Measurement method of high-dynamic Doppler displacement motion capable of identifying initial phase

Abstract

The invention provides a high-dynamic Doppler displacement motion measurement method capable of identifying an initial phase, and belongs to the technical field of radar detection. The measurement method comprises the following steps: step 1, sending an echo signal to a target through a Doppler radar and obtaining the echo signal; step 2, performing ADC sampling on the echo signal to obtain a digital I / Q component; calibrating the digitized I / Q component to obtain an initial phase, then obtaining the phase of a subsequent track point by adopting phase accumulation between adjacent points, and expanding a phase demodulation upper limit by adopting an atan2 function in the phase obtaining process; and step 3, recovering high-dynamic displacement motion of the target according to the linear relation between the phase and the Doppler displacement. The method has the displacement tracking characteristics of high phase difference tolerance, precision and high dynamic performance, can recover the initial phase without phase ambiguity, and has important significance in high-precision measurement of Doppler radar displacement motion and related applications thereof.

Description

Technical Field

[0001] The invention belongs to the technical field of radar detection, and in particular relates to a measurement method for high-dynamic Doppler displacement motion capable of identifying an initial phase. Background Art

[0002] The measurement of radar interferometric phase motion is a basic technology for Doppler radar applications. This technology has a wide range of application scenarios, such as the detection of breathing and heartbeat, dynamic measurement of liquid level, calibration of gesture displacement position, and measurement of object thickness. Taking breathing and heartbeat measurement and liquid level measurement as examples, whether high-dynamic Doppler displacement change tracking can be achieved is an important guarantee to ensure the safe monitoring of personnel life and health and the correct production management of industrial liquids. In actual production practice, transient displacements will lead to sudden and large phase differences, which is summarized as whether it can cope with high-dynamic challenges. For example, deep breathing and apnea events in human breathing, and reservoir water level fluctuations caused by flood discharge or heavy rain. These sudden large phase changes require that the corresponding demodulation technology should have a higher phase difference tolerance (phase difference range) to cope with high-dynamic challenges.

[0003] In addition, previous phase demodulation techniques ignored the initial phase information and simply replaced it with a 0rad initial phase, but the initial phase contains important information, such as the initial position of the target that can be calibrated. For example, in radar ranging based on linear frequency modulated continuous wave (FMCW), high-precision phase measurement is a necessary prerequisite to ensure accurate target thickness measurement. However, previous demodulation techniques did not focus on solving this problem, nor did they develop and utilize the information in the initial phase.

[0004] For Doppler radar, it focuses on demodulating the phase to obtain the displacement waveform of the target, so it pays great attention to the time domain accuracy of the demodulated phase trajectory. A direct way to improve the time domain accuracy of the phase trajectory is to increase the center frequency. For the same movement, the higher the center frequency, the greater the phase difference caused by the movement. However, higher frequency bands will lead to a significant increase in the design cost of the radio frequency (RF) system, including high-speed analog-to-digital converters (ADCs) and high-gain transceiver antennas.

[0005] As the electromagnetic spectrum continues to move towards the millimeter wave and terahertz bands, power consumption actually limits the coverage of high-speed RF systems in daily scenarios. Therefore, when power is limited, demodulation technology that can operate correctly at lower sampling rates (SR) and lower signal-to-noise ratios (SNR) is actually more robust and more adaptable to the actual scenario requirements of high-speed RF systems.

[0006] The earliest technology used for accurate demodulation of interferometric phase was the inverse tangent technique, but it faced the limitation of finite value range. Later, people introduced the small angle approximation to improve the inverse tangent technique, which solved the phase discontinuity problem while avoiding the use of trigonometric functions. Differential cross multiplication method (DACM) and modified differential cross multiplication method (MDACM) are two representative techniques. DACM focuses on phase differential, while MDACM considers displacement differential, so MDACM further reduces the computational complexity. Low-complexity demodulation technology is very beneficial to edge microcontroller units (MCUs) and is conducive to deployment in consumer electronics. However, the small angle approximation also has a significant disadvantage: it requires a high sampling rate to ensure the validity of the approximation conditions. On the other hand, some algorithms focus on accurate phase recovery without using small angle approximation. A typical example is the arcsine technique, which considers the phase difference between two in-phase / orthogonal (I / Q) trajectory points. The arcsine technique is more advantageous under low sampling rate conditions. Although DACM, MDACM and arcsine technologies all solve the phase problem through phase accumulation, the phase difference between adjacent I / Q trajectory points is limited and they cannot demodulate a phase difference exceeding ±π / 2, which also makes it impossible to accurately identify the initial phase. Summary of the invention

