Ranging device

Abstract

Provided is a ranging device capable of executing accurate ranging even in an environment where multiple paths exist.　This ranging device: acquires a plurality of first phases from when another device received a plurality of first signals transmitted to the another device at a plurality of three or more types of frequencies; measures a plurality of second phases from when a second signal was received at a plurality of three or more types of frequencies from the another device; extracts, from a plurality of signal pairs of a first signal and a second signal, N (N ≥ 2) signal pairs corresponding to N signal strengths, excluding one or more signal strengths less than a threshold value, among the signal strengths of the plurality of signal pairs; finds, with respect to the N signal pairs, a round-trip phase found by taking the sum of the first phase and the second phase regarding the first signal and the second signal included in each of the signal pairs; and measures the distance to the another device on the basis of the N round-trip phrases and the plurality of frequencies.

Description

distance measuring device

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

[0002] Conventionally, there has been a ranging device that includes a first device having a first transceiver that transmits 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 receives a third known signal corresponding to the first carrier frequency and a fourth known signal corresponding to the second carrier frequency; a second device having a second transceiver that transmits the third known signal and the fourth known signal and receives the first and second known signals; and a calculation unit that calculates the distance between the first device and the second device based on the phases of the first to fourth known signals, wherein the first transceiver and the second transceiver perform a total of four transmissions and receptions: one transmission and reception each of the first and third known signals, and one transmission and reception each of the second and fourth known signals (see, for example, Patent Document 1).

[0003] JP 2019-128341 A

[0004] However, when performing distance measurement, if there is a multipath in an RF (Radio Frequency) signal such as the first to fourth known signals, the phase of the radio waves that are reflected along the way and arrive will differ from the phase of the radio waves that arrive directly from the transmitting device, and distance measurement may not be performed accurately because the propagation path of the radio waves that are reflected along the way and arrive will differ from the propagation path of the radio waves that arrive directly from the transmitting device.

[0005] Therefore, an object of the present invention is to provide a distance measuring device that can accurately measure distance even in an environment where a multipath exists.

[0006] A distance measuring device according to an embodiment of the present invention includes a transmitter that transmits a first signal to another device, a receiver that receives a second signal from the other device that has received the first signal, a phase acquirer that acquires a plurality of first phases when the other device receives the plurality of first signals transmitted by the transmitter to the other device at three or more different frequencies at different times, a phase measurer that measures a plurality of second phases when the receiver receives the second signals from the other device at the three or more different frequencies at different times, and a phase detector that measures the plurality of first signals and the plurality of second signals. The apparatus includes a signal strength acquisition unit that acquires signal strengths for a plurality of signal pairs of signals having equal wavenumbers; an extraction unit that extracts N signal pairs from the plurality of signal pairs corresponding to N (N is an integer of 2 or more) signal strengths excluding one or more signal strengths of the plurality of signal pairs that are less than a predetermined threshold; a round-trip phase calculation unit that calculates a round-trip phase for the N signal pairs, which is the sum of the first phase and the second phase for the first signal and the second signal included in each signal pair; and a ranging unit that measures the distance to the other device based on the N round-trip phases and the plurality of frequencies.

[0007] It is possible to provide a distance measuring device that can accurately measure distance even in an environment where a multipath exists.

[0008] 1 is a diagram showing a vehicle 10 and a smart key 20 equipped with ranging devices 100A and 100B according to an embodiment, respectively. A diagram showing the ranging device 100A according to an embodiment. A diagram explaining a communication method for ranging performed by the ranging devices 100A and 100B. A diagram showing the relationship between frequency fm and phase φ2wm in ranging. A diagram explaining a direct wave path a and a multipath path b. A diagram showing an example of the relationship between the frequency and round-trip phase of a first signal and a second signal when a multipath exists. A diagram explaining the relationship between round-trip phase and frequency when the radio waves transmitted and received between the ranging devices 100A and 100B are affected by the Doppler effect. A diagram explaining a method for detecting a moving speed v (m / s). A diagram showing the round-trip phase (upper side) for frequencies f0 to fm and the signal strength (lower side) for frequencies f0 to fm obtained by performing a first transmission process and a first reception process during multiple continuous wave transmission periods. 9A to 9C are diagrams showing round-trip phases (upper side) for frequencies f0 to fm obtained by performing a first transmission process and a first reception process during a plurality of continuous wave transmission periods, and signal strengths (lower side) for frequencies f0 to fm.

[0034] FIG. 9B is a diagram showing round-trip phases (upper side) for frequencies f0 to fm obtained by performing a first transmission process and a first reception process during a plurality of continuous wave transmission periods, and signal strengths (lower side) for frequencies f0 to fm.

[0035] FIG. 9C is a diagram showing signal pairs extracted by the extraction unit 177, summarizing the results of FIGS. 9A to 9C.

[0036] FIG. 9B is a diagram explaining the speed correction process of the correction process performed by the correction unit 178.

[0037] FIG. 9C is a diagram explaining the linear correction process of the correction process performed by the correction unit 178.

[0038] FIG. 9C is a diagram explaining the linear correction process of the correction process performed by the correction unit 178.

[0039] FIG. 9B is a flowchart showing an example of processing executed by the control device 170.

[0009] Hereinafter, an embodiment to which the distance measuring device of the present invention is applied will be described.

[0010] FIG. 1 illustrates a vehicle 10 and a smart key 20 equipped with distance measuring devices 100A and 100B according to an embodiment. Here, as an example, the distance measuring device 100A is implemented in a smart entry system mounted on the vehicle 10, and the distance measuring device 100B is implemented in the smart key 20 of the vehicle 10. The distance measuring devices 100A and 100B perform packet communication using Bluetooth Low Energy (registered trademark) as an example. Also, as an example, the vehicle 10 is equipped with an automatic parking assistance system, and the distance measuring device 100A is included in the automatic parking assistance system. The automatic parking assistance system is a system that autonomously parks the vehicle 10 in a parking position or autonomously causes the vehicle 10 to exit from the parking position by remotely transmitting a command to the vehicle 10 from the smart key 20 via wireless communication.

[0011] At least one of the ranging device 100A of the vehicle 10 and the ranging device 100B of the smart key 20 measures the distance between the vehicle 10 and the smart key 20, and the locks on the doors, trunk, etc. of the vehicle 10 are unlocked when the distance measured by the ranging device 100A or 100B is an appropriate distance.

[0012] Here, as an example, it is assumed that the ranging device 100A of the vehicle 10 performs ranging and notifies the ranging device 100B of the smart key 20 of the results of the ranging. The ranging devices 100A and 100B have the same configuration, as an example. Therefore, hereinafter, when there is no need to distinguish between the ranging devices 100A and 100B, they will simply be referred to as ranging device 100. Of the ranging device 100A of the vehicle 10 and the ranging device 100B of the smart key 20, the ranging device 100B, which does not perform ranging, is an example of another device. Here, as an example, the ranging device 100B of the vehicle 10 is an example of another device. It is possible to treat the ranging device 100A as a master device and the ranging device 100B as a slave device, or conversely, it is possible to treat the ranging device 100B as a master device and the ranging device 100A as a slave device, but this will not be used in the following description.

