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Minimum MSE Design for Multiuser MIMO Relay
Seunghun Jang,Janghoon Yang,Dong Ku Kim IEEE 2010 IEEE communications letters Vol.14 No.9
<P>We study a joint optimal design of transceiver and relaying architecture in terms of mean square error (MSE) performance for multi-user multiple-input multiple-output (MIMO) relaying system. We show a duality relationship in the design of MSE-optimal transceiver and relaying architecture. Based on that, we devise an alternating algorithm, which converges and provides a suboptimal joint design of transceiver and relaying. By simulation, we show that the proposed joint design improves on the average MSE performance of the existing transceiver and relaying architectures.</P>
Jang, Seunghun,Im, Jino,Choi, Min,Lee, Jeong-O.,Kong, Ki-jeong,Chang, Hyunju Elsevier 2017 Carbon Vol.119 No.-
<P>The electronic density of states (DOS) in carbon nanotubes (CNTs) was recently measured using a structure comprising a single CNT-based field effect transistor (FET) device with an indium (In) electrode. Here, we report the bonding characteristics and electronic structure of the contact interface between Group 13 metals (In, Ga, Al) and (8,0) semiconducting CNTs using first-principles density functional theory (DFT) calculations. Our calculation results showed that CNTs in contact with Al, Ga, or In surfaces display lower binding energies to their contact metal surfaces than that of Pd surface while also preserving their original electronic properties. These results originate from the absence of d-orbitals in the Group 13 metals near the Fermi level, the large equilibrium distance, and the deficiencies in electron charge density at the metal surfaces. This study deepens our understanding of the contact properties between Group 13 metals and CNTs. (C) 2017 Elsevier Ltd. All rights reserved.</P>
MSE Duality for Multi-User MIMO Relay System
Seunghun Jang,Young-Min Cho,Janghoon Yang,Dong Ku Kim IEEE 2012 IEEE communications letters Vol.16 No.11
<P>This paper shows how uplink (UL)-downlink (DL) mean square error (MSE) duality holds in a single relay aided multi-user multiple-input multiple-output (MU-MIMO) system. Specifically, it is shown that the MSE duality holds for three levels of MSE which are sum-MSE (SMSE), per user MSE, and per stream MSE. For each case of duality level, we consider both total power constraint and separate power constraint. We also provide a conversion method which transforms a given transceiver and scale factor in DL to equivalent ones in UL for each case of duality level and each case of power constraint.</P>
Jang, Seunghun,Joo, Beom Soo,Kim, Sung,Kong, Ki-jeong,Chang, Hyunju,Yu, Byung Deok,Han, Moonsup The Royal Society of Chemistry 2015 Journal of Materials Chemistry C Vol.3 No.33
<▼1><P>The investigation of photoluminescence and first-principles calculations clarifies the relationship between the hydrogen passivation of N at the interface and the observed band gap reduction of the embedded Si nanocrystal (NC) for Si NC/SiO2 multilayers containing interfacial nitrogens after proton irradiation.</P></▼1><▼2><P>Si nanocrystal (NC)/SiO2 multilayers containing interfacial nitrogens are formed by radiofrequency magnetron-sputtering and post-annealing. By analyzing the photoluminescence (PL) of the multilayer structures after proton irradiation (PI), we found that the peak at ∼740 nm was shifted toward shorter wavelengths and that its intensity was considerably suppressed. Furthermore, a new peak simultaneously appeared at ∼500 nm. We interpret that PI not only modifies the shapes of the Si NCs and generate defects at the NC/SiO2 interface, but also induces simultaneously hydrogen passivation (HP) of interfacial nitrogens due to the attenuated protons. To investigate the relationship between the HP of N at the Si NC/SiO2 interface and the observed band gap reduction of Si NC structures within the SiO2 matrix, we modeled the atomic configurations at the interface and applied first-principles calculations. The results clearly indicate that the HP of composite structures containing Si–N bonds at the Si NC/SiO2 interface induces the blue-shift in PL. We expect that this investigation helps to pave the way for developing more efficient Si-based light emitting devices or solar cells.</P></▼2>
다중 안테나 다중 사용자 환경에서 최대 전송율에 근접하는 선형 precoding 기법
장승훈(Seunghun Jang),양장훈(Janghoon Yang),장규환(Kyuhwan Jang),김동구(Dong Ku Kim) 한국통신학회 2009 韓國通信學會論文誌 Vol.34 No.4C
본 논문은 최대 전송률에 가까운 성능을 보이는 선형 precoding 기법을 제안한다. MMSE precoding은 ZF precoding 방식보다 우수한 평균 자승 오차 성능을 가진다. 반면 MMSE precoding 방식의 전송률은 낮은 SNR 범위에서는 ZF 방식에 비해 개선된 성능을 보여주지만 높은 SNR에서는 오히려 성능 열화현상을 보인다. 이와 같은 사실에 착안하여 본 논문에서는 최대 전송률에 근접하는 선형 precoding 기법을 제안한다. 제안된 방식은 ZF precoding방식에서 사용되는 역행렬 연산을 전송율이 최대화될 수 있도록 정규화하는 방식이고 이를 위한 간단한 수치 알고리즘이 제안된다. 또한 그 과정에서 낮은 복잡도를 가지는 간단한 전력 재할당에 의한 정규화 방식이 제안된다. 시뮬레이션과 성능분석을 통해 제안된 방식이 모든 SNR 범위에서 기존의 ZF precoding 방식과 MMSE precoding방식보다 높은 전송률을 가짐을 보인다. 또한 제안된 방식은 채널 추정 오차가 존재하는 경우에도 기존의 선형 precoding 방식들과 비교하여 성능 이득을 유지하면서 채널 추정 오차에 강인함을 가진다. This paper considers a linear precoding scheme that achieves near optimal sum rate. While the minimum mean square error (MMSE) precoding provides the better MSE performance at all signal-to-noise ratio (SNR) than the zero forcing (ZF) precoding, its sum rate shows superior performance to ZF precoding at low SNR but inferior performance to ZF precoding at high SNR, From this observation, we first propose a near optimal linear precoding scheme in terms of sum rate. The resulting precoding scheme regularizes ZF precoding to maximize the sum rate, resulting in better sum rate performance than both ZF precoding and MMSE precoding at all SNR ranges. To find regularization parameters, we propose a simple algorithm such that locally maximal sum rate is achieved. As a low complexity alternative, we also propose a simple power re-allocation scheme in the conventional regularized channel inversion scheme. Finally, the proposed scheme is tested under the presence of channel estimation error. By simulation, we show that the proposed scheme can maintain the performance gain in the presence of channel estimation error and is robust to the channel estimation error.