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IEEE 2017 IEEE Transactions on Vehicular Technology VT Vol.66 No.8
<P>Convergence and density evolution of a low-complexity iterative multiple-input multiple-output detection based on belief propagation over a ring-type pairwise graph are presented for binary data. The detection algorithm to be considered is effectively a forward-backward recursion and was originally proposed by Yoon and Chae in a work published in 2014, in which link-level performance, computational complexity, and convergence for Gaussian input were analyzed in detail. This paper presents the convergence proof and the density evolution framework for binary input to give an asymptotic performance in terms of average signal-to-interference-plus-noise ratio and bit error rate (BER) without channel coding. The BER curve obtained via density evolution shows a good match with the simulation results for uncoded BER in the paper by Yoon and Chae verifying the effectiveness of the analysis provided and the performance of the detection algorithm.</P>
Low-Complexity MIMO Detection Based on Belief Propagation Over Pairwise Graphs
Seokhyun Yoon,Chan-Byoung Chae IEEE 2014 IEEE Transactions on Vehicular Technology VT Vol.63 No.5
<P>This paper considers a belief propagation algorithm over pairwise graphical models to develop low-complexity iterative multiple-input multiple-output (MIMO) detectors. The pairwise graphical model is a bipartite graph where a pair of variable nodes are related by an observation node represented by the bivariate Gaussian function obtained by marginalizing the posterior joint probability density under the Gaussian input assumption. Specifically, we consider two types of pairwise models: the fully connected and ring-type. The pairwise graphs are sparse, compared with the conventional graphical model introduced by Bickson et al., insofar as the number of edges connected to an observation node (edge degree) is only two. Consequently, the computations are much easier than those of maximum likelihood (ML) detection, which are similar to the belief propagation (BP) that is run over the fully connected bipartite graph. The link level performance for non-Gaussian input is evaluated via simulations, and the results show the validity of the proposed algorithms. We also customize the algorithm with Gaussian input assumption to obtain the Gaussian BP run over the two pairwise graphical models, and for the ring-type, we prove its convergence to the linear minimum mean square error (MMSE) estimates. Since the maximum a posterior (MAP) estimator for Gaussian input is equivalent to the linear MMSE estimator, it shows the optimality of the scheme for Gaussian input.</P>
Study of Nitrogen High-Pressure Annealing on InGaZnO Thin-Film Transistors
Yoon, Seokhyun,Tak, Young Jun,Yoon, Doo Hyun,Choi, Uy Hyun,Park, Jin-Seong,Ahn, Byung Du,Kim, Hyun Jae American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.16
<P>We studied the effects of high-pressure annealing (HPA) on InGaZnO (IGZO) thin-film transistors (TFTs). HPA was proceeded after TFT fabrication as a post process to improve electrical performance and stability. We used N<SUB>2</SUB> as the pressurized gas. The applied pressures were 1 and 3 MPa at 200 °C. For N<SUB>2</SUB> HPA under 3 MPa at 200 °C, field-effect mobility and the threshold voltage shift under a positive bias temperature stress were improved by 3.31 to 8.82 cm<SUP>2</SUP>/(V s) and 8.90 to 4.50 V, respectively. The improved electrical performance and stability were due to structural relaxation by HPA, which leads to increased carrier concentration and decreased oxygen vacancy.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-16/am502571w/production/images/medium/am-2014-02571w_0005.gif'></P>
5G Standalone NR-Unlicensed (NR-U) 표준 및 연구 동향
윤석현(Seokhyun Yoon),고영채(Young-Chai Ko) 한국통신학회 2022 한국통신학회 학술대회논문집 Vol.2022 No.2
5G standalone NR-Unlicensed (NR-U)는 비면허대역의 Wi-Fi 와 공존을 하기위해 채널을 사용하려면 Wi-Fi 의 CSMA/CA 방식과 비슷한 Listen-Before-Talk (LBT)을 의무적으로 사용해야한다. 따라서 기지국과 단말이 송수신을 원할 때 항상 채널을 사용할 수 있는 Rel-15 NR 과는 달리 NR-U 에서는 Wi-Fi 가 채널을 사용하고 있으면 LBT 를 실패하여 송수신 할 수 없게 된다. 본 논문에서는 이러한 LBT 사용을 고려한 5G standalone NR-Unlicensed (NR-U)의 전반적인 표준 및 연구 동향을 조사한다.
Jang, Yoon Hee,Kochuveedu, Saji Thomas,Jang, Yu Jin,Shin, Hae-Young,Yoon, Seokhyun,Steinhart, Martin,Kim, Dong Ha Elsevier 2011 Carbon Vol.49 No.6
<P><B>Abstract</B></P><P>Ordered arrays of Au or Ag nanoparticles supported on two-dimensional graphitic carbon films were prepared by direct carbonization of stabilized asymmetric polystyrene-<I>block</I>-poly(4-vinyl pyridine) (PS-<I>b</I>-P4VP) inverse micellar films loaded with metal precursors. Crosslinked PS-<I>b</I>-P4VP thin film templates with metal precursors selectively distributed in P4VP domains were converted to carbonaceous thin films having well-defined, highly dispersed metal nanoparticle (NP) arrays by ultraviolet (UV) irradiation under vacuum and subsequent carbonization. Mesoporous carbon films were also obtained after extracting the metal NPs by sonication in selected solvents. PS-<I>b</I>-P4VP was employed not only as carbon source, but also as template for introducing metal NPs in a nanopatterned configuration. The characteristic features and properties of thus generated hybrid carbon nanostructures were investigated by microscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction measurement, and Raman spectroscopy.</P>