. The frequency of distance measuring operations refers to the number of times distance measuring operations are performed within a predetermined unit time (for example, 60 seconds), or the time interval at which distance measuring operations are performed. A high frequency of distance measuring operations means that distance measuring operations are performed many times within a predetermined unit time, or in other words, the time interval at which distance measuring operations are performed is short.

[0048] When the distance between the distance measuring devices 100 and 200 is far, the frequency of distance measurement processing can be low. This is because the smartphone 20, which is equipped with the distance measuring device 200, is far away from the vehicle 10, which is equipped with the distance measuring device 100, making it unlikely that the owner of the smartphone 20 would immediately unlock the doors or trunk of the vehicle 10. Conversely, when the distance between the distance measuring devices 100 and 200 is close, the frequency of distance measurement processing should be increased. This is because the smartphone 20 is close to the vehicle 10, making it possible that the owner of the smartphone 20 could 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 decreases. How the frequency setting unit 237 sets the frequency measured by the distance measuring unit 235 according to the distance will be described later using the flowcharts in Figures 4A and 4B.

[0049] <Memory 238> The memory 238 stores programs, data, and other information necessary for 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 to perform processing.

[0050] Furthermore, 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 the overall process> Figure 3A is a diagram illustrating an example of the overall processing of the rangefinders 100 and 200. Figure 3B is a diagram illustrating an example of the frequency of rangefinder processing. Figure 3A shows a situation where the owner of a smartphone 20 is walking toward a vehicle 10. Figure 3B shows the frequency of rangefinders 100 and 200 performing rangefinder processing over time. In Figure 3B, rangefinder 100 is an Anchor (fixed station), rangefinder 200 is a Tag (mobile station), and the horizontal axis is the time axis.

[0052] As shown in Figure 3A, as an example, thresholds of 60m (an example of distance 3), 30m (an example of distance 2), and 10m (an example of distance 1) are set for the distance between the rangefinder 100 mounted on the vehicle 10 and the rangefinder 200. Distance 2 is an example of a first predetermined distance, and distance 1 is an example of a second predetermined distance.

[0053] Furthermore, 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 in RTT format or TOA format, 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. That is, the relationship time interval 1 < time interval 2 < time interval 3 holds true. When time interval 1, time interval 2, and time interval 3 are expressed in terms of frequency, they are high frequency, medium frequency, and low frequency, respectively.

[0054] <When the distance between distance measuring devices 100 and 200 is greater than 60m> For example, if the distance between the distance measuring devices 100 and 200 is greater than 60m, the distance measuring unit 235 of the distance measuring device 200 does not perform distance measurement processing, and the signal strength measuring unit 132 of the distance measuring device 100 simply measures the RSSI of the advertisement signal output by the distance measuring device 200. The RSSI is measured at the longest time interval 3. Since the distance between the distance measuring devices 100 and 200 is sufficiently far, it is unlikely that the owner of the smartphone 20 would immediately unlock the doors or trunk of the vehicle 10. In such a situation, the power consumption of the distance measuring devices 100 and 200 can be reduced by not performing distance measurement processing.

[0055] Furthermore, since the signal strength measurement unit 132 of the distance measuring device 100 only measures the RSSI of the advertised signal, the processing load on the distance measuring devices 100 and 200 is small, which improves the responsiveness of the distance measuring devices 100 and 200. In particular, when there are multiple distance measuring devices 200, the high responsiveness of the distance measuring device 100 is useful.

[0056] <When the distance between distance measuring devices 100 and 200 is 60m or less but longer than 30m> As an example, if the distance between distance measuring devices 100 and 200 is 60m or less but longer than 30m, the distance measuring unit 235 of distance measuring device 200 performs distance measurement in RTT format at a time interval of 3 (low frequency). Distance measurement at the longest time interval 3 is low frequency distance measurement. Low frequency distance measurement involves a very long time interval for distance measurement, as shown in the upper part of Figure 3B as an example. Time interval 3 is, for example, 100 seconds.

[0057] RTT (Round-Trip Time) distance measurement is a process in which distance measuring device 200 transmits an RTT signal to distance measuring device 100 once, and distance measuring device 100, upon receiving the RTT signal, sends the RTT signal back to distance measuring device 200 once. The distance between distance measuring devices 100 and 200 is then determined based on the round-trip time of the RTT signal between them. Since distance measuring devices 100 and 200 each transmit an RTT signal only once, the processing load on distance measuring devices 100 and 200 is low, and distance measurement can be performed in a short time. However, the distance measurement accuracy is lower compared to TOA (Time-of-Action) distance measurement.

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

[0059] Furthermore, because the processing load of the distance measuring devices 100 and 200 is low, the responsiveness of the distance measuring devices 100 and 200 can be improved. In particular, when there are multiple distance measuring devices 200, the high responsiveness of the distance measuring device 100 is useful.

[0060] <When the distance between distance measuring devices 100 and 200 is 30m or less but longer than 10m> As an example, if the distance between distance measuring devices 100 and 200 is 30m or less and longer than 10m, the distance measuring unit 235 of the distance measuring device 200 performs distance measurement in the TOA format at time interval 2 (medium frequency). Distance measurement at time interval 2 is a medium frequency measurement. As an example, as shown in the middle of Figure 3B, the time interval 2 for performing medium frequency distance measurement 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] Furthermore, when the distance between the distance measuring devices 100 and 200 is 30m or less and longer than 10m, the angle measuring unit 236, based on the phase difference when the signal transmitted from the distance measuring device 100 is received by the three antennas 210, performs the following at time intervals of 2 (medium frequency): Elevation and azimuth angles are measured in AOA format.

[0062] If the distance determined by TOA-type distance measurement is 30m or less but longer than 10m, it is still unlikely that the owner of the smartphone 20 would be able to immediately unlock the doors or trunk of the vehicle 10. Assuming a human movement speed of approximately 1m / s to 4m / s, if the distance is longer than 10m, it is estimated that it would take several seconds for the owner of the smartphone 20 to reach the vehicle 10. TOA-type distance measurement transmits signals of multiple frequencies bidirectionally between the distance measuring devices 100 and 200, resulting in a relatively large processing load on the devices. However, by reducing the frequency of distance measurement processing, it is possible to reduce the power consumption of the distance measuring devices 100 and 200 and improve their responsiveness. In particular, when there are multiple distance measuring devices 200, the high responsiveness of the distance measuring device 100 is useful. Furthermore, if the distance determined by TOA-type distance measurement is 30m or less but longer than 10m, elevation and azimuth angles are measured using AOA-type measurement at a moderate frequency.

[0063] <When the distance between distance measuring devices 100 and 200 is 10m or less> As an example, when the distance between distance measuring devices 100 and 200 is 10m or less, the distance measuring unit 235 of the distance measuring device 200 performs distance measurement in the TOA format at a time interval of 1 (high frequency). Distance measurement at a time interval of 1 is high-frequency distance measurement. In high-frequency distance measurement, as shown in the lower part of Figure 3B as an example, the time interval for performing distance measurement is shorter than the low-frequency and medium-frequency intervals shown in the upper and middle parts of Figure 3B, and the distance measurement process is repeatedly executed with almost no waiting time. As an example, time interval 1 is 0.1 seconds.

[0064] Furthermore, when the distance between the distance measuring devices 100 and 200 is 10 m or less, the angle measuring unit 236 measures the elevation angle and azimuth angle in AOA format at time intervals of 1 (high frequency) based on the phase difference when the signals transmitted from the distance measuring device 100 are received by the three antennas 210.

[0065] If the distance determined by TOA-type distance measurement is 10m or less, the owner of the smartphone 20 may immediately unlock the doors or trunk of the vehicle 10. Therefore, the frequency of TOA-type distance measurement is increased, authentication processing is performed at a high frequency, and elevation and azimuth angles are measured at a high frequency using AOA-type distance measurement.

