• Journal of Communications and Networks
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• 제12권5호
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• pp.411-432
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• 2010

We consider three different secure broadcasting scenarios: i) Broadcast channels with common and confidential messages (BCC), ii) multi-receiver wiretap channels with public and confidential messages, and iii) compound wiretap channels. The BCC is a broadcast channel with two users, where in addition to the common message sent to both users, a private message, which needs to be kept hidden as much as possible from the other user, is sent to each user. In this model, each user treats the other user as an eavesdropper. The multi-receiver wiretap channel is a broadcast channel with two legitimate users and an external eavesdropper, where the transmitter sends a pair of public and confidential messages to each legitimate user. Although there is no secrecy concern about the public messages, the confidential messages need to be kept perfectly secret from the eavesdropper. The compound wiretap channel is a compound broadcast channel with a group of legitimate users and a group of eavesdroppers. In this model, the transmitter sends a common confidential message to the legitimate users, and this confidential message needs to be kept perfectly secret from all eavesdroppers. In this paper, we provide a survey of the existing information-theoretic results for these three forms of secure broadcasting problems, with a closer look at the Gaussian multiple-input multiple-output (MIMO) channel models. We also present the existing results for the more general discrete memoryless channel models, as they are often the first step in obtaining the capacity results for the corresponding Gaussian MIMO channel models.

• 한국멀티미디어학회논문지
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• 제10권12호
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• pp.1632-1644
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• 2007

Wireless Mesh Networks aim to attain large connectivity with minimum performance degradation, as network size is increase. As such, scalability is one of the main characteristics of Wireless Mesh Networks that differentiates it from other wireless networks. This characteristic creates the need for bandwidth efficiency strategies to ensure that network performance does not degrade as the size of the network increase. Several researches have been done to realize mesh networks. However, the researches conducted were mostly focused on a per TCP/IP layer basis. Also, the studies on bandwidth efficiency and bandwidth improvement are usually dealt with as separate issues. This paper aims to simultaneously study bandwidth efficiency and improvement. Aside from optimizing the bandwidth given a fixed capacity, the capacity is also increased using results of physical layer studies. In this paper, the capacity is improved by using the concept of non-overlapping channels for wireless communication. A channel allocation scheme is conceptualized to choose the transmission channel that would optimize the network performance parameters with consideration of chosen Quality of Service (QoS) parameters. Network utility maximization is used to optimize the bandwidth after channel selection. Furthermore, a routing scheme is proposed using the results of the network utilization method and the channel allocation scheme to find the optimal path that would maximize the network gain.

• 한국산학기술학회논문지
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• 제10권12호
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• pp.3775-3781
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• 2009

본 연구의 목적은 모바일 상거래의 채널만족과 채널선호에 영향을 미치는 요인을 분석하는 것이다. 기술수용모형, 거래비용이론 그리고 서비스 품질에 대한 이론적 배경을 바탕으로 연구모형을 설정하였으며, 모바일 사용자 320명을 대상으로 AMOS 7.0 통계패키지를 이용하여 실증연구를 수행하였다. 연구결과, 유용성, 자산특유성, 불확실성, 신뢰, 응답성이 채널만족에 유의한 영향을 미쳤으며, 채널만족이 채널선호에 유의한 영향을 미치는 것으로 나타났다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 춘계종합학술대회
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• pp.371-374
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• 2007

센서 네트워크에서 효율적인 채널의 사용은 짧은 시간 안에 많은 양의 패킷을 전달하기 위해 중요하며, 채널 활용성을 향상시킨다. 채널 활용성은 MAC 프로토콜의 효율성을 설명하기 위한 좋은 방법이다. 본 논문에서는 효율적인 채널 사용을 위해 B-MAC(Berkeley-MAC)에서 사용한 기법들과 TDMA(Time Division Multiple Access)를 결합시킨 MAC(Media Access Control) 프로토콜을 제안한다. 기본적으로는 backoff, CCA(Clear Channel assessment), LPL(Low Power Listen) 기법 등을 사용하여 충돌과 에너지 소모를 줄이며, 동시에 경쟁 상태에 따라 전송 방식을 다르게 함으로써 채널 활용성을 높이고자 한다. 시뮬레이션을 통하여 기존의 MAC 프로토콜과 비교하여 성능이 향상됨을 보여준다.

