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3-D magnetic recording using microwave-assisted magnetic recording (MAMR) and a spin-torque oscillator (STO) for reading has been proposed as a candidate for prospective recording technologies. In 3-D magnetic recording using STO as a reading, the temporal magnetization dynamics of the STO has the fluctuations for frequency and amplitude which depend on the recorded pattern. In our previous work, we have constructed the STO signal model considering both amplitude and frequency fluctuations to develop a combined signal processing using the amplitude and frequency fluctuation detections. We have applied the STO signal model to the low-density parity-check (LDPC) coding and iterative decoding system with the individual detectors for amplitude modulation (AM) and frequency modulation (FM). Furthermore, we have reported that the dual STO reading system with only AM detection provides the improvement of the bit error rate (BER) performance. In this study, we propose the dual STO reading system with AM–FM combined detection in the hope that the finite impulse response (FIR) filter output distribution will be easier to detect with the decoder. We evaluate the BER performances of the proposed system for carrier-to-noise ratio (CNRS) of the system noise under an areal recording density of 1 Tbits/in2 specification with bit-pattern medium stricture by computer simulation. The results show that the FIR filter output distribution for our proposed dual STO reading system at an FM detector output has become sharper, and the proposed system achieves the “No errors” with CNRS less by about 3.5 dB than the single STO reading system. [ABSTRACT FROM AUTHOR]

A 3-D magnetic recording using microwave-assisted magnetic recording (MAMR) and a spin-torque oscillator (STO) as a reading sensor has been proposed as a candidate for the prospective recording technologies. In the STO reading system, the temporal magnetization dynamics of the STO vary not only in amplitude but also in frequency, depending on the recorded pattern. Therefore, we have constructed the STO signal model which considers both amplitude and frequency fluctuations to develop a combined signal processing using the detection of amplitude and frequency fluctuations. Furthermore, we have applied the STO signal model to the low-density parity-check (LDPC) coding and iterative decoding system with the detectors for amplitude modulation (AM) and frequency modulation (FM) and have proposed the AM–FM combined detection. Then, we have evaluated the bit error rate (BER) performances by computer simulation. The results show that the system with AM–FM combined detection improves the performance of the LDPC coding and iterative decoding system, which achieves “no errors” at the carrier-to-noise ratio for system noise (CNR $_{S}) = 15.9$ dB, whereas the AM and FM detections require CNR $_{S} = 21.2$ and 17.2 dB. [ABSTRACT FROM AUTHOR]

We have previously focused on a log-likelihood ratio (LLR) computed as the decoding reliability by $a$ posteriori probability (APP) decoder on the low-density parity-check (LDPC) coding and iterative decoding system for the shingled magnetic recording (SMR). Then, we clarified that the LLR modulator applying a neural network realizes an effective iterative decoding. In this article, we propose a new neural network LLR modulator considering magnetic transition information obtained from LLRs to reduce the influence of intersymbol interferences (ISIs). [ABSTRACT FROM AUTHOR]

Our previous work focused on a log-likelihood ratio (LLR) computed as the decoding reliability by a posteriori probability (APP) decoder in a two-dimensional magnetic recording (TDMR) system using shingled magnetic recording (SMR). In this article, we propose a neural network LLR modulator to reduce the influence of pattern dependent medium noise and to perform efficiently iterative decoding using a low-density parity-check (LDPC) code. In this study, we clarify that the performance improvement of iterative decoding can be obtained by considering LLRs of the adjacent track bits affecting the decoding bit as the input of the neural network. Furthermore, we clarify that the application of a hybrid genetic algorithm (HGA) selects LLRs by using the adjacent track LLRs affecting the decoding bit and realizes more effective iterative decoding. [ABSTRACT FROM AUTHOR]

This paper focuses on the shingled magnetic recording (SMR) as the recording system for further high-density hard disk drives. Previously, we applied a log-likelihood ratio (LLR) modulator to the low-density parity check coding and iterative decoding system in SMR to improve the decoding performance. In this paper, we propose a new LLR modulator using neural network. Furthermore, we clarify that the proposed LLR modulator using neural network realizes effective iterative decoding in a read/write channel with pattern-dependent medium noise. [ABSTRACT FROM AUTHOR]

The 3-D magnetic recording using the microwave-assisted magnetic recording and a spin-torque oscillator as a reading sensor has been proposed as a candidate of the prospective recording technologies. In our previous research, we have constructed the read/write channel of the envelope model to evaluate a variety of signal processing for the 3-D magnetic recording. In this paper, we apply the low-density parity-check coding and iterative decoding system including turbo equalization to the 3-D magnetic recording channel model with dot position fluctuation and evaluate the bit error rate performance by the computer simulation. The results clarify that the tolerance of dot position fluctuation which “no errors” is able to be achieved. [ABSTRACT FROM AUTHOR]

