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A simple 2D modulation code in single-reader two-track reading BPMR systems
(2021-02-01)
Busyatras, Wiparat
;
Warisarn, Chanon
;
Koonkarnkhai, Santi
;
Kovintavewat, Piya
A reduction in the track width of magnetic recording systems results in a welcome increase in Areal Density (AD), but can severely deteriorate system performance in the unfortunate appearance of extreme Inter-Track Interference (ITI). The effect of severe ITI may be mitigated by using coding schemes. In this paper, therefore, we present a rate-5/6 2-Dimensional (2D) modulation code based on a proposed Single-Reader/Two-track Reading (SRTR) technique to cope with this serious problem in staggered Bit-Patterned Magnetic Recording (BPMR) systems. We then evaluate the Bit-Error Rate (BER) performance of the proposed system in the presence of media noises, e.g., position and size fluctuations. Our simulation results indicate that, at the same User Density (UD), the proposed system performs better than an uncoded system by about 1.0 dB at the BER of 10<sup>−5</sup> and is also superior to the conventional recording system.
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Track Mis-registration Correction Method in Two-Head Two-Track BPMR Systems
(2020-06-01)
Kankhunthod, Kittipon
;
Busyatras, Wiparat
;
Warisarn, Chanon
One of the main problems in a Bit-patterned media recording (BPMR) system at an ultra-high areal density is the effect of track mis-registration (TMR), which can severely degrade the system's performance. Practically, the TMR effect is controlled by the servo system. That requires some areas of record to store redundancy bits. In this paper, we propose a simple linear energy ratio finding (SLERF) technique using only the two readback signals for estimating the TMR level in two- head/two-track (2H2T) BPMR systems, which unrequired the extravagant redundancy bits. Next, we utilize the appropriate equalizers, which are accordingly designed with the estimated TMR levels, to correct the TMR effect. Moreover, we also propose a soft-information adjustment (SIA) technique that operates after obtaining the soft-information from the two-dimensional soft-output Viterbi algorithm (2D-SOVA) detectors in order to improve the bit error rate (BER) performance of recording systems. Computer simulation reveals that the SLERF and SIA techniques can impressively estimate the TMR levels and further effectively correct the TMR effect as well, respectively. Therefore, it leads to obtaining better BER performance in particular where the system is impaired by position jitter noise.
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BER performance improvement using soft-information flipping method in BPMR systems
(2019-07-01)
Busyatras, Wiparat
;
Warisarn, Chanon
Inter-track interference (ITI) cancelation is one of the considerable challenges for high areal density (AD) magnetic recording such as bit-patterned magnetic recording (BPMR) technology. In literature, the two-dimensional (2D) modulation codes have been proposed to cancel the ITI effect which can efficiently improve the overall system performance, e.g., a rate5/6 2D modulation code. Although the rate-5/6 modulation code ensures that the readback signal of the center track will not be corrupted by severe ITI; however, both the upper and lower tracks can still be interfered by their sidetracks, which may lead to some errors in decoding process. To improve this shortcoming, we propose a bit-flipping technique that performs together with the rate-5/6 2D modulation code. Here, the relationship between the data encoding constraint and the soft-information obtained from the soft output Viterbi algorithm (SOVA) detector are utilized to be a criterion for flipping the ambiguous data bits. Simulation results indicate that the proposed system is better than the conventional coded system with and without media noise and track mis-registration (TMR) effects.
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A simple 2/3 modulation code and bit-flipping technique in bit-patterned media recording systems
(2018-07-02)
Busyatras, Wiparat
;
Poompuang, Pitaya
;
Myint, Lin M.M.
;
Warisam, Chanon
Two-dimensional (2-D) modulation code is considered as one of the key schemes to improve the areal density capability for next generation magnetic recording e.g., bit-patterned media recording (BPMR) technology, due to its advantages such as severe inter-track interference (ITI) suppression and user densities escalation. In this work, a rate-2/3 2-D modulation with a three-reader three-track (3R3T) system is studied where the positions of reader are accordingly optimized with the encoded criteria to obtain the highest bit-error rate (BER) performance. Moreover, we also propose a bit-flipping technique which is one way to extremely improve the overall system performance. Here, the soft-information that are obtained from soft-output Viterbit algorithm (SOVA) detectors will be improved according with the encoded criteria before sending to the proposed decoder. Simulation results demonstrate that significant performance gain can be achieved using these two proposed approaches.
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Mitigation of TMR Using Energy Ratio and Bit-Flipping Techniques in Multitrack Multihead BPMR Systems
(2017-11-01)
Warisarn, Chanon
;
Busyatras, Wiparat
;
Myint, Lin M.M.
