[akira2501]

It's not only below the noise floor, but all satellites transmit the code on the same frequencies, so it's several signals all at once below the noise floor. Which makes the known noise unique to each satellite, and you dredge out the same frequency repeatedly with different sets of known noise to recover multiple signals.

Gold sequences are really neat, which is precisely the same pseudorandom scrambling technique, but where each sequence is selected to have low correlation with all other sequences in use, which is what enables the frequency sharing property of the system.