Distance measuring device

Abstract

Provided is a distance measuring device capable of accurately measuring a distance even in an environment in which multiple paths exist. The distance measuring apparatus acquires a plurality of first phases when a plurality of first signals transmitted to the other device at three or more frequencies are received by the other device, and measures a plurality of second phases when a second signal is received from the other device at three or more frequencies. Extracting N signal pairs corresponding to N (N is greater than or equal to 2) signal strengths except one or more signal strengths smaller than a threshold value in the signal strengths of the signal pairs of the first signals and the second signals from the plurality of signal pairs, a round-trip phase obtained by summing up the first phase and the second phase of the first signal and the second signal included in each signal pair is obtained for the N signal pairs, and the distance to the other device is measured on the basis of the N round-trip phases and the plurality of frequencies.

Description

Technical Field

[0001] The invention relates to a distance measuring device. Background Art

[0002] In the past, there was a distance measuring device comprising: a first device comprising a first transceiver, the first transceiver transmitting a first known signal corresponding to a first carrier frequency and a second known signal corresponding to a second carrier frequency different from the first carrier frequency, and receiving a third known signal corresponding to the first carrier frequency and a fourth known signal corresponding to the second carrier frequency; a second device comprising a second transceiver, the second transceiver transmitting a third known signal and a fourth known signal, and receiving the first and second known signals; and a calculation unit, which calculates the distance between the first device and the second device based on the phases of the first to fourth known signals, the first transceiver and the second transceiver performing four transmissions and receptions, namely, transmitting and receiving the first and third known signals once each and transmitting and receiving the second and fourth known signals once each (for example, refer to patent document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-128341 Summary of the invention

[0006] Problems that the invention will solve

[0007] However, when performing distance measurement, if there are multiple paths in the RF (Radio Frequency) signal such as the first to fourth known signals, the phase of the radio wave reflected in the middle is different from the phase of the radio wave directly coming from the device of the transmission source, and there is a hidden danger that the distance measurement cannot be accurately performed. This is because the transmission path of the radio wave reflected in the middle is different from the transmission path of the radio wave directly coming from the device of the transmission source.

[0008] Therefore, an object of the present invention is to provide a distance measuring device capable of accurately measuring distance even in an environment where multiple paths exist.

[0009] Means for solving problems

[0010] The distance measuring device of the embodiment of the present invention comprises: a transmitting unit that transmits a first signal to another device; a receiving unit that receives a second signal from the other device that has received the first signal; a phase acquiring unit that acquires a plurality of first phases when the other device receives a plurality of the first signals transmitted by the transmitting unit to the other device at different timings with a plurality of frequencies of three or more; a phase measuring unit that measures a plurality of second phases when the receiving unit receives the second signal from the other device at different timings with the plurality of frequencies of three or more; and a signal strength acquiring unit that acquires information about the plurality of first signals and the plurality of second signals having the same frequency. The invention relates to a method for preparing an apparatus for measuring the signal strengths of multiple signal pairs of signals relative to each other; an extraction unit for extracting, from the multiple signal pairs, N signal pairs corresponding to N signal strengths except for one or more signal strengths that are less than a specified threshold value, wherein N is an integer greater than 2; a round-trip phase calculation unit for calculating a round-trip phase for the multiple signal pairs, wherein the round-trip phase is a phase obtained by summing the first phase and the second phase of the first signal and the second signal contained in the multiple signal pairs; and a ranging unit for measuring the distance to the other device based on the N round-trip phases and the multiple frequencies.

[0011] Effects of the Invention

[0012] A distance measuring device capable of accurately measuring distance even in an environment where multiple paths exist can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The diagrams show a vehicle 10 and a smart key 20 on which distance measuring devices 100A and 100B according to the embodiment are respectively mounted.

[0014] Figure 2 It is a diagram showing a distance measuring device 100A according to the embodiment.

[0015] Figure 3 It is a diagram for explaining a communication method for distance measurement executed by the distance measuring devices 100A and 100B.

[0016] Figure 4 This is a diagram showing the relationship between the frequency fm and the phase φ2wm in ranging.

[0017] Figure 5 It is a diagram illustrating the path a of the direct wave and the path b of the multi-path.

[0018] Figure 6 This is a diagram showing an example of the relationship between the frequency and the round-trip phase of the first signal and the second signal when there are multiple paths.

[0019] Figure 7This is a diagram for explaining the relationship between the round-trip phase and the frequency when the influence of the Doppler effect is exerted on the radio waves transmitted and received between the distance measuring devices 100A and 100B.

[0020] Figure 8 It is a diagram for explaining a method of detecting a moving speed v (m / s).

[0021] Fig.9A It is a diagram showing round-trip phases (upper side) corresponding to frequencies f0 to fm and signal strengths (lower side) corresponding to frequencies f0 to fm obtained by performing the first transmission process and the first reception process in a plurality of continuous wave transmission periods.

[0022] Fig. 9B It is a diagram showing round-trip phases (upper side) corresponding to frequencies f0 to fm and signal strengths (lower side) corresponding to frequencies f0 to fm obtained by performing the first transmission process and the first reception process in a plurality of continuous wave transmission periods.

[0023] Fig. 9C It is a diagram showing round-trip phases (upper side) corresponding to frequencies f0 to fm and signal strengths (lower side) corresponding to frequencies f0 to fm obtained by performing the first transmission process and the first reception process in a plurality of continuous wave transmission periods.

[0024] Fig.10 It is a summary Figures 9A to 9C A diagram showing the signal pair extracted by the extraction unit 177 based on the result.

[0025] Fig.11 It is a diagram for explaining the speed correction process among the correction processes of the correction unit 178 .

[0026] Fig.12 It is a diagram for explaining the linear correction process among the correction processes performed by the correction unit 178 .

[0027] Fig.13 It is a diagram for explaining the linear correction process among the correction processes performed by the correction unit 178 .

[0028] Fig.14 It is a diagram for explaining the linear correction process among the correction processes performed by the correction unit 178 .

[0029] Fig.15 This is a flowchart showing an example of processing executed by the control device 170 . DETAILED DESCRIPTION

[0030] Hereinafter, an embodiment of a distance measuring device to which the present invention is applied will be described.

[0031] Figure 11 is a diagram showing a vehicle 10 and a smart key 20 respectively equipped with distance measuring devices 100A and 100B of an embodiment. Here, as an example, a method in which the distance measuring device 100A is installed in a smart entry system mounted on the vehicle 10 and the distance measuring device 100B is installed in the smart key 20 of the vehicle 10 is described. As an example, the distance measuring devices 100A and 100B can communicate data packets through BLE (Bluetooth Low Energy (registered trademark)). In addition, as an example, an automatic parking assistance system is installed in the vehicle 10, and the distance measuring device 100A is included in the automatic parking assistance system. The automatic parking assistance system is a system that sends instructions to the vehicle 10 remotely from the smart key 20 through wireless communication, thereby allowing the vehicle 10 to autonomously park at a parking position or to autonomously leave the parking position.

[0032] At least one of the distance measuring device 100A of the vehicle 10 and the distance measuring device 100B of the smart key 20 measures the distance between the vehicle 10 and the smart key 20, and the doors, trunk, etc. of the vehicle 10 are unlocked when the distance measured by the distance measuring device 100A or 100B is an appropriate distance.

[0033] Here, as an example, it is assumed that the distance measuring device 100A of the vehicle 10 performs distance measurement and notifies the distance measuring device 100B of the smart key 20 of the result of the distance measurement. The distance measuring devices 100A and 100B have the same structure as an example. Therefore, in the following, when the distance measuring devices 100A and 100B are not distinguished, they are simply referred to as the distance measuring device 100. The distance measuring device 100A of the vehicle 10 and the distance measuring device 100B of the smart key 20 that does not perform distance measurement are examples of other devices. Here, as an example, the distance measuring device 100B of the vehicle 10 becomes an example of other devices. In addition, the distance measuring device 100A can be treated as a master device and the distance measuring device 100B can be treated as a slave device, or vice versa, the distance measuring device 100B can be treated as a master device and the distance measuring device 100A can be treated as a slave device, but such processing is not performed here for explanation.

[0034] <Configuration of Distance Measuring Device 100A>

[0035] Figure 2 1 is a diagram showing a distance measuring device 100A according to an embodiment. As described above, the distance measuring device 100A of the vehicle 10 and the distance measuring device 100B of the smart key 20 have the same structure. Here, the distance measuring device 100A that performs distance measurement is described. Hereinafter, the signal sent from the distance measuring device 100A to the distance measuring device 100B from the antenna 101 is referred to as a first signal, and the signal sent from the distance measuring device 100B to the distance measuring device 100A from the antenna 101 is referred to as a second signal.

