CN113009476A - Signal extraction method and system based on frequency modulation continuous wave radar - Google Patents
Signal extraction method and system based on frequency modulation continuous wave radar Download PDFInfo
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Abstract
The invention relates to the technical field of signal processing, in particular to a signal extraction method and a system based on a frequency modulation continuous wave radar, which comprises the following steps of firstly preprocessing a chest wall mechanical motion signal of a human body to be detected, which is received by the frequency modulation continuous wave radar, to obtain an echo signal, wherein the echo signal comprises: a respiratory signal, a heartbeat signal, a higher harmonic component of the respiratory signal, a higher harmonic component of the heartbeat signal, and a noise signal; then, filtering a signal without noise in the echo signal to obtain a filtering signal, determining a frequency-power spectrum of the filtering signal in an estimated frequency interval, and separating according to a spectrogram of a peak value of the frequency-power spectrum to obtain a heartbeat signal and a respiration signal; the method for estimating the signal frequency by matching with the power spectrum can achieve the aim of retaining the respiratory signal and the heartbeat signal components and filtering other interference components, thereby extracting the heartbeat signal and the respiratory signal in a complex noise environment.
Description
Technical Field
The invention relates to the technical field of signal processing, in particular to a signal extraction method and a signal extraction system based on a frequency modulation continuous wave radar.
Background
The millimeter Wave Frequency Modulated Continuous Wave Radar (FMCW) is a non-contact detection method, can realize all-weather and all-space detection due to no interference of weather and detection environment shielding objects, has a high working Frequency band, can capture weak respiration and heartbeat signals, and has high detection precision. When a millimeter wave frequency modulation continuous wave radar is used for monitoring physical sign signals, the most important link is how to separate and extract respiratory information and heartbeat information from echo signals received by the millimeter wave frequency modulation continuous wave radar.
The amplitude of thoracic motion caused by respiratory motion of a human body in a static state is large, the energy of a respiratory signal is strong, and the amplitude of thoracic micromotion caused by heartbeat motion is relatively small, and the energy is relatively weak. And frequency analysis of the echo signal shows that: the higher harmonic components of the respiration signal and the heartbeat signal have overlapping portions in the frequency spectrum. Under the condition that the frequency spectrums of the two signals are close and the energy difference is large, the weak heartbeat signal is easily covered by the breathing signal; in addition, the signal wavelength of the millimeter wave frequency modulation continuous wave radar is between the microwave and the far infrared wave, and the displacement of a few tenths of millimeters can be detected, so that a plurality of small disturbances in the measurement process can be detected. Weak heartbeat signals and respiratory signals are mixed in a complex noise environment, so that the heartbeat signals and the respiratory signals are difficult to extract from echo signals.
Disclosure of Invention
The invention provides a signal extraction method and a signal extraction system based on a frequency modulation continuous wave radar, which are used for solving one or more technical problems in the prior art and at least provide a beneficial selection or creation condition.
In order to achieve the purpose, the invention provides the following technical scheme:
a signal extraction method based on a frequency modulated continuous wave radar comprises the following steps:
step S100, preprocessing a chest wall mechanical motion signal of a human body to be detected received by a frequency modulation continuous wave radar to obtain an echo signal, wherein the echo signal comprises: a respiratory signal, a heartbeat signal, a higher harmonic component of the respiratory signal, a higher harmonic component of the heartbeat signal, and a noise signal;
and S200, filtering a signal without noise in the echo signal to obtain a filtering signal, determining a frequency-power spectrum of the filtering signal in an estimated frequency interval, and separating according to a spectrogram of a peak value of the frequency-power spectrum to obtain a heartbeat signal and a respiration signal.
