無線區域網路多媒體串流下編碼器切換和編碼器切換閾值動態調適

Codec Switching with Threshold Adaptation for Multimedia Streaming over Wireless Local Area Networks

吳宗翰(Zhung-Han Wu)

指導教授 ： 葉丙成

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.03465

摘要

在網路多媒體串流環境中，多媒體串流的影像品質會受到網路通道的影響。由於無線網路通道環境隨著時間變化劇烈，並且難以預測，此會嚴重影響到無線網路中多媒體串流的影像品質。因此經由無線網路提供多媒體串流，並具可靠性且穩定的服務品質，是一件困難的挑戰。本論文對於無線網路多媒體串流提出一個創新的跨層演算法，動態調適伺服器編碼器參數，以適應短期和長期的通道變化。在短期的動態調適方面，本演算法將定時把多媒體客戶端所觀察到的圖框錯誤率(Frame Error Rate)回傳給遠端的多媒體伺服器。伺服器將圖框錯誤率和編碼器切換閾值做比較後，伺服器即可調整編碼器參數以適應於當時的通道環境。本論文也提出演算法對長期的通道變化做出調適。在無線通道狀況和編碼器參數已知的情況下，多媒體伺服器可找出最小化調適周期內均方誤差的編碼器調適閾值，並將此閾值做為短期動態調適演算法中編碼器切換所使用之閾值。本論文所提出的演算法複雜度不高，而且在無線通道下的多媒體串流的信噪比，可以大幅提升3到5分貝。

關鍵字

多媒體 ； 串流 ； 編碼器調適 ； 編碼器切換 ； 圖框錯誤率 ； 無線網路

並列摘要

In wireless multimedia streaming, the quality of service (QoS) experienced by the multimedia traffic is subject to the channel variation, which is hard to predict. As a result, transmitting multimedia contents reliably in wireless environments becomes a big challenge in wireless communication. In this thesis, a novel cross-layer algorithm is proposed to deal with both the short-term and the long-term channel variations. To cope with the short-term channel variation, the MAC frame error rate (FER) observed by the client is periodically reported to the multimedia server. The multimedia server then adjusts the codec setting for encoding video bit streams by comparing the reported FER to a set of codec switching thresholds. On the other hand, the algorithm adapts the codec switching thresholds periodically with a longer threshold adaptation period to address the effect of the long-term channel variation. Given the wireless channel state and the codec setting used at the beginning of each threshold adaptation period, the media server selects the codec switching thresholds that minimize the expected transient mean square error (MSE) of the threshold adaptation period. The proposed algorithm reduces the number of computation and the simulation results show that the algorithm significantly improves the PSNR by 3 to 5 dB for multimedia streaming over varying wireless channels.

並列關鍵字

multimedia ； streaming ； codec adaptation ； codec switching ； MAC FER ； wireless networks

參考文獻

[13] International Organization for Standardization Std. [Online]. Available: http://www.iso.org/iso/home.html

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