Joint source/channel coding using arithmetic codes

Reserving space fur a symbol that is not in the source alphabet has been shown to provide excellent error detection. In this paper, we show how to exploit this capability using two sequential decoder structures to provide powerful error correction capability. This joint source/channel coder design provides significant packet loss recovery with minimal rate overhead, and compares favorably with conventional schemes     

Joint source and channel coding using turbo codes over rings

Turbo codes are a practical solution for achieving large coding gains. We present a new turbo coding scheme where the component codes are convolutional codes (CCs) over the ring of integers modulo M, with M being the alphabet size of the source encoder. The a priori knowledge of the source statistics is used during the iterative decoding procedure for improved decoder performance. As an example of application, we examine differential pulse code modulation (DPCM) encoded image transmission     

Joint source/channel coding for multiple images

A joint source/channel coding algorithm is proposed for the transmission of multiple image sources over memoryless channels. The proposed algorithm uses a quality scalable image coder to optimally allocate a limited bit budget among all the sources to achieve the optimal overall distortion reduction for the multiple reconstructed images. In addition to the conventional un gain, it provides channel multiplexing gain, which can be much more significant. Furthermore, an extended scheme is proposed to provide flexibility between the optimization performance and complexity.     

Joint source-channel codes based on irregular turbo codes and variable length codes

Variable length codes (VLCs), used in data compression, are very sensitive to error propagation in the presence of noisy channels. To address this problem, several joint sourcechannel turbo techniques have been proposed in the literature. In this paper, we focus on pairs of source/VLC of low redundancy, i.e., when there is a good match between the source statistics and the length distribution of the VLC. It is a case not considered extensively in the literature so far and the classical concatenation of a VLC and a convolutional code is not satisfying. Through EXIT chart and interleaving gain analysis, we show that the introduction of a repetition code between the VLC and the convolutional code considerably improves global performance. In particular, excellent symbol error rates are obtained with reversible VLCs which are used in recent source codecs.     

一种可变长码在视频编码中的应用

本文所讨论的一种可逆的可变长码,其码长分布与Golomb-Rice和exp-Golomb编码相同。其编码数据格式能够很好地应用于图像和视频的统计编码中,在保持编码效率的同时,很大程度地提高编码在信道传输中的纠错能力。     

Joint source/channel coding of statistically multiplexed real-timeservices on packet networks

The interaction of congestion control with the partitioning of source information into components of varying importance for variable-bit-rate packet voice and packet video is investigated. High-priority transport for the more important signal components results in substantially increased objective service quality. Using a Markov chain voice source model with simple PCM speech encoding and a priority queue, simulation results show a signal-to-noise ratio improvement of 45 dB with two priorities over an unprioritized system. Performance is sensitive to the fraction of traffic placed in each priority, and the optimal partition depends on network loss conditions. When this partition is optimized dynamically, quality degrades gracefully over a wide range of load values. Results with DCT encoded speech and video samples show similar behavior. Variations are investigated such as further partition of low-priority information into multiple priorities. A simulation with delay added to represent other network nodes shows general insensitivity to delay of network feedback information. A comparison is made between dropping packets on buffer overflow and timeout based on service requirements     

Error recovery for variable length codes

When an error occurs in the encoded bit stream produced by a variable length code, the decoder may lose synchronization. A state model for synchronization recovery is developed, and a method for determining the expected span of source symbols lost is presented. The performance of various codes with respect to error recovery is discussed. Two examples are given where equivalent optimal codes have a marked difference in their error recovery characteristics. Some open problems are indicated.     

Reversible variable length codes

Proposes some reversible variable length codes (RVLCs) which can be decoded instantaneously both in the forward and backward directions and have high transmission efficiency. These codes can be used, for example, in the backward reconstruction of video signals from the data last received when some signal is lost midway in the transmission. Schemes for a symmetrical RVLC requiring only a single code table and for an asymmetrical RVLC having short average code length are introduced. They compare favorably with other reversible codes such as B2 codes in several aspects     

Systematic lossy source/channel coding

The fundamental limits of “systematic” communication are analyzed. In systematic transmission, the decoder has access to a noisy version of the uncoded raw data (analog or digital). The coded version of the data is used to reduce the average reproduced distortion D below that provided by the uncoded systematic link and/or increase the rate of information transmission. Unlike the case of arbitrarily reliable error correction (D→0) for symmetric sources/channels, where systematic codes are known to do as well as nonsystematic codes, we demonstrate that the systematic structure may degrade the performance for nonvanishing D. We characterize the achievable average distortion and we find necessary and sufficient conditions under which systematic communication does not incur loss of optimality. The Wyner-Ziv (1976) rate distortion theorem plays a fundamental role in our setting. The general result is applied to several scenarios. For a Gaussian bandlimited source and a Gaussian channel, the invariance of the bandwidth-signal-to-noise ratio (SNR, in decibels) product is established, and the optimality of systematic transmission is demonstrated. Bernoulli sources transmitted over binary-symmetric channels and over certain Gaussian channels are also analyzed. It is shown that if nonnegligible bit-error rate is tolerated, systematic encoding is strictly suboptimal     

Joint source/channel coding for image transmission with JPEG2000 over memoryless channels.

