Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s>  <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>  <s> This paper addresses the important aspect of compressing and transmitting video signals generated by wireless broadband networks while heeding the architectural demands imposed by these networks in terms of energy constraints as well as the channel uncertainty related to the wireless communication medium. Driven by the need to develop light, robust, energy-efficient, and low delay video delivery schemes, a distributed video coding based framework dubbed PRISM is introduced. PRISM addresses the wireless video sensor network requirements far more effectively than current state-of-the-art standards like MPEG. This paper focuses on the case of a single video camera and use it as a platform to describe the theoretical principles and practical aspects underlying distributed video coding. <s> BIB002 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s>  <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>  <s> This paper addresses the problem of optimal minimum mean-squared error reconstruction of quantised samples in Wyner-Ziv video coding systems. Closed-form expressions of the optimal reconstructed values are derived for a Laplacian correlation model. The method is used for both single and multiple side information scenarios (the latter is also referred to as multi-hypothesis Wyner-Ziv decoding). The efficiency of the proposed optimal reconstruction method is confirmed by rate-distortion performance results, showing significant decrease of the distortion of the decoded sequence, compared to simple reconstruction methods that have been employed so far. <s> BIB004 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s>  <s> This paper surveys recent trends and perspectives in distributed video coding. More specifically, the status and potential benefits of distributed video coding in terms of coding efficiency, complexity, error resilience, and scalability are reviewed. Multiview video and applications beyond coding are also considered. In addition, recent contributions in these areas, more thoroughly explored in the papers of the present special issue, are also described. <s> BIB005 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s>  <s> This chapter discusses the state of the art and the major research challenges in architectures, algorithms, and protocols, for wireless multimedia sensor networks (WMSNs). These are networks of wirelessly interconnected smart devices designed and deployed to retrieve video and audio streams, still images, and scalar sensor data. First, applications and key factors influencing the design of WMSNs are discussed. Then, the existing solutions at the application, transport, network, link, and physical layers of the communication protocol stack are investigated. Finally, fundamental open research issues are discussed and future research trends in this area are outlined. <s> BIB006 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s>  <s> Rate-distortion optimization (RDO) selects the mode that achieves the highest coding performance at the minimum cost after all coding modes have been computed. Unfortunately, the extreme complexity of RDO operations can severely impact real-time applications. To save coding time, we propose intra-mode-ignored decision and early skip mode prediction procedures. The former is based on the inter-coding results, such that the intra-mode may be disregarded for predictive frame coding. In the latter, a simple criterion can determine whether skip mode should be employed before performing the intra- and inter-mode procedures. Experimental results show that these two methods can significantly reduce the encoding time, by an average approximately 24 and 15%, respectively. A hybrid of the two methods could save an additional 36%, while maintaining an optimum RD. <s> BIB007 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s>  <s> Since 1990, the Video Coding Expert Group (VCEG) and the Moving Pictures Expert Group (MPEG) have focused their research in video coding techniques for different applications. The International Telecommunication Union (ITU-T) and the MPEG groups joined in a single group to form the Joint Video Team (JVT) and worked together on a new video standard called H.264, H.264/AVC Advanced Video Coding, or MPEG-4 part 10, which achieves more coding efficiency with simpler syntax specifications than the previous standards, more integration with all network protocols, and multiplex architectures. The H.264 is the state-ofthe-art codec and covers a wide range of applications with excellent results such as videoconferencing, video streaming, and video transmission over fixed and wireless networks with different transport protocols among others. <s> BIB008 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s>  <s> This paper presents an efficient method for selecting the best reference frame (RF) and the best inter-mode in H.264/AVC. The proposed method employs a different examination order compared to conventional methods and examines the most important RF for all inter-modes in the first step. Then, in the second step, it further examines the best mode from the first step for all available RFs. Finally, in the third step, it additionally examines the remaining modes for the best RF determined in the second step. Based on the intermediate results after the first and second steps, the proposed method skips many less important RFs in each inter-mode and significantly reduces the coding complexity. However, the proposed method also shows very good performance in terms of the peak signal-to-noise ratio and bit rate, as it does not skip important RFs in each inter-mode. Simulation results show that the proposed method greatly reduces the encoding time while significantly improving the encoding performance of conventional methods. <s> BIB009
Video compression is a relatively complex operation that can consume significant processing and energy resources in resource-limited camera sensor nodes. Conventional compression standards are computation intensive but perform very well when complexity of the encoder is not a major concern. DVC is an emerging video coding paradigm for applications with limited resources available at encoder. It reverses the conventional video coding paradigm by shifting the encoder's complexity entirely or partially to the decoder, which is assumed to be more resourceful than the encoder BIB002 ). Therefore, DVC based encoders are much simpler, and a number of different DVC architectures (e.g. BIB001 BIB003 BIB004 ) have been proposed in literature. The conventional video coding architecture has been challenged by the emergence of WVSNs. Traditional state-of-the-art video coding standards such as H.264 BIB008 , MPEGx (Le Gall 1991) are pertinent to the broader class of applications that support encoders with complexity of at least 5-10 times greater than that of the decoder BIB005 ). These video coding architectures suit applications such as streaming videoon-demand (VoD), video broadcasting, digital home systems, and multimedia collaboration that requires video to be encoded once and decoded several times by consumers BIB006 . Conventional video coding architectures are primarily based on hybrid discrete cosine transformation (DCT) and interframe predictive video coding (PVC) frameworks. These frameworks allocate codec functionalities such that most of the high complexity operations that involve exploiting spatial and temporal correlation, e.g. motion estimation and compensation, are executed at the encoder, while the decoder performs lower complexity operations such as entropy decoding, frame prediction, inverse quantization, and DCT on the bitstream received from encoder BIB007 BIB009 .