【作者】 王晓敏；

【导师】 范晓鹏；

【作者基本信息】 哈尔滨工业大学 ， 计算机科学与技术， 2015， 硕士

【摘要】 随着信息技术的发展以及各种便捷的移动终端的出现,无线视频已经变成我们生活中必不可少的一部分。越来越多的人喜欢随时随地的观看各种高清视频,实时新闻,直播赛事,于是无线视频广播技术也越来越受到研究者的喜爱。然而,现有的无线视频广播技术如传统数字视频广播技术(DVB)不能够充分利用每个用户的信道特性并根据用户的信道状况为用户提供质量最好的视频。一些学者针对这种情况提出了可伸缩视频编码(SVC),但是,这种方法存在着严重的“阶梯效应”。最近几年,人们提出了一个全新的叫做Soft Cast的无线视频软广播技术框架。Soft Cast是一种视频信号模拟传输的技术,不进行量化,熵编码和信道编码,Soft Cast比传统的数字视频广播以及可伸缩编码有更好的编码性能。但是Soft Cast要求用户带宽与编码端每秒传输的信号个数相匹配,当信道带宽大于信源每秒传输的系数个数时,Soft Cast能做的只是重复的传输系数,Layer Cast是在Soft Cast的基础上采用分层陪集编码技术的一种软广播框架,很好的解决了信道扩展的问题。但是当信道带宽小于信源每秒传输的系数个数时,还没有一种很好的方法能够解决这个问题。针对这种情况,本文提出了适用于低带宽用户的Soft Cast编码框架。受到Layer Cast编码框架的启发,本文在3D-Soft Cast的基础上提出了一个系数合并和系数分离的方法,主要用于解决用户带宽小于信源每秒传输的系数个数的情况。也就是当用户带宽小于信源每秒传输的系数个数时,把那些本来要丢弃的系数合并到要传输的系数中,在解码端再把他们分离出来,这样虽然会使得一部分DCT系数的精度下降,但是却避免了大量DCT系数的丢失,这样就能够传输更多有用的系数信息到解码端,从而得到更高质量的重构视频。使得Soft Cast能适用于信道带宽较小的情况,在信道带宽较窄的情况下有效的提高Soft Cast的编码效率。这样就可以使Soft Cast不仅能够适用于不同的信道SNR,还可以适用于不同的信道带宽。在论文中提出的主要技术有基于量化的系数合并分离方法以及对应的不同的band之间的新的能量分配方式等。实验结果显示,在固定带宽与在可变带宽情况下,本文提出的适用于低带宽用户的Soft Cast编码与3D-Soft Cast相比都有0.1-0.5d B的提升。更多还原

【Abstract】 With the development of the information technology the emergence of various convenient mobile terminals, wireless video broadcast has becoming one of the essential parts of our daily lives. The wireless video broadcast is more and more popular because more and more people prefer to watch sport games and real time news whenever and wherever possible. The main challenge for conventional digital video broadcasting(DVB) standard is it difficult to fully utilize each receiver’s channel characteristics and provide the best video quality for each receiver under his channel condition Some researchers proposed scalable video coding(SVC) to improve this situation. However, SVC still cannot avoid the stair effect completely. Recently, a novel wireless video broadcast framework called Soft Cast has been proposed. Soft Cast transmits video signal in the analog channel directly without quantization, entropy coding and channel coding. Soft Cast gets significant gain over the conventional digital video broadcasting and scalable video coding. However, Soft Cast depends on a special situation that the channel bandwidth matches the number of coefficients to transmit per second. The newly proposed Layer Cast method can effectively solve the problem which the channel bandwidth is larger than the video requirement and improves the coding efficiency at the same time, while what Soft Cast can do is just repeat transmission coefficient. Layer Cast is a kind of soft video broadcasting framework using hierarchical coset codi ng based on Soft Cast technology. However, there is no efficient soft video broadcast scheme for the case that the channel bandwidth is smaller than the video requirement. In view of this situation, we propose soft video broadcast for low channel bandwidth receivers.Inspired by Layer Cast, this paper proposes a coefficient combine and coefficient separation method on the basis of 3D-Soft Cast. It is mainly used to solve the channel bandwidth is smaller than the number of coefficients to transmit per second. When the channel bandwidth is smaller than the number of coefficients to transmit per second, we will combine part of the coefficients. At the decoder, we will separate those coefficients. Although it will decrease the precision of the part of the DCT coefficients, it can avoid a large number of DCT coefficients missing. Therefore, we can transfer more information to the decoder and obtain a better video quality, and make the Soft Cast adapt to the low channel bandwidth receivers and effectively improve the coding efficiency of Soft Cast in the case of narrow channel bandwidth. So this can make Soft Cast not only suitable for different channel SNR, but also can be applied to different channel bandwidth. The main techniques presented in this paper are coefficient combine and coefficient separation method based on the quantification as well as the new energy allocation methods for different band. The experimental results show that we proposed scheme soft video broadcast for low channel bandwidth receivers outperforms 0.1-0.5d B than the 3D-Soft Cast not only under the fixed bandwidth but also under the variable bandwidth.更多还原