本論文主要研究在手持式數位廣播系統中之影像品質控制。除了模擬系統物理層的效能之外，為了在一個有限頻寬的網路中控制影像品質並且減低計算的複雜度，我們還提出一個局部搜尋的演算法，此演算可以快速地得到在傳輸上最佳的封包排程以及適當的錯誤更正能力，以達到最佳的重建影像品質；系統是實行在手持式數位廣播系統 (DVB-H) 的連結層中，我們利用當影像的封包遺失所造成的影像
失真來決定封包的重要程度，而根據這些重要程度來決定當傳輸頻寬不夠時需要丟棄的封包，同時考慮所給予的錯誤更正能力，即考慮在連結層中錯誤更正碼的冗餘位元長度；在一個有限的傳輸頻寬中，當所給予的錯誤更正能力強時，雖然能讓錯誤率下降，但卻多浪費了頻寬，會使得所需要丟棄的封包變多；反之，給予的錯誤更正能力低，我們卻能傳輸更多原始影像的資料，使正確性提高，要怎麼在這兩者
間取得平衡而達到最佳化即本篇論文所要探討的。根據實驗的結果，本篇提出的局部搜尋演算所決定的封包排程以及錯誤更正碼的冗餘位元長度能使得影像經過通道後在解調端得到最佳的影像重建品質。

In this thesis, we focus on video quality control in Digital Video Broadcasting Handheld (DVB-H) system. In addition to the performance analysis of physical layer in
DVB-H, we propose a local search algorithm to control video quality in a constrained network. The algorithm helps to indicate both the optimal packet scheduling and the optimal error protection capability in an effective way. We adopt the packet importance to decide the optimal drop set. Moreover, the redundancy for error protection is also taken
into consideration. If the level of error protection is too high, it has to drop more video packets due to the limited channel capacity. On the contrary, if the level of error protection is little, correspondingly we could transmit more video packets to obtain a better reconstructed video quality at decoder side. The key contribution of this thesis is to achieve the best trade-off between these factors. Simulations using H.264/AVC video were conducted to evaluate the performance of the proposed scheme. The simulation results show that the packet schedule and the level of error protection selected from the local search achieve the optimal reconstructed video uality at decoder side.

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