【作者】 王佳京；

【导师】 张文军；

【作者基本信息】 上海交通大学 ， 通信与信息系统， 2008， 硕士

【摘要】 IEEE 802.16e移动宽带无线接入标准的出现推进了多媒体业务与无线移动融合,也引发了对于移动宽带无线接入技术问题的思考,其中包括小区切换问题。移动用户的日益增加,大量高速多媒体数据业务的出现都对WiMAX系统容量提出挑战。如何设计合理的切换方案,引导移动用户及时并智能地进行WiMAX小区切换成为一项值得研究的课题。针对这一问题,本文提出了一种新型的基于容量估计和邻居广播技术的WiMAX切换方案,该方案适用于多WiMAX小区覆盖的网络场景,在移动用户数多,数据流量大的易拥塞网络环境下,该方案具有比较明显的网络优化作用。根据研究过程,本文首先对WiMAX协议标准以及现有的小区切换方案中的算法、策略、控制模式以及切换技术做了基础研究和介绍。在各小区切换方案中,本文深入研究了适用于移动WiMAX网络的802.16g快速切换技术,对该技术的系统性能进行了理论分析和网络仿真验证,并得到结论,即快速切换技术能够降低切换丢包率,但并不能有效解决网络拥塞环境造成的持续丢包问题,具有一定局限性。通过总结现有小区切换方案与WiMAX网络特性相结合的难点与问题,本文随之提出新型的基于容量的小区切换方案。其中的创新点包括:方案基于WiMAX小区容量估计和邻居广播技术,以小区有效空闲容量为策略触发切换,从而达到基站间流量均衡;方案系统模型中根据IEEE 802.16标准中OFDM物理层定义提出了一种准确估算WiMAX基站有效容量的理论公式;方案同时设计了一项原创的全局切换概率参数,能够简单有效地控制小区切换问题中的“切换同步效应”。本文研究工作量中一个重要部分在于实现移动WiMAX网络小区切换的仿真。由于NS-2仿真软件本身不提供WiMAX网络和WiMAX小区切换的支持,研究过程中对NS-2和NIST移动扩展包的数据结构进行了深入研究,并通过修改不同类文件中的大量源代码构架了NS-2下支持WiMAX小区切换的仿真环境,实现了本文提出的切换方案。通过对提出的切换方案进行仿真,证实该方案可以有效降低网络拥塞,快速显著地提升系统吞吐量。更多还原

【Abstract】 The elaboration of IEEE 802.16e specification for mobile broadband wireless access has driven the convergence of multimedia service and mobile wireless technology, but has also arise discussions on issues surrounding mobile BWA technology, among which stands out the handover problem. With the increasing number of mobile subscribers and myriad type of high-speed multimedia applications, the system capacity of WiMAX system is under challenge. How to design an appropriate handover method which helps users to promptly and smartly switch between WiMAX cells has become an interesting subject.Regarding this problem, this thesis proposes a novel WiMAX handover method based on capacity estimation and neighbor advertisement. The method is suitable and has evident enhancement for a network with multiple WiMAX cell coverage with large number of mobile subscribers and heavy data traffic.This thesis presented the WiMAX standards and current handover methods including the handover algorithms, strategy, control mode and techniques in the first place. Among those handover methods, this thesis further studies the 802.16g fast handover technique for mobile WiMAX network, analyses the performance of this technique, verifies with a network simulation and reaches to a conclusion that the fast handover technique could decrease the packet loss due to handover, yet it fails to effectively solve the continuous packet loss due to network congestions.By summarizing the problems and difficulties on applying the current handover methods to WiMAX network, this thesis proposes a novel handover method based on capacity. Innovations of the proposed method include: the method bases itself on WiMAX cell capacity estimation and neighbor advertisement technology, uses effective idle capacity as a trigger metric in order to achieve traffic load balance; in the system model, we proposes a theoretical calculation method which accurately estimates the effective capacity of WiMAX cell inline with the OFDM PHY specifications in the 802.16 standard; the proposed method also originally introduces a global handover probability factor which effectively controls the“handover synchronization effect”problem during cell handover.An important part of the work load during our study is to construct the simulation environment for WiMAX handovers. Since the NS-2 simulation software does not provide native support for WiMAX network and WiMAX handovers, we have studied the structure of NS-2 and NIST mobility package and modified many source codes within different classes to construct the simulation environment under NS-2 with WiMAX handover support and realized the proposed method. The simulation result shows that the proposed handover method could effectively solve network congestions and enhance system throughput in a fast and obvious manner.更多还原