• 한국통신학회논문지
• /
• 제36권5B호
• /
• pp.573-581
• /
• 2011

수중채널은 매질에 의한 신호 감쇄로 인해 전송대역이 제한되며, 수온, 염도, 기하학적 구조 등 다양한 요소의 영향을 받기 때문에 복잡하며 신뢰성을 유지하기 어려운 통신 환경 중의 하나이다. 본 논문에서는 수중채널에 대한 분석을 토대로 보다 실질적인 모의 수중채널을 모델링하였다. 또한 ISI, 주파수 선택적 페이딩, 시간 선택적 페이딩을 동시에 고려한 Coded Orthogonal Frequency Division Multiplexing (OFDM) 시스템을 디자인하였으며 앞서 언급한 실질적인 표의 수중채널에 대한 시뮬레이션을 통하여 디자인된 시스템이 다양한 상태의 채널에서도 성능변화의 폭이 작고 견실하게 작동할 수 있음을 보였다. 제안하는 Coded OFDM 시스템은 Low Density Parity Check (LDPC) 코드를 사용했으며, Un-coded OFDM 시스템에 비해 $10^{-3}$ BER기점을 기준으로 7 dB의 이득이 발생하였다. 뿐만 아니라 채널의 변화에 따른 SNR 차가 8 dB에서 3 dB로 줄였다.

• Wind and Structures
• /
• 제27권6호
• /
• pp.381-397
• /
• 2018

Nonlinear behavior in fluid-structure interaction (FSI) of bridge decks becomes increasingly significant for modern bridges with increasing spans, larger flexibility and new aerodynamic deck configurations. Better understanding of the nonlinear aeroelasticity of bridge decks and further development of reduced-order nonlinear models for the aeroelastic forces become necessary. In this paper, the amplitude-dependent and neutral angle dependent nonlinearities of the motion-induced loads are further highlighted by series of computational fluid dynamics (CFD) simulations. An effort has been made to investigate a semi-analytical time-domain model of the nonlinear motion induced loads on the deck, which enables nonlinear time domain simulations of the aeroelastic responses of the bridge deck. First, the computational schemes used here are validated through theoretically well-known cases. Then, static aerodynamic coefficients of the Great Belt East Bridge (GBEB) cross section are evaluated at various angles of attack, leading to the so-called nonlinear backbone curves. Flutter derivatives of the bridge are identified by CFD simulations using forced harmonic motion of the cross-section with various frequencies. By varying the amplitude of the forced motion, it is observed that the identified flutter derivatives are amplitude-dependent, especially for $A^*_2$ and $H^*_2$ parameters. Another nonlinear feature is observed from the change of hysteresis loop (between angle of attack and lift/moment) when the neutral angles of the cross-section are changed. Based on the CFD results, a semi-analytical time-domain model for describing the nonlinear motion-induced loads is proposed and calibrated. This model is based on accounting for the delay effect with respect to the nonlinear backbone curve and is established in the state-space form. Reasonable agreement between the results from the semi-analytical model and CFD demonstrates the potential application of the proposed model for nonlinear aeroelastic analysis of bridge decks.

• 한국정보통신학회논문지
• /
• 제22권2호
• /
• pp.253-260
• /
• 2018

천해 환경에서의 수중 음향 통신 채널은 전형적으로 시변 다중 경로 페이딩 채널 특성을 나타낸다. 이러한 채널 전송을 통해 수신된 신호는 시간 지연 및 진폭의 중첩에 의해 심볼 간 간섭을 유발한다. 이를 보완하기 위해 여러 기술이 사용되었으며, 그 중 하나가 음향 등화기이다. 본 연구에서는 심볼 간 간섭을 보상하기 위해 feed-forward equalizer (FFE), decision direct equalizer (DDE), decision feedback equalizer (DFE) 및 DFE와 결합된 DDE의 4 종류의 등화기와 등화기의 계수를 조정하기 위해 normalized least mean square (NLMS) 알고리즘과 recursive least square (RLS) 알고리즘의 2 종류의 알고리즘을 적용하였다. 그 결과 비선형 등화기에서는 신호 대 잡음비 6 dB 이상에서 상당한 성능 향상을 발견할 수 있었으며, DFE와 DDE의 조합은 어떤 경우에도 최고의 성능을 발휘하였다.

