在本篇論文中，我們主要探討在無線隨意網路(Wireless Ad-Hoc Networks)上影像串流（Video streaming）的傳輸機制。由於網際網路之成長與漸增之多媒體資料需求，網際網路上之影像串流已經受到學術與工業界之關注。在影像串流應用中，欲撥放影像內文不需要等到全部檔案內容完全下載完成，雖然接收端可以直接撥放已收到的部分影像資料，但是，傳輸真實影像有頻寬與延遲條件之限制。然而現今網際網路對於影像串流並不提供QoS(Quality of Service)的保證，在無線隨意網路中，封包丟棄與傳輸錯誤現象是很正常的，有這些現象產生時，往往造成影像品質低落。若要利用重傳方式將封包重傳，則重傳之時間間隔的設定方式會大大地影響影像品質。若重傳之時間間隔大，會導致增加時間延遲，使得封包抵達時間在播放時間之後；若重傳之時間間隔小，會導致提早重傳(premature)，造成無意義之等待。
所以，我們提出了網路編碼之可調式影像串流(Network Coding for Scalable Video Streaming，NCSV)傳輸機制。網路編碼之可調式影像串流傳輸機制來源端只負責傳送，接收端僅負責接收，由於運用網路編碼理論(Network Coding)使得每一次之傳輸相對於重傳多了多餘資訊(redundancy)，而持續產生網路編碼封包，使得影像串流接收端辨識編碼封包之方式不同於重傳封包之方式，因此，使得接收端能較容易收齊影像串流資料，由於應用影像編碼(Video Coding)，接收端接收完基本層(base-layer)之封包後，保有基本影像品質，多收增強層(enhance-layer)之封包可以使影像更清晰。在我們的實驗分析中，在網路交通負載低之情形下，其效能與使用UDP傳輸相同，但是，在網路交通負載高之情形下，NCSV能夠大大地提升影像品質。在考慮到真實網路環境下，當傳輸錯誤之機率越高，NCSV相對於沒有使用網路編碼理論之方法，越能有效地提高影像品質。

As the Internet grows up and the demand for multimedia information on the web increases, video streaming application over the Internet has gotten a great deal of attention from academia and industry. In the scenario of video streaming application, there is no need to download the whole video content, but the client can play out the video while parts of the content are received and decoded. Although the receiver can play out the video content, transmission of real-time video typically has bandwidth and delay requirements. However, the current best-effort Internet does not offer any quality of service (QoS) guarantees to streaming video, and it is normal that the packet-loss or the transmission error occurs. It always degrades the video quality in the case of packet-loss or packet transmission error. Using retransmission packets against this problem needs to consider the time between the retransmissions, and the method of setting the time affects the performance a lot. A large time interval will result to a bigger delay due to waiting the next retransmission. Packets are arrived to the destination after the playback deadline in vain. A small time interval will lead to be premature. In other words, a small time is a meaningless waiting.
In this thesis, a Network Coding for Scalable Video Streaming (NCSV) is developed to transport packets over an unreliable network. In the protocol, sender continues to generate packets, and the receiver waits to receive them. Due to network coding theorem, every transmission has more redundant information than simple retransmission, and the way to identify the coded packets continuously generated by NCSV is different to retransmission. Therefore, the receiver can recover the video data as soon as possible. Besides, applying the video coding makes that the more packets the receiver received, the higher resolution the receiver gets. Simulation results show that NCSV achieves the same performance as UDP does in low traffic loads, and NCSV outperforms it in high traffic loads in term of video quality. Considering the real networks, NCSV improves the video quality greatly in comparison to the method without network coding when the probability of transmission error gets higher.

[1]. S. Katti, H. Rahul, W. Hu, D. Katabi, M. Médard, and J. Crowcroft, “XORs in The Air: Practical Wireless Network Coding,” in Proc. of 2005 conference on Applications, technologies, architectures, and protocols for computer communications, Jan. 2006.
[2]. B. Girod, J. Chakareski, M. Kalman, Y.J. Liang, E. Setton, and R. Zhang, “Advances in Network-adaptive Video Streaming,” in Proc. of IWDC 2002, Capri, Italy, Sep. 2002.
[3]. Z. Li and B. Li, “Network Coding: The Case for Multiple Unicast Sessions,” in Proc. of Allerton Conference, Sep. 2004.
[4]. Y. Wu, P. A. Chou, and S. Y. Kung, “Information Exchange in Wireless Networks with Network Coding and Physical-layer Broadcast,” in Proc. of the 2005 Conference on Information Sciences and Systems, Johns Hopkins University, Mar. 16-18, 2005.
