智慧化之資源分配演算法以達成無線區域網路最佳化跨層效能

Intelligent resource allocations for wireless LANs via a cross-layer approach

王嘉斌(Chiapin Wang)

指導教授 ： 林宗男

國立臺灣大學/電機資訊學院/電信工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.02502

摘要

由於無線網路的頻寬有限、通道品質時常變動、以及使用者可能有不同的服務需求，無線網路的資源分配變成一個很重要的問題。在本論文中，我們提出跨層式智慧化資源分配演算法，以達成無線網路中不同效能的最佳化，包括支援即時性多媒體服務品質，在異質網路中達成公平的通道使用率，以及提供系統使用效能最大化。“智慧化”指的是我們的演算法能在察覺周周遭環境改變時自動調整系統參數或做出適切回應以提昇整體效能。為了達到“智慧化”的目的，我們使用類神經網路學習上層效能指標(例如傳輸吞吐量及封包成功接收率)、下層系統參數(例如無線區域網路中媒體存取層參數)、以及實體層通道品質之間的跨層非線性關連函數。之後我們的演算法利用學習到的跨層關連知識做出智慧化的交遞決定或參數調整，以達到無線網路中各式效能的最佳化(例如服務品質、公平性、系統使用效益等等)。我們說明這樣一個跨層式資源分配演算法的設計方法，以及如何將它實現在IEEE 802.11無線區域網路。實驗及模擬結果證明我們的方法可以有效達成無線網路中系統效能的最佳化。
此外，我們也提出理論模型以分析在802.11無線區域網路中媒體存取層和實體層之間的跨層關連性。這樣的分析之所以重要是因為無線網路中媒體存取層和實體層之間的跨層交互作用對系統效能有重大的影響。分析結果顯示無線網路的系統傳輸吞吐量是由使用者中最低的傳輸速率所控制；使用者的傳輸吞吐量分配是由各自的連線品質而非傳輸速率所決定。這樣的分析結果也說明了跨層式設計對改善IEEE 802.11無線區域網路系統效能的重要性。

關鍵字

資源分配 ； 跨層方法 ； 無線區域網路

並列摘要

Resource allocation in wireless networks is an important research issue due to scarce radio spectrums, dynamic channel qualities, and varied user demands. In this thesis we present intelligent resource allocation schemes for Wireless Local Area Networks (WLANs) via a cross-layer approach to achieve various goals of performance optimization, including Quality of Service (QoS), fairness, system utility, etc. “Intelligent” refers to the capability of our approach to recognize the changes to surrounding situations and adapt the behavior automatically for performance improvements. For this purpose, our allocation schemes utilize neural networks to learn the cross-layer functions between upper-layer performance metrics (e.g. the achievable throughput and packet success rates), system arguments such as Medium-Access-Control (MAC) parameters, and Physical-layer (PHY) channel conditions. The learned cross-layer knowledge is therefore exploited for our allocation schemes to make handoff decisions intelligently or adjust system parameters dynamically toward various optimization goals (e.g. QoS, fairness, or system utility) respectively. We describe the design of such cross-layer approaches and the implementation in IEEE 802.11 WLAN for illustration. Experiment and simulation results demonstrate the effectiveness of our schemes to achieve performance optimization in WLAN environments.
In addition, we present in this thesis a theoretical model to analyze IEEE 802.11 Distributed Coordination Function (DCF) protocol in the presence of PHY diversity, i.e. varied channel conditions and unequal data rates among stations. Such kind of analysis can be important since the cross-layer dependence of 802.11 PHY and MAC has a significant impact on WLAN system performances. The analysis results show that the system throughput of DCF-based WLANs is determined by the lowest data rate used with a given station; throughput sharing among stations depends on the variation of link qualities rather than the difference of data rates. The results also reveal the need of a cross-layer design for optimizing the overall 802.11 system performance.

並列關鍵字

resource allocation ； cross-layer approach ； wireless LANs

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