Instantaneous frequency estimation of interfering FM signals through time-scale isolevel curves

This paper investigates the possibility of extracting information regarding two or more frequency modulated (FM) signals in almost complete interference. To this aim, a novel wavelet-based approach for the estimation of instantaneous frequency (IF) is presented. It is first proved that the modulus of the Analytic Wavelet Transform (referred to as scalogram) of one or more FM signals obeys a time-scale evolution law whose isolevel curves (ICs) depend on signal IF. Hence, it is shown that scalogram points not belonging to ridge can provide a more robust IF estimate in case of strong interference. Experimental results confirm that the proposed approach improves ridge-based IF estimation, even in presence of noise.

► We prove that the scalogram of FM signals obeys a time-scale evolution law.
► The characteristic curves of the evolution law depend on signal IF.
► In case of interference, non-ridge points give a more robust IF estimate.
► A limited number of scalogram points is required for IF estimation.