Distance measurement device

Abstract

Provided is a distance measurement device that is able to select a distance measurement based on a phase difference and a distance measurement based on a frequency spectrum, in accordance with the conditions of signals transmitted and received with a communication device.　This distance measurement device includes: a first distance measuring unit that carries out distance measurement according to a first distance measurement format based on the phase differences of signals received from a transmitting device, and outputs a first distance; a second distance measuring unit that carries out distance measurement according to a second distance measurement format based on the frequency spectra of the signals received from the transmitting device, and outputs a second distance; and a selecting unit that selects the first distance or the second distance on the basis of the linearity, etc., of the frequency spectra or the phases of the signals received from the transmitting device.

Description

distance measuring device

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

[0002] There have been distance measuring devices that measure distance based on the phase difference of signals of multiple frequencies received from a transmitting device (see, for example, Patent Document 1). There are also distance measuring devices that perform a Fourier transform of the signals received from the transmitting device and measure distance based on the frequency spectrum (see, for example, Patent Document 2).

[0003] JP 2018-197697 A JP 09-152478 A

[0004] Incidentally, whether ranging based on phase difference or ranging based on frequency spectrum is more suitable depends on the condition of the signal received from the transmitting device (communication device), but no one method is used depending on the condition.

[0005] Therefore, an object of the present invention is to provide a distance measuring device that can select distance measurement based on phase difference or distance measurement based on frequency spectrum depending on the status of signals transmitted and received from a communication device.

[0006] A ranging device according to an embodiment of the present invention includes a first ranging unit that performs ranging using a first ranging method based on the phase difference of a signal received from a transmitting device and outputs a first distance, a second ranging unit that performs ranging using a second ranging method based on the frequency spectrum of the signal received from the transmitting device and outputs a second distance, and a selection unit that selects the first distance or the second distance based on the frequency spectral distribution of the signal received from the transmitting device.

[0007] It is possible to provide a distance measuring device that can select distance measurement based on phase difference or distance measurement based on frequency spectrum depending on the status of signals transmitted and received from a communication device.

[0008] 1 is a diagram showing a distance measuring device 100 of an embodiment. FIG. 2 is a task diagram showing processing in a smartphone 50 and a distance measuring device 100. FIG. 3 is a diagram explaining distance measurement by a first distance measuring unit 132. FIG. 4 is a diagram explaining distance measurement by a first distance measuring unit 132. FIG. 5 is a diagram explaining distance measurement by a second distance measuring unit 133. FIG. 6 is a diagram showing an example of a frequency spectrum after FFT is performed by the second distance measuring unit 133. FIG. 7 is a diagram explaining items checked by a selector 134 to determine that the environment is multipath. FIG. 8 is a flowchart showing selection processing performed by the selector 134. FIG. 9 is a flowchart showing selection processing of a modified example performed by the selector 134. FIG. 10 is a flowchart showing selection processing of a modified example performed by the selector 134.

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

[0010] 1 is a diagram showing a distance measuring device 100 according to an embodiment. In addition to the distance measuring device 100, Fig. 1 also shows a smartphone 50. The smartphone 50 is an example of a communication device that transmits and receives signals, and the distance measuring device 100 calculates the distance from the distance measuring device 100 to the smartphone 50 based on signals transmitted and received from the smartphone 50 (performs distance measurement).

[0011] The ranging device 100 includes an antenna 110, a communication unit 120, and an MMC (Micro Computer) 130. The antenna 110 is connected to the communication unit 120 and receives a signal transmitted from the smartphone 50. Note that although a configuration in which the ranging device 100 includes one antenna 110 will be described here, the ranging device 100 may include multiple antennas 110.

[0012] The communication unit 120 includes an analog front end (AFE), an analog to digital (AD) converter, and the like, and performs signal processing such as AD conversion on the signal received by the antenna 110 from the smartphone 50 and outputs the signal to the MMC 130 .

[0013] The MMC 130 includes a transmission / reception processing unit 131, a first distance measurement unit 132, a second distance measurement unit 133, a selection unit 134, and a memory 135. The MMC 130 is realized by, for example, a microcomputer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), an internal bus, etc. The transmission / reception processing unit 131, the first distance measurement unit 132, the second distance measurement unit 133, and the selection unit 134 are functional blocks representing the functions of a program executed by the MMC 130. The memory 135 is a functional representation of the memory of the MMC 130.

[0014] The transmission / reception processing unit 131 transmits and receives signals to and from the smartphone 50 in order to acquire data such as phase difference and frequency components required for the first distance measurement unit 132 and the second distance measurement unit 133 to perform distance measurement.

[0015] The first ranging unit 132 and the second ranging unit 133 perform ranging using a ToA (Time Of Arrival) method. The first ranging unit 132 performs ranging using a first ranging method based on the phase difference of a signal received from the smartphone 50, and outputs a first distance. The second ranging unit 133 performs ranging using a second ranging method based on the frequency spectrum of a signal received from the smartphone 50, and outputs a second distance. TOA is a ranging method also known as TOF (Time Of Flight).

