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Tae-Won Yune,Dongsik Kim,Gi-Hong Im IEEE 2010 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.58 No.4
<P>Cooperative communications can achieve spatial diversity gain and enhance coverage. However, conventional half-duplex relaying schemes suffer from the loss in spectral efficiency, because the two channel uses are required for transmission from the source to the destination. In this paper, we present spectral efficient transmissions for a user cooperative diversity system over multipath fading channels. To increase the spectral efficiency, a node, which acts as a relay, employs a superposition coding to transmit its own data block and the data block from the other node simultaneously. For superposition, we consider two different re-encoding schemes. One is based on complex field superposition coding and the other is based on Galois field superposition coding. In both re-encoding schemes, we introduce a user-specific interleaver to the data blocks for user separation. We also propose an iterative detection scheme to combat the effects of inter-symbol interference caused by multipath fading and to extract diversity gain from the superposed signals. For performance estimation, we develop a density evolution technique. It is shown that the proposed schemes can obtain diversity gain without sacrificing spectral efficiency and the predicted performances are consistent with simulated performances.</P>
SC-FDMA with iterative multiuser detection: improvements on power/spectral efficiency
Tae-Won Yune,Chan-Ho Choi,Gi-Hong Im,Jong-Bu Lim,Eung-Sun Kim,Yoon-Chae Cheong,Ki-Ho Kim IEEE 2010 IEEE communications magazine Vol.48 No.3
<P>This article outlines the basic principles of single-carrier frequency division multiple access with iterative multiuser detection, called grouped frequency division multiple access. GFDMA allows multiple users to share a common set of subcarriers and separates the signals of users by employing distinct interleavers and frequency-domain multiuser detection. Some attractive features of GFDMA are explained, including low-cost iterative multiuser detection, multiuser and frequency diversity gains, and flexibility in resource allocation. We also discuss the applications of GFDMA to spatial diversity schemes and to intercell interference mitigation in the cell edge. It is shown that GFDMA offers advantages over SC-FDMA with respect to power/spectral efficiency. Such power/spectral efficiency can provide considerable performance improvements in future wireless communication networks.</P>
Tae-Won Yune,Jong-Bu Lim,Gi-Hong Im IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.7
<P>In this paper, we present an iterative multiuser detection scheme using frequency-domain equalization (IMDFDE), which can be incorporated into a single carrier frequency division multiple access (SC-FDMA) framework. The IMD-FDE scheme employs a different interleaver for each user at the transmitter, and removes multiuser interference with an iterative detection method in the frequency domain at the receiver. The extrinsic information transfer (EXIT) charts and bit-error rate (BER) plots are presented to investigate the iterative behavior of the IMD-FDE over additive white Gaussian noise and multipath fading channels. In a conventional time-division multiple-access (TDMA)-based relay protocol, cooperative transmission over two time slots leads to a 50% loss in spectral efficiency. We propose two spectral efficient relay protocols, where multiple sources access a relay, destination, or both simultaneously. We also present a new iterative detection scheme that effectively removes multiuser interferences for the proposed relay protocols.With the proposed protocols and the aid of iterative multiuser detection scheme, the proposed relay-assisted SC-FDMA with IMD-FDE can obtain diversity gain without sacrificing spectral efficiency and approaches the single-user bound over time-varying and frequency-selective fading relay channels.</P>
VoIP 보안 위협과 보안요구사항 분석 및 보호프로파일 개발
홍원순 ( Won-soon Hong ),최용준 ( Yong-joon Choi ),성윤기 ( Yune Gie Sung ),심원태 ( Won-tae Sim ) 한국정보처리학회 2009 한국정보처리학회 학술대회논문집 Vol.16 No.1
인터넷망을 이용하여 음성 및 영상통화를 제공하는 VoIP(인터넷전화)서비스가 확대되고, VoIP 서비스가 인터넷망을 이용함에 따라 기존의 인터넷망에서 제기된 보안위협이 증가하고 사이버 공격에 노출되고 있다. 이에 따라 본 고에서는 국제 표준인 공통평가기준(ISO 15408)에서 규정된 방법에 따라 VoIP 서비스를 제공하는 IP Phone 및 IP PBX시스템이 노출되는 사이버 상의 보안위협사항을 도출하고, 보안목적과 VoIP 및 IP PBX 시스템 보안위협에 대응할 수 있는 보안요구사항을 정의하였다.
Hong, Won-Kee,Yune, Dai-Young,Park, Seon-Chee,Yoon, Tae-Ho SAGE Publications 2011 Indoor and Built Environment Vol.20 No.1
<P> Apartments with load-bearing wall construction are used extensively in Korea, but have the disadvantage of a short life, causing serious economic losses in terms of construction waste, materials and energy consumption. This paper presents the findings on multi-residential apartments that utilise a hybrid composite frame as a viable alternative for the energy efficiency associated with construction materials. The hybrid composite frame consists of a structural tee, reinforcement steels and pre-cast concrete. The use of the hybrid composite frame reduces the overall amount of energy consumption. In addition, multi-residential apartments utilising a hybrid composite frame have advantages such as flexibility in planning and easier repair and remodelling. This study investigates tower-shape, multi-residential apartments of various heights and floor areas to compare the energy efficiency of the hybrid composite system with that of the bearing wall system. The multi-residential apartments that utilise the hybrid composite frame are analysed in terms of both reduced principal materials and reduced energy consumption compared with apartments of a load-bearing wall structure. Rapid demand for long life and multi-residential apartment construction is expected. </P>