Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to TDWZ <s> In the current interframe video compression systems, the encoder performs predictive coding to exploit the similarities of successive frames. The Wyner-Ziv theorem on source coding with side information available only at the decoder suggests that an asymmetric video codec, where individual frames are encoded separately, but decoded conditionally (given temporally adjacent frames) could achieve similar efficiency. In the previous work we propose a Wyner-Ziv coding scheme for motion video that uses intraframe encoding instead of interframe decoding. In this paper we improve on our Wyner-Ziv video codec by sending hash codewords of the current frame to aid the decoder in accurately estimating the motion. This allows us to implement a low-delay system where only the previous reconstructed frame is used to generate the side information of a current frame. Simulation results show significant gains above conventional DCT-based intraframe coding. The Wyner-Ziv video codec with hash-based motion compensation at the receiver enables low-complexity encoding while achieving high compression efficiency. <s> BIB001 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to TDWZ <s> A motion-based side-information generation scheme with semi super-resolution for a scalable Wyner-Ziv coder framework is introduced. It is known that the performance of any Wyner-Ziv coder is heavily dependent on the efficiency of the side-information generation. We propose an iterative block based scheme to generate a semi super-resolution frame using the past and future reference frames which should be coded at full-resolution. To enable this side-information generation the framework should allow for low encoding complexity, reducing the spatial resolution only in the non-reference frames. The enhancement layer is produced using a residual frame of the reduced resolution encoded frame. The decoder first decodes the low resolution base layer and iteratively generates the side-information, along with channel decoding, to obtain a higher quality version of the decoded frame. Results of the implementation of the framework using the motion-based side-information in the H.263+ and H.264 standards are presented. <s> BIB002 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to TDWZ <s> Wyner-Ziv video coding is a lossy source coding paradigm where the video statistics are exploited, partially or totally at the decoder. The side information represents a noisy version of the original frame and is generated at the decoder with time consuming motion estimation and compensation tools. This paper proposes a novel bidirectional hash motion estimation framework which enables the decoder to choose between past and/or future reference frames for frame interpolation. New features include the coding of DCT hash with zero-motion, combination of trajectory-based motion interpolation with hash-based motion estimation and adaptive selection of the DCT bands which are sent to the decoder in order to guide the motion estimation procedure. Gains up to 1.2 dB compared to previous motion interpolation approaches may be reached. <s> BIB003 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to TDWZ <s> In this paper, we propose a new rate allocation algorithm for transform domain Wyner-Ziv video coding (WZVC) without feedback. In contrast to conventional video coding, Wyner-Ziv video coding aims to design simple intra-frame encoding and complex inter-frame decoding based on the Slepian-Wolf and Wyner-Ziv distributed source coding theorems. To allocate proper number of bits to each frame, most existing Wyner-Ziv video coding solutions need a feedback channel (FC) at the decoder. However, in many video coding applications, the FC is not allowed. Moreover, the FC will introduce latency and an increase of decoder complexity because several iterative decoding operations may be needed to decode the data to achieve target video quality. The proposed algorithm predicts the number of bits for each Wyner-Ziv frame at the encoder as a function of the coding mode and the quantization parameters. Such predictions will not significantly increase the complexity at the encoder. However, the prediction will be able to properly select the best mode and quantization parameter for encoding each Wyner-Ziv frame. Experimental results show that the proposed algorithms is able to achieve good encoder rate allocation while still maintains consistent coding efficiency. Comparing to the WZVC coder with FC, this new WZVC coder without FC induces only a small loss in Rate-Distortion performance. <s> BIB004 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to TDWZ <s> In Wyner-Ziv video coding (WZVC), the quality of side information (SI) has a critical impact on the coding efficiency. Most existing WZVC schemes generate SI using decoder-side motion estimation (ME), where the current frame is unavailable and the ME accuracy is greatly impaired. In this paper, without introducing additional bitrate overhead, we incorporate fractional-pel motion search, reduced block sizes and multiple hypothesis prediction into our previously proposed decoder-side multi-resolution motion refinement framework [1], where the current frame is progressively decoded, and based on which the decoder iteratively refines the motion to improve its accuracy. Theoretical analysis shows significant gain of the combination of these advanced techniques. A practical SI estimator is implemented and provides prediction performance comparable to H.264/AVC. <s> BIB005 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to TDWZ <s> In most existing Wyner---Ziv video coding schemes, a feedback channel (FC) is expected at the decoder in order to allocate a proper bit rate for each Wyner---Ziv frame. However, FC not only results in additional latency but also increases decoding complexity due to the several feedback-decoding iterations. Moreover, FC may be unavailable in many practical video applications. In this paper, we propose a