通訊在人類的生活中佔有相當的比重，傳遞訊息的方式也隨著科技的進展，更多樣與更快速便捷。無線技術的發展將人類的通訊引導到無障礙的新階段，頻寬的增加讓通訊不再只有聲音與文字，透過無線的技術，影音通訊的時代漸漸到來。

Wireless LAN逐漸的成為市場的主流，利用802.11b與網際網路連結，用以實行即時影音通訊，是一個除了使用GSM、2.5G、3G等系統的一項選擇，並提供了更便宜的通訊費用以及更快的頻寬。

為了因應通訊頻寬的需求量，使資料的傳輸更有效率，新一代影音壓縮的技術，影像壓縮的MPEG-4技術、語音壓縮的GSM-AMR這些演算法也以成為標準並加速著多媒體通訊的實現。也透過公開的技術讓各通訊設備間的信息能夠互相溝通。

要能掌握無線環境下即時影音通訊的技術，使得在不可靠的傳輸環境下能夠保障通訊品質，本論文實作一套即時影音的通訊系統 – Personal Mobile Communicator，提供在IP架構下，針對無線網路環境的特性，使得透過行動設備或是桌上型電腦可以做點對點影音通訊的服務。

Personal Mobile Communicator所採用的技術，在影像方面是採用高壓縮比高畫質的 MPEG-4，並且實作MPEG-4所提供的Error Resilience Tool使資料流有更適合在無線環境下傳輸的特性。另外還有實作Error Concealment技術，在資料透過網路傳輸中發生了錯誤時，利用先前以有的資訊來填補現在發生的錯誤，讓錯誤所造成的影響降低。

我們的目標是實作一個系統提供在無線環境之下的即時影音通訊系統，並透過本系統形成一個測試的驗證平台，提供未來做更進一步無線環境及時影音傳輸的研究基礎。

Increases in bandwidth and computational speed lead to growing interests in real-time audio and video communication over the Internet. With dramatic increase in wireless access recently, a challenging problem associated with audio and video communication lies in how to cope with packet loss and achieve acceptable video quality at the receiver and utilizing the limited wireless bandwidth efficiently.

In this paper, we implement a system, Personal Mobile Communicator, to offer video and audio streaming communication. We employ MPEG-4 and GSM to compress video and audio data. MPEG-4 and GSM provide the standardized technological elements to compress video and audio data. MPEG-4 also takes a number of steps to enable robust transmission of compressed video data over noisy communication channels.

We implement error resilience tools for reliable transmission and error concealment technologies to provide better video quality when error occurred.
The goal of this paper, we design a communication system that is suitable for communication over wireless channel and offer a verification platform for further research.

第一章、 研究動機及背景知識 ………………………………………5
1.1 研究動機 ……………………………………………………5
1.2 背景知識 ……………………………………………………6
第二章、 相關研究探討 ………………………………………………9
2.1 MPEG-4 相關研究探討 ……………………………………………9
2.2 Error-Resilient Video Coding相關研究探討 ………………12
2.3 Source Rate Control 相關研究探討 …………………………15
2.4即時傳輸協定RTP/RTCP …………………………………………17
第三章、 問題定義 …………………………………………………19
第四章、 系統實作架構與機制………………………………………21
第五章、 研究成果與貢獻……………………………………………27
第六章、 結論與未來的發展…………………………………………32
第七章、 參考文獻……………………………………………………33

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