面向VoIP服务质量的无线网络关键技术的研究及应用

发布时间：2018-05-06 10:45

本文选题：无线局域网 + VoIP　；参考：《北京交通大学》2016年博士论文

【摘要】：随着IEEE 802.11无线网络的广泛部署,越来越多的无线应用和服务出现了。IP承载语音技术(VoIP)是以分组形式传输的实时语音业务,它利用了互联网的特点,可以提供多元化的语音服务,并且易于开发和部署,所以在无线网络中的VoIP应用服务具有一定的商业潜力。虽然VoIP在有线网络里已经是很成熟的技术,但是在无线网络里又有了新的挑战。为了支持VoIP业务的服务质量,本文围绕无线局域网在承载VoIP业务时存在的三大问题,切换、容量、呼叫准入控制,展开了详细的研究工作。无线网络中的切换问题是由语音用户的移动性引起的。当语音用户在无线接入点之间移动时会发生切换,在切换的过程中会发生数据连接中断而产生切换时延。当切换时延过大时会影响VoIP的服务质量,本文分析了产生切换时延的原因和影响因素。为了减少切换时延对VoIP业务的影响,本文提出了一个基于预扫描的快速切换算法,该算法能预先扫描选择下跳接入点,比原始的切换方法能减少切换时延。在此基础上,本文又提出了一个基于行为预测的快速切换算法。该算法将接入点信息以切换序列的方式存放在缓存中,通过使用马尔科夫过程模型和指数加权移动平均模型对移动站点的下跳接入点进行预测,使得移动站点可以切换到其行为路径上的接入点,避免短时切换。该算法能在降低切换时延来满足VoIP时延要求的同时,减少不必要的短时切换,对有移动规律的站点能准确预测其移动路径上的接入点。无线网络中的语音容量是在搭建VoIP系统时的一个重要指标,本文对语音业务的容量进行了分析,分别在固定比特率语音流、可变比特率语音流、隐藏终端模式下和网络重传情况下等四个方面分析了无线局域网的语音容量,提出了容量分析模型,并分析了影响语音容量的因素。无线网络中上下行的流量不平衡导致语音容量有限,虽然IEEE 802.11e协议对实时业务提供了服务质量的支持,但并没有提出改进容量的方法,因此本文对增强分布式信道接入模式下的语音容量做了分析与优化。本文提出了基于时延约束和丢包率约束的容量优化分析模型,通过设定不同的最小竞争窗口、仲裁帧间间隔和发送机会限制来区分接入点和站点,使得接入点更易获取信道来发送数据,缓解了接入点处的瓶颈压力从而增加了语音容量。无线网络中的呼叫准入控制是保障VoIP服务质量的有效方法,本文提出了一个基于资源动态调整的呼叫准入策略。当网络资源紧张时,通过加大语音终端的组包间隔来降低当前语音呼叫的QoS等级,为新建呼叫或切换通话提供接入的资源;当有资源空闲时,通过降低语音终端的组包间隔来提高当前语音呼叫的QoS等级,提高网络带宽的利用率。该呼叫准入控制策略能在有效的使用信道资源的同时,提升语音容量,并支持切换通话的接入。最后结合实际的工程项目,本文提出了一个基于无线网络VoIP技术的铁路货运调度电话系统,研究设计了系统的网络架构和功能架构,在货运铁路实验线上部署了电话系统,通过实验分析了系统的性能,验证了在铁路货运调度电话中使用VoIP技术的可行性。
[Abstract]:With the wide deployment of the IEEE 802.11 wireless network, more and more wireless applications and services have emerged the.IP bearer voice technology (VoIP) is a real-time voice service that is transmitted in packet form. It uses the features of the Internet to provide multiple voice services, and is easy to develop and deploy, so the VoIP application in the wireless network is applied. It has a certain commercial potential. Although VoIP has been a mature technology in the wired network, there are new challenges in the wireless network. In order to support the service quality of the VoIP service, this paper focuses on the three major problems, switching, capacity and call access control of the wireless LAN in the VoIP service. The handover problem in the wireless network is caused by the mobility of the voice user. When the voice user moves between the wireless access points, the switching delay occurs during the handover. When the switching delay is too large, the quality of the VoIP service will be affected. The handoff delay is analyzed in this paper. In order to reduce the impact of handoff delay on the VoIP service, a fast switching algorithm based on pre scan is proposed in this paper. This algorithm can scan the hop access point in advance and reduce the handoff delay than the original handoff method. On this basis, a fast algorithm based on behavior prediction is proposed in this paper. By using the Markov process model and the exponential weighted moving average model, the algorithm uses the Markov process model and the exponential weighted moving average model to predict the down hop access point of the mobile site, so that the mobile site can switch to the access point on its behavior path and avoid short time switching. This algorithm can reduce the handover. Time delay satisfies the requirement of VoIP time delay and reduces unnecessary short time handover. It can accurately predict the access point on the mobile path. The voice capacity in the wireless network is an important index in building a VoIP system. The volume of speech service is analyzed in this paper, at fixed bit rate speech, respectively. Flow, variable bit rate speech flow, hidden terminal mode and network retransmission condition are analyzed in four aspects of the voice capacity of WLAN. A capacity analysis model is proposed, and the factors that affect the voice capacity are analyzed. The up and down flow unbalance in the wireless network leads to the limited voice capacity, although the IEEE 802.11e protocol is real time The service provides the support of quality of service, but there is no method to improve the capacity. Therefore, this paper analyzes and optimizes the voice capacity of the enhanced distributed channel access mode. This paper proposes a capacity optimization analysis model based on time delay constraint and packet loss rate constraints, through setting different minimum competitive windows, interframe interframe between arbitral frames. Isolation and transmission opportunities are limited to distinguish access points and sites, making access points easier to obtain channels to send data, alleviate bottleneck pressure at access points and increase voice capacity. Call admission control in wireless networks is an effective way to guarantee VoIP service quality. This paper proposes a call alignment based on resource dynamic adjustment. When the network resources are tense, the QoS level of the current voice call is reduced by increasing the group compartment of the voice terminal to provide the resources for the new call or the switching of the call. When the resources are idle, the QoS level of the current voice call is improved and the utilization rate of the network bandwidth is improved by reducing the group compartment of the voice terminal. The call admission control strategy can improve the voice capacity while using the channel resources effectively, and support the switching of the call access. Finally, a railway freight dispatching telephone system based on the wireless network VoIP technology is proposed in this paper. The telephone system is deployed on the railway experimental line. The performance of the system is analyzed through experiments, and the feasibility of using VoIP technology in railway freight dispatching telephone is verified.

【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN916.5;TN92

【相似文献】