1、Vertical Handoff Decision Algorithms for Providing Optimized Performance in Heterogeneous Wireless Networks SuKyoung Lee, Member, IEEE, Kotikalapudi Sriram, Fellow, IEEE, Kyungsoo Kim,Yoon Hyuk Kim, and Nada Golmie, Member, IEEE 异构无线网络优化 性能 的垂直切换判决算法 SuKyoung Lee， IEEE会员； Kotikalapudi Sriram, IEEE高级
2、会员； Kyungsoo Kim,Yoon Hyuk Kim和 Nada Golmie, IEEE会员 Manuscript received July 18, 2007； revised January 9, 2008 and April 7,2008. First published May 14, 2008； current version published February 17,2009. This work was supported in part by the National Institute of Standards and Technology (NIST)/Offi
3、ce of Law Enforcement Standards and in part by the Ministry of Science and Technology, Korea, under the Korea Science and Engineering Foundation Grant R01-2006-000-10614-0. The review of this paper was coordinated by Prof. X. Shen. S. Lee is with the Department of Computer Science, Yonsei University
4、, Seoul 120-749, Korea (e-mail: skleecs.yonsei.ac.kr). K. Sriram and N. Golmie are with the Advanced Networking Technologies Division, National Institute of Standards and Technology, Gaithersburg, MD 20878 USA (e-mail: ksriramnist.gov； ). K. Kim is with the Department of Mathematics, Kyonggi Univers
5、ity, Suwon 442-760, Korea. Y. H. Kim is with the Department of Mechanical Engineering, Kyung Hee University, Yongin 446-701, Korea. Color versions of one or more of the figures in this paper are available online at http:/ieeexplore.ieee.org. Digital Object Identifier 10.1109/TVT.2008.925301 原稿于 2007
6、,6,18收到；修改版于 2008,1,9收到；第一次发表于 2008,5,14；当前版本发表于 2009,2,17。这个工作得到了美国技术标准局的支持，还有韩国科技部及韩国科学工程基金会的资助。本文的 修订由韩国 Yonsei University的 Prof. X. Shen.S. Lee整理。 Abstract There are currently a large variety of wireless access networks, including the emerging vehicular ad hoc networks (VANETs). A large variety
7、of applications utilizing these networks will demand features such as real-time, high-availability, and even instantaneous high-bandwidth in some cases. Therefore, it is imperative for network service providers to make the best possible use of the combined resources of available heterogeneous networ
8、ks (wireless area networks (WLANs), Universal Mobile Telecommunications Systems, VANETs, Worldwide Interoperability for Microwave Access (WiMAX), etc.) for connection support. When connections need to migrate between heterogeneous networks for performance and high-availability reasons, seamless vert
9、ical handoff (VHO) is a necessary first step. In the near future, vehicular and other mobile applications will be expected to have seamless VHO between heterogeneous access networks. With regard to VHO performance, there is a critical need to develop algorithms for connection management and optimal
10、resource allocation for seamless mobility. In this paper, we develop a VHO decision algorithm that enables a wireless access network to not only balance the overall load among all attachment points (e.g., base stations and access points) but also maximize the collective battery lifetime of mobile no
11、des (MNs). In addition, when ad hoc mode is applied to 3/4G wireless data networks, VANETs, and IEEE 802.11 WLANs for a more seamless integration of heterogeneous wireless networks, we devise a route-selection algorithm for forwarding data packets to the most appropriate attachment point to maximize