[0007] In view of this, the present invention aims at the deficiencies in the prior art and proposes a measurement method and method for high-dynamic Doppler shift motion that can identify the initial phase, so as to solve the two problems that the phase difference tolerance cannot cover the entire demodulation trajectory circle and cannot recover the initial phase, and realizes a lower joint limitation of sampling rate and signal-to-noise ratio, so as to better adapt to the actual scenario requirements of high-speed RF systems.

[0008] The object of the present invention can be achieved by the following technical scheme: A method for measuring high dynamic Doppler shift motion capable of identifying an initial phase, characterized in that it comprises the following steps:

[0009] Step 1, obtaining the original data: electromagnetic waves are transmitted to the target through the transmitter of the Doppler radar, and the electromagnetic waves are received by the radar receiver after being reflected by the target, so as to obtain echo signals, wherein the echo signals include I / Q signals in continuous wave (CW) and equivalent I / Q signals in frequency modulated continuous wave (FMCW);

[0010] Step 2: Calculate the phase of the trajectory point using the APA method: perform ADC sampling on the echo signal to obtain the digitized I / Q components; calibrate the digitized I / Q components to obtain the initial phase, and then use the phase accumulation between adjacent points to obtain the phase of the subsequent trajectory points. In the process of phase acquisition, the atan2 function is used to expand the upper limit of phase demodulation;

[0011] Step 3: Recover the displacement motion: Recover the high-dynamic displacement motion of the target based on the linear relationship between the phase and the Doppler shift based on the linear coefficient 4π / λ.

[0012] Preferably, the CW electromagnetic wave signal emitted by the transmitter can be expressed as follows:

[0013]

[0014] Among them A T is the amplitude of the transmitted signal, f is the carrier frequency, is the initial phase;

[0015] The echo signal received by the receiver can be expressed as follows:

[0016]

[0017] Among them A R is the amplitude of the echo, d0 is the distance, x(t) is the vibration, λ is the wavelength, f is the carrier frequency, is the initial phase, is the phase noise.

[0018] Preferably, the calibration process of the digital I / Q components in step 2 adopts a normalization method based on circle fitting, by corresponding the coordinate points composed of the I / Q signal sequence to the trajectory points on the trajectory circle, and then the center coordinates (DCI, DCQ) and the circle radius R can be obtained by parameter fitting based on the least squares method. The normalization formula is:

[0019] I n =(I o -DC I ) / R

[0020] Q n =(Q o -DC Q ) / R

[0021] Among them I o and Q o The original I / Q signal with DC bias obtained by ADC sampling, I n and Q n It is the normalized I / Q signal with the DC bias removed after circle fitting.

[0022] Preferably, the process further includes supplementing a (1,0) reference point in the signal sequence of the normalized I / Q signal to obtain a reference value of the initial phase, specifically:

[0023]

[0024] Preferably, the phase accumulation between adjacent points comprises the following steps:

[0025] The I / Q sequence obtained by digital sampling is equivalent to a combination of a series of adjacent I / Q vectors. Two adjacent vectors can be expressed as and Their cross multiplication and point multiplication can be expressed as follows:

[0026]

[0027] in, and is the length of the two I / Q trajectory point vectors, I[k] and Q[k] represent the sampling values ​​of the kth sampling points in the I / Q sequence, Δθ[k] represents the phase difference between the kth adjacent I / Q trajectory points, and the tangent value of the phase difference corresponding to the kth sampling point can be expressed as:

[0028]

[0029] Among them, Δθ[k] represents the kth phase difference. After using atan2 to calculate the inverse tangent of Δθ[k], the current accumulated precise phase θ[n] is obtained by integrating it. The calculation formula is as follows:

[0030]

[0031] Where θ[n] is the phase value corresponding to the nth sampling point of phase θ(t).

