外文翻譯---寬帶cdma無(wú)線接入網(wǎng)的基本概念

1、<p><b>　　附錄3：英文資料</b></p><p>　　Basic Concepts of WCDMA Radio Access Network</p><p>　　1. Background</p><p>　　There has been a tremendous growth in wireless communic

2、ation technology over the past decade. The significant increase in subscribers and traffic, new bandwidth consuming applications such as gaming, music down loading and video streaming will place new demands on capacity.

3、The answer to the capacity demand is the provision of new spectrum and the development of a new technology - Wideband CDMA or hereinafter referred to as WCDMA. WCDMA was developed in order to create a global standard fo

4、r rea</p><p>　　2. WCDMA a development from GSM and CDMA</p><p>　　Naturally there are a lot of differences between WCDMA and GSM systems, hut there are many similarities as well.</p><

5、p>　　The GSM Base Station Subsystem (BSS) and the WCDMA Radio Access Network (RAN) are both connected to the GSM core network for providing a radio connection to the handset. Hence, the technologies can share the same

6、core network. Furthermore, both GSM BSS and WCDMA RAN systems are based on the principles of a cellular radio system. The GSM Base Station Controller (ESC) corresponds to the WCDMA Radio Network Controller (RNC). The GSM

7、 Radio Base Station (RBS) corresponds to the WCDMA RES, and the A -</p><p>　　Code Division Multiple Access and WCDMA</p><p>　　Code Division Multiple Access (CDMA) is a multiple access technology

8、 where the users are separated by unique codes, which means that all users can use the same frequency and transmit at the same time. With the fast development in signal processing,' it has become feasible to use the

9、technology for wireless communication, also referred to as WCDMA and CDMA2000.</p><p>　　In CDMA One and CDMA2000, a 1.25MHz wide radio signal is multiplied by a spreading signal (which is a pseudo-noise code

10、 sequence) with a higher rate than the data rate of the message. The resultant signal appears as seemingly random, but if the intended recipient has the right code, this process is reversed and the original signal is ext

11、racted. Using unique codes means that the same frequency is repeated in all cells. which is commonly referred to as a frequency re-use of 1.</p><p>　　WCDMA is a step further in the CDMA technology. It uses a

12、 5MHz wide radio signal and a chip rate of 3.84Mcps, which is about three times higher than the chip rate of CDMA2000. The main benefits of a wideband carrier with a higher chip rate are:</p><p>　　● Support

13、for higher bit rates </p><p>　　● Higher spectrum efficiency thanks to improved trunking efficiency (i.e. a better statistical averaging) </p><p>　　● Higher QoS </p><p>　　Further, e

14、xperience from second-generation systems like GSM and CDMA One has enabled improvements to be incorporated in WCDMA. Focus has also been put on ensuring that as much as possible of WCDMA operators' investments in GSM

15、 equipment can be reused. Examples are the re-use and evolution of the core network, the focus on co-siting and the support of GSM handover. In order to use GSM handover, the' subscribers need dual mode handsets.<

16、/p><p>　　3. Radio Network Functionality</p><p>　　For optimal operation of a complete wireless system i.e. from handset to radio access network (RAN) several functions are needed to control the rad

17、io network and the many handsets using it. All functions described in this section, except' for Handover to GSM,' are essential and therefore necessary for a WCDMA system.</p><p>　　3.1 Power control&

18、lt;/p><p>　　The power control regulates the transmit power of the terminal and base station, which results in less interference and allows more users on the same carrier. Transmit power regulation thus provides

19、 more capacity in the network. With a frequency re-use of 1, it is very important to have efficient power control in order to keep the interference at a minimum. For each subscriber service the aim is that the base stati

20、on shall receive the same power level from all handsets in the cell regardless of </p><p>　　Power control also gives rise to a phenomenon called "cell breathing". This is the trade-off between cove

21、rage and capacity, which means that the size of the cell varies depending on the traffic load. When the number of subscribers in the cell is low (low load), good quality can be achieved even at a long distance from the b

22、ase station. On the other hand, when the number of users in the cell is high, the large number of subscribers generates a high interference level and subscribers have to get c</p><p>　　3.2 Soft and softer ha

23、ndover</p><p>　　With soft and softer handover functionality the handset can communicate simultaneously with two or more cells in two or more base stations. This flexibility in keeping the connection open to

24、more than one base station results in fewer lost calls, which is very important to the operator.</p><p>　　To achieve good system performance with a frequency re-use of 1 and power control, soft and softer ha