[0066] <Flowchart> Figures 4A and 4B are flowcharts illustrating an example of the processes performed by the distance measuring devices 100 and 200. Figures 4A and 4B show the processes of distance measuring device 100 on the left half and the processes of distance measuring device 200 on the right half, thereby illustrating the relationship between the processes of distance measuring devices 100 and 200.

[0067] When processing starts, first, the distance measuring device 200, which is a Tag, transmits an advertisement signal (step S201). For example, the processing of distance measuring devices 100 and 200 starts when distance measuring device 200 transmits a start notification to distance measuring device 100 and distance measuring device 100 receives the start notification.

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

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

[0070] When the distance measuring device 100 determines that the estimated distance is 3 or less (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] Furthermore, if the distance measuring device 100 determines in step S102 that the estimated distance is not less than or equal to distance 3 (S102: NO), it returns the flow to step S101. This is to receive the advertised signal again and remeasure the RSSI.

[0072] When the distance measuring device 100 transmits a permission signal to the distance measuring device 200, it transmits a measurement start notification for RTT-format distance measuring process to the distance measuring device 200 (step S104). The measurement start notification for RTT-format distance measuring process is a notification indicating that distance measuring process will be performed in RTT format. As an example, the transmission / reception processing unit 134 of the distance measuring device 100 performs the processing in step S104.

[0073] When the distance measuring device 100 transmits a measurement start notification for RTT-format distance measuring processing, it performs RTT-format distance measuring processing together with the distance measuring device 200 (step S105). As an example, the processing in step S105 is performed by the transmission / reception processing unit 134 of the distance measuring device 100.

[0074] The distance measuring device 200 determines whether it has received an authorization signal within a predetermined time after transmitting the advertisement signal (step S202). The predetermined time is, for example, 0.01 seconds. If an authorization signal is not received within the predetermined time, a timeout occurs. For example, the main control unit 231 of the distance measuring device 200 performs the process in step S202.

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

[0076] Furthermore, if the distance measuring device 200 determines in step S202 that it has not received a permission signal within a predetermined time (S202: NO), it returns the flow to step S201. This is to retransmit the advertisement signal and restart the process.

[0077] When the distance measuring device 200 receives a notification to start distance measurement processing in RTT format, it performs distance measurement processing in RTT format together with the distance measuring device 100 (step S204). The processing in step S204 is performed integrally with the processing in step S105 performed by the distance measuring device 100, and is performed by the transmit / receive processing unit 134 of the distance measuring device 100 and the transmit / receive processing unit 234 and distance measuring unit 235 of the distance measuring device 200. Specifically, the transmit / receive processing unit 234 transmits an RTT signal, the transmit / receive processing unit 134 sends back an RTT signal, and based on the round-trip time acquired by the transmit / receive processing unit 234, the distance measuring unit 235 measures the distance between the distance measuring devices 100 and 200 in RTT format. In the processing of step S204, the distance between the distance measuring devices 100 and 200 is calculated by the distance measurement processing in RTT format.

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

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

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

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

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

[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). As an example, the main control unit 131 of the distance measuring device 100 performs the processing in step S107.

[0084] If the distance measuring device 100 determines that the time interval represented by the received interval data is not time interval 2 (S107: NO), it sets the waiting time in the distance measuring device 100 to time interval 3 (step S108A). For example, the main control unit 131 performs the processing in step S108A. After completing the processing in step S108A, the distance measuring device 100 returns the flow to step S101. This is to restart the RSSI measurement.

[0085] Furthermore, in step S107, if the distance measuring device 100 determines that the time interval represented by the received interval data is time interval 2 (S107: YES), it sets the waiting time in the distance measuring device 100 to time interval 2 (step S108B). After completing the processing in step S108B, the distance measuring device 100 proceeds to step S109. As an example, the processing in step S108B is performed by the main control unit 131.

[0086] The distance measuring device 100 transmits a measurement start notification for TOA-type distance measuring and AOA-type angle measuring to the distance measuring device 200 (step S109). The measurement start notification for TOA-type distance measuring and AOA-type angle measuring is a notification indicating that TOA-type distance measuring and AOA-type angle measuring will be performed. As an example, the transmission / reception processing unit 134 of the distance measuring device 100 performs the processing in step S109.

[0087] When the distance measuring device 100 transmits a measurement start notification for TOA-type distance measuring processing and AOA-type angle measuring processing, it performs TOA-type distance measuring processing together with the distance measuring device 200 (step S110). As an example, the processing in step S110 is performed by the transmission / reception processing unit 134 of the distance measuring device 100.

[0088] The distance measuring device 200 receives a notification to start measurement for TOA-type distance measuring processing and AOA-type angle measuring processing (step S208). The processing in step S208 is performed, for example, by the main control unit 231 of the distance measuring device 200.

[0089] When the distance measuring device 200 receives a notification to start TOA-type distance measuring processing and AOA-type angle measuring processing, it performs TOA-type distance measuring processing together with the distance measuring device 100, and also performs AOA-type angle measuring processing when it receives a signal from the distance measuring device 100 (step S209). The distance measuring processing in step S209 is performed integrally with the processing in step S110 performed by the distance measuring device 100, and is performed by the transmit / receive processing unit 134 of the distance measuring device 100 and the transmit / receive processing unit 234 and distance measuring unit 235 of the distance measuring device 200. Specifically, the transmit / receive processing unit 234 sequentially transmits signals of multiple frequencies for TOA, the transmit / receive processing unit 134 sequentially sends back signals of the same frequency for TOA, and the transmit / receive processing unit 134 transmits phase data representing the phase when it receives the signal to the distance measuring device 200. Furthermore, the AOA-type angle measurement process in step S209 is a process in which the distance measuring device 200 measures a first phase difference and a second phase difference when it receives a signal for TOA from the distance measuring device 100, and measures the azimuth angle and elevation angle that represent the position of the distance measuring device 100 relative to the distance measuring device 200 based on the first phase difference and the second phase difference.

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

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

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

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

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

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

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

[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 processing in step S112 is performed, for example, by the main control unit 131 of the distance measuring device 100.

[0098] If the distance measuring device 100 determines that the time interval represented by the received interval data is not time interval 1 (S112: NO), it sets the waiting time in the distance measuring device 100 to time interval 2 (step S113A). The main control unit 131 performs the processing in step S113A. After completing the processing in step S113A, the distance measuring device 100 returns the flow to step S104. This is because it restarts the distance measuring process in RTT format.

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

[0100] After completing the processing in step S113B, the distance measuring device 100 determines whether to terminate the process (step S114). Termination occurs, for example, when the authentication process is successful. The main control unit 131 performs the processing in step S114. The distance and angle data obtained by the distance measuring device 200 in the distance measurement and angle measurement processes of step S209 and transmitted to the distance measuring device 100 are used for the authentication process.

[0101] If the distance measuring device 100 determines that it will not terminate (S114: NO), it returns the flow to step S109. This is because it performs TOA-type distance measuring and AOA-type angle measuring processes at a high frequency with a time interval of 1.

[0102] Furthermore, when the distance measuring device 100 determines to terminate (S114: YES), it sends a termination notification to the distance measuring device 200 indicating that it has finished the series of processes (step S115). When the distance measuring device 100 sends the termination notification to the distance measuring device 200, it terminates the series of processes (END).

[0103] When the distance measuring device 200 receives a termination notification from the distance measuring device 100, it terminates the series of processes (END).

[0104] <Effects> The distance measuring system 300 of Embodiment 1 includes a distance measuring device 100 and a distance measuring device 200. The distance measuring device 200 includes a distance measuring unit 235 that performs distance measuring processing to measure the distance between itself and the distance measuring device 100 based on the result of the distance measuring device 200 transmitting signals bidirectionally to and from the distance measuring device 100, and a frequency setting unit 237 that sets the frequency at which the distance measuring unit 235 performs distance measuring processing according to the distance measured by the distance measuring unit 235. Therefore, the frequency at which the distance measuring unit 235 performs distance measuring processing can be set according to the distance measured by the distance measuring unit 235.