[0036] The ranging device 100A includes an antenna 101, a PA (Power Amplifier) ​​110, an LNA (Low Noise Amplifier) ​​120, an OM (Orthogonal Modulator) 130, an ODM (Orthogonal DeModulator) 140, a VCO (Voltage Controlled Oscillator) 150, a PLL (Phase Locked Loop) 155, a codec processing unit 160 and a control device 170.

[0037] The antenna 101 communicates with the antenna 101 of the distance measuring device 100B of the vehicle 10. The antenna 101 is connected to the PA 110 and the LNA 120. Here, a switch for switching the connection destination of the antenna 101 to either the PA 110 or the LNA 120 is omitted. The antenna 101 of the distance measuring device 100A transmits a first signal to the distance measuring device 100B, and receives a second signal from the distance measuring device 100B.

[0038] The PA 110 is provided between the OM 130 and the antenna 101, and amplifies a modulated signal (first signal) for transmission input from the OM 130 and outputs the amplified signal to the antenna 101. The PA 110 is an amplifier for transmission.

[0039] The LNA 120 is provided between the antenna 101 and the ODM 140, and amplifies the second signal received by the antenna 101 by low noise, and outputs the amplified signal to the ODM 140. The LNA 120 is a receiving amplifier.

[0040] The OM 130 is an example of a transmission unit, and modulates the I / Q signal input from the codec processing unit 160 using the high frequency signal input from the VCO 150 , and outputs the modulated signal to the PA 110 as a transmission modulated signal.

[0041] ODM 140 is an example of a receiving unit, and uses a high frequency signal input from VCO 150 to demodulate the signal output from LNA 120 to obtain an I / Q signal, and outputs the I / Q signal to codec processing unit 160. The signal output from LNA 120 is a signal received by distance measuring device 100A from distance measuring device 100B.

[0042] The VCO 150 oscillates at a frequency set by the PLL 155 . The VCO 1500 can oscillate at a plurality of frequencies set by the PLL 155 .

[0043] The PLL 155 sets the frequency at which the VCO 150 oscillates. The PLL 155 can set a plurality of frequencies for the VCO 150 .

[0044] The codec processing unit 160 includes an ADC (Analog to Digital Converter) and a DAC (Digital to Analog Converter) to perform codec processing. The codec processing unit 160 performs detection of BLE (registered trademark) data packets, address determination processing, etc. More specifically, the codec processing unit 160 performs digital conversion (ADC processing) on ​​the I / Q signal processed by the ODM140 and converts it into BLE data packet information. In addition, the codec processing unit 160 generates an I / Q signal (divided into an I signal and a Q signal) based on the BLE data packet (digital signal) input from the control device 170, performs analog conversion through DAC processing, and outputs it to OM130 as a transmission signal, i.e., an I / Q signal.

[0045] Hereinafter, a signal of a predetermined frequency transmitted from the OM 130 of the distance measuring device 100A to the distance measuring device 100B is referred to as a transmission signal. Also, a signal transmitted as a transmission signal by the distance measuring device 100A and received by another device is referred to as a reception signal.

[0046] The control device 170 includes a main control unit 170A, a transmission and reception control unit 171, a switching unit 172, a phase acquisition unit 173, a phase measurement unit 174, a signal strength acquisition unit 175, a round-trip phase calculation unit 176, an extraction unit 177, a correction unit 178, a distance measurement unit 179, and a memory 170M. The memory 170M is an example of a storage unit. The control device 170 is implemented by a microcomputer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), an input / output interface, and an internal bus.

[0047] The main control unit 170A, the transmission and reception control unit 171, the switching unit 172, the phase acquisition unit 173, the phase measurement unit 174, the signal strength acquisition unit 175, the round-trip phase calculation unit 176, the extraction unit 177, the correction unit 178, and the distance measurement unit 179 are shown as functional blocks of the functions of the program executed by the control device 170. In addition, the memory 170M functionally represents the memory of the control device 170.

[0048] The main control unit 170A is a processing unit that controls the processing of the device 170 in general, and performs processing other than the processing performed by the transmission and reception control unit 171, the switching unit 172, the phase acquisition unit 173, the phase measurement unit 174, the signal strength acquisition unit 175, the round-trip phase calculation unit 176, the extraction unit 177, the correction unit 178, and the distance measurement unit 179. The main control unit 170A, for example, notifies the distance measurement device 100B of the vehicle 10 of the result of the distance measurement. In the notification, the BLE packet communication with a frequency different from the communication used for the distance measurement is used. In the notification, the result of the distance measurement, etc. is written in the payload of the BLE packet.

[0049] The transceiver control unit 171 performs control related to the transceiver of the first signal and the second signal between the ranging device 100A and the ranging device 100B. Specifically, the transceiver control unit 171 sets the frequency (prescribed frequency) and phase of the signal sent from the ranging device 100A to the ranging device 100B. In addition, in order for the ranging device 100B to send a signal having the same frequency as the signal sent to the ranging device 100A to the ranging device 100A, the transceiver control unit 171 of the ranging device 100B sets the frequency (prescribed frequency) and phase of the signal sent from the ranging device 100B to the ranging device 100A. In addition, the same frequency of the signals sent to each other by the ranging devices 100A and 100B can be determined in advance between the ranging devices 100A and 100B, or data indicating the frequency can be shared using BLE data packet communication.

[0050] In addition, the transceiver control unit 171 causes OM130 to repeat the transmission process of sending the first signal to the distance measuring device 100B during a specified period, and causes OM130 to send the first signal of more than three frequencies to the distance measuring device 100B at different timings. In addition, the transceiver control unit 171 causes ODM140 to repeat the reception process of receiving the second signal from the distance measuring device 100B during a specified period, and causes ODM140 to receive the second signal of more than three frequencies from the distance measuring device 100B at different timings. The specified period is a continuous wave transmission period in BLE (registered trademark), which is 2.5 milliseconds. During the specified period, the first signal is sent from the distance measuring device 100A to the distance measuring device 100B, and the second signal is sent from the distance measuring device 100B to the distance measuring device 100A.

[0051] In addition, the transceiver control unit 171 causes OM130 to transmit the first signal multiple times for each of the multiple frequencies f1 to fm (m is an integer greater than or equal to 2), and causes ODM140 to receive the second signal multiple times for each of the multiple frequencies. That is, OM130 transmits the first signal multiple times at different timings for each of the frequencies f1 to fm. In addition, ODM140 receives the second signal multiple times for each of the multiple frequencies f1 to fm. The purpose of transmitting the first signal and receiving the second signal multiple times at each frequency is to obtain multiple round-trip phases at each frequency.

[0052] Here, as an example, a method is described in which the transceiver control unit 171 causes the OM 130 to transmit the first signal twice for each of the multiple frequencies f1 to fm, and causes the ODM 140 to receive the second signal twice for each of the multiple frequencies. The OM 130 transmits the first signal through two transmission processes of the first transmission process and the second transmission process for each of the multiple frequencies f1 to fm. In addition, the ODM 140 receives the second signal through two reception processes of the first reception process and the second reception process for each of the multiple frequencies f1 to fm.

[0053] As described above, here is a method in which the transceiver control unit 171 causes the OM 130 to transmit the first signal twice for each of the multiple frequencies f1 to fm through the first transmission process and the second transmission process, and causes the ODM 140 to receive the second signal twice for each of the multiple frequencies f1 to fm through the first reception process and the second reception process. The number of transmission processes (the number of times the first signal is transmitted) and the number of reception processes (the number of times the second signal is received) for each of the multiple frequencies f1 to fm may be equal, or may be three or more.

[0054] The time period during which OM130 performs the first transmission processing for each of the multiple frequencies f1 to fm overlaps with the time period during which ODM140 performs the first reception processing for each of the multiple frequencies f1 to fm. That is, the first transmission processing and the first reception processing are performed in the same time period. In addition, the time period during which OM130 performs the second transmission processing for each of the multiple frequencies f1 to fm overlaps with the time period during which ODM140 performs the second reception processing for each of the multiple frequencies f1 to fm. That is, the second transmission processing and the second reception processing are performed in the same time period. The time period during which the first transmission processing and the first reception processing are performed are different from the time period during which the second transmission processing and the second reception processing are performed.

