【作者】 刘婷婷；

【导师】 杨维；

【作者基本信息】 北京交通大学 ， 通信与信息系统， 2014， 博士

【摘要】 随着互联网的发展,流媒体业务逐渐增多。视频点播、网络电视、远程会议、远程教育已成为互联网的热门应用。P2P (Peer to Peer,对等端到对等端)技术的产生使互联网的工作模式从以客户端/服务器为代表的集中式走向了分布式,为流媒体应用带来了新的发展空间。与此同时,无线Mesh网络(Wireless Mesh Networks, WMN)和移动通信设备的飞速发展使得人们对P2P流媒体业务的需求由有线网络转移到了无线网络。这种用户需求推动了基于WMN的P2P流媒体技术的发展,而WMN的广泛应用前景也吸引了P2P流媒体技术向无线网络的移植。基于WMN的P2P流媒体系统是P2P流媒体在WMN支撑下的应用层实现,由于WMN网络的特殊性,P2P技术在WMN中面临着许多挑战与问题。例如,由于无线网络终端种类繁多造成的网络异构性问题、P2P覆盖层网络与底层网络的拓扑不匹配问题、无线网络链路干扰问题、无线频谱资源有限问题和缺少系统级实验平台的问题。针对上述研究背景和P2P流媒体技术在WMN环境中遇到的问题,本论文在传统的有线网络P2P流媒体组播技术的基础上,从理论和实验两个方面对WMN中的P2P流媒体组播技术进行了研究。论文的主要研究内容和创新点包括：(1)针对覆盖层网络与底层网络的拓扑不匹配问题和无线网络节点异构性问题,提出了一种无线网络通用的应用层组播成员管理协议。该协议通过采用“闲谈”机制、局部概率择优策略和去中心化管理策略,构造了一个稳定的、无标度的覆盖层网络,实现了组播组成员的动态加入与退出管理。基于复杂网络理论对所提协议进行的数学分析证明了其构造的覆盖层网络是稳定的。仿真结果表明,所提出的协议在一定程度上能缓解拓扑不匹配问题,而且比已有的协议模型更能适应异构无线网络环境。(2)针对无线链路干扰问题,提出了一种低代价最少中继树组播路由算法。该算法由组播树构造算法和信道分配算法两部分组成。组播树构造算法在保证中继节点数目最少的同时尽量选择低代价路径进行数据转发,从而充分利用无线链路的一跳广播属性并且降低了端到端时延。信道分配算法通过扩大干扰优化范围、引入更精确的衡量干扰的参数,优化了已有的信道分配算法,从而减少了链路干扰。算法分析和仿真结果表明,所提出的低代价最少中继树组播路由算法降低了已有组播树算法的时间复杂度和组播树代价,减少了用户时延,提高了系统吞吐量。(3)针对无线频谱资源有限和客户端资源受限问题,提出了一种基于SNR(Signal Noise Ratio,信噪比)反馈的多信道组播调度机制。该机制通过SNR反馈判断信道容量的大小,采用将优先级较高的数据块放在信道容量较大的信道上进行传输的策略,减小了流媒体启动时延和下载时间,提高了信道利用率。仿真结果表明,所提出的调度机制与原有调度机制相比,在用户时延、下载时间和带宽利用率方面的性能都有所提高,但其耗费的缓存空间略大于原有调度机制。经分析,在硬件技术日趋发达的今天,存储空间的获取对用户来讲并不困难。而在存储空间充足的条件下,用户对时间的敏感度明显高于对空间的敏感度,因此用少量空间换取时间的做法是可取的。(4)针对缺少系统实验平台的问题,实际搭建了基于WMN的P2P流媒体系统。为了客观和精确地评估WMN中的P2P流媒体性能,启发与流媒体性能相关的下一步研究,在搭建的系统平台上通过现场实验的方式测试了流媒体编解码方式、编码速率、P2P方式的采用与否、跳数和网络拓扑结构五个因素对流媒体性能的影响。实验结果表明,编码方式、编码速率和网络拓扑都是影响视频质量的重要因素;跳数与视频质量没有必然的联系；P2P技术与WMN结合是可行的,但是采用P2P方式对WMN中流媒体质量的影响有利有弊。实验结果对今后的理论创新和实践部署都具有很好的参考意义。更多还原

