Abstract
Continuous-wave Doppler radar (CWDR) can be used to remotely detect physiological parameters, such as respiration and heart signals. However, detecting and separating multiple targets remains a challenging task for CWDR. While complex transceiver architectures and advanced signal processing algorithms have been demonstrated as effective for multiple target separations in some scenarios, the separation of equidistant sources within a single antenna beam remains a challenge. This paper presents an alternative phase tuning approach that exploits the diversity among target distances and physiological parameters for multi-target detection. The design utilizes a voltage-controlled analog phase shifter to manipulate the phase correlation of the CWDR and thus create different signal mixtures from the multiple targets, then separates them in the frequency domain by suppressing individual signals sequentially. We implemented the phase correlation system based on a 2.4 GHz single-channel CWDR and evaluated it against multiple mechanical and human targets. The experimental results demonstrated successful separation of nearly equidistant targets within an antenna beam, equivalent to separating physiological signals of two people seated shoulder to shoulder.
Highlights
Since it was theorized in 1842, the Doppler effect has been used in the context of radar sensing to detect moving objects from stationary backgrounds in a variety of areas, ranging from cosmology to meteorology
This paper presented a multi-target physiological detection and separation method suitable for single-antenna single-channel narrow band Continuous-wave Doppler radar (CWDR)
Proposed phase tuning technique with Fast Fourier transform (FFTs) does not require significant hardware complexity not significant computational resources. This technique does rely on frequency separation of sources, for overlapping frequency spectra other signal processing technique such as multiple signal classification (MUSIC) or empirical mode decomposition (EMD) may be explored in the future
Summary
Since it was theorized in 1842, the Doppler effect has been used in the context of radar sensing to detect moving objects from stationary backgrounds in a variety of areas, ranging from cosmology to meteorology. In [8,9], Boric-Lubecke et al, and Lee et al, demonstrated the feasibility to separate multiple spectral diverse or spatially diverse cardiovascular-related motions with single-antenna and multiple-antenna CWDRs. In [10], Rivera et al, presented a multi-target detection method for heart and respiration rates, which applies clustering and multiple signal classification (MUSIC) algorithms to ultra-wideband (UWB) radar output. MUSIC algorithm involves singular value decomposition (SVD) with near cubic complexity These methods are challenging to implement on low-power, computation-limited radar sensors standards for physiological monitoring. To reduce the implementation cost, this work proposes a simple, single-channel CWDR method for multi-target detection using phase sweeping. The main contributions of this work are highlighted in the following: (1) We presented a theoretical analysis of the proposed singleantenna single-channel phase sweep method for multi-target detection with individuals at similar nominal ranges. The results demonstrated that our system could monitor nearly equidistant subjects seated shoulder to shoulder without changing range, beam angle, or applying other more complex signal separation techniques
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