As discussed in Chap. 7 , the estimation of velocity using Doppler effect and the estimation of distance using a chirp is essentially a problem of estimating the frequency of a sinusoid. A simple method for frequency estimation using DFT/FFT is also presented in Chap. 7 . Estimating the frequency of a finite duration sinusoid using the DFT/FFT method has the “main lobe width” problem; if the frequency separation between two sinusoids is less than the spectral main lobe width of a rectangular window, the two sinusoids cannot be resolved. See Fig. 7.24 of Chap. 7 .