Further, the step S200 includes:
step S210, determining an estimated frequency interval of the echo signal, and setting n frequency points at equal intervals in the estimated frequency interval;
step S220, selecting a frequency point from the estimated frequency interval as an expected frequency point;
step S230, determining a frequency vector matrix of the expected frequency point, and incorporating the frequency vector matrix into an expected subspace;
step S240, determining a difference set of the estimated frequency interval and the selected expected frequency point, and taking a frequency vector matrix of the difference set as an interference subspace;
step S250, constructing an oblique projection operator of the echo signal, and performing oblique projection filtering on a signal without noise in the echo signal according to the oblique projection operator to obtain a filtered signal;
step S260, calculating the power of the filtering signal, and weighting the power P by adopting a self-adaptive weight vector to obtain the weighted power of the filtering signal;
step S270, determining whether the estimated frequency interval is traversed, if not, selecting the remaining frequency points from the estimated frequency interval as expected frequency points, and jumping to the step S230; if yes, go to step S280;
and step S280, determining a frequency-power spectrum of the estimated frequency interval, and separating according to a spectrogram of a peak value of the frequency-power spectrum to obtain a heartbeat signal and a respiration signal.
Further, the estimated frequency interval has a value range of [0.10Hz,3.00Hz ], and n is 290.
Further, it is characterized byThe calculation formula of the oblique projection operator is as follows: eA(θ)|A(V)＝A(θ)/[A(θ)H*A(V)*A(θ)]* A(θ)HA (θ), where θ is the desired frequency point, a (θ) is a frequency vector matrix of the desired frequency point, V is a difference set, and a (V) is a frequency vector matrix of the difference set;
the calculation formula of the filtering signal is as follows: y ═ EA(θ)|A(V)*YFF is the estimated frequency range, YFAnd Y' is a filtering signal for the oblique projection operator to the signal without noise in the echo signal.
Further, the power P of the filtering signal Y' is calculated by the following formula:
Further, the adaptive weight vector calculation formula is: 1/trace (E)A(θ)|A(V) H*EA(θ)|A(V)) U is the adaptive weight vector; the adaptive weight vector calculation formula is as follows: p 'is U × P, and P' is the weighted power of the filtered signal.
A computer readable storage medium having stored thereon a computer program which, when being executed by a processor, carries out the steps of the frequency modulated continuous wave radar based signal extraction method according to any one of the preceding claims.
A frequency modulated continuous wave radar-based signal extraction system, comprising:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement a frequency modulated continuous wave radar-based signal extraction method as claimed in any one of the preceding claims.
The invention has the beneficial effects that: the invention discloses a signal extraction method and a system based on a frequency modulation continuous wave radar.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic flow chart of a method for extracting signals based on frequency modulated continuous wave radar according to an embodiment of the present invention;
FIG. 2 is a flowchart illustrating step S200 according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a simulation of an echo signal in an embodiment of the present invention.
Detailed Description
The conception, specific structure and technical effects of the present disclosure will be clearly and completely described below in conjunction with the embodiments and the accompanying drawings to fully understand the objects, aspects and effects of the present disclosure. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The following explains the principle of radar measurement of physical sign data (respiration rate, heart rate, respiration rate variability, and heart rate variability) of a human body:
the respiration and the heartbeat of the human body cause the micro displacement of the chest wall, wherein the displacement amplitude caused by the respiration is 1mm to 12mm, and the displacement amplitude caused by the heartbeat is 0.01mm to 0.5 mm. Both the displacement caused by breathing and the displacement caused by the heartbeat are quasi-periodic mechanical movements, the frequency of breathing is typically 0.1Hz to 0.6Hz, and the frequency of heartbeat is 0.8Hz to 2.5 Hz. The small displacement of the chest wall can generate a modulation effect on the radar signal, and an echo signal generated by modulation is received by the radar and is processed. The frequency of respiratory and heartbeat movements can be measured in a non-contact manner.
The following is a specific technical scheme provided by the invention:
referring to fig. 1, fig. 1 shows a signal extraction method based on frequency modulated continuous wave radar, which includes the following steps:
step S100, preprocessing a chest wall mechanical motion signal of a human body to be detected received by a frequency modulation continuous wave radar to obtain an echo signal, wherein the echo signal comprises: a respiratory signal, a heartbeat signal, a higher harmonic component of the respiratory signal, a higher harmonic component of the heartbeat signal, and a noise signal;
specifically, a frequency modulation continuous wave radar is adopted to transmit electromagnetic wave signals to a human body to be detected and receive chest wall mechanical motion signals returned by the human body to be detected; then, preprocessing operations such as signal sampling, clutter filtering, extraction of a distance unit where the chest wall is located and the like are carried out on the chest wall mechanical motion signal;
the pretreatment comprises the following steps: the method comprises the steps of sampling a chest wall mechanical motion signal, processing the sampled echo signal by using a multiple signal classification algorithm to obtain a high-resolution range image, and performing chest wall position estimation, pre-whitening processing, I/Q channel imbalance compensation and phase unwrapping on the high-resolution range image.
