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Title: | 網路電話於異質性網路之語音編碼跨層最佳化 Cross-Layer Optimization of VoIP Speech Codec in Heterogeneous Network Environment |
Authors: | Li-Hsiang Chu 朱立翔 |
Advisor: | 葉丙成 |
Keyword: | 網路電話,服務品質,語音編碼器,G.711,G.726,PESQ,封包遺失率, VoIP,QoS,codec,G.711,G.726,PESQ(Perceptual Evaluation of Speech), |
Publication Year : | 2008 |
Degree: | 碩士 |
Abstract: | 隨著線網路的日益普及, 通話費率低廉的網路電話, 可望成為未來行動通訊的主力之一. 網路
電話面臨了許多技術上的問題, 其中最主要的問題是通話品質的穩定度. 不同的語音編碼器 (codec) 在相同的網路環境下, 分數表現並不相同. 若能針對不同的網路環境來動態的切換語 音編碼器, 網路電話系統可望達到最好的語音品質. 在本篇論文中, 我們提出了一個系統架構以 探討如何在異質網路中動態切換語音編碼器以達到最佳的效能. 本論文首先介紹網路電話的基 本技術, 常用之語音編碼器G.711、G.726以及網路電話品質評量標準PESQ. 接著我們建立 有線以及無線通道模型以模擬封包傳輸時所遇到的網路環境. 在該通道模型下, 我們設計出如 何動態的依據封包遺失的狀況來切換語音編碼器的最佳機制. 數值實驗結果顯示, 使用我們的 架構確實能有效改進語音品質. As wireless networks become more and more popular, VoIP has become one of the promising technologies for personal wireless communication due to its low service rate. However, there are many technical challenges in VoIP. One major challenge is the provision of Quality of Service. Due to the fact that different VoIP codecs can have different performance in the same network environment, it is possible to achieve better QoS by employing adaptive codec switching schemes. In this thesis, we propose a framework to obtain the optimal codec switching scheme for VoIP in a heterogeneous network environment. We first give a thorough introduction on the basic VoIP techniques, popular codecs (G.711 and G.726), and the ITU-T standard speech quality evaluation tool (PESQ). Then, the channel model is established for a heterogeneous network which includes both wired and wireless links. With the channel model, we propose the analytical framework to determine the optimal codec switching thresholds based on the packet loss rate observed. Numerical experiments show that the proposed framework is indeed useful in improving the audio quality for VoIP in a heterogeneous network environment. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/27040 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 電信工程學研究所 |
Files in This Item:
File | Size | Format | |
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ntu-97-1.pdf Restricted Access | 1.27 MB | Adobe PDF |
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