[0105] Therefore, by making it possible to set the measurement frequency according to the measured distance, a distance measuring system 300 capable of accurate distance measurement can be provided. In addition, because the measurement frequency is set according to the measured distance, the power consumption of the distance measuring devices 100 and 200 can be reduced 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 that can measure distances with high accuracy.

[0107] Furthermore, the frequency setting unit 237 increases the frequency as the distance measured by the distance measuring unit 235 decreases, so that distance measurement can be performed at a higher frequency as the distance between the distance measuring devices 100 and 200 decreases. Therefore, a distance measuring system 300 can be provided that can measure distance at a higher frequency as the distance between the distance measuring devices 100 and 200 decreases. In addition, by setting the measurement frequency to a lower value as the distance measured decreases, the power consumption of the distance measuring devices 100 and 200 can be reduced as the distance measured decreases.

[0108] Furthermore, the distance measuring device 100 includes a signal strength measurement unit 132 that performs a signal strength measurement process to measure the signal strength (RSSI) of the signal received from the distance measuring device 200, and a permission determination unit 133 that permits the distance measuring unit 235 of the distance measuring device 200 to perform distance measuring processing when the signal strength measured by the signal strength measurement unit 132 is equal to or greater than a predetermined strength. Therefore, when the RSSI of the signal transmitted by the distance measuring device 200 is equal to or greater than a predetermined value and the distance measuring device 200 is relatively close to the distance measuring device 100, the distance measuring unit 235 can perform distance measuring processing, and when the RSSI of the signal transmitted by the distance measuring device 200 is less than a predetermined value, distance measuring processing can be prevented. When the distance between the distance measuring devices 100 and 200 is sufficiently far, it is unlikely that the owner of a device equipped with the distance measuring device 200 (for example, a smartphone 20) would immediately come into contact with the device equipped with the distance measuring device 100 (for example, a vehicle 10). In this situation, the power consumption of the distance measuring devices 100 and 200 can be reduced by not performing the distance measuring process as part of the authentication process for the distance measuring device 200.

[0109] Furthermore, when the distance between the distance measuring unit 235 and the distance measuring device 100 becomes less than or equal to a first predetermined distance (distance 2), the distance measuring unit 235 measures the distance to the distance measuring device 100 in TOA format based on the relationship between the round-trip phase difference and multiple frequencies, which is obtained by the bidirectional transmission of signals of multiple frequencies by the distance measuring devices 100 and 200. For this reason, when the distance between the distance measuring devices 100 and 200 becomes relatively short (distance 2 or less), high-precision distance measurement can be performed in TOA format. However, since the TOA format distance measuring process involves many processing steps to determine the relationship between the round-trip phase difference and multiple frequencies, the power consumption of the distance measuring devices 100 and 200 increases. By limiting this power-intensive distance measuring process to when the distance between the distance measuring devices 100 and 200 becomes less than or equal to distance 2, the power consumption of the distance measuring devices 100 and 200 can be reduced.

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

[0111] Furthermore, the frequency setting unit 237 sets the frequency of the distance measuring unit 235 to perform distance measuring processing more frequently than when the distance to the distance measuring device 100 is greater than when the distance to the distance measuring device 100 is greater than the first predetermined distance (distance 2). Therefore, when the distance between the distance measuring devices 100 and 200 is greater than the first predetermined distance, distance measuring can be performed at a low frequency using RTT type distance measuring processing, and when the distance between the distance measuring devices 100 and 200 is greater than the first predetermined distance (distance 2), distance measuring can be performed at a high frequency using TOA type distance measuring processing. When the distance between the distance measuring devices 100 and 200 is greater than the first predetermined distance, the need for distance measuring is low, so power consumption can be further reduced by using RTT type distance measuring processing, which consumes less power, and by reducing the frequency of distance measuring processing. Furthermore, when the distance between distance measuring devices 100 and 200 is less than or equal to the first predetermined distance (distance 2), the need for distance measurement increases. Therefore, by measuring the distance frequently using the TOA type distance measuring process, which has high distance measurement accuracy, high-frequency and high-precision distance measurement can be achieved.

[0112] Furthermore, the frequency setting unit 237 sets the frequency of the distance measurement unit 235 to perform distance measurement processing more frequently than when the distance to the distance measuring device 100 is greater than when the distance to the distance measuring device 100 is greater than the distance to the distance measuring device 235 is greater than when the distance to the distance measuring device 100 is greater than the distance to the distance measuring device 235. As a result, when the distance between the distance measuring devices 100 and 200 is less than or equal to the first predetermined distance (distance 2), the frequency of TOA-type distance measurement processing can be changed depending on whether the distance is 1 or less, and when the distance measuring device 200 approaches the distance measuring device 100 to a distance of 1 or less, the distance between the distance measuring devices 100 and 200 can be measured with high frequency and high accuracy in TOA format. In addition, when the distance between the distance measuring devices 100 and 200 is less than or equal to the first predetermined distance (distance 2), by changing the frequency of distance measurement processing depending on whether the distance is 1 or less, the power consumption of the distance measuring devices 100 and 200 can be reduced when the distance is greater than 1.

[0113] Furthermore, the distance measuring device 200 has multiple antennas 210, and further includes an angle measuring unit 236 that performs angle measuring processing to measure the angle representing the position of the distance measuring device 100 relative to the distance measuring device 200 based on the phase difference when the multiple antennas 210 of the distance measuring device 200 receive signals from the distance measuring device 100 when the distance measuring device 100 and the distance measuring device 200 transmit signals of multiple frequencies bidirectionally. Therefore, the angle (azimuth angle and elevation angle) of the distance measuring device 100 relative to the distance measuring device 200 can be determined.

[0114] Furthermore, the distance measuring system 300 includes a distance measuring device 100 and a distance measuring device 200. The distance measuring device 100 or the distance measuring device 200 includes a distance measuring unit (135 or 235) that performs distance measuring processing to measure the distance between the distance measuring device 100 and the distance measuring device 200 based on the result of the distance measuring devices 100 and 200 transmitting signals bidirectionally, and a frequency setting unit (137 or 237) that sets the frequency at which the distance measuring unit (135 or 235) performs distance measuring processing according to the distance measured by the distance measuring processing. Therefore, the frequency at which the distance measuring unit (135 or 235) performs distance measuring processing can be set according to the distance measured by the distance measuring unit (135 or 235).

[0115] Therefore, by making it possible to set the measurement frequency according to the measured distance, a distance measuring system 300 capable of accurate distance measurement can be provided. In addition, because the measurement frequency is set according to the measured distance, the power consumption of the distance measuring devices 100 and 200 can be reduced according to the measured distance. Furthermore, the distance measuring unit (135 or 235) and the frequency setting unit (137 or 237) can be located in either the distance measuring device 100 or the distance measuring device 200.

[0116] The communication station (distance measuring device 200) of Embodiment 1 is a communication station (distance measuring device 200) that can communicate with the distance measuring device 100, and the distance measuring device 200 includes a distance measuring unit 235 that performs distance measuring processing to measure the distance between itself and the distance measuring device 100 based on the result of the distance measuring device 200 transmitting signals bidirectionally to and from the distance measuring device 100, and a frequency setting unit 237 that sets the frequency at which the distance measuring unit 235 performs distance measuring processing according to the distance measured by the distance measuring unit 235. Therefore, the frequency at which the distance measuring unit 235 performs distance measuring processing can be set according to the distance measured by the distance measuring 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 distance measurement method of Embodiment 1 is a distance measurement method in a distance measurement system 300 including a distance measuring device 100 and a distance measuring device 200, wherein a distance measurement process is performed to measure the distance between the distance measuring device 100 and the distance measuring device 200 based on the result of the distance measuring device 100 and the distance measuring device 200 transmitting signals bidirectionally, and the frequency of the distance measurement process is set according to the distance measured by the distance measurement process. For this reason, the frequency at 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.

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

[0120] In the above description, we have explained a configuration in which the distance measuring device 100 measures the RSSI of the advertisement signal transmitted by the distance measuring device 200 and performs the distance measuring process. However, the distance measuring device 200 may also measure the RSSI of the advertisement signal transmitted by the distance measuring device 100 and perform the distance measuring process.

