CN113171064A - Vital sign detection method based on radar - Google Patents

Vital sign detection method based on radar Download PDF

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CN113171064A
CN113171064A CN202110315023.1A CN202110315023A CN113171064A CN 113171064 A CN113171064 A CN 113171064A CN 202110315023 A CN202110315023 A CN 202110315023A CN 113171064 A CN113171064 A CN 113171064A
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signal
radar
vital sign
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sequence
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CN113171064B (en
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李牧
田哲嘉
吴彤
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Xian University of Technology
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/0205—Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7225—Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7235—Details of waveform analysis
    • A61B5/725—Details of waveform analysis using specific filters therefor, e.g. Kalman or adaptive filters
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7235—Details of waveform analysis
    • A61B5/7253—Details of waveform analysis characterised by using transforms
    • A61B5/7257—Details of waveform analysis characterised by using transforms using Fourier transforms
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

The invention discloses a radar-based vital sign detection method, which comprises the steps of designing a pseudo-random sequence; modulating the signal to a transmitting signal of a radar; mixing the modulated transmission signal with the received echo signal; performing FFT to obtain an original vital sign signal sequence; processing an original vital sign signal sequence by adopting a trend removing algorithm to obtain a trend removed signal; processing the trend-removed signal by using a BEADS algorithm to obtain a baseline signal, and further obtaining a phase difference signal; processing the phase difference signal by using a BEADS algorithm, and further obtaining a heartbeat signal; and respectively carrying out FFT (fast Fourier transform) on the respiration signal and the heartbeat signal to finish the detection of the respiration and the heartbeat. The invention relates to a radar-based vital sign detection method, which solves the problems that when the radar is adopted to detect vital sign information, electromagnetic waves received by the radar are easily interfered by multipath effect and mutually influenced by respiration and heartbeat signals.

Description

Vital sign detection method based on radar
Technical Field
The invention relates to the technical field of vital sign information detection, in particular to a vital sign detection method based on a radar.
Background
The vital sign parameters of body temperature, respiration, heart rate, blood pressure and the like are already important indexes for clinically evaluating whether vital activities exist, and are also the premise and the basis for the diagnosis and treatment of the patient. At present, methods for detecting vital signs are mainly classified into contact and non-contact methods. The contact detection method relates to the instruments including an electrocardiograph, a breathing belt and a bracelet (watch), wherein the electrocardiograph detects the heart rate by sticking an electrode plate on the skin of a patient, the breathing belt detects the breathing from the chest position, the bracelet (watch) is also tightly attached to the skin and emits green light through an LED to detect the heart rate, and the contact detection method is not suitable for people with large-area skin damage, limb trauma and skin allergy; instruments related to the non-contact detection method comprise a visible light camera, an infrared camera and a radar, wherein the visible light camera and the infrared camera detect breath and heart rate through human face parts, and in addition, the infrared camera can cause errors due to room temperature, shelters and human body swing; while radar detection of vital signs is a penetrating item; the device is not influenced by illumination and temperature; the method has the advantages of privacy protection and the like, but has the problems of multipath effect and mutual influence of respiration signals and heartbeat signals, so that the obtained radar echo generates distortion, and accurate vital sign information cannot be obtained by utilizing a conventional signal processing mode.
Disclosure of Invention
The invention aims to provide a radar-based vital sign detection method, which solves the problems that electromagnetic waves received by a radar are easily interfered by multipath effect when the radar is adopted to detect vital sign information and respiratory and heartbeat signals are mutually influenced in the prior art.
The technical scheme adopted by the invention is a radar-based vital sign detection method, which is implemented according to the following steps:
step 1, designing a pseudorandom sequence with the length of M, wherein each value in the pseudorandom sequence is selected from 1-2M-1；
Step 2, modulating the pseudo-random sequence to a transmitting signal of the radar, so that the starting position of the frequency of the transmitting signal in each period is different;
step 3, mixing the modulated transmission signal with the received echo signal, obtaining a filtering signal by a filter, and simultaneously filtering out the interference of the transmission signals of other periods on the transmission signal of the period;
step 4, FFT conversion is carried out on the filtering signals, instantaneous phases are obtained according to the positions of the target distance radars, and sequences formed by the changes of the instantaneous phases along with time are subjected to phase unwrapping, so that original vital sign signal sequences can be obtained;
step 5, processing the original vital sign signal sequence by adopting a trend removing algorithm, so that the trend of the filtered signal is stabilized near a 0 axis, and obtaining a trend removed signal;
step 6, processing the trend-removed signal by adopting a BEADS algorithm to obtain a baseline signal, and performing phase difference on the baseline signal to obtain a phase difference signal;
step 7, processing the phase difference signal by adopting a BEADS algorithm, extracting a respiration signal, and subtracting the phase difference signal and the respiration signal to obtain a heartbeat signal;
step 8, performing FFT (fast Fourier transform) on the respiratory signal, wherein the maximum value in the normal respiratory frequency range is the respiratory frequency of the current time period; and performing FFT (fast Fourier transform) on the heartbeat signals, wherein the maximum value in the normal heartbeat frequency range is the heartbeat frequency of the current time period, and the detection of respiration and heartbeat in vital signs is finished.
