Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> TDWZ based on discrete wavelet transform (DWT) <s> In this paper we present a wavelet domain distributed coder for video which allows for scalability and does not require any feedback channel. Efficient distributed coding is obtained by processing the wavelet transform with a suitable "folding" function and compressing the folded coefficients with a wavelet coder. At the receiver side, we use the statistical properties between similar frames to recover the compressed frame. Experimental results show that she proposed scheme has good performance when compared with similar asymmetric video compression schemes. <s> BIB001 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> TDWZ based on discrete wavelet transform (DWT) <s> This paper proposes a distributed video coding scheme based on the zero tree entropy (ZTE) coding. Wyner-Ziv theory on source coding with side information is taken as the basic coding principle, which makes independent encoding and joint decoding possible. In this scheme, wavelet transform is used to exploit the spatial correlation of a Wyner-Ziv frame. The quantized wavelet coefficients are reorganized in terms of the zero tree structure so as to identify the significant and insignificant coefficients. The significance map is intra-codec and transmitted. In particular, the significant coefficients are independently encoded with turbo coder, and only the parity bits are transmitted. At the decoder, a predictive frame generated through motion-compensated prediction is used as the side information, with which the Wyner-Ziv frame can be conditionally decoded. Experimental results show that, compared to the traditional intra-frame coding and pixel-domain Wnyer-Ziv video coding, the proposed scheme can achieve a better coding performance, especially at low bit rates. <s> BIB002 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> TDWZ based on discrete wavelet transform (DWT) <s> The error-resilient for video transmission over the Internet in which regarded as the packet erasure channel is always a tough task and has gained lots of attentions. The main contradictory problem lies between error-resilient and bandwidth usage. Additional redundant data has to be added to achieve robust transmission which leads to huge bandwidth usage. In this paper, an error-resilient scheme called Wyner-Ziv Error-Resilient (WZER) based on a receiver driven layered Wyner-Ziv (WZ) coding framework is proposed. The WZER purposely emphasizes on the protection of the Region of Interest (ROI) area in the frame thus to achieve the better tradeoff between the bandwidth usage and error-resilience. WZER is designed to work for the scenario of wavelet based video coding over packet erasure channel, where several techniques including automatic ROI detection, ROI mask generation, Rate distortion optimization (RDO) quantization, WZ coding with layer design, and packet level Low Density Parity Check (LDPC) code are used. The performances of the proposed WZER are simulated based on average PSNR of luminance, perceptual reconstruction and bandwidth usage and compared with normal Forward Error Correction (FEC) full protection scheme and no protection scheme. The results show the advantages of the proposed WZER over traditional FEC protection, especially in the aspects of the recovery of the subject area and bandwidth efficiency. <s> BIB003 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> TDWZ based on discrete wavelet transform (DWT) <s> During the past ten years, Wyner-Ziv video coding (WZVC) has gained a lot of research interests because of its unique characteristics of "simple encoding, complex de coding." However, the performance gap between WZVC and conventional video coding has never been closed to the point promised by the information theory. In this paper, we illustrate the chicken-and-egg dilemma encountered in WZVC: high efficiency WZVC requires good estimation of side information (SI); however, good SI estimation is not possible for the decoder without access to the decoded current frame. To resolve such a dilemma, we present and advocate a framework that explores an important concept of decoder-side progressive-learning. More specifically, a decoder-side multi-resolution motion refinement (MRMR) scheme is proposed, where the decoder is able to learn from the already-decoded lower-resolution data to refine the motion estimation (ME), which in turn greatly improves the SI quality as well as the coding efficiency for the higher resolution data. Theoretical analysis shows that at high rates, decoder-side MRMR outperforms motion extrapolation by as much as 5 dB, while falling behind conventional encoder-side inter-frame ME by only about 1.5 dB. In addition, since decoder-side ME does not suffer from the bit-rate overhead in transmitting the motion information, further performance gain can be achieved for decoder-side MRMR by incorporating fractional-pel motion search, block matching with smaller block sizes, and multiple hypothesis prediction. We also present a practical WZVC implementation with MRMR, which shows comparable coding performance as H.264 at very high bit rates. <s> BIB004
An alternative transformation technique to DCT in use by some TDWZ architectures is DWT, which decomposes a video frame into a set of wavelets with different locations  (shift) and scales (resolution). Any decomposition involves a pair of high or low frequency components (sub-bands) that correspond to the detailed parts, and smooth parts, of the video frame, respectively. The wavelets are represented as coefficients which are organized into multi-resolution levels. The main advantages of DWT over DCT are the absence of blocking artefacts as it works on the whole frame rather than on separate blocks, better de-correlation (redundancy removal) property, and inherent scalability. However, popular wavelet coding schemes such as Embedded Zerotree Wavelet (EZW) and Set Partitioning In Hierarchical Trees (SPIHT) produce code words with variable length, which can make the compressed video streams very susceptible to transmission errors in wireless channels. The effects of these errors can in turn propagate to the entire frame during the video reconstruction BIB003 . BIB001 proposed a wavelet domain WZ codec, which shares a similar architecture as TDWZ, but the DCT/Inverse DCT modules are replaced by their DWT equivalent. In addition, a Motion Evaluation module is introduced at the encoder to predict the quality of side-information that will be generated by the decoder based on the amount of motion between successive frames. This is to enable local rate estimation by the encoder and eliminate the need for a feedback channel. However, in WVSN, the quality of side-information does not depend only on the frame motion, but also on the conditions of the channel through which the bits are received and used for constructing the side-information. The authors also introduced a Modulo Reduction module at the encoder to reduce the range of the wavelet coefficients so that they can be quantized and coded more efficiently. Similarly, BIB002 presented a wavelet-based TDWZ codec in which highorder statistical correlation among wavelet coefficients is exploited to improve the coding efficiency of WZ frames. The authors introduced an Entropy Reorder module at the encoder to reorganize quantized wavelet coefficients into a tree structure using an algorithm based on ZeroTree Entropy (ZTE) coding. The significant coefficients are turbo coded and the parity bits are transmitted. The significance map is intra-coded by an Entropy Coding module and transmitted to the decoder, which uses it to extract the significant coefficients of the side-information for reconstructing the WZ frames. So far the new features introduced above are mainly at the encoder side. For the decoder side, BIB004 proposed a wavelet-based TDWZ codec with improved side-information estimation based on multi-resolution motion refinement (MRMR). The main idea is for the decoder to progressively learn from already-decoded lower-resolution data to refine the motion estimation, which in turn improves side-information quality and coding efficiency for higher resolution data. In order to achieve this, two features are introduced: (1) an Over-Complete DWT module to transform a frame into subbands in an over-complete form to overcome the shift-variance problem of critically sampled DWT; (2) a Motion Refinement module to refine the motion vector by motion estimation between current and previous low frequency subbands, and use the refined motion vector to generate side-information of higher-frequency subbands at the same decomposition level. This process repeats until all levels are decoded.