Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> A general method of constructing error correcting binary group codes is obtained. A binary group code with n places, k of which are information places is called an ( n , k ) code. An explicit method of constructing t -error correcting ( n , k ) codes is given for n = 2 m −1 and k = 2 m −1−R( m , t ) ≧ 2 m −1− mt where R ( m , t ) is a function of m and t which cannot exceed mt . An example is worked out to illustrate the method of construction. <s> BIB001 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> A low-density parity-check code is a code specified by a parity-check matrix with the following properties: each column contains a small fixed number j \geq 3 of l's and each row contains a small fixed number k > j of l's. The typical minimum distance of these codes increases linearly with block length for a fixed rate and fixed j . When used with maximum likelihood decoding on a sufficiently quiet binary-input symmetric channel, the typical probability of decoding error decreases exponentially with block length for a fixed rate and fixed j . A simple but nonoptimum decoding scheme operating directly from the channel a posteriori probabilities is described. Both the equipment complexity and the data-handling capacity in bits per second of this decoder increase approximately linearly with block length. For j > 3 and a sufficiently low rate, the probability of error using this decoder on a binary symmetric channel is shown to decrease at least exponentially with a root of the block length. Some experimental results show that the actual probability of decoding error is much smaller than this theoretical bound. <s> BIB002 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <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> BIB003 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> Distributed source coding principles have been recently applied to video coding in order to achieve a flexible distribution of the complexity burden between the encoder and the decoder. In this paper we elaborate on a pixel based WynerZiv video codec that shifts all the complexity of the motion estimation phase to the decoder, thus achieving light encoding. We observe that the correlation noise statistics describing the relationship between the frame to be encoded and the side information available at the decoder is not spatially stationary. For this reason we introduce a mode decision scheme either at the encoder or at the decoder in such a way that when the estimated correlation is weak we opt for intra coding on a block-by-block basis. Moreover we discuss the effect of using a side information computed either from lossless or from quantized frames. <s> BIB004 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> Distributed video coding is a recent paradigm that enables a flexible distribution of the computational complexity between the encoder and the decoder building on top of distributed source coding principles. In this paper we focus on the scenario where most of the complexity is shifted to the decoder, thus achieving light encoding. We elaborate on a well known pixel based Wyner-Ziv architecture and we improve its coding efficiency by exploiting both spatial and temporal correlation at the decoder side, without the need of performing any transform at the encoder. In order to generate the side information, the decoder adaptively chooses spatial or temporal information, based on the local estimate of the correlation noise. Simulations on test sequences demonstrate that a coding gain of up to +1.8 dB can be obtained with respect to the case that generates the side information by motion interpolation only. <s> BIB005 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> In contrast to conventional video coding, Wyner-Ziv video coders perform simple intra-frame encoding and complex inter-frame decoding. This feature makes this type of coding suitable for applications that require low-complexity encoders. In this paper, we present a model of the coding distortion introduced by pixel-domain WynerZiv video coders. Our distortion model can be used to determine the value of coding parameters under certain coding constraints. Specifically, we show how our model can be used to select the quantization step size of each video frame so that a target distortion can approximately be met. Experimental results show that, even though the accuracy of the distortion predictions is limited by the restricted computational capacity of Wyner-Ziv encoders, the described distortion constraints can be approximately fulfilled by using our model. <s> BIB006 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <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> BIB007 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> This paper describes a hybrid coder/decoder rate control for a Wyner-Ziv video coding scheme with a feedback channel. The approach is first based on a method to estimate at the encoder the minimum rate required for the Slepian-Wolf (SW) encoded data. This estimation makes use only of the Lapacian correlation model. The decoder then estimates the bit error rate (BER) for each decoded bit plane from likelihood ratios computed at the output of the SW decoder. The robustness of the BER estimation is further improved by the use of an error detection mechanism based on a cyclic redundancy checksum. Experimental results show that rate-distortion performances are comparable to those which would be obtained by computing the Hamming distance between the original and the decoded data. In addition the hybrid coder/decoder rate control reduces the decoding complexity as