Distance measuring 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

Technical Field

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

Background Art

[0002] Conventionally, there is a distance measuring device that measures distance based on the phase difference of signals of a plurality of frequencies received from a transmitting device (for example, see Patent Document 1). There is also a distance measuring device that performs Fourier transform on the signal received from the transmitting device and measures distance based on the frequency spectrum (for example, see Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, which of distance measurement based on phase difference and distance measurement based on frequency spectrum is suitable depends on the situation of the signal received from the transmitting device (communication device), but it has not been used properly according to the situation.

[0005] Therefore, an object of the present invention is to provide a distance measuring device capable of selecting distance measurement based on phase difference and distance measurement based on frequency spectrum according to the situation of the signal communicated with the communication device.

Means for Solving the Problems

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

Advantages of the Invention

[0007] It is possible to provide a distance measurement device capable of selecting distance measurement based on a phase difference and distance measurement based on a frequency spectrum according to the situation of a signal transmitted and received by a communication device.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9A

Figure 9B

Embodiments for Carrying Out the Invention

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

[0010] <Embodiment> FIG. 1 is a diagram showing a distance measuring device 100 according to an embodiment. In FIG. 1, in addition to the distance measuring device 100, a smartphone 50 is shown. The smartphone 50 is an example of a communication device that transmits and receives signals, and the distance measuring device 100 obtains the distance from the distance measuring device 100 to the smartphone 50 (performs distance measurement) based on the signals transmitted and received with the smartphone 50.

[0011] The distance measuring 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 signals transmitted from the smartphone 50. Here, a configuration in which the distance measuring device 100 includes one antenna 110 will be described, but the distance measuring device 100 may include a plurality of antennas 110.

[0012] The communication unit 120 includes an AFE (Analog Front End), an AD (Analog to Digital) converter, etc., and performs signal processing such as AD conversion on the signals received by the antenna 110 from the smartphone 50 and outputs them to the MMC 130.

[0013] The MMC 130 has a transmission / reception processing unit 131, a first distance measuring unit 132, a second distance measuring unit 133, a selection unit 134, and a memory 135. The MMC 130 is realized, for example, by a microcomputer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and an internal bus, etc. The transmission / reception processing unit 131, the first distance measuring unit 132, the second distance measuring unit 133, and the selection unit 134 show the functions (functions) of programs executed by the MMC 130 as functional blocks. Also, the memory 135 functionally represents the memory of the MMC 130.

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

[0015] The first distance measurement unit 132 and the second distance measurement unit 133 perform distance measurement in the ToA (Time Of Arrival) format. The first distance measurement unit 132 performs distance measurement by a first distance measurement method based on the phase difference of the signal received from the smartphone 50 and outputs a first distance. The second distance measurement unit 133 performs distance measurement by a second distance measurement method based on the frequency spectrum of the signal received from the smartphone 50 and outputs a second distance. Note that TOA is a distance measurement method also referred to as TOF (Time Of Flight).

[0016] The selection unit 134 selects the first distance output by the first distance measurement unit 132 or the second distance output by the second distance measurement unit 133 according to the state of the radio wave 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 distance measurement unit 132 and the second distance measurement unit 133 to execute processing for performing distance measurement, programs and data necessary for the selection unit 134 to execute processing for selecting the first distance or the second distance, and the like.

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

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

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

[0021] Finally, as (4), the distance measuring device 100 combines the phase on the smartphone 50 side and the phase on the distance measuring device 100 side, performs distance measurement in two methods, the first distance measurement method and the second distance measurement method, by ToA calculation (calculates the distance), and selects the distance calculated by the distance measurement method suitable for the situation. In (4), in the distance measuring device 100, the first distance measurement unit 132, the second distance measurement unit 133, and the selection unit 134 perform the processing.

[0022] <Distance measurement by the first distance measurement unit 132> FIG. 3 is a diagram for explaining distance measurement by the first distance measurement unit 132. The distance measurement by the first distance measurement unit 132 is particularly effective when the signal intensity by the direct path is high and the signal intensity by the multipath is low.

