CN112315452B - Human body respiration tracking method, device and system based on multipath phase cancellation - Google Patents
Human body respiration tracking method, device and system based on multipath phase cancellation Download PDFInfo
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
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Abstract
The present disclosure provides a human body respiration tracking method based on multipath phase cancellation, which includes constructing a first phase shift vector model according to an antenna spacing and a signal bandwidth; calculating sampling frequency offset time delay and packet detection time delay, and constructing a second phase shift vector model according to the calculation result; calculating according to the first phase shift vector model and the second phase shift vector model to obtain a human respiration signal and a receiving and transmitting direct path signal; conjugate multiplication is carried out on the human body respiration signal and the receiving and transmitting direct path signal, and phase offset in the signals is eliminated; filtering the result of conjugate multiplication to obtain a time domain respiratory signal; the respiratory frequency is obtained through the time domain respiratory signal calculation, and compared with the prior art, the efficiency and the accuracy of the method are greatly improved. The disclosure also provides a human body respiration tracking device and system based on multipath phase cancellation.
Description
Technical Field
The disclosure belongs to the field of signal processing, and particularly relates to a human body respiration tracking method, device and system based on multipath phase cancellation.
Background
The respiratory state of human body is an important index for analyzing the health condition of human body, and has important significance for disease diagnosis and monitoring abnormal state of human body. However, most of the existing respiration monitoring technologies require that the sensor and the monitored person have direct physical contact, which affects the normal life of the monitored person and cannot perform long-time monitoring.
Since the respiratory process can cause periodic vibration of the chest cavity to affect the propagation of electromagnetic signals, the radar-based method can realize non-contact human respiratory frequency estimation, however, the radar-based method requires the use of specially designed hardware which is often expensive, and the application of the radar-based respiratory frequency estimation system is limited.
Ubiquitous WiFi devices offer another possibility for contactless breathing frequency estimation. Channel State Information (CSI) in WiFi devices describes the attenuation and phase shift experienced by a signal during propagation. The measured value of the channel state information can be periodically changed by the thoracic cavity vibration caused by the human breathing, so that the possibility of estimating the human breathing frequency by using the channel state information is provided. Due to the limitation of hardware of the WiFi device, the phase of the channel state information is interfered by various phase errors of the receiving end, so the current methods based on the channel state information all use the amplitude of the channel state information to estimate the breathing frequency along with the change of time. However, the existing methods have very limited performance since the amplitude is less sensitive to small movements in the environment. In addition, since the respiratory rate of a human body may be affected by various physical factors, such as speaking, thinking and even some unconscious actions may cause the respiratory rate to change greatly in a short time. Therefore, the method has a great significance in tracking the specific state of human respiration compared with the estimation of the respiratory frequency, and the existing methods cannot achieve the target.
The difficulty in tracking the human breathing using channel state information is the phase offset in the WiFi device. Since the WiFi device itself is manufactured without consideration of the environmental perception requirements, there are a variety of phase offsets in the measured CSI, including Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO), and Packet Detection Delay (PDD). These phase offset values vary randomly over time, making the measured CSI phase unusable for respiration tracking. In addition, another difficulty in estimating the respiratory frequency by using the channel state information is the multipath effect, in an indoor environment, a signal always propagates through a plurality of paths to reach a receiving end, and only signals of a part of the paths are influenced by the human respiration, so that in order to track the change of the human respiration signal, the signals influenced by the human respiration need to be extracted. That is, the technical problem to be solved is how to eliminate the phase shift in the signal and how to accurately extract the signal affected by the respiration of the human body.
Disclosure of Invention
In the prior art, the ratio of CSI (channel state information) of two antennas on the same receiving device is often adopted, and the offset on the phase is eliminated by taking the operation of the ratio of complex CSI (channel state information), but the effect is not very good.
A human body respiration tracking method based on multipath phase cancellation comprises the following steps:
constructing a first phase shift vector model according to the antenna spacing and the signal bandwidth;
calculating sampling frequency offset time delay and packet detection time delay, and constructing a second phase shift vector model according to the calculation result;
calculating according to the first phase shift vector model and the second phase shift vector model to obtain a human respiration signal and a receiving and transmitting direct path signal;
conjugate multiplication is carried out on the human body respiration signal and the receiving and transmitting direct path signal, and phase offset in the signals is eliminated;
filtering the result of conjugate multiplication to obtain a time domain respiratory signal;
and calculating the respiratory frequency through the time domain respiratory signal.
