Hamming Coding of DCT-Compressed Images Over Noisy Channels

Theoretical and simulation results of using Hamming codes with the two-dimensional discrete cosine transform (2D-DCT) at a transmitted data rate of 1 bit/pixel over a binary symmetric channel (BSC) are presented. The design bit error rate (BER) of interest is 10^-2. The (7, 4), (15, 11), and (31, 26) Hamming codes are used to protect the most important bits in each 16 by 16 transformed block, where the most important bits are determined by calculating the mean squared reconstruction error (MSE) contributed by a channel error in each individual bit. A theoretical expression is given which allows the number of protected bits to achieve minimum MSE for each code rate to be computed. By comparing these minima, the best code and bit allocation can be found. Objective and subjective performance results indicate that using the (7, 4) Hamming code to protect the most important 2D-DCT coefficients can substantially improve reconstructed image quality at a BER of 10^-2. Furthermore, the allocation of 33 out of the 256 bits per block to channel coding does not noticeably degrade reconstructed image quality in the absence of channel errors.     

一种新的渐进精细可分级编码算法

文中提出了一种新的渐进精强可分级编码算法.新算法利用基本层运动矢量在增强层进行小窗口搜索来获得更精确的增强层运动矢量,从而提高了原有算法增强层的预测精度.新算法继承了原有算法的所有优点.此仿真结果表明,在同样的码率下,新算法较原有算法的峰值信噪比提高了0.3～0.5dB.     

Uniform Quantizers for Noisy Channels

We consider optimum uniform data quantization for noisy channels. We present a general formulation for natural encoding that results in simple expressions for the mean-square error. Specifically, we show that the optimum location of the center of the quantizer is at the mean of the distribution for all error rates. The optimum levels for quantization and the corresponding mean-square error are presented for Gaussian and uniform data. For the latter the width of the optimum quantizer for noisy channels is shown to be smaller than the entire range of probability distribution.     

可伸缩性视频编码的码率分配算法

本文研究了渐进的精细的可伸缩性(Progressive Fine Granular Scalable,PFGS)视频编码的增强层码流的码率分配问题,它是由PFGS各帧的增强层码流长度不同引起的.我们首先建立了PFGS增强层的多帧联合的率失真(rate-distortion,R-D)函数,并通过MPEG-4标准测试序列检验了它的正确性.然后利用联合率失真函数给出了局部最优的码率分配算法,并进行了简化使得它的复杂性极低,非常适合流化视频(streaming video)服务器使用.实验结果显示本文提出的算法不仅使得各帧图像的解码质量比较平衡,而且将PFGS的编码效率提高了将近0.5dB.     

Trellis Coding for Partial-Response Channels

We consider trellis-coding techniques for improving the reliability of digital transmission over noisy partial-response channels. Such channels are commonly encountered in digital communication systems, and also play a role in devices for data recording. Concentrating on the channels with characteristics(1 mp D), we study methods to obtain codes which increase free Euclidean distance between permitted sequences of channel outputs and avoid the occurrence of unlimited runs of identical outputs at the expense of some loss in data rate. One technique employs the concept of set partitioning. The other is based on using convolutional codes designed for maximum free Hamming distance in conjunction with a precoder. Both methods lead to essentially equivalent codes.     

Chaos Controlled ZCDPLL for Carrier Recovery in Noisy Channels

The objective of this work is to analyze the performance of the chaos controlled first order Zero Crossing Digital Phase Locked Loop (ZCDPLL) in the presence of Additive White Gaussian Noise (AWGN). The nonlinear behaviour of ZCDPLL shows a period doubling to its route to chaos. The amount of ZCDPLL divergency is measured and fed-back in a form of linear stabilization. The introduction of the chaos control widens the lock range of a ZCDPLL and improves the loop’s operation in the presence of AWGN.     

