Distance measurement method, distance measurement system, heart rate measurement method, and heart rate measurement system

Abstract

To provide a distance measurement system capable of accurately measuring the distance from a radar to an object.SOLUTION: A distance measurement system includes: a radar 10 for transmitting a radio wave to an object 1 so as to receive the radio wave reflected by the object 1; a composite signal generation section 301 for generating a composite signal on the basis of the transmitted and received radio waves; a relation acquisition section 302 for analyzing a frequency of the composite signal so as to acquire the relation between the distance from the radar and the amplitude of the composite signal; a dispersion calculation section 303 for calculating dispersion of a time change of the amplitude; and a distance specification section 304 for specifying the distance from the object radar on the basis of the dispersion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a distance measuring method, a distance measuring system, a heart rate measuring method, and a heart rate measuring system. [Background technology]

[0002] It has been proposed to measure the distance from a radar to an object by irradiating the object with radio waves (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7341616 [Patent Document 2] Patent No. 7373754 [Patent Document 3] Patent No. 7436656 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a distance measurement method, a distance measurement system, a heart rate measurement method, and a heart rate measurement system that can accurately measure the distance from a radar to an object. [Means for solving the problem]

[0005] A distance measurement method according to an embodiment includes transmitting radio waves from a radar to a target, receiving the radio waves reflected by the target with the radar, generating a composite signal based on the transmitted radio waves and the received radio waves, performing frequency analysis on the composite signal to obtain the relationship between the distance from the radar and the amplitude strength of the composite signal, calculating the variance of the time change in the amplitude strength, and determining the distance of the target from the radar based on the variance.

[0006] In the distance measurement method described above, the subject may be a human or a non-human animal.

[0007] In the above distance measurement method, the distance from the radar corresponding to the amplitude intensity with the highest variance may be determined to be the distance from the radar of the target.

[0008] In the distance measurement method, the distance from the radar corresponding to the amplitude intensity having a variance equal to or greater than a predetermined threshold may be determined to be the distance from the radar of the target.

[0009] The distance measurement method may further include repeating the determination of the distance of the object from the radar and tracking the movement of the object.

[0010] In the distance measuring method, the radio waves may be millimeter waves.

[0011] The distance measurement system according to the embodiment includes a radar that transmits radio waves to a target and receives the radio waves reflected by the target; a composite signal generation unit that generates a composite signal based on the transmitted and received radio waves; a relationship acquisition unit that performs frequency analysis of the composite signal to acquire the relationship between the distance from the radar and the amplitude strength of the composite signal; a variance calculation unit that calculates the variance of the time change in the amplitude strength; and a distance determination unit that determines the distance of the target from the radar based on the variance.

[0012] In the distance measurement system described above, the object may be a human or a non-human animal.

[0013] In the distance measurement system, the distance determination unit may determine that the distance from the radar corresponding to the amplitude intensity with the highest variance is the distance from the radar of the target.

[0014] In the distance measurement system, the distance determination unit may determine that the distance from the radar corresponding to the amplitude intensity having a variance equal to or greater than a predetermined threshold is the distance from the target radar.

[0015] The distance measurement system may further include a tracking unit that repeatedly determines the distance of the object from the radar and tracks the movement of the object.

[0016] In the distance measurement system, the radio waves may be millimeter waves.

[0017] A heart rate measurement method according to an embodiment includes transmitting radio waves from a radar to a target, receiving the radio waves reflected by the target with the radar, generating a composite signal based on the transmitted radio waves and the received radio waves, performing frequency analysis on the composite signal to obtain a relationship between the distance from the radar and the amplitude strength of the composite signal, calculating the variance of the time change in the amplitude strength, determining the distance from the radar to the target based on the variance, and determining the heart rate of the target based on the time change in the composite signal at the determined distance.

[0018] The above heart rate measurement method may further include determining the subject's respiration rate based on a time variation of the composite signal at the determined distance.