[0121] Furthermore, the above describes a configuration in which the distance measuring unit 235 of the distance measuring device 200 performs RTT-type distance measuring when the distance between the distance measuring devices 100 and 200 becomes distance 3 or less. However, the distance measuring unit 235 may perform only TOA-type distance measuring without performing RTT-type distance measuring. In this case, the frequency of performing TOA-type distance measuring should be changed depending on whether the distance between the distance measuring devices 100 and 200 is distance 1 or less. In this case, the distance measuring device 100 may measure the RSSI of the advertised signal until the distance between the distance measuring devices 100 and 200 becomes distance 2.

[0122] Furthermore, the MUC230 of the distance measuring device 200 may be configured not to include the angle measuring unit 236, so that the distance measuring device 200 does not perform angle measuring processing.

[0123] <Variation> Figure 5 shows an example of a configuration in which a modified version of the distance measuring system 300M 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] Figure 5 shows the arrangement of the two speakers A and B that make up the speaker system. Speakers A and B of the speaker system operate according to their position relative to the smartphone 20M. Therefore, Figure 5 shows the state in which the smartphone 20M is moving relative to the two speakers A and B. For this reason, the smartphone 20M is shown in five locations depending on its position, but one smartphone 20M is provided for each of the two speakers A and B.

[0125] Speakers A and B each include distance measuring devices 100M1 and 100M2, respectively. Distance measuring devices 100M1 and 100M2 are the same as distance measuring device 100 shown in Figure 2 and are capable of measuring the RSSI of the advertised signal transmitted by distance measuring device 200. When distance measuring devices 100M1 and 100M2 are not specifically distinguished, they are simply referred to as distance measuring device 100M. Note that it is sufficient to have either speaker A or B, and the number of distance measuring devices 100M included in the distance measuring system 300M may be just one.

[0126] Furthermore, the smartphone 20M includes a distance measuring device 200M. The distance measuring device 200M is similar to the distance measuring device 200 shown in Figure 2, and communicates with distance measuring devices 100M1 and 100M2, and is capable of performing distance measuring processing to measure the distance between distance measuring devices 100 and 200, and angle measuring processing to determine the angle (azimuth angle and elevation angle) of distance measuring device 100 relative to distance measuring device 200.

[0127] For example, when the smartphone 20M moves, the signal strength measuring unit 132 of the distance measuring device 100M measures the RSSI of the advertisement signal transmitted by the distance measuring device 200M. If the distance between the distance measuring devices 100M and 200M is greater than distance 3, only the RSSI is measured, and the distance measuring device 200M does not perform distance measurement processing.

[0128] When the distance between distance measuring devices 100M and 200M decreases to 3 or less due to the movement of the smartphone 20M, distance measuring device 200M performs RTT-style distance measurement, and when the distance decreases to 2 or less, it performs TOA-style distance measurement. When the distance between distance measuring devices 100M and 200M decreases to 1 or less, distance measuring device 200M notifies distance measuring device 100M1 or 100M2 that the distance is 1 or less, and speaker A or B outputs sound. Speaker A or B outputs sound when the distance between distance measuring device 100M1 or 100M2 and distance measuring device 200M is 1 or less, and stops outputting sound when the distance exceeds 1. The sound may be voice guidance, music, etc.

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

[0130] Therefore, by allowing the measurement frequency to be set according to the measured distance, a distance measuring system 300M capable of accurate distance measurement can be provided. Furthermore, because the measurement frequency is set according to the measured distance, the power consumption of the distance measuring devices 100M and 200M can be reduced 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 measuring and angle measuring 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 measuring and angle measuring 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 distance measuring device 100 of Embodiment 2 differs from the distance measuring device 100 of Embodiment 1 in that it performs a process of selecting one distance measuring device 200 from among a plurality of distance measuring devices 200 that performs both distance measuring and angle measuring processing. Furthermore, the distance measuring device 200 of Embodiment 2 differs from the distance measuring device 200 of Embodiment 1 in that it transmits an advertisement signal that includes distance measuring information related to the distance measuring and angle measuring processing performed by the distance measuring unit 135 and angle measuring unit 136 of the distance measuring device 100.

[0133] In Embodiment 2, unlike Embodiment 1, the rangefinder 100 is an example of a second communication station, and the rangefinder 200 is an example of a first communication station. Below, Embodiment 2 will be described, focusing on the differences from Embodiment 1. Furthermore, redundant explanations of components similar to those of the rangefinders 100 and 200 in Embodiment 1 will be omitted.

[0134] Figure 6 shows an example of the configuration of the distance measuring devices 100 and 200 of Embodiment 2. The system including the distance measuring devices 100 and 200 is a distance measuring system 300. Here, the distance measuring devices 100 and 200 of Embodiment 2 will be described using Figure 6.

[0135] Figure 6 shows one distance measuring device 100 and one 200, but in Embodiment 2, there may be multiple distance measuring devices 100 and 200. Each of the multiple distance measuring devices 100 in Embodiment 2 selects one distance measuring device 200 that performs both distance measuring and angle measuring processing in an environment where multiple distance measuring devices 200 exist. The multiple distance measuring devices 100 are, for example, arranged at a distance of 100m 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 distance measuring device 100 performs distance measurement and angle measurement processing together with the selected distance measuring device 200. In Embodiment 2, the distance measuring unit 135 of the distance measuring device 100 in Embodiment 2 performs the distance measurement processing performed by the distance measuring unit 235 of the distance measuring device 200 in Embodiment 1. The transmission and reception processing unit 134 of the distance measuring device 100 in Embodiment 2 performs the processing performed by the transmission and reception processing unit 234 of the distance measuring device 200 in Embodiment 1. Furthermore, the transmission and reception processing unit 234 of the distance measuring device 200 in Embodiment 2 performs the processing performed by the transmission and reception processing unit 134 of the distance measuring device 100 in Embodiment 1. In addition, the angle measurement unit 136 of the distance measuring device 100 in Embodiment 2 performs the processing performed by the angle measurement unit 236 of the distance measuring device 200 in Embodiment 1. Furthermore, just as the main control unit 231 of the distance measuring device 200 in Embodiment 1 determines the position of the distance measuring device 100 relative to the distance measuring device 200 based on distance and angle (elevation angle and azimuth angle), the main control unit 131 of the distance measuring device 100 in Embodiment 1 determines the position of the distance measuring device 200 relative to the distance measuring device 100 based on distance and angle (elevation angle and azimuth angle).

[0137] <Configuration of the distance measuring device 200 in Embodiment 2> The rangefinder 200 includes three antennas 210, a communication unit 220, and an MCU 230. The configuration of the three antennas 210 and the communication unit 220 is the same as the configuration of the three antennas 210 and the communication unit 220 in Embodiment 1.

[0138] <mcu230> The MCU130 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 MCU230 of Embodiment 2 has a configuration in which the distance measurement information acquisition unit 235A is added to the MCU230 of Embodiment 1.

[0139] <Distance information acquisition unit 235A> The distance measurement information acquisition unit 235A acquires distance measurement information relating to the distance measurement process performed by the distance measurement unit 135 of the distance measurement device 100. The distance measurement information includes, as an example, the identification information of the distance measurement device 100, the time when the previous distance measurement process was performed (distance measurement time), the position of the distance measurement device 200 determined by the distance obtained in the previous distance measurement process and the angle obtained in the previous angle measurement process (previous position), and the relative speed with the distance measurement device 200 that performed the previous distance measurement process together with the distance measurement device 100 (relative speed of distance measurement devices 100 and 200).

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

[0141] Furthermore, the relative speed is determined by the transmission / reception processing unit 134 when it transmits and receives signals with the transmission / reception processing unit 234 of the distance measuring device 200 in order to acquire data such as the round-trip time, phase difference, and frequency components of the signal necessary for the distance measuring unit 135 to perform distance measurement.

