걸어 다니는 사람의 생체신호탐지를 위한 움직임 보상기법 연구

In this paper, we compare the performances of impulse radio ultra-wideband (IR-UWB) and frequency modulation continuous wave (FMCW) radars in measuring noncontact vital signs such as respiration rate and heart rate. These two type radars have been widely used in various fields and have shown their applicability to extract vital signs in noncontact ways. IR-UWB radar can extract vital signs using distance information. On the other hand, FMCW radar requires phase information to estimate vital signs, and the result can be enhanced with Multi-input Multi-output (MIMO) antenna topologies. By using commercial radar chipsets, the operation of radars under different conditions and frequency bands will also affect the performance of vital sign detection capabilities. We compared the accuracy and signal-to-noise (SNR) ratios of IR-UWB and FMCW radars in various scenarios, such as distance, orientation, carotid pulse, harmonics, and obstacle penetration. In general, the IR-UWB radars offer a slightly better accuracy and higher SNR in comparison to FMCW radar. However, each radar system has its own unique advantages, with IR-UWB exhibiting fewer harmonics and a higher SNR, while FMCW can combine the results from each channel.

Non-invasive remote health monitoring plays a vital role in epidemiological situations such as SARS outbreak (2003), MERS (2015) and the recently ongoing outbreak of COVID-19 because it is extremely risky to get close to the patient due to the spread of contagious infections. Non-invasive monitoring is also extremely necessary in situations where it is difficult to use complicated wired connections, such as ECG monitoring for infants, burn victims or during rescue missions when people are buried during building collapses/earthquakes. Due to the unique characteristics such as higher penetration capabilities, extremely precise ranging, low power requirement, low cost, simple hardware and robustness to multipath interferences, Impulse Radio Ultra Wideband (IR-UWB) technology is appropriate for non-invasive medical applications. IR-UWB sensors detect the macro as well as micro movement inside the human body due to its fine range resolution. The two vital signs, i.e., respiration rate and heart rate, can be measured by IR-UWB radar by measuring the change in the magnitude of signal due to displacement caused by human lungs, heart during respiration and heart beating. This paper reviews recent advances in IR- UWB radar sensor design for healthcare, such as vital signs measurements of a stationary human, vitals of a non-stationary human, vital signs of people in a vehicle, through the wall vitals measurement, neonate’s health monitoring, fall detection, sleep monitoring and medical imaging. Although we have covered many topics related to health monitoring using IR-UWB, this paper is mainly focused on signal processing techniques for measurement of vital signs, i.e., respiration and heart rate monitoring.

Being capable of detecting vital signs of human beings, impulse radio ultra wideband (IR-UWB) radar can be applied to search and rescue (SAR) operation in post-disaster scenarios to detect trapped survivors under collapsed buildings. In the application, IR-UWB radar systems with a low center frequency are commonly used to guarantee good penetrability. These systems transmit pulses with nanosecond width. So they have relatively low range resolution, which in turn impacts their performance of detecting the vital signs. To cope with the problem, a dual-frequency IR-UWB radar system is developed. The system combines two IR-UWB radars with different center frequencies, namely 400 MHz and 270 MHz, and utilizes time division multiplexing, composite antenna array and novel signal processing techniques to ensure its compatibility and performance. Experimental results are also presented to show the system's advantages over single-frequency IR-UWB radar systems.

Recently, noncontact vital sign monitors have attracted attention because of issues related to the transmission of contagious diseases. We developed a real-time vital sign monitor using impulse-radio ultrawideband (IR-UWB) radar with embedded processors and software; we then evaluated its accuracy in measuring heart rate (HR) and respiratory rate (RR) and investigated the factors affecting the accuracy of the radar-based measurements. In 50 patients visiting a cardiology clinic, HR and RR were measured using IR-UWB radar simultaneously with electrocardiography and capnometry. All patients underwent HR and RR measurements in 2 postures—supine and sitting—for 2 min each. There was a high agreement between the RR measured using radar and capnometry (concordance correlation coefficient [CCC] 0.925 [0.919–0.926]; upper and lower limits of agreement [LOA], − 2.21 and 3.90 breaths/min). The HR measured using radar was also in close agreement with the value measured using electrocardiography (CCC 0.749 [0.738–0.760]; upper and lower LOA, − 12.78 and 15.04 beats/min). Linear mixed effect models showed that the sitting position and an HR < 70 bpm were associated with an increase in the absolute biases of the HR, whereas the sitting position and an RR < 18 breaths/min were associated with an increase in the absolute biases of the RR. The IR-UWB radar sensor with embedded processors and software can measure the RR and HR in real time with high precision. The sitting position and a low RR or HR were associated with the accuracy of RR and HR measurement, respectively, using IR-UWB radar.