25、ndover is required. Soft and softer handover enables the handset to maintain the continuity and quality of the connection while moving from. one cell to another. </p><p>　　During soft handover, the handset w

26、ill momentarily adjust its power to the base station that requires the smallest amount of transmit power and the preferred cell may change very rapidly. The difference between soft and softer handover is that during soft

27、 handover, the handset is connected to multiple cells at different base stations, while during softer handover, the handset is connected to multiple cells at the same base station. A drawback with soft handover is that i

28、t requires additional har</p><p>　　3.3 Handover to GSM (inter-system handover) </p><p>　　When WCDMA was standardized a key aspect was to ensure that existing investments could be re-used as much

29、 as possible. One example is handover between the new (WCDMA) network and the existing (GSM) network, which can be triggered by coverage, capacity or service requirements. Handover from WCDMA to GSM, for coverage reasons

30、, is initially expected to be very important since operators are expected to deploy WCDMA gradually within their existing GSM network . When a subscriber moves out of the WCDM</p><p>　　Handover between GSM a

31、nd WCDMA can also have a positive effect on capacity through the possibility of load sharing. If for example the numbers of subscribers in the GSM network is close to the capacity limit in one area, handover of some subs

32、cribers to the WCDMA network can be performed.</p><p>　　Another function that is related to inter-system handover is the compressed mode. When performing handover to GSM, measurements have to be made in orde

33、r to identify the GSM cell to which the handover will be made. The compressed mode is used to create the measurement periods for the handset to make the required measurements.</p><p>　　3.4 Inter-frequency ha

34、ndover (intra-system handover)</p><p>　　The need for inter-frequency handover occurs in high capacity areas where multiple 5MHz WCDMA carriers are deployed. Inter-frequency handover, which is handover betwee

35、n WCDMA carriers on different frequencies, has many similarities with GSM handover, for example the compressed mode functionality.</p><p>　　3.5 Channel type switching</p><p>　　In WCDMA there are

36、 different types of channels that can be used to carry data in order to maximize the total traffic throughput. The two most basic ones are common channels and dedicated channels. Channel type switching functionality is u

37、sed to move subscribers between the common and the dedicated channel, depending on how much information the subscriber needs to transmit. The dedicated channel is used when there is much information to transmit, such as

38、a voice conversation or downloading a web </p><p>　　3.6 Admission control</p><p>　　As there is a very clear trade-off between coverage and capacity in WCDMA systems, the admission control functi

39、onality is used to avoid system overload and to provide the planned coverage. When a new subscriber seeks access to the network, admission control estimates the network load and based on the new expected load, the subscr

40、iber is either admitted or blocked out. By this the operator can maximize the network usage within a set of network quality levels, i.e. levels depending on what kind of</p><p>　　3.7 Congestion control </

41、p><p>　　Even though an efficient admission control is used, overload may still occur, which is mainly caused by subscribers moving from one area to another area. If overload occurs, four 'different actions

42、can be taken. First, congestion control is activated and reduces the bit rate of non real-time applications, to resolve the overload. Second, if the reduced bit rate activity is not sufficient, the congestion control tri

43、ggers the inter- or intra-frequency handover, which moves some subscribers to less</p><p>　　3.8 Synchronization </p><p>　　One of the basic requirements when WCDMA was standardized was to avoid d

44、ependence on external systems for accurate synchronization of base stations. This has been achieved by a mechanism, where the handset, when needed, measures the synchronization offset between the cells and reports this t

45、o the network. In addition, there is also an option to use an external source, such as GPS, for synchronizing the nodes, i.e. to always provide the best solution both asynchronous and synchronous nodes are su</p>

46、<p>　　4. Basic architecture concepts/ System overview</p><p>　　4.1 Radio Access Network (RAN) Architecture </p><p>　　The main purpose of the WCDMA Radio Access Network is to provide a conn

47、ection between the handset and the core network and to isolate all the radio issues from the core network. The advantage is one core network supporting multiple access technologies.</p><p>　　The WCDMA Radio

48、Access Network consists of two types of nodes:</p><p>　　Radio Base Station (Node B)</p><p>　　The Radio Base Station handles the radio transmission and reception to/from the handset over the radi

49、o interface (Iu). It is controlled from the Radio Network Controller via the Iub interface. One Radio Base Station can handle one or more cells.</p><p>　　Radio Network Controller (RNC)</p><p>　　

