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研究生:鍾政峰
研究生(外文):CHENG-FENG CHUNG
論文名稱:無線通道可用頻寬之估測技術之研究
論文名稱(外文):On the Estimation Method of Available Bandiwdth in Wireless Channels
指導教授:蔡志宏蔡志宏引用關係
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:電信工程學研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:英文
論文頁數:87
中文關鍵詞:可用頻寬無線環境量測多媒體
外文關鍵詞:Availble bandwidthEstimation MethodsWireless Environmentdelay jitterbuffer size
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由於無線網路的快速成長,以及使用者對於多媒體服務的需求增加。無線網路多媒體變為現代熱門的網際網路服務。多媒體對於傳輸環境非常敏感,故對於頻寬、延遲時間和錯誤率有一定程度的要求。無線網路先天傳輸環境不良,故多媒體的傳輸更為一大挑戰。為了提供使用者良好的品質,一些輔助性質的步驟是必須進行的。首先,一般的多媒體對於最小的傳輸頻寬有一定的要求。故系統在傳輸前對於環境先進行估測。根據估測出的可用頻寬( available bandwidth )決定傳輸多媒體的速率。
無線網路和有線網路在本質上有相當的差異。無線網路具有較高且依時依地變動的錯誤率,故現有的環境量測方法大部分並不適用於無線網路上。且關於可用頻寬的估測方法更為罕見。在此論文中,我們提出一種在無線通道可用頻寬的估測技術。此估測方法在有線網路與無線網路皆可進行正確的量測。系統送出不同速率的探測封包,找尋壓縮比率( decompression ratio )曲線的轉折點。而該轉折點對應的探測速率即為可用頻寬。
量測系統根據量測封包的欄位內容估測出延遲變動(delay jitter)、平均封包連續錯誤個數和封包錯誤率( packet loss rate )。我們觀察封包錯誤率和平均封包連續錯誤個數來判定該無線環境是否適合封包的傳輸。另外,我們提供一個決定撥放程式緩衝區大小的演算法,我們設定撥放程式的緩衝區大小來彌補無線環境對於延遲變動所造成的影響。我們的最終目的在提供給使用者品質良好的無線多媒體服務。

With the emergence of wireless networks and increasing demand of multimedia service on the Internet, wireless multimedia services are foreseen to become widely deployed in the next decade. In most cases, real time video transmission has strict QoS requirement, e.g. bandwidth, delay, and packet error rate requirement, etc. In addition, video transmission require reliable and a minimum level of bandwidth. Hence, we estimate the available bandwidth of transmission path and then suggest the video source to use a video rate according to the estimation results before the video server deliver the streaming video.
Most of current bandwidth estimation tools are not designed for the wireless environment. Some measurement techniques result in error estimation results in wireless environment because of packet losses and bandwidth fluctuation in wireless environment. The technique of estimating available bandwidth is rare. In this thesis, we present a technique of estimating available bandwidth in both wired and wireless environment. We send probing packet trains with different sending rate and find the transition point of the decompression ratio curve. Then its corresponding sending rate is the available bandwidth of the transmission path.
We use the information in the payload of the probing packets to calculate the packet loss rate, the mean length of error bursts, and delay jitter. We use packet loss rate and the mean length of error bursts to judge whether the wireless environment is good for multimedia delivery. Use information of delay jitter to suggest user the adaptive buffer size of the displayer to compensate for bandwidth fluctuation in wireless environment.

Chapter 1 Introduction……………………………………………………1
1.1.Background………………………………………………………………1
1.2.Overview of Current Available Bandwidth Measurement Techniques……………………………………………………………………4
1.3.Research Objective……………………………………………………8
Chapter 2 A Theoretical Framework for Estimating Bandwidth in the wireless Environment…………………………………………………9
2.1 Bottleneck Bandwidth and Available Bandwidth…………………9
2.2 A Theory Framework of Estimating Available Bandwidth………12
2.2.1 THe One-Congestion-Link Case…………………………………12
2.2.2 The Two-Congestion-Links Case………………………………14
2.2.3 Transition Point of The Decompression Ratio Curve……17
2.3 Bottleneck Bandwidth Reference……………………………………19
2.3.1 Packet Forwarding Mode…………………………………………19
2.3.2 Calculating Bottleneck Bandwidth Reference………………20
2.3.3 Using Bottleneck Bandwidth Reference in the Measurement
………………………………………………………………………………23
2.4 The Filtering Function for Packet Loss in Wireless Channels………………………………………………………………………27
Chapter 3 Measurement Techniques for Available Bandwidth in Wireless Channels…………………………………………………………29
3.1 Calculate the Probing Rate…………………………………………29
3.2 Calculate the Bottleneck Bandwidth Reference…………………35
3.3 Adjustments for the Wireless Environment………………………36
Chapter 4 Simulation Results……………………………………………37
4.1 Simulation Environment………………………………………………37
4.2 The Simulation of An Error Free Wireless Channel……………41
4.3 The Simulation of the On-Off Wireless Channel Model………43
4.4 The Simulation of A Geometric Distribution Channel Model…46
Chapter 5 Applications of Channel Bandwidth in WLAN NetTV……51
5.1 Video Rate Selection…………………………………………………51
5.2 Delay Jitter……………………………………………………………54
5.2.1 Buffer Size of Displayer…………………………………………54
5.2.2 Delay Jitter Estimation…………………………………………54
5.3 Video Server Configuration…………………………………………57
5.4 Suggestions for Future Implementation…………………………61
Chapter 6 Conclusions……………………………………………………63
Appendix: Simulation Statistics for Estimating Available Bandwidth……………………………………………………………………65
References……………………………………………………………………73

References
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