A [[continuous-time signal]] is said to be **periodic** if it remains unchanged by a temporal shift of the value $T$: $x(t) = x(t+T) , T \in \mathbb{R} \land \forall t \in \mathbb{R}$ Similarly, a [[discrete-time signal]] is said to be **periodic** if it remains unchanged over a time shift of $N$ samples: $x(n) = x(n+N) , N \in \mathbb{Z_+} \land \forall n \in \mathbb{Z}$ where $\mathbb{Z_+}$ is the set of integers greater than $0$ and $N$ is the period. The smallest value of $N$ that verifies the above equation is called the [[fundamental period]]. The [[discrete-time sinusoidal signal]] and the [[discrete-time complex exponential signal]] are examples of periodic signals.