The invention is also characterized in that:
and M selects any integer larger than 2 according to the design cost and the anti-interference factor.
The step 2 specifically comprises the following steps:
if the transmission signal is a sawtooth wave, the transmission signal of the k-th period is expressed as:
Figure BDA0002990832620000031
in the formula (1), A is the amplitude of a radar emission signal; f. of0The center frequency of the radar emission signal; bkAs a pseudo-random sequence, bk∈{1,2,3...2m-1}, m is more than or equal to 9; p is a positive number greater than 1; t is the modulation period of the radar emission signal; b is the modulation bandwidth of the radar emission signal;
Figure BDA0002990832620000032
an initial phase for a radar transmit signal; t is a time sequence of radar emission signals;
if the transmission signal is a triangular wave, the transmission signal of the k-th period is represented as:
Figure BDA0002990832620000033
Figure BDA0002990832620000034
in step 3, the filter is a cascaded low-pass filter and band-pass filter, and the cut-off frequency of the low-pass filter is fmaxThe passband of the bandpass filter is fmin～fmax；
fmaxMaximum useful beat frequency value, f, obtained after mixing useful target echo with transmitted signalminIs the minimum of the useful difference frequency.
In step 3, the filter is a band-pass filter, and the pass band of the band-pass filter is fmin～fmax；
fmaxMaximum useful frequency, f, obtained after mixing of useful target echo with transmitted signalminIs the minimum of the useful difference frequency.
The position of the target range radar is expressed as:
Figure BDA0002990832620000035
in the formula (4), Δ d is the distance from the target to the radar; Δ f is the frequency difference; t is a modulation period; b is the modulation bandwidth; and c is the speed of light.
In step 5, the trend removing algorithm specifically comprises the following steps:
Figure BDA0002990832620000041
in formula (5), x (t) is the original vital sign signal sequence; m (t) is the trend sequence of x (t); y (t) is the detrended vital sign signal sequence; x is the number ofmax(t) is the upper envelope of x (t); x is the number ofmin(t) is x (t) lower envelope.
The invention has the beneficial effects that:
according to the vital sign detection method based on the radar, the radar waveform is designed by adopting the pseudo-random sequence, so that the interference of multipath effect when the radar detects the vital sign can be reduced; according to the vital sign detection method based on the radar, the obtained phase time sequence is processed by adopting a trend removing algorithm and a BEADS algorithm, so that the anti-interference performance and the measurement precision of a system for detecting the respiration and the heart rate by the radar can be improved.