In recent years, shingled magnetic recording (SMR) has attracted attention as a new recording system of the hard disk drives. Although SMR can realize narrow track by overwriting data track like tile roofing, it has remarkable performance deterioration due to the influence of inter-track interference. Therefore, the performance improvement of the low-density parity-check (LDPC) coding and iterative decoding system using the sum-product decoding is required. In this paper, we propose the LDPC encoding and iterative decoding system with the log-likelihood ratio modulator and show the error floor is eliminated and improvement of signal-to-noise ratio to achieve the error free is obtained in the SMR under an areal recording density of 4 Tbits/in2 specification for the channel bit sequence coded by run-length limited and LDPC encoders by computer simulation. Therefore, the channel bit is composed bit about five magnetic grains. [ABSTRACT FROM AUTHOR]

The 3-D magnetic recording using microwave-assisted magnetic recording has been proposed as one of the prospective recording technologies which uses a spin-torque oscillator (STO) as a reading sensor as well as a write-assisting device. In the reading process using an STO, the reproducing waveform is given as temporal dynamics of magnetization. We simulate the envelope of the waveform from recorded dots with the staggered magnetization configuration, which are calculated by using a micromagnetic simulation. We propose an envelope demodulation using two temporal magnetization dynamics from dual STO, and evaluate the bit error rate (BER) performance for partial response maximum likelihood system by the computer simulation. The result shows that our proposed system provides the signal-to-noise ratio improvement of 2.7 dB at the BER of 10−4. [ABSTRACT FROM AUTHOR]

The shingled magnetic recording (SMR) system is influenced by not only jitter-like medium noise from adjacent bits in the down-track direction but also intertrack interference (ITI) from the adjacent tracks. In this paper, we investigate the relationship between the recording pattern and the decoding reliability by classifying the log-likelihood ratio at the a posteriori probability decoder output according to the recording patterns under an SMR R–W channel specification of 4 Tb/in2 by computer simulation. The result shows that the decoding reliability for the recording pattern “010” heavily affected by transition jitter is the lowest and little improved even if the influence of ITI is mitigated by a 2-D finite-impulse response filter. [ABSTRACT FROM AUTHOR]

Two-dimensional magnetic recording (TDMR), which combines shingled magnetic recording (SMR) with 2-D signal processing attracts attention from the hard disk drive industry. SMR is a magnetic recording system in order to increase the track density by writing tracks without the guard band. Therefore, the influences of writing and reading intertrack interferences (ITIs) deteriorate the quality of reproducing waveforms. Additionally, degradation of track due to overwriting and crosstalk from the adjacent tracks due to the width of reader sensitivity. The equalization using 2-D finite impulse response filter for the waveforms from three adjacent tracks is proposed as a method to reduce the influence of reading ITIs. In this paper, we evaluate the bit aspect ratio (BAR) in TDMR read/write channel under a specification of 4 Tb/in2 using bit error rate of the low-density parity-check (LDPC) coding and iterative decoding system obtained by computer simulation. The results show that the suitable BAR in array head reading is 2.0. [ABSTRACT FROM AUTHOR]

The 2-D magnetic recording (TDMR) by shingled magnetic recording (SMR) draws attention as a technology to increase the recording densities in a hard disk drive. The magnetization pattern is curved by the write field at the corner of the writer in SMR, and the information to read/write (R/W) channel performance is feared. Therefore, it is possible that the bit error rate performance is improved by fitting the reader sensitivity to the bit shape. In this paper, we evaluate the effect of reader sensitivity rotation in the TDMR R/W channel with head skew under a specification of 4 Tb/in2 by computer simulation, applying the low-density parity-check coding and the iterative decoding system with the 2-D finite impulse response filter. The results show that the rotated reader sensitivity fits the recorded bit magnetization shape, and the error-free skew range increases to -3^\circ \sim 6^\circ . Therefore, the reader sensitivity rotation is considered to be an effective way to improve the skew margin in the TDMR system. [ABSTRACT FROM PUBLISHER]

2-D magnetic recording (TDMR) exploits 2-D signal processing using the waveforms reproduced by array head from the intended and adjacent tracks to mitigate the effects of intertrack interference. However, an array head has the issue on the degradation of bit error rate (BER) performance due to head skew. In this paper, we evaluate the BER performance of TDMR R/W channel with head skew under a specification of 4 Tbit/in ^2 employing low-density parity check coding and iterative decoding system using a 2-D finite-impulse response filter by computer simulation. The results show that our system can achieve the reliable BER performances by appropriately setting the reader scanning positions at the head skew angle between 0° and 3°. [ABSTRACT FROM AUTHOR]