• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.8 no.1
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• pp.6-11
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• 2009

This paper presents a new dynamically adaptable polling scheme for efficient support of real-time traffic over an IEEE 802.11 wireless LAN network. The poll scheduling plays an important role in IEEE 802.11 PCF. However, the current version of the polling list management scheme proposed in the IEEE 802.11 standard is inefficient when a variable number of mobile stations have variable packets to transmit. If Point Coordinator has an exact information on the station status, it is possible to efficiently perform polling. In this paper, we suggest an adaptable polling scheme to meet requirements of the stations. In our scheme, each station transmits packets including a piggyback information to inform that it wants to receive a poll in the next polling duration. Simulation results indicate that our scheme may reduces the packet discard ratio and real-time packet transfer delay.

• Journal of Communications and Networks
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• v.2 no.1
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• pp.46-57
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• 2000

Ongoing standardization effort on 3G cellular system in 3GPP (UNTS) is based on GPRS core network and promises a global standard for systems capable of offering ubiquitous access to internet for mobile users. Considered radio access systems(FDD CDMA, TDD CDMA, and EDGE) are optimized for robust mobile use. However, there are alternative relatively high-rate radio interfaces being standardized for WLAN (IEEE802.11 and HIPER-LAN/2) which are capable of delivering significantly higher data rates to static or semi-static terminals with much less overhead. Also WPANs(BLUETOOTH, IEEE802.15), which will be present in virtually every mobile handset in the near future, are offering low cast and considerable access data rate and thus are very attractive for interworking scenarios. The prospect of using these interfaces as alternative RANs inthe modular UMTS architecture is very promising. Additionally, the recent inclusion of M-IP in the UMTS R99 standard opens the way for IP-level interfacing to the core network. This article offers an overview into WLAN-Cellular interworking. A brief overview of GPRS, UMTS cellular architectures and relevant WLAN standards is given. Possible interworking architectures are presented.

• Journal of Communications and Networks
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• v.13 no.2
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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 the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.388-394
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• 2008

In this paper, MAC(Medium Access Control) algorithm for the IEEE 802.11 DCF(Distributed Coordination Function) improving the performance is proposed and analyzed by simulation. The MAC of IEEE 802.11 WLAN to control data transmission uses two control methods called DCF and PCF(Point Coordination function). The DCF controls the transmission based on CSMA/CA(Carrier Sense Multiple Access With Collision Avoidance). The DCF shows excellent performance relatively in situation that competition station is less but has a problem that performance is fallen from throughput and delay viewpoint in situation that competition station is increased. This paper proposes an enhanced DCF algorithm that increases the CW to maximal CW after collision and decreases the CW smoothly after successful transmission in order to reduce the collision probability by utilizing the current status information of WLAN. To prove efficiency of proposed algorithm, a lots of simulations are conducted and analyzed.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.42 no.1
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• pp.53-60
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• 2005

In this paper, we developed a mobile fingerprint identification system using wireless LAN based on IEEE 802.11 or mobile networks based on CDMA. The proposed system contains a server system to register fingerprints and ID data, clients system which is PDA with WLAN or CDMA module and fingerprint identification module.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.249-252
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• 2008

This paper presents a new dynamically adaptable polling scheme for efficient support of real-time traffic over an IEEE 802.11 wireless LAN network. The poll scheduling plays an important role in IEEE 802.11 PCF. However, the current version of the polling list management scheme proposed in the IEEE802.11 standard is inefficient when a variable number of mobile stations have variable packets to transmit. If Point Coordinator has an exact information on the station status, it is possible to efficiently perform polling. In this thesis, we suggest an adaptable polling scheme to meet requirements of the stations. In our scheme, each station transmits packets including a piggyback information to inform that it wants to receive a poll in the next polling duration. Simulation results indicate that our scheme may reduces the packet discard ratio and real-time packet transfer delay.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.05b
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• pp.1485-1488
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• 2003

