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Exact Intersymbol Interference Analysis for Upsampled OFDM Signals with Symbol Timing Errors
HUH, Heon,LU, Feng,KROGMEIER, James V. Institute of Electronics, Information and Communic 2017 IEICE transactions on communications Vol.100 No.8
<P>In OFDM systems, link performance depends heavily on the estimation of symbol-timing and frequency offsets. Performance sensitivity to these estimates is a major drawback of OFDM systems. Timing errors destroy the orthogonality of OFDM signals and lead to inter-symbol interference (ISI) and inter-carrier interference (ICI). The interference due to timing errors can be exploited as a metric for symbol-timing synchronization. In this paper, we propose a novel method to extract interference components using a DFT of the upsampled OFDM signals. Mathematical analysis and formulation are given for the dependence of interference on timing errors. From a numerical analysis, the proposed interference estimation shows robustness against channel dispersion.</P>
Frame Synchronization of Coded Modulations in Time-Varying Channels via Per-Survivor Processing
Heon Huh,Krogmeier, J. V. IEEE 2011 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.59 No.10
<P>In this letter, an optimum frame synchronizer is proposed for coded modulations in channels with uncertainties. Coded modulations include various frame synchronization scenarios, e.g., convolutionally coded transmissions and nonlinear modulations with memory. Frame synchronization is proposed as a maximum a posteriori probability estimation implemented using trellis path search for Markov chain decoding. In addition, time-varying uncertainties such as frequency offset and phase noise are jointly estimated via per-survivor processing as frame synchronization proceeds. The proposed frame synchronizer exploits the coding gain of coded modulations to achieve better performance than conventional frame synchronizers. We show that the resulting frame synchronizer consists of a correlation term and two data correction terms. Numerical results show that the proposed frame synchronizer is robust to uncertainties at the receiver and it exhibits improved performance.</P>
Long-term analysis of PV module with large-area patterned anti-reflective film
Huh, Daihong,Choi, Hak-Jong,Byun, Minseop,Kim, Kwan,Lee, Heon Elsevier 2019 RENEWABLE ENERGY Vol.135 No.-
<P><B>Abstract</B></P> <P>Due to the PV modules are exposed to the external environment, it is necessary to clean or replace the protective glass upon contamination. In this study, we demonstrate a large-area and flexible anti-reflective film with moth-eye pattern fabricated by using a highly straightforward process: nanoimprint lithography. In addition, the fabricated anti-reflective film exhibits self-cleaning capability owing to the hydrophobic self-assembled-monolayer-coated surface. The fabricated anti-reflective film was attached to the surface of photovoltaic (PV) modules and placed outdoor to conduct a seven-month field test in order to observe the increase in the conversion efficiency of the PV modules as a result of the effect of the anti-reflective film. Two types of patterns, moth-eye pattern and micro-cone pattern, were used as the anti-reflective patterns; these were conveniently fabricated by the ultraviolet-nanoimprint lithography process, which does not use vacuum or high-temperature process. In the seven-month analysis, the moth-eye patterned film was observed to exhibit a transmittance that is 5.0% higher than that of the flat film, whereas the PV module with the moth-eye patterned film on its surface exhibited a conversion efficiency that is 2.85% higher than that of the PV module with the flat film.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Self-cleanable anti-reflective structure were fabricated on large flexible film. </LI> <LI> Long-term field test was conducted to measure effect of the anti-reflective patterned flexible film. </LI> <LI> Generated electricity was improved up to 2.85% per month compare to PV module with un-patterned sample. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>In this study, self-cleanable and micro-nano-size anti-reflective structure were fabricated on large area flexible film. Monitoring system was installed and long-term field test was conducted to measure effect of the anti-reflective patterned flexible film. Due to the formed moth-eye patterns, generated electricity was improved up to 2.85% per month compare to PV module with un-patterned sample.</P> <P>[DISPLAY OMISSION]</P>