KR102326781B1 - Sensor, system and method for detecting radar biosignal - Google Patents

Abstract

The present invention relates to a sensor, a system for detecting a radar bio-signal, and a bio-signal detection method using the same, and more particularly, to a radar having a simple structure without a null detection point while detailing the noise effect by a signal source. As having a structure, the radar biosignal detection sensor according to an embodiment of the present invention includes: a transmitter for transmitting a signal to a living organism; a receiver for receiving a signal reflected from the living organism; and a switching signal applying unit directly connected to the receiving unit to apply a switching signal.

Description

Low-IF radar sensor and system for biosignal detection, and biosignal detection method using the same

The present invention relates to a low-IF radar sensor, a system for detecting a biosignal, and a biosignal detection method using the same, and more particularly, to a simple noise effect without a null detection point while detailing the noise effect by a signal source. It relates to a biosignal detection sensor, system and method having a radar structure of the structure.

Recently, research on detecting human biosignals using radar is being actively conducted. A general radar system is a system that transmits a transmitted signal to a living organism and receives a modulated signal by being reflected. The modulated phase signal includes displacement information about the motion of an object with respect to time. The radar bio-signal detection device using this effect receives a signal modulated by a physiological movement caused by a person's heartbeat and respiration, and detects a heart rate or a breathing cycle.

Radar has the advantage of being able to measure a person's bio-signals from a distance in a non-contact method and not being affected by the external environment. Therefore, the biosignal detection sensor using the radar can be applied to various fields such as monitoring a patient's heartbeat, home healthcare, measuring the heartbeat of a vehicle driver, and a smart home.

A human biosignal is basically a signal having a very low frequency of 0.1 Hz to 3 Hz, and is greatly affected by low-frequency noise such as flicker noise and DC offset in a radar receiver. Since such low-frequency noise has a very high power spectral density compared to general thermal noise, there is a problem in that the detection range of the biosignal radar is limited.

Accordingly, in order to detect a biosignal from a long distance or to increase a signal to noise ratio (SNR), it is necessary to reduce the low frequency noise of the radar receiver. In general, there are problems in that the radar transceiver structure of the direct conversion structure, which is commonly used due to its simple hardware structure, is greatly affected by DC offset and is vulnerable to the effect of flickering noise of the mixer and the baseband amplifier.

In order to overcome the shortcomings of the direct conversion structure, a receiver structure for reducing low-frequency band noise of a radar receiver has been proposed. For example, a heterodyne receiver structure was introduced into the biosignal detection radar, or a coherent low-IF structure was used to avoid low-frequency noise of the radar receiver. However, the heterodyne receiver structure has the disadvantage that the range-correlation effect that cancels the phase noise of the signal source cannot be applied, and the coherent low-IF structure has a hardware structure. The disadvantage is that it is very complicated.

In order to overcome the disadvantages of these structures, a method of modulating a signal of a transmitter to use an intermediate frequency (hereinafter referred to as IF) with a simple structure has been proposed. The method of modulating the signal of the transmitter transmits a signal of a double-side band, which causes a null detection point where a signal is not detected depending on the distance of the subject. . In order to solve this problem, there is an additional problem of using an additional RF filter at the transmitting end or adjusting the IF frequency.

Hereinafter, the null detection point problem will be described in detail.

In the conventionally proposed low-IF radar that modulates a transmission signal, a null detection point at which the biosignal of the subject is not detected occurs depending on the IF frequency and the distance of the subject. This null detection point occurs because a double-side band signal is transmitted when the transmission signal is modulated.

,

주파수의 신호가 각각 물체의 움직임에 의해 위상 변조된다. 각각 위상 변조된 신호(

)를 레이더 수신부에서 수신하게 되는데 이는 다음과 같이 표현할 수 있다.When modulating the signal of the radar transmitter,

,

Each frequency signal is phase-modulated by the movement of the object. Each phase modulated signal (

) is received by the radar receiver, which can be expressed as follows.

과

는 각각 양면 밴드(upper-side band 및 lower-side band)의 신호에 의해 변조된 위상 신호이며,

와

는 각각 피 측정자 거리에 따른 위상 오프셋이다.

class

is the phase signal modulated by the signals of the two-sided bands (upper-side band and lower-side band), respectively,

Wow

are the phase offsets according to the target distance, respectively.

At this time, when the difference between the two phase offsets is a multiple of 180 degrees, it becomes a null point at which no signal is detected. That is, there is a problem that the measurement sensitivity changes according to the distance between the radar and the object in the system for transmitting the double-sided band, and in order to solve this problem, the frequency of the IF needs to be adjusted during each measurement.

Such null points appear at regular intervals according to the wavelength of the IF frequency. If the IF frequency is increased in order to be less affected by low-frequency noise, the distance between the null point and the optimal point becomes narrower. Therefore, in a system for transmitting a double-sided band, there is a limit in which the IF frequency can be increased because a trade-off exists between the level of low-frequency noise and the interval between null points.

Hereinafter, a radar structure using a direct conversion receiver for detecting a biosignal used in the prior art will be described in detail with reference to FIG. 1 .

1 shows a radar having a direct conversion structure in the prior art for detecting a biosignal.