[0013] <Configuration of ranging device 100A> Figure 2 is a diagram showing the ranging device 100A of the embodiment. As described above, the ranging device 100A of the vehicle 10 and the ranging device 100B of the smart key 20 have the same configuration. Here, the ranging device 100A that performs ranging will be described. Hereinafter, a signal that the ranging device 100A transmits from the antenna 101 to the ranging device 100B will be referred to as a first signal, and a signal that the ranging device 100B transmits from the antenna 101 to the ranging device 100A will be referred to as a second signal.

[0014] The ranging device 100A includes an antenna 101, a power amplifier (PA) 110, a low noise amplifier (LNA) 120, an orthogonal modulator (OM) 130, an orthogonal demodulator (ODM) 140, a voltage controlled oscillator (VCO) 150, a phase locked loop (PLL) 155, a codec processing unit 160, and a control device 170.

[0015] The antenna 101 communicates with the antenna 101 of the ranging device 100B of the vehicle 10. The antenna 101 is connected to the PA 110 and the LNA 120. Here, a changeover switch for switching the connection of the antenna 101 between the PA 110 and the LNA 120 is omitted. The antenna 101 of the ranging device 100A transmits a first signal to the ranging device 100B and receives a second signal from the ranging device 100B.

[0016] The PA 110 is provided between the OM 130 and the antenna 101, and amplifies the modulated signal for transmission (first signal) input from the OM 130 and outputs the amplified signal to the antenna 101. The PA 110 is an amplifier for transmission.

[0017] The LNA 120 is provided between the antenna 101 and the ODM 140, and amplifies the second signal received by the antenna 101 with low noise and outputs the amplified signal to the ODM 140. The LNA 120 is an amplifier for reception.

[0018] The OM 130 is an example of a transmitting section, and modulates the I / Q signal input from the codec processing section 160 using the high frequency signal input from the VCO 150, and outputs the modulated signal to the PA 110 for transmission.

[0019] The ODM 140 is an example of a receiving unit, and demodulates the signal output from the LNA 120 using the high-frequency signal input from the VCO 150 to obtain an I / Q signal, and outputs the I / Q signal to the codec processing unit 160. The signal output from the LNA 120 is the signal received by the ranging device 100A from the ranging device 100B.

[0020] The VCO 150 oscillates at a frequency set by the PLL 155. The VCO 150 can oscillate at a plurality of frequencies set by the PLL 155.

[0021] 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.

[0022] The codec processing unit 160 includes an ADC (Analog to Digital Converter) and a DAC (Digital to Analog Converter) and performs codec processing. The codec processing unit 160 detects BLE (registered trademark) packets, performs address determination processing, and the like. More specifically, the codec processing unit 160 digitally converts (ADC processing) the I / Q signals processed by the ODM 140 and converts them into BLE packet information. The codec processing unit 160 also generates I / Q signals (divides into I signals and Q signals) from BLE packets (digital signals) input from the control device 170, converts them to analog signals by DAC processing, and outputs the I / Q signals as transmission signals to the OM 130.

[0023] Hereinafter, a signal of a predetermined frequency transmitted from the OM 130 of the ranging device 100A to the ranging device 100B will be referred to as a transmission signal. Also, a signal transmitted as a transmission signal by the ranging device 100A and received by another device will be referred to as a reception signal.

[0024] The control device 170 includes a main control unit 170A, a transmission / 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 realized by a microcomputer including a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), an input / output interface, an internal bus, etc.

[0025] The main control unit 170A, the transmission / 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 functional blocks representing the functions of the program executed by the control device 170. The memory 170M is a functional representation of the memory of the control device 170.

[0026] The main control unit 170A is a processing unit that oversees the processing of the control device 170, and performs processing other than the processing performed by the transmission / 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 ranging unit 179. The main control unit 170A notifies, for example, the ranging result to the ranging device 100B of the vehicle 10. For the notification, BLE packet communication using a frequency different from that used for ranging communication is used. For the notification, the ranging result, etc., may be written in the payload of a BLE packet.

[0027] The transmission / reception control unit 171 controls the transmission and reception of the first signal and the second signal between the ranging device 100A and the ranging device 100B. Specifically, the transmission / reception control unit 171 sets the frequency (predetermined frequency) and phase of the signal transmitted from the ranging device 100A to the ranging device 100B. Furthermore, since the ranging device 100B transmits a signal of the same frequency as the signal transmitted to the ranging device 100A, the transmission / reception control unit 171 of the ranging device 100B sets the frequency (predetermined frequency) and phase of the signal transmitted from the ranging device 100B to the ranging device 100A. Note that the same frequency of the signals transmitted between the ranging devices 100A and 100B may be agreed upon in advance between the ranging devices 100A and 100B, and data indicating the frequency may be shared using BLE packet communication.

[0028] The transmission / reception control unit 171 also causes the OM 130 to repeatedly perform a transmission process for transmitting a first signal to the ranging device 100B during a predetermined period, causing the OM 130 to transmit first signals of three or more different frequencies to the ranging device 100B at different timings. The transmission / reception control unit 171 also causes the ODM 140 to repeatedly perform a reception process for receiving second signals from the ranging device 100B during a predetermined period, causing the ODM 140 to receive second signals of three or more different frequencies at different timings from the ranging device 100B. The predetermined period is a continuous wave transmission period in BLE (registered trademark), which is 2.5 milliseconds. During the predetermined period, the ranging device 100A transmits a first signal to the ranging device 100B, and the ranging device 100B transmits a second signal to the ranging device 100A.

[0029] Furthermore, the transmission / reception control unit 171 causes the OM 130 to transmit the first signal multiple times for each of a plurality of frequencies f1 to fm (m is an integer equal to or greater than 2), and causes the ODM 140 to receive the second signal multiple times for each of the plurality of frequencies. That is, the OM 130 transmits the first signal multiple times at different timings for each of the frequencies f1 to fm. The ODM 140 receives the second signal multiple times for each of the plurality of frequencies f1 to fm. The reason for transmitting the first signal and receiving the second signal multiple times at each frequency is to obtain multiple round-trip phases at each frequency.

[0030] Here, as an example, a configuration will be described in which the transmission / reception control unit 171 causes the OM 130 to transmit a first signal twice for each of the multiple frequencies f1 to fm, and causes the ODM 140 to receive a second signal twice for each of the multiple frequencies. The OM 130 transmits the first signal through two transmission processes, a first transmission process and a second transmission process, for each of the multiple frequencies f1 to fm. Furthermore, the ODM 140 receives the second signal through two reception processes, a first reception process and a second reception process, for each of the multiple frequencies f1 to fm.

[0031] In this manner, a configuration will be described in which the transmission / reception control unit 171 causes the OM 130 to transmit the first signal twice, in two transmission processes, a first transmission process and a second transmission process, for each of the multiple frequencies f1 to fm, and causes the ODM 140 to receive the second signal twice, in two reception processes, a first reception process and a second reception process, for each of the multiple frequencies f1 to fm. 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, and may be three or more.

[0032] 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. Also, 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.

[0033] The switching unit 172 switches between a transmission state in which the OM 130 transmits a signal and a reception state in which the ODM 140 receives a signal. The switching unit 172 enables the PA 110 to amplify the signal in the transmission state, and enables the LNA to amplify the signal in the reception state. When switching between the transmission state and the reception state, the switching unit 172 provides a stabilization time for stabilizing the phase and frequency.

