A discrete-time exponential signal is defined as: $ x(n) = A \alpha^n $ where $\alpha$ and $A$ are real numbers. The evolution in time of the discrete-time exponential signal depends on the value of $\alpha$: - $|\alpha| > 1$: the sequence $|x(n)|$ is increasing; - $|\alpha| < 1$: the sequence $|x(n)|$ is decreasing; - $\alpha > 0$: the samples of the sequence $x(n)$ all have the same $A$ sign; - $\alpha < 0$: the samples of the sequence $x(n)$ are alternately positive and negative.