• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권2호
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• pp.608-627
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• 2016

Wireless mesh networks (WMNs) based on IEEE 802.11s have emerged as one of the prominent technologies in multi-hop communications. However, the deployment of WMNs suffers from serious interference problem which severely limits the system capacity. Using multiple radios for each mesh router over multiple channels, the interference can be reduced and improve system capacity. Nevertheless, interference cannot be completely eliminated due to the limited number of available channels. An effective approach to mitigate interference is to apply dynamic channel switching (DCS) in WMNs. Conventional DCS schemes trigger channel switching if interference is detected or exceeds a predefined threshold which might cause unnecessary channel switching and long protocol overheads. In this paper, a P-learning based dynamic switching algorithm known as learning automaton (LA)-based DCS algorithm is proposed. Initially, an optimal channel for communicating node pairs is determined through the learning process. Then, a novel switching metric is introduced in our LA-based DCS algorithm to avoid unnecessary initialization of channel switching. Hence, the proposed LA-based DCS algorithm enables each pair of communicating mesh nodes to communicate over the least loaded channels and consequently improve network performance.

• 전기학회논문지P
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• 제65권2호
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• pp.108-113
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• 2016

The real-world problems usually show nonlinear and multi-variate characteristics, so it is difficult to establish concrete mathematical models for them. Thus, it is common to practice data-driven modeling techniques in these cases. Among them, most widely adopted techniques are regression model and intelligent model such as neural networks. Regression model has drawback showing lower performance when much non-linearity exists between input and output data. Intelligent model has been shown its superiority to the linear model due to ability capable of effectively estimate desired output in cases of both linear and nonlinear problem. This paper proposes modeling method of daily photovoltaic power systems using ELM(Extreme Learning Machine) based modular networks. The proposed method uses sub-model by fuzzy clustering rather than using a single model. Each sub-model is implemented by ELM. To show the effectiveness of the proposed method, we performed various experiments by dataset acquired during 2014 in real-plant.

• 대한전자공학회논문지SD
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• 제44권2호
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• pp.7-12
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• 2007

고휘도 LED(Light-Emitting Diode)를 구현하기 위한 칩 설계의 최적화에 이용할 수 있는 SPICE 기반의 LED 3차원 회로 모델을 개발하였다. 본 모델은 LED를 일정한 면적의 픽셀로 구획하고, 각각의 픽셀은 n-전극, n-형 반도체, p-형 반도체, 및 p-전극 등의 일반적인 LED 레이어 구조를 반영하는 회로망으로 나타낸다. 개별의 박막 층과 접촉 저항은 저항 네트웍으로, pn-접합부는 일반적인 pn-접합 다이오드로 각각 모델링 한다. 별도의 테스트 패턴을 이용하여 독립적으로 추출한 파라미터를 이용한 시뮬레이션 결과는 실험 결과와 정확하게 일치함을 확인하였다.

• Journal of Communications and Networks
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• 제5권3호
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• pp.275-281
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• 2003

Random Early Detection (RED) [1] is an active queue management scheme which has been deployed extensively to reduce packet loss during congestion. Although RED can improve loss rates, its performance depends severely on the tuning of its operating parameters. The idea of adaptively varying RED parameters to suit the network conditions has been investigated in [2], where the maximum packet dropping probability $max_p$ has been varied. This paper focuses on adaptively varying the queue weight $\omega_q$ in conjunction with $max_p$ to improve the performance. We propose two algorithms viz., $\omega_q$-thresh and $\omega_q$-ewma to adaptively vary $\omega_q$. The performance is measured in terms of the packet loss percentage, link utilization and stability of the instantaneous queue length. We demonstrate that varying $\omega_q$ and $max_p$ together results in an overall improvement in loss percentage and queue stability, while maintaining the same link utilization. We also show that $max_p$ has a greater influence on loss percentage and queue stability as compared to $\omega_q$, and that varying $\omega_q$ has a positive influence on link utilization.

• 충청수학회지
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• 제29권4호
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• pp.573-584
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• 2016

Invertible transformations over n-bit words are essential ingredients in many cryptographic constructions. Such invertible transformations are usually represented as a composition of simpler operations such as linear functions, S-P networks, Feistel structures and T-functions. Among them T-functions are probably invertible transformations and are very useful in stream ciphers. In this paper we will characterize a secure trinomial on ${\mathbb{Z}}_{2^n}$ which generates an n-bit word sequence without consecutive elements of period $2^n$.

• Kyungpook Mathematical Journal
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• 제48권2호
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• pp.165-171
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• 2008

The aim of this paper is to evaluate four finite integrals involving the product of Srivastava's polynomials, a generalized hypergeometric function and $\bar{H}$-function proposed by Inayat Hussian which contains a certain class of Feynman integrals. At the end, we give an application of our main findings by connecting them with the Riemann-Liouville type of fractional integral operator. The results obtained by us are basic in nature and are likely to find useful applications in several fields notably electric networks, probability theory and statistical mechanics.