50、The Radio Network Controller is the node that controls all WCDMA Radio Access Network functions. It connects the WCDMA Radio Access Network to the core network via the Iu interface. There are two distinct roles for the R

51、NC, to serve and to control. The Serving RNC has overall control of the handset that is connected to WCDMA Radio Access Network. It controls the connection on the Iu interface for the handset and it terminates several pr

52、otocols in the contact between the handset and the WCDMA Rad</p><p>　　The Controlling RNC has the overall control of a particular set of cells, and their associated base stations. When a handset must use res

53、ources in a cell not controlled by its Serving RNC, the Serving RNC must ask the Controlling RNC for those resources. This request is made via the Iur interface, which connects the RNCs with each other. In this case, the

54、 Controlling RNC is also said to be a Drift RNC for this particular handset. This kind of operation is primarily needed to be able to provide s</p><p>　　Radio Access Bearers (RAB)</p><p>　　The m

55、ain service offered by WCDMA RAN is the Radio Access Bearer (RAB). A RAB is needed to establish a call connection between the handset and the base station. Its characteristics ate determined by certain Quality of Service

56、 (QoS) parameters, such as bit rate and delay, and are different depending on what kind of service/information to be transported.</p><p>　　The RAB carries the subscriber data between the handset and the core

57、 network. It is composed of one or more Radio Access Bearers between the handset and the Serving RNC, and one Iu bearer between the Serving RNC and the core network. 3GPP has defined four different quality classes of Rad

58、io Access Bearers:</p><p>　　●Conversational (used for e.g. voice telephony) - low delay, strict ordering </p><p>　　●Streaming (used for e.g. watching a video) - moderate delay, strict ordering &

59、lt;/p><p>　　●Interactive (used for e.g. web surfing) - moderate delay </p><p>　　●Background (used for e.g. me transfer) - no delay </p><p>　　4.2 Transport in WCDMA Radio Access Network

60、 </p><p>　　The WCDMA Radio Access Network nodes communicate with each other over a transport network. The 3GPP specification provides a very clear, split between radio related (WCDMA)functionality and the tr

61、ansport technology, meaning that there is no particular bias to any technology. The transport network is initially based on ATM, but IP will soon be included as an option.</p><p>　　附錄4：英文資料譯文</p><

62、;p>　　寬帶CDMA無(wú)線接入網(wǎng)的基本概念</p><p><b>　　一、背景</b></p><p>　　過(guò)去十年，無(wú)線通信技術(shù)有了巨大發(fā)展，用戶量的顯著增加，使得諸如游戲、音樂(lè)下載和視頻流量有了新的容量需求。對(duì)容量需求的解決辦法是，提供新的頻譜和開(kāi)發(fā)新的技術(shù)一一寬帶CDMA或下面所說(shuō)的WCDMA。為創(chuàng)建一個(gè)能夠在全球范圍內(nèi)漫游的實(shí)時(shí)多媒體服務(wù)標(biāo)準(zhǔn)，人們開(kāi)發(fā)

63、了WCDMA，ITU (國(guó)際電信聯(lián)盟)對(duì)此給予支持并為第三代（3G）電信系統(tǒng)分配了一個(gè)2GHz專用頻譜，隨后這項(xiàng)工作由3GPP (第三代伙伴項(xiàng)目)接管，現(xiàn)在它已經(jīng)是代表全球WCDMA的專業(yè)實(shí)體。</p><p>　　二、基于GSM和CDMA發(fā)展起來(lái)的WCDMA </p><p>　　WCDMA與GSM有很多差別，但同樣也有很多相同之處。</p><p>　　GSM基

64、站子系統(tǒng)(BSS)和WCDMA無(wú)線接入網(wǎng)(RAN)是兩個(gè)連接到GSM的核心網(wǎng)絡(luò)，用以提供對(duì)手持設(shè)備的無(wú)線連接。因此，這些技術(shù)可以共享同一核心網(wǎng)絡(luò)。進(jìn)而，GSM BSS與WCDMA RAN兩者都是基于蜂窩無(wú)線系統(tǒng)的。GSM基站控制器(BSC) 相對(duì)應(yīng)于WCDMA無(wú)線網(wǎng)絡(luò)控制器(RNC)。GSM無(wú)線基站(RBS)對(duì)應(yīng)于WCDMA的無(wú)線基站RBS， GSM A接口又是WCDMA Iu接口的發(fā)展基礎(chǔ)，兩者的主要區(qū)別是在WCDMA 提供新業(yè)務(wù)的內(nèi)

