本論文提出一Variational Mode Decomposition-based (VMD-based)演算法組合以抑制生理訊號量測中非穩態雜波造成的影響，並萃取出較高訊雜比的心跳訊號頻譜，藉此提高心率估計之準確度；由於提高對非穩態雜波的抵抗能力代表能夠更貼近實際應用的環境，同時提高心率估計之準確度能夠降低錯誤預警的機率，因此未來的發展方向能夠更廣泛地應用在日常醫療照護環境。在本篇論文中，首先分析了完整的頻率調變連續波雷達基本理論，討論系統之優缺點，並假設兩種實驗情境所產生之非穩態雜波影響: 1. 他人走過待測者身旁 2. 待測者本身產生隨機晃動，並透過模擬及實驗的方式，驗證VMD-based演算法的效能，相較於效能卓越的訊號分析方法，如總體經驗模態分析，其強大的分解效能雖然能夠萃取心跳訊號，然而方法本身因為額外的迭代運算而有較高的計算複雜度較，所引入的雜訊也會造成整體訊雜比下降。本篇實驗利用所使用之VMD-based演算法抑制非穩態雜波的干擾，最後利用VMD運算中維納濾波的響應，提取出高訊雜比之心跳訊號頻譜，高訊雜比之訊號頻譜將提升心率估計的效能並使得多次估計均方根誤差下降，實驗結果表明，訊雜比相對於總體經驗模態分析提高了21 dB，而在非穩態雜波干擾的量測環境下，從參考文獻中得到的心率估計錯誤率約為12 %，而本文所提出之演算法之錯誤率皆小於2.4%，心率估計之均方根誤差皆小於2 bpm，由此可見所提出之演算法的有效性。

This thesis proposes a variational mode decomposition (VMD)-based algorithm to suppress the effect of non-stationary clutter in vital sgin measurement, and extract the heartbeat signal spectrum with a higher signal-to-noise ratio to achieve a hlghly accurate heart rate estimation. This technique can be applied to the environment such as home long-term care and hospitals in the future.
In this thesis, a complete analysis for frequency modulation continuous wave (FMCW) radar system have been reported at the chapter 3.To observe the effect of the non-stationary clutter, two cases of non-stationary clutter are dicussed. Case 1 is that a person passes by the target twice. Case 2 is that the target is moving his upper body randomly within a target range. Simulation and experiments are carried out to validate the proposed VMD-based algorithm.
In order to quantify the effectiveness of the proposed VMD-based algorithm, the relative heart rate error and SNR are defined. The measurement result in case 1 has relative error lower than 1 %, and a good improvent in SNR 8.9 dB compared to EEMD. Moreover, the result in case 2 has relative error lower than 3 %, and a great improvement in SNR 21 dB compared to the result of EEMD, and RMSE of heart rate is lower than 2 bpm.
Key words: Empirical mode decomposition, ensemble empirical mode decomposition, non-stationary clutter, vital sign detection, variational mode decomposition

[1] B.-K. Park, O. Boric-Lubecke, and V. M. Lubecke, "Arctangent demodulation with DC offset compensation in quadrature Doppler radar receiver systems," IEEE transactions on Microwave theory and techniques, vol. 55, no. 5, pp. 1073-1079, 2007.
[2] F.-K. Wang, Y.-R. Chou, Y.-C. Chiu, and T.-S. Horng, "Chest-worn health monitor based on a bistatic self-injection-locked radar," IEEE Transactions on Biomedical Engineering, vol. 62, no. 12, pp. 2931-2940, 2015.
[3] Y. Xiao, J. Lin, O. Boric-Lubecke, and M. Lubecke, "Frequency-tuning technique for remote detection of heartbeat and respiration using low-power double-sideband transmission in the Ka-band," IEEE Transactions on Microwave Theory and Techniques, vol. 54, no. 5, pp. 2023-2032, 2006.
[4] J. C. Lin, "Microwave sensing of physiological movement and volume change: A review," Bioelectromagnetics, vol. 13, no. 6, pp. 557-565, 1992.
[5] J. C. Lin, "Noninvasive microwave measurement of respiration," Proceedings of the IEEE, vol. 63, no. 10, pp. 1530-1530, 1975.
[6] C. Li, V. M. Lubecke, O. Boric-Lubecke, and J. Lin, "A review on recent advances in Doppler radar sensors for noncontact healthcare monitoring," IEEE Transactions on microwave theory and techniques, vol. 61, no. 5, pp. 2046-2060, 2013.
