Symbol-based parallel message-passing decoding on partial-response channels

Idea of parallel message passing (PMP) between detector and decoder has been studied. The PMP aims to achieve very-high speed decoder. This view point is extremely important in magnetic recording systems where data rate must be high but decoding delay should be low. Recently, the result of symbol based (SB) PMP decoding compared with SB-TE (SB-BCJR combined with q-ary LDPC) on PR channels is presented. However, the bit error rate cannot be equivalent to the SB-BCJR. Motivated by this issue, we introduced cycle-free SB-PMP detector combined with usage of optimal schedule in exchanging information between detector and decoder. Our proposed system could achieve both high speed decoding and identical performance to SB-TE. Additional, alternative method to construct a trellis for SB-PMP detector was presented.