• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.425-426
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• 2008

본 논문에서 설계한 802.11 MAC(Medium Access Control)은 하드웨어와 소프트웨어의 통합 구조로 되어 있다. MAC에서 가장 빠르게 동작해야 하는 프레임 전송과 수신블록은 하드웨어로 설계를 하였고, 그 외에는 소프트웨어로 설계가 되었다. 하드웨어로 설계된 MAC은 802.11 표준문서에 포함된 SDL(Specification and Description Language)을 기초하여 설계하였으며, 성능 향상을 위하여 수신블록의 중복 프레임 검사를 수행하는 블록과 프레임을 분석하여 정보를 추출하는 블록을 SDL과 다르게 설계 하였다. 삼성 0.35공정 라이브러리를 이용하여 합성한 결과 3만 게이트의 크기를 갖으며, 최대 동작 주파수는 100MHz이다. 메모리는 47Kbits SRAM을 사용하였다. 실제동작의 검증에 앞서 Mentor Graphics사의 ModelSim을 이용하여 시뮬레이션을 수행하였으며, 동작 검증은 Huins 사의 Altera Excalibur FPGA가 탑재된 XP8000 보드를 이용하여 이루어 졌다.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.05a
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• pp.1656-1660
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• 2006

Distributed coordination function(DCF) is the primary random access mechanism of IEEE 802.11, which is the basic protocol of wireless LAN based on the CSMA/CA protocol. It enables fast installation with minimal management and maintenance costs and is a very robust protocol for the best effort service in wireless medium. The current DCF, however, is known to be unsuitable for real-time applications such as voice message transmission. In this paper, we focus on the performance issues of IEEE 802.11 which accommodate the prioritized messages. Existing results use the initial window size and backoff window-increasing factor as tools to handle the priority of the messages. Instead, we introduce a novel scheme which chooses the backoff timer with arbitrary probabilities. By this, one can greatly reduce the backoff delay of the lower priority messages without degrading the performance of higher priority.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.602-605
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• 2001

This paper focus on a method to use Ethernet Network for Industrial Communication Network. Ethernet use the CSMA/CD MAC(Medium Access Control) Protocol at the Data-Link Layer, Which isn't suit for Industrial Communication Network requiring Real-Time Communication, periodic data processing, critical data processing characteristics. In this paper we proposed the Virtual Polling Algorithm at the Application Layer will be solution of using the Ethernet Network for the Industrial Communication Network, Proposed Algorithm terminate the Collision in the network thus Delay Time is reduced and Real-Time Communication will be implemented.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1266-1269
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• 2003

Many studies have indicated that most of a product's cost is fixed early in its lift cycle, before the original design cycle is complete. This implies that we should consider various aspects of product lift cycle at the design stage. This means the need of collaboration in design stage. Because the Internet provides instant access to a wealth of design information, the Internet is used by the collaborative design team members as a medium to share data, information and knowledge, and in some cases for product data management and project management by integrating the Web with appropriate technologies. This paper presents a real-time collaborative design system for powerful interaction performance, based on the Internet and Web technologies. Using The system use the client/server architecture and the purpose of the system is to provide a method that enables real-time view, review and modification of the 3D model through the Internet.

• Journal of applied mathematics & informatics
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• v.22 no.1_2
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• pp.501-515
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• 2006

The IEEE 802.11 protocol is the most mature technology for WLANs(Wireless Local Area Networks). However, as the number of stations increases, the delay and throughput performance of IEEE 802.11 MAC(Medium Access Control) degrades severely. In this paper, we present the comprehensive performance analysis of IEEE 802.11 MAC protocol by investigating the MAC layer packet service time when arrival packet sizes have a general probability distribution. We obtain the discrete probability distribution of the MAC layer service time. By using this, we analyze the system throughput and the MAC layer packet service time of IEEE 802.11 MAC protocol in wireless LAN environment. We take some numerical examples for the system throughput and the mean packet service time for several special distributions of arrival packet sizes.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.05a
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• pp.1279-1282
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• 2005

