臺灣博碩士論文加值系統

當網路壅塞發生時，無人機(Unmanned Aerial Vehicle, UAV)傳送的影音串流(Video Streaming)封包可能會被丟棄，在終點端的影音串流伺服器由於缺少部分的巨型區塊(Macro Blocks, MB)，即時播放影片時會產生馬賽克與停格的現象。為了解決這個問題，本篇論文提出一個動態調整傳輸位元率與緩衝器(Dynamic Transmission Bit Rate and Buffer Adjustment, DTBA)的機制，此機制分成兩個部分，第一個部分為動態調整影音串流的傳輸位元率(Transmission Bit Rate, TBR)，我們在伺服器量測封包遺失率(Packet Loss Ratio, PLR)與接收位元率(Receiving Bit Rate, RBR)，DTBA根據兩個PLR的閾值來決定TBR是否降為一半或只是細微調降，如果PLR小於第一個閾值，我們將TBR恢復成初始的設定值，也就是最大的編碼位元率(Encoding Bit Rate)。第二個部分為動態調整影片播放時的緩衝器大小，我們先在伺服器量測還原連續兩張畫面之間的時間間隔變化(Picture Jitter, PJ)，伺服器會根據四個PJ的閾值來決定緩衝器的空間是否增加或減少，第一個與第二個閾值分別用來將緩衝器增加為兩倍或只做細微的增加，第三個與第四個閾值分別用來將緩衝器做細微的減少或調降一半，如果PJ介於第二個與第三個閾值之間，我們不調整緩衝器的大小。為了驗證我們提出的DTBA在網路效能的優越性，我們用C語言來撰寫模擬程式，此程式包含三個重要部分，分別是可以產生可變位元率(Variable-Bit-Rate)資料流的程式、可以在緩衝器產生封包遺失的程式、可以在播放器(Player)還原一張畫面且量測PJ的程式。從模擬結果中，我們除了分析在不同背景資料流時的DTBA的接收位元率、封包遺失率、還原連續兩張畫面的時間間隔變化(PJ)，我們還改變PLR的兩個閾值間距並根據四個PJ的閾值來量測DTBA所能節省的頻寬與緩衝器的大小。

When network congestion occurs, video-streaming packets transmitted by Unmanned Aerial Vehicles (UAV) could be lost, which results in mosaic and picture-frozen phenomenon in video playout due to largely missing Macro Blocks (MB). To solve this problem, in this thesis, we propose a Dynamic Transmission-Bit-Rate and Buffer Adjustment (DTBA) scheme. DTBA is divided into two parts. In the first part, Transmission-Bit-Rate (TBR) of the video stream can be dynamically varied based on the measured Packet Loss Ratio (PLR) and Receiving Bit Rate (RBR) at the server. TBR of the video stream will either halve or make a minor adjustment based on two thresholds of PLR. If PLR is below the first threshold, TBR will be restored to its initial value, the maximum encoding bit rate (EBR). In the second part, we dynamically adjust the buffer size based on the measured Picture Jitter (PJ), the variation of time intervals between restoring two consecutive frames. DTBA decides whether to increase or decrease the buffer size based on four PJ thresholds. The first and the second thresholds, respectively, are used to double the buffer size or make a minor increase. The third and the fourth thresholds, respectively, are used to make a minor decrease or halve the buffer size. If PJ is between the second and the third thresholds, we just maintain the buffer size. To demonstrate the superiority of DTBA, we run a simulation written in C. Three major programs are the generation of Variable-Bit-Rate (VBR) streams, the packet loss due to congestion in the buffer, and the measurements of PJ while restoring a frame in the player. From the simulation results, we analyze RBR, PLR, and PJ under different background traffic. Moreover, by changing the intervals of PLR and PJ thresholds, we statistically calculate the saved bandwidth and buffer size by DTBA.

論文審定書 i
致謝 ii
摘要 iii
Abstract iv
目錄 v
圖目錄 vii
表目錄 ix
第一章 導論 1
第二章 無人機的即時影音串流 4
2.1 影音串流 4
2.1.1 RTSP與RTP 4
2.1.2 影像的壓縮 7
2.2 封包的等待延遲 9
2.3 封包與畫面的傳送與接收 10
2.3.1 封包的時間間隔變化 10
2.3.2 畫面的時間間隔變化 12
2.3.3 封包的佇列時間 14
2.3.4畫面還原的時間 15
2.4 相關研究 15
第三章 TBR與緩衝器的動態調整 20
3.1 無人機傳送的影音串流 20
3.2緩衝器的動態調整 22
3.2.1 畫面時間間隔變化的計算 22
3.2.2 畫面停格的避免 23
3.2.3 畫面跳躍的避免 24
3.2.4 調整緩衝器的流程 26
3.3 TBR的動態調整 29
3.3.1 TBRA的回傳 29
3.3.2 動態調整的設計 31
3.3.3回報與調整TBR 32
第四章 模擬與結果分析 34
4.1 模擬拓樸 34
4.2 模擬程式的虛擬碼 35
4.2.1 無人機影音串流的虛擬碼 35
4.2.2 路由器轉傳封包的虛擬碼 43
4.2.3 RTSP伺服器的虛擬碼 49
4.3模擬結果與分析 64
4.3.1 沒有背景資料流時 66
4.3.2 有背景資料流時 67
第五章 結論與未來工作 81
5.1 結論 81
5.2 模擬程式所花的時間 82
5.3 未來工作 82
Reference 83
Acronyms 88
Index 90

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