[0055] The switch 172 switches between the transmission state of the OM 130 transmitting signals and the reception state of the ODM 140 receiving signals. The switch 172 enables the PA 110 to amplify signals in the transmission state and enables the LNA to amplify signals in the reception state. When switching between the transmission state and the reception state, the switch 172 sets a stabilization time for stabilizing the phase and frequency.

[0056] The phase acquisition unit 173 acquires from the ranging device 100B the first phase when the ranging device 100B receives the first signal of a specified frequency sent in the first transmission process and the second transmission process of the ranging device 100A at each frequency of frequencies f1 to fm. At each frequency, the first signal is sent twice, so the phase acquisition unit 173 acquires two first phases at each frequency. The phase acquisition unit 173 acquires data representing the first phase from the ranging device 100B through a BLE data packet communication at a frequency different from the communication used for ranging. The phase data representing the first phase can be written into the payload of the BLE data packet. In addition, the phase data representing the first phase can be measured by the phase measurement unit 174 of the ranging device 100B and sent to the ranging device 100A.

[0057] The phase measuring unit 174 measures the second phase when the ODM 140 receives the second signal in the first receiving process and the second receiving process at each frequency of the frequencies f1 to fm. That is, the phase measuring unit 174 measures multiple second phases when the ODM 140 of the distance measuring device 100A receives the second signal from the distance measuring device 100B at three or more frequencies at different timings. At each frequency, the second signal is sent twice from the distance measuring device 100B, so the phase measuring unit 174 obtains two second phases at each frequency. The second phase is measured for distance measurement.

[0058] The signal strength acquisition unit 175 acquires the second reception strength when the ODM 140 repeatedly performs the first reception process and the second reception process at each frequency of the frequencies f1 to fm and receives a plurality of second signals. In addition, the signal strength acquisition unit 175 acquires the first signal strength when the ranging device 100B receives a plurality of first signals from the ranging device 100B. The first signal strength acquired by the signal strength acquisition unit 175 from the ranging device 100B is measured by the signal strength acquisition unit 175 of the ranging device 100B, written as signal strength data into the payload of the BLE data packet as the second signal, and transmitted to the ranging device 100A.

[0059] In this way, the signal strength acquisition unit 175 acquires the first signal strength based on the signal strength data included in the plurality of second signals received by the ODM 140 by repeatedly performing the reception process.

[0060] Here, a pair of a first signal and a second signal having mutually equal frequencies is referred to as a signal pair. The plurality of first signals transmitted by the first transmission process have mutually different frequencies f1 to fm. In addition, the plurality of second signals received by the first reception process have mutually different frequencies f1 to fm. Similarly, the plurality of first signals transmitted by the second transmission process have mutually different frequencies f1 to fm. In addition, the plurality of second signals received by the second reception process have mutually different frequencies f1 to fm.

[0061] Hereinafter, a signal including a first signal sent by a first sending process and a second signal received by a first receiving process is symmetrically referred to as a first signal pair, and a signal including a first signal sent by a second sending process and a second signal received by a second receiving process is symmetrically referred to as a second signal pair. Hereinafter, when no particular distinction is made between the first signal pair and the second signal pair, they are referred to simply as signal pairs.

[0062] The first signal pair is a signal pair of a first signal and a second signal (signals with the same frequency among a plurality of first signals and a plurality of second signals) transmitted and received in a first transmission process and a first reception process performed in the same time period (first time period) and having frequencies (f1 to fm) equal to each other. In addition, the second signal pair is a signal pair of a first signal and a second signal (signals with the same frequency among a plurality of first signals and a plurality of second signals) transmitted and received in a second transmission process and a second reception process performed in the same time period (second time period) and having frequencies (f1 to fm) equal to each other.

[0063] Since the number of the first signals is equal to the number of the second signals, the first signal pairs exist in a number equal to the number of the first signals and the number of the second signals in the first transmission process and the first reception process. Similarly, the second signal pairs exist in a number equal to the number of the first signals and the number of the second signals in the second transmission process and the second reception process. In addition, the number of the first signal pairs is equal to the number of the second signal pairs.

[0064] The signal strength acquisition unit 175 acquires the first signal strength when the distance measuring device 100B receives a plurality of first signals, or the second reception strength when the ODM 140 repeats the reception process and receives a plurality of second signals, as the signal strengths for the plurality of first signal pairs and the plurality of second signal pairs. The signal strength acquisition unit 175 acquires the first signal strength when the distance measuring device 100B receives a plurality of first signals by performing the first transmission process and the first reception process, or the second reception strength when the ODM 140 repeats the reception process and receives a plurality of second signals. In addition, the signal strength acquisition unit 175 acquires the first signal strength when the distance measuring device 100B receives a plurality of first signals by performing the second transmission process and the second reception process, or the second reception strength when the ODM 140 repeats the reception process and receives a plurality of second signals.

[0065] The signal strength acquisition unit 175 acquires signal strengths of multiple first signal pairs having equal frequencies among multiple first signals and multiple second signals, and acquires signal strengths of multiple second signal pairs having equal frequencies among multiple first signals and multiple second signals.

[0066] The round-trip phase calculation unit 176 obtains a first round-trip phase that is a sum of the first phase and the second phase of the first signal and the second signal included in each first signal pair, for the plurality of first signal pairs obtained by the signal strength acquisition unit 175. In addition, the round-trip phase calculation unit 176 obtains a second round-trip phase that is a sum of the first phase and the second phase of the first signal and the second signal included in each second signal pair, for the plurality of second signal pairs obtained by the signal strength acquisition unit 175. In addition, when the first round-trip phase and the second round-trip phase are not particularly distinguished, they are simply referred to as round-trip phases.

[0067] The extraction unit 177 extracts N signal pairs corresponding to N (N is an integer greater than or equal to 2) signal strengths of the signal strengths of the multiple signal pairs obtained in the first transmission process, the second transmission process, the first reception process, and the second reception process with respect to the frequencies f0 to fm, except for one or more signal strengths less than a predetermined threshold value, from among the signal strengths of the multiple signal pairs obtained in the first transmission process, the second transmission process, the first reception process, and the second reception process with respect to the frequencies f0 to fm. The N signal pairs refer to the N signal pairs obtained by excluding one or more signal pairs whose signal strengths are less than a predetermined threshold value from all the signal pairs (multiple signal pairs) whose signal strengths are obtained by the signal strength acquisition unit 175. The threshold value is a value that can exclude signal pairs whose signal strengths are reduced due to multi-path.

[0068] The extraction unit 177 extracts N first signal pairs from the plurality of first signal pairs except for one or more signal pairs whose signal strength of the first signal or the second signal is less than a predetermined threshold value. In addition, the extraction unit 177 extracts N second signal pairs from the plurality of second signal pairs except for one or more signal pairs whose signal strength of the first signal or the second signal is less than a predetermined threshold value. In order to obtain two round-trip phases from the first signal pair and the second signal pair, the extraction unit 177 does not extract the first signal pair and the second signal pair and excludes them as long as the signal strength of any one of the first signal sent by the first sending process, the second signal received by the first receiving process, the first signal sent by the second sending process, and the second signal received by the second receiving process is less than a predetermined threshold value.

[0069] The correction unit 178 corrects the phase change amount caused by the relative movement with the ranging device 100B for each of the N first round-trip phases. The correction unit 178 uses the difference between the first round-trip phase and the second round-trip phase at frequencies f1 to fm to correct the phase change amount caused by the relative movement with the ranging device 100B. In addition, the correction unit 178 calculates the relative speed with the ranging device 100B based on the difference between the first round-trip phase and the second round-trip phase at frequencies f1 to fm, and corrects the N round-trip phases based on the relative speed of the ranging devices 100A and 100B and the time difference between the multiple first signal pairs and the multiple second signal pairs so that the N frequencies f1 to fm of the N first signal pairs corresponding to the N first round-trip phases have a linear relationship. The specific correction content of the correction unit 178 will be described later. Figures 11 to 13 Narrative.

[0070] The distance measuring unit 179 measures the distance to the distance measuring device 100B based on the N first round-trip phases and the plurality of frequencies corrected by the correction unit 178 .

[0071] The memory 170M stores programs and data necessary for the main control unit 170A, the transmission and reception control unit 171, the switching unit 172, the phase acquisition unit 173, the phase measurement unit 174, the signal strength acquisition unit 175, the round-trip phase calculation unit 176, the extraction unit 177, the correction unit 178, and the distance measurement unit 179 of the control device 170. The memory 170M stores data for setting a predetermined frequency and phase of a signal transmitted between the distance measurement devices 100A and 100B.

