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Characterization of Interference in OFDMA Small-Cell Networks
Yoon, Jongwon,Arslan, Mustafa Y.,Sundaresan, Karthikeyan,Krishnamurthy, Srikanth V.,Banerjee, Suman IEEE 2018 IEEE Transactions on Vehicular Technology VT Vol.67 No.9
<P>The increase in mobile Internet access is pushing mobile network operators toward deploying smaller cells (<I> femtocells</I>) and sophisticated air interface technologies, Orthogonal Frequency Division Multiple Access (OFDMA). The expected high density of deployment and uncoordinated operations of femtocells, however, make interference management both critical and extremely challenging. A significant challenge stems from the fact that femtocells have to use the same synchronous access technology as traditional macrocells. Given this, understanding the impact of the multitude of design choices (originally tailored to well-planned macrocellular networks) on interference management forms an essential first step toward designing efficient solutions for next-generation femtocell networks. This in turn is the focus of our paper. With the help of extensive measurements from our femtocell testbed, we characterize the impact of various system design choices on interference in OFDMA femtocell deployments. The design choices that we examine are categorized across three broad dimensions: 1) <I>resource isolation</I> at the logical (MAC) level across femtocells, 2) <I>resource mapping</I> through sub-channelization at the physical (PHY) level within each femtocell, and 3) <I>synchronization</I> (or lack thereof) between interfering cells. Based on the insights from our measurement study, we discuss several implications on the choice of system design features for multicell operations. We also provide guidelines for the design of efficient interference management solutions for femtocell networks.</P>
Nonvolatile Memory Functionality of ZnO Nanowire Transistors Controlled by Mobile Protons
Yoon, Jongwon,Hong, Woong-Ki,Jo, Minseok,Jo, Gunho,Choe, Minhyeok,Park, Woojin,Sohn, Jung Inn,Nedic, Stanko,Hwang, Hyungsang,Welland, Mark E.,Lee, Takhee American Chemical Society 2011 ACS NANO Vol.5 No.1
<P>We demonstrated the nonvolatile memory functionality of ZnO nanowire field effect transistors (FETs) using mobile protons that are generated by high-pressure hydrogen annealing (HPHA) at relatively low temperature (400 °C). These ZnO nanowire devices exhibited reproducible hysteresis, reversible switching, and nonvolatile memory behaviors in comparison with those of the conventional FET devices. We show that the memory characteristics are attributed to the movement of protons between the Si/SiO<SUB>2</SUB> interface and the SiO<SUB>2</SUB>/ZnO nanowire interface by the applied gate electric field. The memory mechanism is explained in terms of the tuning of interface properties, such as effective electric field, surface charge density, and surface barrier potential due to the movement of protons in the SiO<SUB>2</SUB> layer, consistent with the UV photoresponse characteristics of nanowire memory devices. Our study will further provide a useful route of creating memory functionality and incorporating proton-based storage elements onto a modified CMOS platform for FET memory devices using nanomaterials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-1/nn102633z/production/images/medium/nn-2010-02633z_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn102633z'>ACS Electronic Supporting Info</A></P>
Joint Multicell Beamforming and Client Association in OFDMA Small-Cell Networks
Yoon, Jongwon,Sundaresan, Karthikeyan,Khojastepour, Mohammad Ali Amir,Rangarajan, Sampath,Banerjee, Suman IEEE Computer Society 2016 IEEE TRANSACTIONS ON MOBILE COMPUTING Vol.15 No.9
