无线局域网的IAPP协议

无线局域网用户在各种不同的移动模式下有相对应的移动性管理策略。IAPP协议也即802.11f是在数据链路层解决无线局域网用户在接入点AP间的切换问题,从而保证无线局域网用户在接入点之间的切换问题。本文对IAPP协议的协议结构及协议操作做了详细的介绍,并描述了IAPP协议下数据链路的切换过程以及STA拉入AP的交互过程。     

基于CAPWAP的集中式WLAN实现

针对传统自主式WLAN无法应对大量无线接入点（AP）的管理、检测和控制等问题,文章提出了一种新的基于CAPWAP协议的集中式WLAN网络架构,分析了CAPWAP协议在集中式WLAN中的实现。组网测试表明,该网络架构能实现AP的集中控制管理,解决大规模组网过程中大量AP的配置、管理与安全隐患等问题;同时,网络信号强度、抗干扰性、吞吐率也得到明显的提高。     

WLAN中基于OpenFlow的无缝切换机制设计与实现

在传统的WLAN网络中,因为用户使用的移动终端（Station,STA）具有移动性,STA会出现离开当前网络接入点（Access Point,AP）的覆盖范围进入另一AP覆盖范围的情况,此时STA需要在AP间进行切换.传统WLAN中这样的AP间切换会产生网络延迟突然增大、吞吐量损失、以及掉线等服务质量下降的问题.本文提出并实现了一种基于AP虚拟化和OpenFlow技术的解决方案,通过搭建基于OpenFlow的交换网络对STA的流量进行细粒度的控制从而完成STA在不同AP间的无缝切换.经过实际网络环境测试,本方案具有5ms左右的切换延时、在AP切换时只会造成1秒左右的瞬时吞吐量减少和16ms左右的网络延时.相较于其他方案,本方案由于不需要再次进行认证和重新路由,因而具有更好的无缝切换性能.     

WLAN热得烫手

一、无线局域网的基本常识近几年来,随着局域网应用领域不断拓宽和现代通信方式的不断变化,尤其是移动和便携式通信的发展,无线局域网(WLAN)应运而生。WLAN利用常规的局域网(如10/100/1000Mbps以太网)及其互连设备(路由器)构成骨干支撑网,利用无线接入点(AP)和无线接入服务器(WAS)支持移动终端(MT)的移动和漫游。无线接入服务器的作用是提供无线终端的接入管理和移动性管理。无线接入点的作用是完成WLAN和LAN之间的桥接,实现无线空中接口协议到LAN协议的转换,并实现小区的移动用户管理。     

无线局域网中的“无缝”切换

分析了无线局域网（WLAN）中“无缝”切换的特点。在此基础上，着重讨论了采用“镜像”法实现切换具体过程，并对WLAN中的切换和传统移动IP中的漫游技术进行了比较。     

WiFi终端漫游原理及实现

随着信息网络技术的高速发展,WIFI网络在日常工作和生活中的应用也越来越普及。无线接入点AP是WIFI网络接入的最基本单元,组建一个覆盖区域较大的WIFI网络时,我们完成多个AP接入点的部署。当WIFI终端在多个AP组建的WIFI网络中移动时,终端将根据WIFI信号的强弱来实现不同AP接入点之间的自动切换,我们将该自动切换的过程称为"漫游"。实现WIFI漫游,将有助于提高WIFI网络的体验效果,文章主要介绍WIFI漫游的原理及改善终端漫游行为的综合策略。     

无线网络的融合：技术与挑战

一、引言 无线通信技术的发展，使得无线应用也从早期的简单语音业务（1G，2G）发展到新的综合数据应用。基于IEEE802．11的无线局域网（WLAN）变得普及，它能够以较低的成本提供高数据速率。WEAN接入点（AP）可以在大多数地方提供热点连接，如机场、饭店、购物中心、校园、医院等。     

灵活组网 集中控制——大唐电信胖瘦可转型WLAN整体解决方案

随着在2008年奥运会中的崭露头角和2009年国内的大规模商用，WLAN越来越得到业界的重视。WLAN系统主要由接入控制器（AC）和无线接入点（AP）组成。系统组网方式可分为胖AP组网与瘦AP组网。大唐电信是中国移动WLAN设备主要供货商，中国电信的WLAN重要合作伙伴。凭借卓越的产品性能及良好的工程售后服务，     

IMS业务会话在3G和WLAN间的切换方案

介绍了3GPPR6版本中的3G-WLAN融合网络架构,分析了其移动性管理机制的不足,然后在分析比较了潜在的移动性管理协议后,提出了基于SIP实现3G/WLAN（无线局域网）间IMS（IP多媒体子系统）业务会话的切换方案,并探讨了进一步改进的思路.     

WiFi中多AP间快速切换的研究与实现

目前,WiFi已经成为了高速无线局域网的主要标准并且得到了广泛的应用。鉴于WiFi网络接入点（AP）覆盖范围小、移动用户需要频繁切换的特点,文中提出了多AP连接和嗅探扫描两种技术来实现多AP间的快速切换。多AP连接通过同时和多个AP保持通信切实保障了通信连续性,而嗅探扫描为更有效地获取周围AP信息提供了指导性方法。实验表明这些技术有效地加快了切换的速度,有效保障了用户的QoS。     

基于载干比最优的OFDMA切换算法的研究

 正交频分多址接入（OFDMA, Orthogonal Frequency Division Multiple Access）已经成为3G演进策略（LTE, Long Term Evolution）及4G技术的主要多址接入方式.本文研究了现有的OFDMA的切换算法,分析了其存在的不足之处.本文针对OFDMA多址技术特点,提出新型的OFDMA切换算法 (SBA, Sub-carriers Bidirectional Arrayed handover).并通过仿真验证新型切换算法的性能.仿真结果表明,新型OFDMA切换算法保证了用户在切换过程中的信道质量（CIR,Carrier-Interference Ratio）,减少了切换信道的数目,从而提高了OFDMA系统性能.     