[0016] The selection unit 134 selects the first distance output by the first distance measuring unit 132 or the second distance output by the second distance measuring unit 133 depending on the state of the radio waves received by the antenna 110. The selection method will be described later with reference to FIG. 8 .

[0017] The memory 135 stores programs and data necessary for the transmission / reception processing unit 131 to execute processing for transmitting and receiving signals, programs and data necessary for the first ranging unit 132 and the second ranging unit 133 to execute processing for performing distance measurement, and programs and data necessary for the selection unit 134 to execute processing for selecting the first distance or the second distance.

[0018] 2 is a task diagram showing the processing in the smartphone 50 and the ranging device 100. First, in (1), in order to synchronize the smartphone 50 and the ranging device 100, the smartphone 50 transmits a synchronization CW (Continuous Wave), and the ranging device 100 receives the synchronization CW. In the ranging device 100, the transmission / reception processing unit 131 performs reception processing.

[0019] Next, in (2), the smartphone 50 and the ranging device 100 alternately transmit CW and receive IQ data while hopping among 64 frequencies. In the ranging device 100, the transmission / reception processing unit 131 performs the transmission / reception processing. As an example, 64 channels are randomly hopped among 160 channels in 0.5 MHz increments from 2.4 to 2.48 GHz.

[0020] Next, in (3), the smartphone 50 transmits the IQ data and phases for 64 frequencies to the distance measuring device 100, which receives the data. In the distance measuring device 100, the transmission / reception processing unit 131 performs reception processing.

[0021] Finally, in (4), the ranging device 100 combines the phase of the smartphone 50 and the phase of the ranging device 100, performs ToA calculation to measure the distance (calculate the distance) using two ranging methods, the first ranging method and the second ranging method, and selects the distance calculated using the ranging method that is appropriate for the situation. The process of (4) is performed by the first ranging unit 132, the second ranging unit 133, and the selection unit 134 in the ranging device 100.

[0022] 3 is a diagram for explaining distance measurement by the first distance measurement unit 132. Distance measurement by the first distance measurement unit 132 is particularly effective when the signal strength due to the direct path is high and the signal strength due to the multipath is low.

[0023] 3A and 3B, the phase in which the smartphone 50 receives the CW transmitted from the ranging device 100 is θa, and the phase in which the smartphone 50 receives the CW transmitted from the ranging device 100 is θb. That is, the phase difference between the phase in which the smartphone 50 receives the CW from the ranging device 100 and the phase in which the smartphone 50 receives the CW is θa, and the phase difference between the phase in which the smartphone 50 transmits the CW from the ranging device 100 and the phase in which the smartphone 50 receives the CW is θb. The phase difference θa corresponds to time ta, and the phase difference θb corresponds to time tb.

[0024] The distance between the ranging device 100 and the smartphone 50 is defined as L, and the sum of the phase θa when transmitted from the ranging device 100 and received by the smartphone 50 and the phase θb ​​when transmitted from the smartphone 50 and received by the ranging device 100 is defined as the round-trip phase θsum (= (θa + θb) × n). The phase difference θa corresponds to time ta, and the phase difference θb corresponds to time tb. n indicates the number of CW waves (wavelengths) that travel back and forth between the ranging device 100 and the smartphone 50.

[0025] Here, assuming that the speed of radio waves is C, the frequency of radio waves is f, and the period of radio waves is T (=1 / f), the following (1) and (2) hold true.

[0026]

[0027]

[0028] Since (θa+θb)×n=θsum, equation (3) can be obtained from equations (1) and (2).

[0029]

[0030] By transforming equation (3) and rearranging it with θsum, equation (4) is obtained.

[0031]

[0032] By performing round-trip communication between the ranging device 100 and the smartphone 50 at frequencies f1 and f2, calculating the round-trip phase difference θsum1 at frequency f1 and the round-trip phase difference θsum2 at frequency f2, and using the difference between θsum1 and θsum2, the relationship between equations (5A) and (5B) can be obtained.

[0033]

[0034] From equations (5A) and (5B), the distance L can be calculated as in equation (6).

[0035]

[0036] When measuring distance using two frequencies, the distance L is as expressed by equation (6). However, since even a small phase error results in a distance error and robustness is low, when measuring distance using multiple (M) frequencies, the result shown in Figure 3(C) is obtained. The graph shown in Figure 3(C) represents frequency f on the horizontal axis and phase θa+θb when the radio wave travels back and forth on the vertical axis. Here, Δθsum / Δf in equation (6) represents the slope of the line, so the distance L can be expressed as the following equation (7).

[0037]

[0038] In this way, the distance L is proportional to the inclination. The first distance measurement unit 132 measures the distance based on equation (6).

[0039] Distance measurement by the first distance measurement unit 132 is a method of measuring distance from a phase difference, and since the phase of the round trip between the distance measurement device 100 and the smartphone 50 is obtained at each frequency, if there is a lot of noise due to the influence of multipath, errors are likely to occur when the phases (phase differences) at all frequencies are added up. Also, since a slope is obtained, calculations tend to be easier for short distances than for long distances.