;
Koonkarnkhai, Santi
;
Kovintavewat, Piya
Track misregistration (TMR) in ultra-high density bit-patterned media recording (BPMR) is one of the crucial problems, because it can severely degrade the overall system performance. In practical, TMR can be detected and adjusted by a servo control loop system. However, this paper proposes to utilize multiple readback signals obtained from the optimized positioning of the two side read head closer to the main read head to improve the TMR prediction process in a multitrack multi-head BPMR system with position jitter noise. In addition, we also propose the soft-information exchange and the bit-flipping techniques for the multitrack data detection, so as to improve the bit-error rate (BER) performance of all three data tracks simultaneously. Simulation results indicate that the proposed system is superior to the conventional system, especially, when the amount of TMR and position jitter is high. Furthermore, we also found that the upper and lower read heads, which are moved closer to the center track by 25% of a track pitch, will provide the best BER performance with and without position jitter noise.
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Single-track equalization method with TMR correction system based on cross correlation functions for a patterned media recording system
(2017-01-01)
Myint, Lin Min Min
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Warisarn, Chanon
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Busyatras, Wiparat
;
Kovintavewat, Piya
Bit-patterned media recording (BPMR) is a promising technology for ultra-high density media, however, there are some challenges that need to be addressed including two-dimensional (2D) interference, and track mis-registration (TMR). The system can experience TMR due to misalignment of the head and the track center. Conventionally, TMR is tackled using a servo system in which the head position offset is estimated by processing the overhead servo sequences before reading the data sequences. However, TMR impairment can also occur when the head is reading data sequences that are beyond the servo mechanism. To address this problem, we proposed TMR detection and correction techniques based on our previous work involving a single-track equalization method for a BPMR system using cross-correlation functions between the single readback signal and each of the training sequences from three adjacent tracks. In this proposed technique, the presence and level of TMR is detected and estimated based on the changes in the value of mean square error (MSE) between the equalized and feedback signals from the detectors after passing through a one-dimensional (1D) target for each sequence. Then, the estimated TMR levels are used in selecting the appropriate equalizer and the generalized partial response (GPR) target pair to tackle the TMR from the readback signal. The simulation results show improvement in the data recovery of a BPMR system using the proposed method when the system is experiencing 2D interference and TMR impairment.
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An iterative TMR mitigation method based on readback signal for bit-patterned media recording
(2015-11-01)
Busyatras, Wiparat
;
Warisarn, Chanon
;
Myint, Lin M.M.
;
Supnithi, Pornchai
;
Kovintavewat, Piya
Off-track condition or track misregistration (TMR) is one of the most significant problems in the extremely high-density bit-patterned media recording (BPMR) system, since a track pitch becomes narrower. Typically, the TMR can be detected and handled by a servo system; however, it requires some special data to be inserted in the tracks so as to estimate the amount of head offset. Nonetheless, this paper proposes an iterative TMR mitigation method for BPMR systems based on the readback signals. First, we design several pairs of the 2-D asymmetric target and its corresponding 2-D equalizer that match the BPMR channel for each TMR level. Then, we exploit the three adjacent data tracks obtained from the low-density parity-check decoders to estimate the TMR level. Last, a pair of the 2-D asymmetric target and its corresponding 2-D equalizer that is best fit to the estimated TMR level will be used to alleviate the TMR effect in the readback signal for the next global iteration. Simulation results indicate that the proposed system can effectively estimate the TMR level and performs better than the conventional system without a TMR mitigation method, especially when the TMR level is high and/or the position jitter is large.
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A TMR mitigation method based on readback signal in bit-patterned media recording
(2015-08-01)
Busyatras, Wiparat
;
Warisarn, Chanon
;
Myint, Lin M.M.
;
Kovintavewat, Piya
Track mis-registration (TMR) is one of the major problems in high-density magnetic recording systems such as bit-patterned media recording (BPMR). In general, TMR results from the misalignment between the center of the read head and that of the main track, which can deteriorate the system performance. Although TMR can be handled by a servo system, this paper proposes a novel method to alleviate the TMR effect, based on the readback signal. Specifically, the readback signal is directly used to estimate a TMR level and is then further processed by the suitable target and equalizer designed for such a TMR level. Simulation results indicate that the proposed method can sufficiently estimate the TMR level and then helps improve the system performance if compared to the conventional receiver that does not employ a TMR mitigation method, especially when an areal density is high and/or a TMR level is large.

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