在802.11無線區域網路下，MPEG影像群播可能會因為無線錯誤所導致之封包遺失的原因而大大地降低其品質。向前錯誤修正(FEC)是很頻繁地被使用為錯誤控制機制；它提供冗餘封包給接收端去修復獨立的封包遺失，但是它可能會因為送太多冗餘封包而造成網路擁塞。這篇論文提出一個具有擁塞辨識的錯誤控制機制。這個機制可以經由改進後的封包遺失原因分辨演算法準確地意識到網路狀況；然後依照網路情況決定冗餘封包的數目。因此，這個機制已經能夠全面性的考慮網路層級的品質。更進一步地，當網路處於不擁塞的情況下，經由支援不同型態的MPEG影像框架不相同的保護也考慮應用層級的品質。經由理論分析的呈現和實驗結果說明1)這個機制在網路處於擁塞的情況能夠避免情況惡化，相反地取得了遺失和修復的平衡2)在網路處於不擁塞的情況下支援以網路層級和應用層級為基礎的保護，達到影像品質的最佳化。

　　The quality of MPEG video multicasting may be greatly degraded due to packet losses caused by wireless error in 802.11 Wireless LAN. Forward Error Correction (FEC) is frequently used as an error control scheme; it provides redundant packets for receivers to recover from independent packet losses, but it may result in congestion collapse and degrade bandwidth utilization due to sending more redundant packets. In this thesis, a congestion-aware error control scheme is proposed. Through the improved algorithm to differentiate the causes of packet losses, the proposed scheme can be accurately aware of network condition and then determine number of redundant packets accordingly for both constant and variable rate transmission. Therefore, the proposed scheme is able to address the above problem artfully and consider overall transmission quality of network-layer. Furthermore, when network is non-congested, perceived quality of application-layer is also considered through supporting unequal scope protection for different type of MPEG video frames. A theoretical analysis of the proposed scheme is presented, and the experiment results show that when network is 1) congested, the proposed scheme would avoid worsening congested network and contrarily gets a balance of loss and recovery 2) non-congested, the proposed scheme supprts protection based on network-layer and application-layer to optimal overall video quality.

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