• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2003.06a
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• pp.67-68
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• 2003

IMT-2000에서 지원하는 멀티미디어 서비스는 실시간 데이터(Real-time data)와 비실시간 데이터(Non-relatime data)로 구분할 수 있는데 전송의 실시간성 VBR(Variable Bit Rate)이나 버스트성의 멀티미디어 데이터의 경우 자원의 이용률이 낮아 비효율적이다. 비실시간 데이터는 전송 지연에는 큰 영향을 받지 않으며 다만 오류 없이 전송될 것을 요구된다. 그러므로 채널의 이용률을 높일 수 있는 채널 공유방식에 적합하나 경쟁 시 충돌이 발생할 수 있으므로 이 문제를 해결할 것이 요구된다. 본 연구에서는 실시간 데이터를 위해 고정 액세스 방식으로 고유의 채널을 예약하여 사용하고, 전송 패킷이 없으면 우선 순위(Priority) 방식으로 비실시간 데이터를 전송하는 다중 액세스 방법을 제시한다.

• Journal of Digital Contents Society
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• v.12 no.3
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• pp.347-353
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• 2011

In HIPERLAN/2, the radio channels are assigned by AP(Access Point) that is centrally operated and the MAC protocol is based on TDMA/TDD. Mobile terminal that data transmission is necessary to uplink requests radio resource to AP through RCH channel. The changing number of RCHs in each MAC frame is important because too many RCHs may result in a waste of radio resources and too few RCHs may result in many access collisions and prolong time that connect to AP. Hence the number of RCH should be allocated properly according to traffic. From these point, this paper proposes an scheme that dynamically assigned the number of RCH which is based on the number of success and collision of message in previous MAC frame. To prove efficiency of proposed scheme, lots of simulations are conducted and analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.11A
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• pp.1630-1641
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• 2000

본 논문은 셀룰러 시스템 상향 링크에서 음성데이터 및 실시간 영상데이터로 구성된 화상전화서비스, 고속 및 저속 데이터베이스의 다중 전송률 멀티미디어 서비스를 통합 지원할수 있는 CDMA R-ALOHA 프로토콜을 제안하였다. 제안된 프로토콜은 액세스슬롯과 전송슬롯으로 구분된 프레임의 구조를 이용한 코드할당 방식으로 전송슬롯에서의 간섭을 줄였다. 그리고, 각 서비스의 트래픽 특성에 따른 전송코드 예약과 화상전화서비스 사용자의 핸드오프호를 고려하여 분석된 각 서비스 부시스템의 Markov-chain 모델을 이용한 각 서비스의 채널 경쟁 사용자수 추정을 기반으로 서비스별 액세스 허용확률을 제안하여, 액세스슬롯에서의 패킷 충돌을 감소시키고 핸드오프호의 우선권을 보장할 수있다. 또한 화상전화서비스의 영상데이터 전송정보를 이용한 코드 예약방식을 제안하여, 음성 트래픽을 패킷의 손실이 없이 지원하였고 고속 및 저속 데이터베이스를 통해 채널 이용효율을 극대화하였다.

• Annual Conference of KIPS
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• 2007.05a
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• pp.1042-1044
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• 2007

IEEE 802.15.4 표준을 기반으로 하는 무선 액세스 기술은 진화된 컴퓨팅 시스템을 구축하는 데 있어 광범위하게 사용될 수 있을 것이다. 이러한 기술의 활용은 보안성과 공정성이 보장되어야 하지만, 무선 환경에서 악의적인 디바이스는 불공정한 방법을 사용하여 채널 대역폭을 차지할 수 있다. 본 논문에서는 이러한 공격에 대응할 수 있도록 코디네이터의 결정에 의해 정상적인 디바이스가 채널에 우선적으로 액세스 할 수 있는 메커니즘을 제안하고, 이를 위해 기존의 IEEE 802.15.4 표준을 활용할 수 있는 방안을 제시한다. 시뮬레이션 결과는 본 논문에서 제안하는 메커니즘이 MAC 레이어에서의 공격을 효과적으로 방지할 수 있음을 보여준다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3B
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• pp.138-143
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• 2005

