• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.4 s.334
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• pp.21-28
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• 2005

SC-FDE (Single Carrier with Frequency-Domain Equalization), one of physical layers of IEEE802.16, is less sensitive to nonlinear power amplifiers than OFDM while its complexity and performance is comparable. The guard interval length in SC-FDE should be greater than the maximal delay spread. While a delay spread is small in most wireless communication environments, a very large delay spread can be possibly encountered in the mountain areas or due to the repeaters. This paper proposes SC-FDE with variable-length guard intervals. In the proposed method the guard interval length can be determined per each cell or per each subscriber stations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.5
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• pp.1208-1220
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• 1996

In this paper, the performance of a Carrier Sense Multiple Access/Collision avoidance (CSMA/CA) protocol using stop-and-Wait automatic Repeat reQuest, which is adapted as a draft standard in IEEE 802.11, is analyzed using a mathematical method based on a renewal theory, and simulation checks are performed, which confirm the goodness of our anlysis. In order to anlayze of CSMA/CA, we model that network is composed of finite populationand channel is slotted. And, we consider the CSMA/CA protocol as a hybrid protocol of 1-persistent CSMA and p-persistent CSMA protocol. As resuls of analysis, we have found that the throughput is degraded and packet delay is increased as the number of stations, Acknowledgement (ACK) length and Distributed coordination function Inter Frame Space (DIFS) length are increased.

• Information and Communications Magazine
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• v.27 no.8
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• pp.43-49
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• 2010

향후 다양한 무선/이동 액세스 네트워크가 서로 연동하여 동작하는 환경에서 무선자원을 효율적으로 이용하고 사업자 및 사용자의 요구사항을 만족시킬 수 있는 이동/무선 네트워크를 위한 연동구조가 요구된다. 이에 본 고에서는 IEEEP1900.4및 IEEE 802.21에서 제시하는 표준기술을 이용하여 Smart Radio 시스템의 구조 및 Universal Access를 위한 Framework를 제안하고 동작 시나리오 및 기능 모듈간의 연동절차를 제시한다. 또, 제안된 시스템구조 및 Framework의 기능 및 성능을 분석하기 위해서 시스템수준 시뮬레이터를 설계/구현에 대해서 기술한다. 성능분석의 결과, 제안한 시스템 연동구조 및 Framework를 이용할 경우, 이동단말은 액세스 네트워크의 통신환경을 자율적으로 인지할 수 있었으며 무선자원을 효율적으로 이용할 수 있었다.

• Electronics and Telecommunications Trends
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• v.21 no.4 s.100
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• pp.62-69
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• 2006

유비쿼터스 정보화사회의 도래와 함께 한정된 주파수자원에 대한 수요가 증가됨에 따라 이를 효율적으로 이용하기 위한 기술이 더욱 각광을 받고 있다. 이중에서도 스펙트럼 환경을 측정하여 사용하지 않은 주파수를 선정, 기존의 전파환경과 양립하면서 통신을 하는 CR 기술은 미래 무선통신의 핵심 기술로 인식되고 있다. CR 기술은 SDR 기술을 기반으로 스펙트럼 센싱(spectrum sensing) 기능을 활용하여 가용한 주파수를 선정하여 통신하는 기본적인 기능과 여러 가지 환경 파라미터를 지속적으로 업데이트하는 learning algorithm이 합쳐진 기술이다. 본 고에서는 CR 기술을 설명하고, CR의 응용으로 현재 표준화가 진행되고 있는 IEEE 802.22 WRAN 표준화 활동과 WG에서 검토되고 있는 기술, 즉 physical layer, MAC layer, 그리고 spectrum sensing의 주요기술을 소개한다.

• Information and Communications Magazine
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• v.21 no.6
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• pp.67-88
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• 2004

유비쿼터스 네트워킹 환경은 사람 주변의 모든 기기가 하나의 네트워크로 연결되어 끊김없이 정보를 주고받으며 통신을 가능하게 해 주는 전자공간과 실제 공간의 융합이다［1, 2, 3, 4］. 이와 같은 유비쿼터스 환경이 지원되면 우리가 살고 있는 세상은 평온하고 지능화된 느낌에 상황인지 능력을 갖추게 되어 생산적이며 대응 능력을 지원 받을 수 있는 안락한 상황이 된다. 이러한 유비쿼터스 환경의 제공을 위해서는 "AlWays Connected"와 "Broadband" 그리고 ＂Every Device in One Network"의 세 가지의 키워드가 필수적인 요소［2］이다. 이 세 가지의 요소가 충족되려면 많은 기술들이 필요하게 된다. (중략)되려면 많은 기술들이 필요하게 된다. (중략)