The radar consists of one receiver (120, RX) and one transmitter (110, TX), and uses a direct conversion structure for a simple structure. The radar structure takes the structure of demodulating the I/Q signal in order to solve the problem of the null detection point. By propagating a continuous wave of a single frequency in the transmitter 110, TX of the radar, and receiving the phase-modulated signal in the receiver 120, RX, the heartbeat and respiration signals of the human body are detected.

The radar receiver having a direct conversion structure is affected by DC offset and flickering noise by the mixer 130 and the amplifier, filter, and the like through which the baseband signal passes. In general, since a human biosignal is a signal having a low frequency of 3 Hz or less, it is necessary to reduce low-frequency noise in order to increase the accuracy or distance of measurement. However, in the conventional radar structure, there is a limit to the measurement distance of the biosignal radar because it is directly affected by low-frequency noise.

2 shows a radar having a low-IF structure in the prior art for detecting a biosignal.

The radar of the low-IF structure shown in FIG. 2 shows a double-side band low-IF radar structure using transmission signal modulation in order to overcome the disadvantages of the radar of the direct conversion structure described in FIG. 1 .

Referring to FIG. 2 , a radar having a low-IF structure can be simply implemented by performing double-side band modulation on the transmission signal of the transmitter 211 and adding only a mixer 210 to the transmitter 211 . In this structure, low-frequency noise can be avoided by using the IF frequency of a signal of several kHz to several tens of kHz so as not to be affected by the flickering noise generated by the mixer 220 of the receiving end 221 . In addition, since there is one RF signal source 230 used for the transmitting end 211 and the receiving end 221 , the radar structure according to FIG. 2 applies a range-correlation effect to cancel the phase noise of the signal source. There are advantages to being able to

However, the system for transmitting the double-sided band as shown in FIG. 2 has a problem in that a null detection point at which a biosignal is not detected occurs depending on the distance of the subject. This problem can be adjusted by adjusting the IF frequency, but it is difficult to apply to actual applications. In addition, in order to solve the null detection point problem, a method of transmitting only a single-side band using an RF filter at the transmitting end 211 has been proposed. This can be an impractical method because it is difficult.

(KR) Patent Application No. 10-2018-0009521

An object of the present invention is to provide a sensor, a system for detecting a radar bio-signal, and a bio-signal detection method using the same, which have been devised to solve the above problems.

More specifically, the present invention can 1) apply a range-correlation effect that cancels the effect of a signal source on phase noise, 2) it can be operated with a simple structure, and 3) a signal is detected An object of the present invention is to provide a biosignal detection sensor, system, and method having a switch-based low-IF radar structure having no null detection point.

The present invention also proposes a biosignal radar sensor that is not affected by low-frequency noise of a radar with very simple hardware by applying a digital signal processing method of demodulating an IF signal in a digital stage, and a method for operating the same.

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

A radar biosignal detection sensor according to an embodiment of the present invention includes: a transmitter for transmitting a signal to a living organism; a receiver for receiving a signal reflected from the living organism; and a switching signal applying unit directly connected to the receiving unit to apply a switching signal.

The switching signal applying unit according to an embodiment of the present invention may include a switch or a mixer.

The switching signal according to an embodiment of the present invention may be characterized in that it is a mid-band frequency.

The radar biosignal detection sensor according to an embodiment of the present invention further includes a signal source frequency removal unit, wherein the signal source frequency removal unit is directly connected to a signal source connected to the transmitter and converts the signal output from the signal source to I /Q I/Q modulator that modulates a real-complex signal; a first mixer for combining a real part signal among the signals modulated through the I/Q modulator and a signal modulated through the switching signal applying unit; and a second mixer combining the complex signal among the signals modulated by the I/Q modulator and the signal modulated through the switching signal applying unit.

The radar biosignal detection sensor according to an embodiment of the present invention may include a first analog-to-digital converter for sampling the output of the first mixer and a second analog-to-digital converter for sampling the output of the second mixer .

The radar biosignal detection sensor according to an embodiment of the present invention reflects a carrier signal with respect to the output of the first analog-to-digital converter and the output of the second analog-to-digital converter, respectively, and converts it into a baseband signal. It may further include a down-conversion demodulator for demodulating the output.

The down-conversion demodulator according to an embodiment of the present invention includes: a third mixer for multiplying the _{real part signal (I IF} ) sampled by the first analog-to-digital converter by the first orthogonal carrier signal (I _{c [n]);} a fourth mixer for multiplying the real signal (I_IF) sampled by the first analog-to-digital converter by _{a negative value of a second orthogonal carrier signal (I c [n]);} a fifth mixer for multiplying the _{complex signal (Q IF} ) sampled by the second analog-to-digital converter by a second orthogonal carrier signal (Q _{c [n]);} a sixth mixer for multiplying the _{complex signal (Q IF} ) sampled by the second analog-to-digital converter by a first orthogonal carrier signal (I _{c [n]);} a seventh mixer for adding the output of the third mixer and the output of the fifth mixer; and an eighth mixer that adds the output of the fourth mixer and the output of the sixth mixer.

A radar biosignal detection system according to an embodiment of the present invention includes a radar biosignal detection sensor, and uses an output signal of the biosignal detection sensor using a complex signal demodulation algorithm or an arctangent demodulation algorithm. It may be to detect a biosignal.

