外文翻譯---通用移動通信系統(tǒng)的回顧

1、<p>　　Review of UMTS</p><p>　　1.1 UMTS Network Architecture </p><p>　　The European/Japanese 3G standard is referred to as UMTS. UMTS is one of a number of standards ratified by the ITU-T un

2、der the umbrella of IMT-2000. It is currently the dominant standard, with the US CDMA2000 standard gaining ground, particularly with operators that have deployed cdmaOne as their 2G technology. At time of writing,Japan i

3、s the most advanced in terms of 3G network deployment. The three incumbent operators there have implemented three different technologies: J-Phone is using UMTS,K</p><p>　　The UMTS standard is specified as a

4、migration from the second generation GSM standard to UMTS via the General Packet Radio System (GPRS) and Enhanced Data for Global Evolution (EDGE), as shown in Figure. This is a sound rationale since as of April 2003, th

5、ere were over 847 Million GSM subscribers worldwide1, accounting for</p><p>　　68% of the global cellular subscriber figures. The emphasis is on keeping as much of the GSM network as possible to operate with

6、the new system.</p><p>　　We are now well on the road towards Third Generation (3G), where the network will support all traffic types: voice, video and data, and we should see an eventual explosion in the ser

7、vices available on the mobile device. The driving technology for this is the IP protocol. Many cellular operators are now at a position referred to as 2.5G, with the deployment of GPRS, which introduces an IP backbone in

8、to the mobile core network.The diagram below, Figure 2, shows an overview of the key components in</p><p>　　The interface between the SGSN and GGSN is known as the Gn interface and uses the GPRS tunneling pr

9、otocol (GTP, discussed later). The primary reason for the introduction of this infrastructure is to offer connections to external packet networks, such as the Internet or a corporate Intranet.</p><p>　　This

10、brings the IP protocol into the network as a transport between the SGSN and GGSN. This allows data services such as email or web browsing on the mobile device,with users being charged based on volume of data rather than

11、time connected.</p><p>　　The dominant standard for delivery of 3G networks and services is the Universal Mobile Telecommunications System, or UMTS. The first deployment of UMTS is the Release ’99 architectur

12、e, shown below in Figure 3.</p><p>　　In this network, the major change is in the radio access network (RAN) with the introduction of CDMA technology for the air interface, and ATM as a transport in the trans

13、mission part. These changes have been introduced principally to support the transport of voice, video and data services on the same network. The core network remains relatively unchanged, with primarily software upgrades

14、. However, the IP protocol pushes further into the network with the RNC now communicating with the 3G SGSN us</p><p>　　The next evolution step is the Release 4 architecture, Figure 4. Here, the GSM core is

15、replaced with an IP network infrastructure based around Voice over IP technology.</p><p>　　The MSC evolves into two separate components: a Media Gateway (MGW) and an MSC Server (MSS). This essentially breaks

16、 apart the roles of connection and connection control. An MSS can handle multiple MGWs, making the network more scaleable.</p><p>　　Since there are now a number of IP clouds in the 3G network, it makes sense

17、 to merge these together into one IP or IP/ATM backbone (it is likely both options will be available to operators.) This extends IP right across the whole network, all the way to the BTS.This is referred to as the All-IP

18、 network, or the Release 5 architecture, as shown in Figure 5. The HLR/VLR/EIR are generalised and referred to as the HLR Subsystem(HSS).</p><p>　　Now the last remnants of traditional telecommunications swit

19、ching are removed, leaving a network operating completely on the IP protocol, and generalised for the transport of many service types. Real-time services are supported through the introduction of a new network domain, th

20、e IP Multimedia Subsystem (IMS).</p><p>　　Currently the 3GPP are working on Release 6, which purports to cover all aspects not addressed in frozen releases. Some call UMTS Release 6 4G and it includes such i

21、ssues as interworking of hot spot radio access technologies such as wireless LAN1.2 UMTS FDD and TDD</p><p>　　Like any CDMA system, UMTS needs a wide frequency band in which to operate to effectively spread

22、signals. The defining characteristic of the system is the chip rate, where a chip is the width of one symbol of the CDMA code. UMTS uses a chip rate of 3.84Mchips/s and this converts to a required spectrum carrier of 5MH

