外文翻译----4G异构网络的切换

1、handoffs in fourth generation heterogeneous networksnidal nasser, university of guelph ahmed hasswa and hossam hassanein, queens university4g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abstractas mobile wireless networks increase in popularity and pervasiveness, we are faced with the challenge of combining a div

2、erse 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 seamless mobi

3、lity 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 fourth ge

4、neration 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 also pr

5、esented.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。introduction1.介绍first, second- and third-generat

6、ion 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 led to the necessity of dev

7、eloping 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 generation (4g) of wireless communications

8、 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 undefined,there are many current o

9、utlooks 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 handoff across a multitude of wi

10、reless 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 seamless mobility, quality of servic

11、e, 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、可靠性和安全性，很有必要。the remainder of this article is organized

12、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 handoff decision function (vhdf). we provide a performance

13、 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 handoffs2.切换的分类in principle, each mobile terminal (node) is, at all times, within range of at least one networ

14、k 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 reception power of each base station. usually, cells of the same network

15、 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 within each other. therefore, the key issue for a mobile host is to

16、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

17、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 classification factor. many more factors constitute categorization of handoffs incl

18、uding 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 f

19、actor: 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 network interface or a variety of different network interfaces.horizontal handoff: the hando

20、ff 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 station to a geographically neighboring ieee 802.11b base station is considered as a horizont

21、al 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 802.11b base station to an overlaid cellular network is considered a vertical handoff process.h

22、orizontal 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802.11b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

23、过程。水平和垂直切换在后面的章节中会详细讨论。second factor: frequencies engagedintrafrequency handoff: the handoff process of a mobile terminal across access points operating on the same frequency. this type of handoff is present in code-division multiple access (cdma) networks with frequency-division duplex (fdd).interf

24、requency 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-division 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

25、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 classified 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 l

26、ink 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 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 ba

27、se 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 possible in situations where the mobile node is moving between cells operating on the same frequency.softer handoff: a softer handoff is very simil

28、ar 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

29、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 administrative 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 n

30、etworks as different networks, each controlled by different administrative authorities, become available. consequently, the classification of handoffs in terms of administrative domains is a crucial issue.intra-administrative handoff: a handoff process where the mobile terminal transfers between dif

31、ferent networks (supporting the same or different types of network interfaces) managed by the same administrative domain.inter-administrative handoff: a handoff process where the mobile terminal transfers between different networks (supporting the same or different types of network interfaces) manag

32、ed 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 classifi

33、ed based on need.obligatory handoff: in some situations it is necessary for the mobile terminal to transfer 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 servi

34、ce.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 handof

35、f: in a proactive handoff the mobile terminals user is allowed to decide when to handoff. 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 ov

36、er 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。handoffs in 4g heterogeneous networks3. 4g异构网络

37、的切换as discussed above, handoffs can be defined as the transition of signal transmission between different cells. a handoff scheme is required to preserve connectivity as devices move about, and at the same time curtail disturbance to ongoing transfers. therefore, handoffs must exhibit low latency, s

38、ustain minimal amounts of data loss, as well as scale to large networks. handoff schemes have been thoroughly researched and deployed in cellular systems, also known as wireless wide area networks (wwans), and are escalating in importance in other networks, such as wireless lans (wlans), as research

39、 in 4g wireless communications increases in popularity. handoffs can be classified as either horizontal or vertical,as depicted in fig. 2.如上面讨论的，切换可以定义为不同小区之间传输信号的转移。切换机制要求当设备移动时保持连接性，同时对正在进行的转移减少干扰。因此，切换必须表现出低的反应时间，保持最小的数据丢失和测量大的网络。切换机制在蜂窝网络中已经彻底地研究和配置过，比如无线广域网(wwans)，在无线局域网(wlans)中的重要性也逐渐提高。如图2，切换

40、可划分为水平切换和垂直切换。horizontal handoff is the changeover of signal communication from one base station to a geographically neighboring base station supporting the same technology, as the user roams about. horizontal handoff is also referred to as intra-technology handoff. every time a mobile cellular host

41、 crosses from one cell into a neighboring cell (supporting the same technology),the network routinely and automatically exchanges the coverage responsibility from one base station to another. each base station change, as well as the exchange procedure or method is known as horizontal handoff. in a p

42、roperly operating network, handoff takes place smoothly and efficiently, without gaps in communications and without uncertainty as to which base station should be dealing with the mobile node. mobile users need not get involved in order for horizontal handoff to take place nor do they have to sense

43、the handoff process or identify which base station is managing the signals at any certain time.水平切换是从一个基站到地理上相邻且支持相同技术基站的信号传输的转变，如用户漫游时。水平切换也被当作技术内切换提及。每当一个移动蜂窝主机从一个小区穿越相邻小区(支持相同技术)，网络通常会自动地从一个基站到另一个基站交换覆盖责任。每一次基站的改变，还有交换手续和方法都认为是水平切换。在一个运行良好的网络中，切换会平滑而有效的发生，没有通信上的不通畅，也没有不确定性，即不知道哪个基站应该接管这个移动节点。移动用户

44、不需要涉及水平切换的发生，对切换过程也没有感觉，在任何时间也不涉及识别到底哪个基站正在处理信号。horizontal handoff is the most widespread definition of handoff due to the extensive research that has taken place in this field in the last several years. vertical handoff, on the other hand is a more recent and exciting scheme that promises to transf

