Soft-output decoding of 2D modulation codes for bit-patterned media recording

The two-dimensional (2D) interference is a major impairment in bit-patterned media recording (BPMR) systems because of small bit and track pitches, especially at high recording densities. To mitigate this problem, we introduced 2D modulation codes, which output only the hard decision, for an uncoded BPMR system (i .e ., without error-correction codes). To utilize a rate-4/5 constructive inter-track interference (CITI) code in the coded BPMR system, which employs a low-density parity-check (LDPC) code, we propose the log-likelihood ratio (LLR) algebra implementation in Boolean logic mappings for the CITI coding scheme. Then, this soft CITI coding scheme together with a modified 2D soft-output Viterbi algorithm (2D-SOVA) detector [4] and a LDPC decoder will jointly perform iterative decoding.