【作者】 王超辉；

【导师】 李玉宏；

【作者基本信息】 北京邮电大学 ， 计算机科学与技术， 2010， 硕士

【摘要】 随着无线传输技术、多媒体技术以及移动终端技术的持续发展,移动终端用户对多媒体视频的需求越来越迫切。但由于无线网络带宽的限制以及移动终端设备本身的性能限制,移动终端上的多媒体业务还不能大面积推广普及。本文设计并实现了一个无线局域网(WLAN)中面向移动终端的多媒体广播系统MTG。如何在带宽有限的无线网络中为移动终端提供合适的多媒体数据流并保证移动终端设备能够流畅、清晰地播放这些多媒体数据流是本论文的重点。MTG (Multimedia Transcoding Gateway)系统能够向移动终端设备提供适合的多媒体数据流。它通过将移动广播电视的多媒体数据进行适当的码流转换处理,把原先不适合为移动终端传输的MPEG2-TS格式的多媒体数据流转换成适合为移动终端传输的MPEG4格式的多媒体数据流。这样既节省了无线网络的传输带宽,又能满足移动终端设备自身的性能要求。试验结果表明MTG能很好地向移动终端(Nokia N800)提供多媒体业务。此外,由于无线传输信道的不可靠性,加之广播传输方式的无反馈特性,使得WLAN中采用广播方式传输的多媒体数据存在很大的丢包率。为了解决该问题,本论文提出了一个基于三层架构的无线广播优化方案。仿真实验结果表明采用三层架构优化方案的无线多媒体广播传输方式极大地降低了无线环境下广播业务的丢包率。更多还原

【Abstract】 With the constant development of wireless transmission technologies, multimedia technologies and mobile devices, it becomes more and more important to provide multimedia streams to mobile devices.However, due to the limitation of the bandwidth of wireless networks and the capability of mobile devices, multimedia service has not been widely used for mobile devices.A MTG system has been designed and developed in this thesis, which can provide multimedia broadcasting service to intelligent mobile terminals in WLAN.How to provide appropriate multimedia streams to mobile devices, and to ensure the multimedia streams be displayed smoothly and fluently in mobile devices are the focus of the work in this thesis.The proposed MTG (Multimedia Transcoding Gateway) system can provide appropriate multimedia streams to mobile devices.It transcodes the multimedia streams encoded in MPEG2-TS,which is used in the mobile broadcasting TV and not suitable for receiving by mobile devices, to MPEG4, which is more suitable for transmission in WLAN and receiving by mobile devices.Test results show that the implemented MTG system works well for intelligent mobile devices (Nokia N800).Moreover, because of the unreliability of wireless transmissions,and the no feedback features of broadcasting, the packet loss rate is very high, which somewhat affects the user’s experience for using the multimedia service. To solve this problem, we provide a new Radio Optimization Scheme based on three-layer architecture. The simulation results show that the performance of the multimedia transmission using the proposed scheme becomes much better than using the original mechanism. The packet loss rate decreases a lot and the throughput of the data increases.更多还原