well as the usage of the return channel. <s> BIB008 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> In this paper, we present a new decoding algorithm for the Wyner-Ziv (WZ) video coding scheme based on turbo codes. In this scheme, a video frame is encoded using a turbo code, and only a subset of the parity bits are sent to the decoder. At the decoder, the temporal correlation of the video sequence is exploited by using the previous frame as noisy side information (SI) for the current frame. However, there is a mismatch between the SI, which is available as pixel values, and the binary code bits. Previous implementations of the decoder use suboptimal approaches that convert pixel values to soft information for code bits. We present a new decoding algorithm for this application based on decoding on a hyper-trellis, in which multiple states of the original code trellis are combined. We show that this approach significantly improves performance without changing the complexity of the decoder. We also introduce a new technique for the WZ decoder to exploit the spatial correlation within a frame without requiring transform-domain encoding at the encoder, thereby reducing its complexity. Simulation results for fixed-rate transmission show a 9-10-dB improvement in the peak signal-to-noise ratio when compared to a WZ video codec that does bitwise decoding and utilizes only the temporal correlation. <s> BIB009 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <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> BIB010 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> In recent years, practical Wyner-Ziv (WZ) video coding solutions have been proposed with promising results. Most of the solutions available in the literature model the correlation noise (CN) between the original frame and its estimation made at the decoder, which is the so-called side information (SI), by a given distribution whose relevant parameters are estimated using an offline process, assuming that the SI is available at the encoder or the originals are available at the decoder. The major goal of this paper is to propose a more realistic WZ video coding approach by performing online estimation of the CN model parameters at the decoder, for pixel and transform domain WZ video codecs. In this context, several new techniques are proposed based on metrics which explore the temporal correlation between frames with different levels of granularity. For pixel-domain WZ (PDWZ) video coding, three levels of granularity are proposed: frame, block, and pixel levels. For transform-domain WZ (TDWZ) video coding, DCT bands and coefficients are the two granularity levels proposed. The higher the estimation granularity is, the better the rate-distortion performance is since the deeper the adaptation of the decoding process is to the video statistical characteristics, which means that the pixel and coefficient levels are the best performing for PDWZ and TDWZ solutions, respectively. <s> BIB011 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> Distributed Video Coding (DVC) is a new video coding technique which has low encoder complexity and good error resilience. Rate control is one of the most important problems in DVC. In order to allocate an optimal number of parity bits for the current frame,most distributed video coders use a feedback channel(FC) to perform rate control at the decoder. However,using feedback channel can increase the decoding complexity and result in transmission delay. To solve these problems, we propose a novel encoder rate control (ERC) algorithm for pixel-domain distributed video (PDDV) coder without feedback channel at the cost of slightly increased encoder complexity. The experiment results show that the performance obtained using our ERC algorithm is comparable to that obtained using the decoder rate control (DRC)algorithm. <s> BIB012 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <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> BIB013 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> Distributed Video Coding (DVC) has been proposed as a new video coding paradigm to deal with lossy source coding using side information to exploit the statistics at the decoder to reduce computational demands at the encoder. A virtual channel noise model is utilized at the decoder to estimate the noise distribution between the side information frame and the original frame. This is one of the most important aspects influencing the coding performance of DVC. Noise models with different granularity have been proposed. In this paper, an improved noise model for transform domain Wyner-Ziv video coding is proposed, which utilizes cross-band correlation to estimate the Laplacian parameters more accurately. Experimental results show that the proposed noise model can improve the Rate-Distortion (RD) performance. <s> BIB014 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> Wyner-Ziv video coding (WZVC) is a newly emerged video coding scheme which compresses the input video frames with the side information (SI) frames only available at the decoder. WZVC exploits the statistics between the source frame and the SI frame at the decoder by utilizing their correlation information. This correlation information is important but also difficult to estimate due to the absence of the SI frame at the encoder, and the lack of the source frame at the decoder. In this paper, we focus on this problem and propose a novel transform-domain adaptive correlation estimation method called TRACE for WZVC. In TRACE, the correlation information is progressively learned during the decoding process of each frame. Within TRACE, we also propose