網路協定多媒體串流之最佳化

Cross-layer Optimized IP Multimedia Streaming

蔣俊成(Chun-Cheng Chiang)

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(2007年)

https://doi.org/10.6342/NTU.2007.01577

摘要

由於無線網路的蓬勃發展與高壓縮率的影像壓縮技術，人們可以藉由無線網路來觀看即時視訊串流。然而，在接收視訊串流的同時，由於無線通道的遮蔽效應及無線訊號微弱的影響，造成媒介存取層訊框(frame)錯誤使得影像品質嚴重衰減。在本篇論文中，我們設計一跨階層演算法以根據媒介存取層的訊框錯誤率來動態地切換影像壓縮參數達到最佳化峰值訊號雜訊比(PSNR)，一客觀衡量影像品質的標準。利用理論分析，在觀察固定數目的媒介存取層訊框下，導出最佳化切換影像壓縮參數的臨界值。此外，並考量有線網路下的封包遺失，修改原有的演算法 綜合考慮另一動態換影像壓縮參數藉由觀察有線封包遺失率及無線網路媒介存取層的訊框錯誤率。數值分析與模擬結果同時顯示出我們提出的跨階層演算法可顯著改進串流影像於無線網路上的傳輸品質。

關鍵字

跨階層設計 ； H.264 ； 媒介存取層訊框錯誤率 ； IEEE 802.11 WLAN ； 有限數目狀態馬可夫鏈 ； 吉爾-伯特模型

並列摘要

Due to the popularity of wireless networks and the state-of-the-art video coding techniques, people can watch real-time multimedia through WLANs. However, the fading effects or weak wireless signal strength in WLANs leads to erroneous MAC frames, which introduce undesirable quality degradation as receiving multimedia streaming. In this thesis, we design a cross-layer algorithm to optimize multimedia streaming over WLANs by switching video codec (compress and decompress) settings according to the MAC frame error rate (FER). The objective visual, PSNR, is optimized by our cross-layer design. By using numerical analysis, we derive the optimal switching thresholds for MAC FER to optimize the video quality in a constant number of MAC frames. Besides, the UDP/IP packet loss is taken into account and we design another switching codec policy by jointly observing the packet loss rate (PLR) for the streaming video packets in LANs and MAC frame error rate for the streaming video data in WLANs. Numerical and simulation results show that our design can maintain acceptable video quality in bad wireless states and attain to excellent video quality in good wireless states.

並列關鍵字

Cross-layer design ； H.264 ； MAC frame error rate ； IEEE 802.11 WLAN ； Finite-State Markov Chain ； Gilbert-Elliot model

參考文獻

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