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.6
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• pp.37-47
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• 2009

In this paper fast mobile multicast handover mechanism based on IEEE 802.21 MIH (Media Independent Handover) is proposed. We solve long multicast handover delay time caused by L3 movement detection mechanism of the existing mobile multicast methods. The proposed architecture adopts multicast manager concept to MIH framework in order to efficiently perform mobile multicast handover, and adds the new MIH messages dedicated for mobile multicast. Since multicast channel zapping operations of mobile users effectively make a mobile terminal handover, the architecture should consider the situations. Multicast network selection algorithm is designed by means of terminal speed and fair selection algorithm named AHP/GRA. Finally the performance of the proposed architecture against the legacy mobile multicast mechanisms is evaluated in terms of signaling cost and multicast handover delay time.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.8
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• pp.865-871
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• 2010

A compact dual-band(IEEE 802.11b: 2.4~2.5 GHz, 11a: 5.15~5.825 GHz) 2-channel MIMO antenna for PMP applications is presented. The proposed antenna is composed of a planar inverted F-shape antenna(PIFA) operating at 2 GHz band and a loop antenna operating at 5 GHz band. The proposed antenna is orthogonally arranged at the edge of the ground plane for polarization and pattern diversities with excellent isolation characteristics. The two PIFA antennas operating 2 GHz have connecting line($\lambda_g$/4) face to the feed point for high isolation and low correlation at 2 GHz band. The two loop antennas connected each other in the bottom side to improve the isolation at 5 GHz band. The proposed antenna has a sufficient gain in WLAN service band and is compact sized for the portable media player (PMP) applications.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.10
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• pp.59-65
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• 2007

Recently, ubiquitous sensor network(USN) techniques have been applied to electric power facility management. This paper dealt with the designed and fabricated ubiquitous sensors which monitor transformers and lightning arresters installed in overhead distribution systems. The sensors consist of a 8-[bit] microprocessor unit, a wireless communication nodule specified in IEEE 802.15.4, and associated electronics. A Rogowski coil was fabricated to measure load of transformer and surge current without saturation having good linearity up to 1000[A]. A zero-phase current transformer with a high relative permeability of $10^5$ at 180[Hz] was used to detect small leakage current of $50[{\mu}A]{\sim}1[mA]$ flowing lightning arrester, and the frequency bandwidth of the module is ranges from 12[Hz] to 1.24[kHz] at -3[dB].

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.1
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• pp.75-81
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• 2007

This paper dealt with the design and implementation of an expert system to monitor and diagnose the lightning arresters in GIS substations. The expert system consists of a data acquisition module(DAM) based on microprocessor and diagnostic algorithms. The DAM measures and analyzes several parameters necessary for the arrester diagnosis such as system voltages, leakage current components, and temperatures. Also, it includes an intelligent surge counter which can record the date and tin, the polarity, and the amplitude of surge currents. All the data acquired is transmitted to a remote computer by a low rate wireless network specified in IEEE 802.15.4 to avoid electromagnetic intereference under high voltage and large current environments. The decision-making for the arrester diagnosis completes with a Java Expert System Shell(JESS) which is composed of a knowledge base, an inference engine and a graphic user interface(GUI).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.12
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• pp.2279-2284
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• 2017

Recent wireless communications using the unlicensed band have been on the rise and the range of use is increasing. The license-exempted band is a prerequisite for accepting interference between telecommunication equipment. In particular, the interference phenomenon of Bluetooth, wireless LAN, and RFID (Radio Frequency Identification) using the 2.4 GHz band is getting serious. In such urban areas, the wireless transmission medium may be in a bad state. There are roughly two ways to make effective transmission in this environment. The first is the IEEE 802.11 RTS / CTS method and the second is the frame fragmentation method. In this paper, it is difficult to transmit a frame over a certain size in a jamming environment due to the interference of the wireless environment. In this environment, we implement a frame division transmission scheme that guarantees effective transmission and reliability by dividing a frame into smaller units in order to perform reliability transmission and efficient transmission.