지금까지 무선 통신 기술은 높은 데이터 처리량을 가진 통신에 대하여 집중 개발되었으나, 낮은 처리량과 적은 비용, 낮은 전력소모의 요구사항을 가진 소형 경량의 무선 통신 분야의 기술개발은 활발하지 못했다. 현존하는 무선 통신 기술들을 낮은 처리율과 낮은 가격, 낮은 전력소모의 요구사항에 적용하기에는 필요이상의 성능과 비용이 들어가며, 특히 많은 전력을 소모하는 문제점이 발생한다. 이러한 문제점을 해결하기 위해 소형 경량의 무선 통신 기술인 ZigBee가 생겨나게 되었다. 본 논문에서는 현존하는 무선 통신 기술과 ZigBee 기술을 비교분석하여 ZigBee 기술의 필요성과 장단점을 제시하고, ZigBee의 핵심 기술 중 하나인 IEEE 802.15.4 MAC(Medium Access Control) 프로토콜 개발결과를 기술한다.

• Journal of Information Processing Systems
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• v.10 no.3
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• pp.412-428
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• 2014

Request oriented sensor networks have stricter requirements than conventional event-driven or periodic report models. Therefore, in this paper we propose a minimum energy data aggregation (MEDA), which meets the requirements for request oriented sensor networks by exploiting a low power real-time scheduler, on-demand time synchronization, variable response frame structure, and adaptive retransmission. In addition we introduce a test bed consisting of a number of MEDA prototypes, which support near real-time bidirectional sensor networks. The experimental results also demonstrate that the MEDA guarantees deterministic aggregation time, enables minimum energy operation, and provides a reliable data aggregation service.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10c
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• pp.256-258
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• 1999

본 논문에서는 DS-CDMA 시스템에서 예약 기반 MAC 플로토콜의 성능을 분석한다. 본 논문에서 고려하고 있는 예약 기반 MAC 프로토콜은 NAK 방식과 Request 큐잉 방식이다. NAK 방식은 예약 요구를 수락할 수 없는 경우에 NAK를 전송하여 전송 불가를 통지하는 방식이며, Request 큐잉 방식은 예약 요구를 수락할 수 없을 경우에 기지국에 예약 요구 패킷을 저장하는 방식이다. 그리고 이러한 두 방식에 채널 유지 기능을 추가한 방식을 함께 고려한다. 각 방식에서 패킷의 길이를 변화시키면서 수율과 평균 전달 지연 시간을 비교하였다. 성능 분석 결과 패킷의 길이가 짧은 경우에는 예약 방식의 성능이 매우 낮으며, 패킷의 길이가 길어지면 성능이 향상되는 것을 알 수 있다. 그리고 채널 유지 기능을 추가함으로서 전반적인 성능이 향상되며, 채널 유지 방식에서는 패킷간의 도착 시간, 예약 과정의 지연 시간 등을 고려해서 최적의 채널 유지 시간을 설정해야 함을 알 수 있다.

• International Journal of Contents
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• v.15 no.4
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• pp.97-106
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• 2019

EMI (English as a Medium of Instruction) classes are now accepted policy at Korean universities, yet students often struggle with required academic English writings. The present study examined an EMI class that used direct instruction and access to online assistive English writing software. From preliminary analysis, 26 students expressed interest in how an EMI academic writing class could facilitate improved English writing skills. Study participants completed a survey on self-efficacy and learning needs and assignments for an EMI academic writing class. To establish inter-rater reliability, three trained raters assessed the written essays of students prior to and after instructional intervention. Fleiss' Kappas statistics showed moderate reliability. Students' opinions on the use of online software were also analysed. Paired t-test was run on the quality of students' pre- and post-instruction assignments, and there was significant difference in the rated scores. Self-efficacy was found to have moderate positive association with improved post-essay writing scores.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.5
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• pp.1267-1285
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• 2012

Wireless Body Area Networks (WBANs) deal with variety of healthcare services with diverse Quality of Service (QoS) requirements. However, QoS handling is a challenging problem in such networks. In general, QoS related problems can be addressed from different layers in the networking protocol suite. Design of an efficient QoS aware Medium Access Control (MAC) protocol can address this problem in MAC layer. This paper analyzes the QoS requirements of WBAN, identifies the requisites of QoS handling system, and outlines the trends that are being followed for its advancement with focus on QoS issues at MAC layer. We review some prior works, compare them, and analyze the current research concerned with problem of providing QoS in WBAN. We also explore some open issues and discuss them.