A code division multiple access based near field coherent cardiac radio frequency sensing method and system
By employing a near-field coherent cardiac radio frequency sensing method based on code division multiple access, and utilizing four synchronous signal modulation and demodulation, the problem of accurate analysis of cardiac electromechanical asynchrony was solved, achieving high-isolation signal acquisition and quantification of mechanical asynchrony in the four chambers of the heart.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG UNIV
- Filing Date
- 2023-12-11
- Publication Date
- 2026-06-05
Smart Images
Figure CN117672490B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of radio frequency sensing research, and in particular relates to a near-field coherent cardiac radio frequency sensing method and system based on code division multiple access. Background Technology
[0002] Cardiac asynchrony is an important pathological feature of heart failure associated with ventricular myocardial structural abnormalities, left bundle branch block (LBBB), and right bundle branch block (RBBB). Furthermore, cardiac asynchrony is used as a predictor of CRT response and patient prognosis during cardiac resynchronization therapy (CRT). Cardiac asynchrony is classified into electrical asynchrony and mechanical asynchrony. Electrical cardiac asynchrony is associated with prolonged ventricular conduction time. The traditional method for assessing synchronized ventricular activation is measuring QRS duration, but ventricular asynchrony may exist even when electrical activity parameters are normal. Cardiac mechanical asynchrony is more directly related to cardiac function than electrical activity, and previous studies have found it to be more strongly correlated with the benefits of acute and chronic CRT.
[0003] Doppler radar sensors are used in biomedical and healthcare applications to detect human heartbeats and respiration. They indirectly obtain heartbeat information by extracting vibrations from the skin surface. The obtained heartbeat information is a mixture of ventricular and attrial information, making it impossible to analyze cardiac mechanical asynchrony. Summary of the Invention
[0004] To address the shortcomings of existing technologies, this invention provides a near-field coherent cardiac radio frequency sensing method and system based on code division multiple access.
[0005] In a first aspect, embodiments of the present invention provide a near-field coherent cardiac radio frequency sensing method based on code division multiple access, the method comprising:
[0006] Four synchronous baseband signals with a frequency of f are configured, and four synchronous chips are configured. The synchronous baseband signals are multiplied by the corresponding synchronous chips and modulated to obtain four digital baseband signals. The four digital baseband signals are then subjected to digital-to-analog conversion, up-conversion, and power amplification to obtain four cardiac measurement signals. The four cardiac measurement signals are transmitted to their respective antennas via an RF transceiver and then transmitted. The antennas are respectively located in the left ventricle, left atrium, right ventricle, and right atrium.
[0007] The antenna receives the reflected signal and records it as a heart sensing signal; the heart sensing signal is transmitted to the radio frequency transceiver, and after low noise amplification, downconversion and analog-to-digital conversion, a baseband signal containing information about the heart chamber beating is obtained;
[0008] The baseband signal containing information about the heart chamber beating is multiplied with the corresponding synchronization chip, demodulated, and bandpass filtered to obtain the demodulated signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium, respectively.
[0009] Furthermore, the synchronization chip consists of two parts: a frame header and an orthogonal code. The frame header is used to locate the chip, and the orthogonal code is used to modulate and demodulate the signal.
[0010] Furthermore, the orthogonal codes are set to (1000)2, (0100)2, (0010)2, and (0001)2 respectively, and the frame header is set to (00)2, resulting in four chip paths of (00 1000)2, (00 0100)2, (00 0010)2, and (00 0001)2, with each chip length greater than 2T.
[0011] Furthermore, the process of converting the four digital baseband signals from digital to analog, up-converting, and amplifying them to obtain four cardiac measurement signals includes: converting the four digital baseband signals from digital to analog by a digital-to-analog converter, up-converting them to the RF band by a mixer, and amplifying them by a power amplifier to obtain cardiac measurement signals; wherein, the RF band is set to 1.8 GHz.
[0012] Furthermore, the bandpass filter frequency band is set to 0.8-15Hz.
