【作者】 马彦卓；

【导师】 常义林；

【作者基本信息】 西安电子科技大学 ， 通信与信息系统， 2009， 博士

【摘要】 随着视频编码及无线通信技术的迅速发展,视频已成为无线通信的主要业务之一。无线信道的时域和频域衰落特性复杂多变,并且其传输带宽有限。这都难以满足视频业务高速率和高服务质量的传输要求,使得无线视频通信在实际应用中仍面临着严峻的技术挑战。因此,无线视频传输和相关的编码处理技术成为视频通信领域的核心研究内容之一。为了在有误码的传输信道情况下提高接收端恢复视频的质量,本文从三个方面对无线视频抗误码传输技术进行了深入研究,主要包括视频编码中抗误码工具、OFDM无线视频传输技术,以及二者的结合应用。论文的主要研究成果有:1.提出了适用于视频编码的视频场景分析方法,包括一种实时多测度突变场景检测算法和一种基于运动加速度的关键帧提取算法。综合使用上述两种算法可提取视频序列的关键信息,确定视频序列中各图像的重要性。2.提出了一种基于场景分析的视频编码自适应图像组(AGOP)构造方法。利用所提出的视频场景检测算法和关键帧提取算法,确定视频序列中各图像对整体编码效率和抗误码性能的重要性,自适应划分视频GOP并确定GOP中各图像的编码类型。所提出的AGOP可以为视频码流提供更高层次的分级特性,有利于对不同重要性的图像进行不等保护传输,并且解码端易于实现视频错误掩盖。该方法有利于提高视频码流在无线信道中传输的抗误码能力。另外,针对AGOP编码方法,对已有的码率控制方法作了相应的修改,以有效控制码率,防止恢复视频质量的过大波动。仿真和实验结果表明AGOP不仅可以提高编码效率,也是一个有效的抗误码工具。3.深入研究无线视频传输中的视频码流和无线信道的适配问题。首先分析无线信道的衰落特性以及OFDM调制技术特点,然后结合视频数据特点,提出了一种OFDM无线信道上的三重交织视频传输技术。该技术综合运用空间域、频域和时域交织技术,有效降低了信道时域和频域的衰落特性对视频数据传输的影响,并有利于解码端的视频错误掩盖,提高了接收端恢复视频的质量。4.提出三重交织与应用层视频编码抗误码工具相结合的无线视频传输技术。将三重交织分别与多参考帧选择技术、灵活宏块顺序技术、提出的AGOP技术相结合,综合使用视频编码抗误码和无线传输技术,显著提高了接收端恢复视频的质量。仿真结果表明,当信道质量较差时,恢复视频质量的提高可达2dB以上。更多还原

【Abstract】 Along with the advancement of video encoding and the development of wireless network, video communication has become one of the primary services over wireless networks. However, there are still severe technical challenges in wireless video communications, because the error-prone and time-varying band-limited wireless channels always have difficulty in meeting the requirements for large-data-volume and high-service-quality video transmission. Therefore, the video transmission and related video processing techniques have become part of the key research areas in video communication. In this dissertation, the error control techniques in wireless video transmission are researched from three aspects, i.e., the error resilience tools in video encoding, video transmission over OFDM wireless channels and the effective integration of the above techniques for wireless video transmission.The major contributions of the dissertation are summarized as follows:1. Two content analysis methods based on motion characteristics are proposed, i.e., a new multi-metric scene cut detection method and a key frame extraction method based on acceleration. Based on the two methods, the importance of each frame can be classified, which further facilitates the design of adaptive group of pictures (AGOP) structure.2. Based on the two newly developed scene analysis methods, an adaptive GOP structure construction method is proposed. After performing scene content analysis, the frames in the video sequence can easily be classified according to their impacts on the entire coding efficiency and error resilience performance. Then different coding types are assigned to the pictures, which will facilitate the determination of the service priority to the coding bits of each picture in the transmission scheme using differential service strategy (e.g., unequal error protection). By employing the proposed AGOP video encoding, together with advanced error concealment methods, the quality of the received video can be further secured when transmitted over error-prone channels. Moreover, an improved rate control scheme is also devised for the AGOP encoding scheme to alleviate the fluctuation in the pictures’coding quality. Extensive experiments have shown that AGOP is an effective error resilient tool besides improving the coding efficiency. 3. The key issues of the adaptation of video bitstream and wireless channels are investigated. Based on the analyses on the characteristics of compressed video data and the wireless OFDM channel, a novel three dimensional interleaving technique, namely, spatial-frequency-temporal interleaving (SFTI), is proposed. By introducing frequency and temporal diversity, the proposed method reduces the degradation in video quality caused by the impacts of wireless fading and facilitates error concealment on the application layer at the receiver.4. Several error resilience techniques are integrated to develop a stream transmission scheme over OFDM wireless channels. The general idea of the proposed scheme is to effectively integrate the proposed SFTI with error resilience tools in video coding and transmission. By combining the SFTI with multiple reference picture selection, flexible macroblock technique, and the proposed AGOP, respectively, robustness of video transmission can be well consolidated, which is demonstrated by an average quality improvement of over 2 dB for the reconstructed video at the receiver.更多还原