Benefits of Coherent Low-IF for Vital Signs Monitoring Using Doppler Radar

• Published in: IEEE transactions on microwave theory and techniques Vol. 62; no. 10; pp. 2481 - 2487
• Main Authors: Mostafanezhad, Isar, Boric-Lubecke, Olga
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2014; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Architecture; Baseband; Coherence; Correlation; Direct current; Doppler radar; Flicker; Human; Human subjects; low-IF; Mixers; Monitoring; Noise; physiological signals; Receivers; Signal to noise ratio
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2014.2346151

Homodyne receiver systems have been used extensively in wireless life signs monitoring applications. The main advantage of a homodyne system is range correlation resulting in cancellation of the oscillator phase noise. However, direct down-conversion to dc and the subsequent baseband amplification circuit will introduce additional flicker noise to the signal. Physiological signals have significant content around dc that will make them susceptible to 1/f noise. A coherent low-IF system is applied to solve this problem. This architecture has the range correlation benefits of the homodyne system, while minimizing the baseband flicker noise. Measurements on a mechanical target and a human subject demonstrate a signal-to-noise ratio improvement of 7 dB, which can increase the range of operation by 50%. Measurements on a human subject have demonstrated low-IF heart rate detection with a root-mean-square error of less than 0.8 beats/min at a distance of almost 3 m with transmit power of 0.1 mW, whereas direct conversion architecture output completely failed in this case.