【Abstract】 With the development of the Internet, streaming media business gradually increased. Video on Demand (VoD), Internet Protocol Television (IPTV), tele-conferencing and distance learning have become the most popular applications in Internet. P2P (Peer to Peer) technology makes the Internet transferred from a centralized client-server model to a distributed model, which brought new development space for streaming media applications. At the same time, the rapid development of Wireless Mesh Networks (WMN) and mobile communication devices makes the user demand for P2P streaming media transferred from wired network to wireless network. Users’ demand promotes the developments of the WMN-based P2P streaming media technology. Furthermore, the widely application prospects of WMN also attracted P2P streaming media technology into wireless networks.WMN-based P2P streaming system is a P2P streaming application implemented under the support of WMN. Considering the special characteristics of WMN network, P2P technology faces many challenges and problems in the WMN. For example, heterogeneous problem caused by the wide variety of wireless terminals, the mismatching problem between P2P overlay and underlying network, the interference problem among wireless links, the limited radio spectrum resources and lack of system-level experimental platform.For the above background and take the above problems into account, multicast techniques of P2P streaming media in WMN are focused on in this paper. It is based on the traditional multicast techniques of P2P streaming media in wired networks and is studied both from theoretical and experimental aspects. The contributions of this paper are presented as follows:(1) In order to manage the heterogeneous networks efficiently and to solve the mismatching problem between the WMN and its P2P overlay, a membership management protocol for P2P overlay in wireless network is proposed. The proposed protocol combines traditional BA model with gossip scheme. Decentralization and locally probability-preferential attachment are two key mechanisms in the proposed protocol. Through mathematical analysis based on complex network theory, the proposed protocol is proved stable and scale-free. Simulation results show that the proposed protocol solved the topology mismatch problem to some extent and more suitable for heterogeneous network environment than the traditional protocol.(2) Against the interference problem among wirelss links, a Lower-Cost Minimal Relay Tree (LCMRT) algorithm for WMN is proposed in this paper. The algorithm consists of two parts, multicast-tree construction and channel allocation. The multicast-tree construction algorithm selects a lower-cost path for data delivery on the condition of minimal relay nodes which reduces the end-to-end delay. At the same time, a more precise parameter of interference degree is introduced in channel allocation algorithm which decreases the interference between links and improves the system throughput The simulation results show that the LCMRT algorithm performs better than existed algorithm in time complexity, delay and throughput.(3) In order to use the limited radio spectrum resources more efficiently, a multi-channel multicast scheduling mechanism based on SNR (Signal Noise Ratio, SNR) feedback is proposed. The higher-SNR channel has higher-speed, thus the proposed mechanism allocates higher-priority data ito the higher-SNR channel. Simulation results show that through the proposed mechanism users’start-up delay and waiting time are reduced. Moreover, the bandwidth utilization is improved by new mechanism. However, more buffer space is used by the porpose mechanism than existed mechanism. As the development of hardware technology, it is easy for users to obtain disk space. Therefore, it is reasonable to further reduce users’waiting time in the price of a small increase in buffer requirements.(4) In order to evaluate the performance of P2P streaming media in WMN more precisely and objectivly, the system-level experimental platform of P2P streaming based on WMN is deployed in this paper. Through field experiments five factors are tested. They are the encoding rate, the encoding mode, with P2P methods or not, hops and topology despectively. Different network performance and video quality under the five factors are experimented.The experimental results show that the encoding rate, encoding mode and network topology are important factors affecting the video quality. However, hops and video quality are not related with each other directly. Combining P2P technology with WMN is feasible but there are both advanteges and disadvantages. The results are worth referencing both in theory and practice for future research.更多还原