[0019] The above-described heart rate measurement method may further include obtaining a time change in the movement of the object based on a time change in the phase of the composite signal at the specified distance.

[0020] In the above-described heart rate measuring method, the heart rate of the subject may be determined based on changes in the subject's movement over time.

[0021] In the above-described heart rate measurement method, the subject's respiratory rate may be determined based on changes in the subject's movement over time.

[0022] In the above-described heart rate measuring method, the subject may be a human or a non-human animal.

[0023] In the above heart rate measurement method, the distance from the radar corresponding to the amplitude intensity with the highest variance may be identified as the distance from the radar of the target.

[0024] In the above-described heart rate measurement method, the distance from the radar corresponding to the amplitude intensity having a variance equal to or greater than a predetermined threshold may be determined as the distance from the radar of the target.

[0025] The above heart rate measurement method may further include repeatedly determining the distance of the object from the radar and tracking the movement of the object.

[0026] In the above-described heart rate measuring method, the radio waves may be millimeter waves.

[0027] A heart rate measurement system according to an embodiment includes a radar that transmits radio waves to a target and receives the radio waves reflected by the target; a composite signal generation unit that generates a composite signal based on the transmitted and received radio waves; a relationship acquisition unit that performs frequency analysis on the composite signal to acquire the relationship between the distance from the radar and the amplitude strength of the composite signal; a variance calculation unit that calculates the variance of the time change in the amplitude strength; a distance determination unit that determines the distance of the target from the radar based on the variance; and a heart rate determination unit that determines the heart rate of the target based on the time change in the composite signal at the determined distance.

[0028] The above-described heart rate measuring system may further include a respiration rate determination unit that determines the respiration rate of the subject based on changes in the subject's movement over time.

[0029] The above-described heart rate measurement system may further include a movement acquisition unit that acquires a change in the movement of the object over time based on a change in the phase of the composite signal over time at the specified distance.

[0030] In the above-described heart rate measurement system, the heart rate determination unit may determine the heart rate of the subject based on changes in the motion of the subject over time.

[0031] In the above-described heart rate measuring system, the respiration rate determination unit may determine the respiration rate of the subject based on a change in the motion of the subject over time.

[0032] In the above-described heart rate measuring system, the subject may be a human or a non-human animal.

[0033] In the above-described heart rate measuring system, the distance determination unit may determine that the distance from the radar corresponding to the amplitude intensity with the highest variance is the distance from the radar of the target.

[0034] In the above-described heart rate measurement system, the distance determination unit may determine that the distance from the radar corresponding to the amplitude intensity having a variance equal to or greater than a predetermined threshold is the distance from the radar of the target.

[0035] The heart rate measurement system may further include a tracking unit that repeatedly determines the distance of the object from the radar and tracks the movement of the object.

[0036] In the above-described heart rate measurement system, the radio waves may be millimeter waves. [Effects of the Invention]

[0037] According to the present invention, it is possible to provide a distance measurement method, a distance measurement system, a heart rate measurement method, and a heart rate measurement system that are capable of accurately measuring the distance from a radar to an object. [Brief explanation of the drawings]

[0038] [Figure 1] FIG. 1 is a schematic diagram showing a distance measurement system according to an embodiment. [Figure 2] FIG. 2 is a flowchart of a distance measurement method according to the embodiment. [Figure 3] FIG. 3 is a graph showing an example of a chirp signal. [Figure 4] FIG. 4 is a graph showing an example of transmitted and received radio waves. [Figure 5] FIG. 5 is a graph showing an example of the relationship between the distance from the radar and the amplitude. [Figure 6] FIG. 6 is a graph showing an example of the relationship between distance from the radar, amplitude, and time. [Figure 7]FIG. 7 is a graph showing an example of the relationship between the distance from the radar and the amplitude variance. [Figure 8] FIG. 8 is a schematic diagram showing a heart rate measurement system according to an embodiment. [Figure 9] FIG. 9 is a flowchart of a heart rate measuring method according to the embodiment. [Figure 10] FIG. 10 is a graph showing an example of the relationship between the distance from the radar and the phase. [Figure 11] FIG. 11 is a graph showing an example of the change in phase over time at the position of the target. [Figure 12] FIG. 12 is a graph showing an example of changes in the movement of an object over time. [Figure 13] FIG. 13 is a graph showing an example of changes in the movement of an object over time. [Figure 14] FIG. 14 is a graph showing an example of beat rate and amplitude. [Figure 15] FIG. 15 is a graph showing an example of beat rate and amplitude. DETAILED DESCRIPTION OF THE INVENTION

