The simulation result shows that VPSD is a kind of constant false alarm rate detector, which can detect HFM signal effectively in low SNR, and can adapt to the Doppler mismatch very well.
It uses a conventional constant false-alarm-rate(CFAR) detection procedure but the thresholding scheme is based on regression analysis of power spectrum values along range and Doppler cells.
Since the human beings and the other creatures usually walk or run with a constant velocity, stride and gait frequency, there are some Micro-Doppler signatures on their spectrums.