  In the past decades, continuous Doppler radar sensor-based bio-signal
detections have attracted many research interests. A typical example is the
Doppler heartbeat detection. While significant progresses have been achieved,
reliable, time-domain accurate demodulation of bio-signals in the presence of
unavoidable DC offsets remains a technical challenge. Aiming to overcome this
difficulty, we propose in this paper a novel demodulation algorithm that does
not need to trace and eliminate dynamic DC offsets based on approximating
segmented arcs in a quadrature constellation of sampling data to directional
chords. Assisted by the principal component analysis, such chords and their
directions can be deterministically determined. Simulations and experimental
validations showed fully recovery of micron-level pendulum movements and
strongly noised human heartbeats, verifying the effectiveness and accuracy of
the proposed approach.