A method of detecting a biosignal according to an embodiment of the present invention includes: transmitting, by a transmitter, a radar signal to a living organism; receiving a radar signal reflected from the living body by the bride; and modulating the reflected radar signal by applying a switching signal by a switching signal applying unit directly connected to the receiving unit.

The switching signal according to an embodiment of the present invention may be characterized in that it is an intermediate frequency (IF).

The biosignal detection method according to an embodiment of the present invention comprises the steps of, by a signal source frequency removing unit, removing a signal source frequency by using an I/Q modulator, a first mixer, and a second mixer from a signal modulated through the switching signal applying unit. may further include.

The I/Q modulator according to an embodiment of the present invention is directly connected to a signal source connected to the transmitter, modulates a signal output from the signal source into an I/Q real part-complex signal, and the first mixer comprises: A real signal of the signals modulated through the I/Q modulator and a signal modulated through the switching signal applying unit are combined, and the second mixer includes a complex signal and the switching signal modulated through the I/Q modulator. It may be characterized in that the modulated signal is combined through a signal applying unit.

The method for detecting a biosignal according to an embodiment of the present invention further includes the steps of: a first analog-to-digital converter sampling an output of the first mixer, and a second analog-to-digital converter sampling an output of the second mixer can do.

In the biosignal detection method according to an embodiment of the present invention, a down-conversion demodulator reflects a carrier signal with respect to the output of the first analog-to-digital converter and the output of the second analog-to-digital converter, respectively, to obtain a baseband signal. The method may further include demodulating the output by converting to .

In the step of demodulating the output of the down-conversion demodulator according to an embodiment of the present invention, the third mixer includes the first orthogonal carrier signal (I) with respect to the _{real part signal (I IF ) sampled by the first analog-to-digital converter multiplying c} [n]); multiplying, by a fourth mixer, a negative value of a second orthogonal carrier signal (Q _{c [n]) by a real part signal (I IF} ) sampled by the first analog-to-digital converter; multiplying, by a fifth mixer, a second orthogonal carrier signal (I _c [n]) _{by the complex signal (Q IF} ) sampled by the second analog-to-digital converter; multiplying, by a sixth mixer, a first orthogonal carrier signal (I _c [n]) _{by the complex signal (Q IF} ) sampled by the second analog-to-digital converter; adding, by a seventh mixer, the output of the third mixer and the output of the fifth mixer; and the eighth mixer adding the output of the fourth mixer and the output of the sixth mixer.

The biosignal detection method according to an embodiment of the present invention may further include detecting the biosignal using a complex signal demodulation algorithm or an arctangent demodulation algorithm for the output signal of the biosignal detection sensor. have.

A low-IF radar sensor and system for detecting biosignals and a biosignal detecting method using the same according to an embodiment of the present invention have a structure in which a switch or a mixer is disposed in front of a radar receiver. By modulating the received signal through this structure, it was attempted to reduce the influence of the low-frequency noise of the receiver.

Since the radar using the conventional direct conversion receiver is greatly affected by low-frequency noise from circuits such as mixers and baseband amplifiers, there is a problem in that it is impossible to measure biosignals from a long distance, but according to an embodiment of the present invention, Biosignal detection in a wider range is possible.

The low-IF radar using a switching receiver proposed according to an embodiment of the present invention can overcome the disadvantages of various low-IF radars proposed in the prior art.

The present invention can 1) apply a range-correlation effect that cancels the effect of a signal source on phase noise, 2) it can be operated with a simple structure, and 3) null detection in which a signal is not detected The advantage is that there is no null detection point.

In addition, in the digital signal processing method for demodulating the IF signal in the digital stage according to an embodiment of the present invention, the effect of the phase offset of the IF carrier generated in the digital stage even if the IF carrier is not directly sampled. It has the advantage of being able to demodulate the received IF signal without receiving it.

Using the sensor according to an embodiment of the present invention, it is possible to detect the presence or absence of a person, a breathing signal, and a heartbeat signal in a wide range. In addition, since the system using the sensor according to an embodiment of the present invention has a simple hardware structure compared to other low-IF radars, additional power consumption or cost is not large, so it is cost-effective.

Effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 shows a radar having a direct conversion structure in the prior art for detecting a biosignal.
2 shows a radar having a low-IF structure in the prior art for detecting a biosignal.
3 shows a circuit structure of a radar biosignal detection sensor according to an embodiment of the present invention.
FIG. 4A shows a switching signal applying unit configured as a switch according to an embodiment of the present invention, and FIG. 4B shows a switching signal applying unit configured as a mixer according to another embodiment of the present invention.
5 illustrates a principle of using a switching signal IF in the frequency domain according to an embodiment of the present invention.
6 is a block diagram of a down-conversion demodulator according to an embodiment of the present invention.
7 illustrates coherence between an IF carrier signal and a received IF signal according to an embodiment of the present invention.
8 shows a demodulated signal distorted due to the phase difference shown in FIG. 7 .
9 shows a result of demodulating a baseband signal according to an embodiment of the present invention.
10 shows an experimental design for comparing the performance of the radar according to an embodiment of the present invention and the radar of the conventional direct conversion receiver structure.
11 shows an environment for measuring the performance of a radar according to an embodiment of the present invention.
12 shows experimental results (frequency domain spectrum) comparing the performance of the present invention and the conventional radar in the absence of a human.
13 is a comparison of biosignal waveforms detected when the subject is at a distance of 3 m. FIG. 13A is a result of a radar having a conventional direct conversion receiver structure, and FIG. This is the result of the radar.
14 shows experimental results (frequency domain spectrum) comparing the performance of the present invention and the conventional radar in the case where the subject to be measured is present at a distance of 3 m.
15 is a comparison of bio-signal waveforms detected when the subject to be measured is present at a distance of 6 m. FIG. 15A is a result of a radar having a conventional direct conversion receiver structure, and FIG. 15B is a diagram according to an embodiment of the present invention. This is the result of the radar.
16 shows experimental results (frequency domain spectrum) comparing the performance of the present invention and the conventional radar in the case where the subject to be measured is present at a distance of 6 m.
17 is a flowchart of a biosignal detection method according to an embodiment of the present invention.

