Phakphisut, Watid
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Phakphisut, Watid
Alternative Name
Phakphisut, W.
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watid.ph@kmitl.ac.th
29 results
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Item type:Publication, Reduced-complexity window decoding of spatially coupled LDPC codes for magnetic recording systems(2018-10-24); In channel coding theory, the performance of error correcting codes (ECCs) approaching the Shannon limit can be achieved through increasing code lengths. Unfortunately, the complexity of ECCs will be increased as the code length increases. Nowadays, the magnetic recording (MR) system takes advantage of powerful ECCs by using 4 Kbytes sector. Among the advanced ECCs, the spatially coupled LDPC (SC-LDPC) codes (also known as a LDPC convolutional code) [1] are shown to have the decoding latency and complexity lower than those of the underlying LDPC block codes (LDPC-BC). Moreover, the SC-LDPC codes with threshold decoding outperform the LDPC-BC codes [2]. Hence, the SC-LDPC codes are the strong candidate for the future MR systems, when the sector size is increased beyond 4 Kbytes. An SC-LDPC decoder can use sliding window decoding [3] whereby the received signals are decoded by sliding window along the bit sequence. The window decoder is called "uniform window decoding (U-WD)", when all variable nodes (VNs) within a window are updated. In order to reduce the complexity of window decoding, some researchers proposed the non-uniform window decoding (N-WD) [4], which do not update the VNs with no improvement in the bit error rate (BER). This approach provides about 35-50% reduction in complexity compared to U-WD. In this work, we consider the application of SC-LDPC codes in MR systems, whereby SC-LDPC decoder cooperates with BCJR detector to encounter inter-symbol interference (ISI). We propose the dynamic shifting of window decoding (DS-WD) to reduce the complexity of SC-LDPC codes. Herein, the number of shifted bits is defined according to their soft BERs which are estimated at each decoding position. In addition, we modify the N-WD [4] to reinforce our proposed algorithm called "dynamic-shifting non-uniform window decoding (DS-N-WD)." The DS-WD and DS-N-WD achieve the complexity reduction of 7% and 25% without any loss in performance compared to the N-WD algorithms. i - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Search algorithm of write voltage optimization in NAND flash memory(2017-10-19); In NAND flash memory, the major problem is voltage immigration which is the result of program and erase (PE) cycling number and data retention time. Although previous works study the write voltage optimization for NAND flash memory, the write voltage optimization of multilevel coding (MLC) and bitinterleaved coded modulation (BICM) structure have not been focused, therefore, in this work, we propose the search algorithm of write voltage optimization for MLC and BICM structure. The search algorithm can reduce the number of possible write voltages and provides the optimal write voltage for each PE cycling number. The bit-error rate (BER) performance of optimized write voltage is lower than the fixed write voltage in BICM structure. Moreover, the proposed optimization technique provides the most significant bit (MSB) and least significant bit (LSB) of MLC structure with identical BER performances. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Performance of the hybrid MLPNN based VE (h MLPNN-VE) for the nonlinear PMR channels(2018-05-01); This paper proposes a hybrid of multilayer perceptron neural network (MLPNN) and Volterra equalizer (VE) denoted hMLPNN-VE in nonlinear perpendicular magnetic recording (PMR) channels. The proposed detector integrates the nonlinear product terms of the delayed readback signals generated from the VE into the nonlinear processing of the MLPNN. The detection performance comparison is evaluated in terms of the tradeoff between the bit error rate (BER), complexity and reliability for a nonlinear Volterra channel at high normalized recording density. The proposed hMLPNN-VE outperforms MLPNN based equalizer (MLPNNE), VE and the conventional partial response maximum likelihood (PRML) detector. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, EXIT chart analysis of nonbinary protograph LDPC codes for partial response channels(2014-11-01); ; Low-density parity-check (LDPC) codes over finite fields GF(q) provide an error correction in the noisy partial response (PR) channels. The extrinsic information transfer (EXIT) chart can be used to predict the threshold decoding of protograph LDPC codes, however, previous works only consider the binary protograph LDPC codes in the PR channels. In this paper, we propose to perform the EXIT chart analysis on the nonbinary protograph LDPC codes for the PR channels. Unlike prior works, the actual extrinsic information of the channel detector is measured, then the extrinsic information to the variable nodes is generated with the measured statistics. Moreover, since the mutual information of the variable nodes depends on GF(q), we use the Monte Carlo method to approximate the mutual information. The analysis on the regular (2,4) code, regular (3,6) code, RA code, and AR3A code on the PR channels reveal that, for the PR1 channel, the RA code outperforms the others for q = 2, 4, and 8, but the regular (2,4) code is the best for q = 16 and 32. For the PR2 channel, the RA code is the best code for q = 2 and 4, but the regular (2,4) code is the best code for q > 4. The simulation of the codes for q = 4 and 16 are then used to confirm the theoretical results. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Decoding algorithm of LDPC codes for cascaded BSC-AWGN channels(2014-02-12); The written-in errors in bit patterned media (BPM) recording systems cause the erroneous bits during the writing process, leading to performance degradation. In previous works, the BPM read/write channel is modeled as a binary symmetric channel (BSC) with an additive white Gaussian noise (AWGN) channel or the cascaded BSC-AWGN channels. The initial channel information including the written-in errors probability has been proposed for low-density parity check (LDPC) decoder. However, the decoding algorithm remains the same as in the case of AWGN channels. In this work, we show that the crossover probability of BSC channels will affect the check node processing of LDPC codes. Therefore, we modify the check node computation that takes into account of the crossover probability of BSC channels. The simulation results show that the proposed LDPC decoder outperforms the ones with the conventional and modified likelihood function in terms of the bit error rate performance. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Preliminary results of EPB impact on GBAS performance(2019-06-01); In the low-latitude region, equatorial plasma bubbles (EPBs) frequently occur. Ionospheric irregularity due to EPBs can degrade the performance of ground-based augmentation system (GBAS) in aviation. This work focuses on the impact of multiple EPBs on GBAS performance. The multiple EPBs with varied separation distances are simulated to assess the performance of GBAS in Thailand. From the simulation, the results show that the 100 km separation distance causes a more hazardous error in vertical than 1200 km separation distance between the EPBs. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Neural networks equalizers for nonlinear magnetic recording channels(2017-11-03); Nonlinear distortion in perpendicular magnetic recording channels is known to degrade the overall system performance. In this work, we propose two nonlinear equalizers based on neural network (NN). One involves symbol decision of received signals using a multilayer perceptronNN equalizer (MLPNNE) only, and the other includes the NN equalizer to shape received signal to a partial-response target followed by a maximum likelihood (ML) sequence detection scheme using Viterbi algorithm (ML-MLPNNE). When applied to nonlinear channels generated by Volterra model (VM), it is shown that these two proposed equalizers give similar BER performances. At the BER of 10<sup>-4</sup>, they provide about 10-dB SNR gains over the conventional partial-response maximum likelihood (PRML) technique. The MLPNNE with the simple threshold needs simpler implementation than the ML-MLPNNE although noise correlation is a disadvantage. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Learning Polar Codes using Python Program with Graphical User Interface(2019-06-01) - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Quasi Cyclic-LDPC codes based on PEG algorithm with maximized girth property(2011-12-01); In this paper, we propose a method to construct parity-check matrices of Quasi Cyclic (QC) LDPC codes based on the progressive edge-growth (PEG) algorithm with maximized girth property. The proposed algorithm can eliminate short cycles and improve the decoding performance. Simulation results illustrate that the codes constructed with the proposed algorithm have superior performance to the previous PEG-QC codes over the additive white Gaussian noise (AWGN) channel. At the BER of 10 <sup>7</sup>, the coding gain of 0.005 dB. © 2011 IEEE. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Sliding-window processing of turbo equalization for partial response channels(2019-04-01); Spatially coupled low-density parity-check (SC-LDPC) codes are the attractive candidates for the application requiring a practical constraint on the latency and complexity. In previous works, the turbo equalization consisting the SC-LDPC window decoder and Bahl-Cocke-Jelinek-Raviv (BCJR) detector is used to tackle the inter-symbol interferences (ISIs) in the magnetic recording systems. However, the prior works consider only the SC-LDPC codes which replace the conventional LDPC block codes. In this work, we propose the modification of turbo equalization processing whereby both the SC-LDPC decoder and BCJR detector operate using the sliding window. The results show that the proposed turbo equalization schemes used in the partial response (PR) channel can provide better bit error rate (BER) performances than the conventional turbo equalization.