[0040] 3C is a value of 360° or more for the sake of convenience in explaining the calculation principle, but when the MMC 130 actually receives radio waves, wave numbers are not included, so θsum takes on values ​​between 0° and 360°, as shown in FIG. 4. FIG. 4 is a diagram for explaining distance measurement by the first distance measurement unit 132.

[0041] As shown in FIG. 4A, θsum takes values ​​from 0° to 360°, and the data exhibits characteristics that repeatedly change in a sawtooth waveform. The data in FIG. 4A is converted into a linear data as shown in FIG. 4B to calculate the distance L. This conversion process becomes more difficult as the distance increases. This is because the linearity of the phase is easy to see with data from a short distance (e.g., 5 m) such as in FIG. 4C, and the addition process for distances of 360° or more is easy. However, as can be seen from the data in FIG. 4D for 15 m and the data in FIG. 4E for 60 m, as the distance increases, the slope increases, making the linearity of the phase less visible and the addition process more difficult.

[0042] For this reason, ranging by the first ranging unit 132 is more suitable for short distances than long distances, and is more suitable for direct path environments than multipath environments. Hereinafter, ranging by the first ranging unit 132 will be referred to as a direct path ranging method. The direct path ranging method is an example of the first ranging method.

[0043] 5 is a diagram illustrating distance measurement by the second distance measurement unit 133. Distance measurement by the second distance measurement unit 133 can be used even when the signal strength due to multipath is high and the signal strength due to direct path is low, and calculation is relatively easy even when the smartphone 50 is relatively far from the distance measurement device 100.

[0044] The second distance measurement unit 133 transforms the IQ data for all 64 frequencies using an FFT (Fast Fourier Transform) function. As a result, an example frequency spectrum result shown in Fig. 5 is obtained. In Fig. 5, the horizontal axis represents frequency f, which corresponds to distance, and the vertical axis represents signal strength.

[0045] As shown in Figure 5, the second distance measurement unit 133 extracts the lowest frequency with sufficiently high signal strength as the frequency that gives the optimal peak from the result of the FFT transformation. This is because the direct path signal has a shorter radio wave path than the multipath signal, and therefore, when FFT transformed, the direct path signal always has a lower frequency than the multipath signal. The distance to the smartphone 50 is determined by converting the selected frequency into distance.

[0046] More specifically, the number of sampling buffers performing the FFT is set to N=256, the frequency interval freq_step is set to 0.5 MHz, and 64 channels are randomly hopped from 160 channels in 0.5 MHz increments from 2.4 to 2.48 GHz. Alternatively, as an example, the number of sampling buffers performing the FFT may be set to N=256, the frequency interval freq_step is set to 2 MHz, and 40 channels are hopped at 2 MHz intervals. Of the 256 sampling buffers, IQ data is set in 40 of them. When the FFT is performed, the results shown in Figure 5 are obtained.

[0047] From the result of the FFT, the distance L can be calculated using the following equation (8).

[0048]

[0049] The frequency fb at which the optimum peak is obtained is the frequency at which a spectrum is obtained at the lowest frequency with sufficient magnitude. The horizontal axis of the FFT result takes discrete values ​​of 0, 1, 2, ..., 127 (256 / 2-1), but the frequency component of frequency fb is determined by interpolation from the shape of the FFT waveform, so it is a decimal.

[0050] The distance measurement by the second distance measurement unit 133 is based on the frequency components of the signal received from the smartphone 50, and includes conversion processing using an FFT function, so calculation is relatively easy even when the distance is long.

[0051] Therefore, distance measurement by the second distance measurement unit 133 can be used even when there is a large influence of multipath and a small influence of direct path, and calculation is relatively easy even when the smartphone 50 is relatively far from the distance measurement device 100. Hereinafter, distance measurement by the second distance measurement unit 133 will be referred to as a multipath distance measurement method. The multipath distance measurement method is an example of the second distance measurement method. However, calculation may become difficult when there is a large amount of noise due to multipath.

[0052] <Selection Process by Selector 134> Fig. 6 is a diagram showing an example of a frequency spectrum after FFT is performed by the second ranging unit 133. Here, using Fig. 6, a process of determining whether distance calculation is possible and whether there is multipath based on a signal received from the smartphone 50 will be described. In Fig. 6, the horizontal axis represents frequency, and the vertical axis represents amplitude (height) of the frequency spectrum.

[0053] The selection unit 134 determines whether distance calculation is possible using a threshold value of the signal strength. For example, as shown in (1) of Fig. 6, when the signal strength is less than the threshold value E, the selection unit 134 determines that distance calculation is not possible, and when the signal strength is equal to or greater than the threshold value E, as shown in (2), (3), (4), and (5) of Fig. 6, the selection unit 134 determines that distance calculation is possible.

