PLL based discrete time varying filter for estimation of parameters of a sine signal corrupted by a closely spaced FM interference

A method for the estimation of the parameters of a sine signal corrupted by a strong FM interference is presented. The method consists of two stages. In the first stage, an FM interference is transformed into a harmonic wave with known frequency by using a special time-warping technique. This harmonic interference is then rejected in the transformed time domain by a time-invariant constrained notch filter. The time-warping is implemented using nonuniform sampling obtained by utilizing a phase locked loop (PLL) technique. It is shown that such processing results in a 0-dB signal-to-interference ratio at the output independently of the signal-to-interference ratio at the input (for negative values in decibels). The second stage involves parameter estimation, where a constrained adaptive notch filter is used for the enhancement of a signal under analysis