2-D LDPC Codes and Joint Detection and Decoding for Two-Dimensional Magnetic Recording

Two-dimensional magnetic recording (TDMR) is a promising technology for boosting areal densities (ADs) using sophisticated signal processing algorithms within a systems framework. The read/write channel architectures have to effectively tackle 2-D intersymbol interference (ISI), 2-D synchronization errors, media and electronic noise sources, as well as thermal asperities resulting in burst erasures. The 1-D low-density parity check (LDPC) codes are well studied to correct large 1-D burst errors/erasures. However, such 1-D LDPC codes are not suitable for correcting 2-D burst errors/erasures due to the 2-D span of errors. In this paper, we propose construction of a native 2-D LDPC code to effectively correct 2-D burst erasures. We also propose a joint detection and decoding engine based on the generalized belief propagation algorithm to simultaneously handle 2-D ISI, as well as correct bit/burst errors for TDMR channels. This paper is novel in two aspects: 1) we propose the construction of native 2-D LDPC codes to correct large 2-D burst erasures and 2) we develop a 2-D joint signal detection-decoder engine that incorporates 2-D ISI constraints, and modulation code constrains along with LDPC decoding. The native 2-D LDPC code can correct >20% more burst erasures compared with the 1-D LDPC code over a 128 × 256 2-D page of detected bits. Also, the proposed algorithm is observed to achieve a signal-to-noise ratio gain of >0.5 dB in bit error rate performance (translating to 10% increase in ADs around the 1.8 Tb/in
²
regime with grain sizes of 9 nm) as compared with a decoupled detector-decoder system configuration over a small 2-D LDPC code of size 16 × 16. The efficacy of our proposed algorithm and system architecture is evaluated by assessing AD gains via simulations for a TDMR configuration comprising of a 2-D generalized partial response over the Voronoi media model assuming perfect 2-D synchronization.