In telecommunication, the term signal processing gain has the following meanings:

1. The ratio of (a) the signal-to-noise ratio of a processed signal to (b) the signal-to-noise ratio of the unprocessed signal.

Note: Signal processing gain is usually expressed in dB.

2. In a spread-spectrum communications system, the signal gain, signal-to-noise ratio, signal shape, or other signal improvement obtained by coherent band spreading, remapping, and reconstitution of the desired signal.

Source: from Federal Standard 1037C