The problem of error control and concealment in video communication is becoming increasingly important because of the growing interest in video delivery over unreliable channels such as wireless networks and the Internet. This paper reviews the techniques that have been developed for error control and concealment in the past ten to fifteen years. These techniques are described in three categories according to the roles that the encoder and decoder play in the underlying approaches. Forward error concealment includes methods that add redundancy at the source end to enhance error resilience of the coded bit streams. Error concealment by postprocessing refers to operations at the decoder to recover the damaged areas based on characteristics of image and video signals. Finally, interactive error concealment covers techniques that are dependent on a dialog between the source and destination. Both current research activities and practice in international standards are covered.

This paper examines the effectiveness of combining multiple description coding (MDC) and multiple path transport (MPT) for video and image transmission in a multihop mobile radio network. The video and image information is encoded nonhierarchically into multiple descriptions with the following objectives. The received picture quality should be acceptable, even if only one description is received and every additional received description contributes to enhanced picture quality. Typical applications will need a higher bandwidth/higher reliability connection than that provided by a single link in current mobile networks. For supporting these applications, a mobile node may need to set up and use multiple paths to the desired destination, either simply because of the lack of raw bandwidth on a single channel or because of its poor error characteristics, which reduce its effective throughput. In the context of this work, the principal reasons for considering such an architecture are providing high bandwidth and more robust end-to-end connections. We describe a protocol architecture that addresses this need and, with the help of simulations, we demonstrate the feasibility of this system and compare the performance of the MDC-MPT scheme to a system using layered coding and asymmetrical paths for the base and enhancement layers.

Enabling video transmission over ad-hoc networks is more challenging than over conventional mobile networks because a connection path in an ad-hoc network is highly error-prone and the path can go down frequently. On the other hand, it is possible to establish multiple paths between a source and a destination, which provides an extra degree of freedom in coding algorithm design. This paper presents a feedback-based reference picture selection scheme for video transmission over ad-hoc networks. Encoded video streams are transmitted over multiple paths and the reference frames for motion compensated prediction are selected according to the feedback information about the paths' condition. Simulations under the two paths scenario have shown significant improvement over two standard techniques, layered coding and video redundancy coding, which do not use feedback. A novel statistical model for the ad-hoc multi-path environment is also proposed and used in our simulation of transmission loss.

There is an increasing demand for supporting real-time audiovisual services over next-generation wired and wireless networks. Various link/network characteristics make the deployment of such demanding services more challenging than traditional data applications like e-mail and the Web. These audiovisual applications are bandwidth adaptive but have stringent delay, jitter, and packet loss requirements. Consequently, one of the major requirements for the successful and wide deployment of such services is the efficient transmission of sensitive content (audio, video, image) over a broad range of bandwidth-constrained access networks. These media will be typically compressed according to the emerging ISO/IEC MPEG-4 standard to achieve high bandwidth efficiency and content-based interactivity. MPEG-4 provides an integrated object-oriented representation and coding of natural and synthetic audiovisual content for its

In this paper we review error resilience techniques for real-time video transport over unreliable networks. Topics covered include an introduction to today's protocol and network environments and their characteristics, encoder error resilience tools, decoder error concealment techniques, as well as techniques that require cooperation between encoder, decoder and the network. We provide a review of general principles of these techniques as well as specific implementations adopted by the H.263 and MPEG-4 video coding standards. The majority of the paper is devoted to the techniques developed for block-based hybrid coders using motion-compensated prediction and transform coding. A separate section covers error resilience techniques for shape coding in MPEG-4. I. Introduction A. Error Resilience in Video Communications: Importance and Approach A video communications system typically involves five steps, as shown in Figure 1. The video is first compressed by a video encoder to reduce th...

The ITU-T H.263+ low bit-rate video coding standard is Version 2 of the draft international standard ITU-T H.263. Currently, we are a contributing party in the H.263+ standardization effort. In this paper, we discuss this emerging video coding standard and present compression performance results based on our public domain implementation of H.263+. Keywords : Video compression, H.263 and H.263+ video coding standards, video telephony, video conferencing. 1 Introduction The growing interest in digital video applications led academia and industry to work towards developing video compression techniques. Consequently several successful standards have emerged, e.g. ITU-T H.261, H.263, ISO/IEC MPEG-1 and MPEG-2. These standards address a wide range of video applications with different bit rate, picture quality, complexity, error resilience and delay requirements. While the demand for digital video communication applications such as video conferencing and video telephony has increased cons...

