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This paper presents a hybrid radar system that incorporates a linear frequency-modulated continuous-wave (FMCW) mode and an interferometry mode for indoor human localization and life activity monitoring applications. The unique operating principle and signal processing method allow the radar to work at two different modes for different purposes. Th...
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... complete signal processing flow is shown in Fig. 5. Range information and relative displacement are obtained simultaneously. Notice that the clutter removal algorithm is resource consuming and does not need to be performed at all times. To minimize the computation load, the interferometry mode is employed at the first place to determine the angular direction of the human targets. Since ...
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Radar systems enable remote-less sensing of multiple persons in its field of view. In this paper, we propose a novel people counting system using 60-GHz frequency modulated continuous wave radar sensor. The proposed deep convolutional neural network learns from supervised radar data and also through knowledge distillation via multi-modal cross-lear...
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... The maximum signal energy levels that can be transmitted are not very high, which reduces the precision and signal-tonoise ratio (SNR) of IR-UWB radars [19]. Likewise, because CW Doppler radar lacks a range capacity [20], measurements are subject to interference and are therefore inappropriate for keeping track of the vital signs of moving targets. The FMCW radar combines the advantages of the first two, with good range and speed measurement capabilities, and the millimeter-band FMCW radar is extremely sensitive. ...
... Most radar-based vital signs estimation studies call for subjects to stay still, including standing, sitting in a chair, or resting in bed [2]- [20]. This limits the application of radarbased heart rate measurement methods. ...
... Most radar-based heart rate estimation methods, such as those in [2]- [20], cannot perform tracking measurements on moving targets, whereas the proposed method offers this possibility. ...
The subject must be motionless for conventional radar-based non-contact vital signs measurements. Additionally, the measurement range is limited by the design of the radar module itself. Although the accuracy of measurements has been improving, the prospects for their application could have been faster to develop. This paper proposed a novel radar-based adaptive tracking method for measuring the heart rate of the moving monitored person. The radar module is fixed on a circular plate and driven by stepping motors to rotate it. In order to protect the user's privacy, the method uses radar signal processing to detect the subject's position to control a stepping motor that adjusts the radar's measurement range. The results of the fixed-route experiments revealed that when the subject was moving at a speed of 0.5 m/s, the mean values of RMSE for heart rate measurements were all below 2.85 beat per minute (bpm), and when moving at a speed of 1 m/s, they were all below 4.05 bpm. When subjects walked at random routes and speeds, the RMSE of the measurements were all below 6.85 bpm, with a mean value of 4.35 bpm. The average RR interval time of the reconstructed heartbeat signal was highly correlated with the electrocardiography (ECG) data, with a correlation coefficient of 0.9905. In addition, this study not only evaluated the potential effect of arm swing (more normal walking motion) on heart rate measurement but also demonstrated the ability of the proposed method to measure heart rate in a multiple-people scenario.
... It has been shown that the temporal variation of the reflected wave's magnitude is a good measure for distinguishing human subjects from their stationary surroundings [25]. Stationary objects should reflect the same amount of energy throughout the whole measurement, whereas humans constantly exhibit some degree of movement, meaning that their reflected energy varies. ...
Vital sign monitoring is dominated by precise but costly contact-based sensors. Contactless devices such as radars provide a promising alternative. In this article, the effects of lateral radar positions on breathing and heartbeat extraction are evaluated based on a sleep study. A lateral radar position is a radar placement from which multiple human body zones are mapped onto different radar range sections. These body zones can be used to extract breathing and heartbeat motions independently from one another via these different range sections. Radars were positioned above the bed as a conventional approach and on a bedside table as well as at the foot end of the bed as lateral positions. These positions were evaluated based on six nights of sleep collected from healthy volunteers with polysomnography (PSG) as a reference system. For breathing extraction, comparable results were observed for all three radar positions. For heartbeat extraction, a higher level of agreement between the radar foot end position and the PSG was found. An example of the distinction between thoracic and abdominal breathing using a lateral radar position is shown. Lateral radar positions could lead to a more detailed analysis of movements along the body, with the potential for diagnostic applications.