[7] C.-S. Lin, S.-F. Chang, C.-C. Chang, and C.-C. Lin, "Microwave human vocal vibration signal detection based on Doppler radar technology," IEEE transactions on microwave theory and techniques, vol. 58, no. 8, pp. 2299-2306, 2010.
[8] Z. Peng et al., "A portable FMCW interferometry radar with programmable low-IF architecture for localization, ISAR imaging, and vital sign tracking," IEEE transactions on microwave theory and techniques, vol. 65, no. 4, pp. 1334-1344, 2016.
[9] K.-M. Chen, Y. Huang, J. Zhang, and A. Norman, "Microwave life-detection systems for searching human subjects under earthquake rubble or behind barrier," IEEE transactions on biomedical engineering, vol. 47, no. 1, pp. 105-114, 2000.
[10] F.-K. Wang, T.-S. Horng, K.-C. Peng, J.-K. Jau, J.-Y. Li, and C.-C. Chen, "Detection of concealed individuals based on their vital signs by using a see-through-wall imaging system with a self-injection-locked radar," IEEE transactions on microwave theory and techniques, vol. 61, no. 1, pp. 696-704, 2012.
[11] C. Gu et al., "Accurate respiration measurement using DC-coupled continuous-wave radar sensor for motion-adaptive cancer radiotherapy," IEEE Transactions on biomedical engineering, vol. 59, no. 11, pp. 3117-3123, 2012.
[12] M. Mercuri et al., "Analysis of an indoor biomedical radar-based system for health monitoring," IEEE Transactions on Microwave Theory and Techniques, vol. 61, no. 5, pp. 2061-2068, 2013.
[13] T. Fan et al., "Wireless hand gesture recognition based on continuous-wave Doppler radar sensors," IEEE Transactions on Microwave Theory and Techniques, vol. 64, no. 11, pp. 4012-4020, 2016.
[14] Z. Peng, J.-M. Muñoz-Ferreras, R. Gómez-García, and C. Li, "FMCW radar fall detection based on ISAR processing utilizing the properties of RCS, range, and Doppler," in 2016 IEEE Mtt-S International Microwave Symposium (IMS), 2016: IEEE, pp. 1-3.
[15] Y. Wang and A. E. Fathy, "Micro-Doppler signatures for intelligent human gait recognition using a UWB impulse radar," in 2011 IEEE International Symposium on Antennas and Propagation (APSURSI), 2011: IEEE, pp. 2103-2106.
[16] N. Hafner, I. Mostafanezhad, V. M. Lubecke, O. Boric-Lubecke, and A. Host-Madsen, "Non-contact cardiopulmonary sensing with a baby monitor," in 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007: IEEE, pp. 2300-2302.
[17] M. Younes, "Role of respiratory control mechanisms in the pathogenesis of obstructive sleep disorders," Journal of applied physiology, vol. 105, no. 5, pp. 1389-1405, 2008.
[18] C. Li and J. Lin, "Random body movement cancellation in Doppler radar vital sign detection," IEEE Transactions on Microwave Theory and Techniques, vol. 56, no. 12, pp. 3143-3152, 2008.
[19] K. Han and S. Hong, "Differential Phase Doppler Radar With Collocated Multiple Receivers for Noncontact Vital Signal Detection," IEEE Transactions on Microwave Theory and Techniques, vol. 67, no. 3, pp. 1233-1243, 2018.
[20] C. Gu, G. Wang, Y. Li, T. Inoue, and C. Li, "A hybrid radar-camera sensing system with phase compensation for random body movement cancellation in Doppler vital sign detection," IEEE Transactions on Microwave Theory and Techniques, vol. 61, no. 12, pp. 4678-4688, 2013.
[21] H. Lee, B.-H. Kim, J.-K. Park, S. W. Kim, and J.-G. Yook, "A resolution enhancement technique for remote monitoring of the vital signs of multiple subjects using a 24 GHz bandwidth-limited FMCW radar," IEEE Access, vol. 8, pp. 1240-1248, 2019.
[22] G. Wang, C. Gu, T. Inoue, and C. Li, "A Hybrid FMCW-Interferometry Radar for Indoor Precise Positioning and Versatile Life Activity Monitoring," IEEE Transactions on Microwave Theory and Techniques, vol. 62, no. 11, pp. 2812-2822, 2014, doi: 10.1109/tmtt.2014.2358572.
