Multiview coding and error correction coding for 3D video over noisy channels

We consider the joint source–channel coding problem of stereo video transmitted over AWGN and flat Rayleigh fading channels. Multiview coding (MVC) is used to encode the source, as well as a type of spatial scalable MVC. Our goal is to minimize the total number of bits, which is the sum of the number of source bits and the number of forward error correction bits, under the constraints that the quality of the left and right views must each be greater than predetermined PSNR thresholds at the receiver. We first consider symmetric coding, for which the quality thresholds are equal. Following binocular suppression theory, we also consider asymmetric coding, for which the quality thresholds are unequal. The optimization problem is solved using both equal error protection (EEP) and a proposed unequal error protection (UEP) scheme. An estimate of the expected end-to-end distortion of the two views is formulated for a packetized MVC bitstream over a noisy channel. The UEP algorithm uses these estimates for packet rate allocation. Results for various scenarios, including non-scalable/scalable MVC, symmetric/asymmetric coding, and UEP/EEP, are provided for both AWGN and flat Rayleigh fading channels. The UEP bit savings compared to EEP are given, and the performances of different scenarios are compared for a set of stereo video sequences.     

无线信道中的联合信源信道编码

该文提出了一种噪声信道下传输渐进图像的联合信源信道编码方法。该方法根据信道条件的好坏动态的调整信源编码速率和信道编码速率，因此极大地提高了系统的性能和编码效率。同时该方法还具有结构简单，易于实现等优点。试验证明本方法与以前文献中提出的EEP方法以及UEP方法相比，在信噪比低时即信道条件恶劣的情况下，能够明显提高恢复图像的质量。     

Unequal error protection by modulation with unequal power allocation

In digital communication systems for speech, audio or video signals the individual bits of the transmitted parameters u exhibit different bit error sensitivities. Usually channel coding with unequal error protection (UEP) is applied. However, some transmission systems do not include channel coding for several reasons. For this situation, a novel concept is proposed which achieves UEP by allocating different transmission power to individual bits according to their bit error sensitivities. The optimization criterion for unequal power allocation is the mean square of the error between the original parameter-u and the decoded parameter u which has a strong correlation with subjective perception.     

Progressive image transmission over differentially space‐time coded OFDM systems

In this paper, we consider progressive image transmission over differentially space‐time coded orthogonal frequency‐division multiplexing (OFDM) systems and treat the problem as one of optimal joint source‐channel coding (JSCC) in the form of unequal error protection (UEP), as necessitated by embedded source coding (e.g., SPIHT and JPEG 2000). We adopt a product channel code structure that is proven to provide powerful error protection and employ low‐complexity decision‐feedback decoding for differentially space‐time coded OFDM without assuming channel state information. For a given SNR, the BER performance of the differentially space‐time coded OFDM system is treated as the channel condition in the JSCC/UEP design via a fast product code optimization algorithm so that the end‐to‐end quality of reconstructed images is optimized in the average minimum MSE sense. Extensive image transmission experiments show that SNR/BER improvements can be translated into quality gains in reconstructed images. Moreover, compared to another non‐coherent detection algorithm, i.e., the iterative receiver based on expectation‐maximization algorithm for the space‐time coded OFDM systems, differentially space‐time coded OFDM systems suffer some quality loss in reconstructed images. With the efficiency and simplicity of decision‐feedback differential decoding, differentially space‐time coded OFDM is thus a feasible modulation scheme for applications such as wireless image over mobile devices (e.g., cell phones). Copyright © 2006 John Wiley & Sons, Ltd.     

基于LDPC码的小波图像传输码率优化

LDPC码是一种具有低复杂度,强纠错能力的信道分组编码结构,SPIHT算法是嵌入式小波图像压缩编码中性能较好的一种。文中充分考虑SPIHT算法和LDPC码的特性,提出了根据信源编码后的数据在解码重建时的重要程度进行不等纠错保护的信源信道联合编码方案。实验表明,该方案有利于压缩图像在噪声信道上的可靠传输,提高系统整体纠错性能。     

