• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.11
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• pp.5223-5242
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• 2017

In the last decade, the 2.4 GHz band of IEEE 802.11 WLANs has become heavily congested due to the explosive increase in demand of Wi-Fi connectivity. With the current deployment of enterprise WLANs, channel switching mechanism continues to exhibit inefficiencies because it cannot adapt to real-time channel condition and the inability to support seamless channel switching. Software Defined Networking (SDN) as an emerging architecture is promising to introduce flexibility and programmability for wireless network management. Leveraging SDN to existing enterprise WLANs, channel switching method can be improved significantly. This paper presents a software-defined enterprise WLAN framework with a load aware automatic channel switching solution, which utilizes AP load and channel interference factor (CIF) to provide seamless channel switching. Two automatic channel switching algorithms named Single Switch (SS) and Double Switch (DS) are proposed to improve the overall user experience and the experience of users with highest traffic load respectively. Experiment results demonstrate that our solution can efficiently improve user experience in terms of jitter, transmission delay and network throughout when compared to the conventional channel switching mechanism.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2C
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• pp.200-207
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• 2008

In this paper, a new detector is proposed for code acquisition, which employs the signs and ranks of the received signal samples, instead of their actual values, and so does not require knowledge of the non-Gaussian noise dispersion. The mean acquisition performance of the proposed detector is compared with that of the detector of $^{[1]}$. The simulation results show that the proposed scheme is not only robust to deviations from the true value of the non-Gaussian noise dispersion, but also has comparable performance to that of the scheme of $^{[1]}$ using exact knowledge of the non-Gaussian noise dispersion.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.630-634
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• 2005

본 논문은 신경망을 이용한 간섭 신호 제어 복합 다층 퍼셉트론에서 DS/SS 이동 통신에서 수신된 신호를 검출하는 것에 대하여 연구한다. 수신 신호가 일정한 비트율을 갖는 채널에 전송하기 위하여 신경망을 이용한 새로운 탭 가중치 갱신 제어 방법을 제안한다. 적응 횡단선 필터는 상호 심볼간 간섭을 억압하기 위해 LMS 알고리즘 사용하고, 응답과 실제 출력간의 차인 에러를 이용하여 탭 가중치 조절 메카니즘을 통해 탭 가중치를 갱신함으로서 효과적으로 간섭을 제거한다. 본 논문은 상호 심볼간 간섭을 효율적으로 억압해온 다계층 퍼셉트론 조합을 이용하여 제안된 알고리즘을 통해 탭 가중치 갱신이 보다 효율적으로 이루어질 수 있도록 한다. 시뮬레이션을 통해 평균자승 에러의 수렴 특성이 우월하다는 것을 연구한다.

• Journal of Nutrition and Health
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• v.37 no.6
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• pp.431-439
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• 2004