12、 collective battery lifetime and maintain load balancing. Results based on a detailed performance evaluation study are also presented here to demonstrate the efficacy of the proposed algorithms. Index Terms High availability, intersystem handover, load balancing,mobility management, quality-of-servi
13、ce (QoS) management,seamless mobility, simulation modeling, vehicular ad hoc network (VANET), vertical handoff (VHO), wireless local area net-work (WLAN),Worldwide Interoperability for Microwave Access (WiMAX). 摘要 ： 当前存在着多种无线接入网，包括出现的车载 ad hoc网络 (VANET)。利用这些网络的各种应用需要如下特点，如实时性，很强的实用性，某些场合甚至需要即时的高带宽。因
14、此，对于网络服务提供商来说，必须尽可能 充分整合可用异构网络的资源 支持通信连接 (WLAN， UMTS， WiMAX， VANET等 )。当连接需要在异构网络之间移动时，为了获得好的性能和高的实用性，首先需要无缝的垂直切换 (VHO)。对于 VHO性能， 非常 有必要 提出能支持无缝移动的连接管理和优化资源分 配的算法。本文提出了一种 VHO判决算法，不仅能够让一个无线接入网均衡 所有 AP/BS的 整体负载 ，而且能够使移动节点的集体电池使用时间最大化。例外，当 ad hoc模式应用于 3/4G无线数据网络， VANET， WLAN等异构无线网络的无缝 融合 时，本文设计了一种路由选择算法
15、，可以使数据包转发给最合适的配属点以维持负载均衡和最大延长集体电池使用时间。 基于详细性能评估的研究结果还表明这个算法的功效。 关键词： 高实用性，网间切换，负载均衡，移动性管理， QoS管理，无缝移动，仿真建模， VANET， VHO， WLAN， WiMAX。 I. INTRODUCTION CONNECTION handoff is no longer limited to migration between two subnets in a wireless local area network (WLAN) or between two cells in a cellular net
16、work (generally known as horizontal handoff). In addition to roaming and horizontal handoff within homogeneous subnets (e.g., consisting of only IEEE 802.11 WLANs or only cellular networks),supporting service continuity and quality of service (QoS) requires seamless vertical handoffs (VHOs) between
17、heterogeneous wireless access networks. In general, heterogeneous networks can be combinations of many different kinds of networks, e.g., vehicular ad hoc networks (VANETs), WLANs,Universal Mobile Telecommunications Systems (UMTSs),CDMA2000 (code-division multiple access), and mobile ad hoc networks
18、 (MANETs). Many new architectures or schemes have recently been proposed for seamless integration of various wireless networks. However, the integration of WLANs and cellular networks has attracted the most attention, because, currently, WLANs and cellular networks coexist and many cellular devices
19、have dual radio-frequency (RF) interfaces for WLANs and cellular access. With regard to VHO performance, there is a critical need for developing algorithms for connection management and optimal resource allocation for seamless mobility.In this paper, we focus on developing such algorithms based on s
20、uitable optimization criteria. Since WLAN and cellular access technologies are commonly available and complementary, we focus on these technologies in this paper, but our algorithms are widely applicable across any set of access technologies and applications. I. 介绍 切换的连续性不再局限在 WLAN的两个子网或者一个蜂窝网络的两个小区
21、。除了漫游和在同构子网中的水平切换，支持服务的连续性和 QoS要求在异构接 入网络之间进行无缝 VHO。 通常，异构网络是很多种不同网络的整合，如 VANET， WLAN，UMTS， CDMA2000， MANET等。 最近提出了很多关于各种无线网络无缝融合的新结构和机制。但是， WLAN和蜂窝网络的融合最引人关注，主要是因为当前 WLAN和蜂窝网络的共存，而且很多蜂窝设备同时具有 WLAN和蜂窝网络的 RF接口。对于VHO性能，非常有必要提出支持连接管理和优化 无缝移动资源分配的算法 。基于适当的优化标准本文提出这样一个算法。鉴于 WLAN和蜂窝网络接入技术的广泛应用和互补性，本文集中关注这
22、两个技术，但是我本文提出的算法能够广泛地应用于任何一种接入技术及应用。 Several interworking mechanisms for combining WLANs and cellular data networks into integrated wireless data environments have been proposed in 14. Two main architectures for interworking between IEEE 802.11 WLAN and 3G cellular systems 24 have been proposed: 1) t
