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Author: search.filters.author.Supnithi, Pomchai

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    Neural networks equalizers for nonlinear magnetic recording channels
    (2017-11-03)
    Wongsathan, Rati
    ;
    Phakphisut, Watid
    ;
    Supnithi, Pomchai
    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.
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    Study of GPS instrumental bias and TEC estimations from GPS stations in Thailand
    (2017-11-03)
    Chiablaem, Athiwat
    ;
    Phakphisut, Watid
    ;
    Supnithi, Pomchai
    The Total Electron Content (TEC) or satellite delay can be derived from the dual-frequency of Global Positioning System (GPS). The error of TEC accuracy suffers seriously from the GPS instrumental biases, including satellite bias and receiver bias. In this paper, we apply the singular value decomposition (SVD) to derive TEC, GPS satellite and receiver biases from the 11 GPS receiver stations in Thailand, which are operated by DPT. From the results, the daily satellite bias range between -8 ns and 10 ns. The estimated receiver bias varies from -5.03 ns to 1.88 ns. The biases in TEC are removed. The TEC estimation by SVD method is a good agreement level at each locations. The TEC of SVD estimation is compared with a TEC of general calculation by a GPS receiver from DPT9. The estimated TEC by SVD method at Bangkok area is used. The trend of both TEC are concurrence. Thus, the SVD method can be used to estimate the TEC, GPS satellite and receiver biases in Thailand area.