三維立體動態影像壓縮及無線非同步網路傳輸技術設計

Abstract

本論文的研究目的著重於提供每一個人可以不受地型及空間的限制，透過 立體眼鏡(stereoscopic glasses)共同享有具有三維立體影像的虛擬實 景(Virtual Reality, VR)的世界。目前具體例子如美國登陸火星之探索 者可以傳送三維立體影像使得地球上的研究人員身歷其境以便掌握火星真 實地形。另外一個例子是美國卡乃基美隆(CMU)大學所進行的校園無線網 路計畫。其中的Navigator是透過具有無線傳輸功能的立體眼鏡進行校園 環境導遊及虛擬教學。由於多碼式展頻分碼多工(Multi-code CDMA)系統 即將成為2000年第三代行動通訊的主要關鍵技術。首先我們提出基於動態 影像標準(MPEG)及小波多重編碼(wavelet multiresolution coding)的三 維立體視訊壓縮技術。接著針對該三維立體視訊壓縮資料在時空上的重要 性(priority level)及統計特性，建造具有抗干擾及多重路徑衰落( multipath fading)的非同步傳輸細胞(ATM cell)架構。該ATM細胞架構將 充份與多碼式CDMA通訊系統整合建立無線三維立體視訊傳送架構。並且將 針對實際三維立體視訊進行測試。 This paper investigates the application of multi-code SS-CDMA techniquesto three-dimensional stereoscopic video transmission over wireless ATM networks. 3D visual communications, made through the use of stereoscopic images, are able toachieve total display realism. Such services allow users to share the virtual reality (VR)world without any geographical restrictions. In order to create a 3D system with two images (left and right) that should be transmitted over a bandlimited mobile channelsimultaneously, a cost-effective MPEG-based wavelet multiresolution coding with an joint motion- and disparity- compensation is developed to reduce a large amount of information contained in the images in order to the meet the low transmission rate limitationof mobile channels. However, the rapidly variable bit rate (VBR) characteristics of the MPEG- based 3D videos seems a weakness to the transmission of such videos via a constantbit-rate (CBR) mobile channel.The ATM technique is especially wellsuited for variable bit rate (VBR) MPEG-based 3D video because of its ability to allocate bandwidth on demand to these services.However, since the mobile radio has a limited channel capacity,the overall capacity of the traditional ATM-based SS-CDMA system may not be sufficientto accommodate the MPEG-based 3D video services requested bythe multiple mobile users simultaneously.To tackle this difficulty, a multi-code CDMA technique is proposed to provide VBR MPEG- based 3D video services by varying the number of spreading codes assigned to the 3D video in order to meet its dynamic throughput requirement. Meanwhile, these extra spreading codes would alsocreate the interference to the other videos and degrade their picture quality. Hence, a cost-effectivespreading code assignment mechanism has then been proposed to dynamically assignappropriate number of codes to each video for achieving both the maximum resource utilizationand the best picture quality for multiple video services via the mobile radio channel. However, both the fading and interference on SS-CDMA radio channels tend to cause significanttransmission error and MPEG-based 3D video bit streams are very vulnerable to these errors. Powerfulforward error correction(FEC) codes are therefore necessary to protect the video dataso that it can be successfully transmitted at acceptable signal power levels. Two separate FEC code schemes are applied to the header and payload of a ATM cell containing 3D video data,respectively. The ATM cell header is protected by a relatively powerful FEC code to ensure correctdelivery and low cell loss rate (CLR).On the other hand, the ATM cell payload is encoded for varying degrees of error protection accordingto the priority of the payload data in MPEG2 videos. An adaptive FEC code combining scheme is proposedto provide the good protection for payload data with the maximizationof its code rate in order to minimize the extra bandwidth for FEC overhead.Simulation results would show that our FEC code combining scheme is able to ensurethe average number of ATM cell losses in each typical 3D picture frame bein the order of O(1).