• 대한전자공학회논문지TC
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• 제48권1호
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• pp.32-37
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• 2011

수중에서의 통산은 수중채널의 잔향음이나 소음특성에 영향을 받으며, 다중 음파 경로 등으로 인하여 신호의 지연 현상이 발생하게 된다. 이로 인해 신호는 왜곡되고 송수신시에 많은 오류를 발생시키기 때문에 오류정정을 위한 채널코딩이 필요하다. 본 논문에서는 수신된 신호의 오류를 정정할 수 있는 채널코딩 방법에 대하여 연구하였다. 이 채널코딩 방법을 이용하여 송수신 깊이별로 성능을 비교 분석하였다. 변조방식으로는 QPSK, 부호화율로는 1/2 code rate를 사용하였고 길쌈부호화를 사용하였을 때 성능이 향상되었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권2호
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• pp.629-648
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• 2012

Given a video stream delivering system deployed on a multicast tree, which is embedded in a multi-channel multi-radio wireless mesh network, our problem is concerned about how to allocate interference-free channels to tree links and maximize the number of serviced mesh clients at the same time. In this paper, we propose a channel allocation heuristic algorithm based on best-first search and backtracking techniques. The experimental results show that our BFB based CA algorithm outperforms previous methods such as DFS and BFS based CA methods. This superiority is due to the backtracking technique used in BFB approach. It allows previous channel-allocated links to have feasibility to select the other eligible channels when no conflict-free channel can be found for the current link during the CA process. In addition to that, we also propose a tree refinement method to enhance the quality of channel-allocated trees by adding uncovered destinations at the cost of deletion of some covered destinations. Our aim of this refinement is to increase the number of serviced mesh clients. According to our simulation results, it is proved to be an effective method for improving multicast trees produced by BFB, BFS and DFS CA algorithms.

• 설비공학논문집
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• 제21권9호
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• pp.475-482
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• 2009

The objectives of this paper are to study the characteristics of heat transfer and pressure drop of the zigzag channel PCHE using diffusion bonding technology by numerical analysis. PCHE of five types are designed, which are zigzag channel angle 180$^{\circ}$, 160$^{\circ}$, 140$^{\circ}$, 120$^{\circ}$ and 100$^{\circ}$. The zigzag PCHE was numerically investigated for Reynolds number in a range of 150$\sim$800. The temperatures of the hot side were performed at 80$^{\circ}$ while that of the cold side was conducted at 20$^{\circ}C$. The results show that the performance of heat transfer rate for zigzag channel 100$^{\circ}$ increases about 11.5% compared to that of zigzag channel 180$^{\circ}$. On the other hand, the performance of pressure drop for zigzag channel 100$^{\circ}$ is remarkably higher than that of zigzag channel 180$^{\circ}$, about 2.4 times.

• Transactions on Electrical and Electronic Materials
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• 제17권5호
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• pp.270-274
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• 2016

This article investigates the use of the Gaussian-channel doping profile for the control of the short-channel effects in the double-gate MOSFET whereby a two-dimensional (2D) quantum simulation was used. The simulations were completed through a self-consistent solving of the 2D Poisson equation and the Schrodinger equation within the non-equilibrium Green’s function (NEGF) formalism. The impacts of the p-type-channel Gaussian-doping profile parameters such as the peak doping concentration and the straggle parameter were studied in terms of the drain current, on-current, off-current, sub-threshold swing (SS), and drain-induced barrier lowering (DIBL). The simulation results show that the short-channel effects were improved in correspondence with incremental changes of the straggle parameter and the peak doping concentration.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -2
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• pp.982-985
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• 2000

This paper presents channel estimation of an asynchronous W-CDMA reverse link using the interpolation and moving average algorithm in frequency-selective Rayleigh fading channel. The proposed algorithm is an interpolated decision-directed (IDD) block-wise moving average (BWMA) algorithm. The IDD-BWMA algorithm performs two- stage processes. The first stage performs data decision to make a virtual pilot channel by using linear interpolation channel estimation scheme. Then, the second stage performs the channel estimation of the “block-wise moving average” type by using a virtual pilot channel obtained in the first stage. By using Monte-Carlo computer simulations, we show that the proposed channel estimator is superior to other estimation schemes such as the WMSA(K=1) and DD-RAKE at higher Doppler frequencies, especially.

• Journal of Information Processing Systems
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• 제13권4호
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• pp.1029-1042
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• 2017

A joint channel estimation and data detection technique for a multiple input multiple output (MIMO) wireless communication system is proposed. It combines the least square (LS) training based channel estimation (TBCE) scheme with sphere decoding. In this new approach, channel estimation is enhanced with the help of blind symbols, which are selected based on their correctness. The correctness is determined via sphere decoding. The performance of the new scheme is studied through simulation in terms of the bit error rate (BER). The results show that the proposed channel estimation has comparable performance and better computational complexity over the existing semi-blind channel estimation (SBCE) method.