• 정보와 통신
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• 제30권9호
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• pp.78-84
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• 2013

최근 4세대 이동통신은 기술/경제적인 이유로 클라우드 기지국 (또는 C-RAN: Cloud Radio Access Network) 구조를 택하는 추세이다. C-RAN은 기존 일체형 기지국에서의 MAC/PHY 기능을 담당하는 BBU(Base Band Unit)와 RF신호 송수신 만을 담당하는 RRH(Remote Radio Head)로 분리된 기지국 구조를 가지며, RRH의 무선 송수신 신호는 중앙의 BBU에 집중되어 처리된다. 본고에서는 BBU와 RRH로 분리되어 설치/운용되는 C-RAN의 구조와 기지국 가상화 개념을 소개하며, 향후 이동통신시스템에서의 기술동향과 관련하여 C-RAN에서 발생할 수 있는 이슈들을 살펴본다.

• 정보처리학회논문지C
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• 제12C권1호
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• pp.11-18
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• 2005

본 논문에서는 기가비트 트래픽에서도 높은 패킷 헤더 수집률(packet header collection ratio)을 보이는 멀티프로세서(multi-processor), 멀티쓰레드(multi-thread)를 채용한 네트워크 프로세서 기반의 패킷 헤더 수집기를 제안한다. 제안 패킷 수집기는 기가비트 트래픽 패킷 헤더를 분리하여 여러 대의 100Mbps MAC 포트로 분산하여 전달할 수 있는 구조를 가지고 있다. 제안된 구조는 고속 트래픽 처리를 위해 독창적인 버퍼관리 기법과 프로세서간 부하 분산 기법을 사용하고 있으며, 풍부한 실험을 퐁해 그 성능을 검증하였다.

• 정보처리학회논문지C
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• 제13C권4호
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• pp.455-460
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• 2006

인터넷에서 차등서비스에 관한 연구는 IETF 그룹에서 표준화되었으나, Ad-hoc 네트워크와 같은 무선 환경에서 인터넷의 차등 서비스는 MAC과 같은 하위레벨 지원 없이는 구현하기가 어렵다. 현재 IEEE 802.11 프로토콜은 무선 랜 환경에 광범위하게 쓰이며 사실상의 표준으로 자리 잡았다. 그러나 차등서비스 제공을 위한 모드를 지원하지만, 성능이 낮은 것으로 나타났다. 본 논문에서는 802.11 에서 QoS 제공을 위해 우선순위를 지원하는 다중 큐 기반의 새로운 알고리즘을 제안하고 시뮬레이션을 통해 IEEE 802.11의 큐영시스템과 성능을 비교, 분석하였다. 컴퓨터 시뮬레이션 결과 제안한 알고리즘 방식의 성능이 우수했음을 보였다.

• 기술사
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• 제34권4호
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• pp.41-47
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• 2001

The paper describes SR3 (Synchronous Round Robin with Reservations), a collision-free medium access control protocol for all-optical slotted packet networks based on WDM multi-channel ring topologies where nodes are equipped with one fixed-wavelength receiver and one wavelength-tunable transmitter SR3 is derived from the SRR and MMR protocols previously proposed by the same authors for the same class of all-optical networks. SRR and MMR already achieve an efficient exploitation of the available bandwidth, while guaranteeing a throughput-fair access to each node. SR3, In addition, allows nodes to reserve slots. thereby achieving a stronger control on access delays; it is thus well suited to meet tight delay requirements, as it is the case for multimedia applications. Simulation results show that SR3 provides very good performance to guaranteed qualify traffic, but also brings signigicant performance improvements for best-effort traffic. Energy effciency is an important issue for optical network since they must rely on their batteries. We present a novel MAC protocol that achieves a good energy efficiency of optical interface of the network and provides support for diverse traffic types and QoS. The scheduler of the base station is responsible to provide the required QoS to connections on the optical link and to minimise the amount of energy spend by the High speed Network. The main principles of the MaC protocol are to avoid unsuccessful actions, minimise the number of transitions , and synchronise the mobile and the base-station. We will show that considerable amounts of energy can be saved using these principles.

• 한국통신학회논문지
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• 제32권12C호
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• pp.1188-1193
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• 2007

본 논문은 MANET 환경에서 소스 라우팅 기반의 안전한 데이터 전송 방법에 대해서 제안한다. 본 논문에서 제안하는 방법은 제 3의 신뢰할 수 있는 키 분배 서버로부터 두 개의 해쉬키 체인을 사용하여 생성된 키를 키 서버와 데이터 전달에 참여하는 노드 간에 미리 설정된 비밀키를 사용하여 안전하게 전달하고, 각 노드 간에 데이터 전송시 키 서버로부터 수신한 해쉬키를 사용하여 MAC 코드를 생성함으로써 각 중간 노드마다 데이터를 인증하는 방식이다. 제안된 방법은 인증서 기반의 PKI를 사용하는 방법보다 간단하며, 비밀키 방식의 경우 임의의 ad-hoc 노드 제어들 간에 비밀키를 미리 설정해야하는 부담을 감소시켰다.