According to some embodiments provided by the present disclosure, the constructing the first phase shift vector model according to the antenna spacing and the signal bandwidth comprises: constructing a first phase shift vector model by simultaneously establishing a plurality of antennas and signals on subcarriers, wherein for an iota path of an antenna, a calculation formula of joint phase shift of an m-th antenna and a k-th subcarrier relative to a first antenna and a first subcarrier comprises the following steps:
wherein the content of the first and second substances,
is the joint phase shift, j is the imaginary unit, f0Is the carrier frequency of the signal, Δ f is the frequency spacing between subcarriers, θιIs the direction of arrival, τ, of the path iotaιIs the propagation time of the path iota, d is the antenna spacing, and c is the propagation speed of the signal.
According to some embodiments provided by the present disclosure, the calculating the sampling frequency offset delay and the packet detection delay, and the constructing the second phase shift vector model according to the estimation result includes: estimating sampling frequency offset and packet detection time delay by adopting a spectrum estimation method, constructing a second phase shift vector model by combining signals on a plurality of antennas and subcarriers and matching the estimation result of the spectrum estimation method, wherein a calculation formula of joint phase shift of an mth antenna and a kth subcarrier relative to a first antenna and a first subcarrier comprises the following steps:
wherein the content of the first and second substances,
is a joint phase shift, τSFOIs the sampling frequency shift delay, tauPDDIs the packet detection delay.
According to some embodiments provided by the present disclosure, the calculation formula for obtaining the human respiration signal and the transmit-receive direct path signal by calculating according to the first phase shift vector model and the second phase shift vector model includes:
wherein, yt(θ1，τ1) Is a human respiratory signal, yt(θ2，τ2) Is to receive and transmit a direct path signal, theta1Is the direction of arrival, tau, of the respiratory signal of the human body1Is the propagation time, theta, of the respiratory signal of the human body2Is the direction of arrival, τ, of the transmit-receive direct path signal2Is the propagation time of the transmit-receive direct path signal, superscriptHDenotes a conjugate transpose, fCFOIs the carrier frequency offset, t is the time of signal reception, HtIs the channel state information in the device at time t.
According to some embodiments provided by the present disclosure, the conjugate multiplying the human respiration signal and the transmit-receive direct path signal is used to eliminate a phase offset in the signal, and the calculation formula includes:
yt＝yt(θ1，τ1)×yt(θ2，τ2)*＝(ΦH(θ1，τ1)-ΦH(θ2，τ2))Ht
＝ΦH(θ1，τ1)Ht-yt(θ2，τ2)
wherein, ytIs to eliminate the signal after the phase shift,*representing conjugation.
According to some embodiments provided by the present disclosure, y is a Hampel filter and a high pass filter pairtAnd filtering the signals to obtain time domain respiration signals.
According to some embodiments provided by the present disclosure, a respiratory frequency is calculated for the time-domain respiratory signal using a fast fourier transform.
The present disclosure also provides a human body respiration tracking device based on multipath phase cancellation, which uses the above method to detect the respiration frequency, and the device includes:
the signal transmitting module is used for transmitting wifi signals;
the signal receiving module is used for receiving channel state information, wherein the channel state information is periodically changed under the influence of thoracic cavity vibration when a human body breathes;
the signal operation module is used for calculating the channel state information to obtain a signal with the signal offset eliminated, wherein the channel state information comprises a human body respiration signal and a receiving and transmitting direct path signal, and the calculation mode is conjugate multiplication;
and the signal processing module is used for receiving the signal after the signal offset is eliminated, filtering the signal to obtain a time domain respiratory signal, and calculating according to the time domain respiratory signal to obtain the respiratory frequency.
The present disclosure also discloses a human body respiration tracking system based on multipath phase cancellation, which detects a respiratory frequency by using the above method, including:
the signal transmitter is used for transmitting wifi signals;
the signal receiver comprises at least two antennas and is used for receiving channel state information, wherein the channel state information is periodically changed under the influence of thoracic cavity vibration when a human body breathes;
the signal operation device is used for calculating the channel state information to obtain a signal with the signal offset eliminated, wherein the channel state information comprises a human body respiration signal and a receiving and transmitting direct path signal, and the calculation mode is conjugate multiplication;
and the signal processor is used for receiving the signal subjected to signal offset elimination, filtering the signal to obtain a time domain respiratory signal, and calculating according to the time domain respiratory signal to obtain the respiratory frequency.
