近年來，由於無線都會網路存取技術蓬勃發展，WiMAX已成為最受矚目的高速寬頻無線都會網路存取技術之一。相較於有線網路的傳輸，無線網路在傳輸上較容易受到環境的影響而發生錯誤。WiMAX為了解決在無線網路上資料傳輸的可靠度，使用一套透過傳送額外資訊以及重送錯誤資料的機制來提高資料傳輸的可靠度，也因此帶來了額外的負擔，造成系統效能的降低。另一方面，網路編碼(Network Coding)技術可用來改善網路傳輸上的效能，最近已有研究將之運用在無線網路的傳輸上以改善因傳輸錯誤造成的系統效能下降的問題，但是目前研究所提出來的方案存在著因使用網路編碼伴之而來的系統額外負擔的問題，另外這些研究也忽略在行動式WiMAX網路環境上因使用者移動而產生的訊號劇烈變化對傳輸效能造成的影響。因此本論文針對上述問題，提出一個可適性網路編碼機制，可以有效降低使用網路編碼帶來的負擔，並且提昇在行動式WiMAX網路環境上之系統效能。最後透過分析與模擬結果證明本機制不僅可降低網路編碼負擔，同時也可以改善資源使用效率，大幅提升系統的效能。

Recently, WiMAX has emerged to facilitate high-bandwidth wireless access for metropolitan areas. Like all wireless networks, packet loss is an important issue in WiMAX networks. Although WiMAX standards have provided a retransmission mechanism to combat the packet loss issue, the incurred overhead is significant. On the other hand, network coding techniques are explored to improve system throughput in lossy wireless networks. However, current network coding schemes may not achieve best performance in mobile WiMAX networks since they cause considerable overhead and typically ignore the fluctuation of channel condition due to user mobility. Accordingly, this thesis investigates the impact of dynamics of channel condition in the physical layer and the overhead caused by network coding in mobile WiMAX networks. An adaptive network coding mechanism is proposed to achieve excellent system throughput and reduce network coding overhead in the present of fluctuation of channel condition. The analysis and simulation results show that the proposed mechanism improves the resource utilization dramatically while reducing the network coding overhead significantly.

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