未來的網路環境朝向使用者可以用任何裝置在任何地點、時間，存取網路的各種資源與服務，因此無縫換手的問題是近年來的熱門議題之一。然而從使用者的角度來看，能提供無縫換手不一定等同於能提供無縫服務，特別是視訊串流服務。而無論換手流程的進行有多快，MS都會因為buffer內能提供的解碼資源不足所以遭遇視訊播放中斷的情況。 另外一方面，Scalable Video Coding(SVC)是延伸於H.264/AVC的影像編碼技術，不但擁有低位元輸出率、高抗錯性能和網路友善性等優點，並採用分層編碼概念將不同特性的bit-stream送到IP網路上。SVC還提供了三種擴充性：空間、時間和訊噪比擴充性，因此可以根據網路狀況與用戶端裝置的能力動態調整最適當的bit-stream來傳送。因此SVC視訊編碼技術具有適合網路傳輸的優勢。 本論文提出預先做換手準備的換手機制，利用SVC編碼資料的特性以及802.16e具有的排程機制，將MS的buffer內的播放時間增長以度過換手時服務中斷的時間。 In recent years, many issues around seamless handover have been discussed. From the user’s experience of view, however, seamless handover is not equal to seamless service at all, especially for video streaming services. A mobile station can suffer a service interruption during the handover due to the lack of video data provided regardless how fast to finish the handover. On the other hand, the Scalable Video Coding can provide a flexible combination of layer representations to fit the channel condition and the capacity of the user station to maintain a reasonable video quality through the spatial, temporal, and quality scalabilities. Here, we propose a handover preparation mechanism, by which the SVC play-out buffer of a mobile station can be filled up with the base layer representation of the serving video stream before the handover is executed. Through the proposed mechanism, the video play out time will be extended, and thus, the video service keeps playing without any interruption during handover.