Drawings
Fig. 1 is a flow chart of a radar-based vital sign detection method of the present invention;
FIG. 2(a) is a graph of target detection results on a distance dimension FFT;
FIG. 2(b) is a top view of the target detection result on the distance dimension FFT;
fig. 3 is a sequence of raw vital sign signals in the present invention;
FIG. 4(a) is a time domain waveform of a detected respiration signal of a radar-based vital sign detection method of the present invention;
FIG. 4(b) is a frequency domain waveform of a detected respiratory signal of a radar-based vital sign detection method of the present invention;
FIG. 5(a) is a time domain waveform of a heartbeat signal detected by a radar-based vital sign detection method of the present invention;
fig. 5(b) is a frequency domain waveform diagram of a heartbeat signal detected by a radar-based vital sign detection method of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
According to the vital sign detection method based on the radar, as shown in fig. 1, a group of pseudo-random sequences is designed, the frequency starting point of a transmitting signal of each period of the radar is modulated by adopting different pseudo-random codes, the radar receives an echo signal, then frequency mixing is carried out on the transmitting signal and the echo signal, the position of a target distance radar is obtained through FFT (fast Fourier transform), and then an instantaneous phase of a corresponding frequency on a frequency spectrum is obtained; recording the instantaneous phase value obtained each time on a slow time axis, and obtaining an original vital sign signal sequence through phase unwrapping;
firstly, processing an original vital sign signal sequence by using a trend removing algorithm to enable a signal to be stabilized near a 0 axis, extracting a Baseline from the trended signal by using a sparse Denoising and Baseline Estimation (BEADS) algorithm to obtain a smoother sequence, performing phase difference on the sequence to obtain a phase difference signal, and applying a BEADS algorithm to the phase difference signal to obtain an accurate breathing signal;
subtracting the respiratory waveform from the phase difference waveform to obtain a heartbeat waveform, carrying out Fourier transform on the obtained respiratory waveform according to the respiratory frequency in the range of 0.2 Hz-0.7 Hz and the heartbeat frequency in the range of 0.9 Hz-2 Hz to obtain the respiratory frequency, and carrying out Fourier transform on the obtained heartbeat waveform to obtain the heartbeat frequency.
The method is implemented according to the following steps:
step 1, designing a pseudorandom sequence with the length of M, wherein each value in the pseudorandom sequence is selected from 1-2M-1；
Step 2, modulating the pseudo-random sequence to a transmitting signal of the radar, so that the starting position of the frequency of the transmitting signal in each period is different;
m selects an arbitrary integer larger than 2 according to the design cost and the anti-interference factor;
the step 2 specifically comprises the following steps:
if the transmission signal is a sawtooth wave, the transmission signal of the k-th period is expressed as:
Figure BDA0002990832620000061
in the formula (1), A is the amplitude of a radar emission signal; f. of0The center frequency of the radar emission signal; bkAs a pseudo-random sequence, bk∈{1,2,3...2m-1},m≥9; p is a positive number greater than 1; t is the modulation period of the radar emission signal; b is the modulation bandwidth of the radar emission signal;
Figure BDA0002990832620000062
an initial phase for a radar transmit signal; t is a time sequence of radar emission signals;
if the transmission signal is a triangular wave, the transmission signal of the k-th period is represented as:
Figure BDA0002990832620000063
Figure BDA0002990832620000064
step 3, mixing the modulated transmission signal with the received echo signal, obtaining a filtering signal by a filter, and simultaneously filtering out the interference of the transmission signals of other periods on the transmission signal of the period;
the frequency starting position of the next period of the radar transmitting signal is different from the frequency starting position of the previous period, so that when the echo signals and the transmitting signal of different periods are received to be mixed, only the mixed frequency of the echo signals and the transmitting signal of the same period can be detected by high amplitude, and the purpose of reducing interference is achieved;
step 4, FFT conversion is carried out on the filtering signals, instantaneous phases are obtained according to the positions of the target distance radars, and sequences formed by the changes of the instantaneous phases along with time are subjected to phase unwrapping, so that original vital sign signal sequences can be obtained;
wherein the position of the target from the radar is represented as:
Figure BDA0002990832620000071
in the formula (4), Δ d is the distance from the target to the radar; Δ f is the frequency difference; t is a modulation period; b is the modulation bandwidth; c is the speed of light;
step 5, processing the original vital sign signal sequence by adopting a trend removing algorithm, so that the trend of the filtered signal is stabilized near a 0 axis, and obtaining a trend removed signal;
the trend removing algorithm specifically comprises the following steps:
Figure BDA0002990832620000072
in formula (5), x (t) is the original vital sign signal sequence; m (t) is the trend sequence of x (t); y (t) is the detrended vital sign signal sequence; x is the number ofmax(t) is the upper envelope of x (t); x is the number ofmin(t) is x (t) lower envelope;
step 6, processing the trend-removed signal by using a BEADS algorithm to obtain a baseline signal, removing most of interference, and performing phase difference on the baseline signal to obtain a phase difference signal;
wherein the phase difference represents a difference between a current phase and a phase at a previous time.
Step 7, processing the phase difference signal by adopting a BEADS algorithm, extracting a respiration signal, and subtracting the phase difference signal and the respiration signal to obtain a heartbeat signal;
step 8, performing FFT (fast Fourier transform) on the respiratory signal, wherein the maximum value in the normal respiratory frequency range is the respiratory frequency of the current time period; and performing FFT (fast Fourier transform) on the heartbeat signals, wherein the maximum value in the normal heartbeat frequency range is the heartbeat frequency of the current time period, and the detection of respiration and heartbeat in vital signs is finished.