a convex optimization based band-level correlation estimation method which is optimal in the sense of minimizing the theoretical bit rate. Experiments suggest that, when applied in motion compensated interpolation-based low complexity WZVC, TRACE yields competitive results against the state-of-the-art correlation estimation algorithms. More importantly, different from the existing coefficient-level correlation estimation algorithms, the proposed TRACE can be applied in many other WZVC schemes and can provide considerable gain over the popular band-level correlation estimation methods. <s> BIB015 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> Wyner-Ziv (WZ) video coding is a particular case of distributed video coding (DVC), the recent video coding paradigm based on the Slepian-Wolf and Wyner-Ziv theorems which exploits the source temporal correlation at the decoder and not at the encoder as in predictive video coding. Although some progress has been made in the last years, WZ video coding is still far from the compression performance of predictive video coding, especially for high and complex motion contents. The WZ video codec adopted in this study is based on a transform domain WZ video coding architecture with feedback channel-driven rate control, whose modules have been improved with some recent coding tools. This study proposes a novel motion learning approach to successively improve the rate-distortion (RD) performance of the WZ video codec as the decoding proceeds, making use of the already decoded transform bands to improve the decoding process for the remaining transform bands. The results obtained reveal gains up to 2.3 dB in the RD curves against the performance for the same codec without the proposed motion learning approach for high motion sequences and long group of pictures (GOP) sizes. <s> BIB016 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <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> BIB017 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> In this paper we propose and compare different distributed video coding (DVC) schemes based on the use of the wavelet transform, which naturally allows for spatial and other forms of scalability. In particular, we propose a hybrid encoder which utilizes channel codes, and evaluate its performance in the absence of a feedback channel. The proposed scheme uses statistical models for the estimation of the required bitrate at the encoder. We also propose a scheme that is based on a modulo reduction procedure and does not use channel codes at the receiver/transmitter. These schemes are compared with more conventional coders that do not or only partially exploit the distributed coding paradigm. Experimental results show that the considered schemes have good performance when compared with similar asymmetric video compression schemes, and that DVC can be an interesting option in appropriate scenarios. <s> BIB018 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> Transform Domain Wyner-Ziv (TDWZ) video coding is an efficient Distributed Video coding solution providing new features such as low complexity encoding, by mainly exploiting the source statistics at the decoder based on the availability of decoder side information. The accuracy of the decoder side information has a major impact on the performance of TDWZ. In this paper, a novel multi-hypothesis based TDWZ video coding is presented to exploit the redundancy between multiple side information and the source information. The decoder used optical flow for side information calculation. Compared with the best available single estimation mode TDWZ, the proposed multi-hypothesis based TDWZ achieves robustly better Rate-Distortion (RD) performance and the overall improvement is up to 0.6 dB at high bitrate and up to 2 dB compared with the DISCOVER TDWZ video codec. <s> BIB019 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <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> BIB020 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <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> BIB021 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <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> BIB022 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> Wireless video sensor networks (WVSNs) have drawn significant attention in recent years due to the advent of low-cost miniaturized cameras, which makes it feasible to realize large-scale WVSNs for a variety of applications including security surveillance, environmental tracking, and health monitoring. However, the conventional video coding paradigms are not suitable for WVSNs due to resource constraints such as limited computation power, battery energy, and network bandwidth. In this paper, we evaluated and analyzed the performance of video codecs based on emerging video coding paradigms such as distributed video coding and distributed compressive video sensing for multihop WVSNs. The main objective of this work was to provide an insight into the computational (encoding/decoding) complexity, energy consumption, node and network lifetime, processing and memory requirements, and the quality of reconstruction of these video codecs. Based on the findings, this paper also provides some guidelines for the selection of appropriate video codecs for a given WVSN application. <s> BIB023 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Module Summary References <s> The authors propose a bit-level context-adaptive correlation model to exploit high-order statistical correlation for wavelet-domain distributed video coding (DVC). The magnitude and sign of each coefficient are coded separately in a bit-plane fashion. The context for magnitude bit plane are designed based on the side information (SI), the local neighborhood, and the parent coefficient. The sign bit plane takes the sign of the SI as the context. The authors also introduce SI binning to classify the SI based on its quality. The SI's class is then included in the contexts for both magnitude coding and sign coding. Experimental results show that the proposed scheme provides significant coding gain over existing DVC systems. <s> BIB024