• 한국재료학회지
• /
• 제20권6호
• /
• pp.319-325
• /
• 2010

3-D IC integration enables the smallest form factor and highest performance due to the shortest and most plentiful interconnects between chips. Direct metal bonding has several advantages over the solder-based bonding, including lower electrical resistivity, better electromigration resistance and more reduced interconnect RC delay, while high process temperature is one of the major bottlenecks of metal direct bonding because it can negatively influence device reliability and manufacturing yield. We performed quantitative analyses of the interfacial properties of Al-Al bonds with varying process parameters, bonding temperature, bonding time, and bonding environment. A 4-point bending method was used to measure the interfacial adhesion energy. The quantitative interfacial adhesion energy measured by a 4-point bending test shows 1.33, 2.25, and $6.44\;J/m^2$ for 400, 450, and $500^{\circ}C$, respectively, in a $N_2$ atmosphere. Increasing the bonding time from 1 to 4 hrs enhanced the interfacial fracture toughness while the effects of forming gas were negligible, which were correlated to the bonding interface analysis results. XPS depth analysis results on the delaminated interfaces showed that the relative area fraction of aluminum oxide to the pure aluminum phase near the bonding surfaces match well the variations of interfacial adhesion energies with bonding process conditions.

• 한국지진공학회논문집
• /
• 제6권4호
• /
• pp.23-29
• /
• 2002

지진 발생시 건축물의 내부상태를 탐사하는데 있어 콘크리트 구조물의 두께, 철근의 피복깊이, 공동의 유무를 탐사하게 되고, 이것을 통해 건축물의 손상을 추정할 수 있다. 이때 콘크리트 내부를 탐사하는 방법으로 지중 탐사 레이더(ground penetrating radar)가 효과적으로 이용될 수 있다. 기존의 레이더 측정 방법에서는 콘크리트 내부를 탐사하기 위해 시간영역에 있는 데이터로 콘크리트의 유전상수를 구하고 시간을 거리로 환산하여 육안 식별에 의해서 결과를 분석하였다. 본 연구에서는 콘크리트 시편을 측정한 후 측정된 데이터를 주파수 영역으로 변환하여 스펙트럼 분석과 필터링을 통한 방법으로 신호 처리하여 시간영역에서의 데이터 분석능력을 향상 시켰다. 데이터 획득을 위해 주로 사용되는 900MHz, 1GHz, 그리고 1.5㎓ 중심 주파수를 갖는 세 개의 안테나를 사용하여 철근시편을 탐사하였다. 주파수 영역에서 차단 주파수(cutoff frequency)를 1/3 옥타브에 의하여 변화시키면서 저역 통과, 고역 통과, 그리고, 대역 통과 등의 필터링을 하였고, 각각의 중심 주파수에 대한 가장 효과적인 차단 주파수를 찾으려고 했다. 차단 주파수의 범위는 최대 하위 2옥타브에서 상위 1옥타브와 최소 하위 2옥타브에서 하위 1옥타브가 적합하였고, 주파수 영역에서 필터링을 통해 콘크리트 내부 정보 분석력 향상을 위한 토대를 마련하였다.

• 한국정보처리학회:학술대회논문집
• /
• 한국정보처리학회 2008년도 추계학술발표대회
• /
• pp.1332-1335
• /
• 2008

In order to various service types of real time and non-real time traffic with varying requirements are transmitted over the IEEE 802.16 standard is expected to provide quality of service(QoS) researchers have explored to provide a queue management scheme with differentiated loss guarantees for the future Internet. The sides of a packet drop rate, an each class to differential drop probability on achieving a low delay and high traffic intensity. Improved a queue management scheme to be enhanced to offer a drop probability is desired necessarily. This paper considers multiple random early detection with differential drop probability which is a slightly modified version of the Multiple-RED(Random Early Detection) model, to get the performance of the best suited, we analyzes its main control parameters (max_th, min_th, max_p) for achieving the proportional loss differentiation (PLD) model, and gives their setting guidance from the analytic approach. we propose Dynamic-multiple queue management scheme based on differential drop probability, called Dynamic-VQSDDP(Variable Queue State Differential Drop Probability)T, is proposed to overcome M-RED's shortcoming as well as supports static max_p parameter setting values for relative and each class proportional loss differentiation. M-RED is static according to the situation of the network traffic, Network environment is very dynamic situation. Therefore max_p parameter values needs to modify too to the constantly and dynamic. The verification of the guidance is shown with figuring out loss probability using a proposed algorithm under dynamic offered load and is also selection problem of optimal values of parameters for high traffic intensity and show that Dynamic-VQSDDP has the better performance in terms of packet drop rate. We also demonstrated using an ns-2 network simulation.