[0034] 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 predetermined frequency transmitted by the ranging device 100A in the first transmission process and the second transmission process at each of the frequencies f1 to fm. Since the first signal is transmitted twice at each frequency, 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 in BLE packet communication at a frequency different from the communication for ranging. The phase data representing the first phase may be written to the payload of the BLE packet. Furthermore, the phase data representing the first phase may be measured by the phase measurement unit 174 of the ranging device 100B and transmitted to the ranging device 100A.

[0035] The phase measurement unit 174 measures the second phase when the ODM 140 receives the second signal in the first reception process and the second reception process at each of the frequencies f1 to fm. That is, the phase measurement unit 174 measures multiple second phases when the ODM 140 of the ranging device 100A receives the second signal at three or more frequencies at different timings from the ranging device 100B. Because the second signal is transmitted twice from the ranging device 100B at each frequency, the phase measurement unit 174 obtains two second phases at each frequency. The second phases are measured for ranging.

[0036] The signal strength acquisition unit 175 acquires second reception strengths when multiple second signals are received by the ODM 140 repeatedly performing the first reception process and the second reception process at each of the frequencies f1 to fm. The signal strength acquisition unit 175 also acquires first signal strengths when the multiple first signals are received by the ranging device 100B from the ranging device 100B. The first signal strengths acquired by the signal strength acquisition unit 175 from the ranging device 100B are measured by the signal strength acquisition unit 175 of the ranging device 100B, written as signal strength data in the payload of a BLE packet serving as the second signal, and transmitted to the ranging device 100A.

[0037] In this way, the signal strength acquisition unit 175 acquires the first signal strength from the signal strength data included in the second signals received by the ODM 140 by repeatedly performing the reception process.

[0038] Here, a pair of first and second signals having the same frequency is referred to as a signal pair. The first signals transmitted in the first transmission process have mutually different frequencies f1 to fm. The second signals received in the first reception process have mutually different frequencies f1 to fm. Similarly, the first signals transmitted in the second transmission process have mutually different frequencies f1 to fm. The second signals received in the second reception process have mutually different frequencies f1 to fm.

[0039] Hereinafter, a signal pair including a first signal transmitted in a first transmission process and a second signal received in a first reception process will be referred to as a first signal pair, and a signal pair including a first signal transmitted in a second transmission process and a second signal received in a second reception process will be referred to as a second signal pair. Hereinafter, when there is no particular distinction between the first signal pair and the second signal pair, they will simply be referred to as a signal pair.

[0040] The first signal pair is a signal pair of first and second signals (a plurality of first signals and a plurality of second signals having the same frequency (f1 to fm)) that are transmitted and received in a first transmission process and a first reception process that are performed in the same time period (first time period). The second signal pair is a signal pair of first and second signals (a plurality of first signals and a plurality of second signals having the same frequency (f1 to fm) that are transmitted and received in a second transmission process and a second reception process that are performed in the same time period (second time period).

[0041] Since the number of first signals is equal to the number of second signals, there are a number of first signal pairs equal to the number of first signals and the number of second signals in the first transmission process and the first reception process. Similarly, there are a number of second signal pairs equal to the number of first signals and the number of second signals in the second transmission process and the second reception process. Also, the number of first signal pairs is equal to the number of second signal pairs.

[0042] The signal strength acquisition unit 175 acquires, as the signal strengths for the plurality of first signal pairs and the plurality of second signal pairs, a first signal strength when the plurality of first signals are received by the ranging device 100B, or a second reception strength when the plurality of second signals are received by the ODM 140 by repeatedly performing reception processing. The signal strength acquisition unit 175 acquires the first signal strength when the plurality of first signals are received by the ranging device 100B by performing the first transmission processing and the first reception processing, or the second reception strength when the plurality of second signals are received by the ODM 140 by repeatedly performing reception processing. The signal strength acquisition unit 175 also acquires the first signal strength when the plurality of first signals are received by the ranging device 100B by performing the second transmission processing and the second reception processing, or the second reception strength when the plurality of second signals are received by the ODM 140 by repeatedly performing reception processing.

[0043] The signal strength acquisition unit 175 acquires signal strengths for a plurality of first signal pairs, each consisting of a plurality of first signals and a plurality of second signals, the frequencies of which are equal, and also acquires signal strengths for a plurality of second signal pairs, each consisting of a plurality of first signals and a plurality of second signals, the frequencies of which are equal.

[0044] The round-trip phase calculation unit 176 calculates a first round-trip phase by summing the first phase and the second phase of the first signal and the second signal included in each of the plurality of first signal pairs acquired by the signal strength acquisition unit 175. Furthermore, the round-trip phase calculation unit 176 calculates a second round-trip phase by summing the first phase and the second phase of the first signal and the second signal included in each of the plurality of second signal pairs acquired by the signal strength acquisition unit 175. Note that when there is no particular distinction between the first round-trip phase and the second round-trip phase, they are simply referred to as the round-trip phase.

[0045] The extraction unit 177 extracts N signal pairs from the plurality of signal pairs corresponding to N (N is an integer of 2 or greater) signal strengths, excluding one or more signal strengths that are less than a predetermined threshold among the signal strengths of the plurality of signal pairs obtained in the first transmission process, the second transmission process, the first reception process, and the second reception process for frequencies f0 to fm. The N signal pairs are N signal pairs obtained by excluding one or more signal pairs whose signal strengths are less than a predetermined threshold from all signal pairs (plurality of signal pairs) whose signal strengths have been acquired by the signal strength acquisition unit 175. The threshold is a value that can exclude signal pairs whose signal strength has decreased due to multipath.

[0046] The extractor 177 extracts N first signal pairs from the plurality of first signal pairs, excluding one or more signal pairs in which the signal strength of the first signal or the second signal is less than a predetermined threshold. The extractor 177 also extracts N second signal pairs from the plurality of signal pairs, excluding one or more signal pairs in which the signal strength of the first signal or the second signal is less than a predetermined threshold. To obtain two round-trip phases from the first signal pair and the second signal pair, the extractor 177 excludes any one of the first signal transmitted in the first transmission process, the second signal received in the first reception process, the first signal transmitted in the second transmission process, and the second signal received in the second reception process whose signal strength is less than a predetermined threshold without extracting that first signal pair and second signal pair.

[0047] The correction unit 178 corrects the phase change due to the relative movement with respect to the ranging device 100B for each of the N first round trip phases. The correction unit 178 corrects the phase change due to the relative movement with respect to the ranging device 100B using the difference between the first round trip phase and the second round trip phase at frequencies f1 to fm. The correction unit 178 also calculates the relative velocity with respect to the ranging device 100B from 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 velocity of the ranging devices 100A and 100B and the time difference between the acquisition of 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. Specific corrections made by the correction unit 178 will be described later with reference to FIGS. 11 to 13.

[0048] The distance measuring unit 179 measures the distance to the distance measuring device 100B based on the N first round trip phases corrected by the correcting unit 178 and the plurality of frequencies.

[0049] The memory 170M stores programs, data, etc. necessary for the main control unit 170A, the transmission / 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 to perform the above-mentioned processes. The memory 170M stores data, etc., that sets the predetermined frequency and phase of the signal transmitted between the distance measurement devices 100A and 100B.

[0050] <Communication Method for Distance Measurement Executed by Distance Measuring Devices 100A and 100B> First, a communication method and a distance measurement method when no influence of multipath occurs will be described.