[0023] As shown in FIGS. 3(A) and 3(B), let the phase when the distance measuring device 100 transmits CW and the smartphone 50 receives it be θa, and the phase when the smartphone 50 transmits CW and the distance measuring device 100 receives it be θb. That is, the phase difference between the phase received by the smartphone 50 with respect to the phase transmitted by the distance measuring device 100 is θa, and the phase difference between the phase received by the distance measuring device 100 with respect to the phase transmitted by the smartphone 50 is θb. It is assumed that the phase difference θa corresponds to the time ta, and the phase difference θb corresponds to the time tb.

[0024] Define the distance between the distance measurement device 100 and the smartphone 50 as L, and let the sum of the phase θa when transmitted from the distance measurement device 100 and received by the smartphone 50 and the phase θb when transmitted from the smartphone 50 and received by the distance measurement device 100 be the round-trip phase θsum(=(θa + θb)×n). Assume that the phase difference θa corresponds to the time ta and the phase difference θb corresponds to the time tb. Here, n represents the number of CW waves (wavelengths) that travel back and forth between the distance measurement device 100 and the smartphone 50.

[0025] Here, let the speed of the radio wave be C, the frequency of the radio wave be f, and the period of the radio wave be T(=1 / f). The following (1) and (2) hold.

[0026]

Equation

[0027]

Equation

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

[0029]

Equation

[0030] By transforming Equation (3) and arranging it in terms of θsum, Equation (4) can be obtained.

[0031]

Equation

[0032] Perform two-way communication between the distance measurement device 100 and the smartphone 50 at frequencies f1 and f2, obtain the round-trip phase differences θsum1 at frequency f1 and θsum2 at frequency f2, and utilize the difference between θsum1 and θsum2. Then, the relationships in Equations (5A) and (5B) can be obtained.

[0033]

Number

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

[0035]

Number

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

[0037]

Number

[0038] Thus, the distance L is proportional to the slope. The first distance measurement unit 132 performs distance measurement based on equation (6).

[0039] The distance measurement by such a first distance measurement unit 132 is a method of measuring the distance from the phase difference. In order to obtain the round-trip phase between the distance measurement device 100 and the smartphone 50 at each frequency, when there is a lot of noise due to the influence of multipath, an error is likely to occur when adding the phases (phase differences) at all frequencies. Also, in order to obtain the slope, the calculation is easier for shorter distances than for longer distances.

[0040] The θsum in Fig. 3(C) becomes a value greater than 360° for the convenience of explaining the calculation principle. However, when the MMC130 actually receives radio waves, the wave number is not included, so θsum takes values from 0° to 360°. Therefore, it becomes as shown in Fig. 4. Fig. 4 is a diagram for explaining the distance measurement by the first distance measurement unit 132.

[0041] As shown in Fig. 4(A), θsum takes values from 0° to 360° and becomes data with the characteristic of repeating changes in a sawtooth wave shape. The data in Fig. 4(A) is converted by a conversion process of converting it linearly as shown in Fig. 4(B) to calculate the distance L. This conversion process becomes more difficult to calculate as the distance increases. This is because in the data of a short distance (for example, 5m) as shown in Fig. 4(C), the linearity of the phase is easy to understand and the addition process of 360° or more is easy. However, as can be seen from the data in Fig. 4(D) for a case of 15m as an example and the data in Fig. 4(E) for a case of 60m as an example, as the distance increases, the slope becomes larger, making the linearity of the phase difficult to see and the addition process difficult.

[0042] Therefore, the distance measurement by the first distance measurement unit 132 is more suitable for short distances than for long distances and is more suitable for a direct path environment than a multipath environment. Hereinafter, the distance measurement by the first distance measurement unit 132 is referred to as a direct path distance measurement method. The direct path distance measurement method is an example of the first distance measurement method.

[0043] <Distance measurement by the second distance measurement unit 133> Fig. 5 is a diagram for explaining the distance measurement by the second distance measurement unit 133. The 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 the direct path is low, and can be calculated relatively easily even when the smartphone 50 is relatively far from the distance measurement device 100.