[0039] As shown in Figure 1, the distance measurement system of the embodiment includes a radar 10 that transmits radio waves to a target 1 and receives the radio waves reflected by the target 1, a composite signal generation unit 301 that generates a composite signal based on the transmitted radio waves and the received radio waves, a relationship acquisition unit 302 that performs frequency analysis of the composite signal to acquire the relationship between the distance from the radar and the amplitude of the composite signal, a variance calculation unit 303 that calculates the variance of the time change in amplitude, and a distance determination unit 304 that determines the distance of the target from the radar based on the variance.

[0040] The composite signal generating unit 301, the relationship acquiring unit 302, the variance calculating unit 303, and the distance identifying unit 304 are included in, for example, a computer 300. The object 1 is a human or a non-human animal.

[0041] The radio waves are, for example, millimeter waves. The wavelength of the millimeter waves is, for example, 1 mm to 30 mm, and the frequency of the millimeter waves is, for example, 30 GHz to 300 GHz. The radar 10 is, for example, a frequency-modulated continuous wave (FM-CW) radar. The radio waves include, for example, a chirp signal whose frequency increases or decreases over time, as shown in FIG. 3 .

[0042] A distance measurement method using a distance measurement system according to an embodiment will be described with reference to the flowchart shown in Fig. 2. It takes time ΔT from when the radar 10 shown in Fig. 1 transmits radio waves in step S101 until the radar 10 receives the radio waves reflected by the target 1 in step S102. Therefore, when the transmitted radio waves and the received radio waves are compared simultaneously, as shown in Fig. 4, there is a frequency difference f between the transmitted radio waves and the received radio waves. b The frequency difference f b is called the beat frequency. The propagation speed of radio waves is essentially the same as the speed of light, c. The distance d from the radar 10 to the target 1 is given by the following equation (1): d=cΔT / 2 (1)

[0043] If the starting frequency of the chirp signal is f0, the final frequency is f1, and the time required to sweep from f0 to f1 is T0, the chirp rate k of the chirp signal is given by the following equation (2): Since the starting frequency f0, the final frequency f1, and the time required to sweep T0 are set in advance, the chirp rate k can be calculated from these values. k=(f1-f0) / T0 (2) beat frequency f b is given by the following equation (3). f b =k ΔT (3) From equations (1) and (3), the distance d and beat frequency f b The relationship is given by the following equation (4). d=(c·f b ) / (2 k) (4) Since the propagation speed c and chirp rate k are known, the beat frequency f b If the beat frequency fb From this, the distance d from the radar 10 to the object 1 can be calculated.

[0044] The composite signal generated by the composite signal generation unit 301 shown in FIG. 1 in step S103 is, for example, an intermediate frequency (IF) signal. The composite signal generation unit 301 stores the generated composite signal in the temporary storage device 401. In step S104, the relationship acquisition unit 302 reads the composite signal from the temporary storage device 401. The relationship acquisition unit 302 performs frequency analysis on the composite signal to obtain a beat frequency f b The relationship acquisition unit 302, for example, performs a Fourier transform (FT) on the composite signal. The Fourier transform is, for example, a fast Fourier transform (FFT). The relationship acquisition unit 302 performs a fast Fourier transform on the composite signal to calculate an amplitude spectrum that indicates the relationship between frequency and the absolute value of amplitude. The Fourier transform of the composite signal of the transmitted radio wave and the received radio wave, which includes a chirp signal, is also called a Range-FFT.

