• 적정기술학회지
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• 제7권2호
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• pp.172-187
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• 2021

In remote villages without access to modern IT technology, simple devices such as smartcards can be used to carry out business transactions. These devices typically store multiple business applications from multiple vendors. Although devices must prevent malicious or accidental security breaches among the applications, a secure communication channel between two applications from different vendors is often required. In this paper, first, we propose a method of establishing secure communication channels between applications in embedded operating systems that run on multi-applet smart cards. Second, we enforce the high assurance using an intransitive noninterference security policy. Thirdly, we formalize the method through the Z language and create the formal specification of the proposed secure system. Finally, we verify its correctness using Rushby's unwinding theorem.

• 설비공학논문집
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• 제27권11호
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• pp.559-566
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• 2015

The main objective of this work is to experimentally investigate the effect of angle variation on the distribution of two-phase flow at header-channel junctions. The cross-sections of the header and the channels were fixed at $16mm{\times}16mm$ and $12mm{\times}1.8mm$, respectively. Air and water were used as the test fluids. Four different header-channel positions were tested : Vertical header with Horizontal channels (case VM-HC), Horizontal header with Horizontal channels (case HM-HC), Horizontal header with Vertical Downward channels (case HM-VDC), and Horizontal header with Vertical Upward channels (case HM-VUC). In all cases, liquid flow distribution tended to decrease gradually in the upstream header region. However, in the downstream region, different trends could be seen. The reason for these different tendencies were identified by flow visualization in each case. The standard deviations for the liquid and gas flow distribution in each case were calculated, and the case of VM-HC had the lowest values compared to other cases because of the symmetrically distributed liquid film and strong flow recirculation near the end plate.

• Journal of Communications and Networks
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• 제10권1호
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• pp.28-37
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• 2008

In this paper, we investigate the problem of minimizing the average transmission power of users while guaranteeing the average delay constraints in time-varying uplink channels. We design a scheduler that selects a user for transmission and determines the transmission rate of the selected user based on the channel and backlog information of users. Since it requires prohibitively high computation complexity to determine an optimal scheduler for multi-user systems, we propose a low-complexity scheduling scheme that can achieve near-optimal performance. In this scheme, we reduce the complexity by decomposing the multiuser problem into multiple individual user problems. We arrange the probability of selecting each user such that it can be determined only by the information of the corresponding user and then optimize the transmission rate of each user independently. We solve the user problem by using a dynamic programming approach and analyze the upper and lower bounds of average transmission power and average delay, respectively. In addition, we investigate the effects of the user selection algorithm on the performance for different channel models. We show that a channel-adaptive user selection algorithm can improve the energy efficiency under uncorrelated channels but the gain is obtainable only for loose delay requirements in the case of correlated channels. Based on this, we propose a user selection algorithm that adapts itself to both the channel condition and the backlog level, which turns out to be energy-efficient over wide range of delay requirement regardless of the channel model.

• 유통과학연구
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• 제13권10호
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• pp.57-63
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• 2015

Purpose - This study investigates the effects consumer perceptions of wine attributes have on repurchase intention. It examineshow wine purchase channels (online or offline) influence perceptions about wine attributes and repurchase intention. Research design, data, and methodology - A total of 390 responses from Florida residents over 21 were collected using online surveys. Responses were analyzed using exploratory factor analysis to identify the underlying wine attribute factors. Multiple regression and multi-group analysis were employed to test the hypotheses. Results - Results revealed that consumer perceptions of wine attributes (sensory, origin, reputation, and price point) significantly influence their repurchase intention. Additionally, the effects of wine attributes on repurchase intentions were found to be significantly different based on the channel used. Findings indicated that wine attributes pertaining to reputation and price point strongly influenced repurchase behavior of online consumers, while offline wine consumers were influenced more by sensory and origin attributes. Conclusions - Study findings provide useful information for wine industry sales channels for developing new marketing strategies to effectively attract wine consumers to repurchase wine.

• 한국통신학회논문지
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• 제36권11A호
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• pp.870-877
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• 2011

IEEE 802.11 장비가 널리 사용되고 있으며, 저비용 IEEE 802.11 장비들이 보급됨에 따라 단말들은 다중 IEEE 802.11 라디오를 장착할 수 있게 되었다. 최신 IEEE 802.11 장비들은 다수 채널 (multi-channel)과 전송률 (multi-rate)을 제공한다. 실제 다중 채널 네트워크에서는 같은 노드에 대해 채널들이 서로 다른 신호 특성을 가지는 채널 이질성 (channel heterogeneity)이 있으므로, 네트워크 용량을 향상시키기 위해 다수의 채널을 효율적으로 할당해야 한다. 또한, 다중 전송률 네트워크에서는 같은 채널 상의 낮은 전송률 링크가 높은 전송률 링크의 성능을 심각히 저하시키는 성능 이상 (performance anomaly) 현상이 발생한다. 따라서, 본 논문에서는 채널 이질성과 성능 이성을 반영하여 네트워크 성능을 향상시키는 HACA (Heterogeneity Aware Channel Assignment) 알고리즘을 제안한다. NS-2 시뮬레이션을 통해 HACA 알고리즘이 채널 이질성을 반영하지 못하는 기존 채널 할당 알고리즘에 비해 향상된 성능을 보임을 검증하였다.