According to some embodiments provided by the present disclosure, at least two of the antennas are arranged in a uniform linear array, and a distance between two adjacent antennas is equal to a half wavelength of the wifi signal.
According to the technical scheme, the first phase shift vector model and the second phase shift vector model are respectively established through the antenna distance, the signal bandwidth, the sampling frequency offset time delay and the packet detection time delay, then the human breathing signal and the receiving and transmitting direct path signal can be accurately extracted from the first phase shift vector model and the second phase shift vector model, and then the signal offset is eliminated through the conjugate multiplication operation of the human breathing signal and the receiving and transmitting direct path signal.
Drawings
FIG. 1 schematically illustrates a flow chart of a method for human breath tracking based on multipath phase cancellation in accordance with an embodiment of the present disclosure;
FIG. 2 is a schematic diagram illustrating performance of a respiratory frequency estimation method based on multipath phase cancellation according to an embodiment of the present disclosure;
FIG. 3 schematically illustrates a graph of normal human breathing detected by an embodiment of the present disclosure;
fig. 4 and 5 schematically show a result of a breath tracking of a human body during a breath change state (breath hold/exhalation) according to an embodiment of the present disclosure.
Detailed Description
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
It should be understood that the description is illustrative only and is not intended to limit the scope of the present disclosure. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the disclosure. It may be evident, however, that one or more embodiments may be practiced without these specific details. Furthermore, in the following description, descriptions of well-known technologies are omitted so as to avoid unnecessarily obscuring the concepts of the present disclosure.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The term "comprising" as used herein indicates the presence of the features, steps, operations but does not preclude the presence or addition of one or more other features.
All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It is noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly formal sense, e.g., Carrier Frequency Offset (CFO), being the magnitude by which a Frequency modulated signal deviates from a Carrier Frequency; for example, the direction of Arrival (Angle of Arrival, AoA) refers to the direction of Arrival of the spatial signals (the direction Angle of each signal arriving at the array reference array element, referred to as the direction of Arrival).
The invention provides a human body respiration tracking method based on multipath phase cancellation, which can accurately extract signals influenced by human body respiration and eliminate phase deviation in the signals.
A human body respiration tracking method based on multipath phase cancellation is disclosed, and fig. 1 schematically shows a flow chart of the human body respiration tracking method based on multipath phase cancellation according to the embodiment of the disclosure.
As shown in fig. 1, a method for tracking human breathing based on multipath phase cancellation includes:
s101: and constructing a first phase shift vector model according to the antenna spacing and the signal bandwidth.
S102: and calculating Sampling Frequency Offset (SFO) and Packet Detection Delay (PDD), and constructing a second phase shift vector model according to the calculation result.
S200: and calculating according to the first phase shift vector model and the second phase shift vector model to obtain a human breathing signal and a receiving and transmitting direct path signal.
S300: conjugate multiplication is performed on the human breathing signal and the transmit-receive direct path signal for eliminating phase offset in the signal.
S400: and filtering the result of conjugate multiplication to obtain a time domain respiratory signal.
S500: and calculating the respiratory frequency through the time domain respiratory signal.
According to some embodiments provided by the present disclosure, constructing the first phase shift vector model according to antenna spacing and signal bandwidth comprises: constructing a first phase shift vector model by simultaneously establishing a plurality of antennas and signals on subcarriers, wherein for an iota path of an antenna, a calculation formula of joint phase shift of an m-th antenna and a k-th subcarrier relative to a first antenna and a first subcarrier comprises the following steps:
wherein the content of the first and second substances,
is the joint phase shift, j is the imaginary unit, f0Is the carrier frequency of the signal, Δ f is the frequency spacing between subcarriers, θιIs the direction of Arrival (AoA) of the path iota, τιTime of Flight (ToF) of the path iota, d is the antenna spacing, and c is the propagation velocity of the signal.
