Seongkwon Jeong

Bit-patterned media recording (BPMR) has been considered among the key technologies to extend recording densities to 1 Tb/in2 and beyond. However, the BPMR system encounters the challenges of two-dimensional intersymbol interference and track mis-registration (TMR). In this article, we propose a TMR estimator based on the $K$ -means algorithm for estimating the TMR levels and preventing the performance degradation of the BPMR system. The TMR estimator calculates the distances between the centroid of the readback signal and predetermined centroids according to the TMR level. The equalizer coefficients and partial response target are adjusted to the corresponding TMR level. At a bit error rate of 10−3 and a TMR of 10%, the proposed detection scheme performs better by approximately 1 dB in comparison with the conventional detection.

In bit-patterned media recording (BPMR) systems, the readback signal is affected by neighboring islands that are characterized by intersymbol interference (ISI) and intertrack interference (ITI). Since increasing the areal density encourages the influence of ISI and ITI, it is more difficult to detect the data. Modulation coding can prevent the occurrence of specific data patterns that can cause severe ISI and ITI. In this study, we propose a modulation decoding method based on the K-means algorithm for a BPMR system to improve decoding capabilities. As the K-means algorithm helps understand data patterns and characteristics, the K-means decoder shows the best performance.

As the need for storing significant amounts of data has increased, an increased areal density (AD) of hard disk drives is required. Bit-patterned media recording (BPMR) with the ability to increase AD is regarded as one of the future magnetic storage systems. Reducing the distance between islands storing 1 bit can provide high AD, but it creates problems of intersymbol and intertrack interferences. In this study, we propose a bit-flipping scheme using the K-mean algorithm for the BPMR system. In the proposed scheme, the K-means algorithm, which is an iterative clustering method for identifying similar samples and assigning them to clusters, is used to assign the samples that consist of the main and neighboring data to clusters. The predicted index from K-mean is utilized to compare and flip the sign of the main data when the sign is different. The proposed scheme flips the sign of data that is predicted to be an error and improves the performance using the neighboring information.

As conventional data storage systems are faced with critical problems such as the superparamagnetic limit, bit-patterned media recording (BPMR) has received significant attention as a promising next-generation magnetic data storage system. However, the reduced spacing between islands at increased areal density causes severe intersymbol and intertrack interference, which degrade BPMR system performance. In this study, we introduce a soft-output detector using multi-layer perceptron to predict reliable information. A received signal is equalized and detected by the MLP detector. The MLP detector provides a well-estimated value by using the binary-cross entropy function as a loss function and the identity function as an activation function for the output layer of the MLP detector. This study investigates the received probability distributions out of the detectors and compares the performance of various versions against a conventional detector. Compared with the conventional detection, the proposed MLP detectors provide a small variance and better BER performance than the conventional detection. Simulations of MLP designs show an advantage over conventional detection. Moreover, the proposed MLP detectors with the demodulator exhibit better BER performance than the conventional detector with the demodulator.

Because of the physical and engineering problems of conventional magnetic data storage systems, bit-patterned media recording (BPMR) is expected to be a promising technology for extending the storage density to beyond 1 Tb /in². To increase the storage density in BPMR systems, the separation between islands in both down- and cross-track directions must be reduced; this reduction results in two-dimensional interference from neighboring symbols in those directions, which is a major performance degradation factor in BPMR. Herein, we propose an iterative signal detection scheme between a Viterbi detector and a multilayer perceptron to improve the performance of a BPMR system. In the proposed signal detection scheme, we use the modified output of a multilayer perceptron as a priori information to improve equalization and extrinsic information to decrease the effect of intertrack interference.

To meet the demand for storing large amounts of data, there has been a stronger focus on increasing the recording density of a hard disk drive (HDD). While conventional HDD suffers from thermal effect and superparamagnetic limit, bit-patterned media recording (BPMR) has the potential to resolve these problems and is capable of increasing areal density beyond one terabit per square inch. To increase the areal density of BPMR, the distance between islands in both the down-and cross-track directions must be reduced. Consequently, the decreased bit period and track pitch induce more intersymbol interference and intertrack interference, which degrade the bit error rate performance. In this study, extrinsic information obtained from a multilayer perceptron equalizer is used as a priori information in a partial response maximum likelihood (PRML) detector to improve the detection performance of BPMR. The proposed detection scheme shows better performance compared to both the multilayer perceptron equalizer and conventional PRML alone. Additionally, it was found that the proposed detector provides improved performance when track misregistration occurs.

A bit-patterned media recording (BPMR) system is a type of ultrahigh-capacity magnetic storage system that can extend to an areal density of 1 terabit per square inch or higher. However, because the space between islands in the down- and cross-track directions is reduced to extend the areal density, the effect of two-dimensional interference is increased. However, using a staggered array, which is one of the possible island distributions for BPMR, helps to decrease intertrack interference. A 7/10 modulation code for a staggered BPMR is proposed to avoid the effect of two-dimensional interference and provide distance among nonidentical codewords for improving the correcting capability.

Bit-patterned media recording was invented with the aim of achieving high areal density. However, bit-patterned media recording suffers from two-dimensional (2-D) interference problems, including intersymbol interference in the down-track direction and intertrack interference in the cross-track direction. The 2-D interference corrupts the readback signal and degrades the performance of bit-patterned media recording. Unlike the layout of regular-array bit-patterned media, in the layout of staggered-array bit-patterned media, islands along neighboring tracks are displaced by a half-period from islands on the main data track; hence, in terms of intertrack interference, the islands on the main data track are predominantly affected by the closest four islands on neighboring tracks. To address this problem, a proper signal detection scheme for staggered bit-patterned media recording should be developed. In this letter, we introduce a multipath soft-output Viterbi algorithm for reducing the 2-D interference in staggered bit-patterned media recording. We investigate different partial response targets and compare the performances of the one-dimensional, two-dimensional, and proposed three-path soft-output Viterbi algorithm.

Bit-patterned media recording (BPMR) is regarded as a promising candidate for next-generation magnetic storage systems in order to increase areal density. BPMR exhibits massive two-dimensional interference, however, that consists of horizontal intersymbol interference from neighboring bits and vertical intertrack interference (ITI) from adjacent tracks. In this letter, we investigate the performance of BPMR according to the spacing and position of magnetic islands when we use a partial-response maximum-likelihood detection scheme and low-density parity check code. We compare bit error rate performance when the islands are arranged in a regular array and when the islands are arranged in a staggered array. Simulation results show that substantially increased bit error rate performance can be achieved through the use of trigonal half-delayed layout island patterns that reduce the ITI.