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

[0045] As shown in FIG. 5, the second distance measurement unit 133 extracts, from the result of the FFT conversion, a frequency at which the signal intensity is sufficiently high and the lowest frequency gives an optimal peak. This is because, for the direct path signal, since the radio wave path is shorter than that of the multipath signal, when performing FFT conversion, the direct path signal will always have a lower frequency than the multipath signal. By converting the selected frequency into a distance, the distance up to the smartphone 50 can be obtained.

[0046] More specifically, with the number of sampling buffers for performing FFT being N = 256 and the frequency interval freq_step = 0.5 MHz, out of 160 channels at 0.5 MHz intervals from 2.4 to 2.48 GHz, 64 channels can be randomly hopped. Also, as an example, with the number of sampling buffers for performing FFT being N = 256 and the frequency interval freq_step = 2 MHz, hopping can be performed at 40 channels at 2 MHz intervals. Out of the 256 sampling buffers with N = 256, IQ data is set for 40 of them. When FFT is executed, the result of FIG. 5 can be obtained.

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

[0048]

Equation

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

[0050] The distance measurement by such a second distance measurement unit 133 is a distance measurement based on the frequency component of the signal received from the smartphone 50 and includes the conversion process in the FFT function, so the calculation is relatively easy even when the distance is far.

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

[0052] <Selection process by the selection unit 134> FIG. 6 is a diagram showing an example of the frequency spectrum after the FFT execution of the second distance measurement unit 133. Here, with reference to FIG. 6, a process of determining whether distance calculation is possible and whether it is multipath based on the signal received from the smartphone 50 will be described. In FIG. 6, the horizontal axis represents the frequency, and the vertical axis represents the 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. As shown in (2), (3), (4), and (5) of FIG. 6, when the signal strength is equal to or greater than the threshold value E, the selection unit 134 determines that distance calculation is possible.

[0054] Further, as shown in (2) and (3) of FIG. 6, the selection unit 134 has one peak with a sufficiently large signal strength. When the signal strength is equal to or greater than the threshold value E, it is determined that the environment has little multipath influence and a large direct path component. Further, as shown in (4) of FIG. 6, when there are a plurality of peaks with signal strength equal to or greater than the threshold value, the selection unit 134 determines that the environment has a strong multipath influence. Further, as shown in (5) of FIG. 6, for a situation where a plurality of peaks overlap to form one peak, the selection unit 134 also determines that the environment has a strong multipath influence. However, since it may not be easy to determine whether it 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] FIG. 7 is a diagram for explaining items that the selection unit 134 checks to determine that it 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 3.

[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 them when determining whether it is a multipath environment or a direct path environment in step S2 of FIG. 8 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 axis direction at the level of the threshold value E of the peak height. The peak area is the area of the portion above the threshold value E in the highest peak. The number of peaks is the number of peaks with a peak height equal to or greater than the threshold value E.

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

[0058] When there are a plurality of peaks with a peak height equal to or greater than the threshold value E, if the peak width at the peak height threshold value E is greater than the threshold value D in the bandwidth direction (the horizontal axis direction in FIG. 7), if the peak area is less than the area threshold value S, or if the peak height is less than the peak height threshold value h, the selection unit 134 determines that it is a multipath environment. Note that how the selection unit 134 specifically selects the distance measured by the direct path ranging method (the first distance) or the distance measured by the multipath ranging method (the second distance) will be described below with reference to the flowchart of FIG. 8.

[0059] FIG. 8 is a diagram showing a flowchart of the selection process executed by the selection unit 134. As a premise, it is assumed that the first ranging unit 132 and the second ranging unit 133 have measured the first distance and the second distance from the ranging device 100 to the smartphone 50 by the above-described ranging method.

[0060] When starting the process, the selection unit 134 determines whether distance calculation is possible (step S1). For example, as shown in (1) of FIG. 6, if it is less than the threshold value E, the selection unit 134 determines that distance calculation is not possible (S1: NO), proceeds to step S10 in the flow, and determines that it is an error (a state where ranging calculation cannot be performed) (step S10).