• Journal of Communications and Networks
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• 제7권3호
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• pp.294-306
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• 2005

Group oriented multicast applications are becoming increasingly popular in mobile ad hoc networks (MANETs). Due to dynamic topology of MANETs, stateless multicast protocols are finding increased acceptance since they do not require maintenance of state information at intermediate nodes. Recently, several multicast schemes have been proposed which scale better' with the number of multicast sessions than traditional multicast strategies. These schemes are also known as explicit multicast (Xcast; explicit list of destinations in the packet header) or small group multicast (SGM). In this paper, we propose a new scheme for small group' multicast in MANETs named extended explicit multicast (E2M), which is implemented on top of Xcast and introduces mechanisms to make it scalable with number of group members for a given multicast session. Unlike other schemes, E2M does not make any assumptions related to network topology or node location. It is based on the novel concept of dynamic selection of Xcast forwarders (XFs) between a source and its potential destinations. The XF selection is based on group membership and the processing overhead involved in supporting the Xcast protocol at a given node. If the number of members in a given session is small, E2M behaves just like the basic Xcast scheme with no intermediate XFs. As group membership increases, nodes may dynamically decide to become an XF. This scheme, which can work with few E2M aware nodes in the network, provides transparency of stateless multicast, reduces header processing overhead, minimizes Xcast control traffic, and makes Xcast scalable with the number of group members.

• 한국대기환경학회지
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• 제22권4호
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• pp.459-467
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• 2006

This study was carried out to characteristics and distributions of acid deposition in Korea. Precipitation was collected by acid deposition monitoring networks and analyzed for pH, conductivity, and following major ionic components $SO_4^{2-}$, $CI^-$, $NO_3^-$, $NH_4^+$, $Na^+$, $K^+$, $Ca^{2+}$, $Mg{2+}$. During the investigation period, Volume weighted annual mean pH of precipitation in Korea is 4.8, showing slightly acidic level. The amount of rainfall in the range of pH 5.1$\sim$5.5 charged approximately 28% of annual precipitation,23.4% in pH 4.6$\sim$5.0, and contributed 16.2% under pH 4.5. Among seasons, alkaline precipitation has occurred more often in spring, meanwhile acidic precipitation in which pH is under 4.5 has frequently occurred in autumn. Volume weighted annual mean concentrations of $SO_4^{2-}$, $NO_3^-$, $CI^-$ are 2.558 mg/L, 1.590 mg/L, 1.286 mg/L respectively, and provided that $SO_4^{2-}$, is the major contributor, followed by $NO_3^-$, $CI^-$. In case of cation, annual mean concentration for $NH_4^+$, $Na^+$, $K^+$, $Ca^{2+}$, $Mg{2+}$, $H^+$ are 0.693 mg/L, 0.528 mg/L, 0.439 mg/L, 0.455 mg/L, 0.089 mg/L,0.015 mg/L, and $NH_4$ were decided as the main contributor, followed by $Na^+$, $K^+$, $Ca^{2+}$, $Mg{2+}$, $H^+$. Annual wet deposition rate for sulfate, nitrate and ammonia are $3.316gm^{-2}yr^{-1}$, $2.057gm^{-2}yr{-1}$, $0.894gm^{-2}yr{-1}$, respectively, and it was founded that the deposition flux in summer contributes about 38.42% to 67.62% to total deposition.

• JSTS:Journal of Semiconductor Technology and Science
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• 제2권2호
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• pp.125-131
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• 2002

This paper presents MMIC drive and power amplifiers covering 6-18 ㎓. For simple wideband impedance matching and less sensitivity to fabrication variation, modified distributed topologies are employed in the both amplifiers. Cascade amplifiers with a self-biasing circuit through feedback resistors are used as unit gain blocks in the drive amplifier, resulting in high gain, high stability, and compact chip size. Self impedance matching and high-pass, low-pass impedance matching networks are used in the power amplifier. In measured results, the drive amplifier showed good return losses ($S_11,{\;}S_{22}{\;}<{\;}-10.5{\;}dB$), gain flatness ($S_{21}={\;}16{\;}{\pm}0.6{\;}dB$), and $P_{1dB}{\;}>{\;}22{\;}dBm$ over 6-18 GHz. The power amplifier showed $P_{1dB}{\;}>{\;}28.8{\;}dBm$ and $P_{sat}{\;}{\approx}{\;}30.0{\;}dBm$ with good small signal characteristics ($S_{11}<-10{\;}dB,{\;}S_{22}{\;}<{\;}-6{\;}dB,{\;}and{\;}S_{21}={\;}18.5{\;}{\pm}{\;}1.25{\;}dB$) over 6-18 GHz.

• Journal of Communications and Networks
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• 제13권3호
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• pp.277-285
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• 2011

Real-time multimedia streaming over the Internet is rapidly increasing with the popularity of user-created contents, Web 2.0 trends, and P2P (peer-to-peer) delivery support. While many homes today are broadband-enabled, the quality of experience (QoE) of a user is still limited due to frequent interruption of media playout. The vulnerability of TCP (transmission control protocol), the popular transport-layer protocol for streaming in practice, to the packet losses, retransmissions, and timeouts makes it hard to deliver a timely and persistent flow of packets for online multimedia contents. This paper presents TCP-real-time online multimedia environment (ROME), a novel transport-layer framework that allows the establishment and coordination of multiple many-to-one TCP connections. Between one client with multiple home addresses and multiple co-located or distributed servers, TCP-ROME increases the total throughput by aggregating the resources of multiple TCP connections. It also overcomes the bandwidth fluctuations of network bottlenecks by dynamically coordinating the streams of contents from multiple servers and by adapting the streaming rate of all connections to match the bandwidth requirement of the target video.