[0032] Preferably, atan2 is defined as:

[0033]

[0034] Preferably, the Doppler radar includes a transmitter, a receiver, an amplifier, a multiplier, a power divider, an excitation signal source and a crystal oscillator. The transmitter and the receiver are integrated in the same RF front-end module. The receiver is connected to the excitation signal source via a low-noise amplifier, a multiplier and a power divider in sequence, and the multiplier is connected to the transmitter via a crystal oscillator and an amplifier in sequence. The Doppler radar is a radar system suitable for millimeter wave (30GHz-300GHz) and terahertz (0.1THz-10THz) bands.

[0035] Compared with the prior art, the present invention has a larger phase tolerance limit, has no deviation in the phase demodulation result under low signal-to-noise ratio conditions, and no cumulative offset occurs; the computational complexity is lower, and it can correctly estimate the initial phase and track the correct phase demodulation curve. It is suitable for application fields such as high dynamic displacement and high dynamic liquid level monitoring, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1Schematic diagram of the measurement method according to an embodiment of the present invention.

[0037] Figure 2 This is the phase demodulation model involved in the embodiment of the present invention.

[0038] Figure 3 4 is a flow chart of a phase accumulation algorithm according to an embodiment of the present invention.

[0039] Figure 4 This is the motion measurement result of 12 mm peak-to-peak value of the simulated sliding table using a 120 GHz millimeter-wave radar at a low sampling rate according to the measurement method of this embodiment.

[0040] Figure 5 This is the motion measurement result of 12 mm peak-to-peak value of a simulated sliding table using a 120 GHz millimeter-wave radar under low signal-to-noise ratio conditions according to the measurement method of this embodiment.

[0041] Figure 6 The following is a simulation result of motion measurement of a linear step phase motion with an initial phase of 2 rad using the measurement method of this embodiment.

[0042] Figure 7 The following are the experimental results of a respiratory measurement experiment using the measurement method of this embodiment.

[0043] Figure 8 The following are the measurement results of a liquid level measurement experiment using the measurement method of this embodiment. DETAILED DESCRIPTION

[0044] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but are not to be construed as limiting the present invention.

[0045] Doppler radar focuses on recovering the phase information modulated by the target motion. Since the slow time dimension sampling signal of FMCW can be equivalent to a dual-channel CW signal, when measuring the target motion within a fixed range, FMCW radar uses the same phase demodulation principle as CW radar.

[0046] Figure 1The process of the measurement method of the present invention is demonstrated. The measurement method detects the target motion displacement through a radar sensor and obtains the corresponding I / Q information. After normalization, the initial phase of the target motion can be obtained by supplementing the reference point (1,0), so that the initial phase can be used to assist in locating the target information. After that, the I / Q trajectory is demodulated based on phase accumulation and atan2 function, and the target trajectory of high dynamic displacement motion can be restored without phase ambiguity. With the current situation that the electromagnetic spectrum continues to evolve to the millimeter wave and terahertz bands, this method breaks through the joint limitations of lower sampling rate and signal-to-noise ratio, thereby adapting to the actual scenario requirements of high-speed RF systems.

[0047] Figure 2 The phase demodulation model involved in this embodiment is shown, wherein Figure 2 (a) shows the typical orthogonal structure and various applications of Doppler radar. Figure 2 (b) is the digital sampling I / Q sequence of the I / Q trajectory. Figure 2 As shown in (a), based on the Doppler CW radar zero intermediate frequency orthogonal architecture, the I / Q components in the CW radar original echo signal can be obtained. The radar sensor includes a transmitter and a receiver integrated in the same RF front-end module. The receiver is an orthogonal down-conversion architecture. The receiver is connected to the excitation signal source after passing through a low-noise amplifier, a multiplier, and a power divider in sequence. The multiplier is connected to the transmitter after passing through a crystal oscillator and an amplifier in sequence. The transmitter transmits electromagnetic waves to the person being evaluated, and the electromagnetic waves are reflected by the human body of the person being evaluated and received by the radar receiver. Typical Doppler displacement measurement applications involved include vital signs monitoring, liquid level monitoring, and gesture recognition.

[0048] In this embodiment, the CW electromagnetic wave signal transmitted by the Doppler Rayleigh transmitter can be expressed as follows:

[0049]

[0050] Among them A T is the amplitude of the transmitted signal, f is the carrier frequency, is the initial phase and t is the time.