[0054] Furthermore, as shown in (2) and (3) of FIG. 6, when there is one peak with sufficiently large signal strength and the signal strength is equal to or greater than a threshold E, the selection unit 134 determines that the environment is one in which the influence of multipath is small and the influence of direct path components is large. Furthermore, as shown in (4) of FIG. 6, when there are multiple peaks with signal strength equal to or greater than a threshold, the selection unit 134 determines that the environment is one in which the influence of multipath is large. Furthermore, the selection unit 134 also determines that the environment is one in which the influence of multipath is large when multiple peaks overlap to form a single peak, as shown in (5) of FIG. 6. However, since it may not be easy to determine whether the signal is a direct path or a multipath, the selection unit 134 makes a determination based on each part of the signal, as shown in FIG. 7.

[0055] 7 is a diagram illustrating the items that the selector 134 checks to determine that the environment is a multipath environment. In FIG. 7, the horizontal axis represents frequency, and the vertical axis represents the amplitude (height) of the frequency spectrum. The number of peaks in the frequency spectrum shown as an example in FIG. 7 is three.

[0056] As shown in FIG. 7, the selection unit 134 extracts the peak height, peak width, peak area, and number of peaks for the highest peak, and uses these to determine whether the environment is a multipath environment or a direct path environment in step S2 of FIG. 8, which will be described later. The peak height is the height from the lowest point to the highest point of the highest peak. The peak width is the amplitude in the horizontal direction at the level of the peak height threshold E. The peak area is the area of ​​the part of the highest peak that is equal to or greater than threshold E. The number of peaks is the number of peaks that are equal to or greater than peak height threshold E.

[0057] The selection unit 134 determines whether or not the environment is a multipath environment as follows: When there is a peak equal to or greater than the peak height threshold E, and for the highest peak among one or more extracted peaks, if the peak width at the peak height threshold E is equal to or less than the threshold D in the bandwidth direction (horizontal axis direction in FIG. 7 ), if the peak area is equal to or greater than the area threshold S, or if the peak height is equal to or greater than the peak height threshold h, the selection unit 134 determines that the environment is a direct path environment, not a multipath environment.

[0058] The selector 134 determines that the environment is multipath when there are multiple peaks equal to or greater than the peak height threshold E, when the peak width at the peak height threshold E is greater than a threshold D in the bandwidth direction (horizontal axis direction in FIG. 7 ), when the peak area is less than the area threshold S, or when the peak height is less than the peak height threshold h. Note that the specific process by which the selector 134 selects the distance measured by the direct path ranging method (first distance) or the distance measured by the multipath ranging method (second distance) will be described below with reference to the flowchart in FIG. 8 .

[0059] 8 is a flowchart showing the selection process executed by the selection unit 134. It is assumed that the first distance measurement unit 132 and the second distance measurement unit 133 have measured the first distance and the second distance from the distance measurement device 100 to the smartphone 50 by the above-described distance measurement method.

[0060] When the process starts, the selection unit 134 determines whether distance calculation is possible (step S1). For example, if the distance is less than the threshold E as shown in (1) of Fig. 6, the selection unit 134 determines that distance calculation is not possible (S1: NO), and proceeds to step S10, where it determines that an error has occurred (a state in which distance calculation is not possible) (step S10).

[0061] On the other hand, if the selection unit 134 determines in step S1 that distance calculation is possible (S1: YES), the flow proceeds to step S1A. For example, as shown in (2), (3), (4), and (5) of FIG. 6, when the signal strength is equal to or greater than the threshold E, the selection unit 134 determines that distance calculation is possible (S1: YES) and proceeds to step S2 via steps S1A and S1B. Specifically, the process is as follows.

[0062] The first distance measurement unit 132 performs distance measurement using the direct path distance measurement method based on equation (6) to obtain the distance L (first distance) (step S1A).

[0063] The second distance measurement unit 133 performs distance measurement using the multipath distance measurement method based on equation (8) to obtain the distance L (second distance) (step S1B).

[0064] The selection unit 134 performs FFT on the signal received from the smartphone 50 and determines whether the environment is a multipath environment based on the obtained frequency spectrum (step S2). The determination of whether the environment is a multipath environment is to determine whether the environment is a multipath environment (S2: YES) or a direct path environment (S2: NO). The frequency spectrum of the signal determines whether the environment is a direct path environment as shown in (2) and (3) of Figure 6, or a multipath environment as shown in (4) and (5) of Figure 6.

[0065] In step S2, it is determined that the environment is a multipath environment (S2: YES) when it is determined that the situation corresponds to (4) or (5) in Figure 6, and as explained using Figure 7, when there are multiple peaks equal to or greater than the peak height threshold E, the peak width at the peak height threshold E is greater than the threshold D in the bandwidth direction (the horizontal axis direction in Figure 7), the peak area is less than the area threshold S, or the peak height is less than the peak height threshold h.

[0066] If the selection unit 134 determines in step S2 that the environment is a multipath environment (S2: YES), the selection unit 134 selects the second distance calculated by the second distance measurement unit 133 using the multipath distance measurement method (step S3). That is, the multipath distance measurement method is adopted.