This paper aims to optimize an access probe algorithm for the CDMA 2000 system. The incremental value of PWR_STEP increases as NUM_STEP as 1dBm±0.2 for access probe of the area with good receiving sensitivity when the mobile station transmits via access channel and does not receive any ACK message. However, for the area with weak receiving sensitivity, according to the algorithm of open-loop power control, the transmitting power amplifier becomes saturated and PWR_STEP incremental value keeps performing access probe to 0dBm±0.2. Therefore interference and battery consumption increases according to the transmission of the mobile station. We have optimized the access probe algorithm according to the receiving sensitivity. We transmit the incremental value of access probe power, with delaying as much RT slot value as indicated by IS-95C standard in case of good receiving sensitivity and with delaying RT+l slot value in case of weak receiving sensitivity. Simulation results showed that the proposed algorithm contributes to decrease of the interference and battery consumption according to the transmitting power of the mobile station and improves the call duration.

• The Journal of the Korea Contents Association
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• v.11 no.10
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• pp.93-107
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• 2011

SO and Satellite Broadcaster can operate SO Operating channel in Korea. However, the Broadcasting act does not specify the direction of what purpose the SO operating channel would be operated for. Accordingly, SO and Satellite Broadcaster do not operate SO operating channel or use it as profit channel when operating. In this respect, the cases of U.S. and Japan have been studied to determine how SO operating channel should be operated to make it desirable. In the U.S., it is being used in various ways such as profit channel, multi-access channel and access channel. In Japan, it is mainly focused on the role as local channel, being coordinated with local governments to form public opinion on local news and issues or to announce local events. In Korea, SO is operating local channel similar to the one in Japan rather than SO operating channel, while Satellite Broadcasting is operating SO operating channel mainly for its profits. As SO operating channel is operated on the basis of the broadcasters' expediency without clear stipulation in Korea, we will need to seek the plan to use it for public interests by discussing more the status and operation of SO operating channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5B
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• pp.310-316
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• 2005

In this paper, we proposed and evaluated ARAH(Adaptive Random Access algorithm for HIPERLAN/2) to improve system performance. In this paper, HIPERLAN/2 uses OFDM(Orthogonal Frequency Division Multiplexing) modulation scheme to select appropriate PHY mode by Radio Channel Quality, Proposed the ARAH scheme uses these 7 PHY mode when mobile terminal determines the RCH(Random CHannel) number for random access. In this paper, these 7 PHY mode divided into two group, good and bad, and will be given high priority to mobile terminals which are in a good group. In the result of performance evaluation. ARAH algorithm, ARAH has a better performance of throughput and delay than existing algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.11
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• pp.1031-1041
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• 2014

In this paper, we propose a traffic load control scheme, called fast congestion control (FCC), for a satellite channel using enhanced random access schemes. The packet repetition used by enhanced random access schemes increases not only the maximum throughput but also the sensitivity to traffic load. FCC controls traffic load by using an access probability, and estimates backlogged traffic load. If the backlogged traffic load exceeds the traffic load corresponding to the maximum throughput, FCC recognizes congestion state, and processes the backlogged traffic first. The new traffic created during the congestion state accesses the channel after the end of congestion state. During the congestion state, FCC guarantees fast transmission of the backlogged traffic. Therefore, FCC is very suitable for the military traffic which has to be transmit urgently. We simulate FCC and other traffic load control schemes, and validate the superiority of FCC in latency.

• Journal of the Korean BIBLIA Society for library and Information Science
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• v.22 no.3
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• pp.373-391
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• 2011

To understand the characteristics of open access journals in Korea, this research examined the 1,438 KCI journals in the fields of humanities, social sciences, natural sciences, engineering, medicine, agriculture & oceanography, art & sports, and interdisciplinary. 21% of the KCI journals are freely available at the publisher's websites or open access DBs(OA). 34% are available only in the commercial fulltext DBs(TA) and 34% combined TA and OA. 48% of the OA journals can be found on the free fulltext DBs and 52% are accessed on the publisher's websites. OA journals in humanities and social science are available mainly on the publisher's websites. As compare with this, OA journals of STM fields are available via the free fulltext DBs. Medicine(30%) and social sciences(25%) have the highest overall share of OA. There are field differences in the rate of OA journals. In the fields of social sciences and humanities, 15% of the journal are open access. In case of medicine field, 60% are open access journals. OA journals in natural science and engineering are each 33% and 24%.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1996.10a
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• pp.357-360
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• 1996