[0051] When the target has micro-vibration displacement, the micro-vibration displacement will modulate the phase in the echo based on the Doppler effect. The target echo signal can be expressed as follows:

[0052]

[0053] Among them A R is the amplitude of the echo, d0 is the distance, x(t) is the vibration, λ is the wavelength, f is the carrier frequency, is the phase noise. In practical applications, phase noise does not significantly affect the measurement of the vibration process x(t), so it is often ignored.

[0054] Initial phase in the echo signal Contains information, but previous demodulation technology ignored this point. By obtaining the initial phase, it can actually assist in correcting the initial position of the target.

[0055] The linear relationship between echo phase and target displacement can be expressed as follows:

[0056]

[0057] Among them, θ(t) is the phase information of the change caused by the displacement of the target. The digital I / Q components can be obtained by digitally sampling the echo signal with an ADC. Due to the design limitations of high-speed RF systems, high sampling rates mean expensive economic costs, so technologies that can still operate robustly under low sampling rate conditions are more valuable.

[0058] From the above formula, we can know that θ(t) and x(t) are in a linear relationship based on the linear coefficient 4π / λ, where π is the circumference of a circle and λ is the wavelength. The wavelength is a constant when the frequency of the electromagnetic wave is fixed. For example, for a 120GHz radar, the corresponding wavelength is 2.5mm. Therefore, to dynamically recover the target displacement is equivalent to dynamically demodulating the phase of the echo. The APA technology of the present invention has advantages in demodulation, especially in scenarios with low sampling rates and low signal-to-noise ratios, and the APA technology can identify the initial phase.

[0059] like Figure 2 As shown in (b), the I / Q sequence obtained by digital sampling can be equivalent to a combination of a series of adjacent I / Q vectors. Two adjacent vectors can be expressed as and Their cross multiplication and point multiplication can be expressed as follows:

[0060]

[0061] in, and is the length of the two I / Q trajectory point vectors, I[k] and Q[k] represent the sampling values ​​of the kth sampling points in the I / Q sequence, and Δθ[k] represents the phase difference between the kth adjacent I / Q trajectory points. The tangent value of the phase difference corresponding to the kth sampling point can be expressed as:

[0062]

[0063] Where Δθ[k] represents the kth phase difference. After taking the inverse tangent of Δθ[k] and integrating it, we can get the current accumulated precise phase θ[n]. The intuitive formula is as follows:

[0064]

[0065] Wherein θ[n] is the phase value corresponding to the nth sampling point of the phase θ(t). In order to overcome the π / 2 upper limit of arctan, the APA method of the present invention raises the upper limit of phase demodulation to π by using the atan2 function.

[0066]

[0067] Thereby, the phase accumulation between adjacent points in the APA method of the present invention is realized.

[0068] atan2 returns the azimuth taking into account the quadrant information of the I / Q trajectory points. It is defined as follows:

[0069]

[0070] Figure 3 The algorithm flow chart of this embodiment is shown, which includes calibration of AC coupling, I / Q mismatch and DC offset for the detuned original I / Q signal. Figure 3 As shown in the figure, the specific process of implementing the APA technology is as follows: first, the original I / Q signal is normalized, and then the (1,0) reference point is added to the normalized I / Q signal sequence to obtain the initial phase θ[1] of the I / Q initial trajectory point. Then, the phase accumulation method between adjacent points proposed can be used to obtain the phase θ[n] of the subsequent trajectory point. Because there is a linear relationship between θ(t) and x(t) based on the linear coefficient 4π / λ, the demodulated phase θ(t) can be used to recover the target's Doppler shift x(t). Specifically:

[0071] The calibration process uses normalization based on circle fitting. Specifically, Figure 2 As shown in (b), the coordinate points of the I / Q signal sequence correspond to the trajectory points on the trajectory circle, and then the coordinates of the center of the circle (DC I ,DC Q ) and the circle radius R. This allows the normalization of the I / Q signal, and the normalization formula is as follows:

[0072] I n =(I o -DC I ) / R

[0073] Q n =(Q o -DC Q ) / R

[0074] Among them I o and Qo The original I / Q signal with DC bias obtained by ADC sampling, I n and Q n It is the normalized I / Q signal with the DC bias removed after circle fitting.