... This aligns with the sparsity of the frequency of intermediate signals in FMCW radar systems based on antenna arrays, which is equivalent to the sparsity of the target relative to its background. This similarity makes the application of compressed sensing technology essential for signal processing in antenna array FMCW radar systems [20,21]. The literature [22] introduces a radar signal processing method based on compressed sensing, providing new approaches and technical support for reconstructing radar signals in complex environments. ...
The demand for precise positioning in noisy environments has propelled the development of research on array antenna radar systems. Although the orthogonal matching pursuit (OMP) algorithm demonstrates superior performance in signal reconstruction, its application efficacy in noisy settings faces challenges. Consequently, this paper introduces an innovative OMP algorithm, DTM_OMP_ICA (a dual-threshold mask OMP algorithm based on independent component analysis), which optimizes the OMP signal reconstruction framework by utilizing two different observation bases in conjunction with independent component analysis (ICA). By implementing a mean mask strategy, it effectively denoises signals received by array antennas in noisy environments. Simulation results reveal that compared to traditional OMP algorithms, the DTM_OMP_ICA algorithm shows significant advantages in noise suppression capability and algorithm stability. Under optimal conditions, this algorithm achieves a noise suppression rate of up to 96.8%, with its stability also reaching as high as 99%. Furthermore, DTM_OMP_ICA surpasses traditional denoising algorithms in practical denoising applications, proving its effectiveness in reconstructing array antenna signals in noisy settings. This presents an efficient method for accurately reconstructing array antenna signals against a noisy backdrop.
... In Liu and Liu (2014), stepped frequency radar is employed to monitor vital signs, whereas in Wang et al. (2014a), a linear FMCW idea is applied. In Wang et al. (2014b), a hybrid radar with FMCW and interferometry modes is proposed for vital sign monitoring. Range information is collected using FMCW mode, while chest movement is detected using interferometry mode. ...
... We also compared our proposed method's success with the existing reported literature. We found in the literature that most of the attempts to measure vital signs through the wall utilized either FMCW (Alizadeh et al., 2019;Liu and Liu, 2014;Wang et al., 2014b;Adib et al., 2015) or UWB radar (Wang et al., 2012;Liang et al., 2018). The reason for utilizing FMCW radar or UWB radar is that it can estimate the range of the target and for multiple subject measurements range azimuth plane determination is very critical (Liu and Liu, 2014). ...
Single-channel continuous wave (CW) radar is widely used and has gained popularity due to its simple architecture despite its inability to measure the range and angular location of the target. Its popularity arises in the industry due to the simplicity of the required components, the low demands on the sampling rate, and their low costs. Through-the-wall life signs detection using microwave Doppler Radar is an active area of research and investigation. Most of the work in the literature focused on utilizing multi-channel frequency modulated continuous wave (FMCW), CW, and ultra-wideband (UWB) radar for their capability of range and direction of arrival (DOA) estimation. In this paper, through-the-wall single-subject and two-subject concurrent heart rate detection using single-channel 24-GHz CW radar leveraged with maximal overlap discrete wavelet transform (MODWT) is proposed. Experimental results demonstrated that the repetitive measurement of seven different subjects at a distance of 20 cm up to 100 cm through two different barriers (wood and brick wall) showed an average accuracy of heart rate extraction of 95.27% for varied distances (20–100 cm) in comparison with the Biopac ECG acquisition signal. Additionally, the MODWT method can also isolate the independent heartbeat waveforms from the two subjects’ concurrent measurements through the wall. This involved four trials with eight different subjects, achieving an accuracy of 97.04% for a fixed distance of 40 cm from the Radar without estimating the angular location of the subjects. Notably, it also superseded the performance of the direct FFT method for the single subject after 40 cm distance measurements. The proposed simpler architecture of single-channel CW radar leveraged with MODWT has several potential applications, including post-disaster search and rescue scenarios for finding the trapped, injured people under the debris, emergency evacuation, security, surveillance, and patient vital signs monitoring.
... FMCW has a lower resolution for relative motion than CW-Doppler. Hence, since CW and FMCW utilise the same hardware, [23] [24][25] use a hybrid approach to achieve an absolute distance accuracy of less than 4 cm and millimeter-scale accuracy for relative motion at the 5.8 GHz ISM band. ...