• 드라이브 ㆍ 컨트롤
• /
• 제12권4호
• /
• pp.60-70
• /
• 2015

A front-end loader (FEL) mounted on an agricultural tractor is one of the most commonly used implements for farm work. However, when the tractor carries material using the bucket attached to the FEL on a sloping ground, the materials can spill or roll back over the operator due to the tilted body, thereby requiring the bucket surface to remain level at a constant value regardless of varying slopes. In this study, an active system for controlling the angle of the FEL bucket on a tractor based on the real-time measurement of ground slopes was developed to enable the bucket to constantly remain level. A FEL simulator operated based on an electro hydraulic proportional valve (EHPV) was constructed in the laboratory to develop a proportional-integral-derivative (PID) controller forming a virtual electronic control unit (ECU) on the computer, which could automatically adjust the bucket angles depending on varying input angles while sending SAE-J1939 associated messages via CAN BUS to the EHPV. The different parameter values for the PID controller due to the gravity effect of the bucket were determined using a manual PID tuning method while assuming that the tractor travels on either an ascending slope or a descending slope. The developed PID control-based self-leveling system showed a mean of steady-state errors of within $1^{\circ}$ and a mean of delayed times of ~ 0.8s when the step input of $+20^{\circ}$ was given, implying that the developed system and control algorithm would be effective in maintaining the bucket angle at a certain value. Future studies include the improvement of the control algorithm to reduce such a time delay as well as the application of the developed algorithm to the FEL mounted on a tractor tested at a testing ground.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제8권8호
• /
• pp.2796-2813
• /
• 2014

This paper presents a new algorithm called the adaptive logarithmic increase and adaptive decrease algorithm (A-LIAD), which mainly addresses the Round-Trip Time (RTT) fairness problem in satellite networks with a very high propagation delay as an alternative to the current TCP congestion control algorithm. We defined a new increasing function in the fashion of a logarithm depending on the increasing factor ${\alpha}$, which is different from the other logarithmic increase algorithm adopting a fixed value of ${\alpha}$ = 2 leading to a binary increase. In A-LIAD, the ${\alpha}$ value is derived in the RTT function through the analysis. With the modification of the increasing function applied for the congestion avoidance phase, a hybrid scheme is also presented for the slow start phase. From this hybrid scheme, we can avoid an overshooting problem during a slow start phase even without a SACK option. To verify the feasibility of the algorithm for deployment in a high-speed and long-distance network, several aspects are evaluated through an NS-2 simulation. We performed simulations for intra- and interfairness as well as utilization in different conditions of varying RTT, bandwidth, and PER. From these simulations, we showed that although A-LIAD is not the best in all aspects, it provides a competitive performance in almost all aspects, especially in the start-up and packet loss impact, and thus can be an alternative TCP congestion control algorithm for high BDP networks including a satellite network.

• 제어로봇시스템학회논문지
• /
• 제19권5호
• /
• pp.481-487
• /
• 2013

This paper presents an FIR (Finite Impulse Response) fixed-interval smoothing filter for fast and exact estimating state variables of a discrete nonlinear system with modeling uncertainty. Conventional IIR (Infinite Impulse Response) filter and smoothing filter can estimate state variables of a system with an exact model when the system is observable. When there is an uncertainty in the system model, however, conventional IIR filter and smoothing filter may cause large errors because the filters cannot estimate the state variables corresponding to the uncertain model exactly. To solve this problem, FIR filters that have fast estimation properties and have robustness to the modeling uncertainty have been developed. However, there is time-delay estimation phenomenon in the FIR filter. The FIR smoothing filter proposed in this paper makes up for the drawbacks of the IIR filter, IIR smoothing filter, and FIR filter. Therefore, the FIR smoothing filter has good estimation performance irrespective of modeling uncertainty. The proposed FIR smoothing filter is applied to the integrated navigation system composed of a magnetic compass based DR (Dead Reckoning) and a GPS (Global Positioning System) receiver. Even when the magnetic compass error that changes largely as the surrounding magnetic field is modeled as a random constant, it is shown that the FIR smoothing filter can estimate the varying magnetic compass error fast and exactly with simulation results.

• 한국자동차공학회논문집
• /
• 제21권3호
• /
• pp.88-97
• /
• 2013

This paper presents a robust air-to-fuel ratio (AFR) control algorithm for managing exhaust gas recirculation (EGR) systems. In order to handle production tolerance, deterioration and parameter-varying characteristics of the EGR system, quantitative feedback theory (QFT) is applied for designing the robust AFR control algorithm. A plant model of EGR system is approximated by the first order transfer function plus time-delay (FOPTD) model. EGR valve position and AFR of exhaust gas are used as input/output variables of the plant model. Through engine experiments, parameter uncertainty of the plant model is identified in a fixed engine operating point. Requirement specifications of robust stability and reference tracking performance are defined and these are fulfilled by the following steps: during loop shaping process, a PID controller is designed by using a nominal loop transmission function represented on Nichols chart. Then, the frequency response of closed-loop transfer function is used for designing a prefilter. It is validated that the proposed QFT-based AFR control algorithm successfully satisfy the requirements through experiments of various engine operating points.