[0075] For the normalized I / Q signal obtained after calibration, the reference value of the initial phase can be obtained by adding the (1,0) reference point to the signal sequence. Specifically, it is:

[0076]

[0077] The initial phase identification is achieved. The acquisition of the radar initial phase can assist in locating the initial position of the target, which is of fundamental significance for the high-precision positioning of the radar ranging system.

[0078] The present invention also designs a plurality of experiments to verify the superior effect of the measurement method of the high-dynamic Doppler shift motion that can identify the initial phase proposed in the present invention in various application environments. The experimental process is completed with the aid of a designed 120GHz CW radar, and the radar adopts a DC-coupled orthogonal structure. The 120GHz radar is selected because of its higher frequency and corresponding shorter wavelength, which means that compared with radar systems with lower frequencies such as 60GHz and 24GHz, it has better displacement-phase perception sensitivity when facing the same displacement. At the same time, the 120GHz radar can also better illustrate the sampling rate and signal-to-noise ratio limitations faced by high-speed RF systems in actual power-limited scenarios. Since high-frequency electromagnetic waves attenuate quickly in the air, the radar also uses a lens antenna to appropriately improve the signal-to-noise ratio of the electromagnetic signal. The designed radar lens antenna gain is 15dBi. The radar system is built based on the commercial front-end chip TRA-120-01 (Silicon Radar), which is a 1-transmit 1-receive antenna architecture. The appearance schematic diagram of the radar used can be referred to. Figure 4 (a).

[0079] Figure 4 The 12mm peak-to-peak motion measurement result of the slide table simulation at 0.5Hz in this embodiment is 35cm away from the 120GHz radar to verify the advantages of the proposed technology over other methods in low sampling rate scenarios. The 35cm distance is to ensure that the signal-to-noise ratio of the radar signal is good enough at this time, so as to verify only the limitation caused by the low sampling rate.

[0080] The experimental setup is as follows Figure 4(a) shows: a piece of iron plate is placed on a slide table (model Zaber-T-NA08A50) to generate sinusoidal displacement, and the echo data collected by the radar is recorded by a data sampler (DAQ), so that it can be further processed by the back-end algorithm. The DAQ model used is NI USB-6001. The DAQ is first oversampled at a sampling rate of 1000Hz, and then downsampled to the target sampling rate of 200Hz and 50Hz to ensure that the measurement is strictly the same section of motion.

[0081] Figure 4 (b) and Figure 4 (c) shows the I / Q signals after circular fitting normalization at 200Hz and 50Hz sampling rates respectively. It can be found that the I / Q trajectory of 200Hz is clearer and more intuitive than that of 50Hz, which intuitively shows that the low sampling rate of 50Hz will face greater challenges in accurate phase demodulation. At the same time, there are no obvious stray points in the I / Q trajectory, which means that the signal-to-noise ratio of the signal is good. Compared with the best arcsine technology in the prior art, the measurement method of the present invention shows better performance in low sampling rate scenarios. At 200Hz, the peak-to-peak value of the motion demodulated by these two technologies is 12.443mm, while at 50Hz, the peak-to-peak values ​​demodulated by arcsine and the measurement method of the present invention are 9.963mm and 12.400mm respectively. Some of the original data of this experimental process are shown in Tables 1 and 2 below:

[0082] Table 1: High signal-to-noise ratio 50Hz sampling measurement at 35cm from the slide

[0083]

[0084]

[0085] Table 2: High signal-to-noise ratio 200Hz sampling measurement at 35cm from the slide

[0086]

[0087]

[0088] Figure 5 The results of the motion measurement of 12mm peak-to-peak value at 0.5Hz for the slide table simulation are shown in this embodiment. At this time, the 120GHz radar is 50cm away and the sampling rate is set to 100Hz. The results show the advantages of the proposed technology over other methods in low signal-to-noise ratio scenarios. The experimental settings are as follows Figure 5 (a) shows, with Figure 4Compared with (a), only the distance between the radar and the slide table has changed. Since electromagnetic waves attenuate in the air, it is known that the signal-to-noise ratio of the radar signal will decrease. The sampling rate of 100 Hz is selected to ensure that the sampling rate is good enough at this time, so as to focus on the analysis of the limitations caused by the low signal-to-noise ratio.

