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    Please use this identifier to cite or link to this item: http://tkuir.lib.tku.edu.tw:8080/dspace/handle/987654321/35644


    Title: 適應性編碼技術基於服務品質之丟棄封包機制於IEEE 802.16e網路之研究
    Other Titles: Scalable video coding of H.264/AVC video streaming with QoS-based active dropping in IEEE 802.16e network
    Authors: 江任鈞;Chiang, Jen-chun
    Contributors: 淡江大學電機工程學系碩士班
    李維聰;Lee, Wei-tsong
    Keywords: 適應性編碼;IEEE 802.16;WiMAX;IEEE 802.16e;H.264/AVC;QoS;Scalable Video Coding (SVC)
    Date: 2008
    Issue Date: 2010-01-11 06:56:55 (UTC+8)
    Abstract: IEEE 802.16是針對支援廣域都會型無線網路以及微波頻帶提出的一種新的通訊標準,並且以無線的方式取代最後一哩的寬頻網路接取。因為使用了高效率的無線訊號傳輸,所以傳輸距離最遠到達48km,末端的頻寬有300Kbps~2Mbps,與傳統的有線網路做比較,其硬體鋪設較為快速,且不受地形的影響以及低成本的特性,其主要是應用在單點對多點間的無線寬頻傳輸,並設定在無障礙空間範疇內傳輸。
    早期的影像串流傳輸,其串流資料量相當龐大,因此需要較大的頻寬來支援,但無線網路的頻寬卻是有限且很珍貴。因此Joint Video Team(JVT) formed by the ISO/IEC MPEG and ITU-T develops the extension of H.264/AVC scalable video coding (SVC)。H.264/SVC提供使用者不同的畫面品質,跟據使用者所接收到的資料多寡。但若用極佳的畫面品質來服務每位使用者,將會耗費掉許多頻寬。
    在先前的研究內容中,有利用控制傳輸率,並且降低用戶端的緩衝區,以提高影像畫面傳輸的完整性,達到維持畫面品質的效用。另外也有些研究室利用緩衝區的控管機制,去控制緩衝區內的資料量,並且在特殊的情況之下,丟棄那些較不重要的資料,提高影像串流的細緻度。
    而在此研究中,目標在提供不同的使用者存取不同影像品質的影像服務。在早期影像串流都為單一的傳輸率,較不適用於現今的無線網路區域中,因此我們將使用適應性編碼技術,讓影像串流能有不同的傳輸率以配合不同的使用者存取。而不同的使用者也有不同優先權,根據這個用戶優先權,使用者能存取不同影像畫質的影像串流,這樣的優點能有效提升頻寬使用率。為了達成這樣的成果,我們提出一套QoS-based Active Dropping mechanism,利用這個機制,來選擇性丟棄資料封包。我們賦予使用者有三種使用權限,最高權限的使用者在任何情況下,能有最佳的畫面品質,而最低權限的使用者在網路使用率偏高的情況下,僅能擁有最基本的影像品質。在這套機制之中,搭配著封包丟棄機率,這機率為一線性分布,其組成為當前的網路使用率以及我們所提出的網路限制值。最後我們將進行這套機制的模擬,並觀察運作時的特徵,的確在機制運作時能提供更多的使用者來存取同一個網路系統,表示已有效提升頻寬使用率,而在使用者端的影像品質也能有所區分,符合現代服務的品質要求。
    IEEE 802.16 is a new communication standard for supporting the Wireless Metropolitan Area Network. IEEE 802.16 replaces the last one mile by the way of wireless connects and fetches. Because it used high-efficiency wireless signal transmitting and treatment technology, it is farthest to 48km to transmit the distance, wide 300Kbps- 2Mbps bandwidth of end. Compared with the tradition wired network, IEEE 802.16 possesses the characteristics of the fast laying of hardware, being free from the effect of topography, and low cost.
    Multimedia applications over mobile wireless network are becoming popular in recent years. High video quality depends on the wide bandwidth but the wide bandwidth restricts the number of users in the network system. Effective bandwidth utilization is the major problem in wireless network because the bandwidth resource in wireless environment is limited and precious.
    For this reason, we propose an active dropping mechanism to deal with the effective bandwidth utilization problem. In the proposed mechanism, if the network loading exceeds the threshold, the dropping mechanism starts to drop the enhancement layer data for low level user and the dropping probability is varying with the different network loading. For the multimedia application, we use the characteristic of the Scalable Video Coding (SVC) extension of H.264/AVC standard to provide different video quality for different level user. By the dropping mechanism, base station increases the system capability and users can obtain better quality of service when the system is under heavy loading.
    In this research, we study the network of the 802.16e standard and add the QoS-based Active Dropping mechanism to the MAC layer. The dropping mechanism works when the base station loading is exceeding the bandwidth threshold. We adjust the threshold value dynamically to balance between the bandwidth utilization and video quality. By the dropping mechanism, network system can release bandwidth which is used to transmit the dropped data before and base station can support more users to access this network system. In the simulation results, we improve the bandwidth utilization and the network capability and achieve the QoS for each user.
    Appears in Collections:[Graduate Institute & Department of Electrical Engineering] Thesis

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