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This paper presents a coding scheme based on bilayer low-density parity-check (LDPC) codes for multi-level cell (MLC) NAND flash memory. The main feature of the proposed scheme is that it exploits the asymmetric properties of an MLC flash channel and stores the extra parity-check bits in the lower page, which are activated only after the decoding failure of the upper page. To further improve the performance of the error correction, a perturbation process based on the genetic algorithm (GA) is incorporated into the decoding process of the proposed coding scheme, which can convert uncorrectable read sequences into error-correctable regions of the corresponding decoding space by introducing GA-trained noises. The perturbation decoding process is particularly efficient at low program-and-erase (P/E) cycle regions. The simulation results suggest that the proposed bilayer LDPC coding scheme can extend the lifetime of MLC NAND flash memory up to 10,000 P/E cycles. The proposed scheme can achieve a better balance between performance and complexity than traditional single LDPC coding schemes. All of these findings indicate that the proposed coding scheme is suitable for practical purposes in MLC NAND flash memory. [ABSTRACT FROM AUTHOR]

In this paper, a detector-aware low-density parity-check (LDPC) code optimization algorithm is proposed for the ultra-high density magnetic recording channel, such as bit-patterned magnetic recording and two-dimensional magnetic recording, where a 2-D detector (2D-DET) is employed to combat 2-D intersymbol interference (2D-ISI) effects, by acquiring the variance of the 2D-ISI channel log-likelihood ratios corresponding to the specific 2D-DET. The new parameter builds a bridge of LDPC code optimization between the ISI-channel and the additive white Gaussian noise channel. Numerical results show that our proposed algorithms are more efficient in running time than other recently proposed optimization algorithms. Moreover, the protograph-based quasi-cyclic (QC) codes using the proposed optimization strategy, which have a low-complexity QC encoder structure with an effectual parallelizable protograph decoder composition, enjoy up to one order of magnitude performance gain in bit error rate over the other random codes that suffer from high error floors. [ABSTRACT FROM AUTHOR]

2-D inter-symbol-interference (2-D-ISI), consisting of ISI in the down track direction and inter-track interference along the cross-track direction, is a major factor that severely degrades the performance of ultra-high density magnetic recording systems. Due to its superior performance and the protograph structure which facilitates high-speed encoding and decoding, the protograph codes have shown a high potential to tackle 2-D-ISI. However, so far, no work has been reported on the design of non-binary protograph-based low-density parity-check (NP-LDPC) codes for 2-D-ISI channels. In this paper, we first propose a modified protograph extrinsic information transfer analysis. In conjunction with the asymptotic ensemble weight distribution analysis, they both serve as theoretical tools to analyze the performance of NP-LDPC codes designed for the 2-D-ISI channels. By further applying a fast search approach, we construct two types of NP-LDPC codes for 2-D-ISI channels. Both theoretical analyses and simulated results show that the proposed codes outperform the existing binary LDPC codes that optimized for 2-D-ISI channels as well as the non-binary quasi-cyclic LDPC code, at both low and high SNR regions. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of the protograph-based low-density parity-check (LDPC) codes for 2-D intersymbol interference (ISI) channels with magnetic recording density. The protograph LDPC codes have been shown to possess simple hardware implementation and excellent error performance over additive white Gaussian noise channels and over partial response channels. We propose a design scheme and construct two new protograph LDPC codes for 2-D ISI channel, with the help of extrinsic information transfer chart analysis and asymptotic ensemble weight distribution analysis. The theoretical analyses and simulated results show that the proposed codes outperform the previously optimized irregular LDPC code in both low- and high-SNR regions. Thus, the proposed codes are good alternatives compared with other error-correction codes for the use in magnetic recording systems. [ABSTRACT FROM AUTHOR]

In this paper, 2-D normalized min-sum (NMS) algorithm and offset min-sum (OMS) algorithm are proposed for efficient decoding of low-density parity-check (LDPC) codes in 2-D intersymbol interference (ISI) ultra-high density magnetic recording channels, such as bit-patterned magnetic recording and 2-D magnetic recording, where a reduced-complexity 2-D detector based on the iterative row-column soft detection feedback with Gaussian approximation detector is employed instead of the full 2-D Bahl–Cocke–Jelinek–Raviv (BCJR) detector. The normalization and offset factors of the 2-D NMS and 2-D-OMS, are optimized based on the extended density evolution for LDPC coded 2-D ISI channel, respectively. Simulation results show the performance loss caused by the reduced-complexity LDPC decoder can be almost fully recovered by the proposed approaches, while retaining the benefit of low complexity in decoder compared with the belief propagation (BP) decoding. Furthermore, both the NMS and OMS exhibit a lower error floor than that of BP decoding in high signal-to-noise ratio region. [ABSTRACT FROM AUTHOR]

In this paper, optimization of low-density parity-check (LDPC) codes to approach the symmetric information rate (SIR) of two-dimensional (2-D) intersymbol interference (ISI) channels is proposed for high-density magnetic recording, such as bit-patterned magnetic recording (BPMR) and 2-D magnetic recording (TDMR). The code design makes use of the modified Extrinsic Information Transfer (EXIT) chart, where the optimal variable node degree is searched by selecting the best check node degree to fit the check node decoder (CND) EXIT curve to the EXIT curve of the variable node decoder (VND) curve combined with 2-D detector. Simulation results show that LDPC codes with code length 10^4 bits optimized for a 2-D ISI channel corresponding to 4 \Tb/in^2 recording density can achieve bit error rate 10^-5 at signal-to-noise ratio 0.33 dB away from the SIR. To our knowledge, this is the first capacity-approaching LDPC code successfully optimized for a 2-D ISI channel. [ABSTRACT FROM PUBLISHER]

In this paper, we present a new error-correction scheme, referred to as embedded marker code scheme (EMCS), for channels corrupted by insertions, deletions and additive white Gaussian noise (AWGN). The EMCS uses the pinning bits, which have the potential to lower the error floors of the outer low-density parity-check (LDPC) codes, for both resynchronization and improving error-correction performance. Furthermore, the soft-input synchronization for the inner decoder and the joint iterative decoding between the inner decoder and the outer decoder is employed to further improve the overall performance of the new scheme. Simulations show that the proposed EMCS reduces the code rate loss as compared with the conventional marker code scheme and achieves a better tradeoff between the error performance and the decoding complexity. Therefore, the new scheme can reduce code rate loss and improve storage efficiency when it is used in bit-patterned media recording (BPMR) systems. [ABSTRACT FROM PUBLISHER]