[0013] Secondly, embodiments of the present invention provide a near-field coherent cardiac radio frequency sensing system based on code division multiple access (CDMA) for implementing the aforementioned near-field coherent cardiac radio frequency sensing method based on CDMA. The system includes:
[0014] The cardiac measurement signal acquisition module is used to set the frequency f and amplitude of the synchronous baseband signal via a host computer, configure the synchronous baseband signal accordingly via a digital signal processing module, configure four synchronous chips via the digital signal processing module, and modulate the synchronous baseband signal by multiplying it with the corresponding synchronous chips to obtain four digital baseband signals. The four digital baseband signals are then converted from digital to analog by a digital-to-analog converter, up-converted by a mixer, and amplified by a power amplifier to obtain four cardiac measurement signals. These four cardiac measurement signals are then transmitted to their respective antennas via an RF transceiver. The antennas are respectively located in the left ventricle, left atrium, right ventricle, and right atrium.
[0015] The cardiac sensor signal acquisition module receives reflected signals through an antenna and records them as cardiac sensor signals. The cardiac sensor signals are then transmitted to an RF transceiver, where they are amplified by a low-noise amplifier, down-converted by a mixer, and converted to digital by an analog-to-digital converter to obtain a baseband signal containing information about the heart chambers beating.
[0016] The cardiac sensor signal demodulation module uses a host computer to multiply the baseband signal containing the heart chamber beating information with the corresponding synchronization chip for demodulation and bandpass filtering, to obtain the demodulated signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium respectively.
[0017] An external clock source is used to synchronize the phase of the four cardiac measurement signals.
[0018] Furthermore, upconversion via a mixer includes: setting the RF frequency band via a host computer, and then generating the corresponding RF signal via a phase-locked loop and a voltage-controlled oscillator.
[0019] Furthermore, the system also includes a display module for displaying in real time the demodulated signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium.
[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a near-field coherent cardiac radio frequency sensing method and system based on code division multiple access. By using code division multiple access technology, crosstalk between signals from different channels is reduced, and demodulated signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium are obtained, that is, four highly isolated ventricular motions. Compared with other radio frequency sensing systems, the method of the present invention can not only analyze heart rate and locate P, QRS, and T waves in electrocardiograms, but also obtain the time-series waveform signals of the four ventricles of the heart. It can also be used to further quantify and analyze the mechanical asynchrony between atrioventricular and interventricular systems. Attached Figure Description
[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0022] Figure 1 This is a block diagram of the overall design structure of the near-field coherent cardiac radio frequency sensing method based on code division multiple access provided in this embodiment of the invention;
[0023] Figure 2 This is a hardware system structure block diagram of the near-field coherent cardiac radio frequency sensing method based on code division multiple access designed in this invention;
[0024] Figure 3 This is a schematic diagram of code division modulation of the near-field coherent cardiac radio frequency sensing method based on code division multiple access provided in an embodiment of the present invention;
[0025] Figure 4 This is a schematic diagram of the mechanical signals and synchronous ECG signals of the four chambers of the heart obtained by the near-field coherent cardiac radio frequency sensing method based on code division multiple access provided in this embodiment of the invention.
[0026] Figure 5 This is a schematic diagram of cardiac signal and cardiac asynchrony parameter analysis provided in an embodiment of the present invention. Detailed Implementation
[0027] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.
[0028] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms “a,” “the,” and “the” used in this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.
[0029] It should be understood that although the terms first, second, third, etc., may be used in this invention to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first information may also be referred to as second information without departing from the scope of this invention, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to a determination."
[0030] The present invention will now be described in detail with reference to the accompanying drawings. Unless otherwise specified, the features of the following embodiments and implementations can be combined with each other.
