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Researches On Error Control In Wireless Video Delivery

Posted on:2006-10-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y FangFull Text:PDF
GTID:1118360182460134Subject:Signal and Information Processing
Abstract/Summary:PDF Full Text Request
Today, the support of multimedia (including speech, image and video etc.) servicesin wireless channel or network has become a prosperous field. However, there exist twochallenging problems in wireless video delivery. One is high efficient compression ofsource for fully utilization of channel bandwidth, the other is protection of compressedinformation from errors or packet loss. Since the increase in source compression ratiowill result in the decrease in error resilience of bit stream, at the same time, theimprovement on robustness of bit stream will decrease the coding efficiency. Therefore,error control is an important issue in wireless video delivery. In this dissertation, anin-depth research is made on the issue on error control in wireless video delivery andthe main contributions and innovation points of the thesis are as follows:1. Based on the classic error resilient entropy coding (EREC) algorithm, amodification called bi-directional error resilient entropy coding (BEREC) isproposed. The BEREC method improves error resilience of bit stream anddecreases computational complexity. In the BEREC scheme, every twovariable-length blocks of data constitute one block-pair and are placed in onefixed-length slot back to back, i.e. one block is placed from the beginning of theslot, and the other from the end. To compare the BEREC with the EREC, ananalysis model is set up and an evalution criterion is defined. In addition, atheoretic analysis is made on error robustness of the BEREC and rich simulationresults are included to verify theoretic analysis.2. A new algorithm for progressive fine granularity scalable (PFGS) video coding isproposed which improves coding efficiency of enhancement layers through asmall-window search in enhancement layers. There exists a drawback in the presentPFGS framework, i.e., motion vectors used in enhancement layers are not precise.To overcome it, the new algorithm makes a small-range search in enhancementlayer for more precise motion vectors based on motion vectors of base layer, so theprediction accuracy of present algorithms can be improved. Rich simulation resultsshow that the new algorithm improves the coding efficiency of the PFGS.3. A new method for error detection is proposed which improves the quality ofreconstructed images at decoders. For each inter coded macroblock (MB), the sumof the absolute values of the received residual pixels is calculated. At the same time,the intra complexity of the current MB is estimated by that of the motioncompensated reference block in the previous frame. The inter residue is comparedwith the intra complexity. If the inter residue is larger than the intra complexity by apredefined threshold, the MB is decided to be erroneous and error concealment hasto be applied on it. Simulations show that the new method can remove those MBswith serious errors effectively and improve the quality of reconstructed images.4. An improvement on the partial backward decodable bit stream (PBDBS) scheme isproposed which improves the error robustness of video bit stream. With the PBDBSscheme used, bits at both ends of video packets are safer than those in the middle.The new algorithm exploits syntactic and spatial importance of different parts ofvideo bit stream. First, more important syntax elements are placed at both ends ofvideo packets, while the less important in the middle. Second, macroblocks (MBs)near to the centers of images are placed close to both ends of video packets whilemarginal MBs are placed in the middle. The simulation shows that the newalgorithm improves the quality of reconstructed images at decoders.
Keywords/Search Tags:wireless video delivery, error control, error resilient entropy coding, scalable coding, MPEG-4, H.264
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