1、 Handoffs in Fourth Generation Heterogeneous Networks Nidal Nasser, University of Guelph Ahmed Hasswa and Hossam Hassanein, Queens University 4G异构网络的切换 加拿大安大略省圭尔夫大学 加拿大安大略省 皇后 大学 ABSTRACT As mobile wireless networks increase in popularity and pervasiveness, we are faced with the challenge of combini
2、ng a diverse number of wireless networks. The fourth generation of wireless communications is expected to integrate a potentially large number of heterogeneous wireless technologies in what could be considered a huge step forward toward universal seamless access. One of the main challenges for seaml
3、ess mobility is the availability of reliable horizontal (intrasystem) and vertical (intersystem) handoff schemes. Efficient handoff schemes enhance quality of service and provide flawless mobility. This article presents different and novel aspects of handoff and discusses handoff related issues of f
4、ourth generation systems.Desirable handoff features are presented. Handoff decisions, radio link transfer, and channel assignment are described as stages of the complete handoff process. A vertical handoff decision function, which enables devices to assign weights to different network parameters, is
5、 also presented. 摘要 移动无线网络日益盛行之时，不同网络之间融合的挑战摆在面前。 4G无线通信整合 了 大多数异构 网络 的 无线技术 ，在走向通用的无缝接入方面迈向了一大步 。无缝移动通信面临的主要挑战之一是 可靠的水平 (网间 )切换和垂直 (网内 )切换机制的有效性。有效的切换机制提高了服务质量提供了无缝移动通信。本文提出了新颖不同的切换并讨论了 4G切换的相关问题。 本为给出了令人满意的切换特性。切换判决，无线链路传输和信道分配在整个切换过程中分步描述。本文还给出了一种能够让终端去分配权重给不同网络参数的垂直切换判决函数。 INTRODUCTION 1.介绍 Firs
6、t, second- and third-generation mobile systems depended on the employment of the radio spectrum that was either unlicensed (available for public use) or licensed for use by a very small number of service providers and network operators in each region. Differences in bandwidth and coverage areas have
7、 led to the necessity of developing multi-network interface devices (terminals) that are capable of using the variety of different network services provided. 首先，第二代第三代移动通信系统依赖于 无线频谱的利用， 这些频谱要么被公共使用要么被批 准在各个地区由一些小数量的服务提供商和网络运营商使用。带宽和覆盖范围的差异导致发展多网络接口终端的必要性，多网络接口终端可以使用不同网络服务提供的多样性。 The fourth generatio
8、n (4G) of wireless communications is expected to integrate a potentially large number of different heterogeneous wireless technologies in what could be considered a huge step forward toward universal wireless access and omnipresent computing through seamless mobility 1. Even though 4G is currently u
9、ndefined,there are many current outlooks that delineate the vision of the new wireless technologies.Based on the emergent trends of mobile communication, 4G will have larger bandwidth, higher data rates, smoother and quicker handoff, and will focus on reducing faultless service and allowing seamless
10、 handoff across a multitude of wireless networks. The key concept is integrating the 4G capabilities with all of the existing mobile technologies. Network management will be necessary among different access systems in terms of horizontal (intrasystem)and vertical (intersystem) handoff as well as sea
11、mless mobility, quality of service, dependability,and security. 4G无线通信 融合 了 大多数异构 网络的 无线技术 ，在 通用的无缝接入方面 和通过无缝移动通信进行泛在计算方面 迈向了一大 步 1。 即使4G当前没有明确定义，仍然有很多当前的展望描述了新一代无线技术的景象。基于 移动通信浮现的趋势， 4G拥有更多的带宽和数率以及更平滑快捷的切换，集中致力于减少差错服务和允许通过多种无线网络的无缝切换。关键概念是 使用已存在的移动技术 整合 4G性能 。 网络管理，对于不同的接入系统如垂直和水平切换还有无缝移动性、服务质量、可靠性
12、和安全性，很有必要。 The remainder of this article is organized as follows. We present a novel classification hierarchy for handoffs. A comprehensive study of various handoff decision factors in heterogeneous wireless networks is explained. We then explain and qualitatively evaluate the proposed vertical hand
