| Summary: | 博士 === 國立交通大學 === 電信工程系 === 91 === 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.
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