65、容上。差別最大的，除了在GSM BSCs與GSM Abis接口之間缺乏提供多用戶可操作性的接口之外，大多是系統(tǒng)方面的差別。GSM系統(tǒng)采用基于時(shí)隙管理，具有多種無(wú)線功能的TDMA (時(shí)分多路接入)技術(shù)，而WCDMA系統(tǒng)則是采用CDMA技術(shù)，這意味著硬件和控制功能兩者是不同的。WCDMA特殊功能的例子，是快速功率控制和軟切換。</p><p>　　CDMA與WCDMA</p><p>　　碼分

66、多路接入(CDMA)是一種用戶被惟一編碼劃分的多路接入技術(shù)，這意味著所有用戶在同一時(shí)刻使用同一頻率傳輸。隨著信號(hào)處理的快速發(fā)展，這種技術(shù)對(duì)無(wú)線通信服務(wù)是可行的，即確定為WCDMA與CDMA2000。</p><p>　　在CDMA One and CDMA 2000中，將帶寬為1.25 MHz的射頻信號(hào)與一個(gè)數(shù)據(jù)速率高于信息信號(hào)數(shù)據(jù)率的擴(kuò)頻信號(hào)(是一種偽噪聲編碼序列)相乘，其結(jié)果，信號(hào)表面上呈現(xiàn)隨機(jī)，但預(yù)定接收機(jī)

67、卻有確知的編碼，通過(guò)相反的處理過(guò)程，使原始信號(hào)被提取。采用惟一編碼意味著同一頻率可在所有的小區(qū)中被重復(fù)，通常被認(rèn)為是頻率的一次重復(fù)利用。 </p><p>　　WCDMA是CDMA技術(shù)的進(jìn)一步發(fā)展，它采用一個(gè)5MHz的寬帶無(wú)線信號(hào)和一個(gè)3.84 Mcps的片碼速率，其大約是CDMA 2000片碼速率的3倍，采用高片碼速率寬帶載波的好處是:</p><p><b>　　●支持高比特

68、速率。</b></p><p>　　●具有得益于改善中繼效能的高頻譜效能(即有較好的統(tǒng)計(jì)平均值)。</p><p>　　●具有較高的服務(wù)質(zhì)量。</p><p>　　進(jìn)一步說(shuō)，在第二代系統(tǒng)GSM和CDMA One取得的經(jīng)驗(yàn)，改善了與WCDMA的融合， 重點(diǎn)放在了盡可能地使WCDMA運(yùn)營(yíng)商在GSM設(shè)備上的投資能夠得到重新利用。如核心網(wǎng)絡(luò)的再使用與改造，全面共

69、址和對(duì)GSM切換的支持是問(wèn)題的焦點(diǎn)，為了使用GSM切換，用戶需要雙重模式的切換。</p><p>　　三、無(wú)線網(wǎng)絡(luò)的功能性</p><p>　　一個(gè)完備的無(wú)線系統(tǒng)優(yōu)化運(yùn)行，從手持設(shè)備到無(wú)線接入網(wǎng)(RAN) ，需要一些功能來(lái)控制無(wú)線網(wǎng)絡(luò)和許多手持設(shè)備，除了需要越區(qū)切換到GSM外，本節(jié)描述的所有功能，都是基本的，因而對(duì)WCDMA系統(tǒng)也是必要的。</p><p><

70、b>　　1.功率控制</b></p><p>　　功率控制用來(lái)調(diào)整終端和基站的發(fā)送功率，以獲得干擾小的結(jié)果，同時(shí)允許更多的用戶使用同一載頻。這樣通過(guò)對(duì)發(fā)送功率的調(diào)整，來(lái)提供更多的網(wǎng)絡(luò)容量。隨著頻率可重復(fù)利用，有效的功率控制非常重要，以保持干擾最小。為每個(gè)用戶服務(wù)的目的是，無(wú)論手持設(shè)備距離基站多遠(yuǎn)，基站都將接收到小區(qū)內(nèi)所有手持設(shè)備的功率，且都相等，如果接收到某一手持設(shè)備的功率電平高于預(yù)定功率電平，

71、通信質(zhì)量將會(huì)超過(guò)限值，將造成不按比例共享資源，并對(duì)網(wǎng)絡(luò)中的其他用戶產(chǎn)生不必要的干擾。另一方面，如果功率電平太低，這種情況將會(huì)導(dǎo)致質(zhì)量變壞，為了維持所接收到的功率電平為一個(gè)合適的數(shù)值，WCDMA具有每秒更新1500次的快速功率控制功能，由此對(duì)快速切換無(wú)線信道進(jìn)行處理。為確保最佳運(yùn)行，在上行鏈路與下行鏈路執(zhí)行功率控制，這意味著要不斷更新手持設(shè)備輸出功率與基站輸出功率。</p><p>　　功率控制會(huì)引起一種被稱為是&