The normal respiratory frequency range of the adult is 0.2-0.34 HZ, and the normal heartbeat frequency range of the adult is 1-1.67 HZ; the normal respiratory frequency range of children and old people is set to be 0.2-0.7 HZ, and the normal heartbeat frequency range is set to be 0.9-2 HZ.
Preferably, in step 3, the filter is a cascade of a low-pass filter and a band-pass filter, and the cut-off frequency of the low-pass filter is fmaxThe passband of the bandpass filter is fmin～fmax；
fmaxEcho of a useful targetMaximum useful frequency, f, obtained after mixing of the transmitted signalsminIs the minimum of the useful difference frequency.
Preferably, in step 3, the filter is a band-pass filter, and the passband of the band-pass filter is fmin～fmax；fmaxMaximum useful beat frequency value, f, obtained after mixing useful target echo with transmitted signalminIs the minimum of the useful difference frequency.
The period of the radar emission signal can be customized, and the number of the pseudo-random codes in each period can be one or more; the frequency time chart of the radar emission signal can be a sawtooth wave or a triangular wave; the phase difference of the signals can be chosen or rejected according to the situation; the frequency of the radar may be selected within a frequency range specified by the country, with a higher frequency selection generally being recommended as good as possible.
And (3) experimental verification:
(1) in order to verify the accuracy of the heart rate detection method, the millet wristband 5 is used for a comparison experiment, and the heart rate measured by the wristband is a reference heart rate value. As shown in table 1, the results of the heart rate test comparison between the present invention and the millet bracelet 5 are shown.
Table 1, wrist strap, millet wrist strap and data summary of heart rate detection by the detection method of the invention
Figure BDA0002990832620000081
Figure BDA0002990832620000091
As can be seen from table 1, compared with the millet bracelet 5, the accuracy rate of detecting the heart rate by the radar-based vital sign detection method of the invention reaches 97.3%, and the detection effect is better than that of the millet bracelet 5.
(2) The invention relates to a radar-based vital sign detection method, wherein a pseudorandom sequence with the length of 16 and the M of 9 is selected according to the design cost and the working environment requirement, and b is obtainedkE {1,2,3.. 511}, k being 1,2,3.. 16; setting the frequency spectrum of a radar emission signalThe pseudo random sequence is modulated to a transmitting signal of a radar, wherein the center frequency of the pseudo random sequence is 77GHZ, the modulation period is 50us, and the modulation bandwidth is 4 GHZ;
mixing an echo signal received by a radar with a radar transmitting signal to extract a useful target signal; and performing FFT (fast Fourier transform) on the useful target signal, searching a peak value in a frequency spectrum, solving a frequency value corresponding to the peak value, and obtaining the position of the target from the radar. This FFT is also referred to as a distance dimension FFT, fig. 2(a) is a graph of the detection result of the target on the distance dimension FFT, fig. 2(b) is a top view of the detection result of the target on the distance dimension FFT, and a line segment composed of the peak value (×) at each time in fig. 2(a) can be seen to be substantially at the 1m position in fig. 2 (b);
obtaining an instantaneous phase from the peak position obtained at each moment, and obtaining a signal waveform diagram after trend removing preprocessing shown in fig. 3 after phase unwrapping, wherein the signal waveform diagram is called as a phase time image and can also be called as an original vital sign information sequence; it can be seen from fig. 3 that the detrended signal waveform stabilizes around the 0-axis;
processing the original vital sign information sequence by adopting a trend removing algorithm to obtain a trend removed signal; processing the trend-removed signal by using a BEADS algorithm to obtain a baseline signal, selecting 0.2-0.8 Hz of a cutoff frequency preset by the BEADS algorithm, and performing phase difference on the baseline signal to obtain a phase difference signal;
processing the phase difference signal by using a BEADS algorithm, wherein the cutoff frequency preset by the algorithm is selected to be 0.7-2 Hz, and the extracted baseline signal is a respiration signal, as shown in fig. 4 (a); then subtracting the respiration signal waveform from the phase difference signal waveform to obtain the heartbeat signal waveform, as shown in fig. 5 (a);
finally, performing FFT on the respiratory signal to obtain the maximum value in the normal respiratory frequency range, namely the respiratory frequency of the current time period, as shown in fig. 4(b), the currently measured respiratory frequency is 0.2344Hz, namely about 14 times/minute; then, the FFT of the heartbeat signal is performed to obtain the maximum value in the normal heartbeat frequency range, which is the heartbeat frequency of the current time period, as shown in fig. 5(b), the currently measured heartbeat frequency is 0.9766Hz, which is about 59 times/minute.

