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.

In just a few years the "Internet Multicast Backbone", or MBone, has risen from a small, research curiosity to a large scale and widely used communications infrastructure. A driving force behind this growth was our development of multipoint audio, video, and shared whiteboard conferencing applications that are now used daily by the large and growing MBone community. Because these real-time media are transmitted at a uniform rate to all the receivers in the network, the source must either run below the bottleneck rate or overload portions of the multicast distribution tree. In this dissertation, we propose a solution to this problem by moving the burden of rate-adaptation from the source to the receivers with a scheme we call Receiver-driven Layered Multicast, or RLM. In RLM, a source distr...

This paper deals with 2 ` --ary transmission using multilevel coding (MLC) and multistage decoding (MSD). The known result that MLC and MSD suffice to approach capacity if the rates at each level are appropriately chosen is reviewed. Using multiuser information theory, it is shown that there is a large space of rate combinations such that MLC and full maximum--likelihood decoding (MLD) can approach capacity. It is noted that multilevel codes designed according to the traditional balanced distance rule tend to fall in the latter category and therefore require the huge complexity of MLD. The capacity rule, the balanced distances rules, and two other rules based on the random coding exponent and cut--off rate are compared and contrasted for practical design. Simulation results using multilevel binary turbo codes show that capacity can in fact be closely approached at high bandwidth efficiencies. Moreover, topics relevant in practical applications such as signal set labeling, dimensional...

The scant bandwidth and high error rates of the wireless channel make joint source-channel coding desirable for optimizing resource usage. To this end, we propose a multiple substream abstraction for source traffic, with delay and loss characteristics negotiated between the application and network on a per-substream basis. This model affords flexibility while maintaining network efficiency by only appropriating more resources (e.g. bandwidth and error protection) to more important user information. We describe an algorithm for supporting different quality of service (QOS) requirements for different traffic in an interferencelimited cellular CDMA environment. The algorithm accepts QOS specifications for different substreams, accommodates them by assigning different power levels to each signal, and can be used to add or drop substream connections dynamically while ensuring that QOS specifications are not violated. Present-day power control schemes are used to combat the near-far effect; ...

Real-time audio and video data streamed over unreliable IP networks, such as the Internet, may encounter losses due to dropped packets or late arrivals. This paper reviews error-concealment schemes developed for streaming realtime audio and video data over the Internet. Based on their interactions with (video or audio) source coders, we classify existing techniques into source coder-independent schemes that treat underlying source coders as black boxes, and source coder-dependent schemes that exploit coder-specific characteristics to perform reconstruction. Last, we identify possible future research directions. 1. Introduction Increases in bandwidth and computational speed lead to growing interests in real-time audio and video transmissions over the Internet. In the Internet, packets carrying real-time data may be dropped or arrive too late to be useful because the Internet is a packet-switched, best-effort delivery service, with no guarantee on the quality of service (QoS). Traditi...

We explore joint source-channel coding (JSCC) for time-varying channels using a multiresolution framework for both source coding and transmission via novel multiresolution modulation constellations. We consider the problem of still image transmission over time-varying channels with the channel state information (CSI) available at 1) receiver only and 2) both transmitter and receiver being informed about the state of the channel, and we quantify the effect of CSI availability on the performance. Our source model is based on the wavelet image decomposition, which generates a collection of subbands modeled by the family of generalized Gaussian distributions. We describe an algorithm that jointly optimizes the design of the multiresolution source codebook, the multiresolution constellation, and the decoding strategy of optimally matching the source resolution and signal constellation resolution “trees” in

The properties of chaotic dynamical systems make them useful for channel coding in a variety of practical communication applications. To illustrate this, a novel analog code based on tent map dynamics and having a fast decoding algorithm is developed for use on unknown, multiple, and time-varying signal-to-noise ratio (SNR) channels. This code is shown to be an attractive alternative to both digital codes and linear modulation in such scenarios. Several properties and interpretations of the codes are developed, along with some methods for their optimization. Index Terms--- Broadcast channels, chaotic systems, errorcorrection codes, fading channels, joint source and channel coding, nonlinear dynamics, twisted modulation. I. INTRODUCTION I N MANY communication applications, the information to be transmitted over the channel of interest is inherently analog (i.e., continuous-valued) in nature. Among many examples are speech, audio, or video information. For unreliable channels, the go...

In this paper, we develop an approach toward joint source-channel coding for motion-compensated DCT-based scalable video coding and transmission. A framework for the optimal selection of the source and channel coding rates over all scalable layers is presented such that the overall distortion is minimized. The algorithm utilizes universal rate distortion characteristics which are obtained experimentally and show the sensitivity of the source encoder and decoder to channel errors. The proposed algorithm allocates the available bit rate between scalable layers and, within each layer, between source and channel coding. We present the results of this rate allocation algorithm for video transmission over a wireless channel using the H.263 Version 2 signal-to-noise ratio (SNR) scalable codec for source coding and rate-compatible punctured convolutional (RCPC) codes for channel coding. We discuss the performance of the algorithm with respect to the channel conditions, coding methodologies, layer rates, and number of layers.

The low bandwidth and high error rates of the wireless channel make joint source-channel coding desirable for optimizing resource usage. We argue that a mechanism for providing variable quality of service (QOS) is essential for joint source-channel coding, and show that its implementation by way of power control is a natural choice for CDMA. Present-day power control techniques focus on controlling interference. In this work, we present a power control algorithm which simultaneously minimizes interference and provides variable QOS contracts for different traffic types in a CDMA system. The algorithm accommodates different QOS requirements by assigning different power levels to each traffic type, and can add or drop connections dynamically while ensuring that QOS specifications are satisfied. Both the uplink and downlink are analyzed, and the scheme is statistically formulated to handle variable-rate traffic. 1 INTRODUCTION Power control can substantially impact the capacity and perce...

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