由於傳統的IEEE 802.11無線區域網路存在低傳輸效率的問題，限制了高畫質的影音傳輸與多媒體應用。隨著IEEE 802.11n的提出，雖然改善了傳統IEEE 802.11 於數據鏈路層效能不彰的問題，但在不穩定的無線通道狀況下，因封包遺失或錯誤所使用的重傳機制 (e.g., ARQ or H-ARQ) 卻因沒有考慮訊框聚集 (frame aggregation) 的特性，造成網路傳輸效能低落。近年來網路編碼 (network coding) 理論因其可大幅提升網路傳輸效能而備受矚目。本研究基於網路編碼理論設計一套訊框聚集性隨機網路編碼 (FAR: Frame Aggregation with Random Network Coding) 機制以運用於IEEE 802.11n等網路。另外，目前的IEEE 802.11n在群播 (multicast) 或廣播 (broadcast) 應用中，沒有提供使用者回饋 (feedback) 的機制，然而這些接收者可能因為位置或干擾造成訊號品質不同，為了達到所有使用者接收相同資料，因此通常被迫只能使用最穩定但最低速的調變方式進行廣播，導致大幅降低廣播效能。針對前述的問題，在本論文中，我們參考IEEE 802.11aa標準與其他相關文獻，設計適用於FAR的廣播回饋機制以及調變選擇演算法，以大幅提升廣播效能。最後，本論文分別針對單點傳播 (unicast) 與廣播之訊框聚集性網路編碼進行效能分析，探討在不同通道狀況下的網路吞吐量以及封包延遲的變化，以分析此編碼機制在此網路環境下的效能，並且透過電腦模擬實驗以驗證所提出之數學分析模型的正確性及準確性，結果顯示分析與模擬所獲得的資料攜吻合，顯示FAR機制在通道不穩定的情況下能帶來極大的效能改善。

The low transmission efficiency issue in IEEE 802.11 wireless networks hinders the transmission of high-definition videos and multimedia data. IEEE 802.11n is designed to resolve the transmission efficiency issue by employing a frame aggregation mechanism to minimize the overhead at the MAC layer. Unfortunately, the transmission efficiency issue is not completely resolved in IEEE 802.11n, especially when packets are lost due to unstable channel conditions. A lot of research in the literature proposes various error recovery schemes (e.g., ARQ or H-ARQ) to perform retransmission when packets are lost in a unicast scenario. However, these proposed schemes only achieve limited performance improvement because they do not take advantage of the frame aggregation feature. In this study, a transmission mechanism called Frame Aggregated Random network coding (FAR) is designed to significantly minimize the transmission overhead and improve the system throughput when the channel quality is not stable. FAR applies random network coding while jointly considering the benefit provided by the frame aggregation to dramatically reduce the overhead caused by retransmission and improve the bandwidth utilization. Furthermore, this study extends FAR to provide an efficient transmission scheme for broadcasting to all users covered by a base station. An analytical model is also developed for FAR to evaluate the mean goodput and packet decoding delay under various error rates. Finally, The simulation results and analytical results both show that FAR achieves significant improvement on the system throughput over current existed schemes while providing a comparable delay.

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