Concatenated Codes “Divide and Conquer”
First proposed by Forney over 30 years ago.
Interleaving and De-interleaving break up errors out of Inner Decoder which tend to be Bursty.
Divide complexity between inner and outer decoding - complexity considerably reduced (Reed-Solomon outer code and convolutional inner code used by NASA, ESA, DSB.)
But performance suffers because inner decoder makes “0” or “1” (HARD) decisions, destroying information usable by outer decoder.