Power spectral density of phase noise for a frequency modulated signal plus additive white Gaussian noise after sampling and filtering

In an FM(PM)-transmission system the demodulator transforms the complex baseband noise into amplitude and phase noise components. Without modulation, and at moderate to high carrier-to-noise ratio (CNR), the shape of the phase noise power spectral density (PSD) is modelled by the input noise PSD. The authors derive an approximation for modulated signals, which determines the PSD of phase noise near the threshold of FM demodulators