Research On Distributed Video Coding

With the emergence of the low-power video devices in network communication, some new challenges have been posed to the conventional communication system. These create the need for coding approaches combining low-complexity encoding, robustness and scalability. Distributed video coding (DVC, also called WZ video coding) has emerged as an attractive framework for low-complexity encoding and robust transmission over unreliable channels. This thesis aims to design the schemes of efficient DVC to satisfy network communication. The research focuses on five aspects.1. Research on DVC based on lattice vector quantization. Firstly, LVQ-WZ coding in pixel domain is proposed. Two LVQs, a coarse one and a fine one, are implemented to each 2-dimension input vector, and then the difference between them is channel encoded. Only the parity bits are sent to the decoder to recover the coarse lattice point with the help of side information. Finally, the re-quantization of fine lattice points is also refined by the side information. LVQ-WZ can achieve high efficiency and low-complexity encoding. Furthermore, LVQ scheme is extended to the wavelet domain and a LVQ-WZ in wavelet domain is proposed. Discrete wavelet transform removes the spatial redundancy so this scheme has better rate-distortion performance than pixel domain WZ. The scheme presents an optimized combination quantization to wavelet coefficients. And a gradual refinenment to side information with motion compensation is proposed.2. Research on efficient DVC. Two kinds of efficient DVC, the residual DVC based on LQR and the hybrid DVC with intra-coding mode, are proposed. In the former, LQR Hash, the low quality version of WZ frame compressed by zero-motion based H.264 encoding, is sent to the decoder to help the motion estimation at decoder. LQR Hash is efficient due to the exploration of temporal correlation between frames. Since there is correlation between LQR Hash and WZ frame, the scheme also removes such correlation by using the residual WZ coding to get gains. The other scheme is the hybrid DVC based on intra-mode decision. In view of the characteristics of different wavelet blocks, two kinds of coding modes are determined by an intra-coding mode, including intra-SPIHT and Slepian-Wolf SPIHT. The intra-SPIHT is applied to the block in the case of low correlation estimated; otherwise the Slepian-Wolf SPIHT is implemented. Experimental results show the proposed DVC schemes achieve better performance than the referenced with low-complexity encoding.3. Research on scalable DVC. A scalable DVC scheme is proposed. The basic idea is to use Slepian-Wolf theory to compress SPIHT information. Furthermore, a higher efficiency scalable DVC using block SW-SPIHT is proposed, where side information is refined with the help of feedback channel for each wavelet block. The scheme is scalabe in PSNR and has low-complexity encoding.4. Research on robust DVC. Two kinds of robust DVC schemes based on multiple description coding are proposed. In the first scheme, the video is interpolated and divided into multiple descriptions, and then a DVC codec is applied to each description and transmitted by different channel. When the packet-loss even with high packet-loss rate occurs, the lost can be recovered by the received. In the second scheme, the odd/even frame-splitting partitions a video into two subsequences to produce two descriptions. Each description consists of two parts. Part 1 is a zero-motion based H.264 bitstream of the corresponding subsequence and part 2 is a WZ bitstream of the other subsequence. As a redundancy, WZ bitstream guarantees the lost subsequence is recovered. A residual 2D-DVC is proposed to reduce such redundancy. The optimization scheme is applied to introduce the appropriate amount of redundancy. The experimental results show that the proposed schemes achieve better performance than the referenced especially when the motion is low. Moreover, our schemes maintain low-complexity encoding. Since the amount of redundancy will affect the performance, the redundancy optimization schemes are also presented in these MDDVCs.5. A DVC-based mobile communication system is constructed and a pixel DVC is realized in this system.