Video communication has evolved from a simple tool for visual communication to a key enabler for various video applications. A number of exciting video applications have been successfully deployed in recent years, with the goal of providing users with more flexible, personalized, and content-rich viewing experience. Accompanied with the ubiquitous video applications, we have also experienced a paradigm shift from passive, wired, and centralized video content access to interactive, wireless, and distributed content access. Undoubtedly, wireless video communications have paved the way for advanced applications. However, given the distributed, resource-constraint, and heterogeneous nature of wireless networks, the support of quality video communications over wireless networks is still challenging. Video coding is one of the indispensable components in various wireless video applications, whereas the wireless network condition always imposes more stringent requirements on coding technologies. To cope with the limited transmission bandwidth and to offer adaptivity to the harsh wireless channels, rate control, packet scheduling, as well as error control mechanisms are usually incorporated in the design of codecs to enable efficient and reliable video communications. At the same time, due to energy constraint in wireless systems, video coding algorithms should operate with the lowest possible power consumption. Therefore, video coding over wireless networks is inherently a complex optimization problem with a set of constraints. In addition, the high heterogeneity and user mobility associated with wireless networks are also key issues to be tackled for a seamless delivery of quality-of-experience supported video streams.
To sum up, wireless video communications encompass a broad range of challenges and opportunities that provide the catalyst for technical innovations. To disseminate the most recent advances in this challenging yet exciting field, we bring forth this book as a compilation of high-quality chapters. This book is intended to be an up-to-date reference book on wireless video communications, providing the fundamentals, recent technical achievements, challenges, and some emerging trends. We hope that the book will be accessible to various audiences, ranging from those in academia and industry to senior undergraduates and postgraduates. To achieve this goal, we have solicited chapters from a number of researchers who are experts in diverse aspects of wireless video communications. We received a good response and, finally, after peer review and revision, 15 chapters were selected. These chapters cover a wide spectrum of topics, including the underlying theoretical fundamentals associated with wireless video communications, transmission schemes tailored to mobile and wireless networks, quality metrics, architectures of practical systems, as well as some novel directions. In what follows, we present a summary of each chapter.
In Chapter 1, “Network-Aware Error-Resilient Video Coding,” a network-aware Intra coding refresh method is presented. This method increases the error robustness of H.264/AVC bitstreams, considering the network packet loss rate and the encoding bit rate, by efficiently taking into account the rate-distortion impact of Intra coding decisions while guaranteeing that errors do not propagate.
Chapter 2, “Distributed Video Coding: Principles and Challenges,” is a tutorial on distributed video coding (DVC). In contrast to conventional video compression schemes featuring an encoder that is significantly more complex than the decoder, in DVC the complexity distribution is the reverse. This chapter provides an overview of the basic principles, state of the art, current problems, and trends in DVC.
Chapter 3, “Computer Vision Aided Video Coding,” studies video coding from the perspective of computer vision. Motivated by the fact that the human visual system (HVS) is the ultimate receiver of the majority of compressed videos and that there is a scope to remove unimportant information through HVS, the chapter proposes a computer vision–aided video coding technique by exploiting the spatial and temporal redundancies with visually unimportant information.
In Chapter 4, “Macroblock Classification Method for Computation Control Video Coding and Other Video Applications Involving Motions,” a new macroblock (MB) classification method is proposed, which classifies MBs into different classes according to their temporal and spatial motion and texture information. Furthermore, the implementations of the proposed MB classification method into complexity-scalable video coding as well as other video applications are also discussed in detail in the chapter.
Chapter 5, “Transmission Rate Adaptation in Multimedia WLAN: A Dynamic Games Approach,” considers the scheduling, rate adaptation, and buffer management in a multiuser wireless local area network (WLAN), where each user transmits scalable video payload. Based on opportunistic scheduling, users access the available medium (channel) in a decentralized manner. The rate adaptation problem of the WLAN multimedia networks is then formulated as a general-sum switching control dynamic Markovian game.
In Chapter 6, “Energy and Bandwidth Optimization in Mobile Video Streaming Systems,” the authors consider the problem of multicasting multiple variable bit rate video streams from a wireless base station to many mobile receivers over a common wireless channel. This chapter presents a sequence of increasingly sophisticated streaming protocols for optimizing energy usage and utilization of the wireless bandwidth.
Chapter 7, “Resource Allocation for Scalable Videos over Cognitive Radio Networks,” investigates the challenging problem of video communication over cognitive radio (CR) networks. It first addresses the problem of scalable video over infrastructure-based CR networks and then considers the problem of scalable video over multihop CR networks.
Chapter 8, “Cooperative Video Provisioning in Mobile Wireless Environments,” focuses on the challenging scenario of cooperative video provisioning in mobile wireless environments. On one hand, it provides a general overview about the state-of-the-art literature on collaborative mobile networking. On the other hand, it provides technical details and reports about the RAMP middleware case study, practically showing that node cooperation can properly achieve streaming adaptation.
Chapter 9, “Multilayer Iterative FEC Decoding for Video Transmission over Wireless Networks,” develops a novel multilayer iterative decoding scheme using deterministic bits to lower the decoding threshold of low-density parity-check (LDPC) codes. These deterministic bits serve as known information in the LDPC decoding process to reduce redundancy during data transmission. Unlike the existing work, the proposed scheme addresses controllable deterministic bits, such as MPEG null packets, rather than widely investigated protocol headers.
Chapter 10, “Network-Adaptive Rate and Error Controls for WiFi Video Streaming,” investigates the fundamental issues for network-adaptive mobile video streaming over WiFi networks. Specifically, it highlights the practical aspects of network-adaptive rate and error control schemes to overcome the dynamic variations of underlying WiFi networks.
Chapter 11, “State of the Art and Challenges for 3D Video Delivery over Mobile Broadband Networks,” examines the technologies underlying the delivery of 3D video content to wireless subscribers over mobile broadband networks. The incorporated study covers key issues, such as the effective delivery of 3D video content in a system that has limited resources in comparison to wired networks, network design issues, as well as scalability and backward compatibility concepts.
In Chapter 12, “A New Hierarchical 16-QAM-Based UEP Scheme for 3-D Video with Depth Image–Based Rendering,” an unequal error protection (UEP) scheme based on hierarchical quadrature amplitude modulation (HQAM) for 3-D video transmission is proposed. The proposed scheme exploits the unique characteristics of the color plus depth map stereoscopic video where the color sequence has a significant impact on the reconstructed video quality.
Chapter 13, “2D-to-3D Video Conversion: Techniques and Applications in 3D Video Communications,” provides an overview of the main techniques for 2D-to-3D conversion, which includes different depth cues and state-of-the-art schemes. In the 3D video communications context, 2D-to-3D conversion has been used to improve the coding efficiency and the error resiliency and concealment for the 2D video plus depth format.
Chapter 14, “Combined CODEC and Network Parameters for an Enhanced Quality of Experience in Video Streaming,” presents the research involved in bridging the gap between the worlds of video compression/encoding and network traffic engineering by (i) using enriched video trace formats in scheduling and traffic control, (ii) using prioritized and error-resilience features in H.264, and (iii) optimizing the combination of the network performance indices with codec-specific distortion parameters for an increased quality of the received video.
In Chapter 15, “Video QoS Analysis over Wi-Fi Networks,” the authors present a detailed end-to-end QoS analysis for video applications over wireless networks, both infrastructure and ad hoc networks. Several networking scenarios are carefully configured with variations in network sizes, applications, codecs, and routing protocols to extensively analyze network performance.
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