• Journal of Korean Institute of Industrial Engineers
• /
• v.33 no.2
• /
• pp.237-245
• /
• 2007

In this paper, a modified PCF (Point Coordination Function) MAC (Medium Access Control) Protocol is proposed to support the multiple direct link communication between STAs (STAtions) in infrastructure mode IEEE 802.11 wireless LANs. By the proposed MAC protocol, the direct link communication between STAs, which are located within the communication range of each other, is allowed without the use of AP (Access Point) as a relay. Moreover, when multiple direct data communication between STAs can be simultaneously performed with a sufficiently small interference, multiple simultaneous direct link communication is allowed for the efficient use of radio bandwidth. AP polls STAs to grant the transmission opportunities using the direct link communication by transmitting the polling frames to STAs. An efficient polling method for granting the transmission opportunities to STAs is proposed to reduce the number of the polling frame transmissions and enhance the PCF MAC performance.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.10B
• /
• pp.862-875
• /
• 2003

본 논문에서는 IEEE 802.11 규격을 기반으로 다중 홉 Ad Hoc 모드에서 비실시간 및 실시간 트래픽에 대한 통합 서비스를 지원하는 Wireless LAN을 구성할 때, 분산 방식으로 실시간 서비스의 우선권을 고려한 채널 액세스의 차별화를 제공할 수 있는 매체접근제어(Medium Access Control: MAC) 프로토콜의 구현 방안을 제안한다. 이를 위해 실시간과 비실시간 트래픽의 Contention Window (CW)를 서로 분리하며, 실시간 서비스의 지연 바운드에 따라 정해진 잔여 수명(residual time)을 우선권 설정에 반영함으로써 실시간 트래픽의 지연 요구 사항을 보장할 수 있도록 한다. 또한 실시간 트래픽의 부하에 따라서 적응적으로 offset 값을 조정함으로써 offset에 의해 발생될 수 있는 수율의 저하를 최소화한다. 제안된 방식은 기존 IEEE 802.11 MAC 규격의DCF (Distributed Coordination Function) 방식을 그대로 사용하면서 CSMA/CA 기반의 경쟁 방식을 통해서도 비실시간 트래픽과의 차별화가 가능하고, 또한 잔여 수명 시간을 고려한 동적인 우선권 할당이 가능하도록 하였다. 시뮬레이션에 의한 분석 결과에 따르면 기존 DCF와 비교할 때 실시간 단말의 용량을 2배까지 향상시킬 수 있으며, 트래픽 부하에 따라 적응적 제어를 통해 추가적인 성능 개선 효과를 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.1A
• /
• pp.73-81
• /
• 2011

IEEE 802.11 PHY and MAC layer provide multiple channels and data rates. To improve the performance of IEEE 802.11 multi-radio ad hoc networks, it is required to utilize available channels and data rates efficiently. However, in IEEE 802.11 multi-rate networks, the rate anomaly (RA) problem occurs that the network performance is severely degraded as low-rate links affect high-rate links. Hence, in this paper, we propose a model-based rate separation (MRS) algorithm that uses multiple channels to separate different data rate links so that the RA problem is mitigated. MRS algorithm utilizes an existing throughput model that estimates the throughput of IEEE 802.11 single-hop networks to separate low-rate links and high-rate links. Through simulations, we demonstrate that the MRS algorithm shows improved network performance compared with existing algorithms in multi-radio ad hoc networks.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.5 no.8
• /
• pp.1404-1422
• /
• 2011

In this paper, a new clear channel assessment (CCA) method: cascaded-CCA, is proposed. The primary motivation for the proposed approach is to integrate the respective advantages of two standard CCA mechanisms, energy detect and preamble detect, to arrive at a new dual threshold CCA family that can provide greater flexibility towards tuning MAC performance. Cascaded-CCA integrates energy efficiency of the energy detector (ED) and the reliability of the preamble detector (PD). The probability of detection/false alarm and power consumption of cascaded-CCA in the CCA modules of IEEE 802.11b are analyzed and compared with ED and PD as an example. The performance of cascaded-CCA is explored via MATLAB simulations that implement the CCA modules and medium access control (MAC) protocol for IEEE 802.11 and IEEE 802.15.4. Simulation results showed that cascaded-CCA improves the energy efficiency significantly compared to ED-only or PD-only CCA. In addition, ED, PD, and cascaded CCA are applied to a cognitive network scenario to validate the effectiveness of the proposed cascaded-CCA.

• Proceedings of the IEEK Conference
• /
• 2002.06a
• /
• pp.121-124
• /
• 2002

The IEEE 802.lla PLCP H/W for Processing efficiently control message between MAC and PHY is designed. Slate machine and clock control according to rate is designed and timing diagram is verified on the FPGA simulation environment.

• Proceedings of the KAIS Fall Conference
• /
• 2009.12a
• /
• pp.989-993
• /
• 2009

Wireless LAN(WLAN) is a rather mature communication technology connecting mobile terminals. IEEE 802.11 is a representative protocol among WLAN technologies. With the rising popularity of delay-sensitive real-time multimedia applications(video, voice and data) in IEEE 802.11 wireless LAN, it is important to study the MAC layer delay performance of WLANs. In this paper, performance for packet delay that recently have been proposed schemes is analysed in wireless LAN and proved performance results via simulation.