Rate-control Encoder rate-control algorithm without feedback channel at the expense of increased encoder complexity An efficient block motion-estimation algorithm at encoder for estimating bitplane error probability and low complexity side information A code mode decision algorithm at encoder to improve coding performance BIB012 Encoder based rate-allocation algorithm that computes the number of bits to encode each WZ frame without significantly increasing encoder complexity Uses a Laplacian random variable to represent the difference in bitplane values between the original frame and corresponding side information Defines a probability mass function to estimate the aforementioned random variable Estimates the bit error probability for each bitplane based on the error correcting capacity of the turbo code and frame rate of the video Prevents increase in distortion due to excessive errors in decoded bitplanes by discarding parity bits and sets decoded frame to side information if residual error probability estimated at decoder is above a given threshold Decoding algorithm A mode decision scheme that can be executed at encoder or decoder (or both) to determine if the correlation noise estimation between a frame to be encoded and its side information is weak, and if block-based intra-frame coding should be selected instead of block-based WZ coding Shows that the relationship between the frame to be encoded and the side information at the decoder (defined as correlation noise statistics) is not spatially stationary Determines the selection criteria for mode decision by exploiting spatial and temporal statistics Creates a binary map whose entries indicate which blocks of a frame to be encoded should be intra-or WZ-coded. A simple entropy coding algorithm is used for efficient processing of this information A coding distortion model that can be used to determine the value of coding parameters such as quantization step size, target distortion, distortion predictions under certain coding constraints Selects the quantization step size of each video frame to meet the target distortion Shows that the accuracy of distortion predictions is limited by computation capacity of PDWZ encoders and the stability of distortion constraints BIB006 A decoding algorithm based on turbo codes that requires a small subset of parity bits at the decoder for each WZ frame, and exploits the temporal correlation of the video sequence using previously reconstructed frame as noisy side information Mismatches between the side information and frame to be decoded are represented by pixel values and parity bits Uses a suboptimal approach to convert pixel values to soft information for the parity bits Uses hyper-trellis codes to combine multiple states of original trellis code Improves codec performance without increasing decoder's complexity BIB009 A decoding algorithm that incorporates side information computed from either lossless or quantized frames A mode decision scheme at the decoder (similar to the one in BIB015 is used to improve the correlation noise statistics BIB004 Side information An extrapolation module to generate side information based on motion field smoothening filter to enhance performance of a low-delay PDWZ codec Uses overlapped motion estimation, in particular motion field smoothening filtering and spatial-interpolation for un-overlapped regions  Encoder based motion-compensation module that sends hash codewords of the frame to be decoded to the decoder Hash codewords complements the side information and lead to efficient frame reconstruction Enables low-complexity encoding while maintaining high compression ratio BIB003 ) Imran et al. SpringerPlus (2015) 4:513  Rate-control Rate-allocation scheme without using feedback channel and without significantly increasing the encoder complexity A linear rate estimation model that avoids over or under estimation and achieves optimal rate-distortion performance Shows a reasonably good encoder rate allocation performance while maintaining coding efficiency BIB013 Encoder based rate-allocation scheme that predicts the number of encoding bits as a function of the coding mode and quantization parameters Predictions select the best coding mode and quantization parameters for encoding WZ frame without significantly increasing encoder's complexity Shows relatively low loss in rate-distortion performance as compared to conventional decoder based rate allocation scheme BIB010 The DISCOVER codec generates the band of transform coefficients after performing block-based transformation and quantization on each WZ frame An improved rate-control algorithm that computes the initial number of bits to transmit for each bitplane and band Does not require excessive number of iterations, hence improves the coding efficiency  A feedback channel-driven rate-control codec with improved modules using special coding tools An improved motion learning algorithm with reasonably good rate-distortion performance BIB016 A hybrid procedure for rate estimation at encoder side for wavelet based WZ codec with no feedback channel Quantized high resolution subbands entropy coded using low-complexity intra-coding to avoid under-estimation