Since the present invention can have various changes and can have various embodiments, specific embodiments will be described in detail with reference to the drawings. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

Terms such as first, second, A, and B may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. and/or includes a combination of a plurality of related description items or any of a plurality of related description items.

When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it should be understood that other components may exist in between. something to do. On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that no other element is present in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

It should also be understood that the terms "first" and "second" are used herein for distinguishing purposes only, and are not meant to indicate or anticipate sequences or priorities in any way.

Throughout the specification, it may be referred to as I means a real part, Q means a complex part, f means a frequency, and f _{LO means a frequency of a signal source.} . However, the present invention is not limited thereto.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

Throughout the specification and claims, when a part includes a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

3 shows a circuit structure of a radar biosignal detection sensor according to an embodiment of the present invention.

The circuit structure of the radar biosignal detection sensor according to an embodiment of the present invention has a structure in which the switching signal applying unit 330 for applying a switching signal to the receiving unit 320 is directly connected. That is, the present invention is characterized in that the switching signal applying unit 330 is disposed in front of the receiving unit 320 .

The receiver 320 of the present invention may receive a signal reflected from the living organism when the transmitter 310 transmits a radar signal toward the living organism.

4 shows different embodiments of a switching signal applying unit, FIG. 4A shows a switching signal applying unit including a switch 331 according to an embodiment of the present invention, and FIG. 4B is another embodiment of the present invention. It shows that the switching signal applying unit is constituted by the mixer 332 .

The switching signal applying unit 330 applies a signal of an intermediate frequency (IF) to the circuit, and may be configured in the form of a switch as shown in FIG. 4A or a mixer as shown in FIG. 4B .

The circuit of the radar biosignal detection sensor according to an embodiment of the present invention may include a signal source frequency removal unit at the rear end of the switching signal applying unit 330 . The signal source frequency removal unit may remove the signal source frequency from the received signal modulated by the intermediate frequency (IF).

The signal source frequency removal unit according to an embodiment of the present invention includes a signal source 340 connected to the transmitter 310 , an I/Q modulator 360 directly connected to the signal source 340 , a first mixer 350 , and A second mixer 370 may be included.

The I/Q modulator 360 modulates the signal output from the signal source 340 into an I/Q real-part-complex signal, and the first mixer 350 modulates the signal outputted through the I/Q modulator 360 . The real part signal among the signals and the signal modulated through the switching signal applying unit 330 are combined, and the second mixer 370 includes the complex part signal and the switching signal among the signals modulated through the I/Q modulator 360 . The modulated signal may be combined through the applying unit 330 .

The I/Q signal from which the signal source frequency has been removed through the signal source frequency removal unit may be converted into a digital signal through the A/D converter 380 and then IF-BB downconverted and demodulated. Down-conversion demodulation will be described later with reference to FIG. X.

The circuit structure of the biosignal detection sensor according to an embodiment of the present invention can improve the signal-to-noise ratio (SNR) by avoiding the low-frequency noise of the receiver in the radar.

일 때 변조된 위상신호를

라고 하면 수신부(320)에서 수신하는 신호

는 아래와 같이 나타낼 수 있다.First, after the transmitter 310 propagates the signal, the receiver 320 receives the signal reflected by the object. The reflected signal is a signal that is phase-modulated by the movement of an object, and bio-signals such as human respiration and heartbeat can be obtained from the modulated phase. As such, the frequency of the transmission signal source 340 is

When the modulated phase signal is

A signal received by the receiver 320

can be expressed as below.

는 신호원의 위상 잡음을 나타내며

는 송수신 거리에 의한 시간지연을 나타낸다. 또, 심장박동신호

, 호흡신호

, 그리고 신호원의 파장을

라고 할 때,

는 아래와 같이 나타낼 수 있다.At this time,

is the phase noise of the signal source,

represents the time delay due to the transmission/reception distance. Also, the heartbeat signal

, respiratory signal

, and the wavelength of the signal source

when said,

can be expressed as below.

를 직접 변환하게 되면 저주파 잡음의 영향을 그대로 받는 문제가 있다. 도 3과 같이 본 발명의 일 실시예에 따라 제안하는 회로 구조는 수신기 앞 단에 스위칭 신호 인가부(330)를 배치함으로써, 스위칭 신호 인가부(330)의 스위칭 동작을 통해 수신 신호를 변조할 수 있다. 스위칭 신호(IF)의 주파수와 초기 위상을 각각

,

라고 할 때, 스위치(331)를 통과한 신호

는 다음 수학식 3과 같이 표현된다.As described above, in the prior art, the signal received from the antenna, which is the receiving unit 320 .

