ABSTRACTERROR CONCEALMENT TECHNIQUES IN H.264/AVC,FOR VIDEO TRANSMISSION OVER WIRELESS NETWORKVineeth Shetty Kolkeri, M.S.The University of Texas at Arlington, 2008Supervising Professor: Dr. K. R. RaoNowadays audio-visual and multimedia services are seen as important sources of the traffic within mobile networks. An important characteristic of such networks is that they can not provide a guaranteed quality of service QoS [1] due to issues like interfering traffic, signal to noise ratio fluctuations etc.One of the limitations within the mobile networks is the low transmission bit rate which demands the reduction of the video resolution and a high efficient video compression technique such as H.264/AVC [3] video compression standard. This is the newest standard, which provides a high compression gain. The video compression is based on the elimination of the spatial and temporal redundancies within the video sequence. This makes the video stream more vulnerable against bit stream errors. These errors can have the effect of degrading the quality of the received video.Another important performance parameter is the computational complexity, crucial especially for the wireless video due to the size and power limited mobile terminals and also due to the real-time requirements of services. At present there is no standard criteria used to compare the complexity of the error concealment methods. To evaluate the quality of reconstruction, typically Peak Signal to Noise Ratio (PSNR), Mean Square Error (MSE) and Structural Similarity Index Metric (SSIM) are used. In this research some techniques that allow the concealment of the visual effect of bit stream error, since the retransmission of erroneous data packets is limited by the defined maximum channel delay. Due to the nature of video image there exists significant statistical correlation between adjacent frame pixels in spatial domain and between the adjacent video frames in the temporal domain. This property has been exploited in the design of the error concealment methods. The error concealment can be performed in the spatial domain by interpolating the pixels of the defected part of the video image from the pixels within the surrounding area. The interpolating process can be configured to fit the character of the image. On the other hand the error concealment can be performed in the temporal domain where the pixels of the missing part of the image can be copied from the previously decoded neighboring frames. The copying process can be adjusted to fit the dynamic character of the video sequence by applying the motion compensation to the copied image parts, by using different algorithms, which can estimate the amount of motion within the processed art of video sequence [4]. Finally this research investigates the performance of each method in terms of the computational complexity and the resulting image quality.CHAPTER 1INTRODUCTIONDue to the rapid growth of wireless communications, video over wireless networks has gained a lot of attention. Cellular telephony is the one that had the most important development. At the beginning, cellular telephony was conceived for voice communication; however, nowadays it is able to provide a diversity of services, such as data, audio and video transmission thanks to the apparition of third and fourth generation (3G/4G) developments of cellular telephony [2].Figure 1: Typical situation on 3G/4G cellular telephonyIn Figure 1 it is a possible situation on 3G/4G [11] cellular telephony system where a user, with his mobile terminal, demands a video streaming service. The video stream comes from the application server over the network. Then it is transmitted over the wireless environment to the user. During the transmission video sequence may undergo problem due to the fact that it is an error prone environment. This system, because of the bandwidth limitation, work with low resolution (QCIF 176 x 144) videos so the loss of one packet means a big loss of information. Since this process is a real time application so it is not possible to perform retransmissions. The only way to fix the errors produced by packet losses is using errorconcealment methods in the mobile terminal. The focus of this thesis is on spatial and temporal correlation of the video sequence to conceal the errors. The main task of error concealment is to replace missing parts of video content by previously decoded parts of the video sequence to eliminate or reduce the visual effects of bit stream error. The error concealment exploits the spatial and temporal correlation between the neighboring image parts (macro blocks) within the same frame and the past and future frames [6]. Techniques using these two kinds of correlation are categorized as spatial domain error concealment and temporal domain error concealment. The spatial domain error concealment utilizes from the spatial smoothness nature of the video image, each missing pixel of the corrupted image part can be interpolated from the intact surroundings pixels [10]. The interpolation algorithm has been improved by the preservation of edge continuity using difference edge detection methods. The temporal domain error concealment utilizes from the temporal smoothness between the adjacent frames within the video sequence. The simplest implementation of this method is to replace the missing image part by spatially corresponding part within a previously decoded frame, which has the maximum correlation with the affected frame. The copying algorithm has been improved by considering the dynamic nature of the video sequence. Different motion estimation algorithms have been integrated to apply motion compensated copying.There are still not standardized means for the performance evaluation of error concealment methods. To evaluate the quality of reconstruction, typically peak signal to noise ratio (PSNR) and structural similarity index metric (SSIM) are used.The focus of this thesis is the performance indicators for evaluating the error concealment methods. To test the performance evaluation methods, H.264 [3] video codec is used. H.264 [3] is the newest codec in video compression, which provides better quality with less bandwidth than the other video coding standards such as
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