利用無線網路廣播的特性，我們得以用少量的頻寬來傳輸視訊資料給一群使用者，然而，對於SVC視訊來說，為每個scalable coded block決定適當的傳輸速率是一項相當困難的問題，因為每個使用者都處在不同的環境，因此收訊能力不盡相同，同樣的封包傳給不同使用者會有不同的封包遺失率。先前的研究提到的方法主要是用低速率來傳輸視訊串流來確保每個使用者都能保有最低的視訊品質，然而此方法對於SVC視訊資料而言，也就是同一張影像包含多種視訊品質，反而限制了分配傳輸速率時的彈性。本篇論文針對SVC視訊資料的相依性提出了傳輸速率排程的方法。透過為每個視訊資料決定其重要性，我們能有效利用無線網路頻寬資源，並且讓使用者盡量避免收到無法解碼的視訊資料。我們的實驗結果顯示出因為我們的方法可以有效減少無法解碼的視訊資料量，因此在異質性使用者的無線網路環境下可以比現存的其他方法達到更好的整體視訊品質。

Video multicast exploits the wireless broadcast nature to transmit a video stream to multiple clients with a minimum bandwidth requirement. Assigning a suitable transmission bit-rate to each scalable coded block in a video stream is however a challenging problem because clients in a wireless network have heterogeneous channel quality and experience different packet loss probability. Prior work attempts to transmit the base-layer stream at a low transmission bit-rate to ensure a high reception probability, and hence the basic visual quality. Such methods however are over-simplified for a video stream that supports multiple quality levels in a video frame and needs explicit rate assignment for each block. We propose in this paper a dependency-aware rate scheduling scheme that assigns each block a rate according to dependency between blocks. With consideration of block dependency, we can better utilize limited wireless bandwidth to deliver important blocks, and minimize the number of undecodable blocks due to the lose of their reference blocks at the receivers. The simulation results show that since our scheme reduces the number of undecodable blocks, it achieves a higher overall video quality for a multicast group than the existing schemes under different client
distributions.

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