[0051] 3 is a diagram illustrating a communication method for distance measurement executed by distance measuring devices 100A and 100B. Here, as an example, it is assumed that the transmission / reception control unit 171 of distance measuring device 100A reads data from memory 170M and sets the frequency (predetermined frequency) and phase of a first signal to be transmitted from distance measuring device 100A to distance measuring device 100B. Furthermore, it is assumed that distance measuring device 100B transmits to distance measuring device 100A a second signal having a frequency and phase equal to the frequency and phase of the received first signal. It is assumed that distance measuring devices 100A and 100B share data indicating the frequency and phase of the signal to be transmitted with each other before performing communication for distance measurement.

[0052] In communication for distance measurement, the distance measuring devices 100A and 100B transmit to each other at the same frequency. More specifically, in communication for distance measurement, when one of the distance measuring devices 100A and 100B transmits a signal (first signal or second signal) at a certain frequency, the other transmits a signal (first signal or second signal) at the same frequency. Such mutual transmission constitutes one communication for distance measurement.

[0053] 3, as an example, in the first communication (1), the ranging device 100A transmits a first signal at frequency f1 to the ranging device 100B, and the ranging device 100B transmits a second signal at the same frequency f1 to the ranging device 100A. The phase acquisition unit 173 of the ranging device 100A acquires from the ranging device 100B the phase when the ranging device 100B receives the first signal at frequency f1 transmitted by the ranging device 100A. The phase measurement unit 174 of the ranging device 100A measures the phase when the ranging device 100A receives the second signal at frequency f1 from the ranging device 100B.

[0054] In the second communication (2), the ranging device 100B transmits a second signal at frequency f2 to the ranging device 100A, and the ranging device 100A transmits a first signal at the same frequency f2 to the ranging device 100B. The phase measurement unit 174 of the ranging device 100A measures the phase when the ranging device 100A receives the second signal at frequency f2 from the ranging device 100B. The phase acquisition unit 173 of the ranging device 100A acquires from the ranging device 100B the phase when the ranging device 100B receives the first signal at frequency f2 transmitted by the ranging device 100A.

[0055] In the third communication (3), the ranging device 100A transmits a first signal at frequency f3 to the ranging device 100B, and the ranging device 100B transmits a second signal at the same frequency f3 to the ranging device 100A. The phase acquisition unit 173 of the ranging device 100A acquires from the ranging device 100B the phase when the ranging device 100B receives the first signal at frequency f3 transmitted by the ranging device 100A. The phase measurement unit 174 of the ranging device 100A measures the phase when the ranging device 100A receives the second signal at frequency f3 from the ranging device 100B.

[0056] In the fourth communication (4), the ranging device 100B transmits a second signal at frequency f4 to the ranging device 100A, and the ranging device 100A transmits a first signal at the same frequency f4 to the ranging device 100B. The phase measurement unit 174 of the ranging device 100A measures the phase when the ranging device 100A receives the second signal at frequency f4 from the ranging device 100B. The phase acquisition unit 173 of the ranging device 100A acquires from the ranging device 100B the phase when the ranging device 100B receives the first signal at frequency f4 transmitted by the ranging device 100A.

[0057] While performing ranging, ranging devices 100A and 100B continue to communicate as shown in Figure 3, and the phase measurement unit 174 of ranging device 100A measures the phase when ranging device 100A receives the second signal from ranging device 100B, and the phase acquisition unit 173 of ranging device 100A acquires from ranging device 100B the phase when ranging device 100B receives the first signal transmitted by ranging device 100A.

[0058] Here, it is assumed that the first communication (1) through the fourth communication (4) are repeated at short intervals, and that the distance between the ranging devices 100A and 100B is the same. In this case, the phase when the ranging device 100B receives the first signal of frequency fm transmitted by the ranging device 100A is defined as φAB, and the phase acquisition unit 173 of the ranging device 100A acquires the phase φAB. Furthermore, it is assumed that the phase when the ranging device 100A receives the second signal of frequency fm from the ranging device 100B is defined as φBA, and the phase measurement unit 174 of the ranging device 100A measures the phase φBA. The frequency fm is, for example, one of the frequencies f1 to f4 described above.

[0059] φAB+φBA is the total phase (round-trip phase) when round-trip communication is performed between distance measuring devices 100A and 100B at frequency f. The round-trip phase at frequency fm is represented as φ2w. 2w stands for two-way. The round-trip phase in the first communication (frequency f1) is represented as φ1w1, the round-trip phase in the second communication (frequency f2) is represented as φ2w2, the round-trip phase in the third communication (frequency f3) is represented as φ2w3, and the round-trip phase in the fourth communication (frequency f4) is represented as φ2w4. The wavelengths at frequencies f1 to f4 are represented as λ1 to λ4, respectively. Such round-trip phase φ2w is calculated by the round-trip phase calculation unit 176.

[0060] As described above, if the first communication (1) to the fourth communication (4) are repeated in a short cycle, the distance between the distance measuring devices 100A and 100B during the round-trip communications is considered to be the same. Therefore, if the distance between the distance measuring devices 100A and 100B during the first communication (1) to the fourth communication (4) is L, the following equations (1) to (4) hold. 2L is the round-trip distance. n is an integer equal to or greater than 1. 2L = (n + φ2w1) × λ1 (1) 2L = (n + φ2w2) × λ2 (2) 2L = (n + φ2w3) × λ3 (3) 2L = (n + φ2w4) × λ4 (4)

[0061] Eliminating n from equations (1) and (2) gives the following equation (5A), which can be further transformed into equations (5B) to (5D) to find the distance L. c is the speed of light. 2L / λ1-φ2w1=2L / λ2-φ2w2 (5A) 2L(1 / λ2-1 / λ1)=φ2w2-φ2w1 (5B) 2L(f2-f1) / c=φ2w2-φ2w1 (5C) L / c=(1 / 2)×(φ2w2-φ2w1) / (f2-f1) (5D)

[0062] Similarly, by eliminating n from equations (1) and (3), the equations can be transformed into equation (6): L / c=(1 / 2)×(φ2w3-φ2w1) / (f3-f1) (6)

[0063] Similarly, by eliminating n from equations (1) and (4), they can be transformed into equation (7): L / c=(1 / 2)×(φ2w4−φ2w1) / (f4−f1) (7)

[0064] 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 corresponds to the ratio of the distance L to the speed of light c.

[0065] 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, then equations (5D), (6), and (7) can be expressed as the following equation (8): L / c=(½)×Δφ / Δf (8)

[0066] FIG. 4 is a diagram showing the relationship between frequency fm and phase φ2wm in distance measurement. If the ratios of distance L and the speed of light c obtained from equations (5D), (6), and (7) are designated as slopes A, B, and C, respectively, slopes A, B, and C can be expressed as shown in FIG. 4. Specifically, slope A is A = (1 / 2) × Δφ / Δf = (φ2w2 - φ2w1) / (f2 - f1). Slope B is B = (1 / 2) × Δφ / Δf = (φ2w3 - φ2w1) / (f3 - f1). Slope C is C = (1 / 2) × Δφ / Δf = (φ2w4 - φ2w1) / (f4 - f1). It is also possible to calculate only one of slope A calculated from two frequencies f1 and f2, slope B calculated from two frequencies f1 and f3, and slope C calculated from two frequencies f1 and f4. Furthermore, although a form in which the slopes A, B, and C are determined from two frequencies (f1 and f2, f1 and f3, and f1 and f4) will be described here, it is also possible to use three or more frequencies to determine a straight line by linear approximation using the least squares method for three or more points given by the frequency fm and the phase φ2wm, and to determine the slope of the determined straight line as L / c.