[0072] <Communication Method for Distance Measurement Executed by Distance Measuring Devices 100A and 100B>

[0073] Here, first, a communication method and a distance measurement method in a case where the influence of multipath does not occur will be described.

[0074] Figure 3 1 is a diagram for explaining a communication method for distance measurement performed by the distance measuring devices 100A and 100B. Here, as an example, it is assumed that the transmission and reception control unit 171 of the distance measuring device 100A sets the frequency (predetermined frequency) and phase of the first signal that reads data from the memory 170M and is sent from the distance measuring device 100A to the distance measuring device 100B. In addition, it is assumed that the distance measuring device 100B sends a second signal having a frequency and phase equal to the frequency and phase of the received first signal to the distance measuring device 100A. It is assumed that the distance measuring devices 100A and 100B share data indicating the frequency and phase of the signals sent to each other before performing communication for distance measurement.

[0075] The distance measuring devices 100A and 100B transmit to each other at the same frequency in the communication for distance measurement. More specifically, in the communication for distance measurement, if one of the distance measuring devices 100A and 100B transmits a signal (a first signal or a second signal) at a certain frequency, the other transmits a signal (a first signal or a second signal) at the same frequency. Such mutual transmission constitutes one communication in the communication for distance measurement.

[0076] exist Figure 3 As an example, in the first communication (1), the distance measuring device 100A transmits a first signal at a frequency f1 to the distance measuring device 100B, and the distance measuring device 100B transmits a second signal at the same frequency f1 to the distance measuring device 100A. The phase acquisition unit 173 of the distance measuring device 100A obtains the phase when the distance measuring device 100B receives the first signal at a frequency f1 transmitted by the distance measuring device 100A from the distance measuring device 100B. In addition, the phase measurement unit 174 of the distance measuring device 100A measures the phase when the distance measuring device 100A receives the second signal at a frequency f1 from the distance measuring device 100B.

[0077] In the second communication (2), the distance measuring device 100B transmits the second signal at the frequency f2 to the distance measuring device 100A, and the distance measuring device 100A transmits the first signal at the same frequency f2 to the distance measuring device 100B. The phase measuring unit 174 of the distance measuring device 100A measures the phase when the distance measuring device 100A receives the second signal at the frequency f2 from the distance measuring device 100B. In addition, the phase acquiring unit 173 of the distance measuring device 100A acquires the phase when the distance measuring device 100B receives the first signal at the frequency f2 transmitted by the distance measuring device 100A from the distance measuring device 100B.

[0078] In the third communication (3), the distance measuring device 100A transmits a first signal at a frequency f3 to the distance measuring device 100B, and the distance measuring device 100B transmits a second signal at the same frequency f3 to the distance measuring device 100A. The phase acquisition unit 173 of the distance measuring device 100A obtains the phase when the distance measuring device 100B receives the first signal at a frequency f3 transmitted by the distance measuring device 100A from the distance measuring device 100B. In addition, the phase measurement unit 174 of the distance measuring device 100A measures the phase when the distance measuring device 100A receives the second signal at a frequency f3 from the distance measuring device 100B.

[0079] In the fourth communication (4), the distance measuring device 100B transmits the second signal at the frequency f4 to the distance measuring device 100A, and the distance measuring device 100A transmits the first signal at the same frequency f4 to the distance measuring device 100B. The phase measuring unit 174 of the distance measuring device 100A measures the phase when the distance measuring device 100A receives the second signal at the frequency f4 from the distance measuring device 100B. In addition, the phase acquiring unit 173 of the distance measuring device 100A acquires the phase when the distance measuring device 100B receives the first signal at the frequency f4 transmitted by the distance measuring device 100A.

[0080] During the distance measurement, the distance measuring devices 100A and 100B continue to perform Figure 3 In the communication shown, the phase measuring unit 174 of the distance measuring device 100A measures the phase when the distance measuring device 100A receives the second signal from the distance measuring device 100B, and the phase acquiring unit 173 of the distance measuring device 100A acquires the phase when the distance measuring device 100B receives the first signal transmitted by the distance measuring device 100A.

[0081] Here, it is assumed that the first communication (1) to the fourth communication (4) are repeated in a short cycle, and the distance between the distance measuring devices 100A and 100B is the same. In this case, the phase when the distance measuring device 100B receives the first signal of the frequency fm transmitted by the distance measuring device 100A is set to φAB, and it is assumed that the phase acquisition unit 173 of the distance measuring device 100A acquires the phase φAB. In addition, the phase when the distance measuring device 100A receives the second signal of the frequency fm from the distance measuring device 100B is set to φBA, and it is assumed that the phase measurement unit 174 of the distance measuring device 100A measures the phase φBA. The frequency fm is, for example, one of the above-mentioned frequencies f1 to f4.

[0082] φAB+φBA is the total phase (round-trip phase) when the distance measuring devices 100A and 100B communicate back and forth at the frequency f. The round-trip phase at the frequency fm is represented by φ2w. 2w is the abbreviation of two-way. The round-trip phase in the first communication (frequency f1) is set to φ1w1, the round-trip phase in the second communication (frequency f2) is set to φ2w2, the round-trip phase in the third communication (frequency f3) is set to φ2w3, and the round-trip phase in the fourth communication (frequency f4) is set to φ2w4. In addition, the wavelengths at frequencies f1 to f4 are set to λ1 to λ4, respectively. This round-trip phase φ2w is calculated by the round-trip phase calculation unit 176.

[0083] As described above, if the first communication (1) to the fourth communication (4) are repeated in a short cycle, it is considered that the distance between the distance measuring devices 100A and 100B during the round-trip communication is the same, so if the distance between the distance measuring devices 100A and 100B in the first communication (1) to the fourth communication (4) is set to L, the following equations (1) to (4) are established. 2L is the round-trip distance. N is an integer greater than 1.

[0084] 2L=(n+φ2w1)×λ1 (1)

[0085] 2L=(n+φ2w2)×λ2 (2)

[0086] 2L=(n+φ2w3)×λ3 (3)

[0087] 2L=(n+φ2w4)×λ4 (4)

[0088] Eliminating n from equations (1) and (2) yields the following equation (5A), which is then transformed into equations (5B) to (5D) to yield the distance L. c is the speed of light.

[0089] 2L / λ1-φ2w1=2L / λ2-φ2w2(5A)

[0090] 2L(1 / λ2-1 / λ1)=φ2w2-φ2w1(5B)

[0091] 2L(f2-f1) / c=φ2w2-φ2w1(5C)

[0092] L / c=(1 / 2)×(φ2w2-φ2w1) / (f2-f1)(5D)

[0093] Similarly, if n is eliminated from equations (1) and (3), they can be transformed into equation (6).

[0094] L / c=(1 / 2)×(φ2w3-φ2w1) / (f3-f1) (6)

[0095] Similarly, if n is eliminated from equations (1) and (4), they can be transformed into equation (7).

[0096] L / c=(1 / 2)×(φ2w4-φ2w1) / (f4-f1) (7)

[0097] Equations (5D), (6), and (7) show that the ratio of the phase difference between two round-trip phases φ2wm (where m is 1 to 4) to the frequency difference between two frequencies fm is equivalent to the ratio of the distance L to the speed of light c.

[0098] Therefore, if the phase difference between the two round-trip phases φ2wm is Δφ and the frequency difference between the two frequencies fm is Δf, equations (5D), (6), and (7) can be expressed as in the following equation (8).

[0099] L / c=(1 / 2)×Δφ / Δf (8)

[0100] Figure 4 This is a graph showing the relationship between the frequency fm and the phase φ2wm in ranging. If the ratio of the distance L obtained in equations (5D), (6), and (7) to the speed of light c is set as slopes A, B, and C, then Figure 4 The slopes A, B, and C are represented as shown. Specifically, the slope A is A=(1 / 2)×Δφ / Δf=(φ2w2-φ2w1) / (f2-f1). The slope B is B=(1 / 2)×Δφ / Δf=(φ2w3-φ2w1) / (f3-f1). The slope C is C=(1 / 2)×Δφ / Δf=(φ2w4-φ2w1) / (f4-f1). In addition, only one of the slope A obtained from the two frequencies f1 and f2, the slope B obtained from the two frequencies f1 and f3, and the slope C obtained from the two frequencies f1 and f4 can be obtained. In addition, here, the method of calculating the slopes A, B, and C based on two frequencies (f1 and f2, f1 and f3, f1 and f4) is explained, but more than three frequencies can also be used. For more than three points given by the frequency fm and the phase φ2wm, a straight line is calculated by straight line approximation based on the least squares method, and the slope of the calculated straight line is calculated as L / c.

