Raouf Hamzaoui

Optimized error protection of scalable image bit streams [advances in joint source-channel coding for images]

This article focuses on FEC for scalable image coders. For various channel models, we survey recent progress made in system design and discuss efficient source-channel bit allocation techniques, with emphasis on unequal error protection. This article considered JSCC (joint source-channel coding) at the application layer only. Recent research has studied cross-layer optimization where JSCC is applied to both the application layer and the physical layer. The basic task here is to minimize the average distortion by allocating available power, subcarriers, and bandwidth among users at the physical layer and source-channel symbols at the application layer subject to a total resource constraint. Most of the JSCC systems covered in this article can be readily extended to transmit scalable compressed bit streams of video sequences and 3-D meshes. Due to the stringent delay constraints in video communications and the fact that MPEG is currently exploring a scalable video coding standard, fast JSCC algorithms are expected to play a bigger role and bring more performance gains. This article is also expected to stimulate further research efforts into JSCC and more importantly, prompt the industry to adopt some of these JSCC algorithms in their system designs, thus closing the cycle from algorithm development to implementation.

Unequal Error Protection Using Fountain Codes With Applications to Video Communication

Application-layer forward error correction (FEC) is used in many multimedia communication systems to address the problem of packet loss in lossy packet networks. One powerful form of application-layer FEC is unequal error protection which protects the information symbols according to their importance. We propose a method for unequal error protection with a Fountain code. When the information symbols were partitioned into two protection classes (most important and least important), our method required a smaller transmission bit budget to achieve low bit error rates compared to the two state-of-the-art techniques. We also compared our method to the two state-of-the-art techniques for video unicast and multicast over a lossy network. Simulations for the scalable video coding (SVC) extension of the H.264/AVC standard showed that our method required a smaller transmission bit budget to achieve high-quality video.

Fast algorithm for rate-based optimal error protection of embedded codes

Embedded image codes are very sensitive to channel noise because a single bit error can lead to an irreversible loss of synchronization between the encoder and the decoder. P.G. Sherwood and K. Zeger (see IEEE Signal Processing Lett., vol.4, p.191-8, 1997) introduced a powerful system that protects an embedded wavelet image code with a concatenation of a cyclic redundancy check coder for error detection and a rate-compatible punctured convolutional coder for error correction. For such systems, V. Chande and N. Farvardin (see IEEE J. Select. Areas Commun., vol.18, p.850-60, 2000) proposed an unequal error protection strategy that maximizes the expected number of correctly received source bits subject to a target transmission rate. Noting that an optimal strategy protects successive source blocks with the same channel code, we give an algorithm that accelerates the computation of the optimal strategy of Chande and Farvardin by finding an explicit formula for the number of occurrences of the same channel code. Experimental results with two competitive channel coders and a binary symmetric channel showed that the speed-up factor over the approach of Chande and Farvardin ranged from 2.82 to 44.76 for transmission rates between 0.25 and 2 bits per pixel.

Real-time error protection of embedded codes for packet erasure and fading channels

Reliable real-time transmission of packetized embedded multimedia data over noisy channels requires the design of fast error control algorithms. For packet erasure channels, efficient forward error correction is obtained by using systematic Reed-Solomon (RS) codes across packets. For fading channels, state-of-the-art performance is given by a product channel code where each column code is an RS code and each row code is a concatenation of an outer cyclic redundancy check code and an inner rate-compatible punctured convolutional code. For each of these two systems, we propose a low-memory linear-time iterative improvement algorithm to compute an error protection solution. Experimental results for the two-dimensional and three-dimensional set partitioning in hierarchical trees coders showed that our algorithms provide close to optimal average peak signal-to-noise ratio performance, and that their running time is significantly lower than that of all previously proposed solutions.

Packet loss protection of embedded data with fast local search

Unequal loss protection with systematic Reed-Solomon codes allows reliable transmission of embedded multimedia over packet erasure channels. The design of a fast algorithm with low memory requirements for the computation of an unequal loss protection solution is essential in real-time systems. Because the determination of an optimal solution is time-consuming, fast suboptimal solutions have been used. In this paper, we present a fast iterative improvement algorithm with negligible memory requirements. Experimental results for the JPEG2000, 2D, and 3D set partitioning in hierarchical trees (SPIHT) coders showed that our algorithm provided close to optimal peak signal-to-noise ratio (PSNR) performance, while its time complexity was significantly lower than that of all previously proposed algorithms.

