隨著無線網路技術的蓬勃發展，各種異質的無線網路技術(例如：IEEE 802.1x系列、3GPP等)已逐漸形成一種無所不在的網路環境。而當行動裝置在異質網路環境中移動時，會出現執行換手的情況，會造成行動裝置的網路暫時中斷，進而造成使用者所觀看的多媒體檔案，會有播放延遲與停頓等現象。IEEE為訂定異質性無線網路間的換手標準機制，提出IEEE 802.21標準，其中定義一個中介層函式增加異質網路換手技術間的互通性，而該中介層被稱作Media Independent Handover (MIH) function，而隨著MIH的接受度增加，如何整合上層應用服務與MIH機制，已成為一個重要課題。先前研究已整合多媒體串流服務與MIH機制，實現無縫串流服務，透過在用戶裝置端整合MIH層與緩衝區管理機制，針對影像存量，提出漸進式調整畫面更新率機制，畫面更新率會隨著時間以等差級數下降改變，影像的播放將逐漸減慢，直到換手結束或畫面數不足而影像中斷。然而，直線式的變更畫面更新率，容易產生使用者體驗(Quality of experience, QoE)差異過大、緩衝區存量較少及可支撐換手時間較短的問題。

為改善使用者體驗(QoE)與增加較多緩衝區存量與支撐換手時間，本研究針對影像存量，提出二個改良方法，一個是曲線式的緩降，另一是曲線式的驟降，畫面更新率將以曲線式的方式下降，籍此可調整影像播放的時間長短，讓使用者有更佳的影像體驗。並將二者與漸進式調整作效能比較，前者可提升在換手時使用者觀看網路影片的畫面更新率，但播放時間較漸進式的短，後者則可以讓使用者在換手快結束時的畫面更新率下降的幅度趨緩，可讓使用者在觀看網路影片時有更佳的體驗。

Nowadays more and more people access and exchange information of any kind freely at anytime, from anywhere, and from any appliance through the use of heterogeneous network technologies (such as IEEE 802.1 series protocols and 3GPP). Mobile video streaming services and its’ performance are interrupted by the handover events when switching among the heterogeneous networks. The IEEE organization has provided the standard IEEE 802.21(MIH) to facilitate handover process among different radio technologies. A previous work, so-called Service Specific layer (SSL) scheme, was used to integrate a buffer management scheme with MIH for seamless streaming by extending the playing time of video stream but is short of quality of experience (QoE) consideration. 

A smooth handover mechanism was proposed in this thesis to provide the better QoE in any type of heterogeneous networks environments than previous linear frame rate adjustment methods. Furthermore when the handover is finished, the mobile devices resume the transmission and restore the video steaming to the mobile device buffer. By this mechanism it brings the video stream restore to the buffer more expeditiously.

目　　次
第一章 緒論					1
1.1 前言					1
1.2 研究動機與目的				2
1.3 論文章節架構				4
第二章 相關研究					5
2.1 異質網路間的換手				5
2.1.1 換手的種類				6
2.1.2 換手的相關技術				7
2.1.3 異質網路換手的挑戰			9
2.2 IEEE 802.21(MIH)換手架構			10
2.2.1 IEEE 802.21協定主要功能			10
2.2.2 服務存取點SAP (Session Access Point)	11
2.2.3 MIH的三種服務				12
2.3 異質網路換手流程				17
2.4 特定的服務層SERVICE SPECIFIC LAYER		20
2.5 跨協定無縫影像串流緩衝區存量控制技術	21
2.5.1 針對換手的影像緩衝區管理機制		23
2.5.2 漸進式調整畫面更新率			25
第三章 改良式串流畫面更新率控制機制		26
3.1 整體架構					26
3.2 改良式畫面更新率動態調整機制		28
3.2.1 曲線式緩降調整畫面更新率			29
3.2.2 曲線式驟降調整畫面更新率			30
3.2.3 恢復畫面更新率				31
3.3 參數C、D之討論				33
3.3.1 參數C、D之比較				34
3.3.2 參數C、D的建議值				38
第四章 實驗結果與分析				40
4.1 模擬實驗環境				40
4.1.1 實驗模擬數據				41
4.2 畫面更新率下降機制比較			43
4.3 下降調整機制的特性				45
4.4 模擬恢復畫面更新率實驗			46
4.5 畫面更新率恢復機制比較			48
4.6 恢復調整機制的特性				50
第五章 結論與未來研究				52
參考文獻					55

圖目錄
圖2.1 換手示意圖				5
圖2.2 SAP架構[2]				11
圖2.3 MIH Funtion基本架構圖[2]			13
圖2.4(a) 802.11 to 802.16換手範例[2]		17
圖2.4(b) 802.11 to 802.16換手範例[2]		18
圖2.5 SSL元件架構圖[9]	21
圖2.6 影像傳輸率最佳化[12]			23
圖2.7 換手的緩衝區狀態[7]			24
圖2.8 漸進式畫面更新率示意圖			25
圖3.1 MIH緩衝區管理架構圖			27
圖3.2 漸進式上升				32
圖3.3 曲線式緩升				33
圖3.4 曲線式驟升				33
圖3.5 緩降式調整畫面更新率範例1			34
圖3.6 緩降式調整畫面更新率範例2			35
圖3.7 驟降式調整畫面更新率範例1			36
圖3.8 驟降式調整畫面更新率範例2			36
圖3.9 四種C、D參數調整比較圖			37
圖4.1 模擬實驗環境架構圖			40
圖4.2 三種下降方式的畫面更新率比較		44
圖4.3 三種下降方式的畫面存量比較		44
圖4.4 驟降、緩降與漸進式效能比較圖		45
圖4.5 三種恢復方式的畫面更新率比較		49
圖4.6 三種恢復方式的畫面存量比較		49
圖4.7 驟降、緩降與漸進式效能比較圖		50
 
表目錄
表2.1 MIES LINK EVENT[3]			14
表2.2 MICS Command[3]				15
表2.3 MIIS Information Elements			16
表3.1 驟降式C、D參數的最佳區間表		38
表4.1 漸進式下降 V.S 曲線式緩降調整		42
表4.2 漸進式下降 V.S 曲線式驟降調整		43
表4.3 畫面更新率下降機制比較表			45
表4.4 三種調整機制的特性			46
表4.5 漸進式上升 V.S 曲線式驟升調整		47
表4.6 漸進式上升 V.S 曲線式驟升調整		48
表4.7 畫面更新率恢復機制比較表			50
表4.8 三種調整機制的特性			51

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