And S200, filtering a signal without noise in the echo signal to obtain a filtering signal, determining a frequency-power spectrum of the filtering signal in an estimated frequency interval, and separating according to a spectrogram of a peak value of the frequency-power spectrum to obtain a heartbeat signal and a respiration signal.
In the prior art, one difficulty in vital sign detection by using a biological radar is separating a heartbeat signal from an echo signal, and the method for estimating the signal frequency by matching with a power spectrum can achieve the purpose of retaining components of expected signals (respiratory signals and heartbeat signals) and filtering other interference components, thereby extracting the heartbeat signal and the respiratory signals in a complex noise environment.
Referring to fig. 2, in a modified embodiment, the step S200 includes:
step S210, determining an estimated frequency interval of the echo signal, and setting n frequency points at equal intervals in the estimated frequency interval;
in a specific embodiment, the estimated value range of the frequency interval is [0.10Hz,3.00Hz ]; 290 frequency points are set in an estimated frequency interval F at equal intervals, the interval between two adjacent frequency points is 0.01Hz, the estimated frequency interval is divided into 290 parts at equal intervals (the more frequency interval points are set, the higher the frequency resolution is), namely, the dividing interval of the estimated frequency interval is 0.01Hz, and F is [0.10,0.11,0.12, …,2.99,3.00 ].
In one embodiment, the mathematical model of the echo signal is represented as: y ═ YF+N＝A*S+N；
Wherein Y represents an echo signal, YFRepresenting a signal without noise in the echo signal, and N represents a noise signal;
YF＝A*S，
is a normalized frequency vector matrix of an estimated frequency interval F, S represents a complex envelope matrix of an echo signal, a represents a Fourier basis vector in a frequency domain, and F ═ F1，f2，f3…，fn]， f1，f2，f3…，fnN frequency points which are arranged at equal intervals are represented;
in this embodiment, it is assumed that the echo signal is composed of two parts, namely noise and other signals, and the noise signal is a zero-mean stationary white gaussian noise signal. Wherein Y ∈ C, and C represents a complex field.
Step S220, selecting a frequency point from the estimated frequency interval as an expected frequency point;
step S230, determining a frequency vector matrix of the expected frequency point, and incorporating the frequency vector matrix into an expected subspace;
step S240, determining a difference set of the estimated frequency interval and the selected expected frequency point, and taking a frequency vector matrix of the difference set as an interference subspace (null space);
step S250, constructing an oblique projection operator of the echo signal, and performing oblique projection filtering on a signal without noise in the echo signal according to the oblique projection operator to obtain a filtered signal;
in one embodiment, the calculation formula of the oblique projection operator is: eA(θ)|A(V)＝A(θ)/[A(θ)H*A(V)* A(θ)]*A(θ)HA (theta), where theta is the expected frequency point, A (theta) is the frequency vector matrix of the expected frequency point, V is the difference set, A (V) is the frequency vector matrix of the difference set, (. cndot)HRepresenting a conjugate transpose operation, A (θ)HA conjugate transpose matrix representing a (θ);
the calculation formula of the filtering signal is as follows: y ═ EA(θ)|A(v)*YFF is the estimated frequency range, YFY 'is a signal without noise in the echo signal, and Y' is a filtering signal.
Step S260, calculating the power of the filtering signal, and weighting the power P by adopting a self-adaptive weight vector to obtain the weighted power of the filtering signal;
in one embodiment, the power P of the filtered signal Y' is calculated by the following formula:
In one embodiment, the adaptive weight vector calculation formula is: 1/trace (E)A(θ)|A(V) H* EA(θ)|A(V)) U is the adaptive weight vector; the adaptive weight vector calculation formula is as follows: p 'is U × P, and P' is the weighted power of the filtered signal.
