| With the rapid development of wireless networks, wireless video applications become increasingly popular. However, because wireless channel resources are limited in the characteristics of time-varying, how to measure the decline of video quality timely and accurately, as well as to adopt the necessary ways to maintain and enhance the users'quality of experience (QoE), is a complex and urgent problem.This paper focuses on the theory and simulation about the objective evaluation of video quality, the mapping relations of QoE and QoS and optimization of WLAN video transmission quality. And it makes original contribution in the following five aspects:(1) A no-reference video quality assessment algorithm based on the wavelet transform is proposed. When there is no video source to contrast, the motion intensity and single-frame image quality are chosen as the video-quality evaluation parameters, using temporal and spatial correlation properties among the video sequences. Firstly, the motion intensity is quantitatively described and the frame of intense movement is chosen as the key frame. Then the key frame is performed wavelet transformation, and the frame of image quality is calculated by detecting the changes in statistical characteristics of wavelet coefficients. Finally video quality is obtained by summing the weighted quality of all of key frames. Experiment results show that the proposed quality assessment algorithm can well evaluate the clarity and fluency of video sequences. (2) The sub-mapping models of QoE and QoS video services are proposed. The relationship between the QoE and QoS is quantitative studied by experimental and theoretical methods, after quantitatively analyzing. The main factors affecting QoE and its variation rules are acquired by setting up a test environment and doing a correlative analysis. Finally, the sub-mapping models of QoE and QoS are proposed by multivariate non-linear regression analysis. Experiments show that the proposed mapping model has better fitness.(3) A two-dimensional Markov model which fits a non-saturated load condition is proposed. Average delay and throughput of Media Access Control (MAC) protocol are calculated and analyzed under arbitrary load condition. The results show that the performances of WLAN under non-saturated conditions are much better than those under saturated, and WLAN is capable of supporting QoS in statistical extent.(4) An adaptive retransmission algorithm jointing application layer and link layer is proposed, using the lost package got from M/M/1/K queueing model, which analyzes the overflow of the sending queue on MAC level, and the performance statistical parameters of WLAN calculated. Simulation results show that the cross-layer design in this paper can better improve the video quality.(5) In view of the shortage of the Enhanced adaptive FEC algorithm (EAFEC) based on the queue length of access point (AP) and the retransmission times, proposed by Lin etc., there are two improvements:importing the weight to assign the impact of the queue length and the retransmission times, which takes into account the congestion control and error control to some extent; importing Unequal Error Protection (UEP), which means adopting different control intensity on I frame, P frame and B frame, so as to use the wireless resource efficiently as well as to improve the video quality. Simulation results show that the improved algorithm has achieved the desired result, which can get the better quality of video transmission, as well as reduced the complexity of algorithm and improved the utilization of the wireless resources.
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