新穎WLAN-DCF 通訊協定使用網路回饋資訊之適應最佳化

Novel Adaptive Optimization Scheme for WLAN-DCF Protocol with Feedback Network Information

郭子瑜(Tzu-Yu Kuo)

指導教授 ： 張適宇

國立清華大學/電機資訊學院/資訊工程學系/碩士(2008年)

摘要

摘要 在IEEE 802.11無線網路中的Distributed Coordination Function (DCF)有二個主要的存取機制。 Basic存取機制為 default 機制，另一個為request-to-send/clear-to-send(RTS/CTS) 機制。RTS/CTS機制是使用於對抗隱藏節點問題，發生於當無線網路環境中的某些終端機無法偵測到其他在此網路的終端機。然而，無線頻道的影響，例如：頻道的訊噪比(SNR)，在現有提出的文獻中，較難做出在此二種模式中相關合適的選擇。在這篇論文中，我們設計了一個線性規畫的演算法來減少最佳化生產力的複雜性。計算出關於從一個複雜且困難的非線性整數規劃問題最小競爭期間(contention window)尺寸。由於DCF協定的網路效能與頻道的訊噪比及競爭終端機的個數有著極大的關係，因此我們提出了一個全新的演算法，利用計算回饋網路資訊的參數來選擇存取機制與最小競爭期間的尺寸。我們藉由NS-2模擬器來估算我們提出的新DCF協定，來顯示出效能勝過與其他現存的方法。

關鍵字

無線網路 ； 網路回饋資訊 ； 適應最佳化

並列摘要

Abstract
In the Distributed Coordination Function (DCF) of IEEE 802.11, there are two access modes. The basic access mode is default. Another mechanism known as request-to-send/clear-to-send (RTS/CTS) is used to combat the hidden terminals problem, which occurs when some stations in the network are unable to detect each other. However, the effect of wireless channel, e.g., the channel signal-to-noise ratio (SNR), and the associated appropriate choice between these two access modes are hardly addressed in the
existing literature. In this paper, we design a linear programming algorithm to reduce the complexity of the throughput optimization with respect to the minimum contention window size, which arises from a complicated and difficult nonlinear integer programming problem. Since the network performance of the DCF protocol has been shown to tremendously depend on the channel SNR and the number of competing stations, we propose a new algorithm which selects the access mode and the size of minimum contention window jointly by utilizing the estimated parameters from the feedback network information. We evaluate our proposed new DCF protocol using the NS-2 simulator and our new scheme outperforms other existing methods according to
simulations.

並列關鍵字

WLAN-DCF Protocol ； Feedback Network Information ； Adaptive Optimization

參考文獻

[9] J. Liu, W. Guo, B. L. Xiao, and F. Huang. Rts threshold adjustement algorithm for ieee 802.11 dcf, in Inter. Conf. ITS Telecommunications Proceedings, 2006, pp. 654–658.

[1] IEEE Standard for 802.11 Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, Std., 1999.

[2] R. Zhao, B. Walke, and G. R. Hiertz. An efficient IEEE 802.11 ess mesh network supporting quality-of-service, IEEE J. Select. Areas. Commun., vol. 24, no. 11, pp. 2005–2017, 2006.

[3] L. Guo, X. Ding, H. Wang, Q. Li, S. Chen, and X. Zhang. “Cooperative relay service in a wireless lan,” IEEE J. Select. Areas. Commun., vol. 25, no. 2, pp. 355–368, 2007.

[4] J. Choi, J. Yoo, S. Choi, and C. Kim. Eba: an enhancement of the ieee 802.11 dcf via distributed reservation, IEEE Trans. Mobile Computing, vol. 4, no. 4, pp. 378–390, 2005.