According to some embodiments provided by the present disclosure, calculating a sampling frequency offset delay and a packet detection delay, and constructing the second phase shift vector model according to the estimation result includes: estimating sampling frequency offset and packet detection time delay by adopting a spectrum estimation method, constructing a second phase shift vector model by combining signals on a plurality of antennas and subcarriers and matching the estimation result of the spectrum estimation method, wherein a calculation formula of joint phase shift of an mth antenna and a kth subcarrier relative to a first antenna and a first subcarrier comprises the following steps:
wherein the content of the first and second substances,
is a joint phase shift, τSFOIs the sampling frequency shift delay, tauPDDIs the packet detection delay.
According to some embodiments provided by the present disclosure, the calculation formula for obtaining the human respiration signal and the transmit-receive direct path signal according to the first phase shift vector model and the second phase shift vector model includes:
wherein, yt(θ1，τ1) Is a human respiratory signal, yt(θ2，τ2) Is to receive and transmit a direct path signal, theta1Is the direction of arrival, tau, of the respiratory signal of the human body1Is the propagation time, theta, of the respiratory signal of the human body2Is the direction of arrival, τ, of the transmit-receive direct path signal2Is the propagation time of the transmit-receive direct path signal, superscriptHDenotes a conjugate transpose, fCFOIs the carrier frequency offset, t is the time of signal reception, HtIs the channel state information in the device at time t.
According to some embodiments provided by the present disclosure, a conjugate multiplication is performed on a human respiration signal and a transmit-receive direct path signal for eliminating a phase offset in the signal, and the calculation formula includes:
yt＝yt(θ1，τ1)×yt(θ2，τ2)*＝(ΦH(θ1，τ1)-ΦH(θ2，τ2))Ht
＝ΦH(θ1，τ1)Ht-yt(θ2，τ2) (4)
wherein, ytIs to eliminate the signal after the phase shift,*representing conjugation.
According to some embodiments provided by the present disclosure, y is a Hampel filter and a high pass filter pairtAnd filtering the signals to obtain time domain respiration signals.
According to some embodiments provided by the present disclosure, the respiratory frequency is calculated for the time-domain respiratory signal using a fast fourier transform.
The device detects the respiratory frequency by using the method, and comprises a signal transmitting module, a signal receiving module, a signal operation module and a signal processing module.
And the signal transmitting module is used for transmitting the wifi signal.
And the signal receiving module is used for receiving channel state information, wherein the channel state information is periodically changed under the influence of thoracic cavity vibration when the human body breathes.
And the signal operation module is used for calculating the channel state information to obtain a signal with the signal offset eliminated, wherein the channel state information comprises a human body respiration signal and a receiving and transmitting direct path signal, and the calculation mode is conjugate multiplication.
And the signal processing module is used for receiving the signal after the signal offset is eliminated, filtering the signal to obtain a time domain respiratory signal, and calculating according to the time domain respiratory signal to obtain the respiratory frequency.
The system detects the respiratory frequency by using the method and comprises a signal transmitter, a signal receiver, a signal operation device and a signal processor.
And the signal transmitter is used for transmitting the wifi signal.
And the signal receiver comprises at least two antennas and is used for receiving channel state information, wherein the channel state information is periodically changed under the influence of thoracic cavity vibration when the human body breathes.
And the signal operation device is used for calculating the channel state information to obtain a signal with the signal offset eliminated, wherein the channel state information comprises a human body respiration signal and a receiving and transmitting direct path signal, and the calculation mode is conjugate multiplication.
And the signal processor is used for receiving the signal subjected to signal offset elimination, filtering the signal to obtain a time domain respiratory signal, and calculating according to the time domain respiratory signal to obtain the respiratory frequency.
According to some embodiments provided by the present disclosure, at least two antennas are arranged in a uniform linear array, and a distance between two adjacent antennas is equal to a half wavelength of a wifi signal.
The technical solutions of the present disclosure are described below with reference to some specific embodiments, and it should be understood that these specific embodiments are only for better and clearer illustration of the technical solutions of the present disclosure so as to facilitate the understanding of the technical solutions of the present disclosure by those skilled in the art, and should not be construed as limiting the scope of the present disclosure.
Fig. 2 schematically illustrates a performance diagram of a respiratory frequency estimation of a human respiration tracking method based on multipath phase cancellation according to some embodiments provided by the present disclosure; FIG. 3 schematically illustrates a graph of normal human breathing detected by an embodiment of the present disclosure;
fig. 4 and 5 schematically show a result of a breath tracking of a human body during a breath change state (breath hold/exhalation) according to an embodiment of the present disclosure.
