Signal Processing for Near 10 Tbit/in$^{2}$ Density in Two-Dimensional Magnetic Recording (TDMR)

This paper presents an extrinsic information transfer (EXIT) chart based irregular repeat-accumulate (IRA) code design technique for a two-dimensional magnetic recording (TDMR) turbo-equalizer that employs a Voronoi magnetic grain model. The channel model also includes two-dimensional intersymbol interference (2D-ISI) and additive white Gaussian noise (AWGN). At high bit densities (e.g., between 1 and 3 magnetic grains per coded bit (GPB)), occasionally a bit will not be written on any grain, and hence will effectively be "overwritten" (or erased) by bits on surrounding grains. The proposed code design takes into account the statistics of the TDMR channel to decrease overwrite effects. The proposed receiver uses a 2D-ISI BCJR equalizer and IRA decoder in a turbo-equalization approach. To design the IRA code, we find the experimental EXIT chart curves of the check node decoder (CND) and the combination of the variable node decoder (VND) with the 2D-ISI equalizer. We fit the VND and CND EXIT chart curves to find the IRA code's optimized variable node degree distribution for the TDMR channel. Simulation results show that the IRA codes optimized for the TDMR Voronoi grain model achieve up to a 3.3% density increase in user-bits/grain (U/G) compared to IRA codes designed for AWGN channels. At 1.2 GPB, the designed IRA codes achieve densities as high as 0.455 U/G, corresponding to an areal density of about 4.6 Terabits/in 2 on typical magnetic hard disks with 10 Teragrains/in 2 ; this is nearly a factor of 5 better than the best commercially available systems.

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“…equi-probable values ±1. Matrix w is the discrete AWGN field and h is the 2D read impulse function, given in [4] as…”

Section: A Tdmr Voronoi Model and 2d-isi Channelmentioning

confidence: 99%

“…Thus, occasionally a bit will not be written on any grain, and hence will effectively be "overwritten" (or erased) by bits on the surrounding grains. TDMR channels also suffer from two-dimensional intersymbol interference (2D-ISI) caused by down-track and cross-track direction interferences (e.g., [4], [5]). …”

Section: Introductionmentioning

confidence: 99%

EXIT chart based IRA code design for TDMR

Mehrnoush

Belzer

Sivakumar

et al. 2016

2016 Annual Conference on Information Science and Systems (CISS)

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“…The concept of two-dimensional magnetic recording (TDMR) advocated by Wood et al [4] has inspired research in this field. Related research into, for example, signal processing [3], detection algorithms [1], and simplified channel models [5] has been conducted for TDMR systems.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Symmetric Mutual Information of the Simplified TDMR Channel Model

Wadayama

2015

2015 IEEE Global Communications Conference (GLOBECOM)

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Abstract-In the present paper, a simplified two-dimensional magnetic recording (TDMR) channel model is proposed in order to capture the qualitative features of writing and readback processes of TDMR systems. The proposed channel model incorporates the effects of both linear interference from adjacent bit-cells and signal-dependent noise due to irregular grain boundaries between adjacent bit-cells. The simplicity of the proposed model enables us to derive the closed form of the conditional PDF representing the probabilistic nature of the channel. The conditional PDF is Gaussian distributed and is parameterized by a signal-dependent covariance matrix. Based on this conditional PDF, a Monte Carlo method for approximating the symmetric mutual information of this channel is developed. The symmetric mutual information is closely related to the areal density limit for TDMR systems. The numerical results suggest that we may need low-rate coding, e.g., 2/3 or 1/2, when the jitter-like noise becomes dominant.

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“…Individual bit dimensions at 10 Tb/in 2 are, at most, 8 nm × 8 nm, with substantially smaller values for those systems writing on conventional media where raw error rates are likely to be very high. In particular, TDMR attempts to store a channel bit in very few grains of a conventional magnetic medium in order to achieve 1-1.5 data bits/grain , Hwang 2010. The irregular grain boundaries and random distribution of grains produce extremely low signal-tonoise ratio (SNR).…”

Section: Introductionmentioning

confidence: 99%

Novel system design for readback at 10 terabits per square inch user areal density

2012

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A novel system design for sensing very high density magnetic recording data, such as that envisioned for twodimensional magnetic recording, is proposed. The key idea is a rotated sense head, so that the shields are aligned downtrack, combined with oversampled signal processing to regain the lost down-track resolution. Based on a random Voronoi grain model, simulation indicates that for bits with dimension of 8 nm × 6 nm, 5.5 nm grains, and a reader with 4 nm × 18 nm × 18 nm free layer and 11 nm shield-shield spacing, the bit error rate can drop from 20.9% for a normally positioned head array to 4.2% for a single-rotated single head with sampling period of 2 nm, a minimum mean squared error equalizer, and pattern-dependent noise prediction detector. The user density computed using the Shannon capacity limit is greatly increased to 10.1 Tb/in 2 .

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Signal Processing for Near 10 Tbit/in$^{2}$ Density in Two-Dimensional Magnetic Recording (TDMR)

Cited by 62 publications

References 7 publications

EXIT chart based IRA code design for TDMR

EXIT chart based IRA code design for TDMR

Evaluation of Symmetric Mutual Information of the Simplified TDMR Channel Model

Novel system design for readback at 10 terabits per square inch user areal density

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