Benefits of Coherent Low-IF for Vital Signs Monitoring Using Doppler Radar
- 20 August 2014
- journal article
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Microwave Theory and Techniques
- Vol. 62 (10), 2481-2487
- https://doi.org/10.1109/tmtt.2014.2346151
Abstract
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.Keywords
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