• Information and Communications Magazine
• /
• v.33 no.3
• /
• pp.74-79
• /
• 2016

IT기술의 발전으로 인하여 스마트 폰, 테블릿 PC, 노트북 등의 고사양을 가진 모바일 단말의 보급률이 증가하고 있으며, 모바일 단말이 사용하는 IEEE 802.11 표준 기술 또한 지속적인 보완작업과 개정작업을 통해 지원하는 주파수 대역 확장 되었으며, 데이터 전송속도도 빨라지고 있다. 하지만 기술이 발전하고 있음에도 불구하고, Management Frame의 무결성 확인 과정의 부재로 인한 보안 취약성이 아직 남아 있으며, 이를 악용하는 악성행위자의 ARP Spoofing 공격, AP DoS(Denial of Service) 공격, Mac Spoofing 을 기반한 Rouge AP 공격 등에 취약하다. 공공기관, 회사에서는 위 같은 취약점으로부터 무선네트워크를 보호하기 위해 WIPS 시스템을 도입하였지만, 이 또한 Management Frame의 취약성을 근본적으로 해결 할 수 없었다. 때문에 IEEE 802.11 워킹그룹은 Management Frame 보안성을 향상시킨 IEEE 802.11w-2009 표준 기술이 제안 하였으며, 이로 인해 Management Frame의 무결성을 확인하지 않아 발생하는 취약성으로 인한 보안 위협을 근본적으로 방지 할 수 있게 되었다. 하지만 IEEE 802.11w 표준 환경을 적용함으로써 새로운 유형의 보안 위협이 발생되었다. 따라서 본고에서는 IEEE 802.11w 표준에 대하여 살펴보며, IEEE 802.11w 표준 환경에서의 보안 기술에 대한 동향 알아본다.

• Proceedings of the Korean Information Science Society Conference
• /
• 2007.10d
• /
• pp.585-588
• /
• 2007

WMNs(Wireless Mesh Networks)은 기존 유 무선망 구축 시 발생하는 고가의 비용 및 이동성 제약 등의 단점을 극복하기 위해 제안된 네트워크 구조로써 네트워크 구축비용에 비해 광범위한 인터넷 접근영역을 제공하는 장점을 가진다. 특히, IEEE 802.11e를 MAC 계층으로 사용하는 WMN은 기존 IEEE802.11에서 보다 강화된 QoS(Quality of Service)기능을 가지므로, 안정적 멀티미디어 관련 응용 계층을 지원하는 WMN 구축을 위해 주목받고 있는 기술 중 하나이다. 본 논문은 광주과학기술원에 설치된 MIMC(Multi-Interface Multi-Channel) WMN 테스트베드를 QoS 기능 지원을 위해 IEEE 802.11e 기반으로 확장한다. 특히, 확장에 필요한 소프트웨어 요소 및 하드웨어 요소에 대해 논한다. 또한, 확장된 IEEE 802.11e WMN 테스트베드를 사용하여 현재 주목받고 있는 IEEE 802.11e기반 WMN의 기본 쓰루풋 성능, 쓰루풋 차별화 성능등을 실험적으로 분석한다.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.49 no.11
• /
• pp.132-138
• /
• 2012

VANET(Vehicular Ad-hoc Network), standardization of IEEE 802.11p specification is in process. 802.11 MAC protocol grants all nodes equal opportunity to acquire channel without regard to their bit-rates, making it possible for lower bit-rate nodes to occupy communication channel for a fair amount of time thus keeping the higher bit-rate nodes from acquiring connection channel which downward-equalize the overall network performance. Also with the 802.11p MAC protocol, the probability of collision occurring increases as the number of nodes grow. The proposed algorithm is a new MAC protocol that guarantees nodes with acquired channel a firm priority over other nodes for a fixed amount of time with TXOP concept added to 'packet burst' according to the current transmitting speed. This newly designed algorithm allows the construction of wireless network with enhanced network throughput, decreased probability of collisions as well as providing the means to grant each node a fair chance of acquiring connection according to their channel conditions. The algorithm sets the CW's (Contention Window) width wider than the standard's and modulates the continuous transmitting threshold value depending on channel acquired time, thus improving the overall performance of the network.

• The KIPS Transactions:PartC
• /
• v.13C no.4 s.107
• /
• pp.455-460
• /
• 2006

Currently, the IETF group is working on service differentiation in the Internet. However, in wireless environments such as Ad-hoc networks, where channel conditions are variable and bandwidth is scarce, the Internet differentiated services are suboptimal without lower layers' support. The IEEE 802.11 standard for Wireless LANs is the most widely used WLAN standard today. 1t has a mode of operation that can be used to provide service differentiation, but it has been shown to perform badly. In this paper, we present a new service differentiation scheme for support QoS in the wireless IEEE 802.11, which is based on a multiple queuing system to provide priority of user's flow. We simulate and analyze the performance of our algorithm and compare its performance with the original IEEE 802.11b protocol. Simulation results show that our approach increases overall throughput in the MAC layer.