[0142] Specifically, the transmitting / receiving processing unit 134 transmits and receives signals of multiple frequencies f1 to fm (where m is an integer of 2 or more) with the transmitting / receiving processing unit 234 of the distance measuring device 200. For signals that are transmitted from the distance measuring device 100 to the distance measuring device 200 and then transmitted back to the distance measuring device 200, the unit determines the round-trip phase (first round-trip phase) between the phase when the signal is received by the distance measuring device 200 and the phase when the signal is received by the distance measuring device 100.

[0143] Furthermore, after determining the first round-trip phase, the transmitting / receiving processing unit 134 transmits and receives signals of multiple frequencies f1 to fm (where m is an integer of 2 or more) with the transmitting / receiving processing unit 234 of the distance measuring device 200. For signals that are transmitted from the distance measuring device 100 to the distance measuring device 200 and transmitted back and forth from the distance measuring device 200 to the distance measuring device 100, the transmitting / receiving processing unit 134 determines the round-trip phase (second round-trip phase) between the phase when the signal is received by the distance measuring device 200 and the phase when the signal is received by the distance measuring device 100.

[0144] The transmitting / receiving processing unit 134 then determines the relative speed 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] Furthermore, if the smartphone 20, including the distance measuring device 200, is moving, the distance measuring device 100 with which the distance measuring device 200 performed the previous distance measuring process may be different from the distance measuring device 100 with which the distance measuring device 200 performs the next distance measuring process. The next distance measuring process is the distance measuring process performed immediately after the previous distance measuring process.

[0146] The distance measurement information acquisition unit 235A stores the identification information of the distance measurement device 100, the distance measurement time when the distance measurement device 200 performs distance measurement processing together with the distance measurement device 100, the measured position, and the relative speed as distance measurement information in the memory 238. The distance measurement information is acquired by the distance measurement device 100 when the distance measurement device 200 next performs angle measurement processing together with the distance measurement device 100. For this reason, when angle measurement processing is performed again, the identification information of the distance measurement information is the identification information of the distance measurement device 100 that performed the angle measurement processing together last time (hereinafter referred to as "previous identification information"), the distance measurement time is the previous distance measurement time when the previous angle measurement processing was performed, the measured position is the previous position measured in the previous angle measurement processing, and the relative speed is the relative speed obtained in the previous angle measurement processing (hereinafter referred to as "previous relative speed").

[0147] The distance measuring device 200 stores distance measurement information, including the previous identification information, the previous distance measurement time, the previous position, and the previous relative speed, in an advertisement signal and transmits it.

[0148] Here, we will explain the location where distance measurement information is stored in the advertisement signal using Figure 7. Figure 7 shows an example of the location where distance measurement information is stored in the advertisement signal. Figure 7 shows an example of the data structure of the advertisement signal.

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

[0150] <Configuration of the distance measuring device 100 in Embodiment 2> The rangefinder 100 includes three antennas 110, a communication unit 120, and an MCU 130. The configuration of the three antennas 110 and the communication unit 120 is the same as that of the three antennas 110 and the communication unit 120 in Embodiment 1.

[0151] <mcu130> The MCU130 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 MCU130 of Embodiment 2 has a configuration in which the first processing unit 132A is added to the MCU130 of Embodiment 1. The memory 138 is an example of a storage unit.

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

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

[0154] Multiple distance measuring devices 200 whose RSSI measured by the signal strength measuring unit 132 is above a predetermined value are, for example, distance measuring devices 200 whose distance from distance measuring device 100 is 100m or less. Since the RSSI of the advertisement signal that distance measuring device 100 receives from distance measuring devices 200 is approximately proportional to the distance between distance measuring devices 100 and 200, by using the RSSI when the distance between distance measuring devices 100 and 200 is 100m as a predetermined value (predetermined strength), distance measuring devices 200 whose distance from distance measuring device 100 is approximately 100m or less can be extracted.

[0155] The first processing unit 132A stores in the memory 138 the RSSI values ​​of multiple distance measuring devices 200 and the distance measurement information included in the received multiple advertisement signals, if there are multiple distance measuring devices 200 whose RSSI values ​​are equal to or greater than a predetermined value (predetermined intensity). The distance measurement information includes previous identification information, distance measurement time, previous position, and previous relative speed. The previous identification information is the identification information of the distance measuring device 100 that performed the previous distance measurement processing together with the distance measuring device 200 that transmitted the advertisement signal. The distance measurement time is the previous distance measurement time, representing the time when the distance measuring device 200 that transmitted the advertisement signal performed the previous distance measurement processing. The previous position is the previous position obtained by the distance and angle (elevation angle and azimuth angle) obtained by the distance measuring device 200 that transmitted the advertisement signal in the previous distance measurement processing and previous angle measurement processing. The previous relative speed is the relative speed obtained when the distance measuring device 200 that transmitted the advertisement signal performed the previous distance measurement processing.

[0156] Furthermore, the first processing unit 132A selects from among a plurality of distance measuring devices 200 whose RSSI is equal to or greater than a predetermined value (predetermined intensity) a distance measuring device 200 whose previous identification information is different from that of its own distance measuring device 100, as a distance measuring device 200 to perform distance measuring processing together.

[0157] Furthermore, if there are multiple distance measuring devices 200 whose distance measuring device 100 is different from its own distance measuring device 100, the first processing unit 132A selects the distance measuring device 200 from among the multiple distance measuring devices 200 that has the earliest reception time when the distance measuring device 100 received the advertisement signal, as the distance measuring device 200 that will perform the distance measuring process together.

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

[0159] Furthermore, if there are multiple distance measuring devices 200 with the highest evaluation score based on the previous distance measurement time, previous position, and previous relative speed, the first processing unit 132A predicts the position of the distance measuring device 200 at the time of receiving the signal, based on the previous position, previous distance measurement time, and previous relative speed for each of the multiple distance measuring devices 200. Then, the first processing unit 132A selects the distance measuring device 200 whose predicted position is closest to that of the distance measuring device 100 as the distance measuring device 200 to perform the distance measurement process together.

[0160] <Received information and distance measurement information> Figure 8 shows an example of the received information and distance measurement information received by the distance measuring device 100. For the previous distance measurement time, previous position, and previous relative speed among the distance measurement information, the evaluation criteria and evaluation points are also shown. The evaluation points are shown in parentheses.

[0161] The received information consists of the RSSI and the time of reception of the advertisement signal when the distance measuring device 100 receives the advertisement signal from the distance measuring device 200. When the distance measuring device 100 receives the advertisement signal from the distance measuring device 200, it acquires the RSSI and the reception time and stores them in the memory 138 as received information.

[0162] Furthermore, the distance measurement information includes the previous identification information, the previous distance measurement time, the previous position, and the previous relative speed, and is included in the advertisement signal received by the distance measuring device 100 from the distance measuring device 200. When the distance measuring device 100 receives the advertisement signal, it reads out the distance measurement information and stores the previous identification information, the previous distance measurement time, the previous position, and the previous relative speed in the memory 138.

[0163] Furthermore, when the first processing unit 132A of the distance measuring device 100 evaluates the distance measuring device 200 based on the previous measurement time, previous position, and previous relative speed, it uses the evaluation points shown in Figure 8 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 1 point to all other distance measuring devices 200.

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

[0166] For example, the evaluation criterion for the previous relative speed is whether the previous relative speed is above a threshold. If the previous relative speed is above the threshold, the first processing unit 132A assigns 2 points to the distance measuring device 200, and if the previous relative speed is below the threshold, it assigns 1 point to the distance measuring device 200.

[0167] <Calculation of evaluation score> Figure 9 shows an example of the calculation results of the evaluation score. Here, as an example, we will explain an example of the results of the first processing unit 132A of the distance measuring device 100 calculating the evaluation score for eight distance measuring devices 200, A to H.