Scutellariae Radix (Scu.), one of the immune-regulatory substances, is recognized to play the role in the metabolic process of inflammation, allergy and immunity. It has been traditionally used in the Oriental medicine to treat inflammatory bowel diseases (IBD). The purpose of this study was to evaluate the effects of water extracts of Scutellariae Radix on the spleen lymphocyte immune function in the Balb/c female mice treated with dextran sodium sulfate (DSS) to induce colitis. Water extract of Scutellariae Radix (100 mg/kg) and sulfasalazine (50 mg/kg) were administrated orally for 2 weeks of experimental period. Mice were divided into three experimental groups randomly: DSS group (5％ DSS was ad libitum for 5 days) as control group, DSS ＋ Scu. (water extracts of Scutellariae Radix for 2 weeks after 5％ DSS was ad libitum for 5 days) as experimental group, and DSS ＋ Sulfasalazine group (Sulfasalazine for 2 weeks after 5％ DSS was ad libitum for 5 days) as positive control group. Levels of Ig A, Ig E, CD4$^{＋}$, CD8$^{＋}$, TNF-$\alpha$ and other cytokines were measured. Treatment of DSS for 5 days induced bowel inflammation and the treatment with Scu. water exteract and sulfasalazine significantly recovered the damage. The length of intestine of DSS group was significantly shorter than that of other groups. The serum and fecal concentration of Ig A of SS ＋ Scu group was higher than those of DSS group. The contents of CD4$^{＋}$ T cells was higher in the DSS ＋ Scu. group than the other groups and CD8$^{＋}$ T cells was the lowest in DSS ＋ Sulfasalazine group. The Ig A level of cultured supernatant of spleen lymphocyte was the highest, while the Ig E level was the lowest in SS ＋ Scu group. The concentration of TNF-$\alpha$, cytokine secreted from the Th1 cell in the supernatant spleen lymphocyte, was the highest in the DSS group and the lowest in the DSS ＋ Scu. group. The concentration of IFN-${\gamma}$ and ll...-12 was lower in the DSS ＋ Scu. group than those of the other groups. The concentration of IL-4 in the supernatant of spleen lymphocyte was the lowest in the DSS ＋ Scu. group but IL-10 was not significantly different. Based on these findings, water extract of Scutellariae Radix exhibited the inhibitory effect via IL-4 production thereby inhibited the production of Ig E and strengthened immune system, and alleviated injury in DSS- induced colitis mice model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.8C
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• pp.1025-1033
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• 2004

This paper covers the detection of covert direct sequence spread spectrum signal without the PN(Pseudo Noise) code information. Due to its low probability of interception, the difficulty of spectrum surveillance increases. Detection parameters are the signal existence of given bandwidth, the length of spreading sequence used by transmitter, and the identification of spreading code for detected chip length. The triple correlation function(TCF) value which is one of the higher order statistical signal processing techniques can be used to detect spread spectrum signal without a prior knowledge, but, it has weakness that TCF results depend on the spread data sequence in actual application. This paper proposes the new scheme that not only overcomes the weakness but also presents better performance than the traditional TCF scheme. The performance comparison of conventional TCF with proposed technique shows that the triple correlation estimator(TCE) has better detection capability.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.267.1-267.1
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• 2016

본 연구에서는 nematic 액정의 종류 중 하나인 5CB (4-Cyano-4'-pentylbiphenyl) 물질을 박막 트랜지스터 (TFT)의 passivation 층으로 사용했을 때 그 전기적 특성향상을 확인하였다. RF-magnetron sputtering법으로 증착된 비정질 InGaZnO 박막을 활성층으로 사용한 TFT를 제작하여 그 활성층 위에 drop형식으로 passivation 하였다. 그 결과, drain current (I_DS)가 약 10배 정도 증가하고, linear region(V_D=0.5V)에서 mobility와 subthreshold slope(SS)이 각각 6.7에서 12.2, 0.3에서 0.2로 향상되는 것이 보였다. 이것은 gate bias가 인가되었을 때 freedericksz 전이를 통한 액정의 배향과 이때 형성된 dipole 형성에 의한 것으로 보이며, 이러한 LC의 배향은 편광현미경을 통하여 표면과 수직으로 배향한다는 사실을 확인 할 수 있었고 이 LC-passivation된 a-IGZO TFT의 전기적 특성의 향상에 대한 mechanism을 제시하였다. 그리고 배향한 LC가 가지는 dipole에 의해 bias stress 상황에서 독특한 electron trapping과 recovery의 증폭효과가 나타났다. V_G=+20V의 positive gate bias stress를 1000s동안 가했을 때, passivation되지 않은 a-IGZO TFT의 경우 +4V의 threshold voltage shift(${\Delta}V$_TH)가 발생되었고, 바로 -20V의 negative gate bias를 30s간 가해주었을 때 -2.5V의 ${\Delta}V$_TH가 발생하였다. 반면 LC-passivation된 a-IGZO TFT의 경우 각각 +5V와 -4V의 ${\Delta}V$_TH로 더 큰 변화를 가져왔다. 이러한 LC에 의한 electron trapping/recovery 증폭효과에 대한 model을 제시하였다.