[0089] Figure 5 (b) shows the change of I / Q trajectory after the signal-to-noise ratio decreases. It can be observed that there are spurious points and the trajectory is relatively disordered, which shows the challenge brought by the low signal-to-noise ratio. For a high-frequency system such as 120GHz radar, the working distance of 50cm is still useful in production work. To break the limitation of this working distance, a phase demodulation technology that can resist low signal-to-noise ratio is necessary.

[0090] Figure 5 (c) shows the demodulation results of different technologies, among which only the demodulation result of the measurement method of the present invention is correct and has no deviation, which shows that the measurement method of the present invention shows better performance in low signal-to-noise ratio scenarios. The arcsine technology maintains correct demodulation in the first cycle, but then there will be a downward cumulative offset. The results of DACM show a jagged demodulation error and an upward cumulative offset. The MDACM technology cannot match the correct 12mm demodulation range. Some of the raw data of this experimental process are shown in Table 3 below:

[0091] Table 3: Low signal-to-noise ratio measurement at 50 cm from the slide

[0092]

[0093]

[0094] Since the measurement method of the present invention shows better demodulation performance in low signal-to-noise ratio scenarios, it can improve the working distance of the radio frequency system in actual scenarios and realize the application of motion displacement measurement at a longer working distance. In addition, compared with the arcsine technology, which performs best in the comparison method, the measurement method of the present invention also has lower computational complexity. The reference arcsine phase accumulation formula is as follows:

[0095]

[0096] It can be found that for the molecular part, the measurement method of the present invention and the arcsine technology are both I[k-1]Q[k]-I[k]Q[k-1] , the amount of calculation is the same. However, in the denominator, the arcsine technology is It is necessary to calculate multiplication, addition and square root, and the measurement method of the present invention is I[k-1]I[k]+Q[k]Q[k-1] , only multiplication and addition need to be calculated.

[0097] comprehensive Figure 5 and Figure 6 The results show that when designing demodulation technology for high-frequency radio frequency systems such as millimeter waves or even terahertz, we should expect the technology to be able to operate robustly under lower sampling rates and lower signal-to-noise ratios, so that it is more in line with the measurement requirements in actual scenarios. Therefore, the measurement method of the present invention is more suitable for the actual application scenarios of high-speed radio frequency systems, and can reduce the economic cost of corresponding high-speed ADCs and high-gain transceiver antennas, thereby promoting the promotion of high-frequency radio frequency systems in the field of consumer electronics.

[0098] Another advantage of the measuring method of the present invention is that the initial phase can be identified.

[0099] Figure 6 The simulation results of motion measurement of a linear step phase motion with an initial phase of 2 rad are shown. Among the compared technologies, only the measurement method of the present invention can correctly demodulate the initial phase. Compared with the reference arctan technology, DACM technology, MDACM technology and arcsine technology, it can be found that none of them can correctly demodulate the initial phase of 2 rad. Some of the original data of this experimental process are shown in Table 4 below:

[0100] Table 4: Measurement of initial phase of 2 rad

[0101]

[0102]

[0103] The demodulated initial phase information can assist in locating the initial position of this linear step phase motion, but previous demodulation technologies have never begun to utilize the information in the initial phase. In principle, this is because the measurement method of the present invention has a phase difference tolerance of ±π, so by supplementing the (1,0) reference point, the position of the I / Q initial trajectory point on the entire trajectory circle can be accurately found. However, the comparative reference technology can only provide a phase difference tolerance of ±π / 2, which means that it can only cover half of the trajectory circle, so it is impossible to unambiguously identify the initial phase of the initial trajectory point on the entire trajectory circle. The acquisition of the initial phase can assist in locating the initial position of the target, which is of fundamental significance for the high-precision positioning of the radar ranging system.

[0104] Figure 7The 120GHz radar was demonstrated to measure the respiratory movement of the human body, where deep breathing can cause a displacement of more than 30 mm. For the detection scenarios of vital signs such as breathing and heartbeat, high-precision and wide-dynamic demodulation results can be obtained, thereby providing more reliable and valuable displacement waveform data for the diagnosis of related cardiopulmonary diseases. The respiratory measurement experiment aims to prove that the proposed measurement method of the present invention has a high dynamic demodulation range and has the detection advantage of capturing high dynamic displacement in the radar life detection scenario, thereby achieving a more accurate diagnosis of related cardiopulmonary diseases.

