【作者】 刘娟；

【导师】 龚向阳；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2013， 硕士

【摘要】 随着信息技术的不断发展,人们对各种多媒体业务的需求也在不断提高,多媒体数据流量在未来网络总流量中将占据越来越重的比例。人们期望获得更快速,更流畅,更高质量的媒体服务体验,如何满足这一需求成为当今流媒体技术的一大难点。DASH (HTTP动态自适应流媒体)技术是近年来新兴的流媒体技术。相比于传统RTP/RTSP流媒体技术来说,它具备提供可靠传输,易于部署等诸多优点,因此引起各界广泛关注,并有望成为下一代流媒体技术中的主力军。目前对DASH的研究主要集中在针对单用户有线网络场景下客户端侧自适应机制的性能分析和优化方面,然而对无线多用户场景下DASH的性能研究和优化对DASH未来的广泛部署具有巨大意义。因此,本文主要对无线多用户场景下DASH的性能进行研究分析,同时针对此场景下存在的不公平性,不稳定性等问题提出并实现优化方案。本文首先介绍本研究中涉及的相关技术。对DASH技术的主要标准,3GP-DASH和MPEG-DASH进行了简单介绍,概括性地描述了DASH机制和主要技术特点,对当前DASH技术研究现状进行分类总结,并展望DASH技术的未来研究方向。简述QualNet仿真平台和DASHEncoder媒体处理工具的功能及特点。其次,针对DASH多终端场景,本文分别分析了该场景下DASH存在的四个问题：不公平性问题,不稳定性问题,带宽利用不充分问题和无区分用户优先级问题。针对各个问题,依次阐述问题产生的原因。结合这些分析,本文提出了DASH集中控制码率决策优化方案,引入了DASH效用函数,不公平性指数和不稳定性指数概念用于决策方法和性能评估,同时提出了一种新的集中码率选择算法。该算法使用用户请求媒体分片码率,用户签约等级,实时网络拥塞等级,DASH效用等参数对用户请求媒体分片码率进行集中控制决策,实现对DASH业务公平性和稳定性性能的平衡,同时也确保不同签约等级用户获得相应的媒体质量体验,优化了客户端码率自适应决策。再次,本文在QualNet仿真平台中设计并实现了DASH系统,该系统由DASH服务器,DASH客户端和DASH控制器(DASH Controller)三部分组成,然后在LTE仿真网络中对优化方案性能进行验证和分析。论文的最后总结本工作中存在的不足及下一步可能的完善方向,并列举了本人在攻读硕士研究生期间完成的工作和取得的成果。更多还原

【Abstract】 With the continuous development of information technology, people’s demand for multimedia services is constantly improved. The media streaming traffic will occupy an increasing weight ratio in future network. People expect to get faster, smoother, higher quality media experience, so how to meet this demand becomes a major difficulty of today’s streaming technology.DASH (Dynamic Adaptive Streaming over HTTP) technology is an emerging streaming media technology in recent years. Compared to traditional RTP/RTSP streaming media technology, it has many advantages, e.g. it provides reliable transmission, and it is easy to deploy. Therefore it attracts wide attention and it is expected to become the main force in next generation streaming technology. Currently DASH’s research focuses on the performance analysis and optimization of the client side adaptive mechanism under single-user wired network scenarios. However, studying and optimizing the DASH performance under wireless multi-user scenarios has great meaning to DASH disposition in the future. Therefore, this paper studies and analyzes the DASH performances under wireless multi-user scenarios and proposes optimization scheme to solve the problem of unfairness, instability.This paper firstly introduces the technology involved in the study, briefly summarize the main DASH technology standards, which include3GP-DASH and MPEG-DASH. Then it describes the DASH mechanism and its main technical characteristics. It summarizes the current DASH technical research and prospects the DASH technology directions in future research. It also describes the functions and features of the the QualNet simulation platform and the media processing tool DASHEncoder.Secondly, for the DASH multi-terminal scenes, this paper analyzes the four issues of the DASH performance:unfair issue, instability issue, inadequate bandwidth utilization issue and without distinction user priority issues. For each issue, it analyzes the causes. Combined with the description and analysis, the paper proposes a DASH centralized bitrate-control decision optimization scheme. The scheme introduces the concept of DASH utility function, unfairness index and instability index to the decision-making methods.In the scheme, it uses a new centralized bitrates selection algorithm. The algorithm makes decision of the next segment’s bitrates through a combination of user requests’segment bitrate, user’s subscription level, real-time network congestion level and DASH utility. It can not only achieve a balance between fairness and stability performance of the DASH service, but also ensure that the different subscription level users can get different levels of media quality experience.Again, the paper designs and implements the whole DASH system on QualNet simulation platform.The system consists of the DASH server,DASH client and DASH Controller.Then we verify and analyze the optimization scheme in LTE network.The paper summarizes the shortcomings concluded in this work and the next step may be to improve them. In the last, it cites the work I completed during graduate study and the results achieved.更多还原