【作者】 陈瑜坤；

【导师】 郭更生；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2008， 硕士

【摘要】 近年来,无线局域网(WLAN)的应用越来越广泛,人们对其需求也越来越多。WLAN以其安装便捷,使用灵活等优势,获得了人们的青睐。WLAN所承载的业务也覆盖了从标准互联网业务到实时业务的范围。因此,WLAN的服务质量(QoS)问题成了研究的热点。为了支持WLAN中不同业务QoS的不同要求,IEEE工作组推出了802.11e协议来增强WLAN的QoS性能。这个协议提供了MAC层的区分服务机制,主要针对家庭与企业环境提供服务质量与多媒体通讯,包括实时与非实时的语音、视频、数据等服务。本文详细介绍了802.11e协议,并通过OPNET仿真来分析和论证其区分服务的机制,以及各种QoS参数的作用。虽然802.11e协议可以为WLAN中的业务提供QoS区分保障,为语音视频等业务提供高优先级,但是WLAN的QoS问题仍然面对许多困难和挑战。WLAN的QoS保障需要一个全面复合的体系,而不仅仅是MAC机制的设计。本文综述了WLAN的QoS问题面临的挑战,提出了它们对QoS的影响,并且调查和总结了当前存在的相关技术和解决方案。WLAN的QoS问题主要体现在三个方面:网络时变性处理,业务配置自适应和链路资源管理。其中,在链路资源管理方面,主要的解决方案集中在MAC资源管理,接入控制,以及无线接入点选择。无线接入点选择机制的主旨是通过网络的负载均衡来最大限度的利用链路资源,从而提高OoS。在WLAN的扩展服务集模式下,当节点有多个无线接入点可选时,这个机制显得尤为重要。目前,802.11e协议中并没有相关定义,研究和工程上所采用的机制是基于网络信噪比(SNR)的。基于SNR的无线接入点选择算法不能有效地平衡网络负载,显然无法满足WLAN的QoS需求。本文主要从这一点着手,研究了现有的机制和算法,并提出了一种新的无线接入点选择算法。本算法采用了主动扫描的方式,以网络的上下行时延作为衡量负载和接入点选择的主要参数。最后,本文采用OPNET仿真工具实现提出的新算法,并将其与传统的基于SNR的算法相比较。在同种业务量情况下,新算法可以达到更大的网络吞吐量和更低的时延。结果证明,在保障了语音,视频等业务QoS需求的同时,使用新算法可以获得更大的网络吞吐量。更多还原

【Abstract】 Recently, there has been a growing interest in the use of WLAN technology. WLAN attracts more and more customer because of its easy deployment, flexibility and so on. Examples of application range from standard Internet services, such as Web access, to real-time services with strict latency/throughput requirements, such as multimedia video and voice over IP. So the QoS became one of the most popular research topics.In order to support diverse application requirements, a new standard called IEEE 802.11e is proposed to improve QoS in WLAN networks. This standard provided differentiation mechanisms at the medium access control (MAC) layer, focusing on the QoS requirement of multimedia communication of family and office environment, such as voice, video and data services. In this article, 802.11e standard is described, and its differentiation mechanism, QoS parameters are analyzed and evaluated through OPNET simulation.However, although 802.11e provided WLAN QoS differentiation and endurance, gave high priority to voice and video services, there are a few remaining challenges that need to be addressed in order to enable comprehensive QoS support using 802.11e. Only MAC scheme design is not enough.In this article we provide an overview of a few of these challenges, describe their possible impact on QoS, and provide a survey of techniques that potentially could be used to address the identified challenges. There are three mains aspect: handling time-varying network conditions, adapting to varying application profiles, and managing link layer resources. In the third aspect, solutions mainly focus on MAC resource management, admission control and wireless access point selection. The purpose of wireless access point (AP) selection is to maximize the link resource using efficiency through load balancing. When there are several BSSs in WLAN network, this scheme is particularly important, for there are several access points available for one node. Till now, 802.11e do not define such scheme, what we use in research or industry is the scheme based on signal to noise ratio (SNR). The scheme do not consider load balancing of the network, so can not guarantee QoS. This article focused on AP selection scheme, did a survey of current research and proposed a new AP selection algorithm. This algorithm uses active scan pattern and use the network delay as main parameter of load measurement and AP selection.At last, this article implemented the proposed algorithm and original SNR based algorithm using the simulation tool OPNET. With the same load, the proposed algorithm can achieve larger throughput and lower network delay. The results show that the new algorithm can achieve larger throughput while ensuring the QoS requirement of voice and video services.更多还原