[0045] Furthermore, the relationship acquisition unit 302 converts the frequency that gives the amplitude spectrum into a distance d using, for example, the above equation (4), and calculates an amplitude spectrum that shows the relationship between the distance d and the amplitude, as shown in FIG. 5. The relationship acquisition unit 302 shown in FIG. 1 stores the relationship between the distance d and the amplitude in the temporary storage device 401 for a predetermined time. In the example shown in FIG. 5, a human target 1 is actually located 4.0 m from the radar 10, and an amplitude peak can be confirmed at 4.0 m. However, peaks can also be confirmed at positions other than 4.0 m, such as 3.6 m, where no target 1 is present. These peaks are due to reflections from fixed objects other than target 1, such as furniture, the walls and floor of the room, etc. As such, a situation may arise where it is impossible to determine which peak is caused by target 1 based solely on the amplitude spectrum that shows the relationship between the distance d and the amplitude.

[0046] In step S105, the variance calculation unit 303 shown in FIG. 1 reads the relationship between distance d and amplitude from the temporary storage device 401. The variance calculation unit 303 collects amplitude spectra indicating the relationship between distance d and amplitude over a predetermined time period and calculates the relationship between distance d, amplitude, and time. In the example graph shown in FIG. 6, the horizontal axis represents distance d, the vertical axis represents time, and the area surrounded by the horizontal and vertical axes represents amplitude normalized on a scale from 0 to 1, with darker areas on the grayscale indicating smaller amplitudes and lighter areas indicating larger amplitudes. In the example shown in FIG. 6, the amplitude due to reflection from a fixed object located 3.6 m away is constant over the predetermined time period, but the amplitude due to reflection from human subject 1 located 4.0 m away is not constant but fluctuates over the predetermined time period due to the body movement and breathing of subject 1.

[0047] The variance calculation unit 303 shown in Fig. 1 calculates the relationship between the distance d and the variance of the amplitude over a predetermined time based on the relationship between the distance d, the amplitude, and time. The variance calculation unit 303 stores the relationship between the distance d and the variance of the amplitude over a predetermined time in the temporary storage device 401. In the example graph shown in Fig. 7, a variance peak appears at a position of 4.0 m where the human subject 1 was actually present, and no variance peak appears at a position of 3.6 m where the amplitude peak appeared due to reflection from a fixed object in Fig. 5 in the example graph shown in Fig. 7.

[0048] In step S106, the distance determination unit 304 shown in FIG. 1 reads out the relationship between the distance d and the variance of the amplitude over a predetermined time from the temporary storage device 401. For example, the distance determination unit 304 determines that the distance d from the radar 10 corresponding to the amplitude with the highest variance among the variances calculated by the variance calculation unit 303 is the distance d of the target 1 from the radar 10. Alternatively, the distance determination unit 304 may determine that the distance d from the radar 10 corresponding to the amplitude with a variance equal to or greater than a predetermined threshold among the variances calculated by the variance calculation unit 303 is the distance of the target 1 from the radar 10. The distance determination unit 304 stores the determined distance in the temporary storage device 401. The distance determination unit 304 may also output the determined distance from the output device 402. Examples of the output device 402 include a display and a printer.

[0049] The distance measurement system according to the embodiment may further include a tracking unit 305 that repeatedly determines the distance of the object 1 from the radar 10 and tracks the movement of the object 1 .

[0050] Conventionally, radio waves reflected from fixed objects when the target 1 is not present are acquired in advance as background noise, and the background noise is removed from radio waves received when the target 1 is present. However, in conventional methods, the placement of fixed objects must be the same when the target 1 is present and when it is not present. Furthermore, if the placement of the fixed objects changes, it is not possible to remove the influence of radio waves reflected from fixed objects when the target 1 is present. In contrast, according to the distance measurement system of the embodiment, it is possible to accurately measure the distance from the radar 10 to the target 1 by removing the influence of radio waves reflected from fixed objects without acquiring in advance as background noise radio waves reflected from fixed objects when the target 1 is not present.

