最近幾年，高速無線區域網路被廣泛架設在機場、車站、飯店。在無線區域網路上傳送多媒體資料成為未來重要趨勢。對多媒體資料提供差異性的服務及提升無線區域網路的輸出量成為多媒體無線網路的重要議題。本論文延伸IEEE 802.11e的原有分散式存取模式(Distribution Coordination Function, DCF)，在有干擾及錯誤發生(error-prone)的無線環境下，針對多媒體視訊及語音服務，提供差異性服務並提升無線區域網路的輸出量。我們提出兩階式後退機制(two-stage backoff mechanism) ，可有效減少backoff counter被凍結的時間；並利用二維馬可夫鏈(Markov Chain) ，來分析兩階式後退機制演算法之效能。為了有效提升網路效能，我們利用卡可門濾波器(Kalman Filter) 來估測目前頻道中有企圖傳送資料的站台數目，並利用所得頻道使用者數目來去調整兩階式後退機制的門檻。我們利用ns-2電腦模擬來評估我們所提出兩階式後退機制的效能。結果顯示，我們所提出的方法，相較於IEEE802.11e，在多媒體的輸出量及差異性服務上，達到良好改善。

In recent years, high-speed wirelesses LANs are widely deployed in airports, stations, hotels and street corners. Video and audio over wireless LANs will become important trends in the future. Service differentiation and throughput enhancement are major issues in supporting video and audio over wireless LANs. In this thesis, we extend the IEEE 802.11e Distributed Coordinated Function (DCF) to further provide service differentiation and throughput improvement for live video and audio over error-prone wireless LANs. Specifically, we propose an adaptive two-stage backoff scheme to reduce overheads in blocking backoff counter. To investigate performance of the proposed two-stage backoff scheme, we use the two-dimensional Markov chain to model the two-stage backoff scheme. Since performance of the IEEE 802.11e DCF is very sensitive to network loads, we use the Kalman filter to estimate the number of competing stations such as to obtain the optimal threshold of the two-stage backoff counter. Simultaneously, we run intensive computer simulations to evaluate the proposed two-stage backoff scheme by ns-2. The results demonstrate that the proposed scheme is superior to the IEEE 802.11e DCF in terms of system throughput and service differentiation.

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