Physical fatigue can be assessed using heart rate variability (HRV). We measured HRV at rest and in a fatigued state using impulse-radio ultra wideband (IR-UWB) radar in a noncontact fashion and compared the measurements with those obtained using electrocardiography (ECG) to assess the reliability and validity of the radar measurements. HRV was measured in 15 subjects using radar and ECG simultaneously before (rest for 10 min before exercise) and after a 20-min exercise session (fatigue level 1 for 0–9 min; fatigue level 2 for 10–19 min; recovery for ≥ 20 min after exercise). HRV was analysed in the frequency domain, including the low-frequency component (LF), high-frequency component (HF) and LF/HF ratio. The LF/HF ratio measured using radar highly agreed with that measured using ECG during rest (ICC = 0.807), fatigue-1 (ICC = 0.712), fatigue-2 (ICC = 0.741) and recovery (ICC = 0.764) in analyses using intraclass correlation coefficients (ICCs). The change pattern in the LH/HF ratios during the experiment was similar between radar and ECG. The subject’s body fat percentage was linearly associated with the time to recovery from physical fatigue (R2 = 0.96, p < 0.001). Our results demonstrated that fatigue and rest states can be distinguished accurately based on HRV measurements using IR-UWB radar in a noncontact fashion.

Detecting one's stress state is essential to prevent severe health problems. However, most of the existing stress detection techniques require direct contact between the user and the sensor devices, leading to user inconvenience. Further, it is difficult to provide reliable stress detection because of loosened wearing of sensor devices and the limited battery life of the devices. In this paper, we present i) a non-contact stress detection technique based on the user movement patterns using an impulse-radio ultra-wideband (IR-UWB) radar without estimating vital signals and ii) an attention-based neural network. We design novel radar signal features to accurately represent user movements that are related to the stress state. For the demonstration, we collect a multi-modal dataset from 50 subjects under stress-inducing experiments using both contact and non-contact sensor devices. Consequently, we achieve a binary stress detection accuracy of 76.22% which outperforms the wearable-based approach with movement data by up to 11.57%.

Cardiac x-ray CT imaging is still challenging due to heart motion, which cannot be ignored even with the current rotation speed of the equipment. In response, many algorithms have been developed to compensate remaining motion artifacts by estimating the motion using projection data or reconstructed images. In these algorithms, accurate motion estimation is critical to the compensated image quality. In addition, since the scan range is directly related to the radiation dose, it is preferable to minimize the scan range in motion estimation. In this paper, the authors propose a novel motion estimation and compensation algorithm using a sinogram with a rotation angle of less than 360°. The algorithm estimates the motion of the whole heart area using two opposite 3D partial angle reconstructed (PAR) images and compensates the motion in the reconstruction process. A CT system scans the thoracic area including the heart over an angular range of 180° + α + β, where α and β denote the detector fan angle and an additional partial angle, respectively. The obtained cone-beam projection data are converted into cone-parallel geometry via row-wise fan-to-parallel rebinning. Two conjugate 3D PAR images, whose center projection angles are separated by 180°, are then reconstructed with an angular range of β, which is considerably smaller than a short scan range of 180° + α. Although these images include limited view angle artifacts that disturb accurate motion estimation, they have considerably better temporal resolution than a short scan image. Hence, after preprocessing these artifacts, the authors estimate a motion model during a half rotation for a whole field of view via nonrigid registration between the images. Finally, motion-compensated image reconstruction is performed at a target phase by incorporating the estimated motion model. The target phase is selected as that corresponding to a view angle that is orthogonal to the center view angles of two conjugate PAR images. To evaluate the proposed algorithm, digital XCAT and physical dynamic cardiac phantom datasets are used. The XCAT phantom datasets were generated with heart rates of 70 and 100 bpm, respectively, by assuming a system rotation time of 300 ms. A physical dynamic cardiac phantom was scanned using a slowly rotating XCT system so that the effective heart rate will be 70 bpm for a system rotation speed of 300 ms. In the XCAT phantom experiment, motion-compensated 3D images obtained from the proposed algorithm show coronary arteries with fewer motion artifacts for all phases. Moreover, object boundaries contaminated by motion are well restored. Even though object positions and boundary shapes are still somewhat different from the ground truth in some cases, the authors see that visibilities of coronary arteries are improved noticeably and motion artifacts are reduced considerably. The physical phantom study also shows that the visual quality of motion-compensated images is greatly improved. The authors propose a novel PAR image-based cardiac motion estimation and compensation algorithm. The algorithm requires an angular scan range of less than 360°. The excellent performance of the proposed algorithm is illustrated by using digital XCAT and physical dynamic cardiac phantom datasets.

The Doppler radar-based technique for noncontact vital sign detection has drawn increasing interest in recent years. In this paper, the signal model of human micro-motion is established and the Complex Continuous Basis Pursuit (CCBP)based vital sign detection algorithm for extracting the frequencies of human respiration and heartbeat signal is proposed. By exploiting the sparsity property of the established signal model, the proposed CCBP algorithm can extract the vital signal information by using the polar interpolation and the convex optimization problem solving technique. Simulation experiment results have verified the effectiveness and correctness of the proposed algorithm in the vital sign detection.