一种基于混沌系统的窄带超低速语音加密算法

为了在极低通信速率信道中实现保密语音通信,在北大西洋公约组织的0.6 Kb/s增强型混合激励线性预测声码器算法基础上,提出了基于混沌映射的保密通信算法。算法利用两个Logistic方程产生混沌序列,对声码器码流进行置换和移位。最后对该加密语音通信系统进行了仿真测试。测试结果证明,系统方案切实可行,产生的密钥空间大,能够实现加密强度较高的语音保密通信。     

EVRC语音编码算法研究及仿真

为了解决单一速率语音编码算法所带来的系统容量和频带利用率的浪费,第三代移动通信系统采用了变速率语音编码技术。介绍了一种用于第三代移动通信系统的EVRC(增强型变速率编解码)语音编码算法,简要地介绍了其编解码原理,着重分析了EVRC算法的关键技术:噪声抑制、速率判决、帧错误检测、自适应后置滤波等,并进行了该算法的浮点C代码仿真。仿真结果表明:该算法在较低的平均编码速率下获得了较高的合成语言质量。     

A High-Performance Codec Suitable for the GSM Half-Rate Coding System

1IntroductionTheGSMpanEuropeandigitalradiosystemhas-beendesignedwithaparticularTDMAframestfllcturewhichenablestheusingofeitherfull-rateorhalf-ratechannels.Speechandchannelcodingalgorithmsforfull-ratechannelshavebeenindependentlystandardized,leadingrespectivelytotheRPE-LTPalgorithmandprotectionschemebasedonaconvolutionalcodewithaCRCforerrordetection.StandardiZationofacombinedspeechandchannelhalf-ratecodecataglobalrateofII.4kbpshasstartedunderthecontrolofETSI.Theobjectiveisverychalleng…     

Unequal error protection for MPEG-2 video transmission over wireless channels

This paper proposes an unequal error protection (UEP) method for MPEG-2 video transmission. Since the source and channel coders are normally concatenated, if the channel is noisy, more bits are allocated to channel coding and fewer to source coding. The situation is reversed when the channel conditions are more benign. Most of the joint source channel coding (JSCC) methods assume that the video source is subband coded, the bit error sensitivity of the source code can be modeled, and the bit allocations for different subband channels will be calculated. The UEP applied to different subbands is the rate compatible punctured convolution channel coder. However, the MPEG-2 coding is not a subband coding, the bit error sensitivity function for the coded video can no longer be applied. Here, we develop a different method to find the rate-distortion functions for JSCC of the MPEG-2 video. In the experiments, we show that the end-to-end distortion of our UEP method is smaller than the equal error protection method for the same total bit-rate.     

信道自适应UEP技术在H.264视频通信系统中的应用

在进行基于H．264标准的视频通信系统设计时，为提高编码视频流的抗误码性能以及编码器的编码效率，提出了一种信道自适应非平等误码保护(UEP)技术。该技术可根据反馈的信道状态信息自适应地确定H．264编码视频流在网络适配层(NAL)中的工作模式，在丢包信道中结合人眼的视觉特性重新对编码视频信息进行分区并分别采用不同优先级的误码保护。仿真实验表明，在有效提高H．264视频通信系统中解码器输出重构视频图像视觉质量的同时，进一步降低编码器端数据包的打包开销，从而提高编码器的编码效率。     

自适应多码率语音编码流的可靠传输

自适应多码率语音编码已入选为第三代移动通信系统的语音压缩编码方案。本文提出了一种适合压缩语音传输的联合信源信道编码方法并对其性能进行了统计比较。利用压缩语音比特流中的固用冗余的信道译码算法是本文的研究重点。仿真结果表明利用信源冗余信息的信道译码器可以获得较大的编码增益。本文所用的信道编码方案为适合语音传输的卷积码。     

基于EaacPlus的可分层可分级音频编码系统

在多媒体通信中,一方面要求音频业务质量能适应不断变化的网络带宽,体现一定的层次性;另一方面,要求音频信源能够按码率任意截断从而更好地适应信道变化,以保证音频业务质量要求。这种信源的分层分级码流在网络传输时,更便于信道不对等保护技术的使用。提出了一种音频业务的可分层模型和基于EaacPlus核心编码器的可分层可分级音频编码方案。实验表明,分层模型的使用使得音质具有较强的层次感;可分级码率的增加能够带来音质的连续增强。     