novel feedback-free rate-allocation scheme for transform domain Wyner---Ziv video coding (TD-WZVC), which predicts the rate for each Wyner---Ziv frame at the encoder without significantly increasing the complexity of the encoder. First, a correlation estimation model is presented to characterize the relationship between the source frame and the reference frame estimated at the encoder in TD-WZVC. Then, an efficient FC-free rate-allocation algorithm is proposed and a linear model is built to avoid both overestimation and underestimation of the real rate and obtain an optimal rate-distortion performance. Experimental results show that the proposed scheme is able to achieve a good encoder rate allocation while still maintaining consistent coding efficiency. <s> BIB006 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to TDWZ <s> On the basis of a non-local means denosing process, a novel progressive side information refinement framework for a transform domain Wyner-Ziv video codec is proposed, where the side information is progressively improved, as the decoding proceeds, by exploring both temporal-spatial similarities and already decoded DCT bands. Simulation results show up to 2.5dB in RD performance gain against that of the same codec without including the proposed side information refinement framework for sequences with high motion and/or large group-of-picture sizes. Moreover, the proposed framework adds no significant complexity to the decoder, and even results in a decoding speed-up due to the less required error correcting iterations, for most of the test sequences. <s> BIB007 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to TDWZ <s> This paper focuses on side information (SI) refinement in Wyner-Ziv video coding and proposes to exploit the intrinsic property of channel coding for improving the joint decoding performance. In this paper, we propose to use syndrome and information bits from the encoder to help the decoder in refining the SI. We use extrinsic information transfer (EXIT) chart analysis to deduce the mutual information variation in LDPC iterative decoding during the SI refinement process. The objective is to obtain the same decoding quality under lower coding rates. Simulation results demonstrate the effectiveness of the proposed solution. <s> BIB008 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to TDWZ <s> Over the past few decades, Distributed Video Coding (DVC) has been considered as a compression paradigm suitable for applications which require simple encoding. Yet, the performance obtained with practical architectures is still far from the theoretical bound, mainly due to the inaccurate Side Information (SI) predicted at the decoder. The work presented in this paper tries to improve the correlation between the bit-planes of the SI and the corresponding bitplanes of the Wyner-Ziv (WZ) frame. The proposed algorithm uses the adjacent key frames to predict the quantization intervals for the SI and for the WZ frame. It then chooses whether the quantization module should use the floor or the ceiling operationsuch that theindices generated for the two frames differ by the smallest number of bits possible. Experimental results show that, for a given target quality, the proposed method can reduce the WZ bit-rate by up to 8.4% compared to the traditional coding schemes. <s> BIB009
Similar to PDWZ, several enhancements have been made to the original TDWZ codec design with a focus on modules such as rate-control, decoding algorithm, side information generation, and correlation noise modelling. A table summarizing the enhancements made to TDWZ and their discussions are shown in Table 2 . Some of them are outlined as follows: • It is observed that the accuracy of side information generation has a significant impact on codec's overall performance. Several enhancements have been suggested for the estimation of side information in TDWZ codec. This includes a progressive side information refinement framework introduced in BIB007 , which exploits the spatial and temporal correlation among previously decoded frames to gradually improve the side information as the decoding process progresses. Various approaches for the enhanced side information module based on progressive side information refinement, motion searching, resolution-progressive decoding, and extensive motion exploration are presented in BIB002  BIB005 BIB008 . Research has also been done to transmit the hash signature of each bit-plane to detect and remove any errors during transmission to further enhance the side information module. Reasonable gains in overall codec's performance have been reported at the expense of some additional complexity at the encoder BIB001 BIB003 ). • One of the most challenging tasks of the TDWZ codec is to assign an optimal number of bits to encode the WZ frame. Typically, a feedback channel is employed to inform the encoder about the required encoding rate. Since the encoder itself does not have access to motion compensation information of the WZ frame, significant degradation in rate-distortion performance may occur if insufficient bits have been allocated to the frame. However, for applications that only transmit data in one way such as broadcasting, employing a feedback channel is not possible. BIB004 BIB006 proposed a rate-distortion algorithm for TDWZ in which the encoder estimates the number of bits per bitplane for each coefficient band as a function of quantization parameters and coding mode without using feedback channel to reduce the latency and complexity of the decoder site. BIB009 presented an algorithm to reduce the correlation noise between the bitplanes of WZ frame and the corresponding side information. The algorithm makes use of previously reconstructed key frames to estimate the quantization steps and configure the quantization values such that the mismatches between current WZ frame and its side information is reduced to a minimum. The proposed method is shown to provide significant performance gain as compared to traditional TDWZ codec.