[0061] On the one hand, when the selection unit 134 determines in step S1 that distance calculation is possible (S1: YES), it advances the flow 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 value E, the selection unit 134 determines that distance calculation is possible (S1: YES), and advances the flow to step S2 via steps S1A and S1B. Specifically, it is as follows.

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

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

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

[0065] The determination in step S2 that it is a multipath environment (S2: YES) is the case where it is determined to correspond to (4) and (5) of FIG. 6. As described with reference to FIG. 7, when there are a plurality of peaks with a peak height equal to or greater than the threshold value E, if the peak width at the peak height threshold value E is greater than the threshold value D in the bandwidth direction (the horizontal axis direction in FIG. 7), if the peak area is less than the area threshold value S, or if the peak height is less than the peak height threshold value h.

[0066] In step S2, when the selection unit 134 determines that it is a multipath environment (S2: YES), the selection unit 134 selects the second distance calculated by the second distance measuring unit 133 through distance measurement using the multipath distance measurement method (step S3). That is, the multipath distance measurement method will be adopted.

[0067] In step S2, when the selection unit 134 determines that it is not a multipath environment (S2: NO), since it is a direct path environment, it is possible to select either the result of the direct path distance measurement method or the result of the multipath distance measurement method. Therefore, in order to determine the selectability of the direct path distance measurement method, 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] As an example, the linearity of the phase of the signal received from the smartphone 50 is represented by a correlation coefficient representing the correlation between the frequency and the phase. By obtaining the correlation coefficient representing the correlation between the frequency and the phase for the phases of the CWs obtained by hopping to 64 frequencies, it is determined whether the linearity of the phase of the signal received from the smartphone 50 is equal to or greater than a predetermined degree.

[0069] The correlation coefficient representing the correlation between the frequency and the phase can be represented, as an example, by the absolute value of the Pearson correlation coefficient. When the phases at each frequency lie on a straight line, the correlation is high (the correlation coefficient is large), and when the phases at each frequency vary, the correlation is low (the correlation coefficient is small). The correlation coefficient is represented by the slope of the straight line representing the correlation between the frequency and the phase.

[0070] The closer the absolute value of the correlation coefficient is to 1, the stronger the correlation (the higher the degree of linearity), and the closer it is to 0, the weaker the correlation (the 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 it can be measured by the direct path ranging method from low frequency to high frequency, that is, from short distance to long distance. Therefore, when the absolute value of the correlation coefficient is close to 1, it is suitable for the direct path ranging method. Also, the direct path ranging method is suitable for short distance measurement. For this reason, if it is determined in step S2 that the environment is not a multipath environment (S2: NO), the process proceeds to step S4. If all the determinations in steps S4, S5, S6, S7, and S9 are YES, the distance L (the first distance) obtained by ranging using the direct path ranging method is adopted. That is, basically, if there is linearity and it is a short distance, the direct path ranging method is adopted.

[0071] Also, when the Pearson correlation coefficient (a value that is not an absolute value) takes a positive value, since it is an abnormal state where the distance finally obtained by the direct path ranging method becomes a negative value, it is sufficient not to adopt the direct path ranging method.

[0072] The predetermined degree used for the determination in step S4 may be set to a value close to 1, such as 0.9 to 1. Also, in step S4, it is only necessary to determine whether the value that is not an absolute value is a negative value.

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

[0074] In step S4, when the selection unit 134 determines that the degree of linearity of the phase 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). This is to confirm whether the direct path ranging method can be selected.

[0075] The predetermined frequency band is, for example, the communication frequency band of WiFi. When the signal received from the smartphone 50 is affected by, for example, the radio waves of WiFi, the received signal only exists in the WiFi communication frequency band, and the phase data is in a state of being missing or having a large variation. When these states occur, it becomes difficult to appropriately calculate the distance by the direct path ranging method, so the direct path ranging method may not be adopted.

