Studies On Error-Resilient Video Coding And Transmission

The compressed video data is extremely vulnerable to bit errors, and requires real time deliver, which conflicts to the low bandwidth and high error rate of wireless channels. Therefore, to realize real time transmission of video traffic over wireless channels, the error resilience of video coding must be improved, without significant compromises in video coding efficiency. This problem becomes a hot spot of research in communication area in recent years, since this task is quite challenging. For the state-of-the-art video coding algorithm using DCT and motion compensation, this thesis aims to enhance its error resilience, while preserves its coding efficiency and computation complexity. To restrain the spatial error propagation of video coding, a joint source/channel convolutional coding algorithm for variable-length code (VLC) is proposed. Using the structure of a systematic convolutional code, this algorithm achieves bit-by-bit unequal error protection for VLC-coded bitstream, and thus restrains the error propagation effectively. The work of other researchers on this topic mainly focuses on improving the error resilience of VLC through inserting redundancy, or enhancing the robustness of VLC decoding algorithm. Therefore, this algorithm provides a novel approach to solve the error propagation of VLC, which has theoretical significance. At the same time, to overcome the temporal error propagation of video coding, a chessboard-interpolation-based multiple description video coding algorithm is proposed. In this framework, the temporal error propagation could be eliminated in two steps. In the first step, redundancy is inserted to reduce the possible mismatch between the encoder and the decoder; consequently, in the second step, the residual error drift is eliminated through the encoder imitating the behaviors of the decoder. Simulation results demonstrate that the temporal error propagation is effectively controlled through the above two steps, when bit error rate is 1e-4.In addition, the error concealment algorithms for images corrupted by bit errors, are also discussed, to enhance the subjective visual effects when erroneous image is reconstructed. For block-based DCT coding, an error concealment algorithm based on masked shift interpolation is proposed. The algorithm estimates the positions and directions of edges in a corrupted image block, and then interpolates the image block along proper directions, because edges are more important to human visual effects. Compared with other error concealment algorithm with comparable computation complexity, this algorithm has a better recovered image quality, both in subjective and objective criterion. Moreover, for wavelet-based image coding, a novel technique named adaptive discrete wavelet transform is introduced, which is able to alleviate the ringing artifact near edges in the reconstructed image, in case some high frequency subbands being discarded. Finally, the techniques in the link layer for error-prone wireless channels, including adaptive error-correcting and frame synchronization, are discussed. A frame synchronization algorithm based on Maximum A Posteriori is presented, which significantly enhances the reliability of synchronization in case that slips exist in the communication link, and hence the throughput of the link layer is obviously improved. This work together with previous work concerning error resilient video coding, form a complete solution for robust video transmission over wireless channels. Parts of the achievements have been applied to the military project "Multi-function terminal", which realizes integrated real time communication of voice, video and data, over military wireless integrated digital network, for the first time. The device can provides high quality and reliable communication over error-prone channels. The device has passed the final appraisal and begun to be produced.