• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 한국해양정보통신학회 2005년도 춘계종합학술대회
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• pp.573-577
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• 2005

Recently there are increasing needs for Internet and various kinds of contents. These traffics for various contents need more amount of data to provide high-quality information and require various QoS depending on the characteristics of contents. However, current Internet service supports BE (Best Effort) service only, therefore IntServ (Integrated Service) scheme and DiffServ (Differentiated Service) scheme are represented to support QoS in IP layer. Moreover, while wireless Internet is getting popular, MAC(Medium Access Control)is also becoming important. This is due to the fact that wireless access, resource allocation and packet scheduling, which are done in another layers before, are performed in MAC layer in many new wireless systems. This paper describes new scheme that provides QoS taking into account the traffic characteristics over Mobile IPv6 network based on IEEE 802.11e EDCF and evaluates the performance through computer simulation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• 제12권5호
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• pp.213-217
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• 2012

In this paper, we design dual-band microstrip antenna for IEEE 802.16e mobile WiMAX standard IEEE 802.11 WLAN band at the same time. To solve interference at the desired operating frequency band, impedance matching is improved and simple production method showed the characteristics of the omni-directional and compact size. The proposed structure is considered to bring the effect of the installation costs, and show the antenna for dual-band communication.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제30권2A호
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• pp.80-89
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• 2005

In IEEE 802.11 and 802.11e for ad hoc networks, DCF and EDCA use a contention-based protocol called CSMA/CA, which is simple to implement efficient when the system is light loaded. But the performance of CSMA/CA decreases dramatically when the system load is heavy because of increasing collisions. In PCF and HCF modes, stations are controlled by a base station by polling, no collision ever occurs. However, when the system load is light, the performance is poor because few stations have data to transfer. More important, PCF and HCF can not be used in the ad hoc networks. In this paper, we address a priority-based distributed polling mechanism (PDPM) that implements polling scheme into DCF or EDCA modes for ad hoc networks by adding a polling approach before every contention-based procedure. PDPM takes the advantages of polling mechanism that avoids most of collisions in a high load condition. At the same time, it also keeps the contention-based mechanism for a light loaded condition. PDPM provides quality of service (QoS) with fewer collisions and higher throughput compared with IEEE 802.11e.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 한국해양정보통신학회 2007년도 추계종합학술대회
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• pp.849-852
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• 2007

In this paper, the high gain and the broadband microstrip patch antenna, which is applicable to 5 GHz band wireless LAN, is designed in order to integrate IEEE 802.11a's detailed standards($a:5.15{\sim}5.25$, $b:5.25{\sim}5.35$, $c:5.725{\sim}5.875$ [GHz]). Designed patch antenna has settled resonance frequency by insert substance(polyurethane: ${\varepsilon}_r=6.5$) between the separated parasitic patch and radiation patch for the purpose of miniaturize. And the form (${\varepsilon}_r=1.03$) were to fix the separated radiation patch and ground plans by air. Designed frequency bandwidth(VSWR 2:1) of the antenna showed broadband characteristic of $4.9[GHz]{\sim}6.1[GHz]$ to about 1.2[GHz]. Also the E-plan and H-plan profit 12[dBi] above, the 3[dB] beamwidth showed the characteristic over the E-plan $30^{\circ}$ and H-plan $60^{\circ}$ to be improved.

• Journal of Communications and Networks
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• 제13권2호
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• pp.149-159
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• 2011

In this paper, we study the problem of how to design a medical-grade wireless local area network (WLAN) for healthcare facilities. First, unlike the IEEE 802.11e MAC, which categorizes traffic primarily by their delay constraints, we prioritize medical applications according to their medical urgency. Second, we propose a mechanism that can guarantee absolute priority to each traffic category, which is critical for medical-grade quality of service (QoS), while the conventional 802.11e MAC only provides relative priority to each traffic category. Based on absolute priority, we focus on the performance of real-time patient monitoring applications, and derive the optimal contention window size that can significantly improve the throughput performance. Finally, for proper performance evaluation from a medical viewpoint, we introduce the weighted diagnostic distortion (WDD) as a medical QoS metric to effectively measure the medical diagnosability by extracting the main diagnostic features of medical signal. Our simulation result shows that the proposed mechanism, together with medical categorization using absolute priority, can significantly improve the medical-grade QoS performance over the conventional IEEE 802.11e MAC.

