• 한국정보통신학회논문지
• /
• 제12권8호
• /
• pp.1505-1510
• /
• 2008

대규모 무선 센서 네트워크에서 센서 노드들이 배치된 이후에는 에너지 충전이나 노드의 재배치가 매우 어렵고, 일부 센서 노드들의 에너지가 고갈될 경우 전체 네트워크의 분할로 이어진다. 이러한 제한된 조건하에서 효율적인 에너지 소비를 고려한 데이터 전달은 라우팅 프로토콜 설계의 핵심 요소이다. 본 논문에서는 다수의 소스 노드와 이동성 싱크 노드를 가진 무선 센서 네트워크 환경에서 에너지 효율성을 제공하는 계층적 데이터 전달프로토콜인 HDD (Hierarchical Data Dissemination)를 제안한다. 계층적 데이터 전달 프로토콜은 싱크 노드가 데이터 수집의 중심노드라는 점을 착안하여 싱크 노드 중심의 데이터 전달 경로를 구성하고, 이 경로가 이중계층(Two-Tier)통신을 통해 유지 되도록 한다. 실험을 통해 HDD 라우팅 프로토콜과 기존에 제안된 TIDD (Two-Tier Data Dissemination) 라우팅 프로토콜의 전체 소모된 에너지량, 데이터 전송 시간 및 데이터 전송 성공률을 비교 분석하였다. 그 결과 본 논문에서 제안하는 HDD 라우팅 프로토콜은 TIDD 보다 약 1.5배에서 3배정도의 에너지 절감 효과를 확인할 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제8권2호
• /
• pp.424-442
• /
• 2014

Most recent research on iterative solutions for interference alignment (IA) presents solutions assuming channel reciprocity based on the suppression of interference from undesired sources by using an appropriate decoding matrix also known as a receiver combining matrix for multiple input multiple output (MIMO) interference channel networks and reciprocal networks. In this paper, we present an alternative solution for IA by designing precoding and decoding matrices based on the concept of signal leakage (the measure of signal power that leaks to unintended users) on each transmit side. We propose an iterative algorithm for an IA solution based on maximization of the signal-to-leakage-and-noise ratio (SLNR) of the transmitted signal from each transmitter. In order to make an algorithm removing the requirement of channel reciprocity, we deploy maximization of the signal-to-interference-and-noise ratio (SINR) in the design of the decoding matrices. We show through simulation that minimizing the leakage in each transmission can help achieve enhanced performance in terms of aggregate sum capacity in the system.

• Journal of Welding and Joining
• /
• 제26권6호
• /
• pp.67-73
• /
• 2008

Three-dimensional transient simulation of laser-GMA hybrid welding involving multiple physical phenomena is conducted neglecting the interaction effect of laser and arc heat sources. To reproduce the bubble and pore formations in welding process, a new bubble model is suggested and added to the established laser and arc welding models comprehending VOF, Gaussian laser and arc heat source, recoil pressure, arc pressure, electromagnetic force, surface tension, multiple reflection and Fresnel reflection models. Based on the models mentioned above, simulations of laser-GMA hybrid butt welding are carried out and besides the molten pool flow, top and back bead formations could be observed. In addition, the laser induced keyhole formation and bubble generation duo to keyhole collapse are investigated. The bubbles are ejected from the molten pool through its top and bottom regions. However, some of those are entrapped by solid-liquid interface and remained as pores. Those bubbles and pores are intensively generated when the absorption of laser power is largely reduced and consequently the full penetration changes to the partial penetration.

• International Journal of Aeronautical and Space Sciences
• /
• 제18권2호
• /
• pp.197-205
• /
• 2017

We investigate the slat noise generation mechanism by using large-eddy simulation (LES) and simple source modeling based on linearized Euler equations. An incompressible LES of an MD 30P30N three-element airfoil in the high-lift configuration is conducted at $Re_c=1.7{\times}10^6$. Using the total derivative of the hydrodynamic pressure (DP/Dt) acquired from the incompressible LES, representative noise sources in the slat cove region are characterized in terms of simple sources such as frequency-specific monopoles and dipoles. Acoustic radiation around the 30P30N multi-element airfoil is effectively computed using the Brinkman penalization method incorporated with the linearized Euler equation. The directivity pattern of $p^{\prime}_{rms}$ at $r=20c_{slat}$ in the multiple sources is closely compared to that obtained by the application of the LES/Ffowcs-Williams and Hawking's methods to the entire flow field. The power spectrum of p' at ${\theta}=290^{\circ}$ is in good agreement with the data reported in BANC-III, especially the broadband part of the spectrum with a decaying slope ${\propto}f^{-3}$.