• 대한미생물학회지
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• 제18권1호
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• pp.47-52
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• 1983

During the last three years, it has become evident that patients with tuberculosis-like diseases due to the Mycobacterium avium-intracellulare complex(referred to M. avium complex; MAC) in Korea are more frequently observed than were assumed earlier. However, the incidence of various serotypes of the MAC isolated from patients with tuberculosis-like diseases has not been clarified. In this study, the serotypes of 16 strains of the MAC isolated from sputa of persons who had radiographic abnormalities of the lungs were determined by bacterial agglutination test with reference sera. The serotypable strains belonged to 7 serotypes, i.e., M. avium 13 were 4 strains(25.0%), M. avium 8 and 14 each 3 strains(18.8%), M. avium 5, 7, 12 and 18 one strain(6.3%), respectively. Two strains(12.5%) were not typable.

• Macromolecular Research
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• 제16권8호
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• pp.734-740
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• 2008

A new crosslinked, poly(acrylic acid)-based, dehydrating agent was synthesized through solution polymerization. The Taguchi method, a robust experimental design, was adopted to optimize the synthetic conditions based on the moisture and water absorbing capacities of the dehydrating agent. The method applied for the experiment was a standard L27 ($3^8$) orthogonal array with eight parameters and three levels. By analyzing the variance of the test results, the most effective parameters to control the moisture absorbing capacity (MAC) and its rate were the kind of alkaline base (LiOH, NaOH, or KOH) used as a neutralizing agent of the acrylic acid monomer and the degree of neutralization: The maximum MAC of 40% was achieved at only 2 hat $32^{\circ}C$ and 50% RH when KOH was used as a base and the degree of neutralization was 90%, respectively. However, the water absorbing capacity (WAC) of the resulting dehydrating agent was very low at 158 g/g, indicating that WAC is unaffected by MAC and its rate in this system. The surface morphologies of the agents were examined using scanning electron microscopy (SEM).

• 설비공학논문집
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• 제24권12호
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• pp.823-829
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• 2012

In this study, the performance of mobile air conditioner(MAC) systems to which the refrigerants R134a and R1234yf were used was evaluated to compare the characteristic of automotive refrigeration cycles with refrigerant. The experimental setup of a MAC consists of an belt driven compressor, a condenser, an evaporator and a block type thermal expansion valve. The drop-in test on MAC were carried out under variable compressor speed from 800 to 2500 rpm. Performance test by using R1234yf and R134a in the same system revealed low the charge amount and mass flow rates for using R1234yf, that is, up to 10% and 17%, respectively. The compressor discharge temperature of R1234yf is $8^{\circ}C$ lower than that of R134a. The cooling capacity with R1234yf system decreased by 4~7% compared with R134a system. In addition, The COP of R1234yf system is lower 3~4% than that of R134a system.

• 한국수학교육학회:학술대회논문집
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• 한국수학교육학회 2007년도 제38회 전국수학교육연구대회 프로시딩
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• pp.7-19
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• 2007

During the past 20 years, a small but potentially powerful initiative has established itself in the mathematics education landscape: Mathematics Across the Curriculum (MAC). This curricular reform movement was designed to address a serious problem: Not only are students unable to demonstrate understanding of mathematical ideas and their applications, but also they harbor misconceptions about the meaning and purpose of mathematics. This paper chronicles the brief history of the MaC movement. The sections of the paper correspond loosely tn the typical steps one might take to solve a mathematics problem. The Problem Takes Shape presents a discussion of the social and economic forces that led to the need for increased articulation between mathematics and other fields in the American educational system. Understanding the Problem presents the potential value of exploiting these connections throughout the curriculum and the obstacles such action might encounter. Devising a Plan provides an overview of the support systems provided to early MAC initiatives by government and professional organizations. Implementing the Plan contains a brief description of early collegiate programs, their approaches and their differences. Extending the Solution details the adoption of MAC principles to the K-12 sector and throughout the world. The paper concludes with Retrospective, a brief discussion of lessons learned and possible next steps.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권7호
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• pp.3447-3469
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• 2019

It is well-known that the cooperative communication and error control technology can improve the network performance, but most existing cooperative MAC protocols have not focused on how to cope with the contention process caused by cooperation and how to reduce the bad influence of channel packet error rate on the system performance. Inspired by this, this paper first modifies and improves the basic rules of the IEEE 802.11 Medium Access Control (MAC) protocol to optimize the contention among the multi-relay in a cooperative ARQ scheme. Secondly, a hybrid ARQ protocol with soft combining is adopted to make full use of the effective information in the error data packet and hence improve the ability of the receiver to decode the data packet correctly. The closed expressions of network performance including throughput and average packet transmission delay in a saturated network are then analyzed and derived by establishing a dedicated two-dimensional Markov model and solving its steady-state distribution. Finally, the performance evaluation and superiority of the proposed protocol are validated in different representative study cases through MATLAB simulations.