The high compression efficiency and various features provided by JPEG2000 make it attractive for image transmission purposes. A novel joint source/channel coding scheme tailored for JPEG2000 is proposed in this paper to minimize the end-to-end image distortion within a given total transmission rate through memoryless channels. It provides unequal error protection by combining the forward error correction capability from channel codes and the error detection/localization functionality from JPEG2000 in an effective way. The proposed scheme generates quality scalable and error-resilient codestreams. It gives competitive performance with other existing schemes for JPEG2000 in the matched channel condition case and provides more graceful quality degradation for mismatched cases. Furthermore, both fixed-length source packets and fixed-length channel packets can be efficiently formed with the same algorithm.     

Multiple-symbol parallel decoding for variable length codes

In this paper, a multiple-symbol parallel variable length decoding (VLD) scheme is introduced. The scheme is capable of decoding all the codewords in an N-bit block of encoded input data stream. The proposed method partially breaks the recursive dependency related to the VLD. First, all possible codewords in the block are detected in parallel and lengths are returned. The procedure results redundant number of codeword lengths from which incorrect values are removed by recursive selection. Next, the index for each symbol corresponding the detected codeword is generated from the length determining the page and the partial codeword defining the offset in symbol table. The symbol lookup can be performed independently from symbol table. Finally, the sum of the valid codeword lengths is provided to an external shifter aligning the encoded input stream for a new decoding cycle. In order to prove feasibility and determine the limiting factors of our proposal, the variable length decoder has been implemented on an field-programmable gate-array (FPGA) technology. When applied to MPEG-2 standard benchmark scenes, on average 4.8 codewords are decoded per cycle resulting in the throughput of 106 million symbols per second.     

Universal variable-to-fixed length source codes

A universal variable-to-fixed length algorithm for binary memoryless sources which converges to the entropy of the source at the optimal rate is known. We study the problem of universal variable-to-fixed length coding for the class of Markov sources with finite alphabets. We give an upper bound on the performance of the code for large dictionary sizes and show that the code is optimal in the sense that no codes exist that have better asymptotic performance. The optimal redundancy is shown to be H log log M/log M where H is the entropy rate of the source and M is the code size. This result is analogous to Rissanen's (1984) result for fixed-to-variable length codes. We investigate the performance of a variable-to-fixed coding method which does not need to store the dictionaries, either at the coder or the decoder. We also consider the performance of both these source codes on individual sequences. For individual sequences we bound the performance in terms of the best code length achievable by a class of coders. All the codes that we consider are prefix-free and complete     

Extension of source coding theorems for block codes to sliding-block codes

For arbitrary alphabets and single-letter fidelity criteria, two theorems are given which allow any fixed-rate or variable-rate source coding theorem for block codes to be extended to sliding-block codes. Applications are given to universal coding and to the coding of a stationary nonergodic source.     

Gaussian source coding with spherical codes

A fixed-rate shape-gain quantizer for the memoryless Gaussian source is proposed. The shape quantizer is constructed from wrapped spherical codes that map a sphere packing in ℝ^k-1 onto a sphere in ℝ^k, and the gain codebook is a globally optimal scalar quantizer. A wrapped Leech lattice shape quantizer is used to demonstrate a signal-to-quantization-noise ratio within 1 dB of the distortion-rate function for rates above 1 bit per sample, and an improvement over existing techniques of similar complexity. An asymptotic analysis of the tradeoff between gain quantization and shape quantization is also given     

Universal variable length coding for an integrated approach to image coding

We propose a new entropy coding scheme, denoted in this paper as the UVLC (universal variable length coding). It is universal in the sense that its efficiency is close to one for a large class of images. The UVLC, when it is applied to block orthogonal transforms, processes groups of blocks at the bit level, using universal codes designed for binary memoryless sources. It can be used for every video coding application, from high definition TV (HDTV) to high quality videotelephony (above 2 Mbit/s) for transform or subband coding. Last but not least, its implementation is very regular and can be realized in a single chip for the encoding oftv at theccir 601 format.     

Bit allocation for joint source/channel coding of scalable video

We propose an efficient bit allocation algorithm for a joint source/channel video codec over noisy channels. The approach is to distribute the available source and channel coding bits among the subbands in such a way that the expected distortion is minimized. The constructed distortion curves bound the performance degradation should the channel be estimated incorrectly. The algorithm can be used in other similar distortion minimization problems with two constraints, such as power or complexity.     

Soft-input soft-output decoding of variable length codes

We present a method for utilizing soft information in decoding of variable length codes (VLCs). When compared with traditional VLC decoding, which is performed using "hard" input bits and a state machine, the soft-input VLC decoding offers improved performance in terms of packet and symbol error rates. Soft-input VLC decoding is free from the risk, encountered in hard decision VLC decoders in noisy environments, of terminating the decoding in an unsynchronized state, and it offers the possibility to exploit a priori knowledge, if available, of the number of symbols contained in the packet     

Construction of efficient error-limiting variable length codes

A novel method for generating an optimal binary prefix condition code is described. The proposed code generation method generates optimal variable length codes that have short average error spans compared to the existing self-synchronising codes. A technique for calculating the expected error spans of variable length codes are also presented