Signal Power

In DSP, signal power is the average squared amplitude of a Signal — the mean of $|x[n]{|}^2$ over a window of samples:

$$P=\frac{1}{N}\sum _{n=0}^{N-1}|x[n]{|}^2$$

For a complex IQ signal, $|x[n]{|}^2=I^2+Q^2$ per sample. Averaging over $N$ samples gives a stable measure of signal strength.

The convention is borrowed from physics, where power is proportional to the square of voltage or current. In DSP the units are abstract, but the squaring relationship is the same.