23、z wide. Since this is wider than the 1.25MHz needed for the existing cdmaOne system, the UMTS air interface is termed ‘wideband’ CDMA.</p><p>　　There are actually two radio technologies under the UMTS umbrel

24、la: UMTS FDD and TDD. FDD stands for Frequency Division Duplex, and like GSM, separates traffic in the uplink and downlink by placing them at different frequency channels. Therefore an operator must have a pair of freque

25、ncies allocated to allow them to run a network, hence the term ‘paired spectrum’. TDD or Time Division Duplex requires only one frequency channel, and uplink and downlink traffic are separated by sending them at diffe<

26、;/p><p>　　The Time Division Duplex (TDD) system, which needs only one 5MHz band in which to operate, often referred to as unpaired spectrum. The differences between UMTS FDD and TDD are only evident at the lowe

27、r layers, particularly on the radio interface. At higher layers, the bulk of the operation of the two systems is the same. As the name suggests, the TDD system separates uplink and downlink traffic by placing them in dif

28、ferent time slots. As will be seen later, UMTS uses a 10ms frame structure which</p><p>　　The TDD system should not really be considered as an independent network, but rather as a supplement for an FDD syste

29、m to provide hotspot coverage at higher data rates. It is rather unsuitable for large scale deployment due to interference between sites, since a BTS may be trying to detect a weak signal from a UE, which is blocked out

30、by a relatively strong signal at the same frequency from a nearby BTS. TDD is ideal for indoor coverage over small areas.</p><p>　　Since FDD is the main access technology being developed currently, the expla

31、nations presented here will focus purely on this system.</p><p>　　1.3 UMTS Bearer Model</p><p>　　The procedures of a mobile device connecting to a UMTS network can be split into two areas: the a

32、ccess stratum (AS) and the non-access stratum (NAS). The access stratum involves all the layers and subsystems that offer general services to the non-access stratum. In UMTS, the access stratum consists of all of the ele

33、ments in the radio access network, including the underlying ATM transport network, and the various mechanisms such as those to provide reliable information exchange. All of the non-ac</p><p>　　UMTS radio acc

34、ess network (UTRAN) provides this separation of NAS and AS functions, and allows for AS functions to be fully controlled and implemented within the UTRAN. The two major UTRAN interfaces are the Uu, which is the interface

35、 between the mobile device, or User Equipment (UE) and the UTRAN, and the Iu, which is the interface between the UTRAN and the core network. Both of these interfaces can be divided into control and user planes each with

36、appropriate protocol functions.</p><p>　　A Bearer Service is a link between two points, which is defined by a certain set of characteristics. In the case of UMTS, the bearer service is delivered using radio

37、access bearers.</p><p>　　A Radio access bearer (RAB) is defined as the service that the access stratum (i.e.UTRAN) provides to the non-access stratum for transfer of user data between the User Equipment and

38、Core Network. A RAB can consist of a number of subflows, which are data streams to the core network within the RAB that have different QoS characteristics,such as different reliabilities. A common example of this is diff

39、erent classes of bits with different bit error rates can be realised as different RAB subflows. RA</p><p>　　A Radio Link is defined as a logical association between a single User Equipment (UE) and a single

40、UTRAN access point, such as an RNC. It is physically comprised of one or more radio bearers and should not be confused with radio access bearer.</p><p>　　Looking within the UTRAN, the general architecture mo

41、del is as shown in Figure 8 below. Now shown are the Node B or Base Station (BTS) and Radio Network Controller (RNC) components, and their respective internal interfaces. The UTRAN is subdivided into blocks referred to a

42、s Radio Network Subsystems (RNS), where each RNS consists of one controlling RNC (CRNC) and all the BTSs under its control. Unique to UMTS is the interface between RNSs, the Iur interface, which plays a key role in hando

43、ver pro</p><p>　　All the ‘I’ interfaces: Iu, Iur and Iub, currently3 use ATM as a transport layer. In the context of ATM, the BTS is seen as a host accessing an ATM network, within which the RNC is an ATM sw

44、itch. Therefore, the Iub is a UNI interface, whereas the Iu and Iur interfaces are considered to be NNI, as illustrated in Figure 9.</p><p>　　This distinction is because the BTS to RNC link is a point-to-poi

45、nt connection in that a BTS or RNC will only communicate with the RNC or BTS directly connected to it, and will not require communication beyond that element to another network element.</p><p>　　For each use

