臺灣博碩士論文加值系統

許多已提出的IEEE 802.11e的改良機制，對服務品質有越來越多的需求。它們大部分根據傳輸失敗的與否調整參數(例如CW)，但都未考慮到在傳輸封包時的頻道狀態(頻寬)。在無線網路中，頻道狀態的變動是由於某些因素，像是移動性的站台、不同程度的干擾、位置相依錯誤。本篇提出擁有鏈結調適的增強分散式頻道存取演算法(EDCA-LA)來適應變動的頻道狀態。我們主張使較好頻道的站台設定較小的等待時間以達到較高的整體網路效能。模擬結果可以看出在產能和平均存取延遲方面，EDCA-LA都勝過標準的EDCA。

Abstract – Many enhanced schemes of IEEE 802.11e have been proposed to meet the increasing demand for Quality of Service (QoS). Most of them adjust the parameters, such as Contention Window (CW), according to whether the transmission is successful or failed, but don’t consider the channel condition (bandwidth) at transmitting packets. In a wireless network, the channel condition is time-varying due to some factors such as station mobility, time-varying interference, and location-dependent errors. In this paper, we propose the Enhanced Distributed Channel Access with Link Adaptation (EDCA-LA) algorithm by adapting with the time-varying channel condition. Our idea is to set the smaller backoff time for a station which has a better channel to achieve higher overall performance. Simulation results show that EDCA-LA outperforms the standard EDCA in terms of throughput and mean access delay.

摘要 I
Abstract II
致謝 III
Table of Contents IV
List of Figures V
List of Tables VI
Chapter 1. Introduction 1
Chapter 2. Background 4
2.1. IEEE 802.11 MAC 4
2.2. IEEE 802.11e MAC 5
Chapter 3. EDCA-LA Algorithm 9
Chapter 4. Simulation 12
4.1. Simulation environment 12
4.2. Simulation results 14
Chapter 5. Conclusions 20
References 21

References
[1]Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, ISO/IEC IEEE 802.11 Standard, 1999.
[2]Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Medium Access Control (MAC) Enhancements for Quality of Service (QoS),” IEEE 802.11e, Standard, 2005.
[3]L. Romdhani, Q. Ni, and T. Turletti, “Adaptive EDCF: Enhanced Service Differentiation for IEEE 802.11 Wireless Ad-Hoc Networks,” IEEE Wireless and Communications and Networking Conference (WCNC), March 2003.
[4]S. Kuppa and R. Prakash, “Service differentiation mechanisms for IEEE 802.11-based wireless networks,” IEEE WCNC, March 2004.
[5]C. T. Chou, K. G. Shin and S. Shankar, “Inter-Frame Space (IFS) Based Service Differentiation for IEEE 802.11 Wireless LANs,” IEEE VTC’03-Fall, 2003.
[6]M. Malli, Q. Ni, T. Turletti, and C. Barakat, “Adaptive Fair Channel Allocation for QoS Enhancement in IEEE 802.11 Wireless LANs,” ICC 2004, June 2004, pp. 3470-3475.
[7]L. Vollero, A. Banchs and G. Iannello, "ACKS: A technique to reduce the impact of legacy stations in 802.11e EDCA WLANs", IEEE Communications Letters, vol. 9, no. 4, April 2005.
[8]P. Chevillat et al., “A Dynamic Link Adaptation Algorithm for IEEE 802.11a Wireless LANs,” IEEE ICC ’03, May 2003, pp. 1141–45.
[9]Chai, C.C.; Tjeng Thiang Tjhung; Leng Chye Leck; Combined power and rate adaptation for wireless cellular systems,”, IEEE Transactions on Wireless Communications, vol. 4, no. 1, pp. 6-13, Jan. 2005.
[10]J. Wang, H. Zhai, Y. Fang, and M. C. Yuang, “Opportunistic media access control and rate adaptation for wireless ad hoc networks,” IEEE ICC, June 2004, pp. 154-158.
[11]S. Choi, J. D. Prado, S. Shankar, and S. Mangold, “IEEE 802.11e contention-based channel access (EDCF) performance evaluation,” IEEE ICC'03, May 2003, pp. 1151-1156.
[12]H. Yamada, H. Morikawa, and T. Aoyama, “Decentralized control mechanism suppressing delay fluctuation in wireless LANs”, IEEE VTC’03-Fall, 2003.
[13]http://pcl.cs.ucla.edu/projects/glomosim/