Claims (7)

1. A vital sign detection method based on radar is characterized by being implemented according to the following steps:
step 1, designing a pseudorandom sequence with the length of M, wherein each value in the pseudorandom sequence is selected from 1-2M-1；
Step 2, modulating the pseudo-random sequence to a transmitting signal of the radar, so that the starting position of the frequency of the transmitting signal in each period is different;
step 3, mixing the modulated transmitting signal with the received echo signal, and then obtaining a filtering signal by a filter;
step 4, FFT conversion is carried out on the filtering signals, instantaneous phases are obtained according to the positions of the target distance radars, and the sequences formed by the changes of the instantaneous phases along with time are subjected to phase unwrapping, so that original vital sign signal sequences can be obtained;
step 5, processing the original vital sign signal sequence by adopting a trend removing algorithm to enable the trend of the filtered signal to be stable near a 0 axis, and obtaining a trend removed signal;
step 6, processing the de-trended signals by using a BEADS algorithm to obtain baseline signals, and performing phase difference on the baseline signals to obtain phase difference signals;
step 7, processing the phase difference signal by adopting a BEADS algorithm, extracting a respiration signal, and performing subtraction on the phase difference signal and the respiration signal to obtain a heartbeat signal;
step 8, performing FFT (fast Fourier transform) on the respiratory signal, wherein the maximum value in a normal respiratory frequency range is the respiratory frequency of the current time period; and performing FFT (fast Fourier transform) on the heartbeat signal, wherein the maximum value in the normal heartbeat frequency range is the heartbeat frequency of the current time period, and the detection of respiration and heartbeat in vital signs is finished.
2. The radar-based vital sign detection method of claim 1, wherein M is any integer greater than 2, based on design cost and interference rejection factors.
3. The radar-based vital sign detection method according to claim 1, wherein step 2 specifically comprises:
if the transmission signal is a sawtooth wave, the transmission signal of the k-th period is expressed as:
Figure FDA0002990832610000021
in the formula (1), A is the amplitude of a radar emission signal; f. of0The center frequency of the radar emission signal; bkAs a pseudo-random sequence, bk∈{1,2,3...2m-1}, m is more than or equal to 9; p is a positive number greater than 1; t is the modulation period of the radar emission signal; b is the modulation bandwidth of the radar emission signal;
Figure FDA0002990832610000022
an initial phase for a radar transmit signal; t is a time sequence of radar emission signals;
if the transmission signal is a triangular wave, the transmission signal of the k-th period is represented as:
Figure FDA0002990832610000023
Figure FDA0002990832610000024
4. the radar-based vital sign detection method according to claim 1, wherein in step 3, the filter is a cascade of a low-pass filter and a band-pass filter, and the cut-off frequency of the low-pass filter is fmaxThe passband of the band-pass filter is fmin～fmax；
fmaxMaximum useful beat frequency value, f, obtained after mixing useful target echo with transmitted signalminIs the minimum of the useful difference frequency.
5. The radar-based vital sign detection method according to claim 1, wherein in step 3, the filter is a band pass filter, and the pass band of the band pass filter is fmin～fmax；
fmaxMaximum useful frequency, f, obtained after mixing of useful target echo with transmitted signalminIs the minimum of the useful difference frequency.
6. Method for radar-based vital signs detection according to claim 1, wherein the position of the target distance radar is represented as:
Figure FDA0002990832610000031
in the formula (4), Δ d is the distance from the target to the radar; Δ f is the frequency difference; t is a modulation period; b is the modulation bandwidth; and c is the speed of light.
7. The radar-based vital sign detection method according to claim 1, wherein in step 5, the de-trending algorithm specifically comprises:
Figure FDA0002990832610000032
in formula (5), x (t) is the original vital sign signal sequence; m (t) is the trend sequence of x (t); y (t) is the detrended vital sign signal sequence; x is the number ofmax(t) is the upper envelope of x (t); x is the number ofmin(t) is x (t) lower envelope.
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