Robust transcoder system for wireless image transmission

With the advances in 3G mobile communications, wireless multimedia communications have received increased attention. One of the most serious problems in wireless transmission of image is the loss of macroblock (MB) synchronization. A cornmon solution is to insert unique synchronization markers to the image bitstream. However, this method requires a large amount of redundant bits to maintain MB synchronization. In 1995, Error Resilient Entropy Code (EREC), a transcoding process, has been proposed to minimize the distortion due to the loss of MB synchronization with minimal redundant bits. Although this technique can solve the MB synchronization problem effectively, it creates two new error propagation problems: DC and AC error propagation. In this thesis, a unique set of transcoding techniques is developed to minimize the error propagation problems due to EREC process: (1) Differential DC pattern conversion, (2) Variable-Length Code (VLC) Reshuffling, (3). Adaptive Unequal Error Protection (AUEP), and (4) DC error correction techniques. Since all of the proposed techniques are embedded in a transcoder, no modification of the source coder and decoder is required. In other words, this system can be applied to pre-compressed images and real-time encoding images. Another advantage is that the proposed techniques can solve the error propagation problems with only a few redundant bits. Therefore, we do believe that the proposed transcoder system can be considered as one of the best solutions to the MB synchronization problem