Rateless Coding for Wireless Relay Channels

We propose a novel coding framework for wireless relay channels based on rateless codes, which allows for a natural extension to multiple antenna and multiple relay settings. The relaying protocol is half-duplex, and relays independently choose when to collaborate, if at all. With a simulated fountain code based implementation of this framework, we show that the use of rateless codes is both robust and efficient when the channel state information is not available at the transmitters     

ATM网络的视频编码技术

异步转换模式（ＡＴＭ）的提出对编码技术产生了重大的影响。本文概述了ＡＴＭ下可变比特率（ＶＢＲ）视频编码的优点及存在的问题，扼要介绍了各种信元丢失的预防及补偿方法，着重分析了分层编码技术，并对目前提出的各种可变比特率分层编码算法进行了概括性的评述，指出了有待研究的一些问题。     

Optimal Linear Coding for Vector Channels

This paper is concerned with the problem of obtaining the optimal linear vector coding (transformation) method that matches anr-dimensional vector signal and ak-dimensional channel under a given channel power constraint and mean-squared-error criterion. The encoder converts thercorrelated random variables intorindependent random variables and selects at mostkindependent random variables which correspond to theklargest eigenvaiues of the signal covariance matrixQ. The encoder reinserts cross correlation into thekrandom variables in such a way that the largest eigenvalue ofQis assigned to the smallest eigenvalue of the channel noise covariance matrixRand the second largest eigenvalue ofQto the second smallest eigenvalue ofR, etc. When only the total power for allkchannels is prescribed, the optimal individual channel power assignments are obtained in terms of the total power, the eigenvalues ofQ, and the eigenvalues ofR. When the individual channel power limits are constrained byP_{1}, ..., P_{k}andRis a diagonal matrix, the necessary conditions of an inverse eigenvalue problem must be satisfied to optimize the vector signal transmission system. An iterative numerical method has been developed for the case of correlated channel noise.     

视频流传输中的差错复原视频编码技术

视频压缩技术在采用预测技术、变换编码技术和可变长熵编码技术以减少冗余信息的同时,也降低了视频流的容错能力.传输信道中的差错,不仅严重损害了视频服务质量,甚至会使通信系统崩溃,因此,在有错信道上进行视频传输,差错复原视频编码技术就显得尤为重要.对差错复原视频编码技术进行了概括和总结,首先指出在视频传输过程中存在的由于传输错误而引发的比特流同步丢失及错误蔓延问题,然后研究了解决这些问题的差错复原视频编码方法,最后指出:可伸缩视频编码和多描述视频编码是差错复原视频编码的发展方向;多描述编码同多路径技术相结合,能显著提高压缩视频信号的错误恢复能力和传输信道的性能.     

A Coding Scheme for Duplex Channels

In this paper we describe a coding strategy for binary duplex channels (BDC's) that essentially matches the performance of a system with two identical binary forward channels using a systematic rate-frac{1}{2}convolutional code on each of these channels. In other words, our coding strategy achieves the same effect as would the turning around of the feedback channel.     

运动补偿视频编码的一种非DCT编码方法

本文提出一种新的空间域帧间编码方法－预测信号梯度控制的四叉树编码,模拟实验表明,这种编码方法的效率已经与ＤＣＴ相当,并稍有超出,而其算法比较简单。     

Robust Packet Video Transport Over Wireless Fading Channels Using a Joint Source-channel Coding Approach

In this paper, we address the problem of robust video transmission over wireless networks. Specifically, we consider packet video transmission over wireless IP networks based on the RTP/UDP/IP protocol stack. Digital video delivered over wireless networks is expected to suffer quality degradation from both packet loss and bit errors in the payload. In this paper, both packet loss and bit errors in the payload are considered and the performance of a joint source-channel coding (JSCC) approach employing forward error-correction (FEC) coding schemes for H.263 +  video transmission is studied. Results indicate that with an appropriate JSCC approach, FEC-based error-control techniques can significantly improve the packetization efficiency for a given end-to-end quality requirement and lead to more acceptable video delivery quality over time-varying wireless networks. Another important observation is that with a JSCC approach the fading effects of wireless links upon end-to-end video quality are substantially decreased compared to a system without using channel coding, resulting in attractive robust performance characteristics.

