Iterative detection and decoding for the four-rectangular-grain TDMR model

This paper considers detection and error control coding for the two-dimensional magnetic recording (TDMR) channel modeled by the two-dimensional (2D) four-rectangular-grain model proposed by Kavcic, Huang et. al. in 2010. This simple model captures the effects of different 2D grain sizes and shapes, as well as the TDMR grain overwrite effect: grains large enough to be written by successive bits retain the polarity of only the last bit written. We construct a row-by-row BCJR detection algorithm that considers outputs from two rows at a time over two adjacent columns, thereby enabling consideration of more grain and data states than previously proposed algorithms that scan only one row at a time. The proposed algorithm employs soft-decision feedback of grain states from previous rows to aid the estimation of current data bits and grain states. Simulation results using the same average coded bit density and serially concatenated convolutional code (SCCC) as a previous paper by Pan, Ryan, et. al. show gains in user bits/grain of up to 6.7% over the previous work when no iteration is performed between the TDMR BCJR and the SCCC, and gains of up to 13.4% when the detector and the decoder iteratively exchange soft information.