高速和優質的多媒體通訊引起許多工業與學界的興趣，如何在無線網路連線上提供優質的媒體服務對於多媒體通訊是一個很重要的議題。故我們提出一個跨層投機式排程法則去改善WiMAX基地台多媒體服務的效能，主要是利用位元率失真矩陣與無線通道環境去定義在基地台傳輸佇列內封包的優先權。位元率失真矩陣是考慮接收端收到的影像品質會受到影像壓縮與封包遺失的影響，基地台可以透過串流中的夾帶的失真紀錄去獲得位元率失真矩陣的資訊，因此在傳輸之前可事先預測封包遺失造成解碼後的失真值，以當作排程法則的參考指標；另一方面，我們也考慮時變通道對於WiMAX網路中多媒體服務的影響，我們的機制可以在封包遺失導致解碼失敗時，也不會降低太多使用者觀看的影像品質。不論是否超過系統頻寬的限制，我們的跨層投機式排程法則都可以在WiMAX網路上提供即時且優質的多媒體服務。

In recent years, the high-speed and high-quality multimedia communication has attracted lots of interest from industrial and academic. How to providing premium media service through wireless links is an important issue in multimedia communication. We propose a cross-layer opportunistic scheduler to improve the performance of the base station. In the proposed cross-layer opportunistic scheduler, we derive the priority of the packets in the queues of wireless links from the information of the rate-distortion matrix and the wireless channel condition. We take the advantage on the rate-distortion matrix which is a measure of the quality of video. The distortion profile with the stream includes rate-distortion matrix. The distortion of the reconstructed video sequence is greatly influenced by the bitstream of the compressed video and the loss frame at the decoder. We will forecast the influence resulted from which lost frame to build the rate-distortion as the parameter abstracted from the application layer into the proposed scheduling algorithm. On the other hand, we consider the time-varying channel condition for providing the premium multimedia service in WiMAX network. At the decoder, even if frames are lost, a high-quality reconstructed video is still available through the proposed scheme. No matter what the total bitrates less than or more than the data rate at the physical layer is, the proposed cross-layer opportunistic scheduler with rate-distortion matrix (COSRD) has effective performance for providing the real-time and premium media service in WiMAX network.

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