Partial reverse concatenation for data storage

Coding schemes in data-storage systems use either conventional or reverse concatenation of a modulation code and an error-correction code. A new reverse concatenation scheme, called partial reverse concatenation, is introduced to reduce the coding overhead, improve the error-rate performance and simplify implementation. The proposed concatenation scheme uses an outer error-correction code, a high-rate modulation code and an inner error-correction code. The error-rate performance of partial reverse and conventional concatenation architectures are compared using measurements from tape drive channels. It is shown that, compared with a conventional concatenation scheme, an LDPC-code-based partial reverse concatenation scheme improves the signal-to-noise ratio that is required to achieve a bit-error rate of 1×10^-20 by 1.8 dB.