[jacquesm]

They do a similar thing for GPS data recovery. It is so far below the noise floor that normally speaking the signal is not recoverable. But then you inject some (known) noise and suddenly the noise modulated by the (unknown) signal starts to drown out the noise in the rest of the system and that in turn allows you to recover bits from the signal.

[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.

[rollcat]

https://ciechanow.ski/gps/

[jacquesm]

That's a great article, you should post it separately.

[rollcat]

https://news.ycombinator.com/from?site=ciechanow.ski ;)

[farhanhubble]

This thread brings back fond memories from electronics and digital signal processing.