AMR的信道编码设计及其DSP实现

对于超短波移动通信系统中AMR语音业务的传输，提出了基于码率兼容的删余卷积码和码率兼容的删余Turbo码这2种可变的不等差错保护信道编码方案。通过设计最优的删余方案和合适的速率匹配方法，这2种不等差错保护方案都可达到类内不等保护的目的，将对具有不同重要性的信源比特的作更精确不等保护。并基于DSP芯片TMS320C6416实时实现了这2种方案对AMR语音的不等差错保护。实验结果表明，这种方法具有合理的系统复杂度和很短的处理延时，适合于语音业务的应用。     

基于联合优化技术的信源信道联合编码新策略

针对多媒体无线通信的特点,提出了一种结合自适应纠错技术与联合优化技术的新策略,充分考虑了联合编码的自适应纠错特性和联合优化特性,分析了优化的信源编码算法和优化的信道编码算法.实验仿真结果表明,该方法能够使图像数据在高码率下达到较好的抗噪性能.     

信源信道联合编码技术用于AVS传输的研究

针对误码信道和信源编码的统计特性,提出了一种基于AVS视频序列的联合编码技术,按照重要性对AVS视频层序列码流进行分组重排,信道编码器根据码流信息对其进行比重不等的保护措施,以较低复杂度的运算实现了码率的优化分配.实验表明,与现有的等差错保护相比,在高误码信道中能有效提高AVS码流抗误码性能.     

LZW压缩数据的不均一两分段误码保护编码

由T.A.Welch提出的LZW数据压缩方法已经被广泛地应用于文字压缩。然而，因为误码对压缩数据的危害很大，所以对压缩数据的纠错编码是十分重要且必不可少的。本文分析了误码对LZW压缩数据的影响，指出同样的误码对用于重建辞书的前一部分压缩数据的危害比对后面的其它数据的危害要严重得多，提出用一种不均一两分段误码保护编码方法，对用于重建辞书的前一部分压缩数据进行更好地保护。计算机模拟显示，该方法比传统的误码保护方法更有效。     

Combined turbo coding and hierarchical QAM for unequal error protection of H.264 coded video

This paper investigates the unequal error protected (UEP) transmission of scalable H.264 bitstreams with two-priority layers, where differentiated turbo coding provides better protection for the high priority (HP) base layer than for the low priority (LP) enhancement layer. The drawback of such a method is the high overhead introduced by the channel coding, which results in a low source data rate for the HP layer, and hence lowers video quality. To overcome this problem, we introduce an efficient combination of turbo coding and hierarchical quadrature amplitude modulation (HQAM) to provide a high protection for the HP layer and at the same time maintaining the requisite channel coding redundancy. Simulation results show that, over a wide range of channel signal-to-noise ratio (SNR), our combined technique is superior to non-scalable transmission and outperforms UEP with turbo coding alone.     

移动通信中语音编码技术的应用与发展

移动通信系统采取了多种行之有效的关键技术来提高系统抗衰落和抗干扰能力,语音编码技术即是其中一种。文章主要介绍了几代移动通信系统中使用的不同语音编码技术,旨在阐明语音编码技术基本原理及其重要作用。     

Highly scalable JPEG image transmission with unequal error protection and optimal feedback

This paper investigates the performance of three different Unequal Error Protection (UEP) schemes for progressive JPEG image transmission using delay-constrained hybrid ARQ, with iterative bit and symbol combining. The first UEP scheme considers only the optimization of channel code-rates and keeps the number of retransmissions fixed for all the subbands of the image. The second one optimizes both the channel code-rates and retransmissions, while the third only considers the optimal allocation of retransmission requests. The UEP schemes are designed with two different coding techniques. The first one employs Rate Compatible Punctured Turbo Codes (RCPT) with iterative bit combining and, is suitable for applications requiring high power efficiency. For the second one we propose a new coding strategy, Rate Compatible Punctured Turbo Trellis Coded Modulation (RCPTTCM) with iterative symbol combining, which provides high scalability and bandwidth efficiency. Gains of over 9 dB in Peak-Signal-to-Noise-Ratio are obtained with the UEP schemes as compared to their corresponding Equal Error Protection (EEP) schemes.