[0101] If the slope A is multiplied by the speed of light c, the distance L obtained from the combination of frequencies f1 and f2 can be obtained. If the slope B is multiplied by the speed of light c, the distance L obtained from the combination of frequencies f1 and f3 can be obtained. If the slope C is multiplied by the speed of light c, the distance L obtained from the combination of frequencies f1 and f4 can be obtained. The distance L is obtained by the distance measuring unit 179.

[0102] <Multi-channel>

[0103] If there are multiple paths, the phase of the radio wave reflected in the middle is different from the phase of the radio wave directly coming from the device of the transmission source, and there is a risk that the distance cannot be accurately measured. This is because the transmission path of the radio wave reflected in the middle is different from the transmission path of the radio wave directly coming from the device of the transmission source.

[0104] Figure 5 1 is a diagram illustrating a direct wave path a and a multi-path path b. The direct wave path a is a path for directly transmitting radio waves from the distance measuring device 100B to the distance measuring device 100A. The multi-path path b is a path for transmitting radio waves by reflection from the ground, the wall of a building, and other reflective surfaces when transmitting radio waves from the distance measuring device 100B to the distance measuring device 100A. Compared with the direct wave path a, the multi-path path b is longer.

[0105] Figure 6 FIG. 1 is a diagram showing an example of the relationship between the frequency and the round-trip phase of the first signal and the second signal when there are multiple paths. Figure 6 In FIG. 1 , the horizontal axis represents the frequency (MHz) of the first signal and the second signal transmitted between the distance measuring devices 100A and 100B. The vertical axis on the left represents the round-trip phase, and the vertical axis on the right represents the signal strength (RSSI). Figure 6 In FIG. 1 , the dotted line represents the phase characteristics, and the solid line represents the signal strength (RSSI) characteristics.

[0106] In the absence of multipath, as in the frequency bands of about 2436 MHz to about 2456 MHz and about 2456 MHz to about 2476 MHz, the round-trip phase decreases approximately linearly with increasing frequency. In addition, in the frequency bands of about 2436 MHz to about 2456 MHz and about 2456 MHz to about 2476 MHz, there is no multipath, so the signal strength (RSSI) obtains a good value of more than -40.

[0107] In contrast, in the case of multiple paths, such as a frequency band of about 2416MHz to about 2436MHz, there is a frequency band (a frequency band around about 2424MHz) in which the round-trip phase changes sharply (here, decreases) with the increase of frequency, and in this frequency band, the signal strength (RSSI) decreases sharply. In the frequency band where the round-trip phase decreases sharply, multipath fading occurs, causing the signal strength (RSSI) to decrease. If the round-trip phase changes nonlinearly like this, the round-trip phase of an appropriate value cannot be obtained in the frequency band, and ranging cannot be performed appropriately. In addition, the nonlinear change of the round-trip phase can be detected by the signal strength (RSSI).

[0108] Therefore, the distance measuring device 100A detects a frequency band where the signal strength (RSSI) decreases and excludes the round-trip phase in such a frequency band from the distance measurement data. This is to enable accurate distance measurement even in an environment where multiple paths exist.

[0109] <Doppler effect>

[0110] Figure 7 This is a diagram for explaining the relationship between the round-trip phase and the frequency when the Doppler effect is applied to the radio waves transmitted and received between the distance measuring devices 100A and 100B. For example, if a user holding the smart key 20 including the distance measuring device 100B moves while operating the automatic parking assistance system mounted on the vehicle 10, the distance between the distance measuring devices 100A and 100B changes.

[0111] Here, it is assumed that the distance between the vehicle 10 and the smart key 20 is constant, and the Figure 7 The relationship between the frequencies f0 to fm and the round-trip phases θ0 to θm is shown by the dotted lines in FIG. Here, the frequencies f0 to fm are equally spaced as an example, and it is assumed that the frequencies from f0 to fm increase by 1 MHz in sequence.

[0112] In this case, when the vehicle 10 is stopped, if the user holding the smart key 20 moves away from the vehicle 10 at a certain moving speed v (m / s), the relationship between the frequencies f0 to fm and the round-trip phases θ0 to θm is shifted as shown by the solid line due to the Doppler effect. If the time t is used, θm is shifted as shown by the following equation (1) due to the Doppler effect. As shown by equation (9), the higher the frequency fm, the greater the shift of the round-trip phase θm caused by the Doppler effect.

[0113]

Formula 1

[0114]

[0115] If the user's moving speed v (m / s) is known, then Figure 7 The characteristics of the solid line in are corrected like the characteristics of the dotted line, so the distance measuring device 100A detects the moving speed v (m / s) of the user as follows. Alternatively, the user holding the smart key 20 and the vehicle 10 may both move, in which case the relative moving speed may be detected.

[0116] Figure 8This is a diagram for explaining a method for detecting a moving speed v (m / s). By performing a first transmission process and a first reception process at each frequency of f0 to fm, a first round-trip phase θ0 to θm at frequencies f0 to fm is obtained, and by performing a second transmission process and a second reception process at each frequency of f0 to fm, a second round-trip phase θa0 to θam at frequencies f0 to fm is obtained.

[0117] When the user moves, if the first transmission process and the first reception process are performed in each of the frequencies f0 to fm in the first time period, and the second transmission process and the second reception process are performed in each of the frequencies f0 to fm in the second time period after the first time period, then Figure 8 As shown, the difference Δθ0 to Δθm between the first round-trip phase θ0 to θm and the second round-trip phase θa0 to θam at each frequency f0 to fm becomes a constant value. If the first round-trip phase θk (k = 0 to m) in this case is used, the second round-trip phase θak is expressed by the following equation (10). The frequency of the first round-trip phase θk and the second round-trip phase θak is set to fk.

[0118]

Formula 2

[0119]

[0120] If the difference Δθk (k=0 to m) is obtained based on the equation (10), the moving speed v can be obtained by using the time difference between the first time period and the second time period as the time t. The calculation of the moving speed v is performed by the correction unit 178 .

[0121] Specifically, for example, let the round-trip phase at the end time tA of the first time period be θA, and let the round-trip phase at the end time tB of the second time period be θB. If the time t (= tB - tA), the change in the round-trip phase Δθ (= θB - θA) and the moving speed v are used, then with respect to the Doppler effect, the following equation (11) holds.

[0122]

Formula 3

[0123] Δθ / t=(-4π / λ)×v (11)

[0124] The round-trip phase calculation unit 176 calculates the round-trip phase θA at the end time tA of the first time period, and calculates the round-trip phase θB at the end time tB of the second time period. When the correction unit 178 substitutes the change Δθ (=θB-θA) of the round-trip phase at time t (=tB-tA) into formula (11), the moving speed v can be calculated.

[0125] <Timing of transmission and reception processing>

[0126] As described above, the transceiver control unit 171 performs a first transmission process once during a continuous wave transmission period (2.5 milliseconds) in BLE (registered trademark), performs a first reception process once during another continuous wave transmission period, performs a second transmission process once during another continuous wave transmission period, and performs a second reception process once during another continuous wave transmission period.

[0127] The distance measuring device 100A performs a transmission process or a reception process once in each continuous wave transmission period, thereby transmitting first signals of three or more frequencies f1 to fm to the distance measuring device 100B at different timings, and receiving second signals of three or more frequencies f1 to fm from the distance measuring device 100B at different timings.

[0128] The continuous wave transmission period is very short, such as 2.5 milliseconds, so the transmission process or the reception process is performed once, and the transmission process or the reception process is repeated during a plurality of continuous wave transmission periods, thereby performing distance measurement.

[0129] BLE (registered trademark) data packet communication is also used for other purposes besides ranging (such as the transmission of audio signals), so the time available for ranging is very limited. Therefore, it is required to achieve high-precision positioning in the shortest possible time. It is assumed that the ranging device 100A performs a transmission process or a reception process once during each continuous wave transmission. In addition, by summing up the results obtained by performing a transmission process or a reception process once during multiple intermittent continuous wave transmissions, the relationship between the round-trip phase and the frequency f1~fm is obtained to perform ranging.

