【作者】 袁基睿；

【导师】 陈贺新；

【作者基本信息】 吉林大学 ， 通信与信息系统， 2007， 硕士

【摘要】 针对移动通信信道中的孤立比特错误,本文首先给出了一种基于视频流残留语义冗余的联合解码方案,把检错编码与压缩视频流的语法结构相结合,由检错码提供错误的位置信息,再从视频序列中去掉语法错误。仿真结果表明,采用该方案后,当误比特率下降到10-3时,所提方案重建图像的亮度PSNR仍保持在38.76dB,这是在该信源编码条件下所能达到的最优性能。针对包交换网络中的丢包现象,本文把语义信息和不连续度信息结合起来,在去除视频流语法错误的同时,根据不连续度信息去除直流系数中的错误。仿真结果表明,所提方案能够大大提高恢复图像的亮度PSNR性能。最后本文以H.264视频压缩标准和Turbo理论为基础,提出了一种基于H.264和Turbo码的信源信道联合解码方案。一方面,所提方案利用turbo解码器的信道软输出协助H.264视频解压缩器工作;另一方面,应用视频解压缩器的语义/句法信息对Turbo解码器的外部信息进行更改,以提高其纠错能力。仿真结果表明与只采用Turbo解码的方案相比,所提方案加速了Turbo码的收敛,并且在峰值信噪比、误比特率以及视频重建质量等方面性能都有显著提高。更多还原

【Abstract】 Compression is always used on video signals when they are transmitted due to bandwidth considerations. Compressed video is fragile in that a few channel errors may result in severe quality degradation because of error propagation, synchronization loss, etc. This phenomenon is especially correct for H.264 video stream, for its highest compress ratio among all video compressing schemes. To alleviate this, channel coding is usually applied to protect the compressed video. Since their introduction by Claude Berrou, etc in 1993, turbo codes have been shown to give very good error correction performance. It could provide near Shannon limit performance in terms of bit error rate. In addition, compressed video still contains residual redundancy which can be used to combat channel noise. In this paper, an iterative joint source-channel decoding using turbo codes for MPEG-4 video transmission is investigated.This paper presents a novel iterative joint source-channel decoding scheme for H.264 video transmission over noisy channels. The proposed scheme, on one hand, utilizes the channel soft outputs generated by the turbo decoder to assist video decompression. On the other hand, the syntactic/semantic information from the video decompressor is used to modify the extrinsic information so as to improve the error correction capability of the turbo decoder. Simulation results show significant improvement in terms of PSNR, reconstructed video quality, as well as BER over turbo decoding only.This paper is organized as follows:Chapter 1 gives the background and meaning of joint source-channel decoding schemes.Chapter 2 gives the overview of several video compressing standards, and chief techniques used therein.Chapter 3 gives detail description of H.264 video compressing standard, including techniques of dequant, inverse transform, intra-prediction, inter-prediction and deblocking. Simulation results show its incomparable compressing performance.Chapter 4 introduces Turbo code, including its encoder and decoder, with special attention on MAP decoder algorithm. Simulation result shows that its performance in terms of Bit Error Rate (BER) is close to the Shannon limit.In Chapter 5,first, for data corruption, I propose to combine error control coding together with error concealment. Classical error detection is used to locate errors in the compressed video stream. This information, together with information provided by the syntax of the compressed bitstream is used to perform the error concealment. And a new concealment method which relies in the redundancies provided by the syntax of the compressed bitstream is introduced. Then, for cell loss in packet switched network, I proceed to generate candidates for corrupted slices and test their syntactical integrity and their special smoothness. The smoothest candidate for a slice which is syntactically correct is chosen as the correct slice. The improvement in PSNR performance is shown. At last, I proposed the iterative joint source-channel decoding scheme for H.264 video transmission over noisy channels. The scheme combines the syntax information of compressed video stream and the extrinsic information of Turbo decoder, which could improve the anti-error performance of H.264 decompressor while decreasing the iteration number of Turbo decoder. And this chapter also gives the simulation results of the proposed scheme, in terms of PSNR, reconstructed video quality, as well as BER.更多还原