In recent years, considerable effort has been directed towards non-contact Wi-Fi sensing applications such as fall detection and vital sign monitoring. For emerging technologies in healthcare, it is essential to assess the validity and repeatability of new measurement instruments before real-world implementation. However, the existing literature has not addressed the clinical validity and repeatability of respiration rate measurements obtained from Wi-Fi CSI. This study draws on medical instrumentation statistics to address this research gap by investigating the validity and repeatability of Wi-Fi sensing in measuring respiratory rates. For this purpose, we first implement a non-contact Wi-Fi Channel State Information respiration rate sensing system using off-the-shelf ESP32 devices and signal processing methods. Then, we evaluated the validity of the Wi-Fi sensor’s respiration rate measurement against respiration belt NUL-236 as a ground truth. The Bland-Altman method provided homoscedastic results across the standard range of respiration rates of older adults [12, 28] BPM achieving a validity of [1.29, 1.06] BPM, allowing us to analyze measurement repeatability at a single point. Hence, we assessed the measurement repeatability at 14 BPM using the spread of the data and the implications of random error in the measurements. The Wi-Fi CSI measurements dataset and corresponding belt data were made available for the validity and repeatability experiments. By providing appropriate measurement validity and repeatability metrics, care professionals can make informed decisions about the acceptability and generality of non-contact Wi-Fi sensing systems in measuring respiratory rate.
... The combination of Doppler and FMCW radars detects the target of the precision distance by measuring the detailed motion using the Doppler radar and the coarse distance using the FMCW radar. It achieves high accuracy by unwrapping the phase containing motion information in the Doppler radar operation [12], [13]. However, the phase unwrapping method lacks the ability to detect phase wrapping beyond the range of 2π , which consequently leads to inaccurate estimation of motion and distance of the target object. ...
A mutual compensation range detection method using a multimodulation radar is proposed to detect the absolute distance of a target with high accuracy while using a narrow bandwidth. The waveform of the multimodulation radar consists of a combination of both a chirp of the frequency-modulated continuous wave (FMCW) radar and two-tone signals of the frequency-shift keying (FSK) radar for the precise mixing of the measured distances. The proposed mutual compensation range detection method can simultaneously solve the uncertainty by the phase offset and unambiguous range of the FSK radar and the limitation of the range resolution of the FMCW radar. Using the proposed method, the 5.8-GHz multimodulation radar with a bandwidth of 150 MHz detected the absolute distance of the target in the range of 2.1-5.1 m with a distance error of 2.1%. The distances between two persons located at 5 and 20 m were detected individually and distinguished when they crossed each other. The experimental results show that the proposed method using the multimodulation radar can solve the problem of unknown initial position caused by clutters and multipath interference in the surroundings, and the limited range resolution by the frequency bandwidth of the chirp.
... They are more accurate because of more sensitivity to tiny movements and have been developed as wireless sensing solutions for disaster relief such as earthquake rescue [2]. Many frequency-modulated continuous-wave (FMCW) discrete radars systems have been designed and reported in low gigahertz RF, including [2], [3], and [4], which provide range and movement information with good enough displacement scale accuracy. However, they are usually bulky systems with many connections. ...
This article presents a fully integrated phased array frequency-modulated continuous-wave (FMCW) Doppler radar in 65-nm CMOS for noncontact object localization and movement tracking. The core 5.8-GHz sensor chip with the size of 2.3
$\times$
1.5 mm provides a peak homodyne structure receiver (RX) array gain of 47 dB and a maximum effective isotropic radiated power (EIRP) of 26 dBm on the transmitter (TX) array output with a maximum FMCW bandwidth of 275 MHz. Two
$2$
$\times$
$4$
and
$1$
$\times$
$4$
antenna arrays have been implemented for RX and TX units, respectively, utilizing patch antenna elements each with a gain of 8 dBi. The phased array transceiver radar system achieves
$\pm{50}^{\circ}$
beam-scanning coverage and object localization from 0.5 up to 6 m away, with movement tracking.
... While CW and FMCW radar systems have been investigated and experimentally verified for use in noncontact subject monitoring for many years [42,43], demonstrations of the viability of PMCW radar systems in this application space are still sparse. Many studies on PMCW response simulations have been conducted, but the number of realized systems with measured results is low [35]. ...