[0076] In the determination of step S5, the predetermined frequency band may be determined in advance in relation to the frequency band used for communication between the ranging device 100 and the smartphone 50 and the frequency bands of WiFi and the like that may exist in the surroundings.

[0077] Also, in the determination of step S5, the predetermined number of the number of valid phase data may be determined in advance through experiments or simulations as the number required to appropriately calculate the distance by the direct path ranging method.

[0078] In step S5, when the selection unit 134 determines that the number of valid phase data in a predetermined frequency band is less than the predetermined number (S5: NO), it advances the flow to step S3. This is because it is not appropriate to adopt the direct path ranging method. As a result, the second distance obtained by the multipath ranging method is selected.

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

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

[0081] The fact that the difference between the first distance measured by the first distance measurement unit 132 and the second distance measured by the second distance measurement unit 133 is small indicates that the distance measurement accuracy of the first distance measurement unit 132 and the second distance measurement unit 133 is high. When the flow proceeds to step S7 via steps S4 to S6, it means that the conditions are more suitable for the direct path distance measurement method than the multipath distance measurement method. 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. The fact that the difference between the first distance and the second distance is small indicates that the quality of the direct path is high, and the fact that the difference between the first distance and the second distance is large indicates that the quality of the direct path is low.

[0082] When the selection unit 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 measurement unit 132 (step S8). That is, the first distance measured by the direct path distance measurement 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] Further, in step S7, when the selection unit 134 determines that the difference between the first distance and the second distance is equal to or greater than a second predetermined difference (S7: NO), the flow proceeds to step S3. This is because the quality of the direct path is low. As a result, the second distance obtained by the multipath ranging method is selected.

[0084] Also, in step S6, when the selection unit 134 determines that the second distance measured by the second ranging unit 133 is equal to or greater than 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] In step S9, when the selection unit 134 determines that the difference between the first distance and the second distance is not less than the first predetermined difference (S9: NO), the flow proceeds to step S3. Since the process has proceeded to step S9 via steps S4 to S6, the conditions are satisfied for the direct path ranging method to be more suitable than the multipath ranging method. However, since the quality of the direct path is low, it is not appropriate to adopt the direct path ranging method. As a result, the second distance obtained by the multipath ranging method is selected.

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

[0087] The difference in distance is such that the longer the distance between the distance measuring device 100 and the smartphone 50 (longer distance), the smaller the proportion it occupies in the overall distance, and the shorter the distance between the distance measuring device 100 and the smartphone 50 (shorter distance), the larger the proportion it occupies in the overall distance. For this reason, as an example, in order to make the determination under short distances more stringent, the second predetermined difference used in the determination of step S7 is made smaller than the first predetermined difference used in the determination of step S9, and the first predetermined difference used in the determination of step S9 is made larger than the second predetermined difference used in the determination of 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] Also, in step S9, when the selection unit 134 determines that the difference between the first distance and the second distance is less than the first predetermined difference (S9: Yes), it advances the flow to step S8. This is because although the distance is long, the quality of the direct path is high. As a result, the first distance obtained by the direct path distance measurement method is selected.

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

[0090] Therefore, it is possible to provide a distance measuring device 100 that can select the first distance measurement method based on the phase difference and the second distance measurement method based on the frequency components of the FFT calculation result according to the signal situation of the signal transmitted and received with the smartphone 50.

[0091] Also, the selection unit 134 determines whether it is a multipath environment based on the number of peaks, peak height, or peak area in the frequency spectrum after the FFT execution of the second distance measuring unit 133. When it is determined that it is a multipath environment, the second distance obtained by the multipath distance measurement method is selected. For this reason, it is possible to provide a distance measuring device 100 that appropriately selects the second distance measured by the multipath distance measurement method in the case of a multipath environment.

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

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

[0094] Further, even if the degree of linearity of the phase of the signal received from the smartphone 50 is equal to or greater than a predetermined degree, when the number of valid phase data in a predetermined frequency band is less than a predetermined number, the selection unit 134 selects the second distance obtained by the multipath ranging method. For example, when there is no received signal only in the communication frequency band of WiFi and the phase data is missing, or when the variation is large, it becomes difficult to appropriately calculate the distance by the direct path ranging method. Therefore, it is possible to provide the ranging device 100 that selects the second distance obtained by the multipath ranging method more suitable for such a situation.

