Based on differential AM-FM
signal instantaneous frequency calculation method, the steps are: (1) input AM-FM
signal x(t)=a(t)cos[θ(t)], and carry out denoising and discrete sampling
processing; ( 2) Obtain the local maximum, minimum and
occurrence time of the
signal x(t)=a(t)cos[θ(t)], denoted as (t j , a(t j )); (3) According to the obtained a(t j ) value, using spline interpolation function to fit a(t j ) to obtain the envelope function a(t) of the input signal; (4) obtain the
first order derivative x'(t) of the input signal x(t)=a(t)cos[θ(t)]; (5) Calculate the local maximum and minimum values of x′(t) and the
occurrence time, denoted as (t i , x′(t i )); (6) Calculate t according to the formula i The instantaneous frequency of the input signal f(t i ); (7) carry out phase-shift
processing to x(t)=a(t)cos[θ(t)], obtain x respectively 1 (t),x 2 (t),...x n-1 (t), where n≥1; (8) for the obtained x 1 (t),x 2 (t),...x n-1 (t), repeat steps (2) ~ (6), get (t i , f(t i ))
point sequence; (9) according to the obtained (t i , f(t i ))
point sequence, using spline interpolation function to fit f(t i ), get the instantaneous
frequency function f(t) of x(t)=a(t)cos[θ(t)].