46、r connection to the core network, there is only one RNC, which maintains the link between the UE and core network domain, as highlighted in Figure 10. This RNC is referred to as the serving RNC or SRNC. That SRNC plus th

47、e BTSs under its control is then referred to as the SRNS. This is a logical definition with reference to that UE only. In an RNS, the RNC that controls a BTS is known as the controlling RNC or CRNC. This is with referenc

48、e to the BTS, cells under its control and all th</p><p>　　As the UE moves, it may perform a soft or hard handover to another cell. In the case of a soft handover, the SRNC will activate the new connection to

49、 the new BTS. Should the new BTS be under the control of another RNC, the SRNC will also alert this new RNC to activate a connection along the Iur interface. The UE now has two links, one directly to the SRNC, and the se

50、cond, through the new RNC along the Iur interface. In this case, this new RNC is logically referred to as a drift RNC or DRNC, see </p><p>　　A situation may arise where a UE is connected to a BTS for which t

51、he SRNC is not the CRNC for that BTS. In that situation, the network may invoke the Serving RNC Relocation procedure to move the core network connection. This process is described inSection 3.</p><p>　　通用移動通

52、信系統(tǒng)的回顧</p><p>　　1.1 UMTS網絡架構</p><p>　　歐洲/日本的3G標準，被稱為UMTS。UMTS是一個在IMT-2000保護傘下的ITU-T批準的許多標準之一。隨著美國的CDMA2000標準的發(fā)展，它是目前占主導地位的標準，特別是運營商將cdmaOne部署為他們的2G技術。在寫這本書時，日本是在3G網絡部署方面最先進的。三名現(xiàn)任運營商已經實施了三個不同的技術：

53、J - PHONE使用UMTS，KDDI擁有CDMA2000網絡，最大的運營商NTT DoCoMo正在使用品牌的FOMA（自由多媒體接入）系統(tǒng)。 FOMA是基于原來的UMTS協(xié)議，而且更加的協(xié)調和標準化。</p><p>　　UMTS標準被定義為一個通過通用分組無線系統(tǒng)（GPRS）和全球演進的增強數(shù)據(jù)技術（EDGE）從第二代GSM標準到UNTS的遷移。這是一個廣泛應用的基本原理，因為自2003年4月起，全球有超過

54、847萬GSM用戶，占全球的移動用戶數(shù)字的68％。重點是在保持盡可能多的GSM網絡與新系統(tǒng)的操作。</p><p>　　我們現(xiàn)在在第三代(3G)的發(fā)展道路上，其中網絡將支持所有類型的流量：語音，視頻和數(shù)據(jù)，我們應該看到一個最終的爆炸在移動設備上的可用服務。此驅動技術是IP協(xié)議?，F(xiàn)在，許多移動運營商在簡稱為2.5G的位置，伴隨GPRS的部署，即將IP骨干網引入到移動核心網。</p><p>

55、　　SGSN和GGSN之間的接口被稱為Gn接口和使用GPRS隧道協(xié)議（GTP的，稍后討論）。引進這種基礎設施的首要原因是提供連接到外部分組網絡如，Internet或企業(yè)Intranet。這使IP協(xié)議作為SGSN和GGSN之間的運輸工具應用到網絡。這使得數(shù)據(jù)服務，如移動設備上的電子郵件或瀏覽網頁，用戶被起訴基于數(shù)據(jù)流量，而不是時間連接基礎上的數(shù)據(jù)量。3G網絡和服務交付的主要標準是通用移動通信系統(tǒng)，或UMTS。首次部署的UMTS是發(fā)行

56、9;99架構。</p><p>　　在這個網絡中，主要的變化是在無線接入網絡（RAN的）CDMA空中接口技術的引進，和在傳輸部分異步傳輸模式作為一種傳輸方式。這些變化已經引入，主要是為了支持在同一網絡上的語音，視頻和數(shù)據(jù)服務的運輸。核心網絡保持相對不變，主要是軟件升級。然而，隨著目前無線網絡控制器使用IP與3G的GPRS業(yè)務支持節(jié)點進行通信，IP協(xié)議進一步應用到網絡。</p><p>　　

