Piya Kovintavewat | Nakhon Pathom Rajabhat University (original) (raw)

Papers by Piya Kovintavewat

ECTI Transactions on Electrical Engineering, Electronics, and Communications

Thermal asperities (TAs) cause a crucial problem in magnetic recording systems because they can d... more Thermal asperities (TAs) cause a crucial problem in magnetic recording systems because they can distort the readback signal to the extent of causing possible sector read failure. This problem becomes even 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 ¯lter to mitigate the TA effect. 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 at the expense of increased complexity, and is also robust to large peak TA amplitudes.

2022 International Symposium on Intelligent Signal Processing and Communication Systems (ISPACS)

2019 34th International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC)

To achieve an areal density (AD) of hard disk drives (HDDs) up to 4 Tb/in2, a bit-patterned magne... more To achieve an areal density (AD) of hard disk drives (HDDs) up to 4 Tb/in2, a bit-patterned magnetic recording (BPMR) system is one of the interesting candidates for the emerging magnetic recording technologies. Generally, intertrack interference (ITI) is a major problem for the BPMR system and it can deteriorate the overall system performance. Thus, this paper proposes the soft ITI mitigation method for coded two-head two-track (2H2T) BPMR systems. Specifically, the proposed method subtracts the estimated ITI signal (generated based on the soft decision obtained from a decoder for each turbo iteration) from the original readback signal during the turbo decoding process. Simulation results show that the proposed method outperforms the conventional method employing the hard decision to estimate the ITI signal at 2 and 2.5 Tb/in2.

AIP Advances

A reduction in track width of ultra-high density magnetic recording such as bit-patterned media r... more A reduction in track width of ultra-high density magnetic recording such as bit-patterned media recording (BPMR) results in an increase in areal density. However, the unfortunate appearance of extreme inter-symbol interference (ISI) and inter-track interference (ITI) can severely deteriorate the system performance. To deal with these problems, we propose to use a single-reader/two-track reading (SRTR) technique, where a single reader was employed to read two parallel-track at once and the bit islands were arranged in a staggered manner. Then, a received readback signal was sampled at an over-sampling rate, where an obtained data sequence can be operated using only a one-dimensional equalization and detection scheme. Moreover, we also present the simple constrained coding schemes consisting of the rate-3/5 and -4/6 constrained codes, where both are properly designed for an SRTR BPMR system by avoiding all data patterns that are more susceptible to ISI and ITI effects. Simulation resu...

2021 36th International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC)

In the present work, an energy-efficient hybrid MAC (EEHMAC) protocol is proposed. The proposed p... more In the present work, an energy-efficient hybrid MAC (EEHMAC) protocol is proposed. The proposed protocol utilizes the slots in an energy-efficient manner for time-constraint data traffic applications. EEHMAC can capably handle periodic data generation, time-constraint data traffic, and event-driven data traffic generation in an energy-efficient manner. The general superiority of our proposed EEHMAC protocol is shown by both analytical and simulation performance.

Bit-patterned media recording (BPMR) is a promising technology for ultra-high density media, howe... more 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.

2017 IEEE 13th International Symposium on Autonomous Decentralized System (ISADS), 2017

Autonomous decentralized system is need of the dynamically varying society. Various autonomous de... more Autonomous decentralized system is need of the dynamically varying society. Various autonomous decentralized systems architecture proposed and deployed, use of IEEE 802.11n/ac (Wi-Fi) and IEEE 802.16e (Wi-max) standards for surveillance purposes in different geographical region. These standards use LDPC codes as a channel code having better error correcting performance. This article deals with a construction of less computational complexity method for constructing exponent matrix (3, K) having girth 8, 10, and 12 of quasi-cyclic low-density parity-check (QC-LDPC) codes. In this method, we first generate a base matrix and then the same matrix is further used for expanding till desired size of the exponent matrix. The construction of code deals with the generation of base matrix by a simple algorithm for girth 8, 10, and 12. Our method is flexible for any block-column length K. Finally, a new method is given with less computational complexity with optimized CPM size.