There is a problem in that it is directly affected by low-frequency noise if it is directly converted. As shown in FIG. 3 , in the circuit structure proposed according to an embodiment of the present invention, the receiving signal can be modulated through the switching operation of the switching signal applying unit 330 by disposing the switching signal applying unit 330 in front of the receiver. have. The frequency and initial phase of the switching signal (IF) are respectively

,

When , the signal passed through the switch 331

is expressed as in Equation 3 below.

5 illustrates a principle of using a switching signal IF in the frequency domain according to an embodiment of the present invention.

,

에 위치하게 된다. 본 발명은 LO 신호원 주파수(53, 54)에 의한 널 감지 지점을 피하기 위해, I/Q 믹서인 제1 믹서(350) 및 제2 믹서(370)를 이용하여, 상기 수신 신호(52)를 IF 신호로 변환한다.The reception signal 52 modulated by the switching signal IF and 51 is

,

will be located in The present invention uses the first mixer 350 and the second mixer 370, which are I/Q mixers, to avoid the null detection point due to the LO signal source frequencies 53 and 54, and the received signal 52 is Convert to IF signal.

,

신호는 각각 아래 수학식 4로 나타낼 수 있다.Down-converted through the first mixer 350 and the second mixer 370, which are I/Q mixers

,

Each signal can be represented by Equation 4 below.

는 범위 상관 관계(range-correlation) 효과에 의해 상쇄 될 수 있기 때문에, 본 발명의 일 실시예에 따라 제안된 회로 구조는 고주파 신호원의 위상잡음에 영향을 받지 않는다. The residual phase noise of the LO signal source is

Since can be canceled by the range-correlation effect, the circuit structure proposed according to an embodiment of the present invention is not affected by the phase noise of the high-frequency signal source.

,

신호는 IF 주파수(51)에 위치해 있기 때문에 믹서와 기저대역 증폭기의 저주파 잡음의 영향을 받지 않는다. Down-converted as in Equation 4

,

Because the signal is located at the IF frequency 51, it is not affected by the low-frequency noise of the mixer and baseband amplifier.

The signal converted by the first mixer 350 and the second mixer 370 is sampled and processed through the analog-to-digital converter 380, as shown in FIG. 3, and through this, the effect from the radar receiver noise 5a can be minimized.

,

를 갖는 신호가 생성되기 때문에 IF 주파수에 의해 널 감지 지점이 발생하지 않는 효과가 있다.The circuit structure of the radar bio-signal detection sensor proposed according to an embodiment of the present invention is a frequency through modulation in the receiver 320 of the radar.

,

Since a signal with

6 is a block diagram of a down-conversion demodulator according to an embodiment of the present invention.

_{An unsynchronized demodulation method of demodulating the IF signals I IF} and Q _IF sampled through the analog-to-digital converter 380 into a baseband signal will be described with reference to FIG. 6 .

Referring to FIG. 6 , the downconversion demodulator 390 according to an embodiment of the present invention includes a band pass filter, a plurality of mixers 391 , 392 , 393 , and 394 multiplying a carrier signal, and output values of the mixers. It may include a plurality of mixers 395 and 396 that combine them.

A plurality of mixers 391 , 392 , 393 , 394 multiplying the carrier signal (carrier) is a first orthogonal carrier signal (I _c [n] _{) for the real part signal (I IF ) sampled in the first analog-to-digital converter} ) multiplied by a third mixer 391; a fourth mixer 392 for multiplying the _{real signal (I IF} ) sampled by the first analog-to-digital converter by a negative value of a second orthogonal carrier signal (I _{c [n]);} a fifth mixer 393 for multiplying the _{complex signal Q IF} sampled by the second analog-to-digital converter by a second orthogonal carrier signal I _{c [n];} The second analog-to-digital converter may include a sixth mixer 394 that multiplies the _{sampled complex signal Q IF} by the first orthogonal carrier signal I _{c [n].}

The plurality of mixers for combining the output values of the mixers include: a seventh mixer 395 that adds the output of the third mixer 391 and the output of the fifth mixer 393; and an eighth mixer 396 that adds the output of the fourth mixer 392 and the output of the sixth mixer 394 .

Hereinafter, a digital signal processing method for demodulating a signal sampled by the down-conversion demodulator will be described in detail with reference to FIG. 6 .

In order to obtain a phase signal modulated by the movement of a biosignal, a signal sampled through an analog-to-digital converter must be demodulated in a digital stage. That is, there is a need for a method of obtaining only a desired biosignal signal after removing the IF signal from the IF-modulated signal.

)로 인하여, 왜곡된 복조 신호를 나타낸다.7 shows the coherence between the IF carrier signal and the received IF signal according to an embodiment of the present invention, and FIG. 8 shows the phase difference (

), resulting in a distorted demodulation signal.

발생) 왜곡없이 원하는 신호를 복조할 수 있다.Meanwhile, according to an embodiment of the present invention, a signal sampled by reflecting an IF carrier is demodulated. As shown in FIG. 7 , the downconversion demodulator generates the received IF signal 71 and the digital terminal. Even if the coherency between the IF carrier signals 72 does not match (

The desired signal can be demodulated without distortion.

