Supnithi, Pornchai

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Supnithi, Pornchai
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Supnithi, P.
Supnithi, Pomchai
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pornchai.su@kmitl.ac.th

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    A comparative study on reduced complexity 2-D detectors for bit patterned media
    (2011-12-01)
    Myint, Lin M.M.
    ;
    Supnithi, Pornchai
    In this paper, we compare the performance of the reduced complexity 2-D detection methods: Graph-based detection and Viterbi-based detection for the 2-D interference bit patterned media channels at various areal densities. In the graph-based detection, the complexity is reduced by ignoring the ITI from the cornered islands in designing the factor graph. In Viterbi-based detector, a trellis for the ISI only is considered. However, both methods improve the ITI mitigation with the help of multi-track processing and iterative processing. Between them, the graph-based detection needs higher computational complexity than the Viterbi-based detection. However, the graph-based detection method provides a significant performance gain over the Viterbi-based detect.on © 2011 IEEE.
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    An inter-track interference mitigation technique using partial ITI estimation in patterned media storage
    (2009-01-01)
    Myint, Lin M.M.
    ;
    Supnithi, Pornchai
    ;
    Tantaswadi, Prinya
    The readback signal of patterned media storage (PMS) is corrupted by a two-dimensional interference consisting of inter-symbol interference (ISI) and inter-track interference (ITI). In this paper, we apply the turbo equalization to mitigate the ITI effects. The codeword of the outer code is divided and then written on three separate tracks. After the first iteration, the bit estimates from the outer code provide partial ITI estimates for the branch metric computation in the soft-output viterbi algorithm (SOVA) detectors. Unlike previous works, the number of states of the channel trellis is due to the ISI only since the ITI information is not embedded in the parallel branches. When compared with the modified SOVA detectors with multi-parallel branches, simulation results show that a significant performance gain is achieved by our proposed method. © 2009 IEEE.
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    Performances of GAGAN Satellite-Based Augmentation System in Thailand Region
    (2020-07-01)
    Sophan, Somkit
    ;
    Phakphisut, Watid
    ;
    Myint, Lin M.M.
    ;
    Supnithi, Pornchai
    The ASEAN IVO project currently supports the research related to GNSS and ionospheric data products for disaster prevention and aviation in low-latitude regions. Satellite-Based Augmentation System (SBAS) is vital to air navigation in many regions around the world. In Thailand, the L1-frequency SBAS corrections can be received from the GPS Aided Geo Augmented Navigation (GAGAN) system which is intended for use over Indian airspace. In this work, we analyze the performances of the GAGAN system in Thailand on quiet and disturbed days in March 2019 by applying the entire corrections received at King Mongkut's Institute of Technology Ladkrabang station. The 95-percent horizontal and vertical accuracies on quiet days are 1.52 and 3.18 meters, respectively. In contrast, on disturbed days they are 1.97 and 3.41 meters, respectively.
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    Compatibility of Low-Cost GNSS Receivers for Total Electron Content (TEC) Analysis
    (2025-01-01)
    Rana, Bhim Bahadur
    ;
    Supnithi, Pornchai
    ;
    Myint, Lin M.M.
    ;
    Tongkasem, Napat
    ;
    Budtho, Jirapoom
    Although the geodetic GNSS receivers are highly precise, they are inaccessible to every user, especially in remote areas. Therefore, this work aimed to find the reasons that bolster the low-cost GNSS receivers to be used with high resolution over a wide area, instead of geodetic in space weather studies. A comparative analysis was conducted between a low-cost Ublox ZED-F9P GNSS receiver and a geodetic Novatel Propak6 GNSS receiver, focusing on ionospheric parameters such as slant total electron content (STEC), vertical total electron content (VTEC), and the number of satellites tracked using the Global Positioning System (GPS). Additionally, VTEC values were compared with the GIM model. Both receivers exhibited a similar pattern of TEC, with the R2 value of 0.9734 and the root mean square error of 3.4583. The number of satellites tracked by both receivers during the observed periods was also found to be similar. Moreover, the VTEC results obtained from the low-cost GNSS receiver showed compatibility with the GIM model, demonstrating the reliability of the low-cost receiver in comparison to the geodetic GNSS receiver.
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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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    Precise total electron content map monitoring in low latitude region
    (2022-01-01)
    Tongkasem, Napat
    ;
    Myint, Lin M.M.
    ;
    Supnithi, Pornchai
    The need for accurate Global Navigation Satellite System (GNSS) positioning is necessary for GNSS applications such as Real-Time Kinematic (RTK), Precise Point Positioning RTK (PPP-RTK), etc. The ionosphere delay, especially in low latitude region, is a main cause of positioning error. The usage of electron maps in GNSS applications can help with the first ionosphere correction. The Global Ionosphere Map (GIM) is a large-scale service for the Total Electron Content (TEC) with a resolution of 2.5 for latitude and 5 for longitude which may not be proper to high resolution GNSS applications in the small or regional regions. Over the low latitude region, we apply the local TEC from 4 stations which has similar longitude to observe the differential TEC. Then, we generate the precise grid TEC maps from 18 GNSS stations with different resolution of grid for observe the appropriate values. The results are shown that the resolution of 1.5 for latitude and 3 for longitude has RMS 1.58 of TECu compare with the local TEC value, while GIM has RMS of 2.11 TECu.
