【作者】 刘军清；

【导师】 孙军；

【作者基本信息】 上海交通大学 ， 通信与信息系统， 2007， 博士

【摘要】 数字压缩图像对于信道噪声所起的比特错误十分敏感,而无线信道环境的复杂性使得纠正信道传输中的误码变得很困难,因此如何实现鲁棒的无线图像传输仍是一个极具挑战的研究课题。其中利用联合信源信道编码解决无线图像传输是目前该领域的研究热点之一。本文研究并提出了三种联合信源信道编码方法及对应的解码方法用于无线图象传输。此外,为了分析所提出的联合信源信道编码系统的实际性能与理论值之间的差距,本文还对联合信源信道编码差错指数这一理论问题进行了研究。本文首先提出了一种基于纠错算术码的联合信源信道编码算法,该算法利用算术编码中加入的禁用符号实现整体编码,利用一阶马尔科夫信源模型实现信源的自适应,根据信道状态信息调整禁用符号概率的大小从而调整编码码率的大小实现信道自适应。与一般信道自适应不同的是,所提出的自适应方法仅需调整一个参数(禁用符号)加以实现,而且理论上来说可以获得连续可变的编码码率。以此为基础,推导出了基于最大后验概率(MAP)的解码测度并提出了一种改进的堆栈序列估计算法。实验表明,上述算法的传输性能优于经典的Grangetto基于纠错算术码的联合编码算法和Guionnet纠错算术码的联合编码算法,所提出的改进的堆栈序列估计算法的解码速度也快于传统的堆栈序列估计算法。其次,提出了一个渐进图像在无记忆信道上传输的联合失真模型,该模型联合考虑渐进图像传输中的量化失真和信道失真,并分别计算渐进图像各层对于总体失真的贡献。该模型相比Sabir失真模型而言,具有以下优点:1)利用算术编码加禁用符号实现整体编码,并用禁用符号带来的受控冗余区分量化失真与信道失真;2)用变换系数方差内的值代替信道污染后的系数值,相比传统的用0值代替来说,能更客观地估计信道失真;3)充分考虑了熵编码引起的误码扩散对失真的影响。实验表明,该失真模型相比Sabir所提出的失真模型精度提高了0.5dB。随后以此失真模型为依据设计了一个非均衡差错保护系统用于无线图像传输,获得了较好的传输性能。提出了一种改进的纠错算术码状态机表示方法,详细分析了编码参数对总体状态数目的影响。以此为基础,提出了一种有限状态纠错算术码的联合信源信道编码系统。该更多还原

【Abstract】 The transmission of images over wireless communication channels is still a challenge problem. Digital compressed images are sensitive to bit errors which are typical in wireless communications. Moreover, the bandwidth at the air interface is currently a limiting factor because the first and second generations of mobile phone standards mainly support voice communications. In this thesis, different integrating schemes of joint source-channel coding and decoding for error resilient image transmission over wirelesss channels are examined. In order to comparing the performance of joint coding system proposed in the thesis between the actual simulation and theory limit, we study the error exponent of joint source channel coding, and use the results to analyze the proposed joint source channel coding system. The detailed content is listed in the following.In the second chapter, a joint source channel coding algorithm based on error correcting arithmetic codes is proposed, in this algorithm, the arithmetic coding with the forbidden symbol is used to coding via one step, the probability of the forbidden symbol is adjusted adaptively according to the channel state information (CSI). Unlike the conventional channel adaptive joint coding algorithm, only one parameter needs to adjust in our algorithm. Furthermore, a continuous coding rate could be achieved theoretically. MAP decoding metrics are developed. In addition, a improved sequential search algorithm using stack is proposed. The proposed algotithm is tested in the case of image transmission, and excellent results in terms of packet error rate and decoded image quality are obtained.Secondly, a new joint distortion model for transmission progressive image on the memoryless channel is proposed in chapter 3. In our model, the distortions generated by quantization and the channel errors are considered jointly, and the distortion of every layers is computed separately. The new characteristics lie in. First, the arithmetic codes with the forbidden symbol are used as source channel coders, and the redundancy coming from the forbidden symbol is use to distinguish更多还原