在無線網路上基於中繼點之網路編碼影音多重傳送機制

Abstract

多重速率影片群撥是一種能同時對多個接收者提供影音串流服務的有效率的機制。然而在無線網路下，由於通道情況的異質性，如何提昇整體的效能會是個困難的課題。之前的研究大多專注於如何做速率調節以提昇服務的品質，雖然這些方法可以達到不錯的效果，但是卻只局限於一步之內的傳輸而沒有去考慮多步傳輸的可能性。因此我們提出了一個基於中繼點的機制，讓通道情況比較好的節點幫忙轉送資料給通道情況比較差的節點。首先我們提出兩個不同的時間排程模型以安排中繼點。其中，基於產量之模型用來決定各節點的傳輸時間以最大化整體的產量；而基於品質之模型經由決定各節點應該傳送哪些畫面以最大化整體的收看品質，以更正確的定義整個問題。接著我們提出一個網路編碼機制以避免封包重複傳送的問題。經由模擬實驗的結果證明了我們所規劃的基於中繼點之機制能夠比一步之內的方法所達到的最佳解夠進一步的提昇整體的效能，達到6 dB的峰值信噪比。

Multi-rate video multicast is a effective way to provide streaming video service to many clients. However, it can be a challenging problem over wireless networks because of the heterogeneity of channel condition. Most of prior works focus on the rate-adaptation to improve QoS of such issue; however, all of them focus on the one-hop manner and do not explore the possibility of multiple hops. We present a relay-based scheme such that nodes with better channel condition can forward data to nodes with worse channel condition. First we introduce a time scheduling problem and formulate two optimization models to schedule relays. The throughput-based model schedules the transmission time of each node to maximize total throughput, and the quality-based model describes the problem more specifically through exploring which frames should be transmitted by which nodes to maximize the total visual quality. However, solving the quality-based model is NP-hard, hence we apply the throughput-based model for cost-efficiency. Then we describe a network coding scheme to avoid packet duplication. Simulation results show that the relay-based scheme improve the visual quality by up to 6 db, as compared with the one-hop optimal scheme.