[0031] like Figure 1 As shown, this invention provides a near-field coherent cardiac radio frequency sensing method based on code division multiple access, the method comprising:
[0032] Step S1: Configure 4 synchronous baseband signals with a frequency of f, configure 4 synchronous chips, multiply the synchronous baseband signals with the corresponding synchronous chips for modulation, and obtain 4 digital baseband signals; perform digital-to-analog conversion, up-conversion and power amplification on the 4 digital baseband signals to obtain 4 cardiac measurement signals; transmit the cardiac measurement signals to the antenna through the radio frequency transceiver, and transmit the cardiac measurement signals from the antenna.
[0033] Specifically, step S1 includes the following steps:
[0034] Step S101: Configure 4 synchronous baseband signals with a frequency of f and configure 4 synchronous chips.
[0035] Furthermore, the synchronization chip consists of two parts: a frame header and an orthogonal code. The frame header is used to locate the chip, and the orthogonal code is used to modulate and demodulate the signal. In this example, since the system consists of four RF transceivers, four-bit orthogonal codes are used to encode the four channels as (1000)2, (0100)2, (0010)2, and (0001)2, and the frame header is set to (00)2, resulting in four chips as (00 1000)2, (00 0100)2, (00 0010)2, and (00 0001)2. Each bit of the chip is longer than 2T to ensure that the subsequent cardiac displacement signal is not distorted. Figure 3 As shown in (a) in the figure.
[0036] Step S102: The synchronous baseband signal is multiplied by the corresponding synchronous chip and modulated to obtain four digital baseband signals. The in-phase (I) and quadrature (Q) signals of the four channels after modulation are as follows: Figure 3 As shown in (b) of the diagram.
[0037] Step S103: After performing digital-to-analog conversion, up-conversion, and power amplification on the four digital baseband signals, four cardiac measurement signals are obtained.
[0038] Specifically, Figure 3 The digital baseband signal shown in (b) is converted into an analog baseband signal by a digital-to-analog converter (DAC), then upconverted to the RF band by a mixer, and amplified by a power amplifier to obtain a cardiac measurement signal; the cardiac measurement signal is transmitted to an antenna via an RF transceiver, and the cardiac measurement signal is transmitted from the antenna.
[0039] Furthermore, the RF band must not only be able to couple radio frequency signals into the chest cavity, but also be able to achieve a high degree of local focusing to distinguish the differences in the beating signals of the four chambers of the heart. Preferably, in this embodiment, the RF is set to 1.8 GHz according to the heart rate. It should be noted that the specific frequency is affected by the individual and the experimental environment, and those skilled in the art can adjust the RF band according to the actual situation.
[0040] In step S2, part of the cardiac measurement signal transmitted by the antenna is coupled to the surface of the corresponding heart chamber and then reflected back, while the other part is directly reflected by the skin. The antenna receives both reflected signals and records them as cardiac sensing signals. The cardiac sensing signals are transmitted to an RF transceiver, and after passing through a low-noise amplifier, down-conversion, and analog-to-digital converter, a baseband signal containing information about the heart chamber beating is obtained, such as... Figure 3 As shown in (c), the overlapping non-uniform amplitudes represent the attenuation of different sensing channels.
[0041] Step S3: Multiply the baseband signal containing the heart chamber beating information with the corresponding synchronization chip and demodulate it to obtain the demodulated signal of the heart chamber beating information, such as... Figure 3 As shown in (d) in the figure.
[0042] On the other hand, embodiments of the present invention also provide a near-field coherent cardiac radio frequency sensing system based on code division multiple access (CDMA) to implement the aforementioned near-field coherent cardiac radio frequency sensing method based on CDMA, such as... Figure 2 As shown, the system includes:
[0043] The cardiac measurement signal acquisition module is used to set the frequency f and amplitude of the synchronous baseband signal via a host computer, configure the synchronous baseband signal accordingly via a digital signal processing module, configure four synchronous chips via the digital signal processing module, and modulate the synchronous baseband signal by multiplying it with the corresponding synchronous chips to obtain four digital baseband signals. The four digital baseband signals are then converted from digital to analog by a digital-to-analog converter, up-converted by a mixer, and amplified by a power amplifier to obtain four cardiac measurement signals. These four cardiac measurement signals are then transmitted to their respective antennas via an RF transceiver. The antennas are respectively located in the left ventricle, left atrium, right ventricle, and right atrium.