만큼 신호의 감쇄가 일어나게 된다. 보다 구체적으로,

가 0°인 경우(81)는 신호 감쇄가 일어나지 않고,

가 45°인 경우(82), 60°인 경우(83) 각각 신호 감쇄가 순차적으로 감쇄된 것을 확인할 수 있으며,

가 90°인 경우(84)에는 신호가 완전히 감쇄되어 복조되지 않는다. 즉,

가 π/2+kπ 만큼 차이가 나면 원하는 신호가 복조 되지 않는 문제가 있다. If the coherency between the in-phase signal and the IF carrier signal of the received IF signal does not match (), as shown in FIG.

The attenuation of the signal will occur. More specifically,

When is 0 ° (81), signal attenuation does not occur,

When is 45° (82), when it is 60° (83), it can be seen that the signal attenuation is sequentially attenuated,

When is 90° (84), the signal is completely attenuated and not demodulated. in other words,

If π/2+kπ is different, there is a problem in that the desired signal is not demodulated.

,

신호는 각각 대역 통과 필터를 거쳐 아웃 밴드(out-band) 주파수에 존재하는 잡음들이 제거된다. When a method for demodulating a signal according to an embodiment of the present invention will be described in detail, first sampled

,

Each signal passes through a band-pass filter to remove noises present at out-band frequencies.

,

신호는 상술한 수학식 4로부터 아래 수학식 5와 같이 나타낼 수 있다. sampled

,

The signal can be expressed as Equation 5 below from Equation 4 above.

,

로 표현될 수 있다.A quadrature IF carrier used for down-converting the IF signal is generated at the digital stage, and as shown in Equation 6 below

,

can be expressed as

는 제3믹서(391) 및 제6믹서(394)에 인가되고, 상기 IF 반송파의 복소부

는 제4믹서(392) 및 제5 믹서(393)에 인가될 수 있다. Real part of the IF carrier

is applied to the third mixer 391 and the sixth mixer 394, and the complex part of the IF carrier wave

may be applied to the fourth mixer 392 and the fifth mixer 393 .

와 IF 반송파 신호

를 곱하여 신호를 복조하면, 아래 수학식 7과 같이 표현될 수 있다.At this time, the in-phase signal of the received IF signal is

with IF carrier signal

If the signal is demodulated by multiplying by , it can be expressed as in Equation 7 below.

,

각각을

,

사이의 곱으로 표현하면, 아래와 같다.The coherency problem between the digital IF carrier signal and the received IF signal described above with reference to FIGS. 7 and 8 can be solved by using a product between the orthogonal IF carrier signals. The in-phase signal and the quadrature phase signal of the received IF signal

,

each

,

Expressed as a product between

Equation 8 can be obtained from the third mixer 391 of FIG. 6, Equation 9 is the fourth mixer 392, Equation 11 is the fifth mixer 393, Equation 10 is the sixth mixer 394 ) can be obtained from

와

는 각각 도 6의 제7믹서(395) 및 제8 믹서(396)를 통해 아래 수학식 12와 같이 얻을 수 있다. Using the above results, we use the baseband signal to be unaffected by the phase offset between the two signals.

Wow

can be obtained as in Equation 12 below through the seventh mixer 395 and the eighth mixer 396 of FIG. 6 , respectively.

와

를 복조하면, 도 9에 나타난 바와 같이,

에 의해 신호의 감쇄가 일어나지 않는 기저대역 신호를 얻을 수 있게 된다. 즉,

가 0°인 경우(91),

가 45°인 경우(92),

가 60°인 경우(93) 및

가 90°인 경우(94) 모두에서 신호가 감쇄되지 않을 것을 확인할 수 있다.Baseband signal according to an embodiment of the present invention

Wow

If we demodulate, as shown in Fig. 9,

Thus, it is possible to obtain a baseband signal in which signal attenuation does not occur. in other words,

is 0° (91),

is 45° (92),

is 60° (93) and

It can be seen that the signal is not attenuated in all cases (94) of is 90°.

를 검출할 수 있다.When the signal obtained through the above-described demodulation process is used for complex signal demodulation (CSD) or arctangent demodulation (AD) used in existing biosignal detection radar, the biosignal

can be detected.

The digital IF demodulation method according to an embodiment of the present invention does not require synchronization between an actually received IF signal and a carrier signal used for down-converting the IF signal. Therefore, there is no need to sample the IF carrier used for the actual adjustment through an additional analog-to-digital converter. In addition, the conventional demodulation method using envelope detection has a problem in that a harmonic frequency is generated, but the IF demodulation method according to the present invention has an advantage in that it is free from the harmonic frequency that has occurred in the prior art.

Hereinafter, an experiment to prove the effect of the present invention is performed, and the experimental results will be described.

10 shows an experimental design for comparing the performance of a radar according to an embodiment of the present invention and a radar having a conventional direct conversion receiver structure. A radar structure 1000 according to an embodiment of the present invention and a conventional direct conversion receiver structure 2000 were designed in parallel and compared.

How to measure

In order to verify the operation of the low-IF radar using the switching receiver 330 proposed according to an embodiment of the present invention, measurements and simulations were performed several times. For equal comparison, measurements were simultaneously performed using the radar of the structure 1000 according to the embodiment of the present invention and the radar 2000 of the conventional direct conversion structure, respectively. In the experiment, one transmitter was used, and a power splitter was used for the radar signal input from one receiver antenna.

