http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Filter-and-Forward Transparent Relay Design for OFDM Systems
Donggun Kim,Junyeong Seo,Youngchul Sung IEEE 2013 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.62 No.9
<P>In this paper, the filter-and-forward (FF) relay design for orthogonal frequency-division multiplexing (OFDM) transmission systems is considered for improving system performance over simple amplify-and-forward (AF) relaying. Unlike conventional OFDM relays performing OFDM demodulation and remodulation, to reduce processing complexity, the proposed FF relay directly filters the incoming signal in the time domain with a finite impulse response (FIR) and forwards the filtered signal to the destination. Three design criteria are considered for optimizing the relay filter. The first criterion is the minimization of the relay transmit power subject to per-subcarrier signal-to-noise ratio (SNR) constraints, the second criterion is the maximization of the worst subcarrier channel SNR subject to source and relay transmit power constraints, and the third criterion is the maximization of the data rate subject to source and relay transmit power constraints. It is shown that the first problem reduces to a semi-definite programming (SDP) problem by semi-definite relaxation (SDR), and the solution to the relaxed SDP problem has rank one under a mild condition. For the latter two problems, the problem of joint source power allocation and relay filter design is considered, and an efficient algorithm is proposed for each problem based on alternating optimization and the projected gradient method (PGM). Numerical results show that the proposed FF relay significantly outperforms simple AF relays with an insignificant increase in complexity. Thus, the proposed FF relay provides a practical alternative to the AF relaying scheme for OFDM transmission.</P>
Activation of Aerosols in Shallow Cumulus Clouds Simulated by a Lagrangian Cloud Model
Donggun Oh,Yign Noh 한국기상학회 2021 한국기상학회 학술대회 논문집 Vol.2021 No.4
The activation process and its parameterization in shallow cumulus clouds are investigated by using Lagrangian cloud model (LCM), in which activations of Lagrangian aerosol particles are simulated explicitly. Simulations are carried out for the cloud field simulation based on Barbados Oceanographic and Meteorological Experiment (BOMEX) observation with different CCN concentration N<sub>0</sub> while the collision process is not included. When the activation of aerosols is divided into two groups, aerosols entrained by the updraft at cloud base (CB) and by the lateral entrainment (LE) above the cloud base, the contribution to activation from aerosols by LE is in the range 40-50% while it increase with N<sub>0</sub>. In-cloud activation is negligible. The size distribution of activated droplets shows the mean size decreasing with height and the narrower variance for larger N<sub>0</sub> The dependence of activation on supersaturation S reveals that both C and are much larger for aerosols from CB in the Twomey formula N<sub></sub> = CS<sup> </sup>. The comparison of horizontal mean profiles from LCM and bulk models with two different parameterizations of activation shows that, in bulk models, in-cloud N<sub>c</sub> is larger, the mean volume radius of droplets is smaller at the upper cloud, although the total N<sub>c</sub> is in better agreement. It is due to the fact that turbulent diffusion of droplets across the cloud edge in the bulk model induces more diffused horizontal distribution of q<sub>c</sub> and N<sub>c</sub>.
User centered gesture development for smart lighting
Donggun Park,Yu Shin Lee,Sejin Song,Ilsun Rhiu,Sanghyun Kwon,Yongdae An,Myung Hwan Yun 한국HCI학회 2016 한국HCI학회 학술대회 Vol.2016 No.1
The aim of this study is to investigate hand gesture expression and to understand it when controlling smart lighting system. The technology development has brought us the smart device which we can control multifunction of one or more systems. In order to fully utilize the functions, however, we need Natural User Interface (NUI) and intuitive control hand gesture. Therefore we conducted an experiment of hand gesture expression on 20 subjects to investigate and identify what kinds of hand gestures can be used to control the smart lighting system. The results identify categorization of hand gestures into three types. Also, differences between the gesture types were identified. In addition, the use of hand such as dominant hand and both hands affect the capability of people to express the hand gesture. This preliminary study can identify many important issues regarding hand gesture based interface for the smart lighting system. It can be further improved by verifications with consideration of context of use, preference test of hand, application of different devices or systems, and gesture evaluation.
Two-Stage Beamformer Design for Massive MIMO Downlink By Trace Quotient Formulation
Donggun Kim,Gilwon Lee,Youngchul Sung Institute of Electrical and Electronics Engineers 2015 IEEE Transactions on Communications Vol. No.
<P>In this paper, the problem of outer beamformer design based only on channel statistic information is considered for two-stage beamforming for multi-user massive MIMO downlink, and the problem is approached based on signal-to-leakage-plus-noise ratio (SLNR). To eliminate the dependence on the instantaneous channel state information, a lower bound on the average SLNR is derived by assuming zero-forcing (ZF) inner beamforming, and an outer beamformer design method that maximizes the lower bound on the average SLNR is proposed. It is shown that the proposed SLNR-based outer beamformer design problem reduces to a trace quotient problem (TQP), which is often encountered in the field of machine learning. An iterative algorithm is presented to obtain an optimal solution to the proposed TQP. The proposed method has the capability of optimally controlling the weighting factor between the signal power to the desired user and the interference leakage power to undesired users according to different channel statistics. Numerical results show that the proposed outer beamformer design method yields significant performance gain over existing methods.</P>
Donggun Lee,Youn Sang Kim 한국진공학회 2021 한국진공학회 학술발표회초록집 Vol.2021 No.2
The amorphous indium-gallium-zinc oxide (IGZO) Schottky contact is widely demanded for switching/sensing purpose electronic devices. [1] However, noble metal/IGZO Schottky contact often induces chemical reaction at the interface between the noble metal and IGZO. [2] Here in, we present a new approach to form the ideal Schottky contact via defect-induced physical interface modification (DIPlM). This defect-induced physical interface modifier enables a high-quality IGZO growth with reduced oxygen vacancies at the interface, improving Schottky properties such as rectification ratios and ideality factor.
Electrical Properties of Crystallized 30B2O3-70V2O5 Glass
Donggun Gwoo,김태희,한경석,Wongyu Choi,김종환,류봉기 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.3
30B2O3-70V2O5 binary-system glass was prepared, and variations in structural and electrical property were examined using crystallization. While different related research studies exist, few have evaluated the variations in the structure and properties with changes in the crystallization rate. 30B2O3-70V2O5 glass was annealed in the graphite mold above the glass transition temperature for 2 h and heat-treated at each crystallization temperature for 3 h. 30B2O3-70V2O5 glass showed predominantly electronic conductive characteristic. FTIR was preferentially used for analyzing the structural changes of B-O bond after crystallization, while XRD was utilized to verify the inferred changes in the structure array (BO3 + V2O5 ↔ BO4 + 2VO2). Structural changes induced by heat treatment were confirmed by analyzing the molecular volume determined from the sample density, and conductance was measured to correlate structural and property changes. Conductivity is discussed based on the migration of vanadate ions with different valence states because of the increase in VO2 crystallinity at 130°C, which, however, was not observed at 170°C. After VO2 structures were reinforced,a 1.8-fold increase in conductance was observed (as compared to the annealed sample) after crystallization at 130°C for 3 h.