[23] A. Prat, S. Blanch, A. Aguasca, J. Romeu, and A. Broquetas, "Collimated beam FMCW radar for vital sign patient monitoring," IEEE Transactions on Antennas and Propagation, vol. 67, no. 8, pp. 5073-5080, 2018.
[24] L. Ren, H. Wang, K. Naishadham, Q. Liu, and A. E. Fathy, "Non-invasive detection of cardiac and respiratory rates from stepped frequency continuous wave radar measurements using the state space method," in 2015 IEEE MTT-S International Microwave Symposium, 2015: IEEE, pp. 1-4.
[25] V. Nguyen, A. Q. Javaid, and M. A. Weitnauer, "Spectrum-averaged Harmonic Path (SHAPA) algorithm for non-contact vital sign monitoring with ultra-wideband (UWB) radar," in 2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2014: IEEE, pp. 2241-2244.
[26] G. Wang, J.-M. Munoz-Ferreras, C. Gu, C. Li, and R. Gomez-Garcia, "Application of Linear-Frequency-Modulated Continuous-Wave (LFMCW) Radars for Tracking of Vital Signs," IEEE Transactions on Microwave Theory and Techniques, vol. 62, no. 6, pp. 1387-1399, 2014, doi: 10.1109/tmtt.2014.2320464.
[27] H.-R. Chuang, H.-C. Kuo, F.-L. Lin, T.-H. Huang, C.-S. Kuo, and Y.-W. Ou, "60-GHz millimeter-wave life detection system (MLDS) for noncontact human vital-signal monitoring," IEEE Sensors Journal, vol. 12, no. 3, pp. 602-609, 2011.
[28] L. Chioukh, H. Boutayeb, D. Deslandes, and K. Wu, "Noise and sensitivity of harmonic radar architecture for remote sensing and detection of vital signs," IEEE Transactions on Microwave Theory and Techniques, vol. 62, no. 9, pp. 1847-1855, 2014.
[29] I. Mostafanezhad and O. Boric-Lubecke, "Benefits of coherent low-IF for vital signs monitoring using Doppler radar," IEEE Transactions on Microwave Theory and Techniques, vol. 62, no. 10, pp. 2481-2487, 2014.
[30] M. Han, Y. Liu, J. Xi, and W. Guo, "Noise smoothing for nonlinear time series using wavelet soft threshold," IEEE signal processing letters, vol. 14, no. 1, pp. 62-65, 2006.
[31] C.-C. Liu, T.-Y. Sun, S.-J. Tsai, Y.-H. Yu, and S.-T. Hsieh, "Heuristic wavelet shrinkage for denoising," Applied Soft Computing, vol. 11, no. 1, pp. 256-264, 2011.
[32] N. E. Huang et al., "The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis," Proceedings of the Royal Society of London. Series A: mathematical, physical and engineering sciences, vol. 454, no. 1971, pp. 903-995, 1998.
[33] Y. Lei, Z. He, and Y. Zi, "Application of the EEMD method to rotor fault diagnosis of rotating machinery," Mechanical Systems and Signal Processing, vol. 23, no. 4, pp. 1327-1338, 2009.
[34] C.-H. Chang and W.-H. Chen, "Vital-Sign Processing Receiver With Clutter Elimination Using Servo Feedback Loop for UWB Pulse Radar System," IEEE Transactions on Very Large Scale Integration (VLSI) Systems, vol. 28, no. 1, pp. 292-296, 2019.
[35] C.-C. Chou, W.-C. Lai, Y.-K. Hsiao, and H.-R. Chuang, "60-GHz CMOS Doppler radar sensor with integrated V-band power detector for clutter monitoring and automatic clutter-cancellation in noncontact vital-signs sensing," IEEE Transactions on Microwave Theory and Techniques, vol. 66, no. 3, pp. 1635-1643, 2017.
[36] J.-M. Muñoz-Ferreras, G. Wang, C. Li, and R. Gómez-García, "Mitigation of stationary clutter in vital-sign-monitoring linear-frequency-modulated continuous-wave radars," IET Radar, Sonar & Navigation, vol. 9, no. 2, pp. 138-144, 2015.
[37] M.-C. Tang, F.-K. Wang, and T.-S. Horng, "Single self-injection-locked radar with two antennas for monitoring vital signs with large body movement cancellation," IEEE Transactions on Microwave Theory and Techniques, vol. 65, no. 12, pp. 5324-5333, 2017.
