隨著網路的發展和成熟，各式各樣的網路應用也隨之興起，其中最熱門的應用莫過於視訊串流的發展，一直以來，視訊串流的應用侷限在網路環境的不確定和異質化之下，在播放品質以及規模上無法提升。在非可靠度的網際網路之下，視訊資料無法保證可以順利播放，異質化的網路環境之下，多份滿足不同網路以及播放需求的視訊資料必須被產生及保留下來以保證對各種客戶端的服務，如此的解決方式，對視訊串流伺服器的負擔很重且不實際。是故在本論文之中，我們提出了一個一般化的重要差別性視訊資料編碼的技術，使得（1）在不確定的非可靠性網路傳輸之下，達到比較好的串流品質。（2）在面對各種異質化的客戶端時，只需要同樣的一種編碼方式而可以去服務所有的客戶端需求，大大地節省串流伺服器的負擔。
在這篇論文裡面，我們改良了所謂的Digital Fountain code，它是一種最近幾年所提出的無限制編碼率的糾錯碼，並且解碼率是以機率形式表現出來，其中最有名的是LT Codes，由Luby所提出，LT Codes的編碼以及解碼皆可在線性的時間內完成，並且實作上容易且簡單。但是在LT Codes的理論之下，並無法保證對於可能解開資料的選擇性，我們無法確定解出來的資料是原始資料的哪部分。對於每個部分有有不同重要性的視訊串流資料，直接地套用並不是一個好的解決方法。視訊串流資料的重要性差異來自於編碼方式，檔頭（header）有著最重要的層級，沒有收到並解開的話視訊就無法播放，幀間（intra）╱幀內（inter）資料其次，餘差（residual）最末。這種差異在原始的LT Code上無法被解碼率反映出來，我們透過分析並且重新設計LT Code而達到重要差異性保護的效果，而達到更好的串流效能。
論文中分析了原始LT Code的編碼圖並找出解碼率快慢的差異，然後重新設計編碼的圖形，以適應重要差異性的串流資料，最後提出了幾種重要差異性保護LT 編碼 (UEPLT Code)，以及編碼器實作的架構。在論文實驗中，顯示了重要差異性保護LT 編碼在重要性差異保護效能上勝過原來的LT Code，套用於實際的串流資料時也可以在FGS串流資料上取得較佳的優勢以及串流資料的PSNR大約有2∼5db的提升。足以顯示改良後的LT可以更加勝任視訊串流服務，並且在論文中也對編碼方式和架構提出了相應的編碼器，所提出的編碼架構也保證了在任意大小輸入以及任意編碼冗餘度之下都可以運作正常並有良好的效能。

In this thesis, we proposed a channel coding mechanism for unequal important data protection, such as video streaming or layered videos, based on the concept of Luby-Transform (LT) code in digital fountain. An Unequal important data is that different parts in data have different importance, and needs being protected according to their importance in different parts. Under network environments where clients have heterogeneous bandwidth and computing power, video streaming services that provide coarse-to-fine video quality are required because the usage environments are diverse and changing dynamically. The contributions of this thesis are that we analyzed the coding graph of LT codes to conclude the factors of decoding probability and redesigned the coding graph to achieve the unequal protection requirement. As compared to LT codes, such as Reed-Solomon code, the proposed channel coding approach can better performance on PSNR of video streaming and layered video coding. Furthermore, the decoding complexity of the proposed mechanism is very low so that it can be applied on the real-time decoders, such as mobile phones, which only have limited computing power and request low delay requirement. The experiment results present that the proposed approach reaches about 3 db PSNR improvements on other LT codes on average. More significantly, the results demonstrate that the proposed approach also has better performance when it is applied on layered videos. Finally, we also proposed an novel encoder architecture for the proposed codes, and the architecture provides a flexibility and convenience to design or generate all kinds of LT-like codes.

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