[0067] Multiplying the slope A by the speed of light c makes it possible to find the distance L obtained from the combination of frequencies f1 and f2, multiplying the slope B by the speed of light c makes it possible to find the distance L obtained from the combination of frequencies f1 and f3, and multiplying the slope C by the speed of light c makes it possible to find the distance L obtained from the combination of frequencies f1 and f4. The distance L is found by the distance measuring unit 179.

[0068] <Multipath> When multipath exists, the phase of radio waves that are reflected along the way and arrive differs from the phase of radio waves that arrive directly from the transmitting device, which can make it difficult to measure distance accurately. This is because the propagation path of radio waves that are reflected along the way and arrive directly from the transmitting device differs from the propagation path of radio waves.

[0069] 5 is a diagram illustrating direct wave path a and multipath path b. Direct wave path a is a path along which radio waves propagate directly from distance measuring device 100B to distance measuring device 100A. Multipath path b is a path along which radio waves propagate from distance measuring device 100B to distance measuring device 100A, being reflected by reflective surfaces such as the ground and the walls of a building. Multipath path b is longer than direct wave path a.

[0070] Fig. 6 is a diagram showing an example of the relationship between the frequency and round-trip phase of the first and second signals when multipath exists. In Fig. 6, the horizontal axis represents the frequency (MHz) of the first and second signals transmitted between ranging 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). In Fig. 6, the phase characteristics are shown by dashed lines, and the signal strength (RSSI) characteristics are shown by solid lines.

[0071] When no multipath exists, the round-trip phase decreases approximately linearly with increasing frequency, such as in the frequency bands from about 2436 MHz to about 2456 MHz and from about 2456 MHz to about 2476 MHz. Furthermore, since no multipath exists in the frequency bands from about 2436 MHz to about 2456 MHz and from about 2456 MHz to about 2476 MHz, a good signal strength (RSSI) value of -40 or higher is obtained.

[0072] In contrast, when multipath exists, there is a band (a band around approximately 2424 MHz) where the round-trip phase changes (decreases in this case) rapidly as the frequency increases, such as in the frequency band from approximately 2416 MHz to approximately 2436 MHz, and the signal strength (RSSI) drops rapidly in that band. In the band where the round-trip phase drops rapidly, multi-fading occurs, causing a drop in the signal strength (RSSI). When the round-trip phase changes nonlinearly in this way, an appropriate round-trip phase value cannot be obtained in that frequency band, making it impossible to perform appropriate ranging. Furthermore, nonlinear changes in the round-trip phase can be detected by the signal strength (RSSI).

[0073] For this reason, the ranging device 100A detects frequency bands where the signal strength (RSSI) is low and excludes the round-trip phase in such frequency bands from the ranging data, in order to enable accurate ranging even in an environment where multipath exists.

[0074] 7 is a diagram illustrating the relationship between frequency and round-trip phase when the Doppler effect is present in the radio waves transmitted and received between the distance measuring devices 100A and 100B. For example, when a user carrying the smart key 20 including the distance measuring device 100B moves around while operating the automatic parking assistance system installed in the vehicle 10, the distance between the distance measuring devices 100A and 100B changes.

[0075] Here, when the distance between the vehicle 10 and the smart key 20 is constant, the relationship between the frequencies f0 to fm and the round-trip phases θ0 to θm is as shown by the dashed line in Figure 7. Here, as an example, the frequencies f0 to fm are equally spaced and increase in increments of 1 MHz from f0 to fm.

[0076] In such a case, if the vehicle 10 is stopped and a user holding the smart key 20 moves away from the vehicle 10 at a constant speed v (m / s), the relationship between the frequencies f0 to fm and the round-trip phases θ0 to θm will shift as shown by the solid line due to the Doppler effect. Using time t, θm will shift due to the Doppler effect as expressed by the following equation (1). As expressed by equation (9), the higher the frequency fm, the greater the shift in the round-trip phase θm due to the Doppler effect.

[0077]

[0078] If the user's moving speed v (m / s) is known, the characteristics of the solid line in Figure 7 can be corrected to the characteristics of the dashed line, so the distance measuring device 100A detects the user's moving speed v (m / s) as follows: Note that both the user holding the smart key 20 and the vehicle 10 may be moving, in which case it is sufficient to detect the relative moving speed.

[0079] 8 is a diagram illustrating a method for detecting the moving velocity v (m / s). First round-trip phases θ0 to θm at frequencies f0 to fm are obtained by performing first transmission processing and first reception processing at each of the frequencies f0 to fm, and second round-trip phases θa0 to θam at frequencies f0 to fm are obtained by performing second transmission processing and second reception processing at each of the frequencies f0 to fm.

[0080] If a user is moving and a first transmission process and a first reception process are performed at each of the frequencies f0 to fm during a first time period, and then a second transmission process and a second reception process are performed at each of the frequencies f0 to fm during a second time period following the first time period, the differences Δθ0 to Δθm between the first round-trip phase θ0 to θm and the second round-trip phase θa0 to θam at each of the frequencies f0 to fm will be constant values, as shown in Figure 8. Using the first round-trip phase θk (k = 0 to m) in this case, the second round-trip phase θak can be expressed by the following equation (10). The frequency of the first round-trip phase θk and the second round-trip phase θak is defined as fk.

[0081]

[0082] If the difference Δθk (k=0 to m) is calculated based on equation (10), the moving speed v can be calculated 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.

[0083] Specifically, for example, if the round-trip phase at the end time tA of the first time period is θA, the round-trip phase at the end time tB of the second time period is θB, and the time t (= tB - tA), the amount of change in the round-trip phase Δθ (= θB - θA), and the moving speed v are used, the following equation (11) holds for the Doppler effect.

[0084]

[0085] 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, and the correction unit 178 substitutes the change in the round-trip phase Δθ (= θB - θA) at time t (= tB - tA) into equation (11), thereby determining the moving speed v.

[0086] <Timing of transmission processing and reception processing> As described above, the transmission / reception control unit 171 performs a first transmission processing once during one continuous wave transmission period (2.5 milliseconds) in BLE (registered trademark), performs a first reception processing once during another continuous wave transmission period, performs a second transmission processing once during yet another continuous wave transmission period, and performs a second reception processing once during yet another continuous wave transmission period.

[0087] In this way, by performing a transmission process or a reception process once during each continuous wave transmission period, the ranging device 100A transmits first signals of three or more frequencies f1 to fm at different timings to the ranging device 100B, and receives second signals of three or more frequencies f1 to fm at different timings from the ranging device 100B.

[0088] Since the continuous wave transmission period is very short at 2.5 milliseconds, distance measurement is performed by performing a single transmission process or reception process and then repeating the transmission process or reception process in multiple continuous wave transmission periods.

[0089] Because BLE (registered trademark) packet communication is also used for purposes other than ranging (for example, transmitting audio signals), the time available for ranging is extremely limited. Therefore, it is necessary to achieve highly accurate positioning in as short a time as possible. Therefore, the ranging device 100A performs a transmission process or a reception process once during each continuous wave transmission period. Furthermore, by adding up the results obtained by performing a transmission process or a reception process once during multiple intermittent continuous wave transmission periods, the relationship between the round-trip phase for frequencies f1 to fm is determined, and ranging is performed.

