Linear FM Signal Parameter Estimation Using STFT and FRFT

A new method, TrTF-FrFT, is introduced for parameter estimation of Linear frequency modulated (LFM) signals, which consists of a coarse search and a fine search. In the initial stage, the window length for Short time Fourier transform (STFT) is selected to get the right time-frequency resolution and concentrate the energy to a line in spectrogram according to the LFM signal characteristic, then the line of ridge energy is tracked in the spectrogram, and the parameters of LFM signal can be estimated coarsely. In the second stage, the fine search for correct parameters is implemented in the Fractional Fourier transform (FRFT) domain using Gaussian model to fit the impulse response of the LFM signals under the guidance from the above stage by the property of monotonicity in the limited neighborhood of the optimal value. In the range of the effective SNR from 20dB to -12dB, the accuracy of the parameter estimation are perfect and affected very little by noise with low computational complexity.