[0044] The cardiac sensor signal acquisition module receives reflected signals through an antenna and records them as cardiac sensor signals. The cardiac sensor signals are then transmitted to an RF transceiver, where they are amplified by a low-noise amplifier, down-converted by a mixer, and converted to digital by an analog-to-digital converter to obtain a baseband signal containing information about the heart chambers beating.
[0045] The cardiac sensor signal demodulation module uses a host computer to multiply the baseband signal containing the heart chamber beating information with the corresponding synchronization chip for demodulation and bandpass filtering, to obtain the demodulated signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium respectively.
[0046] An external clock source is used to synchronize the phase of the four cardiac measurement signals.
[0047] The upconversion via mixer includes setting the RF frequency band via a host computer, and then generating the corresponding RF signal via a phase-locked loop and a voltage-controlled oscillator.
[0048] Furthermore, the system also includes a display module for real-time display of the demodulation signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium.
[0049] Example 1
[0050] The following section further elaborates on the near-field coherent cardiac radio frequency sensing method based on code division multiple access (CDMA) provided by this invention, which is based on a four-channel radio frequency transceiver, an external clock source, four pairs of transceiver antennas, a digital signal processing module, and a host computer. The CDMA protocol is used to better isolate signals from the four cardiac chambers.
[0051] In this example, the digital signal processing module uses a DSP (Digital Signal Processing) module.
[0052] The 4-channel RF transceiver includes a first channel (Tx1 / Rx1), a second channel (Tx2 / Rx2), a third channel (Tx3 / Rx3), and a fourth channel (Tx4 / Rx4). The first channel (Tx1 / Rx1) is wired to the first antenna, which is placed in the left atrium of the heart; the second channel (Tx2 / Rx2) is wired to the second antenna, which is placed in the right atrium of the heart; the third channel (Tx3 / Rx3) is wired to the third antenna, which is placed in the left ventricle of the heart; and the fourth channel (Tx4 / Rx4) is wired to the fourth antenna, which is placed in the right ventricle of the heart.
[0053] The method includes:
[0054] Step S1: Configure 4 synchronous baseband signals with a frequency of f, configure 4 synchronous chips, multiply the synchronous baseband signals with the corresponding synchronous chips for modulation, and obtain 4 digital baseband signals; perform digital-to-analog conversion, up-conversion and power amplification on the 4 digital baseband signals to obtain 4 cardiac measurement signals; transmit the cardiac measurement signals to the antenna through the radio frequency transceiver, and transmit the cardiac measurement signals from the antenna.
[0055] like Figure 3 As shown in (b) in the diagram. The first and second bits of the four channels are the frame headers. The third bit of the first channel carries the synchronization baseband signal; the fourth bit of the second channel carries the synchronization baseband signal; the fifth bit of the third channel carries the synchronization baseband signal; and the sixth bit of the fourth channel carries the synchronization baseband signal.
[0056] In step S2, part of the cardiac measurement signal transmitted by the antenna is coupled to the surface of the corresponding heart chamber and then reflected back, while the other part is directly reflected by the skin. The antenna receives both reflected signals and records them as cardiac sensing signals. The cardiac sensing signals are transmitted to an RF transceiver, and after passing through a low-noise amplifier, down-conversion, and analog-to-digital converter, a baseband signal containing information about the heart chamber beating is obtained, such as... Figure 3 As shown in (c), the overlapping non-uniform amplitudes represent the attenuation of different sensing channels.
