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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    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
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    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.
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    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.
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    Rain attenuation of satellite link in Ku-band at Bangkok
    (2005-12-01)
    Boonchuk, T.
    ;
    Hemmakorn, N.
    ;
    Supnithi, P.
    ;
    Iida, M.
    ;
    Tanaka, K.
    Rain attenuation is a major factor to degrade the system performance in a frequency above 10 GHz. This paper presents a statistical analysis of the rainfall rate and the rain attenuation data on satellite to ground propagation path. By measuring 12.7-GHz beacon signal attenuation from JCSAT satellite and the rainfall rate continuously. Yearly cumulative distribution functions were then compared to predicted models. The Crane Global model for the rain zone H provides overestimated predicted values to the measured ones. For the rain zone G, the Crane Global model provides close values to ITU-R model; both are smaller than the measured ones. © 2005 IEEE.
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    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.
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    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.
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    Comparison of the gnss position accuracy on mobile phones in Vientiane, laos
    (2019-07-01)
    Soumphonphakdy, Dethnaphonexay
    ;
    Southisombath, Khanpui
    ;
    Supnithi, Pornchai
    In this research, the position errors derived from Global Navigation Satellite System (GNSS) signals of two different brands of smart phones are assessed. To perform the experiment, two smartphones Samsung Galaxy Note 8 and Google Pixel 1 have been chosen. The main goal of this test is to compare the position accuracy of each phone. As different environments such as open-sky or partially blocked view affect the received satellite signal levels; therefore, we made the test by recording the GNSS signals in crowded city areas, where many buildings can be found, and open areas, where there are no obstructions. The raw data are processed using the recently available open-source software named Google Analysis Tools. The results show that the received GPS signal in the clear environment have lower errors and more accurate than in the city environment. It can be seen that Galaxy Note 8 has the ability to locate places better (less error values) than Google Pixel.
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    Ionospheric variation at Thailand equatorial latitude station: Comparison between observations and IRI-2001 model predictions
    (2010-01-15)
    Wichaipanich, Noraset
    ;
    Supnithi, Pornchai
    ;
    Ishii, Mamoru
    ;
    Maruyama, Takashi
    In this paper, the F2-layer critical frequency (foF2) and peak height (hmF2) measured by the FM/CW ionosonde at Thailand equatorial latitude station, namely Chumphon (10.72°N, 99.37°E, dip 3.22) are presented. The measurement data during low solar activity from January 2004 to December 2006 are analyzed based on the diurnal, seasonal variation. The results are then compared with IRI-2001 model predictions. Our study shows that: (1) In general, both the URSI and CCIR options of the IRI model give foF2 close to the measured ones, but the CCIR option produces a smaller range of deviation than the URSI option. The agreement during daytime is generally better than during nighttime. Overestimation mostly occurs in 2004 and 2006, while underestimation is during pre-sunrise hours in June solstice in 2005. The peak foF2 around sunset is higher during March equinox and September equinox than the other seasons, with longer duration of maximum levels in March equinox than September equinox. Large coefficients of variability foF2 occur during pre-sunrise hours. Meanwhile, the best agreement between the observed foF2 and the IRI model is obtained in June solstice. (2) In general, The IRI (CCIR) model predicts the observed hmF2 well during daytime in June solstice from 2004-2006, but it overestimates during March equinox, September equinox and December solstice. For nighttime, the model overestimates hmF2 values for all seasons especially during March equinox and September equinox. However, the model underestimates hmF2 values during September equinox and for some cases during June solstice and December solstice at pre-sunrise. The agreement between the IRI model and the hmF2(M3000 <inf>OBS</inf> ) is worst around noontime, post-sunset and pre-sunrise hours. All comparative studies give feedback for new improvements of CCIR and URSI IRI models. © 2009.
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    Bi-directional timing recovery for magnetic recording systems
    (2009-12-01)
    Warisarn, Chanon
    ;
    Supnithi, Pornchai
    ;
    Kovintavewat, Piya
    Magnetic recording systems employ conventional timing recovery to synchronize the sampler with the readback signal. However, conventional timing recovery does not perform well when the timing error is large. This paper proposes the bidirectional timing recovery, which utilizes conventional timing recovery to sample the readback signal both in forward direction and in backward direction. The outputs of these two operations are averaged and sent them to the Viterbi detector to determine the most likely input sequence. Results indicate that the bidirectional timing recovery performs better than conventional timing recovery, especially when the timing error is large. ©2009 IEEE.
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    A study of multiple reads of target track prior to detection for two-dimensional magnetic recording
    (2015-07-14)
    Singhaudom, W.
    ;
    Supnithi, P.
    ;
    Warisarn, C.
    Two-dimensional magnetic recording (TDMR) has recently received wide attention as a good candidate for next generation high-density data storage [1]. However, the read-back signal is subject to the combination of inter-track interference (ITI) and inter-symbol interference (ISI). Therefore, a major challenge to apply TDMR depends on the development of two-dimensional signal processing. It is widely studied in a variety of forms, leading to the compromise between detection performance and computation complexity. Some recent works on TDMR channels are presented in [2]-[4]. In [2], performance is enlarged by using 2D iterative detector. As for [3] and [4], multiple readbacks from array-reader were proposed to detect data bit.