[0051] 8 includes, in addition to the components of the distance measurement system, a movement acquisition unit 306 that acquires changes over time in the movement of the target 1 based on changes over time in the phase of the composite signal at the identified distance, and a heart rate identification unit 307 that identifies the heart rate of the target 1 based on changes over time in the movement of the target 1. A heart rate measurement method using the heart rate measurement system according to the embodiment will be described with reference to the flowchart shown in FIG.

[0052] As described above, steps S101 to S106 are performed. In step S107, the motion acquisition unit 306 shown in FIG. 8 performs a fast Fourier transform on the synthesized signal to calculate a phase spectrum indicating the relationship between frequency and phase. Furthermore, the motion acquisition unit 306 converts the frequency that gives the phase spectrum into a distance d, for example, using equation (4) above, and calculates a phase spectrum indicating the relationship between the distance d and the phase, as shown in FIG. 10. The motion acquisition unit 306 shown in FIG. 8 stores the relationship between the distance d and the phase in the temporary storage device 401 for a predetermined time.

[0053] The movement acquisition unit 306 acquires a change over time in phase at the distance d identified by the distance identification unit 304 as shown in Fig. 11. The movement acquisition unit 306 shown in Fig. 8 stores the change over time in phase at the distance d in the temporary storage device 401. When acquiring the change over time in phase at the distance d, a phase unwrapping process may be performed to eliminate phase jumps, if necessary.

[0054] Here, the interval for sampling the composite signal is Δt, and if the distance between the target 1 and the radar 10 changes by Δd during Δt due to the movement of the target 1, the path of the radio waves traveling back and forth between the radar 10 and the target 1 changes by 2Δd. The resulting phase difference Δφ is given by the following equation (5), where λ is the wavelength of the radio waves. Δφ=2π 2Δd / λ (5) By transforming equation (5), we obtain the following equation (6). Δd=Δφ λ / 4π (6) Therefore, it is possible to determine the distance Δd of the movement of the object 1 from the difference Δφ between two successive phases when sampling the composite signal.

[0055] The movement acquisition unit 306 reads out the change in phase over time at the distance d from the temporary storage device 401. The movement acquisition unit 306 acquires the change in movement of the object 1 over time at the distance d as illustrated in FIG. 12 from the change in phase over time at the distance d, for example, using the above equation (6). The movement acquisition unit 306 shown in FIG. 8 stores the change in movement of the object 1 over time at the distance d in the temporary storage device 401.

[0056] The movement of the subject 1 includes body movement due to changes in limb movement and posture of the subject 1, body surface movement due to breathing, and body surface movement due to heartbeat. Body movement is at a lower frequency than body surface movement due to breathing and heartbeat. Therefore, body movement can be removed using a high-pass filter. High-frequency noise contained in the signal can be removed using a low-pass filter. Therefore, the movement acquisition unit 306 removes body movement and high-frequency noise from the time-varying movement of the subject 1 using, for example, a band-pass filter that passes signals in the range of 10 bpm to 120 bpm. FIG. 13 shows a graph of an example of the time-varying movement of the subject 1 after removing body movement and high-frequency noise. The movement acquisition unit 306 shown in FIG. 8 stores the time-varying movement of the subject 1 at a distance d after removing body movement and high-frequency noise in the temporary storage device 401.

[0057] In step S108, the heart rate determination unit 307 reads from the temporary storage device 401 the time change in the movement of the object 1 at the distance d after removing the body movement and high-frequency noise. The heart rate determination unit 307 performs fast Fourier transform processing on the signal of the time change in the movement of the object 1 at the distance d after removing the body movement and high-frequency noise, and obtains the relationship between the heart rate and amplitude as shown in FIG. 14. This fast Fourier transform is also called Doppler FFT. During the Doppler FFT, zero padding may be used to improve the frequency resolution.

