• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.90-95
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• 2002

This thesis is aiming at analysis and implementing Distance Video Lecturing System to guarantee the high quality in service through using less Network resource. Most of the usual Distance Video Lecturing System has been designed not in the system of Multiuser Conference but Point-to-Point. But from now on Distance Video Lecturing System is to be demanded on not only the expansion to Multiuser Distance Video Lecturing System, but high quality in service for users. To solve these problems, the Multicast Transmission Technology as the dimension of Network as well as highly efficient, advanced Compression Technology should be applied to Video Conference System in company with the expansion of Network bandwidth. The system suggested in this thesis is to help to offer an application service as Distance Video Lecturing System that will make popular on the basis of the character that the next generation Internet will be high speed Network.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9C
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• pp.915-921
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• 2009

Lenstra-Lenstra-Lovasz (LLL) algorithm, which is one of the lattice reduction (LR) techniques, has been extensively used to obtain better bases of the channel matrix. In this paper, we jointly apply Seysen's lattice reduction Algorithm (SA), instead of LLL, with the conventional linear precoding algorithms. Since SA obtains more orthogonal lattice bases compared to those obtained by LLL, lattice reduction aided (LRA) precoding based on SA algorithm outperforms the LRA precoding with LLL. Simulation results demonstrate that a gain of 0.5dB at target BER of $10^{-5}$ is achieved when SA is used instead of LLL or the LR stage.

• Journal of Communications and Networks
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• v.6 no.1
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• pp.9-18
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• 2004

Self-encoded multiple access (SEMA) is a unique realization of random spread spectrum. As the term implies, the spreading code is obtained from the random digital information source instead of the traditional pseudo noise (PN) code generators. The time-varying random codes can provide additional security in wireless communications. Multi-rate transmissions or multi-level grade of services are also easily implementable in SEMA. In this paper, we analyze the performance of SEMA in additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. Differential encoding eliminates the BER effect of error propagations due to receiver detection errors. The performance of SEMA approaches the random spread spectrum discussed in literature at high signal to noise ratios. For performance improvement, we employ multiuser detection and Turbo coding. We consider a downlink synchronous system such as base station to mobile communication though the analysis can be extended to uplink communications.

• Journal of Communications and Networks
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• v.6 no.2
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• pp.93-105
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• 2004

This paper discusses cyclostationary interference suppression for multiuser wired communication systems. Crosstalk interference from digital signals in multipair cables has been shown to be cyclostationary. Many crosstalk equalization or suppression techniques have been proposed which make implicit use of the cyclostationarity of the crosstalk interferer. In this paper, the convergence and steady-state behaviors of a fractionally spaced equalizer (FSE) in the presence of multiple cyclostationary crosstalk interference are thoroughly analyzed by using the equalizer's eigenstructure. The eigenvalues with multiple cyclostationary interference depend upon the folded signal and interferer power spectra, the cross power spectrum between the signal and the interferer, and tile cross power spectrum between the interferers, which results in significantly different initial convergence and steady-state behaviors as compared to the stationary noise case. The performance of the equalizer varies depending on the relative clock phase of the symbol clocks used by the signal and multiple interferers. Measued characteristics as well as analytical model of NEXT/FEXT channel are used to compute the optimum and worst relative clock phases among the signal and multiple interferers.

• Journal of Communications and Networks
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• v.18 no.1
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• pp.27-39
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• 2016

This paper derives and analyzes a novel block fast Fourier transform (FFT) based joint detection algorithm. The paper compares the performance and complexity of the novel block-FFT based joint detector to that of the Cholesky based joint detector and single user detection algorithms. The novel algorithm can operate at chip rate sampling, as well as higher sampling rates. For the performance/complexity analysis, the time division duplex (TDD) mode of a wideband code division multiplex access (WCDMA) is considered. The results indicate that the performance of the fast FFT based joint detector is comparable to that of the Cholesky based joint detector, and much superior to that of single user detection algorithms. On the other hand, the complexity of the fast FFT based joint detector is significantly lower than that of the Cholesky based joint detector and less than that of the single user detection algorithms. For the Cholesky based joint detector, the approximate Cholesky decomposition is applied. Moreover, the novel method can also be applied to any generic multiple-input-multiple-output (MIMO) system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.8
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• pp.924-927
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• 2016

In this paper, we consider a cumulative distribution function (CDF)-based opportunistic scheduling for downlink transmission in a cellular network consisting of a base station and multiple mobile stations. We present a closed-form formula for the average starvation period of each mobile station (i.e., the length of the time interval between two successive scheduling points of a mobile station) over Markov time-varying channels. Based on our formula, we investigate the starvation period of the CDF-based scheduling for various system parameters.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10a
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• pp.631-633
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• 2003

시스템의 안전성을 평가하기 위해 프롤로그 기반의 명세 언어인 SPSL을 사용하여 보안 모델을 정형적으로 설계하였다. 보안 모델은 시스템의 3가지 컴포넌트, 시스템 보안 상태(system security states), 접근 통제 규칙(access control rules), 그리고 보안 기준(security criteria)으로 구성된다. 본 논문에서는 NTFS의 다중 사용 권한에 대한 보안 모델을 만들어서 3가지 컴포넌트를 명세하고 안전성 문제 해결 도구인 SPR［1］을 이용하여 검증하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.235-238
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• 2000

In this paper the MUD(Multi-User Detection) schemes and turbo codes are utilized in DS-CDMA mobile communication systems. Theses schemes effectively mitigate the effects of MAI(Multiple Access Interference) and Rayleigh fading. Using Monte Carlo simulation, the performance of the proposed schemes is analyzed for various channel conditions.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.523-523
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• 2006

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.562-562
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• 2006