迅驰＋GPRS——神州数码网络构筑无缝的无线

渴望无线上网的笔记本电脑用户在体验迅驰之外,开始越来越多的关注用GPRS无线上网卡无线上网络,这种方式可以使用户在有手机信号的地方就能无线上网。两种无线接入技术的结合,用武侠一点的话来形容,倒是有点双剑合壁的味道。神州数码等触感敏锐的无线设备厂商就提出了“WLAN+GPRS”的解决方案,即迅驰+GPRS,P4+WLAN/GPRS双模网卡。为用户提供了无缝的无线这一终极无间的无线上网。     

连接切换20秒完成 诺基亚D211提供4种无线接入方式

无线接入的方式很多,但WLAN 由于接入点有限,而GPRS、CDMA 使用成本又偏高,严重影响了用户使用无线的兴趣。而诺基亚 D211将 GPRS 技术和 WLAN 容于一身,插入笔记本或其他手持设备,实现在 GPRS、GSM、HSCSD 和 WLAN 覆盖范     

基于TEASE管道技术的异构网络垂直切换安全认证算法

基于WLAN和UMTS构建的异构网络模型,提出一种适合该模型的垂直切换安全认证算法,用临时管道密钥(TTK)对数据进行加密,在接收端再用TTK进行数据解密。用平均切换次数、传输时延和丢包率三个指标评价所提出算法的性能。与已有垂直切换算法进行性能比较,其结果表明,提出的算法能有效减少切换次数,消除乒乓效应,减少传输时延和丢包率,可为实时业务所需的无缝切换提供有力保障。     

基于可用数据速率的3G与无线局域网垂直切换触发机制

针对传统垂直切换触发机制存在不能保证实时提供最高可用数据速率的问题,提出一种更充分利用网络资源并且能够有效避免不必要切换的方法。引入IEEE 802.21介质独立切换（MIH）标准,利用MIH提供的介质独立信息服务（MIIS）获取能够覆盖到移动终端的候选无线局域网（WLAN）的相关参数,通过获取的相关参数计算其最大可用数据速率,将候选WLAN的可用数据速率与3G网络对比,做出切换决策：当检测到数据速率更高的WLAN时,能够及时地切换到该WLAN;若移动终端移动出WLAN覆盖范围则切换回3G网络。仿真实验表明相比传统垂直切换触发机制,该方案对网络资源的利用更充分,并且能够有效避免不必要的切换。     

基于移动用户位置预测的垂直切换算法

针对异构无线网络环境中现有垂直切换算法存在难以实现移动用户接入网络的无缝切换,无法向用户提供稳定通信服务的问题,提出一种基于移动用户位置预测的垂直切换算法。首先利用用户移动轨迹的相似性,使用用户轨迹数据离线训练LSTM模型以学习各用户普遍具有的移动规律;然后在线加载LSTM模型进行用户位置预测,从而使用模糊逻辑分析计算下一时刻用户对应候选网络的回报值,并选取回报值最高的网络进行切换。实验结果表明,该算法与已有垂直切换算法相比,在不同的用户移动速度和用户规模条件下的切换次数、切换失败次数和切换时延均有明显下降,内存消耗较低,能够实现无缝切换。     

基于业务类别的联合呼叫接纳控制算法

提出了一种基于业务类别的联合呼叫控制算法。在网络接入选择时,实时业务相对于非实时业务来说,应该尽可能地减少切换次数、降低切换时延。非实时业务要求较高的数据传输速率,而对时延不敏感。因此,在两个网络资源都足够的情况下,实时业务首选接入蜂窝网络,非实时业务首选接入WLAN。仿真并分析了异构网络中呼叫接纳控制算法性能的重要指标:新业务阻塞率。仿真结果表明,所提算法考虑了负载均衡,有效地利用了系统中的资源,提高了系统中的资源利用率,新业务阻塞率明显降低。     