[5]. C. Fragouli, J.-Y.L. Boudec, and J. Widmer, “Network Coding: An Instant Primer,” ACM SIGCOMM Computer Comm. Rev., Vol. 36, no. 1, pp. 63-68, Jan. 2006.
[6]. Y. Liao, K. Tan, Z. Zhang, and L. Gao, “Estimation based Erasure­coding Routing in Delay Tolerant Networks,” International Conference On Communications And Mobile Computing, Jul. 2006.
[7]. S. Katti, D. Katabi, W. Hu, H. Rahul, and M. Medard, “The Importance of Being Opportunistic: Practical Network Coding For Wireless Environments,” in Proc. of Allerton Conference, 2005.
[8]. H. Seferoglu, and A. Markopoulou, “Opportunistic Network Coding for Video Streaming over Wireless,” in Proc. of the 16th Packet Video Workshop, Lausanne, Switzerland, Nov. 2007.
[9]. R. W. Yeung, S.-Y. R. Li, N. Cai, and Z. Zhang, “Network Coding Theory,” Communications and Information Theory, Vol. 2, pp. 241-329, 2005.
[10]. S. R. Li, R. W. Yeung, and N. Cai. “Linear Network Coding”, IEEE Trans. on Information Theory, Vol. 49, 2003.
[11]. H. Radha, M. van der Schaar, and Y. Chen, “The MPEG-4 Fine-Grained Scalable Video Coding Method for Multimedia Streaming Over IP,” IEEE Trans. on Multimedia, Vol. 3, Issue 1, Mar. 2001.
[12]. W. Li, “Overview of Fine Granularity Scalability in MPEG-4 Video Standard,” IEEE Trans. on Circuits and Systems for Video Technology, Vol. 11, Issue 3, Mar. 2001.
[13]. Y. Wang, J. Ostermann, and Y. Zhang, “Video Processing and Communications,” Prentice Hall, Englewood cliffs, NJ, 2002.
[14]. P. Chou and Z. Miao, “Rate-Distortion Optimized Streaming of Packetized Media,” IEEE Trans. on Multimedia, Vol. 8, pp. 390-404, Apr. 2006.
[15]. R. Alimi, L. Li, R. Ramjee, H. iswanathan, and Y. R. Yang, “iPack: in-Network Packet Mixing for High Throughput Wireless Mesh Networks,” the 27th Conference on Computer Communications, Mar. 2008.
[16]. “The Network Simulator - ns-2.” Information Sciences Institute. The University of Southern California. 13 Jul. 2006, http://www.isi.edu/nsnam/ns/index.html .
[17]. B. Li, Y. Qu, Y. Keung, S. Xie, C. Lin, J. Liu, and X. Zhang, “Inside the New Coolstreaming: Principles, Measurements and Performance Implications,” the 27th IEEE Conference on Computer Communications, Phoenix, AZ, USA, April 2008.
[18]. D. Ren, Y.-T.H. Li, and S.-H. Chan, “On Reducing Mesh Delay for Peer-to-Peer Live Streaming,” the 27th IEEE Conference on Computer Communications, 2008.
[19]. J. Jin, B. Li, and T. Kong, “Is Random Network Coding Helpful in WiMAX?,” the 27th IEEE Conference on Computer Communications, Apr. 2008.
[20]. T. Ho, R. Koetter, M. Medard, D. Karger, and M. Effros, ”The benefits of coding over routing in a randomized setting,” in Proc. of International Symposium on Information Theory, Vol. 49, 2003.
[21]. W. Wei and A. Zakhor, “Path Selection for Multi-path Streaming in Wireless Ad-Hoc Networks,” in Proc. of the International Conference on Image Processing, Atlanta, Georgia, Sep. 2006
[22]. J.　Apostolopoulos, T.　Wong, W.　Tan, and S. Wee, “On Multiple Description Streaming with Content Delivery Networks,” IEEE INFOCOM, Jun. 2002.
[23]. A. Begen, Y. Altunbasak, and O. Ergun, “Multi-Path Selection for Multiple Description Encoded Video Streaming,” IEEE Internationl Conference on Communications, May. 2003.
[24]. S. Mao, Y. Hou, X. Cheng, H. Sherali, and S. Midkiff, “Multipath Routing for Multiple Description Video in Wireless Ad Hoc Networks,” IEEE INFOCOM, Mar. 2005.