[0090] <Signal Pair Extraction Method> Figures 9A, 9B, and 9C are diagrams showing the round-trip phase (upper panel) versus frequency obtained by performing the first transmission process and the first reception process during one continuous wave transmission period, and the signal strength (lower panel) versus frequency. The signal strengths shown in Figures 9A, 9B, and 9C are the lower of the RSSI values ​​of the first and second signals. Here, an example of a signal pair extraction method will be described using Figures 9A, 9B, and 9C. As an example, the signal strength threshold TH at which the extraction unit 177 extracts signal pairs is set to a level 10 dBm lower than the signal strength RS1 in the absence of multipath. In the following, the multiple frequencies are assumed to be f0 to fm.

[0091] Here, the round-trip phase (upper side) and signal strength (lower side) for the frequency obtained by performing the first transmission process and the first reception process for each continuous wave transmission period are shown, but the same is true for the round-trip phase and signal strength for the frequency obtained by performing the second transmission process and the second reception process for each continuous wave transmission period. Note that times t0 to t2 shown in Figure 9A are at regular intervals, times t3 to t5 shown in Figure 9B are at regular intervals, and times t6 to t8 shown in Figure 9C are at regular intervals. The intervals between times t0 to t2, t3 to t5, and t6 to t8 are all equal.

[0092] 9A shows the round-trip phase (top) for the frequencies obtained by performing one first transmission process and one first reception process at frequencies f0, f1, and f2, and the signal strength (bottom) for frequencies f0, f1, and f2. The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 acquire the signal strength and round-trip phase for frequency f0 at time t0, the signal strength and round-trip phase for frequency f1 at time t1, the signal strength and round-trip phase for frequency f2 at time t2, and the signal strength and round-trip phase for frequency f0 at time t3. For frequency f0, the signal strength acquisition unit 175 and the round-trip phase calculation unit 176 acquire the signal strength and round-trip phase twice, at times t0 and t3.

[0093] 9B shows the round-trip phases (top) for the frequencies obtained by performing one first transmission process and one first reception process at frequencies f3, f4, and f5, and the signal strengths (bottom) for frequencies f3, f4, and f5. The signal strength acquirer 175 and the round-trip phase calculator 176 acquire the signal strength and round-trip phase for frequency f3 at time t4, the signal strength and round-trip phase for frequency f4 at time t5, the signal strength and round-trip phase for frequency f5 at time t6, and the signal strength and round-trip phase for frequency f6 at time t7. For frequency f3, the signal strength acquirer 175 and the round-trip phase calculator 176 acquire the signal strength and round-trip phase twice, at times t4 and t7.

[0094] 9C shows the round-trip phases (top) for the frequencies obtained by performing one first transmission process and one first reception process at frequencies f6, f7, and f8, and the signal strengths (bottom) for frequencies f6, f7, and f8. The signal strength acquirer 175 and the round-trip phase calculator 176 acquire the signal strength and round-trip phase for frequency f3 at time t8, the signal strength and round-trip phase for frequency f4 at time t9, the signal strength and round-trip phase for frequency f5 at time t10, and the signal strength and round-trip phase for frequency f6 at time t11. For frequency f3, the signal strength acquirer 175 and the round-trip phase calculator 176 acquire the signal strength and round-trip phase twice, at times t8 and t11.

[0095] The correction unit 178 also calculates the difference Δθ between the round-trip phases acquired twice for the same frequency. The difference Δθ is the difference Δθ between the first round-trip phase and the second round-trip phase. The correction unit 178 calculates the difference Δθs1 for the frequency f0 shown in FIG. 9A, the difference Δθs2 for the frequency f3 shown in FIG. 9B, and the difference Δθs3 for the frequency f6 shown in FIG. 9C. In FIG. 9A, dashed lines indicate straight lines that fit the round-trip phases at frequencies f0, f1, and f2. In FIG. 9B, dashed lines indicate straight lines that fit the round-trip phases at frequencies f3, f4, and f5. In FIG. 9C, dashed lines indicate straight lines that fit the round-trip phases at frequencies f6, f7, and f8.

[0096] Also, looking at the signal strength in FIGS. 9A to 9C, the signal strength is equal to or greater than the threshold value TH at frequencies f0 to f2, f3, f4, and f6 to f8, but is less than the threshold value TH at frequency f5.

[0097] In such a case, the extraction unit 177 excludes signal pairs whose signal strength is less than the threshold TH, and extracts round-trip phases calculated for signal pairs whose signal strength is equal to or greater than the threshold TH. Fig. 10 summarizes the results of Figs. 9A to 9C and shows signal pairs extracted by the extraction unit 177. As shown in Fig. 10, the extraction unit 177 excludes the signal pair at frequency f5 whose signal strength is less than the threshold TH, and extracts round-trip phases calculated for signal pairs at frequencies f0 to f2, f3, f4, and f6 to f8.

[0098] 11 is a diagram illustrating the velocity correction process of the correction unit 178. The velocity 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.

[0099] For the round-trip phases obtained at frequencies f0, f1, and f2, the correction unit 178 corrects the round-trip phases at frequencies f1 and f2 by equally allocating the difference Δθs1 for frequency f0 to the round-trip phases at frequencies f1 and f2. Since the difference Δθs1 between the round-trip phases obtained twice for frequency f0 is the increase in the round-trip phase of frequency f0 at time t3 relative to the round-trip phase of frequency f0 at time t0, the correction unit 178 subtracts (Δθs1) / 2 from the round-trip phase at frequency f1 and subtracts Δθs1 from the round-trip phase at frequency f2. Because times t0 to t3 are at regular intervals, the correction value used is the difference Δθs1 multiplied by a rate corresponding to the elapsed time from time t0. That is, the correction value for the round-trip phase at frequency f1 is −(Δθs1) / 2, and the correction value for the round-trip phase at frequency f2 is −Δθs1.

[0100] Similarly, since the difference Δθs2 between the round-trip phases acquired 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, the correction unit 178 subtracts (Δθs2) / 2 from the round-trip phase at frequency f4. Because times t4 to t7 are at regular intervals, the correction value used is the difference Δθs2 multiplied by a rate corresponding to the elapsed time from time t4. In other words, the correction value for the round-trip phase at frequency f4 is −(Δθs2) / 2.

[0101] Furthermore, since the difference Δθs3 between the round-trip phases acquired 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, 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. Because times t8 to t11 are constant intervals, the correction value used is the difference Δθs3 multiplied by a rate corresponding to the elapsed time from time t8. 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.

[0102] 12, 13, and 14 are diagrams illustrating the linear correction process performed by the correction unit 178. The correction unit 178 calculates the slope S1 and intercept A1 of a straight line that fits the round-trip phases of the frequencies f0, f1, and f2, as shown in FIG.

[0103] Next, the correction unit 178 uses the calculated slope S and intercept A to offset the round-trip phases of frequencies f3 and f4 so that they are tangent to a straight line that fits to the round-trip phases of frequencies f0, f1, and f2, as shown in Fig. 13. For the round-trip phase θ3 at frequency f3, (θ3 - (f3 x S1 + A1)) is subtracted from θ3, thereby offsetting the round-trip phase θ3 of frequency f3, as shown in Fig. 13. For the round-trip phase θ4 at frequency f4, (θ3 - (f3 x S1 + A1)) is subtracted from θ4, thereby offsetting the round-trip phase θ4 of frequency f4, as shown in Fig. 13. The round-trip phases θ3 and θ4 of frequencies f3 and f4 are offset using the same correction amount (θ3 - (f3 x S1 + A1). Then, the correction unit 178 calculates the slope S2 and intercept A2 of the straight line that fits to the round-trip phases of frequencies f0, f1, f2, f3, and f4.

