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A Combination Approach for 2-D Interference Channel Based on Factor Graph in BPMR System
(2025-02-01)
Sopon, Thanomsak
;
Supnithi, Pornchai
High areal density in bit-patterned media recording (BPMR) systems encounters several challenges, such as two-dimensional (2-D) interference channels and media noises in the presence of severe fluctuations. To combat the effects of the 2-D interference channel, a factor graph-based detector (FGB) is one of the promising detectors for the 2-D detection that can mitigate the channel impairment. In this paper, we propose an improvement of factor graph decoding for 2-D interference channels of the BPMR system. The 2-D interference channel is separated into the two targets that are the upper triangular target and the lower triangular target. After that, the joint outputs are averaged for each detector. The simulation results show that the proposed FGB detector method achieves lower bit error rate (BER) performances than both the conventional FGB detector and the 2-D FGB detector on the BPMR system with an areal density of 3 and 4 Tb/in<sup>2</sup>.
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Optimal Array-Reader and Track Misregistration Mitigation Method in a Three-Reader/Four-Track Reading Bit-Patterned Magnetic Recording System
(2020-01-01)
Kankhunthod, Kittipon
;
Buajong, Chaiwat
;
Warisarn, Chanon
Track misregistration (TMR) is one of several problems in ultrahigh areal density bit-patterned magnetic recording (BPMR) systems, in which the distances between bit-islands are very narrow in both cross-track and down-track directions.Unfortunately,distance reduction leads to intersymbol interference and intertrack interference (ITI) effects,which cause system performance degradation. To deal with these effects, we develop the optimal position of an array-reader based on a three-reader/four-track reading BPMR system that is combined with a simple two-dimensional rate-3/4 modulation code and ITI subtraction technique,which delivers the best avoidance of the ITI effect from sidetracks.We model TMR estimation and mitigation methods using readback signals that are obtained from the optimal array-readers to improve bit error rate (BER) performance.The variance-ratio of these readback signals is used to estimating the TMR levels,whereas a pair of the target’s and equalizer’s coefficients,accordingly designed to the estimated TMR levels,is adopted for mitigating the TMR effect. Simulation results show that our methods provide a high TMR estimation accuracy and gain a superior BER performance compared with the recording system without these techniques under the same user density.
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Modified Multitrack Joint Two-Dimensional Viterbi Detectors for Rate-4/5 and Rate-5/6 Modulation Codes in Bit-Patterned Magnetic Recording Systems
(2020-01-01)
Buajong, Chaiwat
;
Warisarn, Chanon
For an ultrahigh areal-density bit-patterned magnetic recording, system performance is severely degraded by intertrack interference (ITI). Rate-4/5 and rate-5/6 modulation codes were introduced to avoid data patterns that can cause severe ITI. However, their decoders might not be able to correctly perform for data patterns that do not match with their look-up tables during the decoding process. To further improve system performance, we use a multitrack joint two-dimensional (2-D) Viterbi detector for the recommended systems. We also use a modified trellis structure with lower complexity when compared to a conventional joint 2-D detector, which is designed based on their encoding conditions. Simulation results show that our systems outperform the conventional system, especially when they are investigated in a media-noise environment.
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Improvement in Bit Error Rate with a Combination of a Rate-3/4 Modulation Code and Intertrack Interference Subtraction for Array-Reader-Based Magnetic Recording
(2019-01-01)
Buajong, Chaiwat
;
Warisarn, Chanon
To improve the bit-error-rate (BER) performance of an ultrahigh-density bit-patterned magnetic recording (BPMR) system, the intersymbol interference and intertrack interference (ITI) effects resulting from the reduction of spacing between bit islands in both along-track and across-track directions must be efficiently handled. Array-reader-based BPMR is considered a key technology for future magnetic recording due to its advantages, such as its diversity gain against noise and ITI cancellation. This letter proposes a three-reader, four-track system where a simple rate-3/4 two-dimensional (2-D) modulation code and a new ITI subtraction technique are used to improve recording system performance. Moreover, a 2-D Viterbi detector is modified in accordance with the ITI subtraction scheme, which leads to lower complexity and better BER performance. Simulations demonstrate improvement in performance gains under position and size fluctuation effects.
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Impact of Background Interference on Signal-To-Noise Ratio in Heat-Assisted Magnetic Recording
(2018-01-01)
Kaitwanidvilai, Somyot
;
Chaiduangsri, Nuttapon
;
Tongsomporn, Damrongsak
We discuss background interference (BGI) arising from the read-back of preexisting data and adjacent tracks on a recording medium. A signal-To-noise ratio analysis is used to measure the impact of BGI in heat-Assisted magnetic recording in a spin-stand tester. The signal-To-noise ratio for a data track with an alternating field background was compared to a data track written over a pair of background tracks. We considered the effect of background track offsets: The distance between the background and data tracks. BGI, which depends on the background track offset, can degrade read-back performance. The dibit extraction technique is able to separate the linear dibit response and the BGI in the read-back waveform.
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An Intertrack Interference Subtraction Scheme for a Rate-4/5 Modulation Code for Two-Dimensional Magnetic Recording
(2016-01-01)
Pituso, Kotchakorn
;
Warisarn, Chanon
;
Tongsomporn, Damrongsak
;
Kovintavewat, Piya
The performance of a rate-4/5 modulation code is evaluated in two-dimensional magnetic recording (TDMR) channels, where a magnetic medium is described by a discrete Voronoi model, and the two-dimensional sensitivity function of the reader is adopted to generate the TDMR readback signal. Since the read-head sensitivity function covers many tracks, it causes intertrack interference (ITI) that can deteriorate the system performance. Therefore, this letter proposes an ITI subtraction scheme in conjunction with the rate-4/5 modulation code in a coded TDMR channel to mitigate the ITI effect embedded in the readback signals before performing an iterative decoding process. We also investigate the data-dependent readback amplitude distributions and evaluate the TDMR system performance via computer simulation. Results show that the proposed scheme helps improve the TDMR system performance, especially when the areal density is high.
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Effects of Island Volume and Hotspot Position Fluctuation for Heated-Dot Magnetic Recording
(2016-01-01)
Tipcharoen, Warunee
;
Warisarn, Chanon
;
Kovintavewat, Piya
Heated-dot magnetic recording (HDMR), which employs the laser to heat a bit-patterned medium before recording data, is a promising technology to achieve an ultra-high recording density. Generally, many parameters can cause an error during the writing process in an HDMR system; however, this letter investigates only the effect of bit island volume, bit island position fluctuation, and hotspot position fluctuation. Specifically, three bit island volumes are considered, i.e., 1100, 860, and 620 nm<sup>3</sup>. In addition, we also study the 3-by-3 data patterns that easily cause an error when the hotspot and write head positions have fluctuated. To achieve an error-free writing process, the heating temperature is studied using the Brillouin function for thermal calculations. Implementation of treating the hotspot and evaluating the thermal effect is explicitly described. Simulation results indicate that the smaller the position variation, the lower the error percentage. Moreover, we found that the error percentage is decreased as the heating temperature is increased. Finally, it is apparent that the smaller the island volume, the lower the error percentage.

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