What is the power / energy of a discrete time constant signal?
Suppose x(t) = K is a constant signal.

The energy which will be dissipated on a unit 1 ohm resistor by x(t) can be computed as:
$$
\begin{align}
E&amp;=\int_{-\infty }^{\infty }\left | x(t) \right |^{2} dt\\
&amp;=K^2\int_{-\infty }^{\infty }dt \\
&amp;= \infty
\end{align}
$$
The power which will be dissipated on a unit 1 ohm resistor by x(t) can be computed as:
$$
\begin{align}
P&amp;=\lim _{T-&gt;\infty}\frac{1}{2T}\int_{-\infty }^{\infty }\left | x(t) \right |^{2} dt\\
&amp;=K^2\lim _{T-&gt;\infty}\frac{1}{2T}\int_{-T }^{T}dt\\
&amp;=K^2\lim _{T-&gt;\infty}\frac{2T}{2T}\\
&amp;=K^2
\end{align}
$$

Therefore x(t) has finite power but infinite energy. Which implies a constant signal is a power signal.

Refer: Energy and Power Signals