武汉大学
硕 士 学 位 论 文
Research on Sub-band Speech Coding Based on bandwidth Scalability
为了适应不同通信条件下不同的需求，目前多媒体通信和无线网络普遍存在异构性。为适应不同带宽资源和网络环境下的通信需求，各种多媒体信息均希望拥有可伸缩的灵活性。为了保证在不同通信条件下语音通信的正常进行，采用可伸缩编码技术是目前得到广泛认可的方案。在语音可伸缩编码方面，目前已经提出了多种可伸缩编码的方案，国际上也制定了相应的标准。
本文首先将介绍了国内外带宽可伸缩编码的现状，详细介绍其编码原理与结构，并对现有带宽可伸缩编码方案及其中用到的相关技术，主要是针对子带结构带宽可伸缩编码器的原理和性能进行分析。
再对子带滤波器组中常用的正交镜像滤波器组(QMF组)进行原理分析，信号合成与分解的角度分析其原理，根据误差的构成及消除方法，针对滤波器的特性, 在现有正交镜像滤波器组的设计方法的基础上，提出一种改进的蚁群算法对滤波器系数进行优化的算法。实验结果表明,优化后QMF组的重建误差控制在2%以内,表明该方法的有效性。
然后针对子带结构带宽可伸缩编码高频信号缺乏良好解决方案的现状，对其设计方案进行改进并融合现有先进算法提高出一种新的设计方案，详细介绍其编解码的过程，通过部分仿真实验对该方案进行测试。
最后，指出该设计方案的不足之处及需要进一步研究的问题，并展望带宽可伸缩编码的前景。
关键词：带宽可伸缩语音编码器 子带结构 正交镜像滤波器组 蚁群算法 G..729
For the different requirement of various multimedia communication conditions, the heterogeneity exists in multimedia communication and wireless network. In order to adapt different bandwidth resources and the network environment correspondence demand, each kind of multimedia information hoped has the scalable flexibility. Speech scalable coding is widely considered to be a good scheme for multimedia communication under different conditions. In the speech expandable code aspect, at present already proposed the many kinds of scalable coding plans, also have the corresponding international standards.
This paper first study the situation of bandwidth scalable coding in domestic and foreign, introduce its code principle and the structure in detail, then analysis the bandwidth scalable scheme and the related technology mainly will be the sub-band structure.
Then through the research to Quadrature Mirror Filter banks of subband filter banks, we analyzes its principle from the signal’s synthesis and decomposition angle, according to erroneous constitution and elimination method, proposed one kind of improvement ant colony algorithm to optimize the filter coefficients optimize in view of filter’s characteristic. The experimental result indicated that the reconstruction error of QMF banks after optimization is controlled in 2%,indicates this method the validity.
In the face of the present situation that the sub-band structure bandwidth scalable coding high frequency signal lacks the good solution, makes the improvement and the fusion existing advanced algorithm to its scheme enhances one kind of new design, carries on the test through the partial simulations experiment.
Finally, pointed out the deficiency of the scheme and what question needs further study, and forecast bandwidth scalable coding.
Key words: bandwidth scalable speech coder sub-band QMF ACA G..729
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