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

[0169] <Sequence> Figure 10 is a sequence diagram illustrating an example of the processing performed by distance measuring devices 100 and 200. In Figure 10, the left half shows the processing of distance measuring device 100, and the right half shows the processing of the four distance measuring devices 200A to D, thereby explaining the relationships between the processing of distance measuring devices 100 and 200A to D. Here, the four distance measuring devices 200 are referred to as distance measuring devices 200A to D to distinguish them. Also, distance measuring device 100 is an Anchor (fixed station), and distance measuring devices 200A to D are Tags (mobile stations).

[0170] First, the distance measuring devices 200A to D transmit advertisement signals in sequence. Here, we will explain this by assuming that the distance measuring devices 200A to D transmit advertisement signals in that order as an example.

[0171] The distance measuring device 100 executes process 1 each time it receives an advertised signal. The distance measuring device 100 receives advertised signals from multiple distance measuring devices 200 in sequence during a set advertised signal reception period of 10 ms (milliseconds). Here, as an example, the distance measuring device 100 receives advertised signals from distance measuring devices 200A to D in sequence within the advertised signal reception period, and executes process 1 each time it receives a signal. The advertised signal reception period is 10 ms as an example. The details of process 1 will be described later using Figure 11.

[0172] When the advertising signal reception period ends, the distance measuring device 100 executes process 2. Process 2 causes the distance measuring device 100 to select a distance measuring device 200 that performs both distance measuring and angle measuring. Here, as an example, we assume that distance measuring device 200B is selected.

[0173] Each of the distance measuring devices 200A to D transmits an advertisement signal and then waits for a positioning start request to be transmitted, for example, for 20ms. This 20ms is the positioning start request waiting time. If a positioning start request is not received within the positioning start request waiting time, each distance measuring device 200 periodically transmits an advertisement signal.

[0174] The distance measuring device 100 sends a positioning start request to the selected distance measuring device 200B. Upon receiving the positioning start request, the distance measuring device 200B sends an acknowledgment. As a result, the distance measuring device 100 performs distance measurement and angle measurement processing together with the distance measuring device 200B. Thereafter, the distance measuring devices 100 and 200B perform the processing described in Embodiment 1 using Figures 3A, 3B, 4A, and 4B.

[0175] <Process 1> Figure 11 is a flowchart showing an example of the specific processing details of Process 1. Process 1 is performed by the distance measuring device 100.

[0176] The distance measuring device 100 receives the advertisement signal (step S251).

[0177] The first processing unit 132A obtains the time when the advertised signal was received (step S252).

[0178] The first processing unit 132A determines whether the distance from the distance measuring device 100 to the distance measuring device 200 is below a threshold based on the RSSI (signal strength) of the advertised signal measured by the signal strength measuring unit 132 (step S253). Since RSSI is approximately proportional to distance, the first processing unit 132A determines whether the distance from the distance measuring device 100 to the distance measuring device 200 is below a threshold by determining whether the RSSI is above a predetermined strength. For example, the threshold used in step S253 is 100m. For example, the threshold in step S253 is set to a range in which an advertised signal with an RSSI at a level that allows the distance measuring device 100 to receive the advertised signal and read out the distance measurement information can be obtained.

[0179] When the first processing unit 132A determines that the distance from the distance measuring device 100 to the distance measuring device 200 is below a threshold (S253: YES), it stores the RSSI, reception time, and distance measurement information in the memory 138 (step S254). The distance measurement information is read from the received advertisement signal.

[0180] The first processing unit 132A calculates an evaluation point 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). The evaluation criterion for the previous distance measurement time is whether it is the earliest (oldest) time, as described above. The evaluation criterion for the previous position is whether the distance from the distance measuring device 100 to the distance measuring device 200 is below a threshold, and this distance threshold is 50m as an example. The threshold for the evaluation criterion for the previous relative speed is 18km / h as an example.

[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), it returns the flow to step S251. This is to receive advertising signals from other distance measuring devices 200 and calculate the evaluation points.

[0183] Furthermore, if the first processing unit 132A determines in step S253 that the distance from the distance measuring device 100 to the distance measuring device 200 is not below a threshold (S253: NO), it returns the flow to step S251. This is because the distance measuring device 200 is too far from the distance measuring device 100 to obtain an advertisement signal with an RSSI level sufficient for the distance measuring device 100 to receive the advertisement signal and read the distance measurement information.

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

[0185] By performing the above-described process 1, the distance measuring device 100 extracts distance measuring devices 200 whose RSSI is equal to or greater than a predetermined value (predetermined intensity). When multiple distance measuring devices 200 are extracted, process 2 is executed to narrow down the selection to one distance measuring device 200 that performs both distance measuring and angle measuring processing.

[0186] <Process 2> Figure 12 is a flowchart showing an example of the specific processing details of process 2. Process 2 is performed by the distance measuring device 100.

[0187] The first processing unit 132A determines whether there are any distance measuring devices 200 (Tag) among the multiple distance measuring devices 200 (Tag) extracted in process 1 whose previous identification information is different from the identification information of its own distance measuring device 100 (step S261).

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

[0189] A distance measuring device 200 whose previous identification information differs from the identification information of its own distance measuring device 100 is a distance measuring device 200 that performed the previous distance measurement and angle measurement processing with a different distance measuring device 100 than its own, and is a distance measuring device 200 that has moved within the threshold (100m) in step S253 from its own distance measuring device 100. Such a distance measuring device 200 will be given priority in performing distance measurement and angle measurement processing.

[0190] If, in step S262, there is one distance measuring device 200 whose previous identification information differs from the identification information of its own distance measuring device 100, that distance measuring device 200 is selected as the distance measuring device 200 that performs both distance measuring and angle measuring processing.

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

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

[0193] If the first processing unit 132A determines that there are no multiple distance measuring devices 200 with the maximum evaluation points (S264: NO), it selects the single distance measuring device 200 with the maximum evaluation points as the distance measuring device 200 that performs both distance measuring and angle measuring processing (step S265).

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

[0195] The predicted position is a prediction of the position of the distance measuring device 200 at the time the advertised signal is received. The first processing unit 132A calculates the predicted value of the position of the distance measuring device 200 at the time the advertised signal is received by multiplying the time from the previous distance measurement time to the time the advertised signal is received, which is included in the distance measurement information, by the previous relative velocity.

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

[0197] When the first processing unit 132A completes the processing in step S262, S265, or S267, it sends a positioning start request (see Figure 10) to the selected distance measuring device 200. As a result, the distance measuring device 100 performs distance measurement and angle measurement processing together with the selected distance measuring device 200.

[0198] The distance measuring device 100 transmits the positioning result (position determined by distance and angle) to the distance measuring device 200, and also transmits interval data to the distance measuring device 200. Once the above processes are completed, the distance measuring device 100 returns the flow to process 1.

[0199] <Example of calculating predicted position> Figure 13 shows an example of calculating the predicted position. Figure 13 shows the rangefinder 100 (Anchor) and three rangefinders 200 (Tag). Cases (1) to (3) will be explained in order from top to bottom. The previous position is shown as the distance from rangefinder 100 to rangefinder 200. Also, for the sake of simplicity, the elevation angle is assumed to be 0 degrees, and the azimuth angle is assumed to be the angle to the left of rangefinder 100 in Figure 13. The previous positioning time and the time of reception of the advertised signal are shown as elapsed time (seconds) relative to the reference time.

[0200] In case (1), a user holding the distance measuring device 200 is approaching the distance measuring device 100 on a bicycle. The previous position was 50 mm, the previous relative speed was 18 km / h, the previous positioning time was 10.0 seconds, and the time of reception of the advertised signal was 15.0 seconds. In this case, the predicted position will be 25 m.

[0201] In case (2), a user holding the distance measuring device 200 is approaching the distance measuring device 100 on foot. The previous position was 30 mm, the previous relative speed was 3 km / h, the previous positioning time was 10.1 seconds, and the time of reception of the advertised signal was 15.1 seconds. In this case, the predicted position will be 25.8 m.

