• ETRI Journal
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• 제23권2호
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• pp.52-60
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• 2001

In this paper, a medium access control protocol is proposed for integrated voice and data services in wireless local networks. Uplink channels for the proposed protocol are composed of time slots with multiple spreading codes per slot based on slotted code division multiple access (CDMA) systems. The proposed protocol uses spreading code sensing and reservation schemes. This protocol gives higher access priority to delay-sensitive voice traffic than to data traffic. The voice terminal reserves an available spreading code to transmit multiple voice packets during a talkspurt. On the other hand, the data terminal transmits a packet without making a reservation over one of the available spreading codes that are not used by voice terminals. In this protocol, voice packets do not come into collision with data packets. The numerical results show that this protocol can increase the system capacity for voice service by applying the reservation scheme. The performance for data traffic will decrease in the case of high voice traffic load because of its low access priority. But it shows that the data traffic performance can be increased in proportion to the number of spreading codes.

• Journal of Communications and Networks
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• 제6권4호
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• pp.317-330
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• 2004

In this paper, we explore the utility of recently discovered multiple-antenna techniques (namely MIMO techniques) for medium access control (MAC) design and routing in mobile ad hoc networks. Specifically, we focus on ad hoc networks where the spatial diversity technique is used to combat fading and achieve robustness in the presence of user mobility. We first examine the impact of spatial diversity on the MAC design, and devise a MIMO MAC protocol accordingly. We then develop analytical methods to characterize the corresponding saturation throughput for MIMO multi-hop networks. Building on the throughout analysis, we study the impact of MIMO MAC on routing. We characterize the optimal hop distance that minimizes the end-to-end delay in a large network. For completeness, we also study MAC design using directional antennas for the case where the channel has a strong line of sight (LOS) component. Our results show that the spatial diversity technique and the directional antenna technique can enhance the performance of mobile ad hoc networks significantly.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
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• pp.423-425
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• 2007

In this paper, Medium Access Control(MAC) protocol designed for Wireless Body area Sensor Network(Bio-MAC) is proposed, Because in WBSN, the number of node is limited and each node has different characteristics. Also, reliability in transmitting vital data sensed at each node and periodic transmission should be considered so that general MAC protocol cannot satisfy such requirements of biomedical sensors in WBSN. Bio-MAC aims at optimal MAC protocol in WBSN. For this, Bio-MAC used Pattern -SuperFrame, which modified IEE E 802.15.4-based SuperFrame structurely. Bio-MAC based on TDMA uses Medium Access-priority and Pattern eXchange -Beacon method for dynamic slot allocation by considering critical sensing data or power consumption level of sensor no de etc. Also, because of the least delay time. Bio-MAC is suitable in the periodic transmission of vital signal data. The simulation results demonstrate that a efficient performance in WBSN can be achieved through the proposed Bio-MAC.

• 한국콘텐츠학회논문지
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• 제2권3호
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• pp.113-118
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• 2002

HFC(Hybrid Fiber Coax)기반으로 한 CATV망에서 양방향을 제공하기 위해서는 매체접근제어(Medium Access Control)프로토콜이 필요하다. 특히, 가입자에서 헤드앤드로 데이터를 전송하는 상향채널은 500가입자 이상이 공유하기 때문에 충돌이 발생하게 된다. 본 논문은 HFC-CATV망에 적합한 충돌해결알고리즘인 이진 스택 알고리즘의 안정성(stability)을 연구하기 위해 분석 모델을 제안하고 기존 모델과의 시스템 처리율(throughput)을 비교ㆍ분석하였다

• Journal of Communications and Networks
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• 제14권1호
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• pp.40-50
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• 2012

The Berkeley-medium access control (B-MAC) is a lightweight, configurable and asynchronous duty cycle medium access control (MAC) protocol in wireless sensor networks. This article presents an analytic modelling of single-hop B-MAC protocol under a Poisson traffic assumption.Our model considers important B-MAC parameters such as the sleep cycle, the two stage backoff mechanism, and the extended preamble. The service delay of an arriving packet and the energy consumption are calculated by an iterative method. The simulation results verify that the proposed analytic model can accurately estimate the performance of single-hop B-MAC with different operating environments.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2005년도 한국컴퓨터종합학술대회 논문집 Vol.32 No.1 (A)
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• pp.469-471
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• 2005

802.11 기반의 DCF 모드 상에서 하나의 패킷 전송을 위해서는 RTS-CTS-DATA-ACK 의 4가지 단계의 프레임 전송 과정이 이루어져야한다. 다중 홉 상태에서의 패킷 전송 또한 위 4단계를 거쳐서 종단 간에 패킷 전송이 이루어진다. 다중 홉 상태의 패킷 전송 단계에서는 전송 도중 패킷간의 충돌이 발생 할 수 있다. 이와 같은 충돌을 최소화 시키고 종단 간 패킷전송의 성능을 향상시키기 위한 연구가 진행되고 있다. 본 논문에서는 이러한 연구 중에 하나인 DCMA(Data-driven Cut-through Medium Access) 프로토콜[1]의 기능을 파악하고 이에 대한 보완 방법을 제안하여 이를 발전시킨 BCTMA (Bi-directional Cut-Through Medium Access) 프로토콜을 제안 한다.

