這篇論文主要是在現有的802.11e無線網路架構上，提出一個新的動態跨層對映演算法，讓影像在無線網路上傳輸時，可以有動態調整適應的機制，改善影像在無線網路上傳輸的品質。這個跨層的動態對映機制，除了利用階層式影像編碼技術的特性，將不同種類的影像封包在應用層產生的重要性，帶到下層做判斷的依據，使影像傳輸的過程中，給予比較重要的影像封包較高的優先傳送機率，藉此提供影像服務品質，還利用演算法中的適應性調變，對目前網路負載的情形做動態的判斷，將不同重要性的影像封包指派到最適合的佇列中，希望能藉此更有效的利用網路資源，並使這個機制能夠適應各種不同的網路負載狀況。這個新的演算法適用於任何具有階層性的影像壓縮技術，而在本篇論文的實驗中，是以MPEG-4為例。在實驗數據與分析中，我們的機制將與原本的802.11e EDCA和靜態對應演算法做比較，結果顯示我們所提出來的機制確實能夠使佇列空間達到更有效的利用，並經由給予不同重要性的影像封包優先次序，改善影像傳輸的品質。

This essay presents an adaptive cross-layer mapping algorithm to improve the transmission quality of MPEG-4 video stream over IEEE 802.11e wireless network. In this cross-layer design, the MPEG-4 video packets are dynamically mapped to appropriate access category (AC) according to both the significance of the video data and the network traffic load. Furthermore, the proposed QoS algorithm can not only guarantee the prior transmission opportunity of essential video data, but also effectively utilize the queue spaces. This mechanism relies on the different priority of distinct video frames and their corresponding dynamic mapping at the 802.11e-based layer. The obtained experiment results and analyzed performance metrics indicate that our scheme performs superior in all the experimental scenarios than 802.11e (EDCA) and the static mapping scheme. Conclusively, this adaptive cross-layer design completely makes the advantages of the both the characteristic of MAC layer and application layer, and improves the video transmission quality over wireless networks.

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