Supnithi, Pornchai

Loading...
Thumbnail Image
Preferred name
Supnithi, Pornchai
Alternative Name
Supnithi, P.
Supnithi, Pomchai
Main Affiliation
Email
pornchai.su@kmitl.ac.th

Settings

Now showing 1 - 10 of 108
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    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.
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    Equinoctial spread-F occurrence at low latitudes in different longitude sectors under moderate and high solar activity
    (2017-11-01)
    Pietrella, M.
    ;
    Pezzopane, M.
    ;
    Fagundes, P. R.
    ;
    de Jesus, R.
    ;
    Supnithi, P.
    A comparative study aimed to investigate the equatorial and low-latitude spread-F occurrences for moderate solar activity (MSA) and high solar activity (HSA), was carried out considering concurrent observations made in some ionospheric stations, which identify three separate longitudinal sectors: Chiang Mai (CGM; 18.8° N, 98.9° E, mag. Lat. 13.2° N) and Chumphon (CPN; 10.7° N, 99.4° E, mag. Lat. 3.2° N), Thailand; Palmas (PAL; 10.2° S, 311.8° E, mag. Lat. 0.9° S) and São José dos Campos (SJC; 23.2° S, 314.1° E, mag. Lat. 14.0° S), Brazil; Tucumán (TUC; 26.9° S, 294.6° E, mag. Lat. 16.8° S), Argentina. Spread-F phenomena recorded during the equinoctial months of September and October 2010, March and April 2011, for MSA, March and April 2014, September and October 2014, for HSA, were classified in two different modes: range spread-F (RSF) and frequency spread-F (FSF). The satellite trace (ST) occurrence was also investigated as possible precursor of spread-F events. When comparing the results of equatorial (CPN and PAL) and low-latitude (CGM, SJC, and TUC) stations, some common features independently of the solar activity emerge: (1) a prevalence of RSF signatures is observed in the time interval 20:00–03:00 LT, while FSF occurrences prevail in the time interval 03:00–06:00 LT; (2) STs are confirmed to be a possible precursor of RSF occurrences. For HSA, at equatorial latitudes, spread-F occurrences in the Thai sector (CPN) are higher than those observed in the Brazilian sector (PAL). When comparing the results of low-latitude stations of CGM, SJC, and TUC some unusual aspects characterizing the morphology of spread-F occurrences emerge: (1) contrary to the Thai and Argentine sectors, in the Brazilian sector (SJC), RSF and FSF appearances in September, for HSA, are observed with relatively long persistence times between about 03:00-06:00 LT and 01:00-03:00 LT respectively, while balanced RSF and FSF occurrences with short persistence times are observed for months for MSA; (2) a prevalence of FSF at CGM during the first half of September for MSA, never observed in the Brazilian and Argentine areas. During years of LSA and MSA common morphological aspects are found at CGM and SJC, that is a predominance of FSF, with the lowest persistence times characterizing SJC. This suggests that the low-latitude behaviour of spread-F occurrences, under different levels of solar activity, at least in the longitude sectors here analysed, can be to a some extent generalized.
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    A flexible KFCI compensation for head/media optimization in perpendicular magnetic recording systems
    (2010-12-01)
    Supnithi, P.
    ;
    Bunsri, K.
    ;
    Novid, M.
    Head/media matching is one of the key procedures used to ensure acceptable performance, reliability and areal density of perpendicular drives. To achieve the optimal bit error rate (BER) performance, head/media optimization is required to handle the variation of each head/media pair within a single drive. Existing optimization uses kilo flux change per inch (KFCI) compensation technique with the fixed slope KFCI value, however, it is unable to handle large variation of the head/media performance. In this paper, we propose to use a flexible KFCI compensation technique between each head/media combination. The relationship between the KFCI slopes and under/over estimation is also established. The result shows that a better BER performance is obtained when compared with the existing technique. In addition, we offer a graphical explanation of the over- and under-compensation issue.
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    The variation of critical frequency of E layer over Chumphon, Thailand
    (2013-12-09)
    Wongcharoen, Poramintra
    ;
    Kenpankho, Prasert
    ;
    Sepsirisuk, Kasemsuk
    ;
    Supnithi, Pornchai
    ;
    Noppanakeepong, Suthichai
    In this research paper presents the observed critical frequency of E layer (foE) over Chumphon, Thailand which is located at nearly the magnetic equator (lat. 10.72° long. 99.37° dip. 3°) during September 2004 to August 2005. The foE is one of essential parameters in the International Reference Ionsphere (IRI) model. We investigate the variation of the observed foE by comparing to the Sun spot number, ionospheric index, and 10.7 cm. flux. Due to essentially of accurate IRI model can be used to applied in communication such as it may be implied tendency of phenomena in E layer effect on high frequency communication over Chumphon, Thailand. © 2013 IEEE.