[0104] Next, the correction unit 178 uses the slope S2 and intercept A2 of the line that fits the round-trip phases of the frequencies f0, f1, f2, f3, and f4 to offset the round-trip phases of the frequencies f6, f7, and f8 so that the round-trip phases of the frequencies f6, f7, and f8 are tangent to the line that fits the round-trip phases of the frequencies f0, f1, f2, f3, and f4, as shown in Figure 14. For the round-trip phase θ6 at frequency f6, (θ6 - (f6 × S2 + A2)) is subtracted from θ6, thereby offsetting the round-trip phase θ6 of frequency f6 as shown in FIG. 14. For the round-trip phases θ7 and θ8 at frequencies f7 and f8, (θ6 - (f6 × S2 + A2)) is subtracted from θ7 and θ8, thereby offsetting the round-trip phases θ7 and θ8 of frequencies f7 and f8 as shown in FIG. 14. The round-trip phases θ6, θ7, and θ8 of 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 a straight line that fits the round-trip phases of frequencies f0, f1, f2, f3, f4, f6, f7, and f8.

[0105] By performing the above-described processing for the round-trip phases of frequencies f0 to fm, the N round-trip phases are corrected so that a linear relationship exists between the N round-trip phases and the N frequencies of the N signal pairs corresponding to the N round-trip phases. This is the linear correction processing. The ranging unit 179 then measures the distance between the ranging device 100B and the ranging device 100A using the linear relationship thus obtained between the N round-trip phases and the N frequencies of the N signal pairs corresponding to the N round-trip phases (for example, a straight line with an intercept A3 and a slope S3 shown in FIG. 14 ).

[0106] <Flowchart> FIG. 15 is a flowchart showing an example of processing executed by the control device 170.

[0107] When the process starts, the signal strength acquisition unit 175 and the round-trip phase calculation unit 176 execute a first transmission process, a first reception process, a second transmission process, and a second reception process using three different frequencies for each continuous wave transmission period (step S1). The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 execute the first transmission process, the first reception process, the second transmission process, and the second reception process in separate continuous wave transmission periods.

[0108] Step S1 in FIG. 15 shows partial processing 1, partial processing 2, and partial processing 3 as examples. As described with reference to FIG. 9A, partial processing 1 is processing in which one first transmission process and one first reception process are performed at frequencies f0, f1, and f2 to obtain round-trip phases θ0(t0), θ1(t1), θ2(t2), and θ0(t3) and signal intensities RSSI1, RSSI2, and RSSI3. Times t0 to t3 are times when a first signal related to the round-trip phase is transmitted. As described with reference to FIG. 9B, partial processing 2 is processing in which one first transmission process and one first reception process are performed at frequencies f3, f4, and f5 to obtain round-trip phases θ3(t4), θ4(t5), θ5(t6), and θ3(t7) and signal intensities RSSI3, RSSI4, and RSSI5. Times t4 to t7 are times when a first signal related to the round-trip phase is transmitted. As described with reference to FIG. 9C , partial process 3 is a process in which one first transmission process and one first reception process are performed at frequencies f6, f7, and f8 to acquire round-trip phases θ6 (t8), θ7 (t9), θ8 (t10), and θ6 (t11) and signal strengths RSSI6, RSSI7, and RSSI8. Times t8 to t11 are the times when first signals related to the round-trip phases are transmitted. The signal strength acquisition unit 175 and the round-trip phase calculation unit 176 repeatedly perform the same process up to frequency fm.

[0109] 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, first reception process, second transmission process, and second reception process executed in step S1 (step S2). Also, in step S2, the correction unit 178 calculates the difference Δθ between the round-trip phases obtained twice for the same frequency in each process.

[0110] The main control unit 170A aggregates all the data obtained in step S2 (step S3).

[0111] The extraction unit 177 extracts the round-trip phases calculated for the signal pairs whose signal strength is equal to or greater than the threshold value TH (step S4). In step S4, N frequencies of N signal pairs corresponding to the N round-trip phases are extracted.

[0112] The correction unit 178 executes a speed correction process (step S5). In order to correct the influence of the Doppler effect due to the relative movement of the distance measuring devices 100A and 100B, the correction unit 178 executes the speed correction process described with reference to FIG. 11 on the round-trip phases of the three types of frequencies obtained by the multiple processes including partial process 1, partial process 2, and partial process 3.

[0113] The correction unit 178 executes linear correction processing (step S6). As described with reference to Figures 12 to 14, the linear correction processing is processing for correcting the N round-trip phases so that 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. The linear relationship between the frequency and the round-trip phase is obtained as shown in Figure 14, as an example.

[0114] The ranging unit 179 measures the distance to the ranging device 100B based on the intercept and slope of the linear relationship between the N first round trip phases corrected by the correction unit 178 in step S6 and multiple frequencies (step S7).

[0115] In the above, a description has been given of a configuration in which the round-trip phase is acquired twice 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 calculates the difference Δθ between the round-trip phases acquired twice for the same frequency in each partial process. By calculating the difference Δθ between the round-trip phases acquired twice for the same frequency in each partial process, it is possible to more accurately correct the influence of the Doppler effect in accordance with fluctuations in the relative movement speed of the distance measuring devices 100A and 100B. Furthermore, in each partial process, the round-trip phase may be acquired twice for a frequency other than the lowest frequency.

[0116] However, in at least one of the plurality of partial processes, the round-trip phase may be acquired 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 acquired 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 acquired twice for the lowest frequency f0. When the relative moving speed of distance measuring devices 100A and 100B is considered to be constant, doing so can simplify the processing.

[0117] As described above, the round-trip phases and signal intensities of multiple signal pairs are calculated, and N signal pairs corresponding to N (N is an integer of 2 or more) signal intensities are extracted from the multiple signal pairs, excluding one or more signal intensities that are less than a predetermined threshold. The distance to the ranging device 100B is measured based on the N round-trip phases and multiple frequencies. This reduces the effects of multipath.

[0118] Therefore, it is possible to provide a distance measuring device 100 that can accurately measure distance even in an environment where a multipath exists.

[0119] Furthermore, since N signal pairs are extracted from the plurality of signal pairs, excluding one or more signal pairs in which the signal strength of the first signal or the second signal is less than a predetermined threshold, the influence of multipath can be more reliably reduced, and more accurate distance measurement is possible.

[0120] Furthermore, the transmission / reception control unit 171 causes the OM 130 to repeatedly perform a transmission process of transmitting a first signal to the ranging device 100B during a predetermined period, causing the OM 130 to transmit first signals of three or more different frequencies at different timings to the ranging device 100B, and causes the ODM 140 to repeatedly perform a reception process of receiving second signals from the ranging device 100B during a predetermined period, causing the ODM 140 to receive second signals of three or more different frequencies at different timings from the ranging device 100B. Therefore, even when the period for performing the transmission process and the reception process is limited, it is possible to reliably obtain the relationship between the frequency and the round-trip phase, enabling accurate ranging.

[0121] Furthermore, since the phase acquisition unit 173 acquires the multiple first phases from the phase data included in the multiple second signals received by the ODM 140 by repeatedly performing the reception process, the first phase measured by the phase measurement unit 174 of the ranging device 100B at the time of reception of the first signal can be easily and reliably obtained. As a result, accurate ranging can be performed.

