Researches On Joint Source Channel Coding In Wireless Channel

The support of multimedia (including speech, image and video etc.) service in wireless channel or network is the trend of the development of communication system in the twenty first century. However, there are two challenging problems. One is high efficient compression of source for fully utilization of channel bandwidth, the other is the protection of compressed information for combating the error or packet loss. Since the increase of source compression ratio will result in the decrease of its error resilience, at the same time, the improvement of robustness of bit stream will sacrifice the coding efficiency. The source coding and channel coding are conflict in this sense. In the field of source coding, although there have been many standards, the bit streams of compression standard are very sensitive to the error for the variable length coding adopted by the standards. In the field of channel coding, many previous forward error correction (FEC) methods is efficient only when the number of error does not surpass the threshold of their correcting ability, otherwise the performance will decrease drastically, and even worse than that of no FEC. As a result, how to design an efficient coding system to achieve reliable services transmission over wireless channel or network is the key problem for the realization of multimedia mobile communication system.Joint source channel coding has been proved to be an efficient method to solve the problem. It takes both the source coding and channel coding into account, and achieves better performance than their separate selection of optimal design.Although joint source channel coding has been paid more and more widely attention abroad, it's still in its infancy in our country. The dissertation investigates several key problems of joint source channel coding of image and video and obtains many results, which will help the realization of the next generation of mobile communication.The main contributions and innovation points of the thesis are as follows: 1. A novel joint source-channel coding scheme based on SPIHT used to transmit progressive image over wireless channel is proposed. The method provides unequal protection for SPIHT bit stream with different importance, and adaptively adjusts the source and channel coding rates according to the time-varying characteristic of wireless channel, thus yields good performance and high reliability without adding extra bandwidth.2. Based on the analysis of hierarchy and the significant characteristic of MPEG-4 bit stream, a new robust joint source channel coding method for MPEG-4 video over noisy channel is proposed. In the method, the base layer bit streams are reordered according to their relative importance and then interlaced packetized. Multiple sub-layers of texture information are generated based on their rate distortion function, the number of which is adjusted dynamically by the encoder according to the feedback information to minimize the overall distortion. The method has high ability to combat packet loss and is suitable for the video transmission over fading channel or network situation.3. A new multiple description SPIHT coding for region of interest (ROI) is proposed to combat packet loss. The method codes the SPIHT bit stream into multiple descriptions, each with a variable number of fully coded original trees and partially coded redundant trees. After reordering the zero trees of wavelet according to their importance, the method assigns different coding rates of original trees and redundant trees to each description. The more important parts of each tree are sent in more description than the less important parts, and in order to further improve the error resilience of ROI, more redundant trees are assigned to ROI than non-ROI. The relationship among zero trees, redundant trees and their coding rates are analyzed, and the algorithm of sorting process and assigning strategy of redundant trees are also presented in detail. Simulation results show that the method can further improve the reconstructed quality of ROI in the...