of required bit rate For lower resolution subbands, the entropy of the bitplane crossover probability is used as an estimate BIB018 Channel adaptive rate control for feedback-free wavelet-based WZ; priority given to lower frequency subbands that hold more information about a frame than higher frequency subbands  Decoding algorithm A decoding algorithm that exploits previously reconstructed transform bands to reduce the total number of bits needed for reconstructing the remaining bands BIB016 Presents TRACE (TRansform domain Adaptive Correlation Estimation) for WZ decoder Progressively learns the correlation among frames during the frame reconstruction process A convex optimization based band-level correlation estimation method that minimizes the theoretical required bit rate BIB015 A multi-hypothesis based WZ decoder that exploits the redundancy between multiple side information(s) and the source frame Uses both block-based and optical flow-based side information generation methods to generate multiple side information(s) An optical flow based frame interpolation algorithm to compensate side information estimation weaknesses in block based methods Employs multiple soft-inputs for decoding and reconstruction based on a weighted joint distribution, which reduces the required bitrate and improves the quality of reconstructed frames BIB019 A bit-level context-adaptive correlation model for the decoder of a waveletbased WZ codec with MRMR BIB017 ) to achieve better prediction of the bit probability distribution. BIB024 Side information An improved side information refinement framework that utilizes both spatiotemporal correlation and previously reconstructed transform bands Uses a non-local means denoising process that exploits partially decoded side information(s) progressively available at the decoder A denoising process that progressively regenerates side information with improved quality BIB020 where MC-1 and MC-E represents motion-compensation using frame Interpolation, and Extrapolation, respectively. The first 100 even frames of Foreman QCIF sequences were used to evaluate the rate-distortion performance of the luminance component encoded at the frame rate of 15 frames per second. The TDWZ results were also compared with (a) DCT-based intraframe coding where the even frames are encoded as I frames; (b) H.263+ interframe coding with an I-B-I-B predictive structure; and (c) PDWZ codec. The evaluation assumed the same rate and quality for the odd frames of all the schemes, and therefore the rate-distortion performances of odd frames were not included in the plots. It is evident from Fig. 11 that when highly reliable side information (MC-I) is used, the TDWZ codec is 7-8 dB better than the PDWZ codec. On the other hand, using less reliable side information (MC-E), the TDWZ codec yields a PSNR gain of 1-3 dB against DCT-based intraframe coding. It is also observed that compression efficiency loss is approximately 5 dB higher since the motion and occlusions in the foreman sequence make it more difficult to extrapolate the succeeding frames. BIB005 also proposed an algorithm that was integrated into the PDWZ codec and exploited its spatial redundancy without introducing any transform at the encoder side, thereby keeping the complexity of the encoding as low as possible. They presented the rate-distortion curve (Fig. 12) which showed noticeable improvement in the side information quality and rate-distortion performance. However, results may vary depending on the type of video sequence. A side information generation algorithm based on semi super-resolution frame that exploits past and future reference frames for block-based motion estimation process Iteratively generates side information using channel decoder following the decoding of a low resolution base layer to produce high quality decoded frame Low resolution encoding reduces the encoding complexity Encodes the residual WZ frame by cosets BIB007 An extrinsic information transfer (EXIT) chart analysis for minimizing the mutual information variation in iterative low density parity check (LDPC) decoding during side information refinement process Obtains relatively good reconstruction quality with low coding rates BIB021 Correlation noise modeling A correlation noise estimation algorithm that exploits the adjacent key frames to predict the quantization step of the quantization module Indices generated for two frames differ by smallest number of bits possible Shows improved WZ encoding bitrate for a given target quality as compared to the traditional coding schemes BIB022 An online approach for modelling correlation noise model parameters at the decoder Determines the temporal correlation between frames at various levels of granularity (DCT bands, DCT coefficients) Shows good rate distortion performance at higher estimation granularity BIB011 A correlation noise model that utilizes cross-band correlation to precisely estimate the Laplacian parameters Uses a category map based on previously reconstructed bands to classify transformed coefficients of the current band Allocates each transformed coefficient to a Laplacian parameter based on its category More precise estimation of correlation noise model parameters leads to better rate-distortion performance BIB014 Experiments were carried out on Foreman, Mother and Daughter, and News video sequences using frame rate of 15 fps. From Fig. 12 , it is evident that the rate-distortion curve for the TDWZ codec almost always outperforms PDWZ codec, even when the spatio-temporal side information is being used. On the other hand, the enhanced PDWZ BIB005 design BIB005 ) improves the side information with spatial