• Molecules and Cells
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• v.27 no.1
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• pp.47-54
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• 2009

A cDNA clone for a transcript preferentially expressed during an early phase of flooding was isolated from Nicotiana tabacum. Nucleotide sequencing of the cDNA clone identified an open reading frame that has high homology to the previously reported glycine-rich RNA-binding proteins. The open reading frame consists of 157 amino acids with an N-terminal RNA-recognition motif and a C-terminal glycine-rich domain, and thus the cDNA clone was designated as Nicotiana tabaccum glycine-rich RNA-binding protein-1 (NtGRP1). Expression of NtGRP1 was upregulated under flooding stress and also increased, but at much lower levels, under conditions of cold, drought, heat, high salt content, and abscisic acid treatment. RNA homopolymer-binding assay showed that NtGRP1 binds to all the RNA homopolymers tested with a higher affinity to poly r(G) and poly r(A) than to poly r(U) and poly r(C). Nucleic acid-binding assays showed that NtGRP1 binds to ssDNA, dsDNA, and mRNA. NtGRP1 suppressed expression of the fire luciferase gene in vitro, and the suppression of luciferase gene expression could be rescued by addition of oligonucleotides. Collectively, the data suggest NtGRP1 as a negative modulator of gene expression by binding to DNA or RNA in bulk that could be advantageous for plants in a stress condition like flooding.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.1
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• pp.22-33
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• 2005

In this paper, an efficient signal interference control technique to improve the high convergence speed of LMS algorithms is introduced in the adaptive transversal filter of DS/SS. The convergence characteristics of the proposed algorithm, whose coefficients are multiply adapted in a symbol time period by recycling the received data, is analyzed to prove theoretically the improvement of high convergence speed. According as the step-size parameter ${\mu}$ is increased, the rate of convergence of the algorithm is controlled. Also, an increase in the stop-size parameter ${\mu}$ has the effect of reducing the variation in the experimentally computed learning curve. Increasing the eigenvalue spread has the effect of controlling which is downed the rate of convergence of the adaptive equalizer. Increasing the steady-state value of the average squared error, proposed algorithm also demonstrate the superiority of signal interference control to the filter algorithm increasing convergence speed by (B+1) times due to the data-recycling LMS technique.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.12
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• pp.1013-1020
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• 2013

In this paper the super-resolution time delay estimation algorithms based on eigen-analysis are developed for spread spectrum signals along with their comparative performance analysis. First, we shall develop super-resolution time delay estimation algorithms using the representative eigen-analysis based AOA (angle-of-arrival) estimation algorithms such as MUSIC, Minimum-Norm, and ESPRIT, and apply them to the ISO/IEC 24730-2.1 real-time locating system (RTLS) employing a direct sequence spread spectrum (DS-SS) technique to compare their performances in RTLS environments. Simulation results illustrate that all the three algorithms can resolve multipath signals whose delay differences are even smaller than the Rayleigh resolution limit. Simulation results also show that MUSIC and Minimum-Norm provide a similar performance while ESPRIT is inferior to both algorithms in RTLS environments.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.5
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• pp.152-161
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• 2017

The CBTC(Communication based Train Control) system employed on 2.4GHz ISM band adopt the IEEE802.11.x standard. Therefor communication time delay, distortion and data losses will be produced. To overcome these problems, CPSK(Continuous Phase shift keying) modulated DS/SS(Direct Sequence Spread Spectrum) transmitter with 908MHz carrier frequency is proposed. Through the eye diagram and scatter diagram the performance is analysed. And the phase noise characteristic of the local oscillator is measured about 60dBc/Hz, this means that the phase noise performance is very good compared to the signal. Reference frequency suppression of the 2nd local oscillator is 50dB below compared to the signal. Through the polarities of the complementary signal equally probable, the line spectrum of the output spectrum is eliminated. The nonlinear effects which introduce the spectral spreading or spectral regeneration is reduced remarkably.