• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11B
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• pp.1142-1150
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• 2009

In this paper, we propose an novel bandwidth scheduling algorithm for the MAC protocol employed by the Data Over Cable Service Interface Specifications (DOCSIS) 3.0 compliant cable networks. The proposed algorithm statistically improves the chances of request piggybacking to minimize the access delay. It utilizes the piggyback request feature of the segment packets that has been newly specified in DCOSIS 3.0. In DOCSIS 3.0, a bandwidth request can be granted to several upstream channels within an upstream bonding group. The grant on each individual channel is treated as a segment packet. We find the optimal segment placement to minimize the access delay in the proposed algorithm. We also use a self-similar traffic model for simulation and analysis to evaluate the performance of the proposed algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.5C
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• pp.351-360
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• 2008

In cellular mobile radio systems with frequency reuse, the interference signals degrade the channel estimation and signal detection performance due to the low signal-to-interference ratio near coverage boundaries. When the preamble pilot sequences from different cells are orthogonal or located in disjointed positions, they can be used for multi-cell channel estimation and interference cancellation. In time-varying channels caused by Doppler spread, data pilot symbols are needed for channel estimations. However, data pilot symbols are usually located in identical positions for the overhead reduction, which degrades the channel estimation performance. In this paper, we demonstrate a significant amount of performance improvement is achieved by multiplying different pseudonoise(PN) sequences to the data pilot symbols from adjacent interference cells. In particular, for detection scheme using maximal ratio combining(MRC) and inter-cell spatial demultiplexing(ISD), quantitative performance gain of spectral efficiency for different values of Doppler frequency and interference power is presented.

• Journal of the Institute of Convergence Signal Processing
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• v.3 no.4
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• pp.67-73
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• 2002

There have been increased concerns on mobile stratospheric communication system(SCS) for the purpose of advanced service of personal and high speed communication systems. In fact, this SCS is considered and studied for IMT-2000 service by ITU. Although, it is important to make accurate channel model for prediction of the SCS performance, there is no measured channel data in this system. Thus, in this paper, we estimate the performance of SCS bye use of channel model provided by Corazza(2) and modified by You(3). And also, the effects of channel codings on system performance are analyzed by deriving bit error performance based on realistic Rician log-normal fading channel models. The performance results are divided into three kinds of areas with three kinds of elevation angles 20$^\cire$, 45$^\cire$, and 80$^\cire$. And also the effects of forward error correction channel codings on system performance with Hamming(7,4), HCH( IS,7) and convolutional code of constraint length 3 and code rate R=1/2.

• The Journal of the Korea Contents Association
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• v.21 no.11
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• pp.100-111
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• 2021

This study aims to lead the new discussion by looking at variables affecting the number of subscription channels and subscription satisfaction in the absence of academic discussion of users' YouTube subscriptions. To this end, we conducted an online survey and analyzed the factors affecting the number of subscription channels and subscription satisfaction of YouTube users. We conducted hierarchical regression to examine their subscription motivation with exploratory factor analysis and to examine the impact of subscription motivations and the intentionality of Youtubers and the usefulness of YouTube knowledge on the number of subscription channels and subscription satisfaction. The analysis results are as follows: First, YouTube's usage and convenience motivation have had a static impact on the number of subscription channels. Second, factors affecting subscription satisfaction have been shown to be convenience subscription motivation, communication with Youtubers motivation, and perceived usefulness of YouTube. The practical significance of this work is that it can be beneficial to platform and channel operators in the changing new media environment. Furthermore, it aims to expand the interaction research extensions between YouTuber and users in the new media environment.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.528-532
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• 2005

As the current IEEE 802.11 wireless LAN standard provides the unified channel access procedure for each traffic service without considering its own traffic characteristics, it is difficult to get its differentiated service qualities at IEEE 802.11 wireless LAN system. To solve this limit, IEEE 802.11e standard that can provide differentiated service to each traffic is under preparation. In this study, we implemented IEEE 802.11e EDCA channel access scheme with NS-2 simulator, and showed its numerical results in various system environments with using average delay and throughput as performance measures.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11A
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• pp.1827-1840
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• 2001