45、igure the way we communicate.while horizontal handoff is a handover among base stations in service by the same wireless network interface, vertical handoff takes place between different network interfaces that usually represent different technologies 2. vertical handoff architectures and schemes wil

46、l play a major role in the ieee 802.21 standard and shall pave the road for emergence of 4g overlay multinetwork environments.水平切换是范围最为广泛的切换定义，是由于其在这个领域里的广泛研究在最近很多年一直在进行。另一方面，垂直切换更多的是最近提出而令人振奋的切换机制，让大家感觉将来的通信方式会很美好。水平切换是处于相同无线网络接口服务的基站之间的切换，而垂直切换发生在不同网络接口之间，这些接口通常代表了不同的技术2。垂直切换体系和机制在ieee 802.21标准中将扮

47、演主要角色，并为4g重叠多网络环境的融合铺平道路。there are two types of vertical handoffs:upward and downward. an upward vertical handoff 3 is roaming to an overlay with a larger cell size and lower bandwidth such aswans (cellular networks), and a downward vertical handoff is roaming to an overlay with a smaller cell size

48、and larger bandwidth. downward vertical handoffs are less time critical, since a mobile device can always remain connected to the upper overlay and not handoff at all.有两种垂直切换类型：向上和向下。向上垂直切换3是漫游到一个覆盖更大带宽较低的区域如蜂窝网络，向下垂直切换是漫游到一个覆盖更小带宽较大的区域。向下垂直切换的时间急迫性较小，因为移动设备能总是保持同更大覆盖网络的连接而可以不切换。seamless handoffin o

49、ne of the revolutionary drivers for 4g, technologies will complement each other to provide ubiquitous high-speed wireless connectivity to mobile terminals 4. in such an environment, it will be necessary to support seamless handoffs of mobile terminals without causing disruption to their ongoing sess

50、ions. as a result, the need for seamless handoff across the different wireless networks is becoming increasingly important.whereas wired networks regularly grant high bandwidth and consistent access to the internet,wireless networks make it possible for users to access a variety of services even whe

51、n they are moving. consequently, seamless handoff, with low delay and minimal packet loss, has become a crucial factor for mobile users who wish to receive continuous and reliable services. one of the key issues that aid in providing seamless handoff is the ability to correctly decide whether or not

52、 to carry out vertical handoff at any given time. this could be accomplished by taking into consideration two key issues: network conditions for vertical handoff decisions and connection maintenance 5. these two schemes need to be tightly coupled in order to move seamlessly across different network

53、interfaces. to attain positive vertical handoff, the network state ought to be constantly obtainable by means of a suit-able handoff metric. in multinetwork environments,this is very challenging and hard to achieve as there is not a single factor that can provide a clear idea of when to hand off. si

54、gnal strength, which is the chief handoff metric measured in horizontal handoffs, cannot be utilized for vertical handoff decisions due to the overlay nature of heterogeneous networks and the different physical techniques used by each network。thus, a natural question arises as to what factors should

55、 be considered in the handoff decision. in the next sections we discuss desirable handoff features, horizontal and vertical handoff procedures,and newly proposed vertical handoff characteristics in detail, and explain their significance in 4g handover schemes.3.1 无缝切换4g的革命性驱动之一是，技术之间会相互弥补以致于提供泛在的高速无

56、线移动终端连接4。在这样一个环境中，有必要支持移动终端的无缝切换而没有对正在进行的任务造成中断。因此，穿越不同无线网络之间无缝切换的需求变得日益重要。而有线网络能够有规则地获得大的带宽和持续的接入到因特网，无线网络对移动的用户来说将使得他们接入到各种服务成为可能。因此，低延时和最小丢包率的无缝切换已成为至关重要的因素，尤其是对那些想接收持续而可靠服务的移动用户来说。提供无缝切换的关键辅助之一是能够在任何时间正确地决定是否执行垂直切换。完成这个问题要考虑两个问题：垂直切换判决的网络条件和连接维持5。这两个问题对于能够在不同网络接口间无缝移动来说是紧紧联系一起的。为获得实际的垂直切换，网络状态应该

57、能够被合适的公制切换手段时时地获得。信号强度在水平切换中是主要的切换公制计量，但是不能够应用在垂直切换判决中，因为异构网络的覆盖特性和不同网络使用的不同物理技术。因而，一个很自然的问题出现，切换判决应该考虑什么样的因素。下章节将讨论令人满意的切换特性，水平和垂直切换手续，详细地讨论刚刚提到的垂直切换特点，阐述他们在4g切换机制中的重要性。desirable handoff featuresan efficient handoff algorithm can achieve many desirable features by trading off different operating ch

58、aracteristics. some of the major desirable features of any handoff algorithm 6 are described below (refer to fig. 3).3.2 令人满意的切换特点一种有效的切换算法能可以通过权衡不同的运行特点以达到很多令人满意的特点。任何一种切换算法的某些主要的得意特点描述如下(参考图3)。reliable: a handoff algorithm should be reliable.this means that the call should have good quality after

59、handoff. many factors help in determining the potential service quality of a candidate base station. some of these factors include signal-to-interference ratio (sir), signal-to-noise ratio (snr), received signal strength (rss), and bit error rate (ber). many more critical factors are discussed in the next section.3.2.1 可靠性：切换算法应当是可靠的。这意味着切换后通话应该有很好的质量。很多因素有助于决定候选基站的潜在服务质量。这些因素包括信干比(sir)、信噪比(snr)、接收信