data without adding further complexity to the encoder, which bridges the gap between the original PDWZ and TDWZ codecs. The DISCOVER and PRISM architectures were compared to conventional H.264/AVC codec in  ), under a transmission scenario over a network with and without channel errors. The DISCOVER codec has been configured with GOP size 2 under the assumption that lost packets will be requested through the feedback channel, which avoids a deterioration of the frames' reconstruction quality with potential cost of a higher bit rate requirement. The H.264/AVC uses the same key frame setup of the DIS-COVER, which transmits each slice of a given frame in a single packet with GOP size 2 in IBIB 3 mode. The encoded bitstreams were transmitted over a network with a packet loss ratio (PLR) of 0 or 5 %, and the PSNR for foremen sequence was evaluated and analyzed on a frame-by-frame basis. As shown in Fig. 13 , it can be observed that DISCOVER generally outperformed PRISM in terms of PSNR in both error-free case (PLR = 0) and in the presence of channel errors (PLR = 5 %). However, the performance in terms of both compression and error resilience depends upon the content of the test sequence. In contrast to H.264/ AVC, the DISCOVER tends to offer better PSNR performance as PLR increases. This is due to the reason that H.264/AVC is not able to compensate for lost information, whereas the DISCOVER can request for additional parity bits through the feedback channel. As a result of such architectural differences, it may not be considered fair to compare their performances. In the PRISM codec, the visual quality is more uniform than in DISCOVER, because every frame is encoded by combining traditional and WZ encoding in a block wise fashion. However, this uniformity in the perceived quality carries the drawback of an increased sensitivity to drift errors with respect to the DISCOVER architecture. Given that PRISIM is unable to handle drift errors in a satisfactory way, even if the average quality of the video sequence is fine, the presence of a few regions in the frame that contain drift errors could still be visible to the human eye. Table 3 summarizes a functional comparison of the three primary DVC architectures. The following compares these key functional features in more detail: • Block-based and frame-based coding For exploiting spatial correlation to generate bitstream, various DVC architectures employ either a block-based or a frame-based encoding approach, each having its own salient characteristics. Block-based coding is more adaptive to spatial variations, thus exploits local features of a video frame more efficiently and has a better reconstruction quality at the decoder side. On the other hand, frame-based coding has the benefit of being able to deal with larger datasets, and its comparatively lower complexity is a desirable feature for more efficient channel coding. During intermediate processing stages, although a frame-based coding approach may still offer the advantage of block-based coding, the final bitstream is associated with the entire frame rather than providing support for smaller spatial blocks. Berkeley's PRISM architecture and Stanford's Wyner-Ziv architecture are examples of block-based, and frame-based coding approaches, respectively. • Encoder/decoder based rate-control One of the challenging tasks for DVC architecture is to allocate the number of bits associated with each frame/block for transmission to the decoder. In some architectures, this responsibility is placed either on encoder or decoder (or both encoder and decoder). If the decoder is involved in taking a decision about the encoding rate, feedback channel is required to provide a more sophisticated and tighter control over the number of bits transmitted from the encoder to decoder. Decoder performs complex processing during frame reconstruction, and depending upon the requirements to achieve predetermined target quality, the decoder may request the encoder to change its encoding rate. For example, parity bits transmitted from the encoder are analyzed by the decoder to determine whether these bits are insufficient to achieve an acceptable level of performance. If not, it will request additional parity bits from encoder, rather than using the decoded frames with well-built traces. Such approach is applicable to real-time video coding (active communication mode) applications because the decoder can estimate the number of additional bits required only at the time of decoding. Feedback channel also has an impact on decoder's complexity and may introduce latency if used frequently. An improvement to the side information generation module may involve restricting the number of feedback requests from the decoder. Alternatively, the encoder rate-control approach eliminates the need for a feedback channel (passive communication mode) and estimates the number of bits needed to achieve the desired target quality with additional complexity at the encoder side. Berkeley's PRISM architecture, and Stanford's Wyner-Ziv architecture, are examples of encoder, and decoder based rate-control approaches, respectively. A number of hybrid approaches have also been proposed as extensions of the WynerZiv architecture in which the encoder estimates the number of bits, thereby limiting the use of feedback channel and reduce the overall latency BIB008 ). • BCH, turbo and LDPC channel codes BCH channel codes with ability to correct multiple bit errors are very simple and have tighter control on symbol errors during the channel coding process. Decoding of BCH requires performing simple algebraic operations BIB001 . BCH encoding and decoding in video