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Collinear Deflection Method를 이용한 열전도계수 측정에 관한 이론적 연구
정대식(Daesik Jeong),오주현(Juhyun Oh),김현정(Hyunjung Kim),유재석(Jaisuk Yoo) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Collinear deflection method is one of photothermal deflection methods. In the measurement process, both of pump beam and probe beam are irradiated vertically on the transparent sample. And probe beam is deflected by refractive index variation due to the temperature gradient inside samples. The purpose of this study is to measure the thermal property of thin film materials using collinear deflection method. Especially, theoretical basis is built for thermal property measurement using collinear deflection method. From this, parameters such thickness of sample, modulation frequency and so on, that can influence the investigated measurement accuracy of collinear deflection method.
Eunsung Oh,Seungyoup Han,Choongchae Woo,Daesik Hong IEEE 2008 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.56 No.10
<P>This letter presents a call admission control (CAC) strategy for system throughput maximization in wireless uplink systems. This strategy considers not only the call-level quality of service (QoS) (i.e., blocking probability) but also the packet-level QoS (i.e., outage probability). Using the statistical co-channel interference (CCI) model and state diagram, the outage probability and the blocking probability are investigated as a function of the relative traffic load. We formulate the CAC strategy problem based on relative traffic load, and suggest a solution. The numerical results show that maximum system throughput can be achieved by controlling the relative traffic load. In addition, we illustrate the region where system throughput is constrained by call- and packet-level QoSs. This examination shows that the call and packet-level QoSs must be considered together to achieve maximum system throughput.</P>
릴레이 기반의 OFDMA 시스템에서 전송량 증대를 위한 간략화 된 자원 할당 방법
오은성(Eunsung Oh),주형식(Hyungsik Ju),한승엽(Seungyoup Han),홍대식(Daesik Hong) 大韓電子工學會 2009 電子工學會論文誌-TC (Telecommunications) Vol.46 No.9
본 논문은 릴레이 시스템을 기반으로 한 직교 분할 다중 반송파 다중 접속 방식(OFDMA, Orthogonal Frequency Division Multiple Access)에서 전송량을 증대를 위한 자원 할당 방법에 관한 것이다. 최적화 문제를 기반으로 하는 자원 할당 방법은 할당 가능한 자원에 대한 검색 과정을 수반하기 때문에 높은 복잡도를 갖는다. 본 논문에서는 복잡도를 줄이기 위하여 세 단계의 자원 할당 방법을 제안한다. 각각의 단계에서 릴레이, 주파수, 시간 자원이 독립적으로 할당되며, 자원을 분리하여 할당함에 따라 복잡도를 줄일 수 있다. 실험 결과를 통하여 제안하는 방법이 복잡도를 줄이면서 최적화 성능에 근접할 수 있음을 보인다. This paper presents a simple resource allocation scheme for throughput enhancement in relay based orthogonal frequency division multiple access (OFDMA) cellular systems. The resource allocation schemes, which are based on the optimization problem, have high computational complexity. That is why a searching process is required on the overall allocable resources. Since these schemes should be performed in real time, we propose a simple resource allocation scheme which has very low computational complexity. Firstly, we formulate the optimization problem and draw observations for throughput maximization. Based on observations, we propose a three step allocation scheme that separates the allocable resources into three (i.e. relay, frequency and time). By doing so, the computational complexity can be reduced. Simulation results show that the proposed scheme has near-optimum performance in spite of its low computational complexity.