In the step, the oblique projection operator is adjusted by adopting the self-adaptive weight vector, so that the power values of two adjacent signals on the frequency can be balanced, and the problem that the power peaks of heartbeat signals and respiratory signals on a power spectrum are overlapped and are difficult to separate because the power of weak signals is covered by strong signals is solved.
Step S270, determining whether the estimated frequency interval is traversed, if not, selecting the remaining frequency points from the estimated frequency interval as expected frequency points, and jumping to the step S230; if yes, go to step S280;
and step S280, determining a frequency-power spectrum of the estimated frequency interval, and separating according to a spectrogram of a peak value of the frequency-power spectrum to obtain a heartbeat signal and a respiration signal.
In this embodiment, on the premise of the prior knowledge that the frequency ranges of the respiratory signal and the heartbeat signal are known, the interference signals (the higher harmonic component of the respiratory signal and the higher harmonic component of the heartbeat signal) in the frequency range are removed, the heartbeat signal and the respiratory signal are separated from the spectrogram of the frequency-power spectrum peak value, the frequencies of the heartbeat signal and the respiratory signal are obtained, and the unit is converted into: times per minute.
Referring to fig. 3, to verify the feasibility of extracting respiratory signals and heartbeat signals from echo signals, the applicant designed and performed simulation experiments on the MATLAB software platform.
Firstly, collecting an echo signal received by a frequency modulation continuous wave radar, wherein the echo signal comprises a respiration signal, a heartbeat signal, a fifth order high harmonic component of the respiration signal and a Gaussian white noise signal. Wherein, the fundamental frequencies of the respiration signal and the heartbeat signal are respectively 0.3Hz and 1.3Hz, the corresponding respiration frequency is 18 times/minute, and the heartbeat frequency is 78 times/minute. Then, software simulation is carried out by adopting the method provided by the application, finally, the respiratory signal and the heartbeat signal are successfully extracted, the simulation experiment result accords with the expected design, and the fact that the research scheme to be adopted by the patent is feasible in the simulation link is verified.
Corresponding to the method of fig. 1, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the frequency modulated continuous wave radar-based signal extraction method according to any one of the above embodiments.
Corresponding to the method in fig. 1, an embodiment of the present invention further provides a frequency modulated continuous wave radar-based signal extraction system, including:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement a method for frequency modulated continuous wave radar-based signal extraction as described in any one of the embodiments above.
The contents in the above method embodiments are all applicable to the present system embodiment, the functions specifically implemented by the present system embodiment are the same as those in the above method embodiment, and the beneficial effects achieved by the present system embodiment are also the same as those achieved by the above method embodiment.
The Processor may be a Central-Processing Unit (CPU), other general-purpose Processor, a Digital Signal Processor (DSP), an Application-Specific-Integrated-Circuit (ASIC), a Field-Programmable Gate array (FPGA) or other Programmable logic device, a discrete Gate or transistor logic device, a discrete hardware component, or the like. The general purpose processor may be a microprocessor or the processor may be any conventional processor or the like, the processor being the control center for the fm cw radar based signal extraction system, with various interfaces and lines connecting the various parts of the entire fm cw radar based signal extraction system operational apparatus.
The memory may be used to store the computer programs and/or modules, and the processor may implement the various functions of the fm continuous wave radar-based signal extraction system by executing or executing the computer programs and/or modules stored in the memory and calling up the data stored in the memory. The memory may mainly include a storage program area and a storage data area, wherein the storage program area may store an operating system, an application program required by at least one function (such as a sound playing function, an image playing function, etc.), and the like; the storage data area may store data (such as audio data, a phonebook, etc.) created according to the use of the cellular phone, and the like. In addition, the memory may include high speed random access memory, and may also include non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a Smart-Media-Card (SMC), a secure-Digital (SD) Card, a Flash-memory Card (Flash-Card), at least one magnetic disk storage device, a Flash memory device, or other volatile solid state storage device.