According to some embodiments provided by the present disclosure, the method proposed by the present disclosure is adopted to track human breath in the case that the tester is 2m away from the signal transmitter and the signal receiver.
According to some embodiments provided by the present disclosure, a center frequency of a signal is set to be 5.31GHz, a bandwidth is set to be 40MHz, a transmission packet rate is 20 times per second, and a receiving end receives the signal by using two antennas with a distance d of 0.26 cm.
According to some embodiments provided by the present disclosure, in an experiment, the respiratory frequency is expressed by the measured number of breaths per minute, the performance of the respiratory frequency estimation is expressed by accuracy, and the calculation formula comprises,
where Accuracy is the Accuracy, b is the true value of the breathing rate,
is an estimate of the breathing frequency.
According to some embodiments provided by the present disclosure, the tester breathes for one minute at a rate of 12 breaths per minute, 15 breaths per minute, and 20 breaths per minute, respectively, and the breathing of the tester is tracked by the method provided by the present disclosure, and the tracking result is shown in fig. 2, which clearly and unquestionably shows that the method provided by the present disclosure achieves high-accuracy tracking of the breathing frequency in all three cases.
According to some embodiments provided by the present disclosure, the tester breathes 15 times in one minute, and the tracking result of the breathing frequency by the method provided by the present disclosure is shown in fig. 3, and the amplitude change of 15 breathing cycles can be clearly observed.
According to some embodiments provided by the present disclosure, when the tester repeatedly switches between the breathing state and the breath holding state, the result of tracking the breathing frequency by the method provided by the present disclosure is shown in fig. 4 and fig. 5, and the change of the breathing frequency and the amplitude can be clearly observed, that is, the breathing frequency of the tester can be accurately measured.
According to the technical scheme, the first phase shift vector model and the second phase shift vector model are respectively established through the antenna distance, the signal bandwidth, the sampling frequency offset time delay and the packet detection time delay, then the human breathing signal and the receiving and transmitting direct path signal can be accurately extracted from the first phase shift vector model and the second phase shift vector model, and then the signal offset is eliminated through the conjugate multiplication operation of the human breathing signal and the receiving and transmitting direct path signal.
So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. In addition, the above definitions of the components are not limited to the specific structures, shapes or manners mentioned in the embodiments, and those skilled in the art may easily modify or replace them.
It is also noted that, unless otherwise indicated, the numerical parameters set forth in the specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. In particular, all numbers expressing dimensions, range conditions, and so forth, used in the specification and claims are to be understood as being modified in all instances by the term "about". Generally, the expression is meant to encompass variations of ± 10% in some embodiments, 5% in some embodiments, 1% in some embodiments, 0.5% in some embodiments by the specified amount.
Those skilled in the art will appreciate that various combinations and/or combinations of features recited in the various embodiments and/or claims of the present disclosure can be made, even if such combinations or combinations are not expressly recited in the present disclosure. In particular, various combinations and/or combinations of the features recited in the various embodiments and/or claims of the present disclosure may be made without departing from the spirit or teaching of the present disclosure. All such combinations and/or associations are within the scope of the present disclosure.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.
Claims (10)
1. A human body respiration tracking method based on multipath phase cancellation is characterized by comprising the following steps:
constructing a first phase shift vector model according to the antenna spacing and the signal bandwidth;
calculating sampling frequency offset time delay and packet detection time delay, and constructing a second phase shift vector model according to the calculation result;
calculating according to the first phase shift vector model and the second phase shift vector model to obtain a human respiration signal and a receiving and transmitting direct path signal;
conjugate multiplication is carried out on the human body respiration signal and the receiving and transmitting direct path signal, and phase offset in the signals is eliminated;
filtering the result of conjugate multiplication to obtain a time domain respiratory signal;
and calculating the respiratory frequency through the time domain respiratory signal.