72、quot;小區(qū)呼吸"的現(xiàn)象，它平衡了小區(qū)覆蓋范圍與用戶容量的問(wèn)題，意味著小區(qū)大小要隨話務(wù)量載荷而變。當(dāng)小區(qū)中的用戶數(shù)量較低時(shí)（低載荷)，即使是手持設(shè)備距離基站較遠(yuǎn)，也能夠獲得高質(zhì)量的通信效果。另一方面，當(dāng)小區(qū)中的用戶數(shù)量較大時(shí)，就會(huì)產(chǎn)生很高的干擾電平，用戶需要靠近基站很近才能獲得高質(zhì)量的通信效果。 </p><p>　　2.軟切換與次軟切換</p><p>　　采用軟切換與次軟切

73、換功能，手持設(shè)備可與兩個(gè)或兩個(gè)以上基站中的多個(gè)小區(qū)同時(shí)進(jìn)行通信，這種與一個(gè)以上基站保持開(kāi)放連接的靈活性，同時(shí)能獲得較低的呼叫損耗，對(duì)運(yùn)營(yíng)商非常重要。</p><p>　　為使系統(tǒng)獲得具有頻率一次復(fù)用和功率控制的良好運(yùn)行狀態(tài)，需要軟切換和次軟切換。它們能夠使手持設(shè)備從一個(gè)小區(qū)移動(dòng)到另一個(gè)小區(qū)，維持連接不中斷并保持通信的質(zhì)量。</p><p>　　在軟切換和次軟切換期間，手持設(shè)備將對(duì)需要最小發(fā)

74、射功率的基站瞬間調(diào)整自己的功率，并非?？斓厍袚Q首選小區(qū)。軟切換與次軟切換的差別是，在軟切換期間，手持設(shè)備將在不同基站被連接到多個(gè)小區(qū)；而在次軟切換期間，手持設(shè)備是在同一基站被連接到多個(gè)小區(qū)。軟切換的缺點(diǎn)是，它需要在網(wǎng)絡(luò)側(cè)占用額外的硬件資源來(lái)實(shí)現(xiàn)手持設(shè)備的多連接。對(duì)于一個(gè)設(shè)計(jì)良好的無(wú)線網(wǎng)絡(luò)，有30%～40%的用戶是處在軟切換和次軟切換的狀態(tài)。</p><p>　　3.切換到GSM (系統(tǒng)內(nèi)部切換)</p>

75、;<p>　　WCDMA標(biāo)準(zhǔn)化的一個(gè)重要方面，是確?，F(xiàn)有投資盡可能地被利用，例如在新網(wǎng)絡(luò)(WCDMA)與現(xiàn)有網(wǎng)絡(luò)(GSM)兩者之間切換，就需要由覆蓋范圍、用戶容量和服務(wù)需求來(lái)啟動(dòng)。為覆蓋范圍，從WCDMA切換到GSM開(kāi)始變得十分重要，因?yàn)檫\(yùn)營(yíng)商希望在現(xiàn)有GSM網(wǎng)絡(luò)中逐步配置WCDMA網(wǎng)絡(luò)，因而，當(dāng)用戶移出WCDMA的覆蓋范圍時(shí)，為了維持連接，就需要進(jìn)行切換到GSM的操作。</p><p>　　在GS

76、M與WCDMA之間切換，同樣也會(huì)對(duì)載荷共享容量調(diào)整產(chǎn)生積極的效果。例如， 若GSM網(wǎng)絡(luò)中的一些用戶在一個(gè)區(qū)域內(nèi)接近于容量限制時(shí)，一些用戶就會(huì)被執(zhí)行切換到 WCDMA網(wǎng)絡(luò)的操作。</p><p>　　另一個(gè)與系統(tǒng)內(nèi)部切換有關(guān)的功能是壓縮模式，當(dāng)執(zhí)行切換到GSM的操作時(shí)，為識(shí)別 GSM小區(qū)需要執(zhí)行哪一種切換，就需要執(zhí)行測(cè)量。壓縮模式用于對(duì)手持設(shè)備進(jìn)行必要測(cè)量和建立測(cè)量周期。</p><p>　