[0130] <Signal pair extraction method>

[0131] Fig.9A , Fig. 9B as well as Fig. 9C This is a diagram showing the round-trip phase corresponding to the frequency (upper side) and the signal strength corresponding to the frequency (lower side) obtained by performing the first transmission process and the first reception process in one continuous wave transmission period. Fig.9A , Fig. 9B as well as Fig. 9C The signal strength shown is the lower value of the RSSI of the first signal and the second signal. Fig.9A , Fig. 9B as well as Fig. 9C An example of a signal pair extraction method is described below. As an example, the threshold TH of the signal strength at which the extraction unit 177 extracts the signal pair is set to a level that is 10 dBm lower than the signal strength RS1 in the absence of multipath. In the following, it is assumed that the plurality of frequencies are f0 to fm.

[0132] Here, the round-trip phase corresponding to the frequency (upper side) and the signal strength corresponding to the frequency (lower side) obtained by performing the first transmission process and the first reception process during each continuous wave transmission period are shown, but the round-trip phase corresponding to the frequency and the signal strength corresponding to the frequency obtained by performing the second transmission process and the second reception process during each continuous wave transmission period are the same. In addition, Fig.9A The time t0 to t2 shown is a certain interval. Fig. 9B The times t3 to t5 shown are fixed intervals. Fig. 9C The time t6 to t8 shown is a constant interval. The intervals between the time t0 to t2, t3 to t5, and t6 to t8 are all equal.

[0133] Fig.9A The round-trip phase corresponding to the frequency (upper side) and the signal strength corresponding to the frequencies f0, f1, f2 (lower side) obtained by performing a first transmission process and a first reception process at frequencies f0, f1, f2 are shown. The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 acquire the signal strength and round-trip phase corresponding to the frequency f0 at time t0, acquire the signal strength and round-trip phase corresponding to the frequency f1 at time t1, acquire the signal strength and round-trip phase corresponding to the frequency f2 at time t2, and acquire the signal strength and round-trip phase corresponding to the frequency f0 at time t3. The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 acquire the signal strength and round-trip phase twice for the frequency f0 at times t0 and t3.

[0134] Fig. 9B The round-trip phase corresponding to the frequency (upper side) and the signal strength corresponding to the frequencies f3, f4, f5 (lower side) obtained by performing a first transmission process and a first reception process at frequencies f3, f4, f5 are shown. The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 acquire the signal strength and round-trip phase corresponding to the frequency f3 at time t4, acquire the signal strength and round-trip phase corresponding to the frequency f4 at time t5, acquire the signal strength and round-trip phase corresponding to the frequency f5 at time t6, and acquire the signal strength and round-trip phase corresponding to the frequency f6 at time t7. The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 acquire the signal strength and round-trip phase twice for the frequency f3 at times t4 and t7.

[0135] Fig. 9CThe round-trip phase corresponding to the frequency (upper side) and the signal strength corresponding to the frequencies f6, f7, f8 (lower side) obtained by performing a first transmission process and a first reception process at frequencies f6, f7, f8 are shown. The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 acquire the signal strength and round-trip phase corresponding to the frequency f3 at time t8, acquire the signal strength and round-trip phase corresponding to the frequency f4 at time t9, acquire the signal strength and round-trip phase corresponding to the frequency f5 at time t10, and acquire the signal strength and round-trip phase corresponding to the frequency f6 at time t11. The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 acquire the signal strength and round-trip phase twice for the frequency f3 at times t8 and t11.

[0136] In addition, the correction unit 178 obtains the difference Δθ between the round-trip phases obtained twice for the same frequency. The difference Δθ is the difference Δθ between the first round-trip phase and the second round-trip phase. Fig.9A The difference Δθs1 is obtained for the frequency f0 shown in FIG. Fig. 9B The frequency f3 shown in the figure is used to find the difference Δθs2. Fig. 9C The difference Δθs3 is obtained at the frequency f6 shown. Fig.9A In the figure, the dashed line represents the straight line that matches the round-trip phase at frequencies f0, f1, and f2. Fig. 9B In the figure, the dashed lines represent the straight lines that match the round-trip phases at frequencies f3, f4, and f5. Fig. 9C In FIG. 1 , the dashed lines represent the straight lines that match the round-trip phases at frequencies f6, f7, and f8.

[0137] In addition, if Figures 9A to 9C Observing the signal strength, at frequencies f0 to f2, f3, f4, and f6 to f8, the signal strength is above the threshold TH, but at frequency f5, the signal strength is less than the threshold TH.

[0138] In this case, the extraction unit 177 excludes signal pairs whose signal strength is less than the threshold value TH, and extracts round-trip phases calculated for signal pairs whose signal strength is greater than or equal to the threshold value TH. Fig.10 Summary Figures 9A to 9C The result is a diagram showing the signal pair extracted by the extraction unit 177. Fig.10 As shown, the extraction unit 177 excludes the signal pair of frequency f5 whose signal strength is less than the threshold value TH, and extracts the round-trip phases calculated for the signal pairs of frequencies f0 to f2, f3, f4, and f6 to f8.

[0139] Fig.1117 is a diagram for explaining a speed correction process in the correction process of the correction unit 178. The speed correction process is a process for correcting the influence of the Doppler effect caused by the relative movement of the distance measuring devices 100A and 100B.

[0140] The correction unit 178 evenly distributes the difference Δθs1 with respect to the frequency f0 to the round-trip phases at the frequencies f1 and f2, with respect to the round-trip phases obtained at the frequencies f0, f1, and f2, thereby correcting the round-trip phases at the frequencies f1 and f2. The difference Δθs1 of the round-trip phases obtained twice with respect to the frequency f0 is the increase in the round-trip phase of the frequency f0 at the time t3 relative to the round-trip phase of the frequency f0 at the time t0, so the correction unit 178 subtracts (Δθs1) / 2 from the round-trip phase at the frequency f1, and subtracts Δθs1 from the round-trip phase at the frequency f2. The times t0 to t3 are a certain interval, so the value obtained by multiplying the difference Δθs1 by a ratio corresponding to the elapsed time from the time t0 is used as the correction value. That is, the correction value for the round-trip phase at the frequency f1 is -(Δθs1) / 2, and the correction value for the round-trip phase at the frequency f2 is -Δθs1.

[0141] Similarly, the difference Δθs2 of the round-trip phase obtained twice for frequency f3 is the increase in the round-trip phase of frequency f3 at time t7 relative to the round-trip phase of frequency f3 at time t4, so the correction unit 178 subtracts (Δθs2) / 2 from the round-trip phase at frequency f4. Time t4 to t7 is a certain interval, so the value obtained by multiplying the difference Δθs2 by a ratio corresponding to the elapsed time from time t4 is used as the correction value. That is, the correction value for the round-trip phase at frequency f4 is -(Δθs2) / 2.

[0142] In addition, the difference Δθs3 of the round-trip phase obtained twice for frequency f6 is the increase in the round-trip phase of frequency f6 at time t11 relative to the round-trip phase of frequency f6 at time t8, so the correction unit 178 subtracts (Δθs3) / 2 from the round-trip phase at frequency f7, and subtracts Δθs3 from the round-trip phase at frequency f8. Time t8 to t11 is a certain interval, so the value obtained by multiplying the difference Δθs3 by the ratio corresponding to the elapsed time from time t8 is used as the correction value. That is, the correction value for the round-trip phase at frequency f7 is -(Δθs3) / 2, and the correction value for the round-trip phase at frequency f8 is -Δθs3.

[0143] Fig.12 , Fig.13 as well as Fig.14 178 is a diagram for explaining the linear correction process in the correction process performed by the correction unit 178. Fig.12 As shown, the slope S1 and the intercept A1 of the straight line matching the round-trip phase of the frequencies f0, f1, and f2 are calculated.

[0144] Next, the calibration unit 178 uses the calculated slope S and intercept A, as shown in Fig.13 As shown in FIG. 1 , the round-trip phases of frequencies f3 and f4 are shifted in such a way that they are tangent to the straight line that matches the round-trip phases of frequencies f0, f1, and f2. As for the round-trip phase θ3 at frequency f3, since (θ3-(f3×S1+A1) is subtracted from θ3, Fig.13 As shown in FIG. 1 , the round-trip phase θ3 of the frequency f3 is shifted. As for the round-trip phase θ4 at the frequency f4, since (θ3 - (f3 × S1 + A1) is subtracted from θ4, Fig.13 The round-trip phase θ4 of frequency f4 is shifted as shown. The round-trip phases θ3 and θ4 of frequencies f3 and f4 are shifted using the same correction amount (θ3-(f3×S1+A1). Then, the correction unit 178 calculates the slope S2 and intercept A2 of the straight line that matches the round-trip phases of frequencies f0, f1, f2, f3, and f4.