高铁接入网切换问题理论分析(英文)

To handle the handover challenge in Express Train Access Networks(ETAN).mobility fading effects in high speed railway environments should be addressed first.Based on the investigation of fading effects in this paper,we obtain two theoretical bounds:HOTiming upper bound and HO-Margin lower bound,which are helpful guidelines to study the handover challenge today and in the future.Then,we apply them to analyze performance of conventional handover technologies and our proposal in ETAN.This follow-up theory analyses and simulation experiment results demonstrate that the proposed handover solution can minimize handover time up to 4ms(which is the fastest one so far),and reduce HO-Margin to 0.16 dB at a train speed of 350km/h.     

基于OPNET的UMTS切换技术的建模与仿真

切换技术是通用移动通信系统(Universal Mobile Telecommunications System,UMTS)的主要关键技术之一,用于保证用户在移动通信网络中的移动性。对目前主要使用的2种切换技术———软切换和硬切换进行了简要介绍,而软切换是码分多址(Code Division Multiple Access,CDMA)系统所特有的。利用OPNET仿真软件搭建了UMTS网络切换模型,对软切换及硬切换技术进行仿真,并对结果进行了比较分析,得出结论,切换技术的优劣会直接影响到系统提供的服务质量。     

Handover and Uplink Power Control Performance in the 3.84 Mcps TDD mode of UTRA Network

In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out.     

The Performance Analysis of the Multicast Extension Support for Proxy MIPv6

Mobile multicast is based on the traditional multicast protocols and the mobility support protocols to provide the multicast services for the mobile subscribers. Several mobile multicast methods were proposed in the past few years, but most of them are based on Mobile IPv6 and its variants which require the mobile node to support the mobility function. Recently, Proxy Mobile IPv6 (PMIPv6) was proposed to provide the mobility support for the mobile node with or without mobility function, and the previous studies have shown that PMIPv6 can improve the performance in term of the handover performance and protocol cost. However, PMIPv6 mainly concerns on the mobility support for unicast routing and little considers the multicast routing. In this paper, we propose two multicast methods called the MAG (Mobile Access Gateway)-based method and LMA (Local Mobility Anchor)-based method based on the different multicast delivery transmission path to extend PMIPv6, and analyze their performance under the different scenarios. The analytical results show that the LMA-based method is suitable for the higher speed, bigger domain size, and larger network topology scenarios, whereas the MAG-based method is suitable for the lower speed, smaller domain size and smaller network topology scenarios.     

New efficient cross‐layer and multihoming mechanisms at layer 2 for inter‐radio access technology handover between UMTS and WiMAX

Next generation mobile networks will provide seamless mobility between existing cellular systems and other wireless access technologies. To realize a seamless vertical handover (inter‐radio access technology handover) among these different access technologies, a multi‐interfaced mobile station (i.e., multihomed) is a good approach to provide better handover performance in terms of packet loss rate and handover latency. In this article, we propose a novel layer 2 multihoming approach for inter‐radio access technology handover between Universal Mobile Telecommunications System (UMTS) and Worldwide Interoperability for Microwave Access (WiMAX) in both integrated and tight coupling architectures. This layer 2 multihoming approach has the ability of enabling either soft handover or make‐before‐break handover to adapt to mobility scenarios for the sake of a lossless and short latency handover procedure. Our simulation results show that, in case of handover from UMTS to WiMAX for transmission control protocol (TCP) traffics, the layer 2 multihoming approach can achieve a lossless and zero latency handover procedure by enabling soft handover. In case of handover from WiMAX to UMTS, because of the fact that the performance gain of soft handover is more affected by the differences of bandwidth and transmission delay between these wireless links, the make‐before‐break handover is preferred to achieve lossless and short latency handover procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

Impact of L2 Triggering Time on Handover Performance for 4G Wireless Networks

4G wireless networks are based on All-IP architecture integrating cellular networks, Wireless local area networks, Worldwide Interoperability for Microwave Access, Wireless ad hoc networks, and Wireless Personal Area Networks etc. This makes seamless handover an important issue for users roaming among these networks. Anticipation of future events based on layer 2 (L2) trigger information is the basic principle of fast handover. It incurs higher signaling costs compared with the other protocols like Mobile IPv6 and Hierarchical Mobile IPv6. L2 trigger is based on fluctuating wireless channel states. Therefore, the handover anticipation using L2 trigger may sometimes be incorrect. Unnecessary buffer space is used for providing a smooth handover in the case of incorrect anticipation. Therefore, it is very important to analyze overhead costs and compare the performance of IP based handover protocols. This paper investigates the impact of L2 triggering time on the signaling cost, packet delivery cost, total overhead cost, and buffer space. Results show that Session to mobility ratio, L2 trigger time and number of subnets are determining parameters for optimizing handover performance.