A Study Of OFDM Wireless Transmission Technology On Improving The Quality Of Video Communication

With the increasing of the requirement for the video services in the wirelessnetworks, the inherent nature of the video services and the characteristics of the wirelesschannels determined that transmission high quality of video services over the wirelesschannel are bounded to face huge technical challenges. How to improve the quality ofthe video services in wireless environment has became an urgent problem in theresearch of wireless video communications. This dissertation is mainly concerned withthe design and implementation of various transmission schemes to improve the qualityof video services in the OFDM-based wireless transmission systems. The authors’ majorcontributions are outlined as follows:1. An unequal error protection (UEP) method for video transmission using adaptivehierarchical quadrature amplitude modulation (HQAM) is proposed to reduce theimpact of frequency-selective fading and the time-varying nature of wireless channels.Firstly, the video streams are divided into substreams with unequal priorities. Then, theHQAM modulation parameters of each subcarrier are adaptively determined based onthe channel quality of each subcarrier and the upper limit of the bit error rate of thesubstreams with unequal priorities. Finally, UEP is implemented via modulating videostreams onto subcarriers with different channel quality. Simulation results show that theproposed adaptive HQAM method reduces the impact of frequency-selective fading andthe time-varying nature of the wireless channels and improves the quality of thereconstructed video by an average of1dB compared with HQAM-based methods.2. For band-limited wireless video transmission systems with multi-subcarriers, anovel UEP strategy for video transmission over the wireless channel by using HQAM isproposed. Firstly, all the subcarriers available are divided into different classes based ontheir channel quality, and then the HQAM modulation parameters are determinedaccording to the channel quality of those subcarriers and the important of different partsof the video bitstream to the reconstructed video. The UEP of the video bitstream isimplemented by modulating different parts in the video stream to subcarriers withunequal HQAM parameters. Experimental results demonstrate that compared with thereported methods, the proposed method effectively improves the quality of thereconstructed video.3. The problem of packet scheduling and resource allocation for OFDMA wirelessvideo transmission is studied. The problem is first formulated as an optimizationproblem with the objective of minimizing the reconstructed video distortion of each user under the radio resource constraints. In order solve the optimization problem, across-layer optimization algorithm is proposed by taking the radio resource constraintsinto account. Simulation results shows that the proposed cross-layer algorithmoutperforms the state-of art packet scheduling and resource allocation algorithms by upto3dB in terms of the quality of the reconstructed video.4. Fairness across multi-user with different channel quality in the OFDMA wirelesstransmission system is an important issue during the packet scheduling and wirelessresource allocation. In order to maintain the fairness among users in the same cell, across-layer optimization algorithm is proposed by taking the radio resource constraintsand the fairness across multi-user into account. The situation that those subcarriers wthhigher channel quality are all taken up by users with better channel quality is avoided tomaintain the fairness. Simulation results show that the proposed cross-layer algorithmoutperforms the state-of-the-art packet scheduling and resource allocation whilemaintain the fairness across multi-users.