[0105] like Figure 7 As shown in (a), the experimental setup includes a volunteer sitting on a chair with the radar pointed at his chest. The volunteer breathes evenly and rhythmically, and then takes a deep breath. When taking a deep breath, the chest will suddenly move, resulting in a more significant phase difference. The sampling rate of the device is set to 50Hz, and the measured respiratory motion can be approximated as a periodic near-sinusoidal motion with a frequency of about 0.25Hz. The volunteer participating in the test is a 24-year-old young man with good health and no respiratory disease. During the process, a total of two deep breaths were taken for verification.

[0106] The experimental results show that the proposed measurement method has the largest dynamic displacement detection range, thus being able to capture deep breathing more accurately. Figure 7 (b) is shown. Two deep breaths were taken during the process. During the first deep breath, the displacement range demodulated by the APA technology was larger. During the second deep breath, the range detected by the measurement method of the present invention covered the range detected by the DACM technology and the arcsine technology, which means that high dynamic capture of deep breathing is achieved, which also shows that the measurement method of the present invention has the unique advantage of accurately capturing and restoring a large range of displacement changes. Some of the original data of this experimental process are shown in Table 5 below:

[0107] Table 5: Respirometry Experimental Data

[0108] Time(s) DACM displacement (mm) Arcsine displacement (mm) APA displacement(mm) 0 0 0 0 0.020006 0 0 0 0.040011 0 0 0 0.060017 0.040454 0.042751 0.042751 0.080023 0.005241 0.011831 0.011831 0.100029 -0.0394 -0.02808 -0.02808 0.120034 -0.0896 -0.08122 -0.08122 0.14004 -0.11699 -0.10184 -0.10184 0.160046 -0.31555 -0.27761 -0.27761 0.180051 -0.31555 -0.27761 -0.27761

[0109] Figure 8 (a) shows an experimental scene diagram of a liquid level measurement experiment. In the experiment, there are three marking lines on the measuring bucket, located at 0 cm, 4 cm and 8 cm respectively. At the beginning, the liquid level remains stationary. After a period of time, the valve is opened to allow the liquid level to drop quickly to the 4 cm marking line, and then the valve is closed. After the liquid level has been stationary for a period of time, the valve is opened again and closed at the 8 cm marking line. The sampling rate is set to 40 Hz, and the drop in the liquid level can be regarded as a stepping motion in a linear phase. The liquid level measurement experiment aims to prove that the proposed measurement method of the present invention has a high-dynamic displacement tracking characteristic, and has the advantage of accurate tracking in a high-precision liquid level measurement scenario, thereby ensuring the production safety of related industrial liquids.

[0110] Figure 8 (b) shows the results of the liquid level measurement experiment. During the first descent, the DACM technology, arcsine technology and the measurement method of the present invention all accurately tracked the descent of the liquid level. However, the DACM technology began to accumulate errors in the static section. During the second descent, only the measurement method of the present invention can correctly measure the descent to the 8 cm mark. The reason for this result is that the liquid level drops quickly, resulting in a large phase difference between adjacent I / Q trajectory points. Since different technologies have different abilities to resolve the maximum phase difference, cumulative phase errors occur during the measurement process. Some of the original data of this experimental process are shown in Table 6 below:

[0111] Table 6: Liquid level measurement experimental data

[0112]

[0113] Liquid level monitoring may experience instantaneous fluctuations, which will cause the corresponding phase difference to change significantly. The proposed measurement method of the present invention has accurate and highly dynamic liquid level tracking performance, so it has advantages in liquid level measurement. This is particularly relevant for industrial liquids such as petroleum and liquid nitrogen, because high-precision phase measurement can effectively measure the liquid level to ensure production safety in actual work.

[0114] Through the above content, the measurement method of the present invention can identify the initial phase in typical Doppler displacement measurement applications such as vital signs monitoring, liquid level monitoring and gesture recognition, etc., has a phase difference tolerance of ±π, can track the phase trajectory without phase ambiguity, and breaks through the joint limitations of low sampling rate and low signal-to-noise ratio designed for high-speed radio frequency systems. It is more practical and the detection results are more accurate.

