基於行動電子商務多媒體服務之無線多碼式寬頻分碼多工傳輸架構設計

Abstract

在本篇論文，我們提出基於第二代動態影像壓縮技術之無線展頻多碼式分碼多工非同步傳輸網路架構，傳送於有限的無線通訊頻寬中，同時強調無線非同步傳輸網路封包設計， 適應性通道編碼， 時間/空間錯誤消除技術，和展頻碼的管理。 值的一提的是，我們的系統並不限於第二代動態影像壓縮技術，同時也適合H.261‚ H.263 和MPEG-4 動態影像壓縮技術，只要適應性通道編碼，展頻碼的管理機制，錯誤消除技術， 根據它們的特性作適度的修正。 我們也探討著名的展頻技術應用於多媒體服務去發展下一世代的無線行動網路。一個多碼式展頻技術是被提出去提供多速率多媒體服務，藉由變化每個使用者展頻碼的數目，為了符合其傳輸速率的需求。在多碼式展頻系統中，一個展頻碼可以被使用去傳輸一個基本速率。使用者需要較高的傳輸速率可以使用多個碼並聯傳輸。但最大可傳輸展頻碼的數目在多碼式展頻系統中是仍然被限制的。 因此，一個低成本動態展頻碼分配技術已經被提出去動態分配每一個使用者所需傳輸展頻碼的數目為了達到最大的資源使用效率對於使用無線通道的多使用者多媒體服務而言。 本篇論文的另一目標在於發展一個新的JPEG系列靜態影像加密機制，這是無線多媒體通訊的一個重要部份並且提供影像保密傳輸藉由寬頻分碼多工傳輸網路。一個全頻濾波器是被提出去轉換任何機率分佈特性的輸入影像到無記憶高斯分佈信號。一個方法去實現這個全頻濾波器是去掃描輸入影像相位部份藉由加入某些二維隨機信號，爾後再減去此二維隨機信號以恢復原始影像。從加密的觀點，一個新的二維渾沌信號其行為類似隨機碼是被提出去提供此隨機參考相位對於這個全頻濾波器。最後，我們的加密機制也適合運用於其他動態影像壓縮技術如H.261‚ H.263 和MPEG-4 …等。

In this thesis, we propose a generic ATM-based multicode code division multiple access (CDMA) transport architecture for the Motion Picture Experts Group phase 2 (MPEG 2) compressed video services over a bandlimited mobile channel with the emphasis of wireless asynchronous transfer mode (ATM) cell design, adaptive channel coding, spatial/temporal error concealment techniques, spreading code management, and the impact of CDMA systems on the video services. It should be noted that the design concept of our system is not restricted to the MPEG-2 videos and also suitable for the other benchmark H.261 and H.263 video codecs as well as the next in the line of MPEG standards, MPEG-4 when the outer FEC code combing, spreading code assignment mechanism, and error concealment techniques have been modified according to their characteristics. We also investigate a new application of the well-known spread spectrum code-division multiple access(SS-CDMA) techniques to multimedia services related to the development of the next-generation wireless mobile networks interconnecting with a wireline ATM-based broadband network. A multi-code CDMA (MC-CDMA) technique is proposed to provide multirate multimedia services by varying the number of spreading codes assigned to each user in order to meet its throughput requirement. In MC-CDMA, a spreading code can be used to transmit information at a basic bit rate. Users ( video or data) who need higher transmission rates can use multiple codes in parallel. Meanwhile, the maximum available number of codes in the multi-code CDMA system is still limited. Hence, a cost-effective dynamic code allocation scheme has then been proposed to dynamically assign appropriate number of codes to each user for achieving the maximum resource utilization for multi-user multimedia services via the mobile radio channel. This thesis is also aimed at developing a new cryptographic method for encrypting the still JPEG-2000 images which are the important component of wireless multimedia communications, and then provides the secure transmission of image information via wireless WCDMA networks. An all-pass filtering is proposed to convert the input JPEG-2000 images with arbitrary marginal probability distribution function to the memoryless Gaussian-distributed source signals. A way to realize the all-pass filtering is to scramble the phase spectra of the input JPEG-2000 image by adding some randomized reference phase spectra as prefiltering, and then subtracting the same reference phase spectra as postfiltering, to recover the original phase spectra of the image. From a security standpoint, a new 2D chaotic signals which behave like purely random codes were proposed to provide the randomized reference phase spectra for the all-pass filtering whereas the well-known m-sequences and Gold codes provide limited security as they can identified with a number of samples which is much less than their actual length by means of linear regression models. Finally, our error-resilient encryption mechanism is also designed for the application to a combination of wavelet multi-resolution coding and current JPEG standard which will be the key technology for the forthcoming still image compression standard JPEG-2000 as well as the common VOP segmentation mechanism of MPEG-4 codec.