A commercial 24GHz RF transmission module and reception module BGT24MTR12 were used as radar sensors used in the experiment, and the switch used in the proposed switching receiver 330 is an ADRF5020, which has a loss of about 2dB at 24GHz. The power of the transmit signal is 3dB, the gain of the transmit and receive antennas is 14dBi, the noise figure of the receiver is 12dB, and the overall gain of the receiver is 36dB. In addition, in the case of IF frequency, 1kHz or 10kHz was used, and the sampling frequency of the analog-to-digital converter was 50kHz, and measurement was carried out for 20 seconds at one time of measurement.

An example of a measurement scene is shown in FIG. 11 , when a person does not exist (i), when a person is present at a distance of 3 m (ii), and when a person is present at a distance of 6 m to verify radar performance For (iii), each was measured and compared. 11 , the subject 300 maintained stable breathing while standing still.

Measurement result

First, when no one was present (i), the measurement was carried out. At this time, since no object motion is detected, only the residual phase noise of the radar receiver and the signal source is measured.

12 shows experimental results (frequency domain spectrum) comparing the performance of the present invention and the conventional radar in the absence of a human.

Since there is no target signal to be detected, the result according to FIG. 12 is a result of comparison without normalization. When no person is present, in the result (12) using the radar according to an embodiment of the present invention, the magnitude of low-frequency noise around 0 Hz is significantly reduced compared to the result (11) using the direct conversion receiver. Since the low-IF radar proposed according to an embodiment of the present invention is not affected by the low-frequency noise of the mixer and the baseband amplifier, it can be confirmed that the measurement result is reduced by about 12.8 dBmV/Hz.

Next, when the subject to be measured was present at a distance of 3 m (ii), measurement was performed in the same manner as in the previous measurement.

13 is a comparison of biosignal waveforms detected when the subject is at a distance of 3 m. FIG. 13A is a result of a radar having a conventional direct conversion receiver structure, and FIG. This is the result of the radar.

14 shows experimental results (frequency domain spectrum) comparing the performance of the present invention and the conventional radar in the case where the subject to be measured exists at a distance of 3 m.

Referring to FIG. 14 , when the subject 300 is present, it can be confirmed that the subject's breathing is detected at 0.191 Hz and the heart beat signal is detected at 1.001 Hz. In this case, for equal comparison between the noises generated by the two radars, the comparison was performed by normalizing the magnitude of the detected respiration signal.

It can be seen through FIGS. 13A, 13B and 14 that the same biosignal is detected by both the low-IF radar and the radar using the direct-conversion receiver according to an embodiment of the present invention.

However, referring to FIG. 14 , the result 15 of the low-IF radar according to an embodiment of the present invention has much lower frequency noise in the vicinity of the biosignal than the result 14 of the radar using the direct-conversion receiver. decreased The magnitude of low-frequency noise existing around the measured biosignal was reduced by about 12.9 dBmV/Hz in the present invention. That is, by using a low-IF radar using a switching receiver according to an embodiment of the present invention, a biosignal can be detected with an improved signal-to-noise ratio.

Finally, the experiment was carried out in the case where the subject to be measured was present at a distance of 6 m (iii). 15 is a comparison of bio-signal waveforms detected when the subject to be measured is present at a distance of 6 m. FIG. 15A is a result of a radar having a conventional direct conversion receiver structure, and FIG. 15B is a diagram according to an embodiment of the present invention. This is the result of the radar.

16 shows the experimental results (frequency domain spectrum) comparing the radar performance of the present invention and the conventional one in the case where the subject to be measured is present at a distance of 6 m.

When the measured object is at a distance of 6 m (iii), the size of the reflected and received signal is about 12 dB smaller than when the measured subject is located at 3 m. When the size of the signal received from the antenna decreases, the signal may not be properly received because the signal is buried in the radar receiver noise.

Referring to FIG. 16 , a result 16 using the conventional direct-conversion receiver shows that a human biosignal such as breathing or heartbeat is not properly detected. On the other hand, the result 17 of the low-IF radar using the switching receiver according to an embodiment of the present invention indicates that a breathing signal is detected at 0.238 Hz and a heartbeat signal is detected at 0.91 Hz.

In addition, in the present invention, the magnitude of low-frequency noise was reduced by about 16 dBmV/Hz compared to the direct conversion radar. That is, when the radar according to an embodiment of the present invention is used, it is possible to determine the presence or absence of a person in a wider range compared to the existing direct conversion radar structure, and the accuracy thereof can be improved.

17 is a flowchart of a biosignal detection method according to an embodiment of the present invention.

A biosignal detection method according to an embodiment of the present invention includes the steps of: (S100) transmitting, by a transmitter, a radar signal to a living organism; receiving, by a receiver, the radar signal reflected from the living organism (S110); and modulating the reflected radar signal by a switching signal applying unit applying a switching signal (S120); removing, by a signal source frequency removal unit, a signal source frequency by using an I/Q modulator, a first mixer, and a second mixer from the signal modulated through the switching signal application unit (S130); A first analog-to-digital converter sampling the output of the first mixer, the second analog-to-digital converter sampling the output of the second mixer (S140); Demodulating the output by a down-conversion demodulator reflecting a carrier signal to the sampled output and converting it into a baseband signal (S150) and detecting a biosignal from the demodulated signal (S160) can do.

