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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]

In this paper, protograph-based quasi-cyclic (QC) low-density parity-check (LDPC) codes are proposed for the efficient structure coding of LDPC codes in 2-D intersymbol interference (ISI) ultrahigh 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 is employed instead of the full 2-D Bahl–Cocke–Jelinek–Raviv detector. The proposed protograph-based codes, whose base matrices are constructed according to the degree sequences for 2-D-ISI channels, have a low-complexity QC encoder structure with a readily parallelizable protograph decoder structure. Simulation results show that the proposed protograph-based QC-LDPC codes outperform the random LDPC codes optimized for additive white Gaussian noise channels. Furthermore, the performance of the QC codes is similar to that exhibited by ISI-optimized random LDPC codes designed for 2-D-ISI channels, while retaining the implementational benefits. [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]

Shingled magnetic recording (SMR) with 2-D magnetic recording has recently emerged as a promising technology to sustain the growth of magnetic storage areal density. However, with the reduction of track pitch, the intertrack interference (ITI) becomes a major impairment. Furthermore, in SMR, the ITI is non-uniform among the top and lower tracks. A 2-D read channel which makes use of an array of read heads can effectively detect and compensate the severe ITI. In this paper, based on a read-array SMR channel model with non-uniform ITI, a shuffled multi-track detection (SMTD) detector, which shuffles and propagates the most reliable extrinsic information among the upper, lower, and middle detectors, is proposed to mitigate ITI more effectively. With the optimized non-binary low-density parity-check code, the performance of the proposed SMTD over the read-array SMR channel is evaluated. [ABSTRACT FROM AUTHOR]

A method of capillary electrophoresis (CE) with capacitively coupled contactless conductivity detector (C4D) was developed to detect Cu-EDTA and its degradation intermediates simultaneously. The target compounds included oxalic acid, EDTA, Cu-EDTA, glyoxylic acid, iminodiacetic acid, formic acid and copper ion. The optimum electrophoretic conditions were determined by varying the running solution, injection voltage, injection time, and separation voltage. The anions in the reaction solution were separated and detected successfully under the conditions of 20 mmol L−1 acetate acid, electrokinetic injection of −13 kV×10 s, and separation voltage of −15 kV. Furthermore, copper ion was detected when 20 mmol L−1 acetate acid solution, electrokinetic injection of +11 kV×6 s and separation voltage of +13 kV were applied. The detection method was verified to track the degradation of Cu-EDTA with H2O2/UV. [ABSTRACT FROM AUTHOR]