Phenomenological Classification

The initial classification, based on the signal's temporal evolution, reveals two fundamental types:

  • Deterministic Signals : A mathematical model can precisely describe the evolution of these signals over time. They stem from phenomena governed by known physical laws [2]. For instance, in the case of an oscillator producing a sinusoidal signal with amplitude A and frequency , we can predict the signal's value at any time using the mathematical model \(x(t)=Asin(2\pi f_0t)\) (a mathematical formula perfectly defines the signal). Within this category, we find periodic, aperiodic, and transient signals, represented in Figure 4.

Figure 4: Deterministic Signals.

  • Random (or Probabilistic or Stochastic) Signals : description: signals with unpredictable temporal behaviour, requiring the use of statistical properties for their description. We refer to them as stationary if their statistical properties stay constant over time.