This paper presents a Doppler radar sensor system with camera-aided random body movement cancellation (RBMC) techniques for noncontact vital sign detection. The camera measures the subject's random body motion that is provided for the radar system to perform RBMC and extract the uniform vital sign signals of respiration and heartbeat. Three RBMC strategies are proposed: 1) phase compensation at radar RF front-end, 2) phase compensation for baseband complex signals, and 3) movement cancellation for demodulated signals. Both theoretical analysis and radar simulation have been carried out to validate the proposed RBMC techniques. An experiment was carried out to measure a subject person who was breathing normally but randomly moving his body back and forth. The experimental result reveals that the proposed radar system is effective for RBMC.

Simulations were performed based on a model developed in ADS to demonstrate the effects of non-linear cosine transfer function in non-contact vital sign detection. Harmonics and intermodulation effects have been analyzed theoretically and demonstrated by simulation. It is shown that in contrast to the observation from simple linear approximation that detection sensitivity always increases with carrier frequency, there is an optimum carrier frequency for non-contact Doppler radar vital sign detection. For typical values of human chest wall movement, the simulation shows that the upper bound of the carrier frequency should be limited to the lower region of the Ka-band to improve detection accuracy

The integration of sensing and communication functions in one platform has become a pivotal use case in future communication systems. This research investigated the optimal integrated sensing and communication (ISAC) waveforms for the purpose of vital signs detection. In order to incorporate both functions in the system and make it favorable for sensing the micro-doppler effect associated with vital signs, orthogonal frequency division multiplexing (OFDM) and phase-coded frequency modulated continuous wave (PC-FMCW) signals were adopted and compared, and the performances were evaluated against the system based on the classic frequency modulated continuous wave (FMCW). Several phase coded FMCW signals have been investigated and the simulated results indicated that the Frank-coded PC-FMCW waveform exhibited an optimal performance for vital signs detection in a line-of-sight setting. The work is beneficial for search and rescue applications where high-performance sensing such as vital signs detection and limited communication capability is required.

In order to solve the problem of the null detection point in the vital signs detection based on continuous wave(CW) Doppler radar, a novel dual-band hybrid down-conversion radar transceiver system is proposed. The proposed radar system operating frequency is 2.05 GHz and 1.64 GHz. Correlation between signals can improve the overall performance of the system. At λ/4 distance, the single-band single-channel detection has the problem of null detection point, and the proposed dual-band double-channel detection can solve the null detection point. On the other hand, at the non-λ/4 distance, the results of the dual-band detection double-channel can be mutually verified, ensuring the detection accuracy of the vital sign detection system. The simulation results prove the feasibility of the radar system. Regardless of whether the detected distance is at the λ/4 distance, the proposed vital sign detection system can always obtain the vital sign.

A novel low-power transceiver topology for noncontact vital sign detection including the power management technique

To validate Impulse radio ultra wideband pulse-doppler radar technology against polysomnography (PSG) for sleep assessment. In all, 12 participants were recruited and their overnight sleep was assessed both by a Novelda XeThru radar and PSG. Two subjects had two nightly recordings, whereas 10 had one recording. Epoch by epoch (30 seconds) comparisons from bedtime to rise time were conducted. Concordance was estimated in terms of the mean difference between the radar and the PSG estimates regarding sleep onset latency, wake time after sleep onset and total sleep time. In addition, accuracy, sensitivity, specificity and Cohen kappa were calculated. The mean difference (minutes) between the radar and the PSG registrations was -5.7 minutes (standard deviation [SD] = 22.1 minutes) for sleep onset latency, 6.4 minutes (SD = 32.5 minutes) for wake after sleep onset, and 1.5 minutes (SD = 24.6 minutes) for total sleep time. The mean values obtained for accuracy, sensitivity, specificity and Cohen kappa were 0.931, 0.961, 0.695 and 0.670, respectively. Impulse radio ultra wideband radar technology is a promising tool in terms of affordable and practical objective sleep assessment. Further technical development and more validation studies are needed in order to conclude about the utility potential of this device.

For spotlight synthetic aperture radar (SAR) on circular trajectories, the phase error caused by motion error is 2-D space-variant. For the conventional motion compensation (MOCO) algorithm, the imaging scene is generally segmented into many sub-regions to compensate for the space-variant phase error. However, the complex phase error results in that fact that it is difficult to obtain the quantitative criterion of scene segmentation. To address this issue, we propose a novel MOCO algorithm. This method contains three steps; the first step is non-space-variant phase error compensation; the second step is to remove the height term; the third step is space-variant phase error compensation. Among these steps, the most critical operation is removing the height term. In the distance equation, the height term is independent of the ground target coordinate. Hence, it can be removed by a serial of operations containing resampling and phase compensation. Through removing height term, it doesn't only compensate the height error but also makes the residual phase error into 1-D space-variant. Then, the phase error is exclusively related to the radius error and the target abscissa. Hence, after compensating for the space-variant error, it only needs to segment scene along the abscissa direction. Meanwhile, it can gain the quantitative criterion of scene segmentation to guarantee the phase error variation range is less than π/4 in each sub-scene. Eventually, some simulations are conducted to illustrate that the proposed method is valid.