Real-time unequal error protection algorithms for progressive image transmission

We consider unequal error protection strategies for the efficient progressive transmission of embedded image codes over noisy channels. In progressive transmission, the reconstruction quality is important not only at the target transmission rate but also at the intermediate rates. An adequate error protection strategy may, thus, consist of optimizing the average performance over the set of intermediate rates. The performance can be the expected number of correctly decoded source bits or the expected distortion. For the rate-based performance, we prove some interesting properties of an optimal solution and give an optimal linear-time algorithm to compute it. For the distortion-based performance, we propose an efficient linear-time local search algorithm. For a binary symmetric channel, two state-of-the-art source coders (SPIHT and JPEG2000), we compare the progressive ability of our proposed solutions to that of the strategies that optimize the end-to-end performance of the system. Experimental results showed that the proposed solutions had a slightly worse performance at the target transmission rate and a better performance at most of the intermediate rates, especially at the lowest ones.

Efficient channel code rate selection algorithms for forward error correction of packetized multimedia bitstreams in varying channels

We study joint source-channel coding systems for the transmission of images over varying channels without feedback. We consider the situation where the channel statistics are unknown to the transmitter and focus on systems that enable good performance over a wide range of channel conditions. We first propose a linear-time channel code rate selection algorithm for a hybrid transmission system that combines packetization of an embedded wavelet bitstream into independently decodable packets and forward error correction with a concatenated cyclic redundancy check/rate-compatible punctured convolutional (RCPC) channel coder. We then consider an extension of this hybrid system with additional Reed-Solomon (RS) coding across the packets and give a linear-time algorithm for the efficient selection of both the RS and RCPC code rates. Experimental results for a wireline/wireless link modeled as the combination of a packet erasure channel and a Rayleigh flat-fading channel showed that our schemes significantly outperformed the best previous forward error correction systems in many situations where the actual channel parameter values deviated from the ones used in the optimization of the source-channel rate allocation.

Adaptive Unicast Video Streaming With Rateless Codes and Feedback

Video streaming over the Internet and packet-based wireless networks is sensitive to packet loss, which can severely damage the quality of the received video. To protect the transmitted video data against packet loss, application-layer forward error correction (FEC) is commonly used. Typically, for a given source block, the channel code rate is fixed in advance according to an estimation of the packet loss rate. However, since network conditions are difficult to predict, determining the right amount of redundancy introduced by the channel encoder is not obvious. To address this problem, we consider a general framework where the sender applies rateless erasure coding to every source block and keeps on transmitting the encoded symbols until it receives an acknowledgment from the receiver indicating that the block was decoded successfully. Within this framework, we design transmission strategies that aim at minimizing the expected bandwidth usage while ensuring successful decoding subject to an upper bound on the packet loss rate. In real simulations over the Internet, our solution outperformed standard FEC and hybrid automatic repeat request approaches. For the quarter common intermediate format Foreman sequence compressed with the H.264 video coder, the gain in average peak signal to noise ratio over the best previous scheme exceeded 3.5 dB at 90 kb/s.

Fast algorithm for distortion-based error protection of embedded image codes

We consider a joint source-channel coding system that protects an embedded bitstream using a finite family of channel codes with error detection and error correction capability. The performance of this system may be measured by the expected distortion or by the expected number of correctly decoded source bits. Whereas a rate-based optimal solution can be found in linear time, the computation of a distortion-based optimal solution is prohibitive. Under the assumption of the convexity of the operational distortion-rate function of the source coder, we give a lower bound on the expected distortion of a distortion-based optimal solution that depends only on a rate-based optimal solution. Then, we propose a local search (LS) algorithm that starts from a rate-based optimal solution and converges in linear time to a local minimum of the expected distortion. Experimental results for a binary symmetric channel show that our LS algorithm is near optimal, whereas its complexity is much lower than that of the previous best solution.

A review of the fractal image compression literature

D ince the conception of fractal image compression by Michael F. Barnsley around 1987, the research literature on this topic has exper ienced a rapid growth. Following is a brief description of the major advances in the field and the largest, comprehensive bibliography published on this topic to date. While JPEG is becoming the industry standard for image compression technology, there is ongoing research in alternative methods. Currently there are at least two exciting new developments: wavelet based methods and fractal image compression. This article is intended to provide the reader with an overview and a resource of the research on the latter. We attempt to put the work into historical perspective and to provide the most comprehensive and up-to-date list of references in the field, truly a considerable number as shown in the following table.