57、未來的進化步驟是第4版架構。在這里，GSM的核心被以語音IP技術為基礎的IP網絡基礎設施取代。</p><p>　　海安的發(fā)展分為兩個獨立部分：媒體網關（MGW）和MSC服務器（MSS）的。這基本上是打破外連接的作用和連接控制。一個MSS可以處理多個MGW，使網絡更具有擴展性。</p><p>　　因為現(xiàn)在有一些在3G網絡的IP云，合并這些到一個IP或IP/ ATM骨干網是很有意義的（它很

58、可能會提供兩種選擇運營商）。這使IP權利拓展到整個網絡，一直到BTS(基站收發(fā)信臺)。這被稱為全IP網絡，或推出五架構，如圖五所示。在HLR/ VLR/VLR/EIR被推廣和稱為HLR的子系統(tǒng)（HSS）。</p><p>　　現(xiàn)在傳統(tǒng)的電信交換的最后殘余被刪除，留下完全基于IP協(xié)議的網絡運營，并推廣了許多服務類型的運輸。實時服務通過引入一個新的網絡域名得到支持，即IP多媒體子系統(tǒng)（IMS）。</p>

59、<p>　　目前3GPP作用于第6版，意在包含冷凍版本沒有涵蓋所有方面。有些人稱UMTS 第6版為4G和它包括熱點無線電接入技術，如無線局域網互聯(lián)互通的問題。</p><p>　　1.2 UMTS的FDD和TDD</p><p>　　像任何CDMA系統(tǒng)，UMTS需要一個寬的頻帶，在這個頻帶上有效地傳播信號。該系統(tǒng)的特點是芯片的速度，芯片是一個符號的CDMA代碼的寬度。 UMTS

60、使用的芯片速率為3.84Mchips/秒，這轉換到所需的頻譜載波寬度為5MHz。由于這比現(xiàn)有的cdmaOne系統(tǒng)所需的1.25MHz帶寬要寬，UNTS空中接口被稱為“寬帶”CDMA.</p><p>　　實際上在UMTS下有兩個無線電技術：UMTS軟盤驅動器和時分雙工。FDD代表頻分雙工，如GSM，通過把它們放置在不同的頻率信道分離為交通上行和下行。因此，一個運營商必須有一對頻率分配，使他們能夠運行網絡，即術語成

61、對頻譜。TDD或時分雙工只需要一個頻率通道，上行和下行流量是在不同的時間分開發(fā)送。 ITU-T的頻譜使用。對于FDD是1920 - 1980MHz的為上行流量，2110-2170MHz為下行的。運營商需要的最小分配是兩個成對5MHz的信道，一個用于上行，一個用于下行的，兩者相分離190MHz。然而，為了給客戶提供全面的覆蓋和服務，建議給予每個運營商三個信道?？紤]到頻譜分配，有12對可用的渠道，現(xiàn)在許多國家都完成了這個頻譜的許可過程，每個

62、許可證配置兩個到四個信道。這趨向給運營商造成一個昂貴的花費，因為一些國家的監(jiān)管部門，特別是在歐洲，已經將這些許可證拍賣給出價最高的人。這就造成了頻譜費用在一些國家高達數(shù)十億美元。</p><p>　　時分雙工（TDD）系統(tǒng)，只需要一個5MHz的帶寬在其中操作，通常被稱為非成對頻譜。UMTS FDD和TDD之間的差異只有在較低層明顯，特別是在無線接口。在更高的層次，兩個系統(tǒng)的運作大部分是相同的。正如它的名字表明，T

63、DD系統(tǒng)通過把它們放置在不同的時間空擋分為上行流量和下行流量。正如我們以后可以看到的， UMTS使用一個分為15個相等的時隙的10ms幀結構。 時分雙工可以分配這些為上行或下行，在一個確定的幀結構中這兩者間可以有一個或多個斷點。以這種方式，這是非常適合數(shù)據(jù)包通信的，因為這對于不對稱的通信流的動態(tài)標注可以有極大的靈活性。</p><p>　　TDD系統(tǒng)真的不應該被視為一個獨立的網絡，而是作為一個FDD系統(tǒng)的補充，提