[0058] Generally, the heart rate of an adult human is between 60 bpm and 100 bpm. Therefore, the heart rate determination unit 307 processes the signal indicating the relationship between the rate and amplitude using, for example, a bandpass filter that passes signals in a band between 50 bpm and 120 bpm. An example of the processed signal is shown in FIG. 15. In the example shown in FIG. 15, the highest peak appears at 97 bpm. The heart rate determination unit 307 determines the rate that gives the highest peak within the normal range of heart rates as the heart rate of the subject 1. The heart rate determination unit 307 stores the determined heart rate in the temporary storage device 401. The heart rate determination unit 307 may output the determined heart rate to the output device 402.

[0059] The heart rate measurement system according to the embodiment may further include a respiratory rate identification unit 308 that identifies the respiratory rate of the subject. Generally, the respiratory rate of an adult human is between 12 bpm and 18 bpm. In the example shown in FIG. 14 , the highest peak appears at 15 bpm. The respiratory rate identification unit 308 reads, from the temporary storage device 401, the time change in the movement of the subject 1 at the distance d after removing body movement and high-frequency noise. The respiratory rate identification unit 308 identifies the beat rate that gives the highest peak within the normal range of respiratory rates as the respiratory rate of the subject 1. The respiratory rate identification unit 308 stores the identified respiratory rate in the temporary storage device 401. The respiratory rate identification unit 308 may output the identified respiratory rate to the output device 402.

[0060] Although the present invention has been described above by way of the embodiments, the description and drawings that form part of this disclosure should not be understood to limit the present invention. From this disclosure, various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art. It should be understood that the present invention encompasses various embodiments not described herein. [Explanation of symbols]

[0061] 1. Object, 10. Radar, 300. Computer, 301. Synthetic signal generation unit, 302. Relationship acquisition unit, 303. Variance calculation unit, 304. Distance determination unit, 305. Tracking unit, 306. Motion acquisition unit, 307. Heart rate determination unit, 308. Respiratory rate determination unit, 401. Temporary storage device

Claims

1. Transmitting radio waves from the radar to the target; receiving the radio waves reflected by the object with the radar; generating a composite signal based on the transmitted radio waves and the received radio waves; performing a frequency analysis on the composite signal to obtain a relationship between a distance from the radar and an amplitude of the composite signal; calculating a variance of the amplitude change over time; determining a distance of the object from the radar based on the variance; A distance measurement method, comprising:

2. The distance measurement method according to claim 1 , wherein the object is a human or a non-human animal.

3. The distance measurement method according to claim 1 , wherein the distance from the radar corresponding to the highest amplitude of the variance is identified as the distance of the object from the radar.

4. The distance measurement method according to claim 1 , wherein a distance from the radar corresponding to an amplitude having the variance equal to or greater than a predetermined threshold is identified as the distance of the target from the radar.

5. The distance measurement method of claim 1 , further comprising repeating the process of determining the distance of the object from the radar and tracking the movement of the object.

6. The distance measuring method according to claim 1 , wherein the radio waves are millimeter waves.

7. a radar that transmits radio waves to an object and receives the radio waves reflected by the object; a composite signal generator that generates a composite signal based on the transmitted radio wave and the received radio wave; a relationship acquisition unit that performs frequency analysis on the composite signal to acquire a relationship between a distance from the radar and an amplitude of the composite signal; a variance calculation unit that calculates the variance of the time change of the amplitude; a distance determination unit that determines a distance of the target from the radar based on the variance; A distance measurement system comprising:

8. The distance measurement system according to claim 7 , wherein the object is a human or a non-human animal.

9. The distance measurement system according to claim 7 , wherein the distance determination unit determines that the distance from the radar corresponding to the amplitude where the variance is highest is the distance from the radar to the target.

