Abhik Majumdar

Distributed video coding in wireless sensor networks

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.

Distributed multimedia transmission from multiple servers

We address the problem of streaming video efficiently from multiple servers in a distributed manner. Invoking a scalable video encoding format, we describe a network-friendly, rate-distortion efficient distributed streaming algorithm based on a robust distributed encoding paradigm. The algorithm is efficiently matched dynamically to both the video content and the network channel conditions. Due to the diversity effect of multiple servers, our distributed algorithm is immune to single points of failure, provides natural load-balancing of the multiple servers and a graceful degradation in quality with an increase in multi-server load or a decrease in network throughput.

PRISM: an error-resilient video coding paradigm for wireless networks

We describe PRISM (power-efficient, robust, high-compression, syndrome-based multimedia coding), an error-resilient video-coding paradigm built on the principles of distributed source coding from multi-user information theory. PRISM represents a radical departure from the current state-of-the-art video coding architectures, like MPEG, that are based on a motion-compensated prediction framework. These are hampered by: (i) a rigid computational complexity partition between encoder (heavy) and decoder (light); and (U) high fragility to drift between encoder and decoder in the face of prediction mismatch due to channel loss. In contrast, PRISMs architectural goals are: (i) to have a channel-adaptive distribution of computational complexity between encoder and decoder; and (ii) to have built-in robustness to drift between encoder and decoder due to wireless channel loss. These features make PRISM ideally suited for low-latency multimedia transmission over wireless networks, particularly for uplink-rich applications.

Complexity/performance trade-offs for robust distributed video coding

In this work, we analytically study the complexity-performance trade-offs associated with video codecs based on the principle of source coding with side information at the decoder. We address three important aspects. First, we quantify the theoretical performance gains attained with side-information based codecs over prediction-based coders like MPEG under a lossy transmission scenario when there is drift. Secondly, we show that it is possible to closely approach MPEGs compression performance using side-information video coding principles with accurate DFD (displaced frame difference) modeling even without sophisticated channel codes. Thirdly, we analytically show that the value of accurately estimating DFD statistics diminishes as the channel gets noisier.

Robust wireless video multicast based on a distributed source coding approach

In this paper, we present a scheme for robust scalable video multicast based on distributed source coding principles. Unlike prediction-based coders, like MPEG-x and H.26x, the proposed framework is designed specifically for lossy wireless channels and directly addresses the problem of drift due to packet losses. The proposed solution is based on recently proposed PRISM (power efficient robust syndrome-based multimedia coding) video coding framework [R. Puri. K. Ramchandran, PRISM: a new robust video coding architecture based on distributed compression principles, in: Allerton Conference on Communication, Control and Computing, Urbana-Champaign, IL, October 2002] and addresses SNR, spatial and temporal scalability. Experimental results show that substantial gains are possible for video multicast over lossy channels as compared to standard codecs, without a dramatic increase in encoder design complexity as the number of streams increases.

Video multicast over lossy channels based on distributed source coding

We present an algorithm for robust scalable video multicast based on distributed source coding techniques. Unlike prediction based coders, like MPEG, the proposed framework directly addresses the problem of drift due to packet losses. Building on the recently proposed PRISM video coding framework (R. Puri and K. Ramehandran, 2002), we show that substantial gains are possible for video multicast over lossy channels as compared to standard codecs, without a dramatic increase in encoder complexity as the number of streams increases.

Robust Video Transmission With Distributed Source Coded Auxiliary Channel

We propose a novel solution to the problem of robust, low-latency video transmission over lossy channels. Predictive video codecs, such as MPEG and H.26x, are very susceptible to prediction mismatch between encoder and decoder or ldquodriftrdquo when there are packet losses. These mismatches lead to a significant degradation in the decoded quality. To address this problem, we propose an auxiliary codec system that sends additional information alongside an MPEG or H.26x compressed video stream to correct for errors in decoded frames and mitigate drift. The proposed system is based on the principles of distributed source coding and uses the (possibly erroneous) MPEG/H.26x decoder reconstruction as side information at the auxiliary decoder. The distributed source coding framework depends upon knowing the statistical dependency (or correlation) between the source and the side information. We propose a recursive algorithm to analytically track the correlation between the original source frame and the erroneous MPEG/H.26x decoded frame. Finally, we propose a rate-distortion optimization scheme to allocate the rate used by the auxiliary encoder among the encoding blocks within a video frame. We implement the proposed system and present extensive simulation results that demonstrate significant gains in performance both visually and objectively (on the order of 2 dB in PSNR over forward error correction based solutions and 1.5 dB in PSNR over intrarefresh based solutions for typical scenarios) under tight latency constraints.

Analysis of Motion-complexity and Robustness for Video Transmission

In this work, we study the problem of end-to-end video transmission over a noisy communication link, and analytically characterize the complexity (of motion search) and robustness metrics for this problem. The presence of channel noise results in an uncertainty at the encoder as to the information available at the decoder, naturally invoking the framework of source coding with side information (distributed source coding) used in our analysis. We address three important aspects. First, we quantify the theoretical performance gains attained with side-information based codecs over prediction-based coders like MPEG under a lossy transmission scenario when there is drift. Secondly, we show that by accurate DFD (displaced frame difference) modeling we can closely approach MPEGs compression performance using side-information video coding principles without resorting to long block-length channel codes. Thirdly, we quantify analytically that the value of accurately estimating DFD statistics diminishes, as the channel gets noisier

Distributed Video Coding and Its Applications

Publisher Summary This chapter introduces PRISM, a practical video-coding framework built on distributed source coding principles. Based on a generalization of the classical Wyner-Ziv setup, PRISM is characterized by an inherent system uncertainty about the state of the relevant side information that is known at the decoder. The two main architectural goals of PRISM that makes it radically different from existing video codecs are flexible distribution of complexity between encoder and decoder and naturally in-built robustness to drift between encoder and decoder caused by a lack of synchronization as a result of channel loss. This renders PRISM as an attractive candidate for wireless video applications. The fundamental architectural traits of PRISM are also well suited for the multi-camera regime. Indeed, as the scale of video sensor networks increases in the future, the architectural benefits of PRISM will be magnified. The full potential of large-scale ubiquitous video sensor networks of the future will require an interdisciplinary approach involving signal and video processing, computer vision, multi-terminal information theory, and wireless networking.

Channel Protection Fundamentals

In many ways, the Internet (or a wireless network for that matter) can be regarded simply as a communication channel in a classical communication system. This chapter discusses the fundamentals of channel protection that lie beneath the error control techniques used to communicate multimedia over the Internet and wireless networks.