OFDMA 시스템에서 그리디 방법을 기반으로 한 동적 채널 할당 알고리즘의 성능분석
오은성(Eunsung Oh),한승엽(Seungyoup Han),홍대식(Daesik Hong) 대한전자공학회 2007 電子工學會論文誌-TC (Telecommunications) Vol.44 No.11
본 논문은 직교 분할 다중 반송파 다중 접속 방식(OFDMA, Orthogonal Frequency Division Multiple Access)에서 그리디 방법(GA, Greedy Approach)을 사용한 동적 채널 할당 알고리즘의 성능분석에 관한 것이다. GA를 기반으로 한 동적 채널 할당의 경우 사용자간의 다이버시티 효과를 통하여 성능 이득을 얻을 수 있다. 본 논문에서는 동적 채널 할당 알고리즘에서 다중 사용자 다이버시티 계수인 할당 가능한 사용자 수(NAU, Number of Allocable Users)를 모델링하고, 이를 통하여 GA를 기반으로 한 동적 채널 할당 알고리즘의 성능(실패 확률 및 데이터 전송량)을 분석한다. 분석된 결과를 기반으로 GA를 기반으로 한 동적 채널 할당 알고리즘의 성능을 최대화 할 수 있는 조건을 제시할 수 있다. This paper presents a performance analysis of dynamic channel allocation (DCA) based on the greedy approach (GA) for orthogonal frequency division multiple access (OFDMA) systems over Rayleigh fading channels. The GA-based DCA achieves its performance improvement using multi-user diversity. We analyze the statistics of the number of allocable users (NAU), which represents the multi-user diversity order at each allocation process. The derived statistics are then used to analyze the performance of GA-based DCA. The analysis results show that the number of subcarriers allocated to each user must be equal to achieve the maximum system performance (i.e., based on outage probability and data throughput).
Hyungsik Ju,Eunsung Oh,Daesik Hong IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.8
<P>This letter presents a new full duplex relay (FDR) system that features more efficient use of time resource and antennas. The proposed FDR system is constructed based on time and antenna-sharing and elimination of underlying interference. The underlying interference caused by time- and antenna-sharing is eliminated using precoding. We propose a design for the precoder and decoder, and investigate the achievable rate of the proposed FDR system when the precoder and decoder are applied. Simulation results show improved achievable rate and BER performances with the proposed FDR system compared to half duplex and conventional full duplex relay systems.</P>
Youngbo Cho,Eunsung Oh,Daesik Hong IEEE 2009 IEEE Transactions on Vehicular Technology VT Vol.58 No.3
<P>This paper introduces a novel analytical model for analyzing the performance of handoff algorithms based on absolute and relative signal strength measurements. The performance is analyzed in multicell and multisector environments where cochannel interference (CCI) is present. The model presented in this paper accounts for the distinct features of intersector handoff compared with intercell handoff. Numerical results show that the performance metrics are affected by the CCI level. The occurrence condition of unnecessary handoffs in multisector systems is also presented.</P>
Seungyoup Han,Eunsung Oh,Myeongsu Han,Choongchae Woo,Daesik Hong IEEE 2009 IEEE Transactions on Vehicular Technology VT Vol.58 No.3
<P>In this paper, we present an accurate analytical method for an asynchronous time-hopping (TH) ultrawideband (UWB) system using multistage interference cancellation (MIC) in multipath fading channels. To model the asynchronous transmission, we first investigate the chip-asynchronous case and extend the results of chip-asynchronous transmission into completely asynchronous transmission as a more general environment. Specifically, the approximate closed-form expression is derived for numerically calculating the average bit-error probability (BEP) of the MIC receivers, which are based on the hard-decision (HD) and soft-decision (SD) detections, respectively. In performing the analysis, the effect of multiple-access interference (MAI) is modeled as a Gaussian process. The results of an interference cancellation (IC) receiver as a function of the ratio between the two types of processing gain-1) pulse combining gain <I>N</I> <SUB>s</SUB> and 2) pulse spreading gain <I>N</I> <SUB>c</SUB>-are analyzed and compared under the constraint that the total processing gain of the system is large and fixed. To build up intuitive knowledge, some remarks on the analytic results are presented to describe the design criterion for the interference suppression. In numerical results, the theoretical analysis is verified via comparison with simulation results in terms of the number of IC stages, the set of cancellation parameters, and the number of users.</P>
Asymmetric diversity modulation scheme in wireless fading relay channels
Jaemin Han,Eunsung Oh,Hyungsik Ju,Daesik Hong IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.7
<P>In this paper, we propose an asymmetric diversity modulation (ADM) scheme for a single-source relay system that utilizes the relay's higher transmission ability as a form of diversity. To achieve this, the proposed method transmits multiple source bits over a high-order modulating relay as a way to provide additional time diversity. The spatial and time diversity then undergo 'bit'-based combining at the destination. Using the proposed 'bit'-based channel combining method, we derive the theoretical bit error rate (BER) for such a system. Moreover, we investigate the fact that the proposed scheme shows a performance trade-off between bit power and time diversity resulting from the reduced bit power caused by a high-order modulating relay.</P>