[0057] Furthermore, Figure 3As shown in (c), the first and second bits of the four channels are the frame header. The third bit of the first channel carries the baseband signal of the left atrial beating information, and the fourth, fifth, and sixth bits of the first channel carry crosstalk signals from the beating information of other heart chambers. The fourth bit of the second channel carries the signal of the right atrial beating information, and the third, fifth, and sixth bits of the second channel carry crosstalk signals from the beating information of other heart chambers. The fifth bit of the third channel carries the baseband signal of the left ventricular beating information, and the third, fourth, and sixth bits of the third channel carry crosstalk signals from the beating information of other heart chambers. The sixth bit of the fourth channel carries the baseband signal of the right ventricular beating information, and the third, fourth, and fifth bits of the fourth channel carry crosstalk signals from the beating information of other heart chambers.
[0058] Step S3: Multiply the baseband signal containing the heart chamber beating information with the corresponding synchronization chip and demodulate it to obtain the demodulated signal of the heart chamber beating information, such as... Figure 3 As shown in (d), the in-phase signal received from the first channel is multiplied by the chip (00 1000)2 corresponding to the first channel to extract the... Figure 3 The signal corresponding to the left atrial mechanical motion information of the first channel is shown in (c) dashed box.
[0059] Figure 4 This image displays cardiac mechanical vibration signals from four chambers obtained using a near-field coherent cardiac radio frequency sensing method based on code division multiple access. The five curves from top to bottom represent the electrocardiogram (ECG), left atrium, right atrium, left ventricle, and right ventricle signals, with a time resolution of 1 ms. Using the ECG as a reference, the atrial volume reaches its maximum at the T wave and its minimum at the end of the R wave. The P wave corresponds to the pre-constricted left atrial volume, represented by point A on the atrial curves (CH1 and CH2). p A v and A m This indicates that ventricular volume reaches its maximum near the R peak, its minimum at the end of the T wave, and the inflection point between the slowing filling phase and atrial systole near the P wave. These are represented by points V on the ventricular curves (CH3 and CH4). p V v and V m express.
[0060] Figure 5 Figure (a) shows the electrocardiogram (ECG) signals of a person, including the left atrial and left ventricular signal curves. The time difference between the left atrium and left ventricle reaching diastolic peak (AVMPP) was used to characterize atrioventricular mechanical dyssynchrony. Figure 5 (b) shows a person's electrocardiogram (ECG) signal, including the left and right ventricular signal curves. The systole and diastole of the left and right ventricles are basically overlapping, but there is a significant time difference between the peak values of the left and right ventricles (IVMPP), which can be used to measure interventricular mechanical asynchrony.
[0061] Figure 5 (c) in the figure represents the changes in AVMPP and heart rate interval over one minute. Figure 5 In the diagram, (d) represents the changes in IVMPP and heart rate interval within one minute. The trends in AVMPP and IVMPP are similar to those of the heart rate interval, consistent with the characteristics of a normal human heart. To verify the relationship between peak time difference (PP) and heart rate interval, this example plots the PP-heart rate interval distribution as shown below. Figure 5 (e) and Figure 5 As shown in (f), the results indicate that as the heart rate interval increases, both AVMPP and IVMPP also increase.
[0062] In summary, this invention provides a near-field coherent cardiac radio frequency sensing method and system based on code division multiple access (CDMA). By using CDMA technology, crosstalk between signals from different channels is reduced, and demodulated signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium are obtained, i.e., four highly isolated ventricular motion signals. Compared with other radio frequency sensing systems, this invention can not only analyze heart rate and locate P, QRS, and T waves in electrocardiograms, but also obtain the time-series waveform signals of the four ventricles of the heart. Furthermore, it can be used to further quantify and analyze atrioventricular mechanical asynchrony and interventricular mechanical asynchrony.
[0063] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only.
[0064] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.