IEEE Access, 2020

Generally, an intertrack interference (ITI) is a critical problem in bit-patterned magnetic recor... more Generally, an intertrack interference (ITI) is a critical problem in bit-patterned magnetic recording (BPMR) systems that can attain an areal density (AD) up to 4 Tb/in 2. Unavoidably, at high ADs, a very narrow track width must be employed, leading to severe ITI and unacceptable system performance. To tackle the ITI; therefore, this article introduces a novel ITI suppression technique for coded dual-track dual-head (DTDH) BPMR systems. At the first turbo iteration, the weighted readback signal of the adjacent track served as an estimated ITI signal is utilized for subtracting from the target readback signal to subside the ITI effect, before passing the refined readback signal to a turbo equalizer. Nonetheless, for the second turbo iteration onwards, the estimated ITI signal generated by the soft information obtained from a decoder at each turbo iteration will be then employed to subtract from the target readback signal during the turbo decoding process. Computer simulation results demonstrate that the proposed system can provide better performance than the DTDH system using a hard ITI suppression technique as well as the conventional system using one read head to decode one data track for all ADs, because the proposed technique can estimate the ITI signal well. Furthermore, when considering the recording system under the effects of media noise and track mis-registration, we also found that the proposed system is more robust than other systems. INDEX TERMS Bit-patterned magnetic recording, ITI suppression, soft information, turbo decoding.

Recently, low-density parity-check (LDPC) codes are widely used in wireless communication as a ch... more Recently, low-density parity-check (LDPC) codes are widely used in wireless communication as a channel code and recommended for future standards. However, higher orders Galois Fields (GFs) for LDPC codes have not been extensively studied. In this paper, we present extended GFs to analyze the performance of non-binary LDPC codes. The parity-check matrix H is analyzed for IEEE 802.11n standard with half rate and block-size of 648. Decoding is done by using Fast Fourier Transform (FFT) based belief propagation for fast decoding. Code performance is measured in terms of bit error rate (BER) at higher order of Galois Fields.

2019 34th International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC), 2019

Medical imaging technology plays an important role for the current healthcare diagnosis and appli... more Medical imaging technology plays an important role for the current healthcare diagnosis and application. Psoriasis is a common skin disease characterized by red plaques which are covered with silvery scales. Psoriasis Area and Severity Index (PASI) is currently the standard to assess the treatment efficacy by evaluating the area and other features. In this paper, we proposed an automatic region of interest segmentation algorithm that can objectively measure the PASI area score. The color space analysis is applied based on YCbCr and YIQ. K-mean clustering is used to separate the background from the skin region and segment the region of interest (ROI) from the normal skin. Ten skin image samples from the hospital experimental database have been analyzed in the experiments. The results presented that the proposed algorithm is effective to segment the psoriasis area and measure the region of interest with practical precision for psoriasis diagnosis.

AIP Advances, 2021

An achievement of an areal density (AD) up to 4 Tb/in2 in hard disk drives (HDDs) is expected und... more An achievement of an areal density (AD) up to 4 Tb/in2 in hard disk drives (HDDs) is expected under a bit-patterned magnetic recording (BPMR) system. One of major problems in HDDs is a skew angle (SA), which depends on a read/write head position on a disk platter. Practically, if precaution is not taken, the SA can easily deteriorate the overall system performance. To maintain an acceptable system performance; therefore, we present a simple SA detection and suppression method for BPMR systems. Here, one readback sequence is used to compute a specific target coefficient before employing it to estimate the SA amount. To mitigate the SA effect, a couple of suitable two-dimensional (2D) target and its compatible one-dimensional equalizer associated with the estimated SA is utilized in the data detection process. We also propose the flipped-cross-track symmetric 2D target to reduce the complexity of the detector. Simulation results reveal that the utilization of our proposed SA method ca...

