Phakphisut, Watid
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Phakphisut, Watid
Alternative Name
Phakphisut, W.
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Email
watid.ph@kmitl.ac.th
47 results
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Item type:Publication, Reliability Ratio-Based Serial Algorithm of LDPC Decoder for Turbo Equalization Schemes(2022-02-01); Serial decoding algorithms of low-density parity-check (LDPC) code converge efficiently with low errors. Previously, a serial decoding algorithm, named a shuffled belief-propagation (SBP), was applied in turbo equalization of bit-patterned magnetic recording (BPMR) systems. With the SBP algorithm, an LDPC decoder converged twice as fast as one using conventional BP algorithms. We further improved the convergence speed of SBP by updating the messages in an adaptive order, which played a flexible role throughout decoding. We proposed two adaptive-serial algorithms for LDPC codes in turbo equalization. One updated the messages using the extrinsic loglikelihood ratio (LLR) and the result of the parity-check equation checking. The second contained an additional rule that tracked the LLR sign changes in each iteration. Both algorithms converged faster and with lower bit error rates (BERs) than the SBP and previous adaptive-serial algorithms in a BPMR system with media noise. - Some of the metrics are blocked by yourconsent settings
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, Construction of punctured polar codes based on genetic algorithm(2021-05-19); In this work, we propose a new construction of punctured polar codes, which provides a good error-correcting performance at arbitrary code lengths and code rates. We exploit the density evolution to evaluate the error probability of punctured polar codes. Then, the puncturing pattern and frozen bit positions are selected by genetic algorithm to construct a punctured polar code with low error probability. The results show that the proposed technique provides superior block error rate performance than the quasi-uniform puncturing technique at a high code rate. At a low code rate, the proposed technique can show the better performance than the shortening technique. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Improvement of Kalman Filter for GNSS/IMU Data Fusion with Measurement Bias Compensation(2020-07-01); ; The ASEAN IVO project currently supports the research related to GNSS and ionospheric data products for disaster prevention and aviation in low-latitude regions. In vehicle navigation, Real Time Kinematic (RTK) positioning distorted from the environment often contaminates the measurement vectors (such as position or speed of a rover). In this situation, the conventional Kalman filter with a linear motion model could not reduce positioning errors sufficiently due to existing bias. Hence, the measurement bias compensation method based on the mean of residual vectors is proposed. We modify the conventional Kalman filter by including this compensation in the estimation step. We test the algorithm in both of the simulations and actual experiments. From the results, the proposed method outperforms the baseline method in terms of positioning error by 60% and 12% for the simulation test and the field test respectively. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Performances of GAGAN Satellite-Based Augmentation System in Thailand Region(2020-07-01); - 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, Jamming Detection and Distance Calculation of L1 and E1 Frequencies(2020-07-01); GNSS jammers in the form of small portable devices are able to transmit the interference signals to GNSS receivers with the goal of misleading or disrupt the positioning. The interference or jamming can be detected from the carrier-tonoise (C/N0) values. In this work, we apply the Moving Variance (MV) to detect the occurrence of jamming from L1, E1 frequencies of GPS, Galileo satellites. In addition, we use Friis equation and random variable matching to calculate the distance between the GNSS receiver and jammer.