[0145] Next, the correction unit 178 uses the slope S2 and intercept A2 of the straight line matching the round-trip phase of the frequencies f0, f1, f2, f3, and f4, as shown in FIG. Fig.14 As shown in FIG. 1 , the round-trip phases of frequencies f6, f7, and f8 are shifted so that they are tangent to the straight line that matches the round-trip phases of frequencies f0, f1, f2, f3, and f4. As for the round-trip phase θ6 at frequency f6, since (θ6-(f6×S2+A2) is subtracted from θ6, Fig.14 As shown in FIG. 1 , the round-trip phase θ6 of the frequency f6 is shifted. As for the round-trip phases θ7 and θ8 at the frequencies f7 and f8, since (θ6 - (f6 × S2 + A2) is subtracted from θ7 and θ8, Fig.14 The round-trip phases θ7 and θ8 of the frequencies f7 and f8 are offset as shown. The round-trip phases θ6, θ7 and θ8 of the frequencies f6, f7 and f8 are offset using the same correction amount (θ6 - (f6 × S2 + A2). Then, the correction unit 178 calculates the slope S3 and intercept A3 of the straight line that matches the round-trip phases of the frequencies f0, f1, f2, f3, f4, f6, f7 and f8.

[0146] By performing the above processing on the round-trip phases of frequencies f0 to fm, the N round-trip phases of frequencies f0 to fm are corrected in such a way that the N round-trip phases have a linear relationship with the N frequencies of the N signal pairs corresponding to the N round-trip phases. This is a linear correction process. Then, the distance measuring unit 179 uses the linear relationship between the N round-trip phases and the N frequencies of the N signal pairs corresponding to the N round-trip phases obtained in this way (for example, Fig.14The distance between the distance measuring device 100B and the distance measuring device 100A is measured by using a straight line having an intercept A3 and a slope S3.

[0147] <Flowchart>

[0148] Fig.15 This is a flowchart showing an example of processing executed by the control device 170 .

[0149] When the process starts, the signal strength acquisition unit 175 and the round-trip phase calculation unit 176 perform the first transmission process, the first reception process, the second transmission process, and the second reception process using three frequencies in each continuous wave transmission period (step S1). The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 perform the first transmission process, the first reception process, the second transmission process, and the second reception process in a single continuous wave transmission period.

[0150] exist Fig.15 In step S1, as an example, partial processing 1, partial processing 2, and partial processing 3 are shown. Partial processing 1 is as follows: Fig.9A As described above, the first transmission process and the first reception process are performed at frequencies f0, f1, and f2 to obtain round-trip phases θ0(t0), θ1(t1), θ2(t2), θ0(t3) and signal strengths RSSI1, RSSI2, and RSSI3. Time t0 to t3 is the time when the first signal related to the round-trip phase is transmitted. Part 2 is performed using Fig. 9B As described above, the first transmission process and the first reception process are performed at frequencies f3, f4, and f5 to obtain round-trip phases θ3(t4), θ4(t5), θ5(t6), θ3(t7) and signal strengths RSSI3, RSSI4, and RSSI5. Time t4 to t7 is the time when the first signal related to the round-trip phase is transmitted. Part 3 is as follows: Fig. 9C As described above, the first transmission process and the first reception process are performed once at frequencies f6, f7, and f8 to obtain round-trip phases θ6 (t8), θ7 (t9), θ8 (t10), θ6 (t11) and signal strengths RSSI6, RSSI7, and RSSI8. Time t8 to t11 is the time when the first signal related to the round-trip phase is transmitted. The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 repeatedly perform the same process until the frequency fm is reached.

[0151] The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 output the round-trip phase and signal strength obtained in the first transmission process, the first reception process, the second transmission process, and the second reception process performed in step S1 (step S2). In step S2, the correction unit 178 obtains the difference Δθ between the round-trip phases obtained twice for the same frequency in each process.

[0152] The main control unit 170A collects all the data obtained in step S2 (step S3).

[0153] The extraction unit 177 extracts the round-trip phases calculated for the signal pairs whose signal strengths are equal to or greater than the threshold value TH (step S4). Through step S4, N frequencies of the N signal pairs corresponding to the N round-trip phases are extracted.

[0154] The correction unit 178 performs a speed correction process (step S5). In order to correct the influence of the Doppler effect caused by the relative movement of the distance measuring devices 100A and 100B, the correction unit 178 uses the round-trip phases of the three frequencies obtained in the multiple processes including partial processing 1, partial processing 2, and partial processing 3. Fig.11 The speed correction process has been described.

[0155] The correction unit 178 performs a linear correction process (step S6). The linear correction process is performed using Figure 12 to Figure 14 As explained above, the N round-trip phases are corrected so that the N round-trip phases have a linear relationship with the N frequencies of the N signal pairs corresponding to the N round-trip phases. As an example, the linear relationship between the frequency and the round-trip phase is: Fig.14 Obtained as shown.

[0156] The distance measuring unit 179 measures the distance to the distance measuring device 100B based on the intercepts and slopes of the linear relationship between the N first round-trip phases and the plurality of frequencies corrected by the correction unit 178 in step S6 (step S7 ).

[0157] In addition, the above describes a method in which two round-trip phases are obtained for the lowest frequency in a plurality of partial processes including partial process 1, partial process 2, and partial process 3, and in step S2, the correction unit 178 obtains the difference Δθ of the round-trip phases obtained twice for the same frequency in each partial process. By obtaining the difference Δθ of the round-trip phases obtained twice for the same frequency in each partial process, the influence of the Doppler effect can be corrected more accurately according to the change in the relative moving speed of the distance measuring devices 100A and 100B. In addition, in each partial process, two round-trip phases may be obtained for a frequency other than the lowest frequency.

[0158] However, in at least one of the plurality of partial processes, the round-trip phase is obtained twice for the lowest frequency, and the influence of the Doppler effect may be corrected in step S5 using the moving speed calculated based on the difference Δθ between the round-trip phases obtained twice. For example, in partial process 1, the influence of the Doppler effect may be corrected for partial processes other than partial process 1 using the moving speed calculated based on the difference Δθ between the round-trip phases obtained twice for the lowest frequency f0. In the case where the relative moving speed of the distance measuring devices 100A and 100B is assumed to be constant, the process can be simplified by doing so.

[0159] As described above, round-trip phases are obtained for a plurality of signal pairs, and signal strengths are acquired, and N signal pairs corresponding to N (N is an integer greater than or equal to 2) signal strengths other than one or more signal strengths less than a predetermined threshold value are extracted from the plurality of signal pairs, and the distance to the distance measuring device 100B is measured based on the N round-trip phases and the plurality of frequencies. Therefore, the influence of multipath can be reduced.

[0160] Therefore, it is possible to provide the distance measuring device 100 that can accurately measure distance even in an environment where multiple paths exist.

[0161] In addition, since N signal pairs other than one or more signal pairs whose signal strength of the first signal or the second signal is less than a specified threshold are extracted from multiple signal pairs, the influence of multi-path can be reduced more reliably and the distance can be measured more accurately.

[0162] In addition, the transceiver control unit 171 causes OM130 to repeat the transmission process of sending the first signal to the distance measuring device 100B during a predetermined period, and causes OM130 to send the first signal of more than three frequencies to the distance measuring device 100B at different timings, and causes ODM140 to repeat the reception process of receiving the second signal from the distance measuring device 100B during a predetermined period, and causes ODM140 to receive the second signal of more than three frequencies from the distance measuring device 100B at different timings. Therefore, even in a state where the period for performing the transmission process and the reception process is limited, the relationship between the frequency and the round-trip phase can be reliably obtained, and the distance can be accurately measured.

[0163] In addition, the phase acquisition unit 173 acquires a plurality of first phases from the phase data included in a plurality of second signals received by the ODM 140 through repeated reception processing, and thus can easily and reliably obtain the first phase of the first signal received and measured by the phase measurement unit 174 of the distance measuring device 100B. As a result, accurate distance measurement can be performed.

[0164] In addition, the signal strength acquisition unit 175 acquires, as the signal strengths for the plurality of signal pairs, the first signal strength when the ranging device 100B receives a plurality of first signals, or the second reception strength when the ODM 140 repeatedly performs reception processing and receives a plurality of second signals. Therefore, the round-trip phase can be calculated using the phase when the signal is received, and the ranging can be performed more accurately.

