基于信道协同扫描技术的WiFi网络MAC层切换机制

发布时间：2018-01-06 20:26

本文关键词：基于信道协同扫描技术的WiFi网络MAC层切换机制　出处：《长安大学》2016年硕士论文　论文类型：学位论文

【摘要】：基于IEEE802.11系列标准的无线wifi技术已经广泛应用于无线局域网的接入服务,各大运营商在全国多个城市提出开展”无线城市”计划,将无线局域网与其他移动通信网络GPRS、3G、LTE等网络融合,为整个城市提供随时随地随需的无线网络接入服务。由于无线访问接入点(Access Point,AP)的信号发射功率比较有限,其覆盖范围受到限制。移动终端(Mobile Terminal,MT)需要在多个AP之间切换,而切换过程中所带来的较大的切换时延将显著地影响诸如VoIP之类的实时性服务的质量。本文主要针对大规模部署的无线WiFi网络在用户密集时MT切换引发的服务质量下降问题开展研究,通过引入辅助节点协同扫描可用信道,降低切换时延,提高终端在多AP切换环境下的连接可靠性与实时性。本文所作的主要研究工作如下:(1)分析了MT在MAC层的切换过程及其时延成因,对其中最耗时的探测扫描阶段的时延产生及改善机理进行了研究,提出了基于信道协同扫描技术的WiFi网络MAC层切换方法并对其流程进行了描述;(2)在MT启动MAC层切换过程之前,设计了采用接入AP的信号强度阀值触发的预扫描过程,针对实际场景中可用辅助扫描节点的不确定性,提出了距离优先的辅助节点选择算法;(3)同时,对于扫描过程中的邻道干扰问题,提出了选择性并行信道协同扫描算法,该算法在进行分布式探测的同时,利用MT收集辅助节点响应的AP信息,实现了切换辅助信息的高效收集;(4)为进一步提高MT在历史AP间的切换速度,提出了一种使用最近AP列表高速缓存的方案。该方案能有效避免较短时间间隔内重复扫描次数,减少扫描时延。通过NS-2仿真软件部署大量的移动节点,在引入信道协同扫描等算法的基础上对WiFi网络中的切换进行了测试。实验结果表明,本文所提切换方案能够有效减少切换时延,改善诸如VoIP、视频流传输等实时应用的服务质量。
[Abstract]:Wireless wifi technology based on IEEE802.11 series standards has been widely used in wireless local area network access services, the major operators in many cities in the country to carry out the "wireless city" program. The wireless local area network (WLAN) is integrated with other mobile communication networks, such as GPRSU 3G / LTE and so on. The wireless network access service is provided to the whole city at anytime, anywhere, anytime. Because of the limited signal transmitting power of the wireless access point (access Point APs). Its coverage is limited. Mobile terminal terminal MTT needs to switch between multiple APs. However, the large handoff delay will significantly affect the quality of real-time service such as VoIP. This paper focuses on MT cutting of large-scale deployed wireless WiFi networks when users are dense. The problem of service quality decline caused by exchange is studied. By introducing auxiliary nodes to co-scan the available channels, the handoff delay can be reduced. The main research work in this paper is as follows: 1) analyze the switching process of MT in MAC layer and the cause of delay. In this paper, the delay generation and improvement mechanism of the most time-consuming detection scanning phase is studied, and the MAC layer handoff method based on channel cooperative scanning technology is proposed and its flow is described. Before MT starts the switching process of MAC layer, the pre-scanning process which is triggered by the signal intensity threshold of AP is designed, aiming at the uncertainty of the available auxiliary scanning nodes in the actual scene. A distance first auxiliary node selection algorithm is proposed. At the same time, a selective parallel channel cooperative scanning algorithm is proposed to solve the problem of adjacent channel interference in the scanning process, which performs distributed detection at the same time. The AP information of the auxiliary node response is collected by using MT, which realizes the efficient collection of the switching auxiliary information. In order to further improve the switching speed of MT between historical APs, a scheme using the most recent AP list cache is proposed, which can effectively avoid repeated scanning times in short time intervals. A large number of mobile nodes are deployed through NS-2 simulation software, and the handoff in WiFi network is tested on the basis of introducing channel cooperative scanning algorithm. The experimental results show that. The proposed handoff scheme can effectively reduce the handoff delay and improve the quality of service for real-time applications such as VoIP video stream transmission and so on.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TN92

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