改良IEEE 802.11 集中式協調功能與IEEE 802.11e進階分散式傳輸媒介存取的機制

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研究生：	藍怡雯 Yi-Wen Lan
論文名稱：	改良IEEE 802.11 集中式協調功能與IEEE 802.11e進階分散式傳輸媒介存取的機制 Enhancement of IEEE 802.11 PCF scheduling and IEEE 802.11e EDCA
指導教授：	陳志成 Jyh-Cheng Chen
口試委員:
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 資訊工程學系 Computer Science
論文出版年：	2005
畢業學年度：	93
語文別：	英文
論文頁數：	44
中文關鍵詞：	IEEE 802.11 、集中式諧調功能、進階分散式傳輸媒介存取機制、頻寬分配演算法、省電
相關次數：	點閱：3 下載：0
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隨著多媒體應用程式的變化與成長，服務品質保證(QoS)已變成了一個很重要的議題。由於無線網路本身傳輸媒介的不穩定性，在無線網路裡的服務品質保證比有線網路中要來的更有挑戰性。這篇論文提出了兩種方法，第一種為改良現今最廣為流傳的無線網路技術—IEEE 802.11，第二種方法則是用來改進IEEE 802.11e。
在這篇論文的第一部份，我們提出一個方法來改善IEEE 802.11的集中式協調功能(PCF)。集中式協調功能是一個集中式的媒介管理機制，而且可以保障對於延遲與頻寬有要求的使用者的服務品質。但是，在IEEE 802.11中並沒有提出明確的分配頻寬演算法，而分配頻寬的演算法卻對整體網路效能有極大的影響。根據模擬所做的分析，本論文中所提出的演算法在封包延遲可以得到很好的效能。
本論文的第二部份是針對IEEE 802.11e進階分散式傳輸媒介存取機制所提出的改進方法；IEEE 802.11e是為了改進IEEE 802.11服務品質保證的不足所提出的草案。與前面所述的集中式協調功能不同，進階分散式傳輸媒介存取機制為一個分散式的傳輸媒介競爭方式。本論文所提出的機制僅需引入兩個參數，就可以有效的減少使用者的能源消耗。除此之外，本方法也可以降低平均的封包延遲時間。

ABSTRACT
Enhancement of IEEE 802.11 PCF and IEEE 802.11e EDCA

As the growth of various multimedia applications, quality of service (QoS) has become an important issue. Lacking of link stability, QoS in wireless environment has more challenge compared with that in wired network. This thesis provides two enhanced approaches based on the most widely deployed wireless LAN technology, IEEE 802.11, and its amendment, 802.11e.
In the first part of this thesis, we propose a solution which aims to improve the performance of Point Coordination Function (PCF) in 802.11. PCF is designed as a centralized
scheme and is suitable for delay-sensitive or bandwidth-demand trafc. However, the standard only recommends Round Robin as the scheduling mechanism. The scheduling scheme
has critical inuence on the nal performance of PCF. The simulation results have shown that the proposed method outperforms Round Robin both in delay and throughput.
The second part of the thesis targets at the IEEE 802.11e Enhanced Distributed Channel Access (EDCA), which is the QoS complement to the original 802.11 standard. Contrary to PCF, EDCA is dened as a distributed medium access scheme. Contrary to PCF, EDCA is defined as a distributed medium access scheme. By only introducing two parameters, the proposed scheme could signicantly reduce the total energy consumption compared with the original EDCA. Besides, the numerical results show that the proposed method could reduce the average packet delay as well.
The solutions proposed in this thesis are fully complied with IEEE 802.11 and 802.11e. By extensive simulation, they have been shown to be both efcient and practical.

Contents
Acknowledgments : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : iii
Abstract : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : iv
List of Tables : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : viii
List of Figures : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : ix
Introduction : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1
1. IEEE 802.11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Point Coordination Function (PCF) . . . . . . . . . . . . . . . . . 2
1.2. Distributed Coordination Function (DCF) . . . . . . . . . . . . . . 4
2. IEEE 802.11e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. HCF Controlled Channel Access (HCCA) . . . . . . . . . . . . . . 6
2.2. Enhanced Distributed Channel Access (EDCA) . . . . . . . . . . . 7
Enhancement of PCF scheduling : : : : : : : : : : : : : : : : : : : : : : : : 10
1. Background and literature work . . . . . . . . . . . . . . . . . . . . . . . 10
2. The proposed solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3. Simulation and Numerical Results . . . . . . . . . . . . . . . . . . . . . . 21
4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
vi
Enhanced Distributed Channel Access with Contention Adaption : : : : : : : 26
1. Background and literature work . . . . . . . . . . . . . . . . . . . . . . . 26
2. The proposed solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3. Simulation and Numerical Results . . . . . . . . . . . . . . . . . . . . . . 30
4. Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Conclusion : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 39
Bibliography : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 41
vii
List of Tables
1. MWFQ simulation parameters . . . . . . . . . . . . . . . . . . . . . . . . 21
1. System parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2. Trafc parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
viii
List of Figures
1. Structure in IEEE 802.11 MAC . . . . . . . . . . . . . . . . . . . . . . . . 2
2. IEEE 802.11 PCF process . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Foreshortened PCF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IEEE 802.11 DCF operation . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IEEE 802.11e HCF operation . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. IEEE 802.11e EDCA operation . . . . . . . . . . . . . . . . . . . . . . . . 8
7. The Contention Free Burst (CFB) operation . . . . . . . . . . . . . . . . . 8
1. The “More Data” eld in MAC frame control eld . . . . . . . . . . . . . 16
2. The state transition diagram of the three states: backlogged, bad channel,
and unbacklogged states . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3. The format of 802.11 Association Request message . . . . . . . . . . . . . 18
4. The process of MWFQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5. MWFQ simulation topology . . . . . . . . . . . . . . . . . . . . . . . . . 21
6. The error model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7. The delay results of RR and MWFQ with same packet size 400bytes . . . . 23
8. The delay results of RR and MWFQ with same trafc rate 64kbps . . . . . . 24
ix
1. Simulation topology . . . . . . . . . . . . . . . . . . . . . . . 30
2. Packet delay: comparison of EDCA and EDCA/CA . . . . . . . . . . . . . 34
3. Energy consumption: comparison of EDCA and EDCA/CA . . . . . . . . . 34
4. Energy consumption: varying  and Nacc . . . . . . . . . . . . . . . . . . 35
5. Packet delay of AC VO: varying  and Nacc . . . . . . . . . . . . . . . . . 35
6. Packet delay of AC VI: varying  and Nacc . . . . . . . . . . . . . . . . . 36

                                

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