异构网络垂直切换决策算法仿真

在异构网络无缝切换的研究中,切换判决是实现异构网络无缝切换中最为关键的一步。在不同接入网之间,为保证业务连续性,需要考虑终端及网络的多方因素,进行综合判决,选择最合适的网络进行接入。以往的垂直切换决策算法普遍存在一些未解决的问题,如考虑的判决因素不全面,决策权值太过主观,对不确定性因素难以描述,算法复杂度和性能无法很好的权衡等。为进一步提高算法性能,针对WLAN/UMTS的异构无线网络环境,提出一种更客观科学的垂直切换决策算法。并用Matlab/Simulink平台进行仿真建模,通过和传统的决策算法的对比分析,验证改进算法的有效性。仿真结果表明,新算法能及时准确地切换至最优网络,各网络负载均衡,且减少了不必要的切换。     

软件定义无线局域网的切换接入机制

软件定义无线局域网（WLAN）是管理无线网络的一个趋势。针对无线访问接入点（AP）部署密集环境中频繁切换、接入失败等问题，提出了基于惩罚因子的全局关联记忆保留的接入控制的方法。首先，扩展OpenFlow协议；其次，利用扩展数据报文通过AP向控制器报告网络的质量、负载、吞吐量以及利用率等指标；接着，引入变异系数法确定网络指标的系数，然后利用这些指标参数构建AP接入权值；最后，引入全局惩罚因子记录网络中发生频繁来回切换的情况，根据全局记忆保留的惩罚因子修正AP接入权值和发射功率。通过与信号最强接入法和负载均衡接入法的实验对比表明，终端站点（STA）在复杂网络环境中移动时，该方法能有效地降低切换的“乒乓效应”，减少网络的切换次数和切换时延并提高网络切换成功率。与传统信号最强接入法相比，所提方法的切换请求次数减少了21.7%，增强了网络接入性能的稳定性。     

一种具有AAA功能的移动IPv6快速切换方案的研究和实现

和目前WCDMA／GPRS、WLAN网络中的移动性相比，移动IPv6是一种网络层移动性解决方案。具有一定的优势。如垂直切换．但是移动IPv6的切换性能和安全性影响了其商业部署，提出了一种将快速切换和AAA结合起来的机制．并在基于网络处理器的接入路由器和Linux主机上实现了该方案．实验表明，该方案具有较小的切换时延．     

基于WLAN快速移动接入仿真研究

IEEE 802.11（WLAN）无线局域网标准原本是为提供室内外固定接入网络服务而设计的,由于大范围无线服务应用的推动,其在快速移动环境下的接入应用需求也随之产生。通过Matlab仿真工具,对WLAN快速移动接入进行了仿真分析,研究了移动速度、数据发送速率、接收信噪比等因素对移动接入性能的影响,分析得出WLAN的移动接入应用关键是在高移动速度与高数据速率之间做出优化选择,最后提出了WLAN移动接入应用方案。     

A distributed-request-based CDMA CAC for DiffServ multimedia services in wireless cellular mobile networks

In this paper, a distributed-request-based CDMA DiffServ (differentiated service) call admission control (CAC) scheme is proposed to provide various multimedia services seamlessly in wireless mobile Internet. Conventional CDMA CAC schemes cannot fully support DiffServ QoS (Quality of Service) and seamless handoff due to lack of consideration on service priority and seamless mobility. Therefore, in order to achieve QoS guarantee for each service class, seamless fast-handoff, and high utilization of the scarce wireless resource, we define a code assignment policy and an adaptive access permission scheme taking each user’s service priority and mobility into consideration. For that purpose, in the proposed scheme, the DQRUMA/CDMA is combined with the new code assignment scheme and the adaptive access permission probability (APP). Numerical examples show that the forced termination ratio of handoff calls is guaranteed to be much less than the blocking ratio of new calls for a seamless fast-handoff while proposed scheme provides QoS guarantee for each service class efficiently.     

