| Summary: | 博士 === 國立成功大學 === 電腦與通信工程研究所 === 102 === Because transmission resources are limited in WiMAX networks, Adaptive Modulation and Coding (AMC) is employed to utilize transmission resources efficiently. However, when AMC is employed in video multicast, a tradeoff exists between the video quality and the bandwidth utilization efficiency. Because video quality is very important for video multicast, the most robust modulation scheme is conventionally employed to ensure that all SSs are able to acquire full video quality without regard to bandwidth utilization efficiency. Non-adaptive multicast is proposed to improve the bandwidth utilization efficiency, but it decides modulation scheme in accordance with the importance of the data without regard to network status and thus a sub-optimal transmission performance is obtained.
In this dissertation, a scheme, called Performance-Driven Robust Video Multicast (PDRVM), is proposed to address these problems. PDRVM combines adaptive multicast and Forward Error Correction (FEC). In PDRVM, the BS would classify all video traffic into several types of traffic with different levels of importance and then adaptively decide modulation scheme and FEC ratio based on network status. To acquire these parameters, the video quality and bandwidth utilization efficiency are analyzed mathematically. MyEvalvid_RTP is used to verify the mathematical analyses and evaluate the performance of PDRVM. From results, it is shown that the mathematical analyses are very precise and PDRVM is able to improve bandwidth utilization efficiency as much as possible while the average video quality is good simultaneously for video multicast over WiMAX networks.
To avoid traffic collision and utilize transmission resources efficiently, WiMAX employs request-grant scheme to allocate transmission resources. Some studies propose the number of BR slots without regard to the utilization efficiency of the BR slots and result in low bandwidth utilization efficiency. When it comes to the number of BR slots, studies usually assume that each SS has only one connection. It is unrealistic over WiMAX networks. To address the problems, Efficiency-Driven Selection of Bandwidth Request (EDSBR) is proposed in this dissertation. The number of active connections is analyzed based on ON-OFF model. Then EDSBR would select the mechanism to request bandwidth and the number of BR slots adaptively in accordance with the mathematical analysis. Simulations are conducted to verify the analysis and evaluate the performance of EDSBR. From results, it is shown that the mathematical analysis is precise and EDSBR is able to improve the utilization efficiency of the BR slots.
In this dissertation, two schemes are proposed to improve the bandwidth utilization efficiency in WiMAX. By these two schemes, WiMAX network is able to utilize transmission resources efficiently and thus each WiMAX network is able to serve more SSs.
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