[0122] Furthermore, the signal strength acquisition unit 175 acquires, as the signal strengths of the plurality of signal pairs, the first signal strengths when the plurality of first signals are received by the ranging device 100B, or the second reception strengths when the plurality of second signals are received by repeatedly performing reception processing by the ODM 140. This allows the round-trip phase to be calculated using the phase at the time of signal reception, enabling more accurate ranging.

[0123] Furthermore, the signal strength acquisition unit 175 acquires the first signal strength from signal strength data included in the multiple second signals received by the ODM 140 through repeated reception processing. The first signal strength when the first signal is received by the ranging device 100B 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, allowing for more accurate ranging. Note that the ranging device 100B may have the signal strength acquisition unit 175, or the second signal strength may be written in the first signal transmitted by the ranging device 100A, and the signal strength acquisition unit 175 of the ranging device 100B may acquire the second signal strength.

[0124] The distance measuring unit 179 further includes a correction unit 178 that corrects, for each of the N round trip phases, a change in the round trip phase due to relative movement with the distance measuring device 100B, and measures the distance to the distance measuring device 100B based on the N round trip phases corrected by the correction unit 178 and the multiple frequencies. This makes it possible to correct the influence of the Doppler effect due to relative movement with the distance measuring device 100B, thereby enabling more accurate distance measurement.

[0125] The transmission / 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, the round-trip phase calculation unit 176 calculates multiple round-trip phases for each of the N signal pairs for each of the multiple frequencies, and the correction unit 178 corrects changes in the round-trip phase due to relative movement with the ranging device 100B for each of the N signal pairs using differences between the multiple round-trip phases calculated for each of the multiple frequencies by the round-trip phase calculation unit 176. Based on the differences between the multiple round-trip phases, the influence of the Doppler effect can be corrected in accordance with changes in the relative movement speed with the ranging device 100B, allowing for more accurate ranging.

[0126] The correction unit 178 calculates the relative velocity with respect to the ranging device 100B from the differences between the multiple round-trip phases calculated for each of the N signal pairs, and corrects the N round-trip phases based on the relative velocity and the time difference at which each signal pair was obtained, so that 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. Therefore, the N round-trip phases and N frequencies calculated in an intermittent period such as a continuous wave transmission period in BLE (registered trademark) can be aligned on a straight line, and accurate ranging can be performed even in a situation where the acquisition of the N round-trip phases and the N frequencies is divided into multiple intermittent periods.

[0127] The predetermined period is a continuous wave transmission period, and therefore, accurate ranging can be performed based on N round trip phases and N frequencies obtained in multiple intermittent continuous wave transmission periods in BLE (registered trademark).

[0128] The continuous wave transmission period is 2.5 milliseconds, so accurate ranging can be performed based on N round-trip phases and N frequencies obtained in multiple intermittent periods of 2.5 milliseconds in BLE (registered trademark).

[0129] The predetermined threshold is a threshold that can exclude one or more signal pairs whose signal strength has decreased due to multipath, thereby eliminating the influence of multipath and enabling accurate distance measurement.

[0130] The above describes a distance measuring device according to an exemplary embodiment of the present invention, but the present invention is not limited to the specifically disclosed embodiment, and various modifications and changes are possible without departing from the scope of the claims.

[0131] This 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.

[0132] 10 Vehicle 20 Smart key 100A, 100B Distance measuring device 100R Radio device 110 PA 120 LNA 130 OM (an example of a transmitter) 140 ODM (an example of a receiver) 150 VCO 155 PLL 160 Codec processing unit 170 Control device 170A Main control unit 171 Transmission / reception control unit 172 Switching unit 173 Phase acquisition unit 174 Phase measurement unit 175 Signal strength acquisition unit 176 Round-trip phase calculation unit 177 Extraction unit 178 Correction unit 179 Distance measuring unit 170M Memory

Claims

1. A transmitter for transmitting 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 acquisition unit that acquires a plurality of first phases when the plurality of first signals transmitted by the transmission unit to the other device at three or more types of frequencies at different timings are received by the other device; a phase measurement unit that measures a plurality of second phases when the receiving unit receives the second signal at the three or more frequencies from the other device at different timings; a signal strength acquisition unit that acquires signal strengths of a plurality of signal pairs, each of which is a plurality of the first signals and a plurality of the second signals and has the same frequency; a round-trip phase calculation unit that calculates a round-trip phase for the plurality of signal pairs 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 that extracts, from the plurality of signal pairs, N signal pairs corresponding to N (N is an integer of 2 or more) signal strengths excluding one or more signal strengths that are less than a predetermined threshold value among the signal strengths of the plurality of signal pairs; a distance measuring unit that measures a distance to the other device based on the N round trip phases and the plurality of frequencies; A transmission / reception control unit that controls transmission and reception; a correction unit that corrects a change in the round-trip phase due to a relative movement with respect to the other device for each of the N round-trip phases; Including, The transmission / reception 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, and causing the transmitting unit to transmit the first signals of the three or more types of frequencies to the other device at different timings; causing the receiving unit to repeatedly perform a receiving process for receiving the second signal from the other device during the predetermined period, and causing the receiving unit to receive the second signals of the three or more types of frequencies from the other device at different timings; 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 multiple frequencies.

2. The distance measuring device according to claim 1 , wherein the extraction unit extracts N signal pairs from the plurality of signal pairs, excluding 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 the phase acquisition section acquires the first phases from phase data included in the second signals received by the receiver section repeatedly performing the reception process.

4. 2. The distance measuring device of claim 1, wherein the signal strength acquisition unit acquires, as the signal strength for a plurality of signal pairs, a first signal strength when a plurality of the first signals are received by the other device, or a second reception strength when a plurality of the second signals are received by the receiving unit by repeatedly performing the reception processing.

5. 5. The ranging device of claim 4, wherein the signal strength acquisition unit acquires the first signal strength from signal strength data contained in the multiple second signals received by the receiving unit by repeatedly performing the receiving process, or acquires the second signal strength from signal strength data contained in the multiple first signals received by the receiving unit by repeatedly performing the receiving process.

6. the transmission / reception control unit causes the transmitting unit to transmit the first signal a plurality of times for each of the plurality of frequencies and causes the receiving unit to receive the second signal a plurality of times for each of the plurality of frequencies; the round-trip phase calculation unit calculates a plurality of round-trip phases for each of the N signal pairs at each of the plurality of frequencies; 2. The distance measuring device according to claim 1, wherein the correction unit corrects a change in round-trip phase due to relative movement with the other device for each of the N signal pairs by using differences between the multiple round-trip phases calculated for each of the multiple frequencies by the round-trip phase calculation unit.

7. The correction unit is calculating a relative velocity with respect to the other device from a plurality of differences in the round-trip phases calculated for each of the N signal pairs; 7. The distance measuring device of claim 6, wherein the N round trip phases are corrected based on the relative velocity and the time difference at which each signal pair is obtained, so that 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.

8. The distance measuring device according to claim 1 , wherein the predetermined period is a continuous wave transmission period.

9. 9. The ranging device of claim 8, wherein the continuous wave transmission period is 2.5 milliseconds.

10. The distance measuring device according to claim 1 , wherein the predetermined threshold is a threshold capable of excluding one or more of the signal pairs whose signal strength has decreased due to multipath.