A systematic encoder reliably transferring a source data block (SDB) is configured for an outer transform matrix and an inner transform matrix. An inner encoder receives the SDB and generates an output constraint block (OCB) as an SDB image under an inverse of a submatrix of the inner transform matrix. An outer encoder receives a fixed data block (FDB) and the OCB and generates a transform output block (TOB) as a transform input block (TIB) image under the outer transform matrix. The TIB contains the FDB transparently in a sub-block of the TIB, and the TOB contains the OCB transparently in a sub-block of the TOB. The inner encoder receives the TOB and generates a transmitted code block (TCB), transparently containing the SDB in a sub-block therein.