Multiple Description Coding is a forward error correction scheme where two or more descriptions of the source are sent to the receiver over different channels. If only one channel is received the signal can be reconstructed with distortion D 1 or D 2 . On the other hand, if both channels are received the combined information is used to achieve a lower distortion D 0 . Our approach is based on the Multiple State Video Coding with the novelty that we achieve a flexible unbalance rate of the two streams by varying the quantization step size while keeping the original frame rate constant. The total bitrate R T is fixed which is to be allocated between the two streams. If the assigned bitrates are not balanced there will be PSNR (peak signal to noise ratio) variations between neighbouring frames after reconstruction. Our goal is to find the optimal rate allocation while maximizing the average reconstructed frame PSNR and minimizing the PSNR variations given the total bitrate R T and the packet loss probabilities p 1 and p 2 over the two paths. The reconstruction algorithm is also taken into account in the optimization process. The paper will report results presenting optimal system designs for balanced (equal packet loss probabilities) but also for unbalanced path conditions (different packet loss probabilities).

This paper presents a multiple description (MD) video-coding scheme, which uses interlaced high signal to noise ratio (H-SNR) and low signal to noise ratio (L-SNR) coded frames to produce two bitstreams. At the decoder, when both bit-streams are received a high quality video will be reconstructed. If either one is received, a poorer but acceptable quality video can be reconstructed. In this approach, we also considered the mismatch between the encoding and decoding loops due to motion compensation if only one bit-stream is received. We first give the results of the rate distortion performance of our scheme assuming that only one description is received. We then present simulation results under packet loss circumstances, which are simulated by real-world IP networks and adhoc networks. It is shown that the proposed scheme has a superior performance when compared with the single description MPEG-4 video coder and MD coding using video redundancy coding. 1.

Abstract — Multiple Description Coding (MDC) can be used as an Error Resilience (ER) technique for video coding. In case of transmission errors, Error Concealment can be combined with MDC to reconstruct the lost frame, such that the propagated error to the following frames is reduced. In this paper, we propose a new temporal error concealment method named Threeloop Temporal Interpolation (TLTI). TLTI can be well combined with temporal sub-sampling ER methods, such as MDC and Alternative Motion-Compensated Prediction. In the simulation, we compare the performance of TLTI with Unidirectional Motion Compensated Temporal Interpolation (UMCTI). Both visual and quantitive results show that TLTI can achieve a better video quality than UMCTI.

The increasing demand on multimedia communication over wired and wireless net-works imposes a continuous pressure on developing more robust coding schemes. Recently, joint source-channel coding with multiple description codes has become an attractive solution to ensure robust communication over noisy channels. In this thesis, we conduct analysis and design of multiple description codes for wired and wireless communication channels. First, a multiple description quantizer (MDQ) de-sign method based on channel optimized quantization is developed. The proposed multiple channel optimized quantizer design scheme does not require index assignment and offers the benefit of resilience to both symbol and erasure errors. Low complex-ity MDQ is further explored and used to build a multiple description audio coder. Next, the advantages of employing multiple description coding over multiple-input multiple-output wireless channels are investigated. Information theoretical analysis is conducted and practical MDQ codes are designed. Finally, a new E-model based performance measure accounting for both rate-distortion performance and delay im-pairment is proposed to compare multiple description coding and layered coding for communication over packet networks. i Acknowledgments First of all, I would like to express my sincere thanks to my supervisor, Professor Wai-Yip Geoffrey Chan, for his excellent academic guidance and endless encouragement to my research. This thesis would not be possible without his dedication, support and advices over the years. I am very grateful to Professor Fady Alajaji, who gave me valuable suggestions and encouragement throughout the studies of my research. My gratitude also goes to Professor Il-Min Kim for his valuable suggestions on my studies on MIMO commu-nication systems. I would like to thank my thesis examiners, Professor Fady Alajaji, Professor Tamás Linder, Professor Il-Min Kim and Professor Fabrice Labeau, for offer-ing their time to review my work. Thank all members of the Multimedia Coding and