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    Reduced-complexity window decoding of spatially coupled LDPC codes for magnetic recording systems
    (2018-10-24)
    Khittiwitchayakul, S.
    ;
    Phakphisut, W.
    ;
    Supnithi, P.
    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
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    Latitudinal GRBR-TEC estimation in Southeast Asia region based on the two-station method
    (2014-10-01)
    Watthanasangmechai, Kornyanat
    ;
    Yamamoto, Mamoru
    ;
    Saito, Akinori
    ;
    Tsugawa, Takuya
    ;
    Yokoyama, Tatsuhiro
    Total electron content (TEC) is an important parameter for revealing latitudinal ionospheric structures, such as the equatorial ionization anomaly (EIA) in Southeast Asia. Understanding the EIA is beneficial for studying equatorial spread F. To reveal the structures, the absolute TEC as a function of latitude must be accurately determined. In early 2012, we expanded a GNU Radio Beacon Receiver (GRBR) network to provide latitudinal coverage in the Thailand-Indonesia sector. We employed the GRBR network to receive VHF and UHF signals from polar low-Earth-orbit satellites. The TEC offset is an unknown parameter in the absolute TEC estimation process. We propose a new technique based on the two-station method to estimate the offset for the latitudinal TEC estimation, and it works better than the original method for a sparse network. The TEC estimation system requires two iterations to minimize the root-mean-square error (RMSE). Once the RMSE reaches the global minimum, the absolute TECs are estimated simultaneously over five GRBR stations. GPS-TECs from local stations are used as the initial guess of the offset estimation. The height of the ionospheric pierce point is determined from the ionosonde hmF2. As a result, the latitudinal GRBR-TEC was successfully estimated from the polar orbit satellites. The two EIA humps were clearly captured by the GRBR-TEC. The result was well verified with the TEC reconstructed from the C/NOFS density data and the ionosonde bottomside data. This is a significant step showing that the GRBR is a useful tool for the study of low-latitude ionospheric features.
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    Low-latitude equinoctial spread-F occurrence at different longitude sectors under low solar activity
    (2013-02-05)
    Pezzopane, M.
    ;
    Zuccheretti, E.
    ;
    Abadi, P.
    ;
    De Abreu, A. J.
    ;
    De Jesus, R.
    We present the results of a comparative study of spread-F signatures over five low-latitude sites: Chiangmai (CGM; 18.8° N, 98.9° E, mag. Lat. 8.8° N), Thailand; Tanjungsari (TNJ; 6.9° S, 107.6° E, mag. Lat. 16.9° S), Indonesia; Palmas (PAL; 10.2° S, 311.8° E, mag. Lat. 0.9° S) and São José Dos Campos (SJC; 23.2° S, 314.1° E, mag. Lat. 14.0° S), Brazil; and Tucumán (TUC; 26.9° S, 294.6° E, mag. Lat. 16.8° S), Argentina. The investigation was based on simultaneous ionograms recorded by an FMCW (frequencymodulated continuous-wave) at CGM, an IPS-71 (digital ionosonde from KEL aerospace) at TNJ, a CADI (Canadian Advanced Digital Ionosonde) at PAL and SJC, and an AIS-INGV (Advanced Ionospheric Sounder-Istituto Nazionale di Geofisica e Vulcanologia) at TUC, during the equinoctial periods March-April (R<inf>12</inf> = 2.0 and R <inf>12</inf> = 2.2) and September-October (R<inf>12</inf> = 6.1 and R <inf>12</inf> = 7.0) 2009, for very low solar activity. Spread-F signatures were categorized into two types: the range spread-F (RSF) and the frequency spread-F (FSF). The study confirms that the dynamics and the physical processes responsible for these phenomena are actually complicated. In fact, the features that arise from the investigation are different, depending on both the longitude sector and on the hemisphere. For instance, TUC, under the southern crest of the ionospheric equatorial ionization anomaly (EIA), shows a predominance of RSF signatures, while both SJC, under the southern crest of EIA but in a different longitude sector, and CGM, under the northern crest of EIA, show a predominance of FSF signatures. Moreover, the spread-F occurrence over the longitude sector that includes CGM and TNJ is significantly lower than the spread-F occurrence over the longitude sector of PAL, SJC, and TUC. © Author(s) 2013.
