Could be coding (Turbo coding is where it's at, while hamming (no relation) error correcting codes are purely digital and ubiquitous), could be simple double tr

Could be coding (Turbo coding is where it's at, while hamming (no relation) error correcting codes are purely digital and ubiquitous), could be simple double transmissions separated in the time domain as in FEC SITOR/AMTOR. My money's on Turbo coding. https://en.wikipedia.org/wiki/Turbo_code https://en.wikipedia.org/wiki/Turbo_code