【作者】 范震；

【导师】 杨宗凯；

【作者基本信息】 华中科技大学 ， 通信与信息系统， 2004， 硕士

【摘要】 无线自组织(Ad hoc)网络是一种无须固定通信设施支持的新型无线网络,具有很高的可靠性和灵活性。它可以广泛应用于紧急的和不易建设固定通信设施的环境中,如野战通信、紧急搜救、临时会议等。近年来随着多媒体应用的普及和Ad hoc网络在商业应用的进展,在Ad hoc网络上提供必要的服务质量(QoS)保证显得越来越重要。但是因为Ad hoc网络自身的特点,比如其网络资源极其有限、信道共享、网络拓扑结构动态变化以及信道通信质量很差,导致在这种网络下提供端到端的服务质量保证十分困难。这就需要综合研究QoS模型设计、资源预留信令机制、QoS路由、网络层队列管理和QoS媒体接入控制,所以目前研究进展缓慢。本文着重研究如何在Ad hoc网络的动态环境和有限的带宽情况下提供端到端的服务质量保证的问题。以支持多媒体业务为目标,分别对媒体接入QoS机制,网络层QoS机制,传输层QoS机制进行了性能分析比较,系统地研究了这些QoS机制的设计及系统配置问题,并提出了一些新颖的改进方案。首先,详细介绍了区分服务机制,并研究了其关键机制RIO(RED with IN/OUT)的参数设置问题。从仿真角度详尽分析了RIO参数设置对确保服务质量的影响。实验结果为下一步将RIO机制和区分服务机制应用到Ad hoc网络打下了坚实的基础。接着,系统分析比较了不同Ad hoc网络环境下媒体接入层和网络层QoS机制的性能,并得到了很有意义的研究结论。然后,着重建模分析了双窗口TCP协议的性能,并通过大量仿真实验验证了模型的正确性。由于双窗口TCP对于提高区分服务网络中确保服务的带宽保证和公平性十分有效,希望能够充分理解解它的特点、性能和基本思想,进而在以后的工作中设计出新的适合Ad hoc网络特点的传输层协议。最后,对Ad hoc网络上采用TFRC(TCP Friendly Rate Control)协议传输多媒体业务的性能进行了分析。通过大量的仿真试验揭示了TFRC在无线网络上存在的问题,并对产生这些问题的原因进行了分析。而且参考现有TCP改进思路,利用断路信息反馈机制,提出了改进TFRC的初步方案。更多还原

【Abstract】 A mobile Ad hoc wireless network is a new kind of wireless networks which has no infrastructure. It has high reliability and flexibility. Consequently, they are widely used in some emergent application environments or when the wired network is not available, such as battlefield communications, disaster recovery, occasional conferences, etc. In recent years, multimedia applications are more and more popular, and Ad hoc networks are widely used in commercial environments. So, it is crucial for Ad hoc networks to support Quality-of-Service. However, some distinct characters of Ad hoc networks, such as the constrained bandwidth, shared channel, dynamic topology and poor link quality, make it very difficult. Then, many elements should be investigated, including QoS architectures, QoS resource reservation signaling, QoS routing and QoS medium access control. As a result, the research on this subject is very slow.This thesis researches on how to provide the QoS in Ad hoc wireless networks where the topology is dynamic and the bandwidth is constrained. Towards to providing QoS, the work investigates several mechanisms design and setting, such as media access control, transmission and congestion control. And some original schemes are propposed.First, the Differentiated Services network is introduced, and the key component in the Differentiated Services networks, RIO queue management scheme, is investigated. The impact of setting and configurations of RIO parameters on the performance of Assurance Services is analyzed through a number of network simulations. Simulations results are helpful for future research to apply RIO and the Differentiated Services mechanisms to Ad hoc networks.Second, two major classes of QoS schemes for Ad hoc networks in MAC layer and network layer are compared respectively. Based on the observations, a new hybrid scheme is proposed, which is able to support QoS of real-time applications. Third, an analytical model is developed to calculate the throughput achieved by individual Two-windows TCP flows. Extensive simulations validate the model. Since the Two-windows TCP is effective on solving the bandwidth guarantee and fairness issues, it is possible that a new protocol of transport layer in Ad hoc networks could be designed based on the idea of Two-windows TCP. <WP=5>Last, the performance of TFRC in Ad hoc networks is investigated. Through a number of network simulations, the problems of TFRC used in Ad hoc networks are shown. Subsequently, the reasons are analyzed. Furthermore, the revised TFRC is proposed according to the revised TCP and by use of the open circuit feedback mechanism.更多还原