While the present disclosure has been described in considerable detail and with particular reference to a few illustrative embodiments thereof, it is not intended to be limited to any such details or embodiments or any particular embodiments, but it is to be construed with references to the appended claims so as to provide a broad, possibly open interpretation of such claims in view of the prior art, and to effectively encompass the intended scope of the disclosure. Furthermore, the foregoing describes the disclosure in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the disclosure, not presently foreseen, may nonetheless represent equivalent modifications thereto.
Claims (8)
1. A signal extraction method based on a frequency modulation continuous wave radar is characterized by comprising the following steps:
step S100, preprocessing a chest wall mechanical motion signal of a human body to be detected received by a frequency modulation continuous wave radar to obtain an echo signal, wherein the echo signal comprises: a respiratory signal, a heartbeat signal, a higher harmonic component of the respiratory signal, a higher harmonic component of the heartbeat signal, and a noise signal;
and S200, filtering a signal without noise in the echo signal to obtain a filtering signal, determining a frequency-power spectrum of the filtering signal in an estimated frequency interval, and separating according to a spectrogram of a peak value of the frequency-power spectrum to obtain a heartbeat signal and a respiration signal.
2. The method for extracting signals based on frequency modulated continuous wave radar as claimed in claim 1, wherein the step S200 comprises:
step S210, determining an estimated frequency interval of the echo signal, and setting n frequency points at equal intervals in the estimated frequency interval;
step S220, selecting a frequency point from the estimated frequency interval as an expected frequency point;
step S230, determining a frequency vector matrix of the expected frequency point, and incorporating the frequency vector matrix into an expected subspace;
step S240, determining a difference set of the estimated frequency interval and the selected expected frequency point, and taking a frequency vector matrix of the difference set as an interference subspace;
step S250, constructing an oblique projection operator of the echo signal, and performing oblique projection filtering on a signal without noise in the echo signal according to the oblique projection operator to obtain a filtered signal;
step S260, calculating the power of the filtering signal, and weighting the power P by adopting a self-adaptive weight vector to obtain the weighted power of the filtering signal;
step S270, determining whether the estimated frequency interval is traversed, if not, selecting the remaining frequency points from the estimated frequency interval as expected frequency points, and jumping to the step S230; if yes, go to step S280;
and step S280, determining a frequency-power spectrum of the estimated frequency interval, and separating according to a spectrogram of a peak value of the frequency-power spectrum to obtain a heartbeat signal and a respiration signal.
3. A method as claimed in claim 2, wherein the estimated frequency range is [0.10Hz,3.00Hz ], and n is 290.
4. According to claim2, the signal extraction method based on the frequency modulation continuous wave radar is characterized in that the calculation formula of the oblique projection operator is as follows: eA(θ)|A(V)＝A(θ)/[A(θ)H*A(V)*A(θ)]*A(θ)HA (θ), where θ is the desired frequency point, a (θ) is a frequency vector matrix of the desired frequency point, V is a difference set, and a (V) is a frequency vector matrix of the difference set;
the calculation formula of the filtering signal is as follows: y ═ EA(θ)|A(V)*YFF is the estimated frequency range, YFAnd Y' is a filtering signal for the oblique projection operator to the signal without noise in the echo signal.
5. A frequency modulated continuous wave radar based signal extraction method according to claim 4, characterized in that the power P of the filtered signal Y' is calculated by the following formula:
6. The method of claim 5, wherein the adaptive weight vector is calculated by the following formula: 1/trace (E)A(θ)|A(V) H*EA(θ)|A(V)) U is the adaptive weight vector; the adaptive weight vector calculation formula is as follows: p 'is U × P, and P' is the weighted power of the filtered signal.
7. A computer-readable storage medium, having stored thereon a computer program which, when being executed by a processor, carries out the steps of the frequency modulated continuous wave radar-based signal extraction method according to any one of claims 1 to 6.
8. A frequency modulated continuous wave radar-based signal extraction system, comprising:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement a frequency modulated continuous wave radar-based signal extraction method as claimed in any one of claims 1 to 6.
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