寬頻網路之即時視訊品質控制系統; Jong-Tzy Wang

NCU Institutional Repository > 資訊電機學院 > 電機工程研究所 > 博碩士論文 > Item 987654321/8871

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题名:	寬頻網路之即時視訊品質控制系統;Jong-Tzy Wang
作者:	王仲資;Jong-Tzy Wang
贡献者:	電機工程研究所
关键词:	錯誤漫延;錯誤補償;寬頻網路;視訊;ATM網路;雙層優先順序傳輸機制;視訊編碼;訊務;error propagation;error concealment;Broadband network;Video;ATM network;dual-priority transmission scheme;Video coding;traffic
日期:	2000-06-12
上传时间:	2009-09-22 11:36:48 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文針對在寬頻網路上傳輸視訊時之視訊品質如何維護，以及當傳輸訊號發生錯誤時視訊品質如何改善等重要議題，提出幾項創新方案與技術如下: 即時視訊的傳輸往往因網路擁塞造成傳輸訊號封包流失(loss)，形成視訊資料發生錯誤影響接收端重建之視訊品質，一般研究常透過各種補償技術(error concealment) 以降低因封包流失而造成的視訊品質影響，但無法有效阻止錯誤漫延(error propagation)，也有以複雜的運算追蹤方法來阻止錯誤漫延，但往往需修改目前現有的視訊標準，而無法廣泛普遍應用於現有的視訊標準，從短程(short-term)方面考量，本論文提出之ECP (error concealment and prevention)技術不僅有效阻止錯誤漫延，且不需修改目前現有的視訊編碼標準，能廣泛應用於現有的視訊編解碼的技術。為因應異質性網路特性本論文進一步研究擴展ECP技術於雙層視訊編碼技術，以符合不同使用者使用功能，另外一方面研究結合雙層優先順序傳輸機制使錯誤發生率儘量發生於enhancement layer，而達到充分結合ATM網路特性的雙層ECP技術，進一步有效提昇視訊品質。為更有效控制視訊品質，從長程(long-term)方面考量須從降低視訊錯誤率著手，一般常見研究有流量平滑技術或non-tagging rate control，但往往這些技術透過位元率的降低以獲得較低的錯誤發生率，但也使得視訊品質降低，亦無充分利用到ATM網路特性，本論文針對此項問題提出調適性視訊品質控制系統，此系統結合兩項創新技術 (a).使用者連接層調整機制，以符合異質性網路特性。(b).網路訊號流失監控機制，有效監控網路狀況提供視訊品質控制重要參考依據。最後結合short-term與long-term兩方面的方法與技術得到一個全面及完整的視訊傳輸品質控制系統研究。本論文不僅適用於ATM網路，亦可適用於未來具有優先順序傳輸特性的網路系統，本論文從各方面、各角度考量都具有良好的完整性與連貫性。 Broadband networks have many applications' instead of requiring real-time and high quality video communications between media offices, field offices, banks, brokers, hospitals, teaching facilities, research facilities, health maintenance organizations, and physicians' offices. This study addresses the problems involved in streaming video over a high-speed channels. Novel approaches to quality control, feedback control, error concealment and prevention, and two-layer coding transmission scheme are discussed herein. This study presents several novel approaches to satisfying video quality with a feedback mechanism, when cell losses occur during network congestion. 1). Short-term quality control case (the cell losses occur during of Group of Pictures): First, an efficient temporal error propagation prevention method is presented, a method that involves a hybrid error concealment and error propagation prevention (ECP) technique. Simulation of MPEG-2 coding over ATM networks shows that error concealment with feedback can effectively isolate the error and reduce damage, producing a satisfactory performance even when the cell loss rate exceeds 1%. Again, the ECP technique of non-layer video coding is extended to two-layer video coding. The layered video coding can be matched with a priority transmission to create a high performance video compression and delivery system. This work presents an efficient error resilient system against video loss combining the ECP technique with a dual-priority transmission scheme (DPTS). Therefore, the ECP technique can still be employed to reduce the error damage and limit the impact of cell loss on the erroneous slices. 2). Long-term quality control case (the cell losses occur during of a video sequence): Although ATM can deliver VBR traffic, the burst traffic may still be dropped due to network congestion. However, the quality of the reproduced video may be sacrificed owing to insufficient peak rate available. This investigation presents an end-to-end quality adaptation mechanism for MPEG traffic on ATM. The adaptive quality control scheme (AQC) includes a connection-level adjustment unit and a quality-monitoring unit. The connection-level adjustment unit at the encoder end adjusts the connection-level based on the message of the network condition from the quality-monitoring unit at the decoder. Simulation results show that the AQC system can effectively utilize the channel bandwidth and maintain satisfactory video quality in various network conditions. In sum, this study demonstrates how to achieve satisfactory video quality with short-term error case and long-term error case control, an achievement which is crucial to quality control in broadband networks.
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