• 한국전자통신학회논문지
• /
• 제16권3호
• /
• pp.457-464
• /
• 2021

본 논문은 3명의 사용자의 상관 정보원에 대한 non-SIC 비직교 다중 접속의 전송률 용적을 고찰한다. 먼저, non-SIC 3명의 사용자의 상관 정보원의 비직교 다중 접속의 전송률 용적의 폐쇄형 표현 식을 유도한다. 다음, 수치적 결과를 통해, 큰 상관 관계 계수에 대해서, non-SIC 3명의 사용자의 상관 정보원의 비직교 다중 접속의 전송률 용적이 SIC 3명의 사용자의 독립 정보원의 비직교 다중 접속의 전송률 용적보다 크다는 것을 보여준다. 또한, 다양한 비교를 통하여, 약 채널 사용자들의 상관 관계 계수들이 강 채널 사용자들의 상관 관계 계수들보다 전송률 용적에 미치는 영향이 더 크다는 것을 입증한다.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2000년도 추계종합학술대회 논문집(1)
• /
• pp.279-282
• /
• 2000

As digital systems continue to use components with faster edge rates and clock speeds, transmission of the digital information in these systems approaches the microwave realm. At these speeds digital signal fidelity becomes both a critical success factor and design challenge. The noise sources in digital systems include the noise in power supply, ground and packaging media due to simultaneous switching of drivers, signal reflections and distortions on single and multiple transmission lines. This paper presents theory, case studies and design considerations of gigabit interconnection for network and communication systems. The case studies show HSPICE and Ampredictor simulations of alternate approaches. Various subjects including skin effect and dielectric losses, interconnect simulations and crosstalks of connector, affected signal discontinuity, are addressed.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2002년도 하계종합학술대회 논문집(5)
• /
• pp.51-54
• /
• 2002

As digital systems continue to use components with faster edge rate and clock speeds, transmission of the digital information can take place many troubles. The increasing requirement for controlled impedance PCBs becomes both a critical success factor and a design challenge. Especially, the noise sources in digital system include the noise in power supply, ground and packaging due to simultaneous switching of signal, signal reflections and distortions on single and multiple transmission lines. This paper simulates the tracks controlled impedance with the test coupon. So, it can saves the design time and supports the economical PCB design.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2008년도 제39회 하계학술대회
• /
• pp.673-674
• /
• 2008

팬케이크 형태로 권선된 고온초전도 마그넷의 경우 모든 팬케이크 권선을 직렬로 연결하여 단일전원으로 여자할 경우 가장 큰 수직자장을 받는 팬케이크 권선에 의해 모든 팬케이크 권선의 임계전류가 제한된다. 본 논문에서는 별도전원으로 여자되는 YBCO 고온초전도 마그넷의 특성을 계산하여 단일전원으로 여자되는 경우와 비교하였다. 계산 결과 별도전원으로 여자되는 YBCO 고온초전도 마그넷의 모든 팬케이크 권선들은 각각의 임계전류까지 통전되었으며 중심자장의 세기가 단일전원으로 여자되는 마그넷보다 증가함을 확인하였다.

• Journal of the Optical Society of Korea
• /
• 제8권4호
• /
• pp.156-162
• /
• 2004

The spectroscopic model is proposed to analyze the gain bandwidth of a fiber Raman amplifier (FRA) with a multiple wavelength pumping scheme based on Raman gain theory. The oscillatory lineshape, which is the analytic function to analyze Raman gain spectra, allows us to estimate the gain bandwidth of the FRA. Based on the proposed theoretical modeling, we design and analyze the characteristics of the FRA using the combined multiwavelength pumping sources. We achieved the extended gain bandwidth of the FRA over 80 nm with the small gain ripple less than 0.5 dB. Threshold pumping power and effective noise figure for the FRA can be also analyzed by using the proposed model, which is also applicable for versatile fibers with other doping materials. The proposed analysis method can be useful for the design of FRA with the multiwavelength pumping scheme.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2008년도 추계학술대회 논문집
• /
• pp.1435-1440
• /
• 2008

High-speed train under development is a type of EMU(electric multiple units). Since power sources like motors and gears are distributed in the high-speed EMU, the high-speed EMU generates vibration and sound more than the articulated high-speed train. Vibration of vehicle, vibration between rails and wheels, hunting of bogie and snake motion reduce ride comfort. In this paper, to decrease the vibration of the articulated high-speed train, improvements were presented using an analytical model and a simulation model. The simulation model of the high-speed EMU was designed on the basis of the korean high-speed train and the design parameters for ride comfort were showed and the dynamic characteristics of the vehicle was understood. To consider the characteristics of the vehicle suspension, the analytical model was designed and the simulation model was verified with it.