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Special Graduate Schools
Graduate School of Information and Communication Technology
Department of Information and Communication
3. Theses(Master)
단거리 무선망을 위한 분산 충돌 해결 및 채널시간할당 방법
- Alternative Title
- Sun-Myeng Kim
- Author(s)
- Sun-Myeng, Kim
- Alternative Author(s)
- Sun-Myeng Kim
- Advisor
- 조영종
- Department
- 정보통신전문대학원 정보통신공학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2006-02
- Language
- eng
- Keyword
- Wireless LAN; Wireless PAN; MAC; Quality of Service
- Alternative Abstract
- Basically, there are three kinds of wireless networks: wireless local area networks (WLANs), wireless personal area networks (WPANs), and wireless wide area networks (WWANs). WLANs and WPANs are used for short distance communications and WWANs cover wide areas. This dissertation focuses on improving the performance and provisioning the quality of service (QoS) to the medium access control (MAC) layers for the short-range wireless networks, especially the IEEE 802.11/11e WLANs and the IEEE 802.15.3 high-rate WPANs. The IEEE 802.11 WLAN employs a distributed coordination function (DCF) MAC, which is a contention-based distribution channel access mechanism for stations to share the wireless medium. However, performance of the DCF drops dramatically in terms of throughput, delay, and jitter due to high collision probability as the number of active stations becomes larger. To improve the performance of the IEEE 802.11 DCF mechanism, we propose a distributed collision resolution (DCR) scheme. Our idea is based on the estimation of the channel contention level, by measuring collision probability observed on the channel at each station. In order to reduce collision probability, the proposed scheme limits the number of stations contending at the same time according to the channel contention level. Performance of the proposed scheme is investigated by numerical analysis and simulation. Our results show that the proposed scheme is very effective in terms of high throughput and low delay and jitter under a wide range of contention levels. The DCF does not differentiate between traffic classes. In this scheme a station might have to wait for an arbitrarily long time to send a frame so that real-time applications such as voice and video may suffer intolerable delay. To support multimedia applications with tight QoS requirements in the IEEE 802.11 DCF MAC, the IEEE 802.11e EDCA (Enhanced distributed channel access) has been drafted. However, at high loads, the EDCA does not guarantee the QoS of multimedia applications even though it provides higher priority since it is a contention-based MAC protocol. We propose a QoS supporting DCR (QDCR) scheme, which enhances the QoS performance for higher priority classes by reducing the collision probability and providing better service differentiation. It is an enhanced version of the DCR scheme. In the WPANs, the successful design of channel time allocation algorithm is a key factor in guaranteeing the various QoS requirements for the stringent real-time constraints of multimedia services. For providing delay guarantees to multimedia traffics such as MPEG streams in the IEEE 802.15.3 high-rate WPANs, we propose two channel time allocation algorithms: dynamic and deterministic. The algorithms exploit the characteristics of MPEG stream. The dynamic algorithm uses mini packets for feedback control in order to deliver dynamic parameters for channel time requests from devices (DEVs) to the piconet coordinator (PNC). In this scheme, the duration of channel time allocated to a DEV for a superframe is changed dynamically depending on the MPEG frame type, traffic load, and delay bound of the frame, etc. In the dynamic scheme, the PNC is able to change their channel time allocation positions within each superframe. If a DEV does not receive a beacon frame, it is unable to use the allocated channel time. To avoid performance degradation due to lost beacons, we propose a deterministic scheme, which exploits the pseudo-static channel time allocation and the periodic nature of MPEG stream. Performance of the proposed schemes is investigated by simulation. Our results show that the proposed schemes are highly effective when it comes to high performance while guaranteeing the delay bound compared to conventional schemes.
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