64、供更高的數(shù)據(jù)傳輸率的熱點覆蓋。由于站點之間的干擾，它相當不合適用作大規(guī)模部署，因為一個基站可以嘗試從UE檢測微弱信號，這被來自鄰近基站的相同頻率的相對較強的信號阻止了。 時分雙工對于小面積的室內覆蓋是理想的。</p><p>　　由于FDD是目前正在發(fā)展的主要的接入技術，這里介紹的解釋將完全專注于這個系統(tǒng)。</p><p>　　1.3 UMTS承載模型</p><p&g

65、t;　　移動設備連接到UMTS網絡的程序可以分成兩領域：接入層（AS）和非接入層（NAS）。接入層涉及所有提供普遍服務的非接入層和子系統(tǒng)階層。在UMTS接入層包括無線接入的所有元素網絡，包括潛在的ATM傳輸網絡，各種機制提供可靠的信息交換等。所有的非接入層功能都在移動設備和核心網絡之間，例如，移動性管理。圖7顯示了結構模型。AS通過使用服務接入點（SAPS）與NAS交互。</p><p>　　UMTS無線接入網（

66、UTRAN）提供NAS和AS功能的分離，并允許AS功能在UTRAN中被完全控制和實施。兩大UTRAN的接口是UU，這是移動設備之間的接口，或者用戶設備（UE）和UTRAN之間，Iu，這是UTRAN和核心網之間的接口。這些接口都可以分為控制平面和用戶平面，每個都有適當?shù)膮f(xié)議功能。承載服務是兩點間的連接，這是由一組特定的特點定義的。在UMTS的情況下，使用無線接入承載提供承載服務。</p><p>　　無線接入承載（

67、RAB）被定義為用戶設備和核心網絡之間的服務，即接入層（ieUTRAN）為非接入層提供用戶數(shù)據(jù)傳輸。一個RAB可以由一些支流組成，這是數(shù)據(jù)流在有不同的QoS特性的RAB流向核心網絡，如不同的可靠性。一個常見的例子是不同類別的位有不同的位錯誤率，可以實現(xiàn)不同的RAB子流。RAB子流在RAB建立和釋放的同時建立和釋放，并通過相同的傳輸承載一起傳輸。</p><p>　　無線電鏈路被定義為一個單一的用戶設備（UE）和一

68、個單一的UTRAN接入點之間的邏輯關聯(lián)，如一個RNC。它實際上是由一個或多個無線承載組成和不應和無線接入承載混淆。</p><p>　　在UTRAN內部來看，總體架構模型在下面的圖8所示?，F(xiàn)在顯示的是節(jié)點B基站（BTS）和無線網絡控制器（RNC）組件，以及它們各自的內部接口。UTRAN分為被稱為無線網絡子系統(tǒng)（RNS）的塊，其中每個RNS由一個控制RNC和控制下的所有基站組成。UMTS的獨特之處是RNS之間的接口

69、，Iur接口，在交接過程起了關鍵作用。基站和RNC之間的接口是Iub接口。</p><p>　　所有“I”接口：Iu，Iur和Iub，currently3將ATM用作傳輸層。在ATM的背景下，BTS被看作是ATM網絡的主機訪問，在這個網絡中RNC是一個ATM交換機。因此，Iub是一個UNI接口，而Iu和Iur接口被認為是NNI。</p><p>　　這種區(qū)別是因為基站到RNC的鏈接是一個點

70、至點連接，在這個連接中一個基站或RNC只和與它直接連接的RNC或基站通信，并且不會要求和其他網絡元素的元素。</p><p>　　對于每個用戶連接到核心網絡，這里只有一個RNC，保持UE和核心網域之間的聯(lián)系。RNC是指服務RNC或SRNC。SRNC加上在其控制下的基站被稱為SRNS。這是一個只以UE為參考的邏輯定義。在一個RNS中，控制基站的RNC被稱為控制RNC或CRNC。這是以基站為參考，其控制下的部分和所有

71、常見的和共享的渠道內。</p><p>　　因為UE移動，它可能執(zhí)行軟或硬切換到另一個蜂窩。在軟切換的情況下，SRNC將啟動新的連接到新的基站。新的基站應該是在另一個RNC控制下，SRNC中也會提醒這個新的RNC啟動沿Iur接口連接。UE現(xiàn)在有兩個連接，一個直接連接SRNC，第二個通過新的RNC連接Iur接口。在這種情況下，這個新的RNC在邏輯上被稱為漂移RNC或DRNC。它不涉及任何呼叫處理，只是將它中繼到SR