13、off decision function (VHDF). We provide a performance evaluation of the described solution.Finally, an article summary is given. 下面的文章内容如下。给出了一种新的用于切换的分类层次。 对 异构无线网络中各种切换判决因子的全面研究进行解释 ，解释和定量地评估本文提到垂直切换函数 (VHDF)。 提供所述解决方案的性能评估及文章 概要 。 CLASSIFICATION OF HANDOFFS 2.切换的分类 In principle, each mobile term
14、inal (node) is, at all times, within range of at least one network access point, also known as a base station. The area serviced by each base station is identified as its cell. The dimensions and profile of every cell depend on the network type, size of the base stations,and transmission and recepti
15、on power of each base station. Usually, cells of the same network type are adjacent to each other and overlap in such a way that, for the majority of time,any mobile device is within the coverage area of more than one base station. Cells of heterogeneous networks, on the other hand, are overlaid wit
16、hin each other. Therefore, the key issue for a mobile host is to reach a decision from time to time as to which base station of which network will handle the signal transmissions to and from a specific host and handoff the signal transmission if necessary. 大体 上， 每个移动终端 (节点 )总是归类于至少一种网络接入点即基站。每一个基站的服
17、务区定义为它的小区。每个小区的大小和外形依赖于网络类型、基站大小、基站的传输和接收功率。通常相同类型的小区 以这样一种方式彼此 相邻和重叠 ，大多数时间内任一移动终端所 处的 覆盖面积超过一个基站 。另一方面，异构网络的小区相互覆盖。因此，移动主机的关键问题是 要 时不时地做出 选择，哪个网络的哪个基站来处理具体移动主机的信号传输和接收以及必要时切换信号的传输。 We classify handoffs based on several factors as shown in Fig. 1. No longer is the network type the only handoff clas
18、sification factor. Many more factors constitute categorization of handoffs including the administrative domains involved, number of connections and frequencies engaged. The following are categorization factors along with the handoff classifications that are based on them. 如图 1所示，基于几种 因素 给出了切换的分类。 网络
19、类型不再是唯一的切换分类的因素。 这个切换的分类因素有很多组成包含涉及的管理区域、连接和使用的频率数。下图是基于它们的切换类型的分类因素。 图 1：切换的分类树 FIRST FACTOR: NETWORK TYPES INVOLVED This is the most common classification factor.Handoffs can be classified as either horizontal or vertical. This depends on whether a handoff takes place between a single type of netw
20、ork interface or a variety of different network interfaces. Horizontal handoff: the handoff process of a mobile terminal between access points supporting the same network technology. For example,the changeover of signal transmission (as themobile terminal moves around) from an IEEE 802.11b base stat
21、ion to a geographically neighboring IEEE 802.11b base station is considered as a horizontal handoff process. Vertical handoff: the handoff process of a mobile terminal among access points supporting different network technologies. For example, the changeover of signal transmission from an IEEE 802.1
22、1b base station to an overlaid cellular network is considered a vertical handoff process.Horizontal and vertical handoffs are discussed in more detail in the following sections. 2.1 因素 一： 涉及的网络类型： 这是最普遍的分类因素。切换能被分为水平切换或者垂直切换。这主要看切换是发生在同种网络类型之间还是不同网络类型之间。 水平切换： 移动终端在支持相同网络技术 的 接入点之间的切换 过程 ，例如，从 802.1
23、1b基站到地理上相邻 802.11b基站的信号传输的转变就是水平切换过程。 垂直切换： 移动终端在支持 不 同网络技术 的 接入点之间的切换 过程 ， 例如， 从 802.11b基站到 重叠覆盖蜂窝网络 的信号传输的转变就是垂直 切换过程。 水平和垂直切换在后面的章节中会详细讨论。 SECOND FACTOR: FREQUENCIES ENGAGED Intrafrequency handoff: the handoff process of a mobile terminal across access points operating on the same frequency. This
24、 type of handoff is present in code-division multiple access (CDMA) networks with frequency-division duplex (FDD). Interfrequency handoff: the handoff process of a mobile terminal across access points operating on different frequencies. This type of handoff is present in CDMA networks with time-divi