Claims
1. A near-field coherent cardiac radio frequency sensing method based on code division multiple access, characterized in that, The method includes: Four synchronous baseband signals with a frequency of f are configured, and four synchronous chips are configured. The synchronous baseband signals are multiplied by the corresponding synchronous chips and modulated to obtain four digital baseband signals. The four digital baseband signals are then subjected to digital-to-analog conversion, up-conversion, and power amplification to obtain four cardiac measurement signals. The four cardiac measurement signals are transmitted to their respective antennas via an RF transceiver and then transmitted. The antennas are respectively located in the left ventricle, left atrium, right ventricle, and right atrium. The antenna receives the reflected signal and records it as a heart sensing signal; the heart sensing signal is transmitted to the radio frequency transceiver, and after low noise amplification, downconversion and analog-to-digital conversion, a baseband signal containing information about the heart chamber beating is obtained; The baseband signal containing information about the heart chamber beating is multiplied with the corresponding synchronization chip, demodulated, and bandpass filtered to obtain the demodulated signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium, respectively.
2. The near-field coherent cardiac radio frequency sensing method based on code division multiple access according to claim 1, characterized in that, The synchronization chip consists of two parts: a frame header and an orthogonal code. The frame header is used to locate the chip, and the orthogonal code is used to modulate and demodulate the signal.
3. The near-field coherent cardiac radio frequency sensing method based on code division multiple access according to claim 1 or 2, characterized in that, The orthogonal codes are set to (1000)2, (0100)2, (0010)2, and (0001)2 respectively, and the frame header is set to (00)2, resulting in four chip paths of (00 1000)2, (00 0100)2, (00 0010)2, and (00 0001)2.
4. The near-field coherent cardiac radio frequency sensing method based on code division multiple access according to claim 1, characterized in that, After performing digital-to-analog conversion, up-conversion, and power amplification on the four digital baseband signals, four cardiac measurement signals were obtained, including: The four digital baseband signals are converted into analog baseband signals by a digital-to-analog converter, then upconverted to the RF band by a mixer, and amplified by a power amplifier to obtain the cardiac measurement signal; the RF band is set to the UHF band.
5. The near-field coherent cardiac radio frequency sensing method based on code division multiple access according to claim 1, characterized in that, The bandpass filter frequency band is set to 0.8-15Hz, which can be adaptively adjusted according to the heart.
6. A near-field coherent cardiac radio frequency sensing system based on code division multiple access, characterized in that, The system is used to implement the near-field coherent cardiac radio frequency sensing method based on code division multiple access as described in any one of claims 1-5, wherein the system is: The cardiac measurement signal acquisition module is used to set the frequency f and amplitude of the synchronous baseband signal via a host computer. The digital signal processing module configures the synchronous baseband signal accordingly, configures four synchronous chips, and modulates the synchronous baseband signal by multiplying it with the corresponding synchronous chips to obtain four digital baseband signals. The four digital baseband signals are then converted from digital to analog by a digital-to-analog converter, up-converted by a mixer, and amplified by a power amplifier to obtain four cardiac measurement signals. The four cardiac measurement signals are transmitted to their respective antennas via a radio frequency transceiver and then transmitted; the antennas are respectively located in the left ventricle, left atrium, right ventricle, and right atrium. The cardiac sensor signal acquisition module receives reflected signals through an antenna and records them as cardiac sensor signals. The cardiac sensor signals are then transmitted to an RF transceiver, where they are amplified by a low-noise amplifier, down-converted by a mixer, and converted to digital by an analog-to-digital converter to obtain a baseband signal containing information about the heart chambers beating. The cardiac sensor signal demodulation module uses a host computer to multiply the baseband signal containing the heart chamber beating information with the corresponding synchronization chip for demodulation and bandpass filtering, obtaining the demodulated signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium respectively; An external clock source is used to synchronize the phase of the four cardiac measurement signals.
7. A near-field coherent cardiac radio frequency sensing system based on code division multiple access according to claim 6, characterized in that, Upconversion via a mixer includes: The RF frequency band is set by the host computer, and then the corresponding RF signal is generated by the phase-locked loop and voltage-controlled oscillator.
8. A near-field coherent cardiac radio frequency sensing system based on code division multiple access according to claim 6, characterized in that, The system also includes: The display module is used to display the demodulated signals corresponding to the beating information of the left ventricle, left atrium, right ventricle, and right atrium in real time.