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研究生:陳信欽
研究生(外文):Hsin-Chin Chen
論文名稱:針對WiMAX網路的註冊程序及頻寬請求機制做佳化設計
論文名稱(外文):Optimized Backoff Parameters for Initial Ranging and Bandwidth Request in WiMAX Networks
指導教授:鄧德雋鄧德雋引用關係
指導教授(外文):Der-Jiunn Deng
學位類別:碩士
校院名稱:國立彰化師範大學
系所名稱:資訊工程學系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2009
畢業學年度:97
語文別:英文
論文頁數:55
中文關鍵詞:IEEE 802.16競爭決策方法後退法則頻寬請求初始化註冊程序
外文關鍵詞:IEEE 802.16contention resolutionbackoffbandwidth requestinitial ranging
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根據最新的IEEE 802.16的標準,在初始化的註冊程序及提出頻寬請求的機制中,IEEE 802.16的標準採用傳統的後退法則(Backoff scheme),然而使用這個方法,在很多使用者存取網路資源的情況下,造成無線網路環境非常壅塞,導致傳送出去的頻寬請求訊息會產生很高的碰撞率,並且造成頻帶的利用度降低,整體的效能不佳。因此,如何針對目前的網路環境去適當地調整Backoff的參數成為一個熱門的研究議題,目前似乎沒有一個最好的方法。基於上述的問題,我們提出了一個利用傳統Backoff方法來觀察競爭視窗(CW)目前的使用情形,來預測目前提出頻寬請求的個數,再求出符合目前環境,最適當的競爭視窗(CW parameter),因此,在這篇論文中,我們提出一個簡單且實用的方法,讓WiMAX基地台(Base station)可以根據目前的網路環境連線的數目來即時調整Backoff的參數,除了一些數學理論的分析,我們使用NS2模擬出來的結果顯示,我們提出來的方法可以有效地降低頻寬請求訊息的碰撞率,提升整體的網路傳輸效能,尤其是在WiMAX網路環境處於非常壅塞的情況下,表現出來的效果比IEEE 802.16 標準所制定的方法更好。
According to the latest version of the IEEE 802.16 standard, the backoff parameters of its contention resolution mechanism are far from the optimal setting since this strategy incurs a high collision probability and channel utilization is degraded in congested scenario. Besides, the problem of choosing the right set of backoff parameters for the current network level remains unsolved and left as an open issue. Based on above observations, we propose that a proper choice of the CW parameter values based on channel status has a great influence on overall network performance. Hence, in this thesis, we propose a simple, yet pragmatic algorithm that allows the base station to dynamically adjust its backoff parameters based on run-time measurements of channel status. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the scheme. The proposed solution works very well in providing a remarkable performance improvement in heavy loaded BWA systems.
摘要 I
Abstract II
誌謝 III
Table of contents IV
List of figures VI
List of tables VIII
Chapter 1 Introduction 1
1.1 Motivation 1
1.2 Related work 4
1.3 Contributions 7
1.4 Organization 9
Chapter 2 Preliminaries 10
2.1 WiMAX Evolution 10
2.2 IEEE 802.16-2004 standard 11
2.3 IEEE 802.16e-2005 standard 13
2.4 Wireless technologies 15
2.5 IEEE 802.16 MAC layer 17
2.5.1 Quality of service class 19
2.5.2 TDD frame structure 20
2.6 Bandwidth request mechanisms 22
2.6.1 Random backoff mechanism 22
2.6.2 Exponential Increase Exponential Decrease mechanism 26
2.6.3 Linear Increase Linear Decrease mechanism 28
Chapter 3 The Proposed Scheme 30
3.1 Adaptive contention resolution scheme 30
3.1.1 Run-time estimation of channel status 31
3.1.2 Number of active connections estimation 34
3.1.3 Contention window optimization 36
Chapter 4 Performance Evaluation 38
4.1 Simulation environment 38
4.2 Simulation results 42
Chapter 5 Conclusions 51
Bibliography 52


List of figures
Fig. 1. Broadband wireless access system 2
Fig. 2. IEEE 802.16 Mesh network topology 12
Fig. 3. The technology of OFDMA 13
Fig. 4. The comparisons of wireless standards 16
Fig. 5. IEEE 802.16 protocol stack 18
Fig. 6. IEEE 802.16 TDD frame structure 20
Fig. 7. BS broadcasts the contention period to SSs 23
Fig. 8. SSs use random backoff scheme to
transmit messages 23
Fig. 9. IEEE 802.16 Random backoff scheme 25
Fig. 10. The operation of EIED scheme 26
Fig. 11. The operation of LILD scheme 28
Fig. 12. The channel status of IEEE 802.16 contention
resolution mechanism 31
Fig. 13. Simulation topology 39
Fig. 14. Collision rate as a function of start contention
window size and traffic load 42
Fig. 15. Collision rate versus number of connections 44
Fig. 16. The distribution of CW in random back off scheme 45
Fig. 17. The distribution of CW in our proposed scheme 46
Fig. 18. Average access delay versus
number of connections 47
Fig. 19. Achievable throughput versus
number of connections 48
Fig. 20. Fairness index versus number of connections in the
coexisted environments 49

List of tables
Table. 1 The comparisons of WiFi and WiMAX 15
Table. 2 Notations and variables used in analytical analysis 30
Table. 3 Default attribute values used in the simulation 40
Bibliography
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