The incorporation of digital modulation into radar systems poses various challenges in the field of radar design, but it also offers a potential solution to the shrinking availability of low-noise operating environments as the number of radar applications increases. Additionally, digital systems have reached a point where available components and technology can support higher speeds than ever before. These advancements present new avenues for radar design, in which digitally controlled phase-modulated continuous wave (PMCW) radar systems can look to support multiple collocated radar systems with low radar-radar interference. This paper proposes a reconfigurable PMCW radar for use in vital sign detection and gesture recognition while utilizing digital carrier modulation and compares the radar responses of various modulation schemes. Binary sequences are used to introduce phase modulation to the carrier wave by use of a field programable gate array (FPGA), allowing for flexibility in the modulation speed and binary sequence. Experimental results from the radar demonstrate the differences between CW and PMCW modes when measuring the respiration rate of a human subject and in gesture detection.
... It can be used to probe respiration disorders, such as obstructive sleep apnea (OSA) and sudden infant death syndrome (SIDS), as well as used in medical sleep labs and earthquake or fire search-and-rescue scenarios [17,18]. The radiofrequency (RF) signal is more robust to temperature changes or environmental thermal noise compared with infrared thermal imaging methods [12] and is better able to avoid insufficient image resolution, blind areas, or potential privacy problems compared with vision-based monitoring methods [19]. ...
... The standard deviation of normal to normal (SDNN) measures the standard deviation of all IBIs and can be calculated by using (19). ...
Noncontact vital sign monitoring based on radar has attracted great interest in many fields. Heart Rate Variability (HRV), which measures the fluctuation of heartbeat intervals, has been considered as an important indicator for general health evaluation. This paper proposes a new algorithm for HRV monitoring in which frequency-modulated continuous-wave (FMCW) radar is used to separate echo signals from different distances, and the beamforming technique is adopted to improve signal quality. After the phase reflecting the chest wall motion is demodulated, the acceleration is calculated to enhance the heartbeat and suppress the impact of respiration. The time interval of each heartbeat is estimated based on the smoothed acceleration waveform. Finally, a joint optimization algorithm was developed and is used to precisely segment the acceleration signal for analyzing HRV. Experimental results from 10 participants show the potential of the proposed algorithm for obtaining a noncontact HRV estimation with high accuracy. The proposed algorithm can measure the interbeat interval (IBI) with a root mean square error (RMSE) of 14.9 ms and accurately estimate HRV parameters with an RMSE of 3.24 ms for MEAN (the average value of the IBI), 4.91 ms for the standard deviation of normal to normal (SDNN), and 9.10 ms for the root mean square of successive differences (RMSSD). These results demonstrate the effectiveness and feasibility of the proposed method in emotion recognition, sleep monitoring, and heart disease diagnosis.
... Anitori et al. found that the respiratory and heartbeat information can be calculated from the FMCW signal's phase [2]. On this basis, a hybrid radar system that combines the linear-frequency-modulated continuous-wave (LFMCW) mode and the interference measurement mode was developed to continuously track individuals' vital signs within complex indoor environments [3]. Adib et al. proposed a vital-radio technology to increase the vital sign detection range [4]. ...
In recent years, radar, especially frequency-modulated continuous wave (FMCW) radar, has been extensively used in non-contact vital signs (NCVS) research. However, current research does not work when multiple human targets are close to each other, especially when adjacent human targets lie in the same resolution cell. In this paper, a novel method based on complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN)–independent component analysis (ICA) was proposed to obtain the vital-sign information (including respiratory rate and heart rate) of adjacent human targets by using a single FMCW radar. Firstly, the data observed at a single angle were decomposed by the CEEMDAN separation algorithm to construct virtual multi-angle observations. It can effectively transform the undetermined blind source separation (UBSS) problem into an overdetermined blind source separation (BSS) problem. Thus, a BSS algorithm based on FastICA can be used to reconstruct each person’s vital-sign signal and then calculate their respiratory rate/heart rate. To validate the effectiveness of the proposed method, experiments based on the measured data were conducted and the results show that the proposed method can obtain multi-target vital-sign information even when they are in the same resolution cell.
