  The paper centres on an assessment of the modelling approaches for the
processing of signals in CW and FMCW radar-based systems for the detection of
vital signs. It is shown that the use of the widely adopted phase extraction
method, which relies on the approximation of the target as a single point
scatterer, has limitations in respect of the simultaneous estimation of both
respiratory and heart rates. A method based on a velocity spectrum is proposed
as an alternative with the ability to treat a wider range of application
scenarios.