[0115] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for measuring high-dynamic Doppler shift motion capable of identifying initial phase, characterized in that: The following steps are involved: Step 1: Acquisition of raw data: Electromagnetic waves are emitted to the target through the transmitter of the Doppler radar. After being reflected by the target, the electromagnetic waves are received by the radar receiver, thereby obtaining an echo signal; Step 2: Calculate the phase of the trajectory point using the APA method: perform ADC sampling on the echo signal to obtain the digitized I / Q components; calibrate the digitized I / Q components to obtain the initial phase, and then use the phase accumulation between adjacent points to obtain the phase of the subsequent trajectory points. In the process of phase acquisition, the atan2 function is used to expand the upper limit of phase demodulation; Step 3: Recover the displacement motion: Recover the high-dynamic displacement motion of the target based on the linear relationship between the phase and the Doppler shift based on the linear coefficient 4π / λ.

2. A method for measuring high dynamic Doppler shift motion capable of identifying initial phase according to claim 1, characterized in that: The echo signal is an orthogonal I / Q signal obtained by using a zero intermediate frequency architecture in a CW radar, or an equivalent I / Q signal obtained at a fixed distance bin in an FMCW radar.

3. A method for measuring high dynamic Doppler shift motion capable of identifying initial phase according to claim 2, characterized in that: The electromagnetic wave signal emitted by the transmitter can be expressed as follows: Among them A T is the amplitude of the transmitted signal, f is the carrier frequency, is the initial phase; The echo signal received by the receiver can be expressed as follows: Among them A R is the amplitude of the echo, d0 is the distance, x(t) is the vibration, λ is the wavelength, f is the carrier frequency, is the initial phase, is the phase noise.

4. A method for measuring high dynamic Doppler shift motion capable of identifying initial phase according to claim 3, characterized in that: The calibration process of the digital I / Q components in step 2 adopts a normalization method based on circle fitting. The coordinate points composed of the I / Q signal sequence are corresponded to the trajectory points on the trajectory circle, and then the center coordinates (DCI, DCQ) and the circle radius R are obtained by parameter fitting based on the least squares method. The normalization formula is: I n =(I o -DC I ) / R Q n =(Q o -DC Q ) / R Among them I o and Q o The original I / Q signal with DC bias obtained by ADC sampling, I n and Q n It is the normalized I / Q signal with the DC bias removed after circle fitting.

5. A method for measuring high dynamic Doppler shift motion capable of identifying initial phase according to claim 4, characterized in that: It also includes a process of adding a (1,0) reference point to the signal sequence of the normalized I / Q signal to obtain a reference value of the initial phase, specifically:

6. A method for measuring high dynamic Doppler shift motion capable of identifying initial phase according to any one of claims 1 to 5, characterized in that: The phase accumulation between adjacent points comprises the following steps: The I / Q sequence obtained by digital sampling is equivalent to a combination of a series of adjacent I / Q vectors. Two adjacent vectors can be expressed as and Their cross multiplication and point multiplication can be expressed as follows: in, and is the length of the two I / Q trajectory point vectors, I[k] and Q[k] represent the sampling values ​​of the kth sampling points in the I / Q sequence, Δθ[k] represents the phase difference between the kth adjacent I / Q trajectory points, and the tangent value of the phase difference corresponding to the kth sampling point can be expressed as: Among them, Δθ[k] represents the kth phase difference. After using atan2 to calculate the inverse tangent of Δθ[k], the current accumulated precise phase θ[n] is obtained by integrating it. The calculation formula is as follows: Where θ[n] is the phase value corresponding to the nth sampling point of phase θ(t). Preferably, atan2 is defined as:

7. A method for measuring high dynamic Doppler shift motion capable of identifying initial phase according to any one of claims 1 to 5, characterized in that: The Doppler radar comprises a transmitter, a receiver, an amplifier, a multiplier, a power divider, an excitation signal source and a crystal oscillator. The transmitter and the receiver are integrated in the same radio frequency front-end module. The receiver is connected to the excitation signal source via a low-noise amplifier, a multiplier and a power divider in sequence. The multiplier is connected to the transmitter via a crystal oscillator and an amplifier in sequence.

8. A method for measuring high dynamic Doppler shift motion capable of identifying initial phase according to any one of claim 7, characterized in that: The Doppler radar is a radar system suitable for millimeter wave (30GHz-300GHz) and terahertz (0.1THz-10THz) bands.

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