[38] W. Yin, X. Yang, L. Li, L. Zhang, N. Kitsuwan, and E. Oki, "Hear: Approach for heartbeat monitoring with body movement compensation by ir-uwb radar," Sensors, vol. 18, no. 9, p. 3077, 2018.
[39] I. Mostafanezhad, E. Yavari, O. Boric-Lubecke, V. M. Lubecke, and D. P. Mandic, "Cancellation of unwanted Doppler radar sensor motion using empirical mode decomposition," IEEE Sensors Journal, vol. 13, no. 5, pp. 1897-1904, 2013.
[40] A. D. Droitcour, O. Boric-Lubecke, V. M. Lubecke, J. Lin, and G. T. Kovacs, "Range correlation and I/Q performance benefits in single-chip silicon Doppler radars for noncontact cardiopulmonary monitoring," IEEE Transactions on Microwave Theory and Techniques, vol. 52, no. 3, pp. 838-848, 2004.
[41] A. Anghel, G. Vasile, R. Cacoveanu, C. Ioana, and S. Ciochina, "Short-range wideband FMCW radar for millimetric displacement measurements," IEEE Transactions on Geoscience and Remote Sensing, vol. 52, no. 9, pp. 5633-5642, 2014.
[42] H.-I. Choi, H. Song, and H.-C. Shin, "Target range selection of FMCW radar for accurate vital information extraction," IEEE Access, 2020.
[43] K. Dragomiretskiy and D. Zosso, "Variational Mode Decomposition," IEEE Transactions on Signal Processing, vol. 62, no. 3, pp. 531-544, 2014, doi: 10.1109/tsp.2013.2288675.
[44] P. J. Sparto, M. Parnianpour, E. A. Barria, and J. M. Jagadeesh, "Wavelet and short-time Fourier transform analysis of electromyography for detection of back muscle fatigue," IEEE Transactions on rehabilitation engineering, vol. 8, no. 3, pp. 433-436, 2000.
[45] F. Riaz, A. Hassan, S. Rehman, I. K. Niazi, and K. Dremstrup, "EMD-based temporal and spectral features for the classification of EEG signals using supervised learning," IEEE Transactions on Neural Systems and Rehabilitation Engineering, vol. 24, no. 1, pp. 28-35, 2015.
[46] A. Boudraa, J. Cexus, and Z. Saidi, "EMD-based signal noise reduction," International Journal of Signal Processing, vol. 1, no. 1, pp. 33-37, 2004.
[47] P. Flandrin, P. Goncalves, and G. Rilling, "Detrending and denoising with empirical mode decompositions," in 2004 12th European signal processing conference, 2004: IEEE, pp. 1581-1584.
[48] Y.-H. Wang, C.-H. Yeh, H.-W. V. Young, K. Hu, and M.-T. Lo, "On the computational complexity of the empirical mode decomposition algorithm," Physica A: Statistical Mechanics and its Applications, vol. 400, pp. 159-167, 2014.
[49] Y. Wu, C. Shen, H. Cao, and X. Che, "Improved morphological filter based on variational mode decomposition for MEMS gyroscope de-noising," Micromachines, vol. 9, no. 5, p. 246, 2018.
[50] Q. Lv et al., "Doppler vital signs detection in the presence of large-scale random body movements," IEEE Transactions on Microwave Theory and Techniques, vol. 66, no. 9, pp. 4261-4270, 2018.
[51] E. Cardillo, C. Li, and A. Caddemi, "Vital Sign Detection and Radar Self-Motion Cancellation Through Clutter Identification," IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 3, pp. 1932-1942, 2021.
[52] W. Hu, Z. Zhao, Y. Wang, H. Zhang, and F. Lin, "Noncontact accurate measurement of cardiopulmonary activity using a compact quadrature Doppler radar sensor," IEEE Transactions on Biomedical Engineering, vol. 61, no. 3, pp. 725-735, 2013.
[53] S. Wang et al., "A novel ultra-wideband 80 GHz FMCW radar system for contactless monitoring of vital signs," in 2015 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2015: IEEE, pp. 4978-4981.
[54] A. Lazaro, D. Girbau, and R. Villarino, "Analysis of vital signs monitoring using an IR-UWB radar," Progress In Electromagnetics Research, vol. 100, pp. 265-284, 2010.
[55] Z. Wu and N. E. Huang, "Ensemble empirical mode decomposition: a noise-assisted data analysis method," Advances in adaptive data analysis, vol. 1, no. 01, pp. 1-41, 2009.