2. The method of claim 1, wherein constructing the first phase shift vector model based on antenna spacing and signal bandwidth comprises: constructing a first phase shift vector model by simultaneously establishing a plurality of antennas and signals on subcarriers, wherein for an iota path of an antenna, a calculation formula of joint phase shift of an m-th antenna and a k-th subcarrier relative to a first antenna and a first subcarrier comprises the following steps:
wherein the content of the first and second substances,
is the joint phase shift, j is the imaginary unit, f0Is the carrier frequency of the signal, Δ f is the frequency spacing between subcarriers, θιIs the direction of arrival, τ, of the path iotaιIs the propagation time of the path iota, d is the antenna spacing, and c is the propagation speed of the signal.
3. The method of claim 2, wherein the calculating the sampling frequency offset delay and the packet detection delay, and the constructing the second phase shift vector model according to the estimation result comprises: estimating sampling frequency offset and packet detection time delay by adopting a spectrum estimation method, constructing a second phase shift vector model by combining signals on a plurality of antennas and subcarriers and matching the estimation result of the spectrum estimation method, wherein a calculation formula of joint phase shift of an mth antenna and a kth subcarrier relative to a first antenna and a first subcarrier comprises the following steps:
wherein the content of the first and second substances,
is a joint phase shift, τSFOIs the sampling frequency shift delay, tauPDDIs the packet detection delay.
4. The method of claim 3, wherein the formulas for calculating the respiratory signal and the transmit/receive direct path signal according to the first and second phase shift vector models comprise:
wherein, yt(θ1，τ1) Is a human respiratory signal, yt(θ2，τ2) Is to receive and transmit a direct path signal, theta1Is the direction of arrival, tau, of the respiratory signal of the human body1Is the propagation time, theta, of the respiratory signal of the human body2Is the direction of arrival, τ, of the transmit-receive direct path signal2Is the propagation time of the transmit-receive direct path signal, superscriptHDenotes a conjugate transpose, fCFOIs the carrier frequency offset, t is the time of signal reception, HtIs the channel state information in the device at time t.
5. The method of claim 4, wherein the conjugate multiplication of the breathing signal and the transmit-receive direct path signal is used to eliminate phase offset in the signal, and the calculation formula comprises:
yt＝yt(θ1，τ1)×yt(θ2，τ2)*＝(ΦH(θ1，τ1)-ΦH(θ2，τ2))Ht
＝ΦH(θ1，τ1)Ht-yt(θ2，τ2)
wherein, ytIs to eliminate the signal after the phase shift,*representing conjugation.
6. The method of claim 5, wherein y is a Hampel filter and a high pass filter pairtAnd filtering the signals to obtain time domain respiration signals.
7. A method for human breath tracking based on multipath phase cancellation as claimed in claim 5 wherein the respiratory rate is calculated from the time domain respiratory signal using a fast Fourier transform.
8. An apparatus for tracking human breathing based on multipath phase cancellation, the apparatus detecting breathing frequency using the method of any one of claims 1 to 7, the apparatus comprising:
the signal transmitting module is used for transmitting wifi signals;
the signal receiving module is used for receiving channel state information, wherein the channel state information is periodically changed under the influence of thoracic cavity vibration when a human body breathes;
the signal operation module is used for calculating the channel state information to obtain a signal with the signal offset eliminated, wherein the channel state information comprises a human body respiration signal and a receiving and transmitting direct path signal, and the calculation mode is conjugate multiplication;
and the signal processing module is used for receiving the signal after the signal offset is eliminated, filtering the signal to obtain a time domain respiratory signal, and calculating according to the time domain respiratory signal to obtain the respiratory frequency.
9. A human breathing tracking system based on multipath phase cancellation, the system detecting breathing frequency using the method of any one of claims 1 to 7, comprising:
the signal transmitter is used for transmitting wifi signals;
the signal receiver comprises at least two antennas and is used for receiving channel state information, wherein the channel state information is periodically changed under the influence of thoracic cavity vibration when a human body breathes;
the signal operation device is used for calculating the channel state information to obtain a signal with the signal offset eliminated, wherein the channel state information comprises a human body respiration signal and a receiving and transmitting direct path signal, and the calculation mode is conjugate multiplication;
and the signal processor is used for receiving the signal subjected to signal offset elimination, filtering the signal to obtain a time domain respiratory signal, and calculating according to the time domain respiratory signal to obtain the respiratory frequency.
10. The system of claim 9, wherein at least two of the antennas are arranged in a uniform linear array, and a distance between two adjacent antennas is equal to a half wavelength of the wifi signal.
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