• Journal of KIISE:Computing Practices and Letters
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• 제16권11호
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• pp.1066-1070
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• 2010

In wireless network, energy efficiency is an important design consideration for continuous multimedia streaming service. This paper proposes a new streaming system, called BACASS (Buffer-Aware and Content-Aware Streaming System) that working on the 802.11e U-APSD (Unscheduled Automatic Power Save). The BACASS leads the DP (Doze Period) of U-APSD for improving energy efficiency by utilizing the PSNR based on content-aware and client buffer occupancy that is hinged on a network-aware streaming system using SVC. The simulation results demonstrate the effectiveness of the proposed streaming system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제49권7호
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• pp.6-11
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• 2012

A mobile station(MS) in an 802.16e network manages its limited energy using the sleep mode operation. An MS can power down its physical operation components during the unavailability interval of the sleep mode. To reduce energy consumption by increasing the unavailability interval, this paper proposes an enhanced power saving mechanism(ePSM) when both activated Type I and Type II power saving classes(PSCs) exist in an MS. A performance evaluation confirms that ePSM results in the improved performance in terms of the unavailability interval as well as the energy consumption than conventional schemes.

• Proceedings of the Korean Information Science Society Conference
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• 한국정보과학회 2005년도 가을 학술발표논문집 Vol.32 No.2 (1)
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• pp.412-414
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• 2005

무선 랜 표준인 IEEE 802.11은 원래 best effort service를 위해 탄생된 기술이기 때문에 QoS(Quality of Service)에 대한 연구가 부족했다. 무선 랜에서는 기존 유선 랜보다 한정된 자원과 희박한 bandwidth, 다양한 노드들의 채널 공유로 인해 QoS를 보장하기가 어렵다. 이를 보완하기 위한 연구가 IEEE 802.11e 워킹그룹에서 진행되고 있다. 본 논문에서는 충돌방지를 위한 CSMA/CA 알고리즘의 back-off값 설정을 매개변수를 두어 idle 시간을 조정함으로써 QoS를 보장하는 알고리즘을 제안한다. 특히, QoS가 요구하는 패킷전달 간격 임계값(threshold)에 따른 매개변수를 조절하여 contention window 크기를 달리 조정함으로써 QoS를 요구하는 노드들의 수에 상관없이 균일한 서비스 성능을 유지하도록 한다. 이 때, 매개변수 값의 선택은 QoS를 제공하는 노드들의 서비스 성능 뿐 아니라 best effort service만을 제공해도 되는 일반 노드들의 서비스 성능도 함께 고려할 수 있도록 하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.586-589
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• 2001

This paper focuses on a method to connect mobile devices such as mobile robot, Automated Guided Vehicle(AGV) to a fieldbus. In this paper, the IEEE 802.11 wireless LAN is used to extend a Profibus-DP network for the mobile devices. In order to integrate these two networks, a protocol converter is developed with two process(i.e., master process of Profibus-DP and virtual master process of IEEE 802.11) and an transmission buffer. Futhermore, a virtual polling algorithm is developed at the protocol conveter in order to satisfy real-time requirements on data communication.

• Proceedings of the Korean Information Science Society Conference
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• 한국정보과학회 2012년도 한국컴퓨터종합학술대회논문집 Vol.39 No.1(D)
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• pp.303-304
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• 2012

본 논문에서는 IEEE 802.11e 무선 애드 혹 네트워크 환경에서의 Throughput 향상을 위한 자원 할당 기법을 제안하였다. 제안하는 기법은 무선 애드 혹 네트워크에서 전송 홉 수 증가 및 네트워크 혼잡 상황에 따른 전송 손실을 최소화 하기 위한 기법으로 전송 큐 상태를 주기적으로 측정하여 큐에 쌓여지는 데이터의 가속도와 전송 큐에 쌓여있는 데이터의 비율을 측정한다. 측정된 가속도와 데이터의 비율을 통해 네트워크 상황에 적합한 자원을 할당하는 기법이다. 제안한 기법을 통해 무선 애드 혹 네트워크 환경에서 전송 홉 수 증가 및 네트워크 혼잡 상황에서의 성능 감소를 개선할 수 있었다.