IPv6 based relay gateway protocol in hybrid networks

During the past few years, WMAN (Wireless Metropolitan Area Network) and WLAN (Wireless Local Area Network) provided fast, convenient and reliable solution for all kinds of users. With the development of the communication technology, the future wireless networks will allow mobile users access Internet anywhere, anytime. Therefore, it is a natural trend to combine different wireless networks to provide a seamless roaming for users. It is feasible for mobile terminal which have multiple modes to handoff between different networks. A relay gateway protocol for the WLAN-mode nodes (mono-mode WLAN nodes and dual-mode nodes) in the hybrid network of IEEE 802.16 WMANs and IEEE 802.11 WLANs is proposed to provide wider mobility. Dual-mode mobile nodes with good service can provide WLAN links to nearby WLAN-mode nodes with bad service or out of the WLAN coverage. Simulation results show that the relay gateway scheme can improve network performance of the hybrid networks. Moreover, the relay gateway method can bring additional service coverage and increase the capacity of WMANs and WLANs.     

OmniCon: a Mobile IP‐based vertical handoff system for wireless LAN and GPRS links

Wi‐Fi based hotspots offer mobile users broadband wireless Internet connectivity in public work spaces and corporate/university campuses. Despite the aggressive deployment of these hotspots in recent years, high‐speed wireless Internet access remains restricted to small geographical areas due to the limited physical coverage of wireless LANs. On the other hand, despite their lower throughput, cellular networks have a significantly wider coverage and are thus much more available. Recognizing that 2.5G or 3G cellular networks can effectively complement wireless LANs, we set out to develop a vertical handoff system that allows mobile users to seamlessly fall back to such cellular networks as the general packet radio service (GPRS) or 3G whenever wireless LAN connectivity is not available. The resulting handoff mechanism allows a network connection of a mobile node to operate over multiple wireless access networks in a way that is transparent to end user applications. In this paper, we present the design, implementation, and evaluation of a fully operational vertical handoff system, called OmniCon, which enables mobile nodes to automatically switch between wireless LAN and GPRS, based on wireless LAN availability, by introducing a simple extension to the existing Mobile IP implementation. We discuss the design issues in the proposed vertical handoff system for heterogeneous networks, including connection setup problems due to network address translation, and the disparity in link characteristics between wireless LANs and GPRS. A detailed performance evaluation study of the OmniCon prototype demonstrates its ability to migrate active network connections between these two wireless technologies with low handoff latency and close to zero packet loss. Copyright © 2006 John Wiley & Sons, Ltd.     

TEASE: A novel Tunnel-based sEcure Authentication SchemE to support smooth handoff in IEEE 802.11 wireless networks

With the growing popularity of WiFi-based devices, WiFi-based wireless networks have received a great deal of interest in the wireless networks community. However, due to the limited transmission range of WiFi-based networks, mobile users have to switch their associated access points constantly to maintain continuing communications during their movement. The process of switching access points is called handoff. Handoff management is a key service in mobile networks, because providing seamless roaming in wireless networks is mandatory for supporting real-time applications in a mobile environment, such as VoIP, online games, and eConference. Security is another important issue in network communications, and to prevent possible attacks, authentication is required during the handoff process to guarantee the reliability of mobile clients and access points. In this paper, we propose a novel authentication scheme to achieve a smooth handoff in WiFi-based networks, which we refer to as TEASE. A tunnel is introduced to forward data packets between the new access point and the original reliable access point. The processing of a complete secure authentication and the transmitting of data between mobile terminals and their correspondence nodes can go on simultaneously. The security of handoff is achieved without increasing overhead to authentication servers, and handoff latency can be minimized to support seamless roaming. Simulation results show that our proposed scheme reduces significantly the communication interruption time and generates low packet loss ratio, and our method is suitable to be used for secure handoff in real-time applications.     

嵌入式智能无线接入点系统的设计

该文提出了一种支持蓝牙、IEEE802.11b和GPRS三种不同的无线接入方式的智能无线接入点(AP)系统的实现方案。设计了在嵌入式Linux平台上智能无线AP的软硬件,重点讨论了蓝牙WPAN与Internet/GPRS以及WLAN的互连。     

A novel network mobility handoff scheme using SIP and SCTP for multimedia applications

In a heterogeneous wireless environment, seamless mobility is the basis of network support with which mobile users who roam between or among various wireless access networks are able to fully enjoy uninterrupted wireless services. When users are in a mass transportation vehicle, e.g., a bus or a train that provides network service, the vehicle can be regarded as a network which is serving users as it moves from one location to another. The movement of a network is called network mobility (NEMO). The network mobility protocol based on Mobile IPv6 as proposed by the Internet Engineering Task Force (IETF) in 2005 has some fundamental drawbacks, such as header overhead and the pinball problem. In this paper, we propose a novel hybrid method for network mobility called Hybrid-NEMO, which provides a soft handoff scheme at the transport layer basically utilizing SIP and SCTP protocols to ensure a lossless packet-transmission environment and less handoff-delay variation, which are critical in providing QoS voice and multimedia applications. Experimental validation and performance evaluation were also conducted in this study.     