[0165] In addition, the signal strength acquisition unit 175 acquires the first signal strength from the signal strength data included in the plurality of second signals received by the ODM 140 through repeated reception processing. The first signal strength when the ranging device 100B receives the first signal can be acquired from the second signal, and the round-trip phase can be calculated based on the first signal strength acquired from the second signal, so that the ranging can be performed more accurately. In addition, the ranging device 100B can also include the signal strength acquisition unit 175, and the second signal strength can be written into the first signal sent by the ranging device 100A and the second signal strength can be acquired by the signal strength acquisition unit 175 of the ranging device 100B.

[0166] The apparatus further includes a correction unit 178 that corrects the amount of change in the round-trip phase caused by the relative movement with the distance measuring device 100B for each of the N round-trip phases, and a distance measuring unit 179 measures the distance with the distance measuring device 100B based on the N round-trip phases and the plurality of frequencies corrected by the correction unit 178. The influence of the Doppler effect caused by the relative movement with the distance measuring device 100B can be corrected, and the distance can be measured more accurately.

[0167] The transmission and reception control unit 171 causes the OM 130 to transmit the first signal multiple times for each of the multiple frequencies, and causes the ODM 140 to receive the second signal multiple times for each of the multiple frequencies, and the round-trip phase calculation unit 176 obtains multiple round-trip phases for each of the N signal pairs for the multiple frequencies, and the correction unit 178 uses the differences of the multiple round-trip phases obtained by the round-trip phase calculation unit 176 for the multiple frequencies to correct the change in the round-trip phase caused by the relative movement with the distance measuring device 100B for each of the N signal pairs. Based on the differences of the multiple round-trip phases, the influence of the Doppler effect can be corrected according to the change in the relative movement speed with the distance measuring device 100B, and the distance can be measured more accurately.

[0168] The correction unit 178 obtains the relative speed with the distance measuring device 100B based on the difference of the multiple round-trip phases obtained for each of the N signal pairs, and corrects the N round-trip phases in a manner that makes the N round-trip phases and the N frequencies of the N signal pairs corresponding to the N round-trip phases have a linear relationship based on the relative speed and the time difference of obtaining each signal pair. Therefore, the N round-trip phases and N frequencies obtained during a discontinuous period such as the continuous wave transmission period in BLE (registered trademark) can be arranged on a straight line, and even in a situation where the acquisition of the N round-trip phases and N frequencies is divided into a plurality of discontinuous periods, accurate distance measurement can be performed.

[0169] The predetermined period is a continuous wave transmission period. Therefore, accurate distance measurement can be performed based on the N round-trip phases and N frequencies obtained in a plurality of intermittent continuous wave transmission periods in BLE (registered trademark).

[0170] The continuous wave transmission period is 2.5 milliseconds. Therefore, accurate distance measurement can be performed based on N round-trip phases and N frequencies obtained in a very short period of multiple intermittent 2.5 milliseconds in BLE (registered trademark).

[0171] The predetermined threshold is a threshold that can exclude one or more signal pairs whose signal strength is reduced due to multipath, so that the influence of multipath can be eliminated and the distance can be accurately measured.

[0172] As mentioned above, the distance measuring device according to the exemplary embodiment of the present invention has been described, but the present invention is not limited to the specifically disclosed embodiment, and various modifications and changes can be made without departing from the scope of the claims.

[0173] In addition, the present international application claims priority based on Japanese patent application No. 2022-099835, filed on June 21, 2022, the entire contents of which are incorporated herein by reference.

[0174] Description of Reference Numerals

[0175] 10 Vehicles

[0176] 20 Smart Key

[0177] 100A, 100B Distance Measuring Device

[0178] 100R Wireless Device

[0179] 110 PA

[0180] 120 LNA

[0181] 130 OM (An example of a sending unit)

[0182] 140 ODM (An example of a receiving unit)

[0183] 150 VCO

[0184] 155 PLL

[0185] 160 Codec Processing Unit

[0186] 170 Control Device

[0187] 170A Main control unit

[0188] 171 Transceiver Control Unit

[0189] 172 Switching Department

[0190] 173 Phase Acquisition Unit

[0191] 174 Phase Measurement Unit

[0192] 175 Signal strength acquisition unit

[0193] 176 Round trip phase calculation unit

[0194] 177 Extraction Department

[0195] 178 Correction Department

[0196] 179 Distance Measurement Department

[0197] 170M Memory

Claims

1. A distance measuring device, wherein: have: A sending unit, sending a first signal to other devices; A receiving unit, receiving a second signal from the other device that receives the first signal; a phase acquisition unit that acquires a plurality of first phases when the other device receives a plurality of the first signals transmitted by the transmission unit to the other device at different timings and at a plurality of frequencies of three or more; a phase measuring unit configured to measure a plurality of second phases when the second signal is received by the receiving unit from the other device at different timings at the three or more frequencies; a signal strength acquisition unit for acquiring signal strengths of a plurality of signal pairs having the same frequency among the plurality of the first signals and the plurality of the second signals; a round-trip phase calculation unit that obtains a round-trip phase for the plurality of signal pairs, the round-trip phase being a phase obtained by summing the first phase and the second phase of the first signal and the second signal included in the plurality of signal pairs; an extracting unit, extracting, from the plurality of signal pairs, N signal pairs corresponding to N signal strengths other than one or more signal strengths less than a predetermined threshold value, wherein N is an integer greater than 2; and The distance measuring unit measures the distance to the other device based on the N round-trip phases and the plurality of frequencies.

2. The distance measuring device according to claim 1, wherein: The extracting unit extracts N signal pairs from the plurality of signal pairs except for one or more signal pairs in which the signal strength of the first signal or the second signal is less than the predetermined threshold.

3. The distance measuring device according to claim 1, wherein: It also includes a transceiver control unit for controlling transceiver transmission. The transceiver control unit, causing the transmitting unit to repeatedly perform a transmission process of transmitting the first signal to the other device during a predetermined period, so that the transmitting unit transmits the first signal of the three or more frequencies to the other device at different timings; The receiving unit is caused to repeatedly perform a receiving process of receiving the second signal from the other device during the predetermined period, so that the receiving unit receives the second signals of the three or more frequencies from the other device at different timings.

4. The distance measuring device according to claim 3, wherein: The phase acquisition unit acquires the plurality of first phases from phase data included in a plurality of second signals received by the receiving unit by repeatedly performing the receiving process.

5. The distance measuring device according to claim 3, wherein: The signal strength acquisition unit acquires, as signal strengths for a plurality of signal pairs, a first signal strength when the other device receives a plurality of the first signals, or a second reception strength when the receiving unit repeatedly performs the reception process and receives a plurality of the second signals.

6. The distance measuring device according to claim 5, wherein: The signal strength acquisition unit acquires the first signal strength from signal strength data included in a plurality of second signals received by the receiving unit by repeatedly performing the receiving process, or acquires the second signal strength from signal strength data included in a plurality of first signals received by the receiving unit by repeatedly performing the receiving process.

7. The distance measuring device according to claim 3, wherein: The device further comprises a correction unit that corrects, for each of the N round-trip phases, a change in the round-trip phase caused by relative movement with the other device. The distance measuring unit measures the distance to the other device based on the N round-trip phases corrected by the correction unit and the plurality of frequencies.

8. The distance measuring device according to claim 7, wherein: The transmission and reception control unit causes the transmission unit to transmit the first signal multiple times for each of the multiple frequencies, and causes the reception unit to receive the second signal multiple times for each of the multiple frequencies, The round-trip phase calculation unit calculates a plurality of round-trip phases for each of the N signal pairs at the plurality of frequencies, respectively. The correction unit corrects, for each of the N signal pairs, a change in the round-trip phase caused by relative movement with the other device, using differences between the plurality of round-trip phases obtained by the round-trip phase calculation unit for the plurality of frequencies.

9. The distance measuring device according to claim 8, wherein: The correction unit, The relative speed with respect to the other device is obtained based on the differences of the plurality of round-trip phases respectively obtained for the N signal pairs, Based on the relative speed and the time difference of obtaining each signal pair, the N round-trip phases are corrected in such a way that the N round-trip phases have a linear relationship with the N frequencies of the N signal pairs corresponding to the N round-trip phases.

10. The distance measuring device according to any one of claims 1 to 9, wherein: The predetermined period is a continuous wave transmission period.

11. The distance measuring device according to claim 10, wherein: The continuous wave transmission period is 2.5 milliseconds.

12. The distance measuring device according to claim 1, wherein: The predetermined threshold is a threshold that can exclude one or more signal pairs whose signal strength is reduced due to multipath.

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