In digital data transmission/storage systems, the compensation for channel distortion is conducted normally using a training sequence that is known a priori to both the sender and receiver. The use of the training sequences results in inefficient utilization of channel bandwidth. Sometimes, it is also impossible to send training sequences such as in the burst-mode communication. As such, a great deal of attention has been given to the approach requiring no training sequences, which has been called the blind equalization technique. On the other hand, to utilize the limited bandwidth effectively, the concept of partial response (PR) signaling has widely been adopted in both the high-speed transmission and high-density recording/playback systems such as digital microwave, digital subscriber loops, hard disk drives, digital VCRs and digital versatile recordable disks and so on. This paper is concerned with blind adaptive equalization of partial response channels whose transfer function zeros are located on the unit circle, thereby causing some problems in performance. Specifically we study how the problems of blind channel equalization associated with the PR channels can be improved. In doing so, we first discuss the existing methods and then propose new structures for blind PR channel equalization. Our structures have been extensively tested by computer simulation and found out to be encouraging in performance. The results seem very promising as well in terms of the implementation complexity compared to the previous approach reported in literature.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2B
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• pp.141-147
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• 2011

In this paper, field trials for co-sited transmitters with 600kHz channel separation are performed to investigate the available FM spectrum resource of Korea. Requirements of subjective voice quality and electric field intensity levels are quite well fulfilled during overall field trials. Experimental results show that 600kHz channel separation in co-sited transmitter can be permitted after reasonable pre-simulation and field trial.

• Information and Communications Magazine
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• v.13 no.8
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• pp.103-122
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• 1996

초고속정보통신망의 구축이 효율적이고 신뢰성 있는 서비스를 제공하기 위하여 위성/지상망을 통합한 혼합망 구조로 개발됨에 따라 지상 광파이버를 기반으로 개발된 ATM 전송프로토콜을 위성망에 직접적으로 적용하기 위한 기술개발이 요구된다. 이러한 점을 고려하여 본 고에서는 위성 ATM(Asynchronous Transfer Mode) 전송에 따른 문제점 분석, 개선방안 및 성능평가를 수행하였다. 혼합망 구성에 따른 위성망의 구조를 접속된 지상노드의 유형 및 위성시스템 특성에 따라 3가지 유형으로 분류하여 제시하였고, 위성 ATM 전송에 따른 기술적인 문제점을 채널 BER과 위성지연 측면으로 분류하여 제시하였다. 위성채널 BER 성능개선을 위한 2가지 방안(인터리빙, HEC 보강)을 제시하였으며 위성지연분석은 고정지연(Fixed delay)과 셀지연변이(CDV : Cell Delay Variation) 측면에서 성능평가를 수행하였다.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.2
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• pp.279-284
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• 2013

In this paper, to evaluate the performance of solenoidal typed injector, research and development had been performed on injector controller in order to respond to various performance tests, which is not only economical but easy extensible on its channels. The developed controller based on embedded system is able to precisely control the injection timing and quantity by high-pressured from the injector. Also, it is able to performance evaluation by measuring the electrical characteristics of solenoid. Additionally, it is enable precision timing control of light source and high speed camera as it is able to precisely photograph the timely spray pattern of injector.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 2000.11a
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• pp.236-241
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• 2000

가상환경 하에서의 임장감을 객관적으로 계측하기 위한 방법으로 생체신호를 이용한 감성의 계측을 시도하였다. 여러 가지 가상환경 하에서 뇌파, 심전도, 호흡 등 다 채널의 생체신호를 계측하고 이때 피실험자가 느끼는 객관화된 임장감 지표들을 동시에 평가하여 이를 신경 회로망을 이용하여 분석하였다. 계측된 생체 신호를 사전 처리하여 일차적인 생체분석 지표들을 도출하고 이를 신경회로망의 입력으로 활용하였다. 임장감을 분석할 수 있도록 신경회로망을 학습시키고, 이를 이용하여서 가상환경 하에서 계측된 생체신호를 분석하여 임장감을 정량화하여 평가하였다.