IEEE 802.11 무선 랜 환경에서 멀티미디어 트래픽이 효과적으로 전송퇴기 위해서는 정해진 딜레이 바운드내에서 전송이 완료되어야 한다 대표적인 멀티미디어 트래픽인 음성신호를 전송할 때의 단방향 딜레이 바운드는 echo canceller를 쓰지 않았을 경우 $25ms{\sim}30ms$ 이다. 딜레이 바운드를 지키지 못하고 전송된다면 시간에 민감한 음성신호의 특성 때문에 음성품질이 유지되지 않을 뿐만 아니라 채널의 혼잡을 유발하게 된다. 본 논문에서는 음성의 품질이 보장되는 기준을 95%이상의 패킷이 성공적으로 전달되는 경우로 제한하여 음성의 딜레이 바운드에 관한 분석을 시도하였다. 이를 위해 음성패킷이 drop될 확률을 수학적인 분석을 통해 유도하고 시뮬레이션을 통한 검증을 시도하였다. 시뮬레이션에서는 IEEE 802.11의 두 가지 기본적인 MAC(Multiple Access Control) 프로토콜인 DCF와 PCF를 사용해서 음성신호를 전송할 때 딜레이 바운드를 지키지 못하는 음성 패킷을 사전에 drop 시킴으로써 몇 개의 음성 노드가 손실율 5% 이내 (음성의 품질이 유지되는 한계)를 만족시키는지를 음성신호를 발생시키는 STA 수와 손실율의 관계를 통해 알아보았다.

• Proceedings of the Korean Information Science Society Conference
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• 2004.04a
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• pp.505-507
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• 2004

IEEE 802.11 무선랜 표준에서 MAC(Media Access Control)은 동기와 비동기의 두 가지 타입의 서비스를 지원한다. 동기적 실시간 트래픽은 PCF(Point Coordination Function)에 의해서 폴링 엑세스 기법에 의해 처리된다. 비동기적 비실시간 트래픽은 CSMA/CA 프로토콜 기반의 DCF(Distributed Coordination function)에 의해 처리된다. 그래서 실시간 트래픽은 지연과 패킷손실에 민감하고 비실시간 트래픽은 에러와 처리율에 민감하기 때문에 적당한 트래픽 스케줄링 알고리즘이 설계되어질 필요가 있다. 하지만 IEEE 802.11 무선랜 표준은 실시간 트래픽을 효율적으로 서비스를 해주지 못하고 있다. 그래서 본 논문에서는 PCF 구간내에서 서비스를 받지 못한 실시간 트래픽 스테이션들을 DCF 구간에서 우선적으로 서비스함으로써 QoS를 향상시킬 수 있다.

• Proceedings of the KAIS Fall Conference
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• 2007.11a
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• pp.92-94
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• 2007

IEEE 802.11 WLAN(Wireless LAN)은 그 편리함과 효율성으로 인하여 수요의 증가 및 기술의 개발이 계속되고 있다. MAC(Medium Access Control)계층 중 기본적인 매체 접근 방식인 DCF(Distributed Coordination Function)는 CSMA/CA 알고리즘을 이용하여 충돌문제를 해결한다. 본 논문에서는 IEEE 802.11 MAC 계층 DCF 방식에서 스테이션간의 충돌확률을 줄이기 위하여 각 스테이션의 경쟁 윈도우 범위 사이에서 임의의 Backoff Time을 설정하는 것에 착안하여 최소 경쟁 윈도우(Minimum Contention Window)의 값이 성능에 어떠한 영향을 미치는가를 시뮬레이션을 이용하여 분석한다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.2
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• pp.7-16
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• 2000

In this paper, IEEE 802.11 MAC layer protocol is modeled by p-persistent CSMA method. And We introduce performance analysis model based on Basic CSMA/CA protocol, CTS/RTS protocol and hidden node effect reflected Basic CSMA/CA Protocol, Which is mathematically assayed by renewal theory. In this throughput, the result shown that Basic CSMA/CA protocol is profitable when the number of active node is smaller, or the length of packet is shorter, and CTS/RTS protocol is lucrative when the number of active node is larger, or the length of packet is longer. Also the result shown that hidden node less affected when the active node has small one, rather than when the active node has larger one.