23、ight coupling and 2) loose coupling (see Fig. 1). When the loose coupling scheme is used, the WLAN is deployed as an access network complementary to the 3G cellular network. In this approach, the WLAN bypasses the core cellular networks, and data traffic is more efficiently routed to and from the In
24、ternet, without having to go over the cellular networks, which could be a potential bottleneck. However, this approach mandates the provisioning of special authentication, authorization, and accounting (AAA) servers on the cellular operator for interworking with WLANsAAA services. On the other hand,
25、 when the tight coupling scheme is used, the WLAN is connected to the cellular core network in the same manner as any other 3G radio access network so that the mechanisms for the mobility, QoS, and security of the 3G core network such as UMTS can be reused.As a result, a more seamless handoff betwee
26、n cellular and WLAN networks can be expected in the tightly coupled case,compared to that in the loosely coupled case. 参考文献 14提出了 WLAN和蜂窝网络间无线数据环境融合的几种协同 工作 机制。 参考文献 24提出了 WLAN和 3G蜂窝网络协同工作的 两种主要结构： 1) 紧密 融合 结构 ， 2)松散融合 结构 ， 如图 1。 当使用松散的融合机制时， WLAN作为 3G蜂窝网络 的补充接入网络部署，这时 WLAN绕过核心蜂窝网络，与因特网交换数据流量的路由更有效，
27、 而没有必要通过蜂窝网络，这会造成潜在的瓶颈。 但是，这种方法提供了蜂窝网络 3A服务与 WLAN网络 3A服务的操作。另一方面，当使用 紧密 融合结构时，为了重新利用 移动性管理， QoS和 3G核心网络如 UMTS的安全性， WLAN同任何其他 3G无线接入网络一样与核心的蜂窝网络连接。 结果是，同松散融合情况相比，紧密融合结构更能让人期待去实现 WLAN和蜂窝网络 更为紧密的无缝切换。 Fig. 1. Architecture of an integrated heterogeneous network consisting of a WLAN, cellular network, an
28、d VANET/MANET. 图 1异构网络的融合结构 There have also been some research efforts to connect a mobile device equipped with multiple RF interfaces to the most optimal network among a set of available heterogeneous access networks. Vertical mobility is achieved by switching the interface of the mobile device to
29、connect to an alternative target network. 还有一些研究成就如，具有多种 RF接口的终端设备在一组可用的异构接入网络中连接最理想的网络。 通过转换终端接口到备选目标网络接口从而实现垂直切换。 McNair and Zhu 6 introduced important performance criteria to evaluate seamless vertical mobility, e.g., network latency,congestion, battery power, service type, etc. In 7,Guo et al. p
30、roposed an end-to-end mobility management system that reduces unnecessary handoff and ping-pong effects by using measurements on the conditions of different networks. In 8, various network-layer-based internetwork handover techniques have been addressed, and their performances are evaluated in a rea
31、listic heterogeneous network testbed. Nasser et al.9 proposed a VHO decision (VHD) method that simply estimates the service quality for available networks and selects the network with the best quality. However, there still lie ahead many challenges in integrating cellular networks and WLANs (or any
32、combination of heterogeneous networks in general). As pointed out in 5, 6, and 9, known VHO algorithms are not adequate in coordinating the QoS of many individual mobile users or adapting to newly emerging performance requirements for handoff and changing network status. Furthermore, under the curre
33、nt WLAN technology, each mobile device selects an access point (AP) for which the received signal strength (RSS) is maximum, irrespective of the neighboring network status. McNair和 Zhu 6介绍了评估无缝垂直移动的重要性能标准，如网络反应时间，拥塞，电池功率，服 务类型等。参考 文献7中， Guo et al.提出了 一种端 到端的移动管理系统，可以减少不必要的切换和在不同网络条件下使用测量造成的乒乓效应。参考文献