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

[0203] If the predicted positions for cases (1) to (3) are calculated in step S266 described above, the first processing unit 132A, in step S267, selects the distance measuring device 200 for case (1), which has the smallest difference between the predicted position and the previous position, as the distance measuring device 200 that performs both distance measuring and angle measuring. The closest distance measuring device 200 is selected preferentially, and both distance measuring and angle measuring can be performed.

[0204] <Effects> The distance measuring system 300 of Embodiment 2 includes a distance measuring device 100 and a distance measuring device 200. The distance measuring device 200 includes a distance measuring unit 235 that performs distance measuring processing to measure the distance to the distance measuring device 100 based on the result of the distance measuring device 200 transmitting an advertisement signal bidirectionally to and from the distance measuring device 100, and a frequency setting unit 237 that sets the frequency at which the distance measuring unit 235 performs distance measuring processing according to the distance measured by the distance measuring unit 235. The distance measuring device 100 (second communication station) may also include a signal strength measurement unit 132 that performs signal strength measurement processing to measure the RSSI of the advertisement signal received from the distance measuring 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 plurality of distance measuring devices 200 is above a predetermined strength, and selects a distance measuring device 200 to perform distance measuring processing together from among the plurality of distance measuring devices 200 whose RSSI is above the predetermined strength. Therefore, the frequency at which the distance measuring unit 235 performs distance measurement can be set according to the distance measured by the distance measuring unit 235. In addition, if there are multiple distance measuring devices 200 with RSSI of a predetermined strength or higher, one distance measuring device 200 can be selected to perform distance measurement together.

[0205] Furthermore, the distance measuring device 200 transmits an advertisement signal containing distance measurement information related to distance measurement processing, and the distance measuring device 100 receives multiple advertisement signals from multiple distance measuring devices 200. The distance measuring device 100 also has a memory 138 (storage unit), and the first processing unit 132A may store in the memory 138 multiple RSSIs and multiple distance measurement information contained in the received multiple advertisement signals for multiple distance measuring devices 200 whose RSSI is above a predetermined intensity. As a criterion for selecting one distance measuring device 200, the RSSIs and distance measurement information for multiple distance measuring devices 200 whose RSSI is above a predetermined intensity can be stored in the memory 138, making it easier to select one distance measuring device 200.

[0206] Furthermore, there are multiple distance measuring devices 100, and the distance measurement information includes previous identification information that identifies the distance measuring device 100 that one of the multiple distance measuring devices 100 performed the previous distance measurement with. The first processing unit 132A may select from among the multiple distance measuring devices 200 whose RSSI is equal to or greater than a predetermined intensity a distance measuring device 200 whose previous identification information represents a distance measuring device 100 that is different from its own distance measuring device 100 as the distance measuring device 200 to perform the distance measurement with. The distance measuring device 200 that performed the previous distance measurement with a distance measuring device 100 that is different from its own distance measuring device 100 is a distance measuring device 200 that has moved close to its own distance measuring device 100. It becomes possible to preferentially select such a distance measuring device 200.

[0207] If there are multiple distance measuring devices 200 whose previous identification information represents a distance measuring device 100 other than its own distance measuring device 100, the first processing unit 132A may select the distance measuring device 200 that received the advertisement signal earliest from among the multiple distance measuring devices 200 as the distance measuring device 200 to perform the distance measuring process together with the distance measuring device 100. If there are multiple distance measuring devices 200 that have moved close to the own distance measuring device 100, by selecting the distance measuring device 200 that received the advertisement signal earliest, the first processing unit 132A can preferentially select the distance measuring device 200 that has moved close to the own distance measuring device 100 and has had the longest elapsed time since the previous distance measuring process.

[0208] Furthermore, the distance measuring device 100 further includes a plurality of antennas 110 and an angle measuring unit 136 that performs angle measuring processing to measure the angle representing the position of the distance measuring device 200 relative to the distance measuring device 100 based on the phase difference when the plurality of antennas of the distance measuring device 100 receive signals from the distance measuring device 200 when the distance measuring device 200 and the distance measuring device 100 transmit signals of multiple frequencies bidirectionally. The distance measuring information includes the time of the previous distance measuring process when the previous distance measuring process was performed, the previous position determined by the distance measured in the previous distance measuring process and the angle measured in the previous angle measuring process, and the previous relative velocity determined in the previous distance measuring process. The first processing unit 132A may select the distance measuring device 200 with the highest evaluation score based on at least two of the information from the previous distance measuring time, previous position, and previous relative velocity as the distance measuring device 200 to perform the distance measuring process with. The evaluation score can be used as a judgment criterion to easily determine which distance measuring device 200 should be prioritized for distance measuring processing.

[0209] Furthermore, the distance measurement information includes the previous distance measurement time, previous position, and previous relative speed. If there are multiple distance measuring devices 200 with the highest evaluation score based on the previous distance measurement time, previous position, and previous relative speed, the first processing unit 132A may predict the position of the distance measuring device 200 at the time of receiving the advertisement signal based on the previous position, previous distance measurement time, and previous relative speed for each of the multiple distance measuring devices 200. The distance measuring device 200 whose predicted position is closest to that of the distance measuring device 100 may be selected as the distance measuring device 200 to perform the distance measurement process together. The closest distance measuring device 200 can be selected preferentially to perform the distance measurement process together.

[0210] The distance measuring system 300 of Embodiment 2 includes a distance measuring device 100 and a distance measuring device 200. The distance measuring device 100 (second communication station) includes a signal strength measurement unit 132 that performs signal strength measurement processing to measure the RSSI of an advertisement signal received from the distance measuring 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 distance measuring devices 200 is above a predetermined strength, and selects a distance measuring device 200 to perform distance measuring processing together from among the multiple distance measuring devices 200 whose RSSI is above the predetermined strength. Therefore, if there are multiple distance measuring devices 200 whose RSSI is above the predetermined strength, one distance measuring device 200 can be selected to perform distance measuring processing together.

[0211] While exemplary embodiments of the ranging system, communication station, and ranging method of this disclosure have been described above, this disclosure is not limited to the specifically disclosed embodiments, and various modifications and changes 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 13 October 2022, the entire contents of which are incorporated herein by reference. [Explanation of Symbols]

[0213] 10 vehicles 20, 20M Smartphone 100, 100M, 100M1, 100M2 distance measuring device (an example of a first communication station in Embodiment 1, an example of a second communication station in Embodiment 2) 110 Antenna 120 Communications Department 131 Main Control Unit 132 Signal strength measurement unit 132A First Processing Unit 133 Permission Judgment Department 134 Transmit / Receive Processing Unit 135 Ranging section 136 Angle measurement section 137 Frequency setting section 138 memory 200, 200M range measuring device (an example of a second communication station in Embodiment 1, an example of a first communication station in Embodiment 1) 210 Antenna 220 Communications Department 231 Main Control Unit 232 Signal strength measurement unit 233 Permission Judgment Department 234 Transmit / Receive Processing Unit 235 Ranging section 235A Distance information acquisition section 236 Angle measurement section 237 Frequency setting section 238 memory 300, 300M ranging system

Claims

1. First Communications Station and Second Communications Station and Includes, The aforementioned second communications station, A distance measuring unit performs distance measuring processing to measure the distance between the second communication station and the first communication station based on the result of the second communication station transmitting signals bidirectionally to and from the first communication station, A frequency setting unit sets the frequency at which the distance measuring unit performs the distance measuring process, according to the distance measured by the distance measuring unit. It has, The aforementioned second communications station, A signal strength measurement unit performs a signal strength measurement process to measure the signal strength of the signal received from the first communication station, A first processing unit determines whether the signal strength measured by the signal strength measuring 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 from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength to perform the distance measurement process together. It has, The first communication station transmits the signal containing the distance measurement information relating to the distance measurement process, The second communication station receives multiple signals from multiple first communication stations, The second communications station further has a storage section, The first processing unit stores in the storage unit, for the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength, the plurality of signal strengths and the plurality of distance measurement information included in the plurality of received signals. There are multiple such second communications stations. The distance measurement information includes previous identification information that identifies the second communication station with which the first communication station, among a plurality of second communication stations, previously performed the distance measurement process. A distance measuring system in which the first processing unit selects from among the plurality of 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 the distance measuring process will be performed.