An analytical evaluation of mobility management in integrated WLAN-UMTS networks

Ensuring uninterrupted service continuity for handoff calls in an all-IP inter-networked heterogeneous environment requires successful session management among participating access networks. As such, a mobility-aware novel interworking architecture is presented in this article that facilitates session management including session establishment and seamless session handoff across different networks. This framework conveniently enables any 3G cellular technology such as the Universal Mobile Telecommunications System (UMTS) to interwork with a given Broadband Wireless Access (BWA) technology such as the Worldwide Interoperability for Microwave Access (WiMAX) network or the Wireless Local Area Network (WLAN) under a common signaling platform. This framework exploits the IP Multimedia Subsystem (IMS) as a universal coupling mediator for real-time session negotiation and management. Next, a Queuing Theory based analytical model for evaluating the performance of vertical handoff management between these interworked 3rd Generation (3G) cellular networks and the WLANs is presented. The analysis includes vertical handoff performance measures such as delay, transient packet loss, jitter, and signaling overhead/cost. The latter part of this paper presents some results from OPNET based simulations for the verification of the analytical model and results.     

Design and evaluation of a novel MAC layer handoff protocol for IEEE 802.11 wireless networks

In recent years, the IEEE 802.11 wireless network family has become one of the most important set of standards in the wireless communications industry. IEEE 802.11 compliant devices are inexpensive and easier to configure and deploy than other wireless technologies. In an IEEE 802.11 wireless network, wireless terminals can move freely. As a result, when the wireless terminal moves away from its current access point, it must switch to another access point to maintain the active connection. This is known as the MAC layer handoff process. MAC layer handoff latency should be minimized to support real-time applications and to provide mobile devices with seamless roaming in IEEE 802.11 wireless networks. This paper proposes a novel MAC layer handoff protocol over IEEE 802.11 wireless networks by introducing advertisement messages sent from other mobile nodes and from which wireless terminals are able to receive the information of access points in their neighborhood. A mobile node can try to associate with access points based on the prediction before starting the probe process. The experimental results demonstrate that our solution can reduce MAC layer handoff latency to meet the requirements of real-time applications.     

Case study on handoff strategies for wireless overlay networks

One of the most challenging topics for next‐generation wireless networks is the process of vertical handoff since many of wireless technologies overlap each other and build a heterogeneous topology. Several parameters, pertaining to user/application requirements and network conditions, such as data rate, service cost, network latency, speed of mobile, and etc. must be considered in the handoff process of heterogeneous networks along with RSSI information. In this paper, adaptive fuzzy logic‐based vertical handoff decision‐making algorithms are presented for wireless overlay networks which consist of GSM/GPRS/Wi-Fi/UMTS/WiMAX technologies. The parameters data rate, monetary cost, speed of mobile and RSSI information are processed as inputs of the proposed fuzzy‐based systems. According to these parameters, an output value, which varies between 1 and 10, is produced. This output value is utilized to determine whether a handoff process is necessary or not and to select the best candidate access point in the vicinity. The results show that, compared to the traditional RSSI‐based algorithm significantly enhanced outcomes can be achieved for both user and network as a consequence of the proposed fuzzy‐based handoff systems. The simulation results are also compared with those of classical MADM (Multiple Attribute Decision Making) method, i.e. SAW (Simple Additive Weighting). According to the results obtained, the proposed vertical handoff decision algorithms are able to determine whether a handoff is necessary or not, properly, and select the best candidate access network considering the aforementioned parameters. Moreover, fuzzy‐based algorithm noticeably reduces the number of handoffs compared to SAW‐based algorithm.