Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to PDWZ <s> In some video coding applications, it is desirable to reduce the complexity of the video encoder at the expense of a more complex decoder. Distributed video (DV) coding is a new paradigm that aims to achieve this. To allocate a proper number of bits to each frame, most DV coding algorithms use a feedback channel (FBC). However, in some cases, a FBC does not exist. In this paper, we therefore propose a rate allocation (RA) algorithm for pixel-domain distributed video coders without FBC. Our algorithm estimates at the encoder the number of bits for every frame without significantly increasing the encoder complexity. Experimental results show that our RA algorithm delivers satisfactory estimates of the adequate encoding rate, especially for sequences with little motion. <s> BIB001 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to PDWZ <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> BIB002 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to PDWZ <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> BIB003 </s> Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures <s> Enhancements to PDWZ <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> BIB004
Several enhancements have been made to the original PDWZ codec design with a focus on modules such as rate-control, decoding algorithm, side information generation and correlation noise modelling. Table 1 summarizes the enhancements made to the aforementioned modules and their discussions from a number of well-known works in literature. Some of them are outlined as follows: • Hyper-Trellis decoding for PDWZ video coding is proposed in BIB003 to optimize the approach for the reconstruction of WZ frames. A new decoding algorithm is presented which encapsulates and combines various states of the original trellis code. The results show that the proposed approach not only reduces the complexity of the decoder, but also increases the reconstruction quality by 9-10 dB. • In contrast to the original PDWZ codec design, where decoder controls the encoding rate via feedback channel, a low complexity rate-control algorithm that executes at the encoder is proposed in BIB004 BIB001 ). The proposed design shifts the rate-control functionality from decoder to encoder, and eliminates the feedback channel, which not only reduces the decoding complexity, but also the delays. • A distortion control algorithm is presented in BIB002 ) to overcome the coding distortions in PDWZ codec. The algorithm helps in choosing the optimal steps size for quantization levels associated with certain target quality. However, the experimental results showed that the accuracy in prediction of distortion function is primarily dependent on the encoder's computational power. • In  , an algorithm to refine side information generation module is proposed which utilizes an intra-frame encoding/inter-frame decoding architecture. In addition, the complexity of the decoder can be further reduced if the key frames (used to generate side information) are extrapolated from previously decoded frames. The extrapolation module exploits the motion field smoothening filter for efficient and accurate reconstruction of side information.