An FFT-Based DC Offset Compensation and I/Q Imbalance Correction Algorithm for Bioradar Sensors

• Published in: IEEE transactions on microwave theory and techniques Vol. 72; no. 3; pp. 1900 - 1910
• Main Authors: Tian, Fuze, Zhu, Lixian, Shi, Qiuxia, Jin, Xiaokun, Cai, Ran, Dong, Qunxi, Zhao, Qinglin, Hu, Bin
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Arctangent demodulation; Ballistocardiograms; Baseband; Biomedical materials; bioradar sensor; Biosensors; Compensation; Demodulation; Direct current; direct current (dc) offset; Doppler effect; Doppler heartbeat diagram (DHD); Fast Fourier transformations; Fourier transforms; Heuristic algorithms; Higher harmonics; in-phase and quadrature-phase (I/Q) imbalance; Intermodulation; Intervals; Linear phase; Monitoring; Phase demodulation; Quadratures; Signal to noise ratio
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2023.3308190

The challenge of noncontact presentation of human cardiopulmonary activity using a bioradar sensor is to linearly demodulate the Doppler cardiopulmonary diagram (DCD) signal from baseband signals. Arctangent demodulation can perform linear phase demodulation to obtain the DCD signal. However, the high-order harmonics and intermodulation terms (ITs) caused by the time-varying direct current (dc) offset and in-phase and quadrature-phase (I/Q) imbalance in the baseband signals significantly degrade the signal-to-noise ratio (SNR) of the Doppler heartbeat diagram (DHD) signal. In this work, a fast Fourier transform (FFT)-based algorithm is proposed to simultaneously perform time-varying dc offset compensation and I/Q imbalance correction without the need for an auxiliary device to improve the accuracy of the arctangent demodulation. The obtained results show that the SNRs of the algorithm-processed DHD signals are increased from 30.08 ± 2.41 to 68.88 ± 10.57 dB. In addition, the root mean square errors (RMSEs) of the C-C intervals of the DHD signals for eight subjects with respect to the J-J intervals of the ballistocardiogram (BCG) signals are 17.79 ± 2.72 ms (2.80% ± 0.43%), suggesting a promising potential of the DHD signal for noncontact biomedical applications.