Time-Frequency-Modulation Representation of Stochastic Signals

When a noise process is modulated by a deterministic signal, it is often useful to determine the signal´s parameters. A method of estimating the modulation index m is presented for noise whose amplitude is modulated by a periodic signal, using the magnitude modulation spectrum (MMS). The method is developed for application to real discrete signals with time- varying parameters, and extended to a 3D time-frequency- modulation representation. In contrast to squared-signal approaches, MMS behaves linearly with the modulating function allowing separate estimation of m for each harmonic. Simulations evaluate performance on synthetic signals, compared with theory, favouring a first-order MMS estimator.