近年來由於無線網路產品的價格不斷下降及無線網路具有移動性及便利性之優勢，使的以802.11相容之無線區域網路越來越普及。雖然之前由於頻寬的限制使的無線傳輸主要應用於資料的傳遞，但隨著無線傳輸的頻寬因為新標準而不斷提升的同時，無線環境下之多媒體應用將會越來越趨增加。由於無線傳輸介質與有線傳輸比起來更容易受到環境之干擾，使的以無線通道傳輸多媒體訊息仍有許多問題待克服。因此我們提出以MPEG-4 FGS之編碼方式來壓縮將利用無線通道傳輸之視訊，使其符合無線環境下頻寬易變動之特性。另一方面，針對無線網路環境之下容易產生封包遺失之問題，我們提出對於FGS的加強層加入非均勻式的錯誤保護並對於有發生封包遺失狀況且已經解碼之視訊資料施以特定之後處理。這樣做的理由是因為以FGS方式壓縮所得到之加強層資料，其所包含的各種訊息之間存在著不相等之重要性。為了避免因為重要訊息於傳輸期間丟失使的正常收到的資料受到影響而變的無法被解碼。我們所提出的分均勻式保護方式將針對FGS加強層中較重要的訊息施以較重的保護，使其即使在被丟失的情況下仍可利用預先插入的保護碼而將它復原。經由模擬的結果我們發現，對於802.11b無線區域網路下視訊資料的傳輸，若在有封包丟失的狀況下使用我們所提出的策略將可有效的提升視訊資料的錯誤容忍回復能力。

For reducing cost of wireless gadgets and taking advantage of mobility offered by wireless network, the 802.11 wireless local area networks (WLANs) has become popular in recent years. Although current WLANs are predominantly used for data transfer, the higher bandwidth provided by new WLAN technologies will lead to increasing use for multimedia transmissions. But to transmit a video stream over the WLANs poses several challenges, including bandwidth variation and data loss. In order to provide a reliable and efficient transmission of compressed video over WLANs, we propose to employ Fine-Granular-Scalability (FGS) coding for the compression of video data. The video coded with FGS can provide a continuous video quality adapting to bandwidth variations. Furthermore, we propose a novel strategy which incorporates with unequal error protection for packets of FGS enhancement layer and post-processing for decoded video data. Usually the compressed data of FGS enhancement layer in each packet has different priority. We protect part of data with higher priority, and recover the most important information when a packet is lost during transmission. From the simulation results, we find that the proposed error protection strategies can improve the error resilience and enhance the video quality under the packet loss.

[1] Matthew S. Gast, “802.11 Wireless Networks: The Definitive Guide,” O’Reilly, 2002.
[2] W. Li, “Overview of fine granularity scalability in MPEG-4 video standard,” IEEE Transactions on Circuits and Systems for Video Technology, vol. 11, no. 3, pp. 301--317, March 2001.
[3] ISO/IEC JTC1/SC29/WG11, MPEG2002/M9182, “FGS-Based Video Streaming Test Bed for Media Coding and Testing in Streaming Environments,” International Organization for Standardization, National Chiao Tung University (NCTU), Dec. 2002.
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[5] Yao Wang, Jörn Ostermann, and Ya-Qin Zhang, “Video Processing and Communications,” Prentice-Hall, 2002.
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