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    Analysis of ionospheric and geomagnetic fields changes in Thailand during the May 2024 geomagnetic storm
    (2025-12-15)
    Myint, Lin M.M.
    ;
    Perwitasari, Septi
    ;
    Nishioka, Michi
    ;
    Saito, Susumu
    ;
    Kaewthongrach, Rungnapa
    The extreme geomagnetic storm of May 2024, the most severe in two decades of space weather history up to date, had widespread effects on the ionosphere, from the polar regions to the magnetic equator. This study examines the responses of the equatorial ionosphere and geomagnetic field over Thailand during this geomagnetic storm, utilizing data from GNSS receivers, magnetometers, and ionosondes near the magnetic equator and low-latitude regions of Thailand. We analyze the direct and indirect impacts of interplanetary magnetic field (IMF) and interplanetary electric field (IEF) variations, driven by solar storms, on local equatorial magnetic fields and ionospheric parameters. Our finding reveals that storm-driven electric fields, particularly prompt penetration electric fields (PPEF) and disturbance dynamo electric fields (DDEF), strongly influenced equatorial electric field (EEF), causing notable fluctuations in total electron content (TEC), critical frequency of F2 (foF2), and virtual height of F layer (h’F). The Pearson correlation analysis highlights the rapid coupling between interplanetary magnetic field (IMF) and local equatorial magnetic fields during geomagnetic storms. These observations enhance our understanding of geomagnetic storm impacts in equatorial regions, which is crucial for improving space weather forecasting and mitigation strategies, especially for GNSS-dependent systems and radio communications.
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    Serial belief propagation for the high-rate LDPC decoders and performances in the bit patterned media systems with media noise
    (2011-01-01)
    Phakphisut, Watid
    ;
    Supnithi, Pornchai
    ;
    Sopon, Thanomsak
    ;
    Myint, Lin M.M.
    In this work, we propose to use the serial belief propagation or serial scheduling in the 2-D bit patterned media (BPM) system with media noise. The serial scheduling methods are applied to the random LDPC codes and quasi-cyclic LDPC (QC-LDPC) codes of high code rates. Both are constructed from the progress-edge growth (PEG) algorithm. We compare the performance of the LDPC codes using the serial belief propagation and the conventional belief propagation (BP) decoding. The simulation results show that the serial scheduling provides a faster convergence speed and a better bit error rate performance than the conventional BP in an AWGN channel. The serial belief propagation is also shown to offer the performance gains over the BP decoding for the BPM system with various media noise levels. © 2011 IEEE.
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    Improvement of single point positioning accuracy by using GAGAN satellite-based augmentation system in Thailand Region
    (2021-05-19)
    Sophan, Somkit
    ;
    Phakphisut, Watid
    ;
    Myint, Lin M.M.
    ;
    Supnithi, Pornchai
    Although GAGAN satellite-based augmentation system (SBAS) provides ionospheric correction service to India and surrounding areas, the correction values do not cover the entire region of Thailand and even at provided grids, they may not be sufficiently accurate. Hence, this work, we propose a local ionospheric delay estimation method based on the geo-free ionospheric delay estimation. Then the estimated ionospheric delays are applied together with the fast and long-term corrections of GAGAN SBAS to improve the positioning errors. The results show that the estimated ionospheric delays can improve the user positioning errors in terms of horizontal and vertical errors up to 0.5 and 1 meter, respectively.
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    Performance improvement of the GAGAN satellite-based augmentation system based on local ionospheric delay estimation in Thailand
    (2022-10-01)
    Sophan, Somkit
    ;
    Myint, Lin M.M.
    ;
    Saito, Susumu
    ;
    Supnithi, Pornchai
    Satellite-Based Augmentation System (SBAS) is essential to support aircraft navigation. L1 SBAS operates on the L1 frequency (1575.42 MHz) and is currently still of interest since all GNSS satellites and receivers do not fully support additional frequencies such as L5 (1176.45 MHz). Although the Global Positioning System (GPS) aided Geo Augmented Navigation (GAGAN) SBAS is available, the performances are degraded due to the discrepancies of the ionospheric correction over Thailand and surrounding areas. Hence, in this work, we propose a new method based on the geometry-free ionospheric delay estimation with a single frequency (L1) and a single reference station requirement. The local ionospheric delays are estimated based on the proposed method with the observed GPS and GAGAN data in Thailand. Then the ionospheric corrections are obtained from the estimated local ionospheric delays. The analysis shows that using the estimated corrections, the positioning errors are reduced both on quiet days and locally disturbed days in 2019. More reductions in the positioning errors are found in September and December than other months. In addition, we perform a preliminary availability assessment of two critical phases of flights. The GAGAN performances with the proposed method for the APV-I and LPV-200 categories are improved up to 57% and 53%, respectively, in comparison with the baseline method of the IGP correction.