[0067] If the selection unit 134 determines in step S2 that the environment is not a multipath environment (S2: NO), the environment is a direct path environment, and therefore it is possible to select either the result of the direct path ranging method or the result of the multipath ranging method. Therefore, in order to determine whether the direct path ranging method can be selected, the selection unit 134 determines whether the degree of linearity of the phase of the signal received from the smartphone 50 is equal to or greater than a predetermined degree (step S4).

[0068] The linearity of the phase of the signal received from the smartphone 50 is represented, for example, by a correlation coefficient that indicates the correlation between frequency and phase. Whether the linearity of the phase of the signal received from the smartphone 50 is equal to or greater than a predetermined degree is determined by calculating the correlation coefficient that indicates the correlation between frequency and phase for the CW phase obtained by hopping to 64 frequencies.

[0069] The correlation coefficient, which represents the correlation between frequency and phase, can be expressed as the absolute value of Pearson's correlation coefficient, for example. When the phase at each frequency is on a straight line, the correlation is high (the correlation coefficient is large), and when the phase at each frequency varies, the correlation is low (the correlation coefficient is small). The correlation coefficient is expressed as the slope of the line that represents the correlation between frequency and phase.

[0070] The closer the absolute value of the correlation coefficient is to 1, the stronger the correlation (higher the degree of linearity), and the closer it is to 0, the weaker the correlation (lower the degree of linearity). When the absolute value of the correlation coefficient is close to 1, it is suitable for the direct path ranging method. The fact that the absolute value of the correlation coefficient between frequency and phase is close to 1 indicates that the direct path ranging method can measure frequencies from low to high, i.e., from short distances to long distances. Therefore, when the absolute value of the correlation coefficient is close to 1, it is suitable for the direct path ranging method. The direct path ranging method is also suitable for short distance measurements. Therefore, if it is determined in step S2 that the environment is not multipath (S2: NO), the process proceeds to step S4. If the determinations in steps S4, S5, S6, S7, and S9 are all YES, the distance L (first distance) obtained by the direct path ranging method is adopted. In other words, if the environment is basically linear and the distance is short, the direct path ranging method is adopted.

[0071] Furthermore, if the Pearson correlation coefficient (not the absolute value) is positive, this is an abnormal condition in which the final distance obtained by the direct path ranging method will be a negative value, so the direct path ranging method should not be adopted.

[0072] The predetermined degree used for the determination in step S4 may be set to a value close to 1, for example, between 0.9 and 1, and step S4 may determine whether a value that is not an absolute value is a negative value.

[0073] If the selection unit 134 determines in step S4 that the degree of phase linearity of the signal received from the smartphone 50 is less than the predetermined degree (S4: NO), the selection unit 134 causes the flow to proceed to step S3. This is because it is not appropriate to adopt the direct path ranging method. Furthermore, if the Pearson correlation coefficient (a value other than the absolute value) is a positive value, the selection unit 134 also causes the flow to proceed to step S3. As a result, the second distance calculated by the multipath ranging method is selected.

[0074] If the selection unit 134 determines in step S4 that the degree of phase linearity of the signal received from the smartphone 50 is equal to or greater than a predetermined degree (S4: YES), it determines whether the number of valid phase data in a predetermined frequency band is equal to or greater than a predetermined number (step S5), in order to confirm whether the direct path ranging method can be selected.

[0075] The predetermined frequency band is, for example, a Wi-Fi communication frequency band. If the signal received from the smartphone 50 is affected by, for example, Wi-Fi radio waves, the received signal will be absent only in the Wi-Fi communication frequency band, resulting in a state in which phase data is missing or has large variations. If these conditions occur, it will be difficult to properly calculate the distance using the direct path ranging method, so it is best not to adopt the direct path ranging method.

[0076] The predetermined frequency band used in the determination of step S5 may be determined in advance based on the relationship between the frequency band used for communication between the distance measuring device 100 and the smartphone 50 and the frequency band of Wi-Fi or the like that may be present in the vicinity.

[0077] The predetermined number of valid phase data used in the determination in step S5 may be determined in advance by experiment or simulation as the number required to properly calculate the distance using the direct path distance measurement method.

[0078] If the number of valid phase data in the predetermined frequency band is less than the predetermined number (S5: NO) in step S5, the selector 134 proceeds to step S3 because it is not appropriate to adopt the direct path ranging method. As a result, the second distance calculated by the multi-path ranging method is selected.

[0079] If the selection unit 134 determines in step S5 that the number of valid phase data in the predetermined frequency band is equal to or greater than the predetermined number (S5: YES), the selection unit 134 determines whether the second distance measured by the second distance measurement unit 133 is equal to or greater than the predetermined distance (step S6). As described above, the direct path ranging method is more suitable for measuring short distances than long distances. Therefore, the predetermined distance may be set to 30 m, for example, for the determination.

[0080] When the selection unit 134 determines that the second distance measured by the second ranging unit 133 is less than the predetermined distance (S6: NO), it determines whether the difference between the first distance measured by the first ranging unit 132 and the second distance measured by the second ranging unit 133 is less than a second predetermined difference (step S7).

