Estimating the period length of periodic signals

A numerical technique for determining the rotor-blade frequency of a helicopter from a noise-perturbed Doppler radar signal is developed analytically and demonstrated by means of numerical simulations. A method based on maximum-likelihood analysis yields an optimum estimate in the case of white noise, but requires additional adaptive bandpass filtering for clutter suppression in the case of colored noise (as when the antenna is mounted on an aircraft). An alternative nonlinear processing technique employing parameter approximation is shown to avoid this difficulty, generating the cepstrum without ambiguity.