25、sion duplex (TDD) and is the only handoff type supported in GSM cellular systems. 2.2 因素二 ： 使用的频率 频间切换 ： 移动终端 穿越在相同频率上运行的 接入点之间的切换 过程。这种切换的典型例子就是 FDD的 CDMA网络。 频内切换 ： 移动终端 穿越在不同频率上运行的 接入点之间的切换 过程。这种切换的典型例子就是 TDD的 CDMA网络和只支持 GSM蜂窝系统的切换类型。 THIRD FACTOR: NUMBER OF CONNECTIONS INVOLVED Handoffs can be cl
26、assified as hard, soft, or softer. Hard handoff: In a hard handoff the radio link to the old base station is released at the same time a radio link to the new base station is established. In other words, using hard handoff,a mobile node is allowed to maintain a connection with only one base station
27、at any given time. Soft handoff: Contrary to hard handoffs, in a soft handoff a mobile node maintains a radio connection with no less than two base stations in an overlapping handoff region and does not release any of the signals until it drops below a specified threshold value. Soft handoffs are po
28、ssible in situations where the mobile node is moving between cells operating on the same frequency. Softer handoff: A softer handoff is very similar to a soft handoff, except the mobile terminal switches connections over radio links that belong to the same access point. 2.3 因素三 ： 涉及连接数 切换被分为硬切换，软切换和
29、更软切换。 硬 切换 ： 在硬切换中，目标基站无线链路建立的同时释放原基站的无线链路 。 也就是说，使用硬切换时，在任何时间，移动节点只能同一个基站保持连接。 软 切换 ： 与硬切换相比，在软切换中，移动节点在重叠覆盖的切换区内和不少于 2个基站保持连接，并且不会释放任何信号直到某信号低于给定的阀门值。 当移动节点在相同频率上运行的小区间移动时可能会发生 软切换 。 更软 切换 ： 除了 移动终端在同一个接入节点的无线链路上交换连接 这点特性之外，更软切换同软切换很类似 。 FOURTH FACTOR: ADMINISTRATIVE DOMAINS INVOLVED An administra
30、tive domain is a group of systems and networks operated by a single organization of administrative authority. Administrative domains play a significant role in 4G wireless networks as different networks, each controlled by different administrative authorities, become available. Consequently, the cla
31、ssification of handoffs in terms of administrative domains is a crucial issue. Intra-administrative handoff: a handoff process where the mobile terminal transfers between different networks (supporting the same or different types of network interfaces) managed by the same administrative domain. Inte
32、r-administrative handoff: a handoff process where the mobile terminal transfers between different networks (supporting the same or different types of network interfaces) managed by different administrative domains. 2.4 因素四 ： 涉及的管理区域 管理区域是由同一个管理者管理的一组系统和网络。管理区域在 4G 无线网络如不同的网络中扮演重要的角色，不同的网络都有不同的管理者 。因
33、此，根据管理区域划分的切换类型是一个很重要的研究问题。 管理域之 内 的 切换 ： 移动节点在相同管理域管理的不同网络 (支持相同或不同类型网络接口 )之间切换过程。 管理域之 间 的 切换 ： 移动节点在不同管理域管理的不同网络 (支持相同或不同类型网络接口 )之间切换过程。 FIFTH FACTOR: NECESSITY OF HANDOFF Handoffs can be classified based on need. Obligatory handoff: In some situations it is necessary for the mobile terminal to t
34、ransfer the connection to another access point in order to avoid disconnection. Voluntary handoff: In other situations transfer of connection is optional and may or may not improve the quality of service.Voluntary and obligatory handoffs are discussed in more details later on. 2.5 因素五 ： 切换的必要性 基于需要而
35、划分的切换 强制 切换 ：在有些情况下，为了避免掉线，有必要将移动终端的连接转移到另一个接入点。 自愿 切换 ：在其他情况下，连接的转移是可选择的，对于提高服务质量不确定。 自愿 切换和强制切换 在以后的章节中详细讨论。 SIXTH FACTOR: USER CONTROL ALLOWANCE Handoffs can be classified as proactive or passive. Proactive handoff: In a proactive handoff the mobile terminals user is allowed to decide when to han
36、doff. The handoff decision can be based on a set of preferences specified by the user.Proactive handoff is expected to be one of the radical features of 4G wireless systems. Passive handoff: The user has no control over the handoff process. This type of handoff is the most common in first-, second-, and third-generation wireless systems. 2.6 因素六 ： 用户控制允许 切换可分为主动的和被动的。 主动 切换 ：在主动切换中，移动终端用户可以选择何时切换。这种切换判决基于用户事先设定好的参数。主动切换是 4G无线网络系统的基本特点之一。 被动 切换 ：用户不控制切换过程。这种类型的切换在前 3代无线通信系统中最为普遍。