[0081] A small difference between the first distance measured by the first distance measuring unit 132 and the second distance measured by the second distance measuring unit 133 indicates high accuracy of the distance measurements by the first distance measuring unit 132 and the second distance measuring unit 133. If the flow proceeds to step S7 via steps S4 to S6, it means that the conditions more suitable for the direct path distance measuring method than the multi-path distance measuring method are met. Therefore, the difference between the first distance and the second distance determined in step S7 indicates whether the quality of the direct path is high. A small difference between the first distance and the second distance indicates high quality of the direct path, and a large difference between the first distance and the second distance indicates low quality of the direct path.

[0082] If the selector 134 determines that the difference between the first distance and the second distance is less than the second predetermined difference (S7: YES), it selects the first distance output by the first distance measuring unit 132 (step S8). That is, the first distance measured by the direct path distance measuring method is selected. This is because the difference between the first distance and the second distance is smaller than the second predetermined difference and the quality of the direct path is high.

[0083] If the selector 134 determines in step S7 that the difference between the first distance and the second distance is equal to or greater than the second predetermined difference (S7: NO), the flow proceeds to step S3 because the quality of the direct path is low. As a result, the second distance calculated by the multi-path ranging method is selected.

[0084] Furthermore, when the selection unit 134 determines in step S6 that the second distance measured by the second ranging unit 133 is greater than or equal to a predetermined distance (S6: YES), it determines whether the difference between the first distance measured by the first ranging unit 132 and the second distance measured by the second ranging unit 133 is less than a first predetermined difference (step S9).

[0085] If the selector 134 determines in step S9 that the difference between the first distance and the second distance is not less than the first predetermined difference (S9: NO), it causes the flow to proceed to step S3. By proceeding to step S9 via steps S4 to S6, the conditions for favoring the direct path ranging method over the multi-path ranging method are met, but the quality of the direct path is low, making it inappropriate to adopt the direct path ranging method. As a result, the second distance calculated by the multi-path ranging method is selected.

[0086] Here, the first predetermined difference used in the determination of step S9 may be larger than the second predetermined difference used in the determination of step S7. In other words, the second predetermined difference used in the determination of step S7 may be smaller than the first predetermined difference used in the determination of step S9. The process proceeds to step S9 when it is determined in step S6 that the second distance measured by second distance measuring unit 133 is equal to or greater than the predetermined distance (S6: YES), and the process proceeds to step S7 when it is determined in step S6 that the second distance measured by second distance measuring unit 133 is less than the predetermined distance (S6: NO).

[0087] The longer the distance between the distance measuring device 100 and the smartphone 50 (the longer the distance), the smaller the proportion of the distance difference in the total distance, and the shorter the distance between the distance measuring device 100 and the smartphone 50 (the closer the distance), the larger the proportion of the distance difference in the total distance. Therefore, as an example, in order to make the determination at a short distance more stringent, the second predetermined difference used in the determination at step S7 is smaller than the first predetermined difference used in the determination at step S9, and the first predetermined difference used in the determination at step S9 is larger than the second predetermined difference used in the determination at step S7. Note that the first predetermined difference being larger than the second predetermined difference is just an example, and the first predetermined difference may be smaller than the second predetermined difference.

[0088] Furthermore, if the selector 134 determines in step S9 that the difference between the first distance and the second distance is less than the first predetermined difference (S9: Yes), it causes the flow to proceed to step S8. This is because the quality of the direct path is high despite the long distance. As a result, the first distance calculated by the direct path ranging method is selected.

[0089] As described above, the selection unit 134 selects the first distance or the second distance based on the result of FFT processing of the IQ data transmitted and received between the smartphone 50 and the distance measuring device 100, the linearity of the phase, and the like.

[0090] Therefore, it is possible to provide a ranging device 100 that can select between a first ranging method based on phase difference and a second ranging method based on the frequency components of the FFT calculation results, depending on the conditions of the signals transmitted and received from the smartphone 50.

[0091] Furthermore, the selection unit 134 determines whether the environment is a multipath environment based on the number of peaks, the peak height, or the peak area in the frequency spectrum after FFT by the second ranging unit 133, and selects the second distance calculated by the multipath ranging method if it is determined to be a multipath environment. This makes it possible to provide a ranging device 100 that appropriately selects the second distance calculated by the multipath ranging method when the environment is a multipath environment.

[0092] Furthermore, when there are multiple peaks equal to or greater than the peak height threshold in the frequency spectrum after FFT is performed by the second ranging unit 133, the selecting unit 134 determines that the environment is multipath if the peak width at the peak height threshold E is greater than the threshold in the bandwidth direction, if the peak area is less than the area threshold S, or if the peak height is less than the peak height threshold h. Therefore, it is possible to provide a ranging device 100 that can reliably determine whether the environment is multipath using the peak height threshold E, the peak area threshold S, and the peak height threshold h, and that, if the environment is multipath, appropriately selects the second distance measured by the multipath ranging method.

