Santi Koonkarnkhai

Thermal asperity suppression based on least-squares fitting in perpendicular magnetic recording systems

Thermal asperity (TA) causes a major problem in data detection process. Without the TA detection and correction algorithm, the system performance (even with perfect synchronization) can be unacceptable, depending on how severe the TA effect is. This paper proposes a new method to suppress the TA effects in perpendicular magnetic recording channels. The TA detection is a threshold-based approach, while the TA correction is done by averaging the readback signal and applying a least-squares fitting technique to estimate the TA signal. Then, the corrected readback signal is obtained by subtracting the TA-affected readback signal by the reconstructed TA signal. Results indicate that the proposed method performs better than the existing one in terms of bit-error rate and is robust to changes in the peak TA amplitude.

Joint TA Suppression and Turbo Equalization for Coded Partial Response Channels

Thermal asperities (TAs) cause a crucial problem in magnetic recording systems because they can cause a burst of errors in data detection process. Without a TA detection and correction algorithm, the system performance can be unacceptable, depending on how severe the TA effect is. This paper proposes an iterative scheme to suppress the TA effect. This scheme jointly performs TA suppression and turbo equalization on the partial-response channels with error-correction codes. At each turbo iteration, an improved readback signal is obtained by subtracting the reconstructed TA signal from the TA-affected readback signal, where the reconstructed TA signal is computed based on a least-squares fitting technique with an aid of soft decisions from previous turbo iterations. Simulation results indicate that the proposed scheme outperforms the conventional receiver with separate TA suppression and turbo equalization, and is only marginally more complex than the conventional receiver.

The effect of bandpass filters for thermal asperity suppression in perpendicular recording systems

Thermal asperity (TA) causes a crucial problem in magnetic recording systems because it can distort the readback signal to the extent of causing possible sector read failure. This problem becomes more severe in perpendicular recording channels because these channels contain a d.c. component. This paper presents a novel TA suppression method by use of a bandpass filter. We also investigate the effect of different bandpass filters for TA suppression. Results indicate that the proposed TA suppression method using a bandpass filter polynomial G(D) = (1+D)2(1−D) yields lower bit-error rate than the existing ones, and is robust to large peak TA amplitudes.

A Concatenate Code for Error Correcting Code in Bit Pattern Media Recoding System

Bit Pattern Media Recording (BPMR) is the modern HDD recording technique which can overcome the constraint of conventional technique by offering tremendous areal density. However, narrow track of BPMR can cause noise generating from inter-track interference (ITI) and In. inter-symbol interference (ISI). One traditional technique used to improve BER of the system is the introducing of error control coding. In this paper, we investigate concatenate code applied to BPMR. We proposed inner code with low-density parity-check (LDPC) and Reed-Solomon (RS) codes as outer code. The obtained simulation results confirmed to us that the concatenated coding scheme yielded better performance compared with the single LDPC code deployment.

Two-dimensional cross-track asymmetric target design for high-density bit-patterned media recording

In bit-patterned media recording (BPMR) channels at ultra high areal densities, the inter-track interference (ITI) is extremely severe, which significantly degrades the system performance. The partial-response maximum-likelihood (PRML) technique that uses a one-dimensional (1D) partial response target might not be able to cope with this severe ITI, especially in the presence of media noise and track mis-registration (TMR). This paper proposes a two-dimensional (2D) cross-track asymmetric target, based on a minimum mean-squared error approach, for high-density BPMR channels. Result indicates that the proposed 2D target performs better than previously proposed 2D targets especially when media noise and TMR is severe.

A TMR mitigation method with 3-track data detection for multi-track multi-head BPMR system

An off-track situation from misalignment between the center of read head and that of target track is also known as track mis-registration (TMR), which is one of major problems in bit-patterned media recording (BPMR), especially at high areal density (AD) [1–4].

Mitigation of TMR Using Energy Ratio and Bit-Flipping Techniques in Multitrack Multihead BPMR Systems

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.

Head Instability Detection for Testing Process in Perpendicular Magnetic Recording System

During hard disk drive (HDD) testing process, the magneto-resistive read (MR) head is analyzed and checked if the head is defective or not. Baseline popping (BLP) is one of the crucial problems caused by head instability, whose effect can distort the readback signal to the extent of causing possible sector read failure. Without BLP detection algorithm, the defective read head might pass through HDD assembling process, thus producing an unreliable HDD. This situation must be prevented so as to retain customer satisfaction. This paper proposes a simple (but efficient) BLP detection algorithm for perpendicular magnetic recording systems. Results show that the proposed algorithm outperforms the conventional one in terms of both the percentage of detection and the percentage of false alarm, when operating at high signal-to-noise ratio.