Deep space communications proceeds many dB below the noise floor
enabled through technology that has become ubiquitous in cell phones -
Spread Spectrum. I have developed pulsed measurement applications for
which any single pulse has a poor S+N/N, but through repetition
improves S+N/N response with the square root increase of samples
taken.

73's
Richard Clark, KB7QHC

And others call it autocorrelation?

W4ZCB