coding architecture is also widely known as syndrome coding and decoding, respectively. Turbo codes, on the other hand, are forward error correction codes that can achieve a channel capacity comparable to theoretical bounds. They guarantee reliable communication even in the presence of noise and under bandwidth or delay constraints  . Finally, LDPC channel codes, which are the most sophisticated among the three, are the linear error correction codes specifically designed to transmit information under noisy channel conditions. Similar to turbo codes, they can achieve a channel capacity close to the theoretical maximum with a very low bit error rate. LDPC decoding time is dependent on the information block length BIB002 . Berkeley's PRISM and early Stanford's Wyner-Ziv architectures employ BCH and turbo channel codes, respectively. However, in later years, LDPC replaced the turbo codes in both Stanford's pixel and transform domain WZ architectures. In addition to the aforementioned factors considered for functional comparison of DVC architectures, there are still other issues not sufficiently addressed in the existing literature: • Chroma components coding In all three architectures including their enhancements, there is no mentioning of encoding and decoding procedures for Chroma component. Moreover, the performance comparisons have been done only for Luma components. Considering the significance of Luma component, more details on Luma coding in terms of compression mechanism as well as its impact on overall performance, should be provided. • Standardization To date, there is still a lack of a standard implementation of DVC architectures. There exist a number of different implementations. For the sake of interoperability, standardization is an issue that needs to be addressed for practical and commercial adoption of DVC. • Compressed video transport bitstream In literature, for all the WZ architectures (pixels/transform domain), the WZ bitstream and H.264 (or conventional Intra coder) bitstream are sent separately to the decoder. However, for practical applications, a single transport bitstream that combines the compressed WZ and H.264 frames is required. Moreover, regarding DVC application to WVSN, there are still challenges to be overcome in order to enable the delivery of high quality video stream, such as: • Latency The conventional DVC codecs ideally assumes the block interleaver size in Slepian-Wolf turbo code is large enough to encode an entire WZ frame, which is unrealistic for practical use since it will add significant computational delay to the end-to-end system. Unlike the WVSN requirement, the system will be unable to respond with a timely WZ decoded output due to the intense Slepian-Wolf turbo coding and decoding delay. • Bitrate allocation In most of the DVC codecs (PDWZ/TDWZ), the bitrate of WZ frame is determined by exploiting the statistical correlation between the side information and original WZ frame. Due to the architectural constraint, the encoder does not have access to side information. Therefore, the accurate estimation of the number of parity bits that will be sufficient for decoding is very complex. This rate control problem is commonly addressed by using the feedback channel between encoder and decoder. In case of decoding failure, a request for more parity bits will be sent to encoder via feedback channel. However, the request is unable to inform the encoder the number of parity bits that should be sent. Sending redundant parity bit increases the transmission energy consumption, a situation that will be exacerbated in multihop WVSN scenario. On the other hand, architectures without feedback channel usually compute the side-information at encoder to predict the bitrate, which results in greater computational complexity (and associated energy consumption) at the encoder that consequently decreases the lifetime of the source node and the entire network. In our work presented in BIB023 , we also evaluated and analyzed the performance of DVC architectures against conventional PVC-based codec for multihop WVSNs to provide an insight about the computational (encoding/decoding) complexity, energy consumption, node and network lifetime, processing and memory requirements, and the quality of reconstruction between them. Our findings revealed that DISCOVER (a transform-domain Wyner-Ziv Codec) is the most energy-efficient encoder for singlehop WVSN environment. However, considering its dependency on feedback channel for decoding operation and higher communication energy, it is only suitable for real-time applications. However, we also discussed other feedback-less DVC variants that can be used in both real-time and non-real time applications with comparable energy requirements as DISCOVER. H.264 Intra is found to have lower communication energy consumption than DVC codecs due to its better compression ratio. However, it consumes higher computation energy due to its greater encoding complexity, which significantly increases its overall energy consumption BIB023 . We also investigated the lifetime of both source and relay nodes and the overall network for each of the video codecs. The relative order of the codecs in terms of the lifetime of the source node, which is considerably shorter than that of relay node and thus dictates the network lifetime, expectedly follows the computational energy results. Further findings on processing and memory requirements supported our assessment that DVC-based codecs outperform the conventional codec. The variation in the processing and memory requirements between the DVC-based codecs is primarily due to the GOP difference and the compression technique.