• 한국정보통신학회논문지
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• 제19권10호
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• pp.2465-2472
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• 2015

무선 MAC (Medium Access Control)과 라우팅 기술은 사물인터넷의 핵심 네트워크 기술 요소로서. 최근 이와 관련된 집중적인 연구가 진행 되고 있다. 그러나 사물인터넷을 위한 새로운 표준이 제안되고, 다른 네트워크 관련 기술들이 패치되면서, 이러한 네트워크의 성능을 평가하는 방식은 명확하지 않다. 본 연구에서는 사물인터넷을 위한 최근의 MAC과 라우팅 프로토콜 기술을 분석 정리하고, 이들 간의 상호작용에 대하여 설명하였다. 특히, 현재 많은 사물인터넷 관련 분야에서 고려되고 있는 IEEE 802.15.4 MAC 과 RPL (Routing Protocol for Low-power Lossy Network) 라우팅 프로토콜의 기술을 설명하고 이들 간의 상호 작용에 대하여 설명하였다. 이러한 분석에 따라 경쟁기반의 MAC 프로토콜의 경우 라우팅의 성능에 치명적인 영향을 줄 수 있으므로 MAC과 라우팅 관련 시스템 파라미터를 최적화 할 수 있는 모델링을 제시하였다.

• 동아시아경상학회지
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• 제4권3호
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• pp.18-24
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• 2016

Delivery of microfinance services to operators of small and medium enterprises (SMEs) is increasingly being viewed as a strategic means of assisting growth and development. The purpose of this study was to assess the contribution of microfinance to entrepreneurship development in Mogadishu. Survey research design was adopted and Primary data was collected by using questionnaires. This research study used purposive sampling method to select 120 respondents; but 108 were found usable and analyzed. The data was analyzed using descriptive statistics. This study found the access of microfinance services to the SMEs is poor. This study also found due to the collateral, short term repayment challenges, small and medium businesses are difficult to access loan from microfinance institutions which hinder their entrepreneurship development. In addition to these, this study found that the Microfinance institutions play significance role to the growth and sustainable development of SMEs and also increases the productivity and profitability of small and medium enterprises. This study recommends the guidelines of microfinance institutions to finance SMEs needs to be flexible and microfinance institutions should give technical assistant to the SME to ensure success in the SME sector. The study also suggests access of microfinance services to the SMEs should be facilitated and awareness to microfinance purposes and activities should be created.

• 한국통신학회논문지
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• 제30권6B호
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• pp.406-415
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• 2005

IEEE 802.11 무선 랜과 같이 단일 매체를 사용하는 무선망의 단말들은 경쟁을 통하여 매체를 점유하게 되며, 매체의 충돌이 발생하게 될 때 백오프 알고리즘을 사용하게 된다. 백오프 알고리즘은 매체의 충돌 확률을 줄임으로써 매체의 이용률을 높이고 효율적인 매체의 운영을 가능하게 하는 매체 접속 제어 방법의 중요한 요소이다. 본 논문에서는 QoS를 제공하기 위한 표준인 IEEE 802.11e를 기본으로 하여 네트워크의 매체 부하 및 혼잡 상태에 따라 능동적으로 경쟁 윈도우의 크기를 변화시키는 새로운 방법인 로드 기반 동적 매체 접속 제어 백오프 알고리즘을 제안한다. 제안된 부하 및 혼잡 상태의 예측과 우선순위에 따른 가중치의 차별화를 통한 동적 경쟁 윈도우 변경 방법이 기존의 IEEE 802.11e에서 사용하는 BEB 방법보다 매체의 이용률을 높이고 효율적으로 데이터의 충돌을 줄일 수 있음을 보인다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 D
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• pp.3040-3042
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• 2005

During the last several years, interest in broad-band power line communications (PLC) has been grown over medium voltage(MV) power distribution lines as well as low voltage lines. This paper introduces a medium voltage PLC test field that is set up in the suburbs of Euiwang city in Korea. This test field could be used not only for the measurement of communication channel environment but also for internet service. This paper shows the configuration of medium voltage test field with network devices like MV signal coupler and the results of channel environment like noise and impulse response. It also shows the service performance of PLC access network through network management system.