34、 8提出了很多基于网络层的网间切换技术，并在真实的异构网络测试床中评估了这些性能。参考文献 9中 Nasser et al.提出了 VHD方法，简单地评估了可用网络的服务质量和选择质量最佳的网络。但是，异构网络的融合依然存在很多问题挑战。如参考文 献 569指出的， 已知的 VHO算法不能 调整很多个别终端用户的 QoS或者适应新突发的切换和改变网络状态的性能 要求。 而且，在当前 WLAN技术下，每个终端设备只选择 RSS最大的 AP，而不考虑相邻网络状态。 Although the attachment to the closest AP is known to consume the l
35、east power for the individual mobile device at a given instant, in a situation where many mobile devices try to hand off to the same AP, there would be, in effect,significantly more power consumption at the mobile devices collectively due to increased congestion delays at the AP. In this paper, we t
36、ackle the following problem: Given a network of base stations (BSs), APs, and mobile nodes (MNs), and given that an MN is currently experiencing weak or degrading RSS from its current attachment point (BS or AP), how do we find an appropriate attachment point for the MN to connect to (via vertical o
37、r horizontal handoff) while optimizing a well-defined objective function? Our objective function includes consideration of the battery life of MNs and load balancing across attachment points. For seamless integration of WLAN and 3/4G wireless networks, we propose a VHD algorithm that not only maximi
38、zes the overall battery lifetime of MNs in the same coverage area but also seeks to equitably distribute the traffic load across available APs and BSs. 虽然靠近 AP的 接入点 在 某个 瞬间知道个别移动终端消耗的最小功率， 但是在 很多移动终端 都 试图切换到相同 AP的情况下 ，由于在 AP增加的拥塞延时， 移动终端 都会 很明显 的 消耗更多的功率。 本文中，解决了下列问题：假设一个具有 BS， AP和移动终端的网络， 还假设一个移动终端
39、同当前基站保持连接的 RSS正在下降 或变弱 ，如何在最优化一个定义 明确 的目标函数同时，去 寻找 一个合适的基站让移动终端继续保持连接 (通过垂直或水平切换 )？ 这个目标函数包含移动终端电池使用时间的考虑和接入点的负载均衡。对于 WLAN和 3/4G无线网络的无缝融合，本文提 出了 VHD算法，不仅在相同覆盖范围内最大延长终端的电池使用时间，还寻求公平地分配在可用 AP和 BS上的流量负载。 We suggest that this proposed algorithm be implemented in multiple VHD controllers (VHDCs). These V
40、HDCs are located in the access networks and can provide the VHD function for a region covering one or multiple APs and/or BSs. We envision that the decision inputs for the VHDCs will be obtainable via the media-independent handover function (MIHF), which is being defined in IEEE 802.21 10. Moreover,
41、 when ad hoc mode is applied to 3/4G wireless data networks, VANETs, and IEEE 802.11 WLANs formore seamless integration of heterogeneous wireless networks (see Fig. 1), we devise a route selection algorithm for forwarding data packets to the most appropriate AP/BS to maximize the same objective func
42、tion, as previously stated. Results based on a detailed performance evaluation study are also presented here to demonstrate the efficacy of the proposed algorithms. It may be mentioned here that route-selection algorithms have previously been studied in the context of WLANs or cellular networks sepa
43、rately 11, 12. 建议本文提出的算法在 VHD控制器中执行。这些 VHDC位于接入网络，能为一个或多个 AP或 BS提供 VHD功能。假设VHDC的判决输入通过 MIHF可以获得， MIHF在 IEEE 802.21 10里有定义。而且，当 ad hoc模式应用于 3/4G无线数据网络，VANET， WLAN构成异构无线网络的无缝融合 (如图 1)，本文设计了一种路由选择算法，可以使数据包转发给最合适的 AP/BS最大化相同的目标函数，如前面所述。 基于详细的性能评估研究结果论证了所提算法的功效。参考文献 1112的内容分别提到了以前研究的路由 选择算法。 The rest of this paper is organized as follows: We first describe our heterogeneous wireless networking system model and the high-level procedure, followed by the VHDC in Section II. Then, in Section III, we describe the details of optimization algorithms to