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 increases the frequency as the distance measured by the distance measuring unit decreases.

4. The aforementioned first communications station is, A signal strength measurement unit performs a signal strength measurement process to measure the signal strength of the signal received from the second communication station, A permission determination unit grants permission to the distance measuring unit of the second communication station to perform the distance measuring process if the signal strength measured by the signal strength measuring unit is equal to or greater than a predetermined strength. A distance measuring system according to claim 1, comprising:

5. The distance measuring system according to claim 1, wherein when the distance to the first communication station falls below a first predetermined distance, the distance measuring unit measures the distance to the first communication station based on the relationship between the round-trip phase difference and the multiple frequencies, which is obtained by the first communication station and the second communication station transmitting signals of multiple frequencies bidirectionally.

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

7. The distance measuring system according to claim 6, wherein the frequency setting unit sets the frequency at which the distance measuring unit performs the distance measuring process to be higher than when the distance to the first communication station is not less than or equal to the first predetermined distance, when the distance to the first communication station is less than or equal to the first predetermined distance.

8. The distance measuring system according to claim 5, wherein the frequency setting unit sets the frequency at which the distance measuring unit performs the distance measuring process to a higher value than when the distance to the first communication station is not less than or equal to the second predetermined distance, when the distance to the first communication station is less than or equal to the first predetermined distance.

9. The aforementioned second communications station, Multiple antennas, When the first and second communication stations transmit signals of multiple frequencies bidirectionally, the angle measuring unit performs angle measuring processing to measure the angle representing the position of the first communication station relative to the second communication station based on the phase difference when the multiple antennas of the second communication station receive signals from the first communication station. The distance measuring system according to claim 5, further comprising:

10. The distance measurement information includes the reception time at which the second communication station received the signal from the first communication station. The distance measuring system according to claim 1, wherein if there are multiple first communication stations in which the second communication station represented by the previous identification information is different from its own second communication station, the first processing unit selects the first communication station with the earliest reception time from among the multiple first communication stations as the first communication station in which the distance measuring process will be performed together.

11. The aforementioned second communications station, Multiple antennas, When the first and second communication stations transmit signals of multiple frequencies bidirectionally, the angle measuring unit performs angle measuring processing to measure the angle representing the position of the first communication station relative to the second communication station based on the phase difference when the multiple antennas of the second communication station receive signals from the first communication station. It further includes, The distance measurement information is, The time of the previous distance measurement when the previous distance measurement process was performed, The previous position is 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, Includes, The distance measuring system according to claim 1, wherein the first processing unit selects the first communication station with the highest evaluation score based on at least two of the information of the previous distance measurement time, the previous position, and the previous relative speed as the first communication station that performs the distance measuring process together.

12. The distance measurement information includes the time of the previous distance measurement, the previous position, and the previous relative velocity. If there are multiple first communication stations that have the highest evaluation score based on the previous distance measurement time, previous position, and previous relative speed, the first processing unit predicts the position of the first communication station at the time of receiving the signal for each of the multiple first communication stations based on the previous position, the previous distance measurement time, and the previous relative speed. The distance measuring system according to claim 11, wherein the first communication station whose predicted position is closest to the second communication station is selected as the first communication station that performs the distance measuring process together.

13. First Communications Station and Second Communications Station and Includes, The aforementioned second communications station, A signal strength measurement unit performs a signal strength measurement process to measure the signal strength of the signal received from the first communication station, A first processing unit determines whether the signal strength measured by the signal strength measuring 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 from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength to perform distance measurement processing together. It has, The aforementioned second communications station, A signal strength measurement unit performs a signal strength measurement process to measure the signal strength of the signal received from the first communication station, A first processing unit determines whether the signal strength measured by the signal strength measuring 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 from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength to perform the distance measurement process together. It has, The first communication station transmits the signal containing the distance measurement information relating to the distance measurement process, The second communication station receives multiple signals from multiple first communication stations, The second communications station further has a storage section, The first processing unit stores in the storage unit, for the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength, the plurality of signal strengths and the plurality of distance measurement information included in the plurality of received signals. There are multiple such second communications stations. The distance measurement information includes previous identification information that identifies the second communication station with which the first communication station, among a plurality of second communication stations, previously performed the distance measurement process. A distance measuring system in which the first processing unit selects from among the plurality of 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 the distance measuring process will be performed.

14. First Communications Station and Second Communications Station and Includes, The first or second communications station is A distance measuring unit performs distance measuring processing to measure the distance between the first and second communication stations based on the results of the first and second communication stations transmitting signals bidirectionally, A frequency setting unit sets the frequency at which the distance measuring unit performs the distance measuring process, according to the distance measured by the distance measuring process. It has, The aforementioned second communications station, A signal strength measurement unit performs a signal strength measurement process to measure the signal strength of the signal received from the first communication station, A first processing unit determines whether the signal strength measured by the signal strength measuring 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 from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength to perform the distance measurement process together. It has, The first communication station transmits the signal containing the distance measurement information relating to the distance measurement process, The second communication station receives multiple signals from multiple first communication stations, The second communications station further has a storage section, The first processing unit stores in the storage unit, for the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength, the plurality of signal strengths and the plurality of distance measurement information included in the plurality of received signals. There are multiple such second communications stations. The distance measurement information includes previous identification information that identifies the second communication station with which the first communication station, among a plurality of second communication stations, previously performed the distance measurement process. A distance measuring system in which the first processing unit selects from among the plurality of 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 the distance measuring process will be performed.

15. A communications station that is a second communications station capable of communicating with the first communications station, The aforementioned second communications station, A distance measuring unit performs distance measuring processing to measure the distance between the second communication station and the first communication station based on the result of the second communication station transmitting signals bidirectionally to and from the first communication station, A frequency setting unit sets the frequency at which the distance measuring unit performs the distance measuring process, according to the distance measured by the distance measuring unit. It has, The aforementioned second communications station, A signal strength measurement unit performs a signal strength measurement process to measure the signal strength of the signal received from the first communication station, A first processing unit determines whether the signal strength measured by the signal strength measuring 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 from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength to perform the distance measurement process together. It has, The first communication station transmits the signal containing the distance measurement information relating to the distance measurement process, The second communication station receives multiple signals from multiple first communication stations, The second communications station further has a storage section, The first processing unit stores in the storage unit, for the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength, the plurality of signal strengths and the plurality of distance measurement information included in the plurality of received signals. There are multiple such second communications stations. The distance measurement information includes previous identification information that identifies the second communication station with which the first communication station, among a plurality of second communication stations, previously performed the distance measurement process. The first processing unit selects from among the plurality of 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 the ranging process will be performed.

16. First Communications Station and Second Communications Station and A distance measuring method in a distance measuring system including, Based on the results of the first and second communication stations transmitting signals bidirectionally, a distance measurement process is performed to measure the distance between the first and second communication stations. The frequency of performing the distance measurement process is set according to the distance measured by the distance measurement process. The aforementioned second communications station, A signal strength measurement unit performs a signal strength measurement process to measure the signal strength of the signal received from the first communication station, A first processing unit determines whether the signal strength measured by the signal strength measuring 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 from among the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength to perform the distance measurement process together. It has, The first communication station transmits the signal containing the distance measurement information relating to the distance measurement process, The second communication station receives multiple signals from multiple first communication stations, The second communications station further has a storage section, The first processing unit stores in the storage unit, for the plurality of first communication stations whose signal strength is equal to or greater than the predetermined strength, the plurality of signal strengths and the plurality of distance measurement information included in the plurality of received signals. There are multiple such second communications stations. The distance measurement information includes previous identification information that identifies the second communication station with which the first communication station, among a plurality of second communication stations, previously performed the distance measurement process. A distance measurement method comprising: the first processing unit selecting from among the plurality of 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 the distance measurement process will be performed.

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