<P>Small cells form a critical component of next generation cellular networks, where spatial reuse is the key to higher spectral efficiencies. Interference management in the spatial domain through beamforming allows for increased reuse without having to sacrifice resources in the time or frequency domain. Existing beamforming techniques for spatial reuse, being coupled with client scheduling, face a key limitation in practical realization, especially with OFDMA small cells. In this context, we argue that for a practical spatial reuse system with beamforming, it is important to decouple beamforming from client scheduling. Further, we show that jointly addressing client association with beamforming is critical to maximizing the reuse potential of beamforming. Towards our goal, we propose ProBeam - a system for multi-cell beamforming and client association in OFDMA small cell networks. ProBeam incorporates two key components - a low complexity, highly accurate SINR estimation module that helps determine interference dependencies for beamforming between small cells; and an efficient, low complexity joint client association and beam selection algorithm for the small cells that accounts for scheduling at the small cells without being coupled with it. We have prototyped ProBeam on a WiMAX-based network of four small cells. Our evaluations reveal the accuracy of our SINR estimation module to be within 1 dB, and the reuse gains from joint client association and beamforming to be as high as 115 percent over baseline approaches.</P>
Jongwon Cho,Seungjun Ryu,Hyun-Jun Jang,Jeong-Yoon Park,Yoon Ha,Sung-Uk Kuh,Dong-Kyu Chin,Keun-Su Kim,Yong-Eun Cho,Kyung Hyun Kim 대한신경외과학회 2023 Journal of Korean neurosurgical society Vol.66 No.1
Objective : This study aimed to investigate the efficacy of transverse process (TP) hook system at the upper instrumented vertebra (UIV) for preventing screw pullout in adult spinal deformity surgery using the pedicle Hounsfield unit (HU) stratification based on K-means clustering. Methods : We retrospectively reviewed 74 patients who underwent deformity correction surgery between 2011 and 2020 and were followed up for >12 months. Pre- and post-operative data were used to determine the incidence of screw pullout, UIV TP hook implementation, vertebral body HU, pedicle HU, and patient outcomes. Data was then statistically analyzed for assessment of efficacy and risk prediction using stratified HU at UIV level alongside the effect of the TP hook system. Results : The screw pullout rate was 36.4% (27/74). Perioperative radiographic parameters were not significantly different between the pullout and non-pullout groups. The vertebral body HU and pedicle HU were significantly lower in the pullout group. K-means clustering stratified the vertebral body HU ≥205.3, <137.2, and pedicle HU ≥243.43, <156.03. The pullout rate significantly decreases in patients receiving the hook system when the pedicle HU was from ≥156.03 to < 243.43 (p<0.05), but the difference was not statistically significant in the vertebra HU stratified groups and when pedicle HU was ≥243.43 or <156.03. The postoperative clinical outcomes improved significantly with the implementation of the hook system. Conclusion : The UIV hook provides better clinical outcomes and can be considered a preventative strategy for screw-pullout in the certain pedicle HU range.
한국어 쓰기 교육을 위한 ‘형용사+-어지다’ 구성의 사용 양상에 대한 연구 -자기소개서 분석을 중심으로-
윤종원 ( Jongwon Yoon ) 사단법인 아시아문화학술원 2019 인문사회 21 Vol.10 No.6
본고는 외국인 학습자를 위해 한국인 예비 대학생의 자기소개서 말뭉치 분석을 통해 ‘형용사+-어지다’ 구문의 결합 및 사용 양상을 어휘적으로 분류하는 것을 목적으로 한다. 말뭉치 분석 결과 과거 경험을 비교하는 표현이 가장 많이 사용되었다. 2회 이상 사용된 형용사는 총 21개로 ‘-어지다’ 보조용언 구성과 결합하여 108회 중 78%인 84회의 상태 변화 의미를 기술하는 데 사용되었고, 상황 맥락은 ‘교내외 활동’과 ‘학업/학습’을 묘사할 때 가장 많이 사용됐다. 이 연구를 통해 외국인 학습자에게 보조용언 교수 시 선행 용언의 어휘 정보와 서술어의 상황 맥락 그리고 공기하는 부사 정보 등을 종합적으로 제공하는 어휘·문법적 교수가 가능하다. 후속 연구에서는 부사어 목록과 ‘-어지다’와 결합하는 동사 목록의 연구도 필요하다. The purpose of this study is to lexically classify the combination and usage of the phrase ‘adjective+-eojida’ through the analysis of the corpus of prospective university students. As a result of the corpus analysis, expressions that compare one’s past experiences were used the most. A total of 21 adjectives, used more than once, were used to describe the meaning of 84 state changes, 78% of 108, combined with the ‘-eojida’ adjective composition. And the context of the situation was most often used to describe ‘in or out of school activities’ and ‘study.’ In this study, we propose a lexical approach teaching method that comprehensively provides foreign learners with lexical knowledge of lexicon, context of situation of narrative language, and adverbials information. In addition to the collocating adverbs, we need to investigate the list of adverbs and studies of verb lists combined with ‘-eojida’.