[0093] Furthermore, even if the number of multiple peaks in the frequency spectrum after FFT by the second ranging unit 133 is not equal to or greater than a predetermined number, if the degree of linearity of the phase of the signal received from the smartphone 50 is less than a predetermined degree, the selecting unit 134 selects the second distance calculated by the multipath ranging method. When the degree of linearity is less than the predetermined degree, the absolute value of the correlation coefficient is small and the signal is not suitable for the direct path ranging method. Therefore, it is possible to provide a ranging device 100 that appropriately selects the second distance calculated by the multipath ranging method. Even if it is determined in step S2 that the environment is not multipath, if the linearity between frequency and phase is less than the predetermined degree in step S4, this indicates that the signal is not suitable for measurement by the direct path ranging method in some or all frequency bands from low to high frequencies. For this reason, if it is determined in step S2 that the environment is not a multipath environment (S2: NO), and then step S4 is performed, and if any of the determinations in steps S4, S5, S6, S7, and S9 is NO, it is determined that the environment is a multipath environment, and the multipath ranging method is adopted. Basically, if there is no linearity or the distance is long, the multipath ranging method is adopted.

[0094] Furthermore, even if the degree of phase linearity of the signal received from the smartphone 50 is equal to or greater than a predetermined degree, if the number of valid phase data in a predetermined frequency band is less than a predetermined number, the selector 134 selects the second distance calculated by the multi-path ranging method. For example, when there is no received signal only in the Wi-Fi communication frequency band and phase data is missing or has large variations, it becomes difficult to properly calculate the distance using the direct-path ranging method. Therefore, it is possible to provide a ranging device 100 that selects the second distance calculated by the multi-path ranging method that is more suitable for such a situation.

[0095] Furthermore, even if the number of valid phase data in a predetermined frequency band is equal to or greater than a predetermined number, if the second distance measured by the second distance measuring unit 133 is equal to or greater than a predetermined distance, the selector 134 selects the second distance calculated by the multi-path ranging method. Since the direct path ranging method is more suitable for measuring short distances than long distances, it is possible to provide a ranging device 100 that selects the multi-path ranging method that can also handle long distances.

[0096] Furthermore, even if the second distance measured by the second distance measuring unit is equal to or greater than a predetermined distance, if the difference between the first distance measured by the first distance measuring unit and the second distance measured by the second distance measuring unit is equal to or greater than a first predetermined difference, the selection unit 134 selects the second distance calculated using the multi-path ranging method. Since the quality of the direct path is low and it is not appropriate to adopt the direct path ranging method, it is possible to provide a ranging device 100 that selects the multi-path ranging method when the quality of the direct path is low.

[0097] Furthermore, the selector 134 selects the second distance calculated by the multi-path ranging method when the number of valid phase data in the predetermined frequency band is equal to or greater than a predetermined number and the difference between the first distance calculated by the first ranging method and the second distance calculated by the second ranging method is equal to or greater than a second predetermined difference, even if the second distance calculated by the second ranging method is less than the predetermined distance. Since the direct path quality is low and it is not appropriate to adopt the direct path ranging method, it is possible to provide a ranging device 100 that selects the multi-path ranging method when the direct path quality is low.

[0098] Furthermore, the selection unit 134 selects the first distance calculated by the direct path ranging method when the number of valid phase data in the predetermined frequency band is equal to or greater than a predetermined number, the second distance measured by the second ranging unit is less than a predetermined distance, and the difference between the first distance measured by the first ranging unit and the second distance measured by the second ranging unit is less than a second predetermined difference. It is possible to provide a ranging device 100 that selects the first distance calculated by the direct path ranging method when multiple conditions (steps S2 to S6) for selecting the direct path ranging method are satisfied and the quality of the direct path is high.

[0099] Furthermore, the first predetermined difference is greater than the second predetermined difference. The longer the distance between the distance measuring device 100 and the smartphone 50 (the longer the distance), the smaller the proportion of the distance difference in the total distance, and the shorter the distance between the distance measuring device 100 and the smartphone 50 (the shorter the distance), the larger the proportion of the distance difference in the total distance. Therefore, by making the first predetermined difference greater than the second predetermined difference, it is possible to make the conditions for determination at short distances stricter.

[0100] <Selection Process of Modified Example> FIGS. 9A and 9B are flowcharts showing the selection process of a modified example executed by the selection unit 134. FIG.

[0101] The flowchart shown in Fig. 9A represents a process in which step S5 has been deleted from the flowchart shown in Fig. 8. In Fig. 9A, if the selection unit 134 determines in step S2 that the environment is a direct path environment rather than a multipath environment (S2: NO), and determines in step S4 that the degree of phase linearity of the signal received from the smartphone 50 is equal to or greater than a predetermined degree (S4: YES), the selection unit 134 proceeds to step S6 and determines whether the second distance measured by the second ranging unit 133 is equal to or greater than a predetermined distance (step S6). In this way, if the selection unit 134 determines that the environment is a direct path environment (S2: NO), the selection unit 134 may proceed from step S4 to step S6 without performing step S5 shown in Fig. 8.