• 전자공학회논문지 IE
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• 제43권2호
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• pp.80-86
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• 2006

제4세대 무선 통신은 송신기와 수신기양단에 다중 안테나와 순시 채널의 상태 정보를 이용함으로써 LDPC와 OFDM 무선 전송에 있어서 MQAM(M-ary Quadrature Amplitude Modulation)을 사용하는 적응 공간 부반송파 부호화 변조 방식에 기반으로 하고 있다. 적응 부호화 변조는 시변 협대역 무선 채널에 대해서 대역 효율이 좋은 전송방식으로 인식되어 가고 있다. 전력이 제한된 AWGN 채널에 대해서, LDPC 부호들은 오류 제어 부호의 한 부류이며 이는 어떤 조건하에서는 터보부호보다 오류 정정 능력이 더 좋은 것으로 알려져 왔다. 본 논문에서는 MIMO 시스템에 적용된 LDPC 부호를 갖는 OFDM 방식과 적응 변조방식에 대해서 서술한다. 채널의 순시 정보를 알고 있다고 가정함으로써 각 부반송파에 대해서 비트와 전력 할당을 얻기 위한 최적화 알고리즘이 사용되였다. 시뮬레이션 결과는 제안한 시스템이 가능성을 가짐을 보여준다.

• ETRI Journal
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• 제34권6호
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• pp.858-868
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• 2012

In this paper, stochastic models for the cross-correlation of multiple channels are established based on measurement data collected using a wideband multiple-input multiple-output relay Band Exploration and Channel Sounder system at 3.7 GHz. We propose models for the cross-correlation characteristics of large-scale parameters (LSPs) between two links, that is, the base station and mobile station (MS) link and the relay station and MS link. The LSPs include shadow fading, Rician K-factor, delay spread, angle spread of arrival, and angle spread of departure. Furthermore, models are established for the cross-correlation of the small-scale fading in the impulse responses of two links. The statistics of these model parameters are investigated as functions of geometrical features of the multilink. They are extracted from a large amount of cross-correlation observations, which are obtained in three measurement sites along more than one hundred measurement routes. These models can be used together with the standard single-link channel models for the generation of correlated components, for example, path clusters, in two separate channels.

• 한국인터넷방송통신학회논문지
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• 제11권2호
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• pp.63-72
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• 2011

방송 기반의 데이터 전파는 모바일 컴퓨팅 환경에서 보편적으로 받아들여지는 통신 방식이다. 그러나 많은 데이터를 방송해야 할 경우에 방송 채널의 순차성으로 인하여 원하는 데이터를 수신하기까지의 예상 지연시간이 증가한다. 이 대기시간을 줄이기 위하여 본 논문은 다중 채널을 통하여 데이터를 방송하는 문제를 연구한다. 기존의 기법들은 각 채널의 평형 방송을 가정하고 데이터들을 액세스 확률에 근거하여 분할하고 다중 채널에 할당한다. 만일 동일 채널에 할당된 데이터들도 그들의 액세스 확률에 근거하여 방송빈도를 다르게 한다면 성능은 더 향상될 것이다. 이와 같은 관점에서 본 논문은 동일 채널에 할당된 데이터들의 액세스 확률의 차이를 방송 스케줄에 반영할 수 있는 두 단계 동적프로그래밍 기법으로 명명된 새로운 방송 스케줄링 기법을 제안한다.

• 한국통신학회논문지
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• 제37권8A호
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• pp.601-611
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• 2012

본 논문에서는, 다중 안테나 다중 사용자가 존재하는 3-cell 간섭 Broadcast 채널 (IFBC: interference broadcast channel) 에서 얻을 수 있는 공간 다중화 이득 (spatial multiplexing gain)에 대해서 소개한다. 이러한 공간 다중화 이득을 최대화하면서 총 수율을 높이기 위하여, 우리는 간섭 정렬 기법 (IA: interference alignment)에 스케쥴링 기법을 더한 방법을 제안하며, 이는 IFBC 환경에서 TDMA 기법보다 높은 수율 성능을 보인다. 최적의 스케쥴링 방법은 다중 사용자 이득을 이용하여 총 수율을 최대화하는 전수 조사 알고리즘을 이용한다. 또한, 전수 조사의 계산 복잡도가 매우 높기 때문에, 이를 효과적으로 줄이는 coordinated ascent 방법을 이용한 부최적 스케쥴링 방법도 제안 한다.

• Journal of Communications and Networks
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• 제9권1호
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• pp.50-55
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• 2007

We propose to apply chip interleaving and iterative detection to self-encoded multiple access (SEMA) communications. In SEMA, the spreading code is obtained from user bit information itself without using a pseudo noise code generator. The proposed scheme exploits the inherent diversity in self encoded spread spectrum signals. Chip interleaving not only increases the diversity gain, but also enhances the performance of iterative detection. We employ user-mask and interference cancellation to decouple self-encoded multiuser signals. This paper describes the proposed scheme and analyzes its performance. The analytical and simulation results show that the proposed system can achieve a 3 dB power gain and possess a diversity gain that can yield a significant performance improvement in both Rayleigh and multipath fading channels.