Yasuaki Nakamura

Read/Write Channel Modeling and Two-Dimensional Neural Network Equalization for Two-Dimensional Magnetic Recording

An accurate medium modeling method of discretized granular medium with non-magnetic grain boundaries using a discrete Voronoi diagram is proposed for two-dimensional magnetic recording. A simple closed-form representation of a double-shielded reader sensitivity function is also proposed for modeling the reading process. Moreover, a two-dimensional neural network equalizer (2D-NNE) is proposed to mitigate the influence of intertrack interference and jitter-like medium noise. The bit-error rate performance of partial response class-I maximum likelihood (PR1ML) system with the 2D-NNE is obtained by computer simulation based on the proposed read/write channel model. The performance is far superior to that of PR1ML system with a two-dimensional finite impulse response equalizer.

Modeling of Writing Process for Two-Dimensional Magnetic Recording and Performance Evaluation of Two-Dimensional Neural Network Equalizer

Modeling of a simple writing process considering intergranular exchange fields and magnetostatic interaction fields between grains is studied for two-dimensional magnetic recording (TDMR). A new designing method of a two-dimensional neural network equalizer with a mis-equalization suppression function (2D-NNEMS) for TDMR is also proposed. The bit-error rate (BER) performance of a low-density parity-check coding and iterative decoding system with the designed 2D-NNEMS is obtained via computer simulation using a read/write channel model employing the proposed writing process under TDMR specifications of 4 Tb/in2, and it is compared with those for one- and two-dimensional finite impulse response equalizers (FIREs). It is clarified that the BER performance for the designed 2D-NNEMS is far superior to those for the FIREs.

Simplified Neural Network Equalizer With Noise Whitening Function for GPRML System

A new design method of the simplified neural network equalizer (NNE) with the noise whitening function for a generalized partial response (GPR) channel is proposed. The long-term bit error rate performance of GPR class-I maximum likelihood (GPR1ML) system employing NNE in perpendicular magnetic recording (PMR) channel with thermal decay is also obtained by computer simulation using our thermal decay model for a CoPtCr-SiO2 PMR medium with KuV/kT=60. The performance of GPR1ML system with NNE (GPR1ML-NNE) is superior to that of GPR1ML with a transversal filter equalizer. The PR1ML system using a noise whitening NNE and a two-state Viterbi detector provides almost equivalent performance to that of GPR1ML-NNE having a 16-state detector.

A Study of TDMR Signal Processing Opportunities Based on Quasi-Micromagnetic Simulations

This paper presents the results of a comprehensive study of the shingled writing process and various signal processing and data detection approaches applied to the readback waveforms. The recording simulations include realistic head fields, a random granular media, magnetostatic and exchange interactions, and a READ head sensitivity function. Readback waveforms are examined in both one and two dimensions in terms of signal characteristics (linear and nonlinear), noise behavior (stationary and signal-dependent), and intertrack interference. Different equalization and detection approaches are compared and about a 10% density gain is reported for such 2-D magnetic recording compared with traditional single-track recording. These gains depend strongly on the number of readers, the reader positioning, and the reader width.

Nonbinary LDPC Coding and Iterative Decoding System With 2-D Equalizer for TDMR R/W Channel Using Discrete Voronoi Model

A 2-D magnetic recording (TDMR) by shingled magnetic recording (SMR) is one of the most promising technologies for realizing ultra-high areal densities. We have developed the discretized granular medium model with nonmagnetic grain boundaries and the simple writing process considering intergranular exchange fields and magnetostatic interaction fields between grains on the discrete Voronoi model for TDMR. In this paper, the bit-error rate (BER) performance of the iterative decoding system using a nonbinary low-density parity-check (LDPC) code over Galois field GF(q) with the 2-D finite-impulse-response equalizer (2D-FIRE) is obtained via computer simulation using an R/W channel model employing the writing process under TDMR specifications of 4.12 Tb/in2, and it is compared to that with the 1-D FIRE (1D-FIRE). The results show that the BER performance of the nonbinary LDPC coding and iterative decoding system with the 2D-FIRE is better than that with the 1D-FIRE.

A Study of LDPC Coding and Iterative Decoding System in Magnetic Recording System Using Bit-Patterned Medium With Write Error

In this paper, low-density parity-check (LDPC) coding and iterative decoding system is studied in the magnetic recording system using a bit-patterned medium (BPM). The magnetic recording system using BPM has a serious problem of requiring precise write synchronization to correctly write the recording sequence on each intended island. In this paper, an error locator using the parity-check matrix of LDPC code is utilized to curb the influence of write error on the iterative decoding process. The performance of the proposed system with the error locator is evaluated by computer simulation for magnetic recording system using BPM with synchronization write error at a recording density of 2 Tb/in2, and it is compared with a conventional Reed-Solomon (RS) encoding and decoding system. The results show that the proposed system provides better performance.

Performance Evaluation of ITI Canceller Using Granular Medium Model

The performance of an iterative decoding system is evaluated in shingled magnetic recording (SMR). The medium model is made by a discrete Voronoi model, and the 2-D sensitivity function of reader is used to obtain the reproducing waveform. As the sensitivity function extends to adjacent tracks, intertrack interference (ITI) deteriorates the signal detection system. In order to recover the intrinsic performance, it is required to reduce the influence of ITI to the system. Then, the ITI canceller is employed to combat ITI for the iterative decoding system, and the performance is evaluated by computer simulation. The results show that the introduction of ITI canceller improves the bit-error-rate performance in SMR system.

A Study on Nonbinary LDPC Coding and Iterative Decoding System in BPM R/W Channel

In this paper, the iterative decoding system using the nonbinary low-density parity-check (LDPC) code is studied in the magnetic recording system using a bit-patterned media (BPM) R/W channel affected by the write head field gradient, the media switching field distribution (SFD), the demagnetization field from adjacent dots, and the dot position deviation in an areal recording density of 2 Tb/in2. The performance of iterative decoding system using the nonbinary LDPC code over Galois field of GF(28) is evaluated by the computer simulation, and it is compared with the conventional iterative decoding system using the binary LDPC code. The results show that the nonbinary LDPC system provides better performance compared with the binary LDPC system.

Iterative Decoding Using Attenuated Extrinsic Information from Sum-Product Decoder for PMR Channel With Patterned Medium

An LDPC coding and iterative decoding system is studied in perpendicular magnetic recording (PMR) with a bit-patterned medium. We propose an iterative decoding scheme using attenuated extrinsic information from a sum-product decoder, and the bit error rate (BER) performance of the LDPC coding and iterative decoding system is evaluated by R/W computer simulations. It has been clarified that at an areal density of 1 Tbpsi the proposed system provides a jitter margin of the island edges of approximately 0.6% larger than the conventional system using (3, 18)-regular LDPC code

Bit error rate performance for head skew angle in shingled magnetic recording using dual reader heads

The two-dimensional magnetic recording (TDMR) exploits two-dimensional signal processing using the neighboring read-back waveforms. We allocate dual readers for the intended tracks and evaluate the effects of head skew angle on the bit error rate performance in partial response class-I maximum likelihood system with a two-dimensional finite impulse response filter using two read-back waveforms under TDMR R/W channel specifications of 4 Tbit/in.2. The results show that the effect of positive skew angle is larger than that of negative skew angle, and the center of skew angle should be shifted to minus direction.