[0102] 9B represents a process in which step S4 has been deleted from the flowchart of FIG. 8 . In FIG. 9B , if the selection unit 134 determines in step S2 that the environment is a direct path environment rather than a multipath environment (S2: NO), the flow proceeds to step S5, where it determines whether the number of valid phase data in the predetermined frequency band is equal to or greater than a predetermined number (step S5). If the selection unit 134 determines that the number of valid phase data in the predetermined frequency band is equal to or greater than a predetermined number (S5: YES), it determines whether the second distance measured by the second ranging unit 133 is equal to or greater than a predetermined distance (step S6). In this way, if the selection unit 134 determines that the environment is a direct path environment (S2: NO), it may proceed from step S2 to step S5 without performing step S4 shown in FIG. 8 .

[0103] 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.

[0104] This international application claims priority based on Japanese Patent Application No. 2022-098457, filed on June 17, 2022, the entire contents of which are incorporated herein by reference.

[0105] 50 Smartphone 100 Distance measuring device 110 Antenna 120 Communication unit 130 MMC 131 Transmission / reception processing unit 132 First distance measuring unit 133 Second distance measuring unit 134 Selection unit 135 Memory

Claims

1. a first distance measuring unit that performs distance measurement by a first distance measuring method based on a phase difference between a signal transmitted to and received from the communication device, and outputs a first distance; a second distance measuring unit that performs distance measurement by a second distance measuring method based on a frequency spectrum of the signal transmitted to and received from the communication device, and outputs a second distance; a selection unit that selects the first distance or the second distance based on a frequency spectrum of the signal transmitted to and received from the communication device; Including, The selection unit is Determining whether the signal is in a multipath environment based on the number of peaks, the height of the peaks, or the area of ​​the peaks in the frequency spectrum of the signal; When it is determined that the environment is a multipath environment, the second distance is selected; When it is determined that the environment is not a multipath environment and the number of valid phase data in a predetermined frequency band is equal to or greater than a predetermined number, the selection unit determines whether the second distance measured by the second ranging unit is equal to or greater than a predetermined distance, or when it is determined that the environment is not a multipath environment and the degree of linearity of the phase of the signal transmitted to and received from the communication device is equal to or greater than a predetermined degree, the selection unit determines whether the second distance measured by the second ranging unit is equal to or greater than a predetermined distance, A ranging device in which the selection unit selects the second distance measured by the second ranging unit when the difference between the first distance measured by the first ranging unit and the second distance measured by the second ranging unit is equal to or greater than a first predetermined difference, even if the second distance measured by the second ranging unit is equal to or greater than a predetermined distance.

2. 2. The ranging device of claim 1, wherein the selection unit determines that the environment is a multipath environment when there are multiple peaks in the frequency spectrum of the signal that are equal to or greater than the peak height threshold, when a peak width at the peak height threshold is greater than a threshold in a bandwidth direction, when the peak area is less than an area threshold, or when the peak height is less than the peak height threshold.

3. The distance measuring device according to claim 1 , wherein the selection unit selects the second distance when it determines that the environment is not a multipath environment and the degree of phase linearity of the signal transmitted and received from the communication device is less than a predetermined degree.

4. The distance measuring device according to claim 1 , wherein the selection section selects the second distance when the number of valid phase data in a predetermined frequency band is less than a predetermined number.

5. The distance measuring device of claim 1, wherein the selection unit selects the first distance when the second distance measured by the second distance measuring unit is equal to or greater than a predetermined distance and a difference between the first distance measured by the first distance measuring unit and the second distance measured by the second distance measuring unit is less than a first predetermined difference.

6. The distance measuring device of claim 1, wherein the selection unit selects the second distance when the difference between the first distance measured by the first distance measuring unit and the second distance measured by the second distance measuring unit is a second predetermined difference or more, even if the second distance measured by the second distance measuring unit is less than a predetermined distance.

7. The distance measuring device of claim 1 , wherein the selection unit selects the first distance when the second distance measured by the second distance measuring unit is less than a predetermined distance and a difference between the first distance measured by the first distance measuring unit and the second distance measured by the second distance measuring unit is less than a second predetermined difference.

8. the selection unit is configured to select the second distance when a difference between the first distance measured by the first distance measuring unit and the second distance measured by the second distance measuring unit is a first predetermined difference or more even if the second distance measured by the second distance measuring unit is less than the predetermined distance, when a difference between the first distance measured by the first distance measuring unit and the second distance measured by the second distance measuring unit is a second predetermined difference or more, The distance measuring device according to claim 1 , wherein the first predetermined difference is greater than the second predetermined difference.

9. the selection unit is configured to select the first distance when the second distance measured by the second distance measuring unit is equal to or greater than a predetermined distance and a difference between the first distance measured by the first distance measuring unit and the second distance measured by the second distance measuring unit is less than a first predetermined difference, or to select the first distance when the second distance measured by the second distance measuring unit is less than the predetermined distance and a difference between the first distance measured by the first distance measuring unit and the second distance measured by the second distance measuring unit is less than a second predetermined difference, The distance measuring device according to claim 1 , wherein the first predetermined difference is greater than the second predetermined difference.