Distributed Video Coding

Distributed coding is a new paradigm for video compression, based on Slepian and Wolf's and Wyner and Ziv's information-theoretic results from the 1970s. This paper reviews the recent development of practical distributed video coding schemes. Wyner-Ziv coding, i.e., lossy compression with receiver side information, enables low-complexity video encoding where the bulk of the computation is shifted to the decoder. Since the interframe dependence of the video sequence is exploited only at the decoder, an intraframe encoder can be combined with an interframe decoder. The rate-distortion performance is superior to conventional intraframe coding, but there is still a gap relative to conventional motion-compensated interframe coding. Wyner-Ziv coding is naturally robust against transmission errors and can be used for joint source-channel coding. A Wyner-Ziv MPEG encoder that protects the video waveform rather than the compressed bit stream achieves graceful degradation under deteriorating channel conditions without a layered signal representation.     

On the Coding Gain for Degraded Channels

This correspondence deals with the coding gain for harddecisioned codes used over realistic channels. A simulation-based procedure is described, by which the performance (BER) curve of a coded system can be straightforwardly determined. The coding gain for real, i.e., "degraded" channels is discussed, vis-a-vis that for idealized channels. A formula for asymptotic coding gain for the latter type of channel is extended to channels with degradation. Finally, the coding gain for multiple-hop systems is briefly discussed.     

Turbo-Like Codes for Transmission of Correlated Sources over Noisy Channels

In this article we focus on distributed coding of correlated sources that are transmitted through either separated noisy channels (one per source) or over a multiple access channel (MAC). For simplicity, we consider only two sources, but the proposed approach can be easily extended to the case of more sources. The two sources are encoded independently of each other (i.e., for a given source neither the realization from the other source nor the correlation model are available at the encoder site) and transmitted through the channel. Then, the correlation between the sources is exploited at a common receiver, aiming at the reconstruction of the two sources. Although this problem has many practical applications e.g., in the case of sensor networks (where correlated data has to be communicated between the different nodes) and video/image applications, we will focus in the key ideas without discussing specific applications. For simplicity, we will assume simple correlation models and binary sources.     

Multiresolution Vector Quantization for Video Coding

In this work, we propose a coding technique that is based on the generalized block prediction of the multiresolution subband decomposition of motion compensated difference image frames. A segmentation mask is used to distinguish between the regions where motion compensation was effective and those regions where the motion model did not succeed. The difference image is decomposed into a multiresolution pyramid of subbands where the highest resolution subbands are divided into two regions, based on the information given by the segmentation mask. Only the coefficients of the regions corresponding to the motion model failure are considered in the highest resolution subbands. The remaining coefficients are coded using a multiresolution vector quantization scheme that exploits inter-band non-linear redundancy. In particular, blocks in one subimage are predicted from blocks of the adjacent lower resolution subimage with the same orientation. This set of blocks plays the role of a codebook built from coefficients inside the subband decomposition itself. Whenever the inter-band prediction does not give satisfactory results with respect to a target quality, the block coefficients are quantized using a lattice vector quantizer for a Laplacian source.     

Motion Estimation for Video Coding Standards

Motion-compensated estimation is an effective means in reducing the interframe correlation for image sequence coding. Therefore, it is adopted by the international video coding standards, ITU H.261, H.263, ISO MPEG-1 and MPEG-2. This paper provides a comprehensive survey of the motion estimation techniques that are pertinent to video coding standards.There are three popular groups of motion estimation methods: i) block matching methods, ii) differential (gradient) methods, and iii) Fourier methods. However, not all of them are suitable for the block-based motion compensation structure specified by the aforementioned standards. Our focus in this paper is to review those techniques that would fit into the standards. In addition to the basic operations of these techniques, issues discussed are their extensions, their performance limit, their relationships with each other, and the other advantages or disadvantages of these methods. At the end, an example of evaluating block matching algorithms from a system-level VLSI design viewpoint is provided.     

视频编码新技术12题第一讲视频压缩编码

本文首先介绍了经典视频编码的国际新标准H.264/AVC中采用的主要新技术,然后以3D-DCT为例,介绍了结合二维平面空间和时间维形成的三维视频编码技术,最后介绍了编码效率非常高、但实现难度也很大的新一类基于内容的编码方法模型基视频编码。