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    The occurrence of equatorial spread-F at conjugate stations in Southeast Asia
    (2015-04-15)
    Klinngam, Somjai
    ;
    Supnithi, Pornchai
    ;
    Rungraengwajiake, Sarawoot
    ;
    Tsugawa, Takuya
    ;
    Ishii, Mamoru
    In this study, the probability of equatorial spread-F (ESF) occurrence at the conjugate stations in Southeast Asia: Chiangmai station (CMU), Thailand, and Kototabang station (KTB), Indonesia, and near the magnetic equator, Chumphon station (CPN), Thailand, is presented. We analyze the ionogram data recorded by the Frequency Modulated Continuous Wave (FM/CW) ionosondes for the periods of minimum solar activity from September 2008 to April 2009 and in the equinoctial months (March and April) from 2006 to 2013. The spread-F signatures are manually categorized into three types: the frequency spread-F (FSF), the range spread-F (RSF) and the mixed spread-F (MSF) and the monthly average percentage of the occurrence of each ESF type is presented. The results show that the percentage of RSF occurrence at CPN, which is located around the magnetic equator, is higher than at other stations and the RSF mostly occurs during the equinoctial months. On the other hand, the FSF occurrence at CMU and KTB, that are located in the northern and southern hemispheres, respectively, are higher than at CPN. The RSF occurrence typically has the peaks before midnight, while the maximum occurrence rate of FSF is after midnight. Furthermore, the RSF onsets normally precede the FSF onsets by about 1-2 h. As the solar activity levels go up, the percentages of RSF occurrence increase, but the percentages of FSF tends to decrease. In addition, we compare the statistics of observed RSF occurrence with the prediction of the IRI-2012 model. The results show that the IRI model overestimates the observed RSF occurrence at all stations during most of the solar activity levels and seasons, except in June 2008 (21:00-03:00 LT), March 2011 (23:30-01:00 LT) and March 2013 (01:00-02:30 LT) when the IRI model underestimates our observations. However, the IRI model gives closer probability of RSF occurrence to our observed values at CPN, especially in equinoctial months and during the periods of medium solar activity. This work is important for an improvement of the IRI model in the prediction of the spread F occurrence probability in the low-latitude region.
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    Prediction of foF2 using Neural Network at Thailand equatorial latitude station, Chumphon
    (2014-01-01)
    Wichaipanich, Noraset
    ;
    Supnithi, Pornchai
    This paper proposes the development of a Neural Network (NN) model for the prediction of the F2 layer critical frequency (foF2) at the magnetic equator over Chumphon (10.72°N, 99.37°E, dip angle 3.3°N), Thailand and then compared with the IRI model and the experimental ones. The feed forward network with backpropagation algorithm has been developed for predicting the foF2 values. The NN is trained with the daily hourly values of foF2 during the period from 2004 to 2008 and the input parameters affecting the foF2 variability including the hour number, day number, F10.7 index and sunspot number (SSN). To examine the performance of the proposed NN, the root mean square error (RMSE) of the observed foF2, the proposed NN model and the IRI (both CCIR and URSI options) model are compared in 2009. The results show that the NN model predicts the foF2 values close to the observed data, particularly during daytime. Moreover, the NN model can predicts more accurate than the IRI model that is supported by the lower RMSE. However, the NN model provides slightly deviation of prediction during pre-sunrise hours since the observed foF2 data for NN training in this periods are fewer than those during daytime. © 2014 IEEE.
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    Total electron content observations by dense regional and worldwide international networks of GNSS
    (2018-06-01)
    Tsugawa, Takuya
    ;
    Nishioka, Michi
    ;
    Ishii, Mamoru
    ;
    Hozumi, Kornyanat
    ;
    Saito, Susumu
    Two-dimensional ionospheric total electron content (TEC) maps have been derived from ground-based Global Navigation Satellite System (GNSS) receiver networks and applied to studies of various ionospheric disturbances since the mid-1990s. For the purpose of monitoring and researching ionospheric conditions and ionospheric space weather phenomena, we have developed TEC maps of areas over Japan using the dense GNSS network, GNSS Earth Observation NETwork (GEONET), which consists of about 1300 stations and is operated by the Geospatial Information Authority of Japan (GSI). Currently, we are providing high-resolution, two-dimensional maps of absolute TEC, detrended TEC, rate of TEC change index (ROTI), and loss-of-lock on GPS signal over Japan on a real-time basis. Such high-resolution TEC maps using dense GNSS receiver networks are one of the most effective ways to observe, on a scale of several 100 km to 1000 km, ionospheric variations caused by traveling ionospheric disturbances and/or equatorial plasma bubbles, which can degrade single-frequency and differential GNSS positioning/navigation. We have collected all the available GNSS receiver data in the world to expand the TEC observation area. Currently, however, dense GNSS receiver networks are available in only limited areas, such as Japan, North America, and Europe. To expand the two-dimensional TEC observation with high resolution, we have conducted the Dense Regional and Worldwide International GNSS TEC observation (DRAWING-TEC) project, which is engaged in three activities: (1) standardizing GNSS-TEC data, (2) developing a new high-resolution TEC mapping technique, and (3) sharing the standardized TEC data or the information of GNSS receiver network. We have developed a new standardized TEC format, GNSS-TEC EXchange (GTEX), which is included in the Formatted Tables of ITU-R SG 3 Data-banks related to Recommendation ITU-R P.311. Sharing the GTEX TEC data would be easier than sharing the GPS/GNSS data among those in the international ionospheric researcher community. The DRAWING-TEC project would promote studies of medium-scale ionospheric variations and their effect on GNSS.