Enhanced Message Passing in Turbo Product Code

Turbo product code with single parity check (TPC/SPC) has demonstrated superior error correction capability over the conventional PRML channel. However, the performance usually suffers at higher code rate. A scheme to improve BER of TPC/SPC at higher code rate is proposed. By adding cyclic redundancy check (CRC) to TPC/SPC, a sub-block can be ensured error free after passing both the parity check and CRC. At the completion of each iteration, the messages from the error free sub-blocks are modified to greatly increase their confidence levels. The artificially high confidence level from those error free sub-block bits results in much more efficient iterations subsequently and greatly lowers the ultimate BER. It is found that enhanced message passing combined with noise prediction maximum likelihood (NPML) detection in the soft output Viterbi algorithm (SOVA) gives the best performance. Spinstand head/media signals passed through software channel are used to validate the channel performance.