| With the development of wireless communication network from narrow-band that only supports services of voice and low speed data transmission to wide-band that supports services of voice, high-speed packet data and video streams transmission, wireless multimedia communication network has become a platform of driving the development of public services in society and the need of mobile users for wireless video services is prominent. However, the time-variance and the burst of errors of wireless channel, and the sensitivity of high compression ratio video streams to the errors impact the transmission of high quality of video services. Therefore, it is of both theoretical and practical significance to study wireless transmission technology of improving the quality of video communication and efficient video coding technology in wireless channel.This thesis mainly focused on the coding approach of improving video coding efficiency and the wireless transmission technology of improving video quality, and how to make the reasonable tradeoff between the algorithm complexity and the quality of reconstructed video under the time-delay constraint of video services in MIMO-OFDM system. This thesis mainly includes as follows:1. The video object segmentation algorithm, which is the key technology of content-based video coding system, was studied. Since the accurate extraction of video object is a prerequisite for ROI-based scalable video coding technology, this thesis proposed the automatic video object segmentation algorithm with accurate segmentation results to meet the requirements of real-time communication. In addition, this thesis proposed another semi-automatic video object tracking algorithm to effectively track the video object moving slow or fast in a non-real time context. The simulations showed that the video object segmentation algorithm has higher accuracy and lower complexity compared with other algorithms, and has a better tracking effect for the video object with a large range of motion speed.2. The superposition space-time coding algorithm was studied to obtain the unequal error protection for layered video sources in the MIMO System. The closed-form expressions of outrage probability for Alamouti and V-BLAST coding respectively are derived under the assumption of high SNR. With the analysis of the monotonic dependence of the outrage probability cross-point of the two space-time coding algorithms on data rate, the superposition space-time coding algorithm was designed; different space-time coding methods are used for the data of different importance in layered video sources to implement the unequal error protection for video data. In addition, the method of power allocation was considered to guarantee the optimal video quality. The simulations showed that the quality of reconstructed video based on the superposition space-time coding algorithm is better than that based on the Alamouti or V-BLAST coding algorithm respectively.3. A joint optimization algorithm for cross layer resource allocation and HQAM modulation in the multiuser OFDMA video system was studied. For the multiuser OFDMA video system, the cross layer resource allocation algorithm was proposed, which took both the video content in the application layer and the wireless channel response in the physical layer into consideration, so as to optimize video transmission performance. Through analyzing the cross layer optimization model and algorithm, the band-width allocation theorem that could minimize the total distortion of video signal was derived, and then the cross layer iterative optimization algorithm which based on the theorem was proposed which could implement the optimal power and sub-carrier resources allocation. Meanwhile, according to the quality of sub-carriers allocated for each user the joint QAM-HQAM modulation algorithm based on sub-carriers categorization was proposed to implement the unequal error protection of video transmission for each user. In the process of cross-layer optimization of video transmission, the joint QAM-HQAM modulation algorithm could choose the modulation parameters reasonably, which can guarantee the improvement of the overall performance of video transmission in multi-user OFDMA system and the robustness of the reconstructed video quality of each user.4. The channel estimation and detection algorithm in the MIMO-OFDM system was studied. Firstly, the OFDM channel estimation algorithm based on the pilot symbol insertion was proposed,which could estimate adjacent sub-carrier response based on the channel estimation of central sub-carrier located in the time-frequency window according to the polynomial-based model. The continuous polynomial estimation was adopted in the algorithm. There will be no loss of high frequency and no frequency leakage, so the algorithm has better performance. Secondly, the sphere decoding algorithm improving the search radius in MIMO system was studied, and then it was combined with EM (Expectation-maximization) iterative algorithm to jointly detect the MIMO-OFDM system. The simulations show that the joint detection algorithm could converge quickly just after few iterations with ideal channel estimation and detection results. |
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