• Journal of Korean Institute of Industrial Engineers
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• v.41 no.2
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• pp.220-224
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• 2015

The DCF (Dcistributed Coordination Function) and PCF (Point Coordination Function) are the basic MAC (Medium Access Control) protocols of IEEE 802.11 wireless LANs. According to the DCF, each node performs the exponential backoff algorithm before the transmission of its data frame. Each node doubles the backoff waiting time before the transmission of its data frame whenever it detects the transmission collision with other nodes. Therefore, as the number of the active nodes having the data frames to transmit increases, the overall MAC performance of the DCF decreases. On the other hand, according to the PCF, each node is granted the transmission opportunity by which the PCF transmission is possible without the collision with other nodes. Therefore, as the number of the active nodes increases, the MAC performance of the PCF increases, In this paper, considering the tradeoff of MAC performance between the DCF and PCF, a hybrid MAC protocol is proposed to enhance the performance of IEEE 802.11 wireless LANs.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.11a
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• pp.1413-1416
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• 2008

최근 들어 IEEE 802.11 WLAN 서비스에 대한 수요의 증가와 함께 WLAN 환경에서 실시간 멀티미디어 서비스를 이용하려는 사용자의 관심이 날로 증가하고 있다. 그러나 IEEE 802.11i 의 보안 정책은 MS 의 이동이 빈번하게 발생하는 WLAN 환경에서 끊김 없는 실시간 멀티미디어 서비스를 제공하기에는 핸드오프 지연 시간이 너무 길다. 본 논문은 DoS 공격에 취약한 기존 802.11i 에서의 4-way Handshake 를 대체하는 신속하고 효율적인 인증 및 세션키 분배 메커니즘을 제안한다.

• Journal of KIISE:Information Networking
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• v.32 no.6
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• pp.723-731
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• 2005

Wide spread deployment of infrastructure WLANs has made Wi Fi an integral part of today's Internet access technology. Despite its crucial role in affecting end to end performance, past research has focused on MAC protocol enhancement, analysis and simulation based performance evaluation without sufficient consideration for modeling inaccuracies stemming from inter layer dependencies, including physical layer diversity, that significantly impact performance. We take a fresh look at IEEE 802.11 WLANs, and using experiment, simulation, and analysis demonstrate its surprisingly agile performance traits. Contention based MAC throughput degrades gracefully under congested conditions, enabled by physical layer channel diversity that reduces the effective level of MAC contention. In contrast, fairness and jitter significantly degrade at a critical offered load. This duality obviates the need for link layer flow control for throughput improvement but necessitates traffic control for fairness and QoS. We use experimentation and simulation in a complementary fashion, pointing out performance characteristics where they agree and differ.

• Journal of KIISE:Information Networking
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• v.31 no.2
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• pp.217-223
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• 2004

This paper proposes a new backoff scheme to improve the throughput of stations over wireless local area networks. It is designed to carry out the proposed backoff scheme using information of basic service area, such as number of stations, in terms of the throughput. Basic idea of the proposed backoff scheme is that we change the contention window size for backoff time as collisions increase. We evaluate the performance of the proposed backoff scheme using Markov model analysis and compare it with the IEEE 802.11e backoff scheme. The numerical results indicate that the Proposed backoff scheme may offer better performance than the conventional backoff scheme in terms of the throughput.

• Proceedings of the KAIS Fall Conference
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• 2004.11a
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• pp.179-181
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• 2004

This study presents a cylindrical WLAN antenna for MIMO systems. Three typical inverted-F antennas, which have individual ground plane, are placed on the cylindrical rod. An optimum antenna is fabricated by theoretical prediction and numerical simulation. The proposed antenna here can operate in the 5GHz bands(IEEE 802.1la) and be adopted in small wireless communication systems.

• Proceedings of the Korea Multimedia Society Conference
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• 2004.05a
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• pp.143-146
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• 2004

무선 사용자의 증가에 따라 802.11 표준에 대한 취약점이 대두되었다. 무선랜에서 보안을 위한 IEEE 워킹 그룹에서는 EAP, 802.1x, RADIUS, TKIP, 802.lli등의 표준안을 제시 하여 최근 WPA 가 Wi-Fi 에 의해 802.lli의 중간 단계로써 제안되어 구현되고 있다. 본 논문에서는 향후 각 회사 별 WEP 취약점 보완을 위한 패켓단위의 IV변경을 PRF 알고리즘에 기반하여 암호화를 리눅스 디바이스 드라이버 레벨에서 시험 구현하였다. 임베디드 시스템에 적용하기 위한 구현 타당성을 위하여 PXA255 프로세서에서 client를, 인텔 PC에서 HOST AP 환경을 시험환경으로 사용하였다.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.32 no.3
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• pp.10-19
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• 2009

Wireless LAN systems have been widely implemented for supporting the wireless internet services especially in the hotspot areas such as hospitals, homes, conference rooms, and so on. Compared with wired LAN systems, wireless LAN systems have the advantages of the users' mobility support and low implementation and maintenance costs. IEEE 802.11 wireless LAN systems employ the backoff algorithm to avoid contentions among STAs when two or more STAs attempt to transmit their data frames simultaneously. The MAC efficiency can be improved if the CW values are adaptively changed according to the channel state of IEEE 802.11 wireless LANs. In this paper, a dynamic contention window control algorithm is proposed using the genetic algorithm to improve the MAC throughput of IEEE 802.11 wireless LANs.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.427-428
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• 2009

무선 네트워크 환경에서 합법적인 AP(Access Point)의 MAC 주소, SSID(Service Set Identifier), 채널등의 정보를 이용하여 복제된 AP(Cloned Access Point)를 만들 수 있다. 복제된 AP는 합법적인 AP와 연결되어 있는 무선 스테이션들의 연결 설정을 끊고 자신과 연결 설정을 하게 한다. 무선 스테이션들이 복제된 AP와 통신을 하게 되면서 많은 공격으로부터 노출되게 된다. 본 연구에서는 복제된 AP가 설치되었을 때 무선 스테이션들이 합법적이 AP의 비콘 프레임과 복제된 AP 비콘 프레임의 시퀀스 번호를 이용하여 복제된 AP을 판별하였다. 시뮬레이터 NS-2를 이용하여 실험한 결과 본 논문에서 제안하는 메커니즘을 통해 무선 스테이션들이 복제된 AP의 등장을 판별할 수 있게 되어 보다 안전한 무선랜 환경을 구축할 수 있게 되었다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.6
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• pp.116-126
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• 2008

This paper describes the Dual-band WLAN transmitter with 2.4[GHz], 5[GHz]. Dual-band WLAN transmitter was designed at 2.4[GHz] and 5[GHz]. The Dual-band WLAN transmitter has a amplifier which operate at 2.4[GHz] and 5[GHz] frequency and two VCO(Voltage Controlled Oscillator) or VCO has a wide scope of frequency. these problem cause a size and a power consumption, The Dual-band WLAN transmitter module was proposed to solve these. the transmitter was designed to get output signals of IEEE 802.11a's 5.8[GHz] band signal using frequency multiplication way or to act a amplifier about the 2.4[GHz] band signal of IEEE 802.11b/g, according to inputed frequency and bias voltage that a eve using single transmission block. The output spectrum get the improved specification of ACPR of 4[dB], 6[dB], 16[dB] at +11[MHz], +20[MHz], +30[MHz] offset of center frequency compared to no linearization, was satisfied to transmit spectrum mask of IEEE 802.11a wireless Lan.

• Proceedings of the Korean Information Science Society Conference
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• 2008.06a
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• pp.257-258
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• 2008