Reverse Concatenation of Product and Modulation Codes

Reverse concatenation (RC) architectures, which recently have been deployed in hard-disk-drive (HDD) products, offer crucial advantages in coding such as (i) avoiding error propagation through the modulation decoder, (ii) allowing the use of efficient high-rate modulation codes, and (iii) passing of soft information from the detector to the decoder, which facilitates parity-post processing and iterative coding schemes. In HDDs, error-correcting codes essentially consist of a single high-rate Reed-Solomon code, whereas in tape recording, large product codes are used that require a new RC architecture. Such a novel RC architecture for product codes is presented and illustrated by an example based on the linear tape open standard, generation 4 (LTO-4). Compared with the rate-16/17 modulation code of the LTO-4 standard, the proposed RC scheme has a modulation scheme of rate 0.9951, i.e., achieves 5.7% improvement in rate while maintaining the same interleaved I = 11 modulation constraint, but at the cost of a slight weakening of the G-constraint.