[0095] Further, even if the number of valid phase data in a predetermined frequency band is equal to or greater than a predetermined number, when the second distance measured by the second ranging unit 133 is equal to or greater than a predetermined distance, the selection unit 134 selects the second distance obtained by the multipath ranging method. Since the direct path ranging method is more suitable for ranging at a shorter distance than at a longer distance, it is possible to provide the ranging device 100 that selects the multipath ranging method that can also handle long distances.

[0096] Further, even if the second distance measured by the second ranging unit is equal to or greater than a predetermined distance, 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, the selection unit 134 selects the second distance obtained by the multipath 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 the ranging device 100 that selects the multipath ranging method when the quality of the direct path is low.

[0097] Further, even if the number of valid phase data in a predetermined frequency band is equal to or greater than a predetermined number and the second distance measured by the second ranging unit is less than a predetermined distance, 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 second predetermined difference, the selection unit 134 selects the second distance obtained by the multipath 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 the ranging device 100 that selects the multipath ranging method when the quality of the direct path is low.

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

[0099] Also, the first predetermined difference is larger than the second predetermined difference. Since the ratio of the distance difference to the total distance is smaller when the distance between the distance measurement device 100 and the smartphone 50 is long (long distance), and the ratio of the distance difference to the total distance is larger when the distance between the distance measurement device 100 and the smartphone 50 is short (short distance), by making the first predetermined difference larger than the second predetermined difference, the determination in the short distance can be made under stricter conditions.

[0100] <Selection process of modified example> FIGS. 9A and 9B are diagrams showing a flowchart of a selection process of a modified example executed by the selection unit 134.

[0101] The flowchart shown in FIG. 9A represents a process in which the process of step S5 is deleted from the flowchart shown in FIG. 8. In FIG. 9A, in step S2, the selection unit 134 determines that it is not a multipath environment but a direct path environment (S2: NO), and in step S4, when it determines that the degree of linearity of the phase of the signal received from the smartphone 50 is equal to or greater than a predetermined degree (S4: YES), the process proceeds to step S6 to determine whether the second distance measured by the second distance measurement unit 133 is equal to or greater than a predetermined distance (step S6). In this way, when the selection unit 134 determines that it is a direct path environment (S2: NO), the process may proceed from step S4 to step S6 without going through the process of step S5 shown in FIG. 8.

[0102] Also, the flowchart shown in FIG. 9B represents a process in which the process of step S4 is deleted from the flowchart shown in FIG. 8. In FIG. 9B, when the selection unit 134 determines in step S2 that it is a direct path environment rather than a multipath environment (S2: NO), the flow proceeds to step S5, and it is determined whether the number of valid phase data in a predetermined frequency band is equal to or greater than a predetermined number (step S5). When the selection unit 134 determines that the number of valid phase data in a predetermined frequency band is equal to or greater than the predetermined number (S5: YES), it is determined whether the second distance measured by the second distance measurement unit 133 is equal to or greater than a predetermined distance (step S6). Thus, when the selection unit 134 determines that it is a direct path environment (S2: NO), the process may proceed from step S2 to step S5 without going through the process of step S4 shown in FIG. 8.

[0103] As described above, the distance measurement device according to the exemplary embodiment of the present invention has been described. However, the present invention is not limited to the specifically disclosed embodiments, and various modifications and changes can be made 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.

Explanation of Reference Numerals

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

Claims

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

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

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

4. When the number of valid phase data in a predetermined frequency band is less than a predetermined number, the selection unit selects the second distance. The ranging device according to claim 1.

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

6. The selection unit selects the second distance when the second distance measured by the second distance measuring unit is less than the predetermined distance, and 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 greater than or equal to a second predetermined difference. The distance measuring device according to claim 1.

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

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

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

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