10. The distance measurement system according to claim 7 , wherein the distance determination unit determines that the distance from the radar corresponding to the amplitude having the variance equal to or greater than a predetermined threshold is the distance of the target from the radar.

11. The distance measuring system according to claim 7 , further comprising a tracking unit that repeatedly determines the distance of the object from the radar and tracks the movement of the object.

12. The distance measuring system according to claim 7 , wherein the radio waves are millimeter waves.

13. Transmitting radio waves from the radar to the target; receiving the radio waves reflected by the object with the radar; generating a composite signal based on the transmitted radio waves and the received radio waves; performing a frequency analysis on the composite signal to obtain a relationship between a distance from the radar and an amplitude of the composite signal; calculating a variance of the amplitude change over time; determining a distance of the object from the radar based on the variance; determining a heart rate of the subject based on a time variation of the composite signal at the determined distance; A method for measuring heart rate, including:

14. and acquiring a time change in the motion of the object based on a time change in the phase of the composite signal at the specified distance; determining a heart rate of the subject based on a time change in the motion of the subject; 14. The method of claim 13, comprising:

15. The method of claim 13 , further comprising determining a respiration rate of the subject based on a time variation of the composite signal at the determined distance.

16. and acquiring a time change in the motion of the object based on a time change in the phase of the composite signal at the specified distance; determining a respiratory rate of the subject based on a time change in the subject's movement; 16. The method of claim 15, comprising:

17. The method for measuring heart rate according to claim 13, wherein the subject is a human or a non-human animal.

18. The method for measuring a heart rate according to claim 13, wherein the distance from the radar corresponding to the highest amplitude of the variance is identified as the distance of the object from the radar.

19. The method for measuring a heart rate according to claim 13 , wherein a distance from the radar corresponding to an amplitude having the variance equal to or greater than a predetermined threshold is identified as the distance of the object from the radar.

20. The method of claim 13 , further comprising repeating the process of determining the distance of the object from the radar and tracking the movement of the object.

21. The method for measuring a heart rate according to claim 13, wherein the radio waves are millimeter waves.

22. a radar that transmits radio waves to an object and receives the radio waves reflected by the object; a composite signal generator that generates a composite signal based on the transmitted radio wave and the received radio wave; a relationship acquisition unit that performs frequency analysis on the composite signal to acquire a relationship between a distance from the radar and an amplitude of the composite signal; a variance calculation unit that calculates the variance of the time change of the amplitude; a distance determination unit that determines a distance of the target from the radar based on the variance; a heart rate determination unit that determines a heart rate of the subject based on a time change of the composite signal at the determined distance; A heart rate measurement system comprising:

23. a motion acquisition unit that acquires a time change in motion of the object based on a time change in the phase of the composite signal at the specified distance; The heart rate measuring system according to claim 22 , wherein the heart rate determination unit determines the heart rate of the subject based on a change in the motion of the subject over time.

24. The heart rate measuring system according to claim 22 , further comprising a respiration rate determination unit that determines the respiration rate of the subject based on a change in the motion of the subject over time.

25. a motion acquisition unit that acquires a time change in motion of the object based on a time change in the phase of the composite signal at the specified distance; The heart rate measuring system according to claim 24 , wherein the respiration rate determination unit determines the respiration rate of the subject based on a change in the motion of the subject over time.

26. 23. The heart rate measuring system of claim 22, wherein the subject is a human or a non-human animal.

27. The heart rate measurement system according to claim 22 , wherein the distance determination unit determines that the distance from the radar corresponding to the highest amplitude of the variance is the distance of the object from the radar.

28. The heart rate measurement system according to claim 22 , wherein the distance determination unit determines that a distance from the radar corresponding to an amplitude having the variance equal to or greater than a predetermined threshold is the distance of the object from the radar.

29. The heart rate measurement system according to claim 22 , further comprising a tracking unit that repeatedly determines the distance of the object from the radar and tracks the movement of the object.

30. The heart rate measuring system according to claim 22, wherein the radio waves are millimeter waves.

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