【作者】 肖嵩；

【导师】 吴成柯；

【作者基本信息】 西安电子科技大学 ， 信号与信息处理， 2004， 博士

【摘要】 在无线信道中，能够提供对多媒体(包括话音、图像和数据等)业务的支持已成为二十一世纪通信系统发展的必然趋势。然而它的实现势必要解决两大问题，其一是对信源进行高效的压缩以充分利用有限的信道带宽——即信源编码问题；其二是对压缩后的信息进行错误保护以抗击信道或网络所带来的误码或数据丢失——即信道编码问题。由于信源编码压缩率的提高将导致码流抗误码能力的降低，同时提高码流的抗误码性能又要以牺牲编码效率为代价，因此信源编码和信道编码所要解决的问题在此意义上是相互矛盾的。对于信源编码问题，虽然在视频编码方面已形成了很多标准，但其压缩算法中采用的可变长编码，使得编码后比特流对误码极为敏感；对于信道编码问题，虽然一些成熟的纠错码的使用可以在一定程度上降低信道误码率，但它们通常针对某种固定信道进行设计，一旦信道条件发生变化且产生的错误超出编码自身的纠错范围时，系统性能将急剧下降。因此，如何在信源编码及信道编码间进行权衡，设计一套有效的系统编码方案从而更加可靠地在无线信道或网络上传输各种业务(尤其是视频)，是实现多媒体移动通信的关键问题之一。 联合信源信道编码已被证明是一种行之有效的解决上述问题的编码技术。该技术将信源与信道编码结合在一起考虑，比将最优的信源编码方案与最优的信道编码方案相级联的传统方法更加有效。 联合信源信道编码方面的研究在国外已经得到广泛的重视，而在国内还处于起步阶段，许多问题有待进一步深入的研究。本文对静止图像以及视频的联合信源信道编码问题中的若干关键技术进行了深入研究，并取得了一些成果，这将对下一代移动通信系统中多媒体通信的实现具有重要意义。 本文的主要工作和研究成果如下： 1．提出了一种基于小波SPIHT编码图像的联合信源信道编码方法。该方法针对SPIHT编码码流的重要性不同而进行不同程度的保护，并利用无线信道的时变特性自适应地调整信源和信道编码速率，从而在不增加额外带宽的前提下有效地提高了系统的性能和可靠性。 2．在分析MPEG-4码流层次结构及其重要性的基础上，提出了一种用于提高MPEG-4码流在噪声信道下的抗误码性能的联合信源信道编码方法。该方法将MPEG-4基本层按重要性进行码流重排后进行交织打包，并根据率失真函数将基本层纹理信息进一步划分为多个子层。编码器根据反映信道状态的反馈信息动态地调整传输的子层数目，使得系统失真最小。该方法抗丢包能力强，无线信道中的联合信源信道编码研究适用于衰落信道及无线网络中的视频传输。提出了一种感兴趣区域的多描述SPIHT编码方法。该方法将本身具有分层内嵌特性的SPIHT码流编码成多个描述子，每个描述子包含不同数目的完全编码零树码流和部分编码零树码流—即冗余码流。通过对所有零树重新进行重要性排序后，为每个描述子分配不同编码速率的完全编码码流和冗余码流来完成多描述SPIHT编码。在分配冗余树时，优先对感兴趣区域分配较多的冗余，而对背景区域或非感兴趣区域分配速率较低的冗余，以进一步增强感兴趣区域的抗误码以及抗分组丢弃能力，从而在不增加信道带宽的情况下，使得感兴趣区域即使在描述子丢失的情况下，也能获得较高的恢复质量。提出一种自适应插入过渡帧的多描述视频编码方法。该方法根据相邻帧的相对运动自适应地插入过渡帧，然后将视频序列分成两个描述子，每个描述子采用自己的预测环路独立编码。在解码端描述子合成时，系统利用正确接收到的描述子的信息自适应地选择运动补偿插值或直接替代方法来恢复另一描述子中的错误或丢失信息。同以往方法相比，该方法能够更加有效地缓解误匹配问题，快速帮助译码器从随机错误或突发错误中恢复，并且能够提供更加稳定的重建视频质量。分析了信源信道编码速率对图像质量的影响，提出了一种联合信源信道编码的速率分配方案。该方案针对渐进图像的速率分配问题建立了数学模型，对模型的求解进行了简化，并采用拉格朗日乘数法，在满足一定的约束条件下实现了速率的最优化分配。关键词:联合信源信道编码SPIHT MPEG一4多描述感兴趣区域速率分配西安电子科技大学博士学位论文更多还原

【Abstract】 The support of multimedia (including speech, image and video etc.) service in wireless channel or network is the trend of the development of communication system in the twenty first century. However, there are two challenging problems. One is high efficient compression of source for fully utilization of channel bandwidth, the other is the protection of compressed information for combating the error or packet loss. Since the increase of source compression ratio will result in the decrease of its error resilience, at the same time, the improvement of robustness of bit stream will sacrifice the coding efficiency. The source coding and channel coding are conflict in this sense. In the field of source coding, although there have been many standards, the bit streams of compression standard are very sensitive to the error for the variable length coding adopted by the standards. In the field of channel coding, many previous forward error correction (FEC) methods is efficient only when the number of error does not surpass the threshold of their correcting ability, otherwise the performance will decrease drastically, and even worse than that of no FEC. As a result, how to design an efficient coding system to achieve reliable services transmission over wireless channel or network is the key problem for the realization of multimedia mobile communication system.Joint source channel coding has been proved to be an efficient method to solve the problem. It takes both the source coding and channel coding into account, and achieves better performance than their separate selection of optimal design.Although joint source channel coding has been paid more and more widely attention abroad, it’s still in its infancy in our country. The dissertation investigates several key problems of joint source channel coding of image and video and obtains many results, which will help the realization of the next generation of mobile communication.The main contributions and innovation points of the thesis are as follows: 1. A novel joint source-channel coding scheme based on SPIHT used to transmit progressive image over wireless channel is proposed. The method provides unequal protection for SPIHT bit stream with different importance, and adaptively adjusts the source and channel coding rates according to the time-varying characteristic of wireless channel, thus yields good performance and high reliability without adding extra bandwidth.2. Based on the analysis of hierarchy and the significant characteristic of MPEG-4 bit stream, a new robust joint source channel coding method for MPEG-4 video over noisy channel is proposed. In the method, the base layer bit streams are reordered according to their relative importance and then interlaced packetized. Multiple sub-layers of texture information are generated based on their rate distortion function, the number of which is adjusted dynamically by the encoder according to the feedback information to minimize the overall distortion. The method has high ability to combat packet loss and is suitable for the video transmission over fading channel or network situation.3. A new multiple description SPIHT coding for region of interest (ROI) is proposed to combat packet loss. The method codes the SPIHT bit stream into multiple descriptions, each with a variable number of fully coded original trees and partially coded redundant trees. After reordering the zero trees of wavelet according to their importance, the method assigns different coding rates of original trees and redundant trees to each description. The more important parts of each tree are sent in more description than the less important parts, and in order to further improve the error resilience of ROI, more redundant trees are assigned to ROI than non-ROI. The relationship among zero trees, redundant trees and their coding rates are analyzed, and the algorithm of sorting process and assigning strategy of redundant trees are also presented in detail. Simulation results show that the method can further improve the reconstructed quality of ROI in the更多还原