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Achievable Degree of Freedom on K-User Y Channels with Heterogeneous Messages
Kwangwon Lee,Namyoon Lee,Inkyu Lee IEEE 2013 IEEE COMMUNICATIONS LETTERS Vol.17 No.2
<P>In this letter, we introduce a new system model for a multi-way communication where multiple users exchange information with each other by sharing an intermediate relay with multiple antennas. Particularly, we focus on the system where each user intends to send multiple unicast messages for dedicated users and a single multicast message for a group of users. We refer to this system as a K-user MIMO Y channel with heterogenous messages. For this channel, we propose a new cooperative beamforming method and study an achievable degree of freedom (DOF) using this scheme.</P>
Achievable Degrees of Freedom on K-user Y Channels
Kwangwon Lee,Namyoon Lee,Inkyu Lee IEEE 2012 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.11 No.3
<P>In this paper, we consider K-user Y channels where K users simultaneously exchange messages with each other via an intermediate relay. Degrees of freedom (DOF) of Y channels with multiple antennas is not known in general. Investigation of the feasibility conditions of signal space alignment for network coding is an initial step for addressing this open problem. We verify that when user i with M_i antennas sends K-1 independent messages to the other users through a relay with N antennas and each message achieves the DOF of d, the total DOF of dK (K-1) is attained if M<SUB>i</SUB> ≥ d(K-1), N ≥ {dK(K-1)/2} and N<; min {M<SUB>i</SUB>+M<SUB>j</SUB> -d|∀ i ≠ j}. It is accomplished by adopting the signal space alignment for the network coding during both the multiple access phase and the broadcast phase. It is shown that the proposed scheme obtains not only a network coding gain but also an alignment gain in terms of the normalized DOF, as K → ∞. Also for Y channels where all nodes have a single antenna, we show that the DOF of 2 is achieved regardless of the number of users by using the rational dimension framework.</P>
이시진(Sijin Lee),배상윤(Sangyoon Bae),이광원(Kwangwon Lee),이강인(Kangin Lee),이종훈(Jonghoon Lee) 한국생산제조학회 2011 한국생산제조시스템학회 학술발표대회 논문집 Vol.2011 No.4
레이저를 이용하여 유기물 필름을 유기발광 다이오드(OLED) 기판에 입히는 방법에는 레이저 승화법(laser induced pattern-wise sublimation;LIPS)과 레이저 열전사법(laser induced thermal printing;LITI)이 있다. 이 두 방법에 사용하는 공여 기판에 대하여 공여기판과 수여기판 사이의 두께를 조절하면서 레이저 입사 시간에 따른 유기 필름의 승화와 OLED 기판에 부착된 유기 필름을 광학현미경, 형광현미경, 원자현미경을 이용하여 관측하고 유기물이 이동하는 과정을 분석하였다.
Fabrication of metal nanoparticles using hydroxylated ionic liquids.
Lee, Kwangwon,Kim, Sanghyun,Han, Da-Hee,Hong, Yeon Ki,Lee, Hyunjoo,Kang, Jeong Won,Kim, Ki-Sub American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.1
<P>Metal nanoparticles were successfully synthesized from the self-regulated reduction of hydroxylated ionic liquids in aqueous phase without additives. A new water-phase synthesis of gold and palladium nanoparticles using N-(2-hydroxyethyl)-N-methylmorpholinium tetrafluoroborate is described. Transmission electron microscopy was performed to characterize the metal nanoparticles. The average sizes of the gold and palladium nanoparticles were 4.3 nm and 3.2 nm, respectively. Hydroxylated ionic liquids served as both reductants and protective agents, significantly simplifying the preparation of nanoparticles. The produced particles were highly crystalline in structure with a face-centered cubic (fcc) lattice. Finally, we showed preliminary results that suggest different hydroxylated ionic liquids can also be used to prepare various metal nanoparticles.</P>
A Compact Wideband Crossover Coupler with Lumped Elements
Kwangwon Park,Hyunkyu Lee,Iljin Lee,In-Woong Kang,Sanggeun Jeon 한국전자파학회JEES 2019 Journal of Electromagnetic Engineering and Science Vol.19 No.2
A compact wideband crossover coupler with fully lumped elements is presented. To achieve a wideband operation, a three-section branch-line structure is employed for the crossover coupler. The size is significantly minimized by replacing transmission lines with lumped elements. The measurement shows that the insertion loss, isolation, and return loss are 1.7 ㏈, 24 ㏈, and 14.5 ㏈, respectively, at 2 ㎓. The fractional bandwidth of 20-㏈ isolation and 3-㏈ insertion loss is 27%. The size of the crossover coupler is 11 ㎜ × 9 ㎜, which corresponds to 0.07λ × 0.06λ at 2 ㎓. This is significantly smaller than a conventional three-section branch-line crossover coupler by 95%.
Performance Analysis of Generating Function Approach for Optimal Reconfiguration of Formation Flying
Lee, Kwangwon,Park, Chandeok,Park, Sang-Young 한국우주과학회 2013 Journal of Astronomy and Space Sciences Vol.30 No.1
The use of generating functions for solving optimal rendezvous problems has an advantage in the sense that it does not require one to guess and iterate the initial costate. This paper presents how to apply generating functions to analyze spacecraft optimal reconfiguration between projected circular orbits. The series-based solution obtained by using generating functions demonstrates excellent convergence and approximation to the nonlinear reference solution obtained from a numerical shooting method. These favorable properties are expected to hold for analyzing optimal formation reconfiguration under perturbations and non-circular reference orbits.
Effect of Laser Beam Trajectory on Donor Plate in Laser Induced Thermal Printing Process
Kwangwon Lee,Sijin Lee,권진혁,이종훈 한국광학회 2011 Current Optics and Photonics Vol.15 No.4
Organic (Alq3) film, which was coated on a donor plate, was transferred to an organic light emitting diode (OLED) substrate with help of heat generated by a dithering laser beam. The laser beam was diffracted in an acousto-optic modulator (AOM), then focused on the laser-to-heat converting layer of the donor plate; the focused spot followed trajectories guided by rotation of a Galvano-mirror. Three different functional waveforms, sine wave, square wave, and saw tooth wave were applied to the AOM as modulation signal to generate the dithering beam. The fluorescence microscope images of the donor plate showed that the patterns of removed Alq3 film were affected considerably by the modulation waveforms and the phase difference between adjacent dithering beams. Further, the printed images of Alq3 film on the OLED substrate were different from the patterns of removed Alq3 film. Atomic force microscope images indicated that not only direct transfer but also deposition by sublimated vapor of Alq3 contributed to the pattern formation. Printed patterns affected considerably the electricity-to-light conversion characteristics of OLEDs. For uniform transfer, not only the phase relation of dithering beam lines but also adequate waveform were important.