The description of the biosignal detection method according to the embodiment of the present invention may be equally applied to the description of the radar biosignal detection sensor and its system.

The above description is merely illustrative of the technical idea of the present invention, and a person of ordinary skill in the art to which the present invention pertains may make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

300 : life
310: transmitter
320: receiver
330: switching signal applying unit
331: switch
332 : mixer
340: signal source
350: first mixer
360 : I/Q modulator
370: second mixer
380: analog-to-digital converter
390: down-conversion demodulator

Claims (15)

In the radar biosignal detection sensor,
a transmitter for transmitting a signal to a living organism;
a receiver for receiving a signal reflected from the living organism; and
a switching signal applying unit directly connected to the receiving unit to apply a switching signal;
The switching signal is an intermediate frequency (IF),
Further comprising a signal source frequency removal unit,
The signal source frequency removal unit,
an I/Q modulator directly connected to a signal source connected to the transmitter and modulating a signal output from the signal source into an I/Q real-part-complex signal;
a first mixer for combining a real part signal among the signals modulated through the I/Q modulator and a signal modulated through the switching signal applying unit; and
A radar biosignal detection sensor comprising a; a second mixer for combining the complex signal of the signal modulated through the I/Q modulator and the signal modulated through the switching signal applying unit. The method of claim 1,
The switching signal applying unit is a radar biosignal detection sensor including a switch or a mixer. delete delete According to claim 1,
a first analog-to-digital converter for sampling the output of the first mixer; and
and a second analog-to-digital converter for sampling the output of the second mixer. 6. The method of claim 5,
The radar living body further comprising a down-conversion demodulator for demodulating the output by reflecting a carrier signal with respect to the output of the first analog-to-digital converter and the output of the second analog-to-digital converter, respectively, and converting it into a baseband signal. signal detection sensor. 7. The method of claim 6,
The down-conversion demodulator,
a third mixer for multiplying the _{real part signal (I IF} ) sampled by the first analog-to-digital converter by the first orthogonal carrier signal (I _{c [n]);}
a fourth mixer for multiplying the _{real part signal (I IF} ) sampled by the first analog-to-digital converter by a negative value of a second orthogonal carrier signal (Q _{c [n]);}
a fifth mixer for multiplying the _{complex signal (Q IF} ) sampled by the second analog-to-digital converter by a second orthogonal carrier signal (Q _{c [n]);}
a sixth mixer for multiplying the _{complex signal (Q IF} ) sampled by the second analog-to-digital converter by a first orthogonal carrier signal (I _{c [n]);}
a seventh mixer for adding the output of the third mixer and the output of the fifth mixer; and
and an eighth mixer for adding the output of the fourth mixer and the output of the sixth mixer. Including the radar biosignal detection sensor according to claim 1,
A radar biosignal detection system for detecting a biosignal by using a complex signal demodulation algorithm or an arctangent demodulation algorithm for the output signal of the biosignal detection sensor. In the biosignal detection method,
transmitting, by a transmitter, a radar signal to a living organism;
receiving, by a receiver, a radar signal reflected from the living organism; and
and modulating the reflected radar signal by applying a switching signal by a switching signal applying unit directly connected to the receiving unit,
The switching signal is an intermediate frequency (IF),
The signal source frequency removal unit further comprises removing the signal source frequency using an I/Q modulator, a first mixer, and a second mixer from the signal modulated through the switching signal applying unit,
The I/Q modulator is directly connected to a signal source connected to the transmitter, and modulates a signal output from the signal source into an I/Q real-part-complex signal,
The first mixer combines the real part signal among the signals modulated through the I/Q modulator and the signal modulated through the switching signal applying unit,
and the second mixer combines the complex signal among the signals modulated through the I/Q modulator and the signal modulated through the switching signal applying unit. delete delete 10. The method of claim 9,
The method further comprising: by a first analog-to-digital converter sampling an output of the first mixer; and by a second analog-to-digital converter, sampling an output of the second mixer. 13. The method of claim 12,
Demodulating the output by a down-conversion demodulator reflecting a carrier signal with respect to the output of the first analog-to-digital converter and the output of the second analog-to-digital converter, respectively, and converting it into a baseband signal, further comprising the step of demodulating the output Biosignal detection method. 14. The method of claim 13,
multiplying, by a third mixer, a first orthogonal carrier signal (I _c [n]) _{by the real part signal (I IF} ) sampled by the first analog-to-digital converter;
multiplying, by a fourth mixer, a negative value of a second orthogonal carrier signal (Q _{c [n]) by a real part signal (I IF} ) sampled by the first analog-to-digital converter;
multiplying, by a fifth mixer, a second orthogonal carrier signal (Q _c [n]) _{by the complex signal (Q IF} ) sampled by the second analog-to-digital converter;
multiplying, by a sixth mixer, a first orthogonal carrier signal (I _c [n]) _{by the complex signal (Q IF} ) sampled by the second analog-to-digital converter;
adding, by a seventh mixer, the output of the third mixer and the output of the fifth mixer; and
and adding, by an eighth mixer, an output of the fourth mixer and an output of the sixth mixer. 10. The method of claim 9,
The biosignal detection method further comprising the step of detecting a biosignal using a complex signal demodulation algorithm or an arctangent demodulation algorithm for an output signal of the biosignal detection sensor.

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