Digital Communications and Networks, 2020

Bit-Patterned Magnetic Recording (BPMR) is one of the emerging data storage technologies, which p... more Bit-Patterned Magnetic Recording (BPMR) is one of the emerging data storage technologies, which promises an Areal Density (AD) of about 4 Tb/in 2. However, a major problem practically encountered in a BPMR system is Inter-Track Interference (ITI) that can deteriorate the overall system performance, especially at high ADs. This paper proposes an iterative ITI cancellation method for an m-head m-track BPMR system, which uses m heads to read m adjacent tracks and decodes them simultaneously. To cancel the ITI, we subtract the weighted readback signals of adjacent tracks, acting as the ITI signals, from the readback signal of the target track, before passing the refined readback signal to a turbo decoder. Then, the decoded data will be employed to reconstruct the ITI signal for the next turbo iteration. Experimental results indicate that the proposed system performs better than the conventional system that uses one head to read one data track. Furthermore, we also find out that the proposed system is more robust to media noise and track misregistration than the conventional system.

Digital Communications and Networks, 2019

A reduction in the track width of magnetic recording systems results in a welcome increase in Are... more 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 À5 and is also superior to the conventional recording system.

IEICE Transactions on Electronics, 2015

Advanced Materials Research, 2014

High-density bit-patterned media recording (BPMR) can be obtained by reducing the spacing between... more High-density bit-patterned media recording (BPMR) can be obtained by reducing the spacing between data bitislands in both the along-and across-track directions, thus leading to severe intersymbol interference (ISI) and intertrack interference (ITI) because of small bit and track pitches, respectively. Here, we propose to use the graph-based detector, instead of the trellis-based detector, in iterative decoding to combat the ISI and the ITI for a multi-head multi-track BPMR system. Specifically, the readback signal is sent to the graph-based detector before iteratively exchanging the soft information with a decoder. Experimental results indicate that at low to moderate complexity, the proposed scheme outperforms the existing schemes, especially at high recording density.

Procedia Engineering, 2012

A novel method for reducing the effect of a thermal asperity (TA) in perpendicular recording chan... more A novel method for reducing the effect of a thermal asperity (TA) in perpendicular recording channels is proposed, which consists of two channels running in parallel, one for the H(D) target and the other for the G(D)H(D) target equipped with a bandpass filter G(D) = 1-D 2. The Viterbi detector (VD) in the H(D) channel has a lower bit-error rate (BER) in the absence of a TA, whereas that in the G(D)H(D) channel has a lower BER in the presence of a TA. Therefore, the overall decoded bit stream is selected from these two VDs, depending on whether a TA is detected. Because the noise after G(D) filtering is correlated, we also propose a noise predictor filter of the form P(D) =-0.5D 2 to whiten this correlated noise in a per-survivor manner. Experimental results indicate that the proposed TA suppression method outperforms the existing methods for all peak TA amplitudes.

Code Division Multiple Access (CDMA) is one of the most flexible multiple access methods suitable... more Code Division Multiple Access (CDMA) is one of the most flexible multiple access methods suitable for supporting many new services such as speech, video, multimedia applications and so on, which are becoming increasingly important for mobile communications. Besides supporting multiple data rates, future systems will also need to enhance the performance and capacity demands. Direct Sequence Code Division Multiple Access (DS-CDMA) is the most commonly proposed CDMA system for the third generation of wireless mobile systems. A DS-CDMA system using conventional receiver techniques is limited in capacity because the multiple access interference (MAI) and the near-far effect will substantially degrade its performance. These problems, however, can be mitigated by employing multiuser detection techniques, including optimum detectors and suboptimum ones. Although optimum detectors offer high performance and high capacity, it is very difficult to implement them because of excessive computatio...

IEEE Transactions on Magnetics, 2002

In this paper, we propose new generalized partial-response (GPR) targets for perpendicular record... more In this paper, we propose new generalized partial-response (GPR) targets for perpendicular recording whose transition response is modeled as an error function and compare their performance with the partial-response (PR) targets both in the presence and absence of jitter noise. Regardless of any jitter noise amount, results indicate that the GPR targets outperform the PR targets, especially at high linear-recording densities. We also determine that the dominant error sequence for this perpendicular recording is the same for all targets when jitter noise is low. Therefore, the system performance can be further improved by designing and using codes to avoid this dominant error sequence. Another significant point is the fact that the dominant error sequence of perpendicular recording is different from longitudinal recording, thus requiring design of different types of codes than the ones used for longitudinal recording. Finally, we show that the effective signal-tonoise ratio can be equivalently used instead of the bit-error-rate as a measure to compare the performance of different targets.

IEEE Transactions on Magnetics, 2000