77、　4.內(nèi)部頻率切換(系統(tǒng)內(nèi)部切換)</p><p>　　內(nèi)部頻率切換出現(xiàn)在倍頻為5MHz WCDMA的大用戶容量區(qū)域，切換是在不同頻率下的 WCDMA載頻之間的切換，與GSM的切換有很多類似之處，例如，壓縮模式功能。</p><p><b>　　5.信道類型交換 </b></p><p>　　WCDMA有很多不同類型的信道，為使總的通話能力達(dá)到

78、最大，這些信道被用于承載數(shù)據(jù)。有兩種最為基本的信道，一種是公共信道，另一種是專用信道。信道類型交換功能用于在公共與專用信道之間轉(zhuǎn)移用戶，這取決于用戶需要發(fā)送的信息量有多大，諸如語(yǔ)音會(huì)話或下載網(wǎng)頁(yè)。它有效地利用無(wú)線資源作為對(duì)功率控制和軟切換的支持。</p><p><b>　　6.準(zhǔn)入控制</b></p><p>　　在WCDMA系統(tǒng)中，由于覆蓋范圍與用戶容量之間交替切

79、換是透明的，因而準(zhǔn)入功能被用于避免系統(tǒng)過(guò)載及保護(hù)預(yù)定的覆蓋范圍。當(dāng)一個(gè)新的用戶尋求接入網(wǎng)絡(luò)，準(zhǔn)入控制對(duì)網(wǎng)絡(luò)載荷進(jìn)行估計(jì)，基于新的預(yù)期載荷，用戶要么被準(zhǔn)入，要么被阻斷。據(jù)此，運(yùn)營(yíng)商可在網(wǎng)絡(luò)質(zhì)量等級(jí)允許范圍內(nèi)最大限度地使用網(wǎng)絡(luò)，即網(wǎng)絡(luò)質(zhì)量等級(jí)取決于用戶想要使用的服務(wù)等級(jí)或信息類型。</p><p><b>　　7.搪塞控制</b></p><p>　　即使采用有效的準(zhǔn)入控

80、制，過(guò)載仍可能發(fā)生，這種情況主要發(fā)生在用戶從一個(gè)區(qū)域移動(dòng)到另一個(gè)區(qū)域，如果出現(xiàn)過(guò)載，將會(huì)采取四種不同的動(dòng)作。第一種動(dòng)作是激活擁塞控制，降低非實(shí)時(shí)應(yīng)用的比特速率，以解決過(guò)載問(wèn)題；第二種動(dòng)作是如果不足以降低比特速率，擁塞控制會(huì)激發(fā)內(nèi)部頻率切換，將用戶切換到載荷較少的頻率上；第三種動(dòng)作是將一些用戶切換到GSM；第四種動(dòng)作是斷開(kāi)連接，以保護(hù)剩余連接的通信質(zhì)量。</p><p><b>　　8.同步</b&

81、gt;</p><p>　　基站精確同步作為WCDMA標(biāo)準(zhǔn)化的基本必要條件之一，可避免依賴外部系統(tǒng)，這項(xiàng)任務(wù)由一種機(jī)制來(lái)完成，即手持設(shè)備處在什么位置，需要在什么時(shí)間，測(cè)量出小區(qū)之間的同步偏差，并將此偏差報(bào)告給網(wǎng)絡(luò)。此外，同樣還可以選擇使用外部同步源，如采用GPS來(lái)同步節(jié)點(diǎn)，為支持非同步節(jié)點(diǎn)和同步節(jié)點(diǎn)提供最佳的解決方案。</p><p>　　四、基本體系結(jié)構(gòu)概念/系統(tǒng)概要</p>

82、<p>　　1.無(wú)線接入網(wǎng)(RAN)的結(jié)構(gòu) </p><p>　　WCDMA無(wú)線接入網(wǎng)的主要目的是提供手持設(shè)備與核心網(wǎng)之間的連接，同時(shí)隔離來(lái)自于核心網(wǎng)的所有無(wú)線連接。其優(yōu)點(diǎn)是一個(gè)核心網(wǎng)可以支持多接入技術(shù)。 </p><p>　　WCDMA無(wú)線接入網(wǎng)由兩種類型的節(jié)點(diǎn)組成:</p><p>　　·無(wú)線基站(節(jié)點(diǎn)B)</p><

83、p>　　無(wú)線基站通過(guò)無(wú)線接口（Iu)處理到達(dá)或來(lái)自于手持設(shè)備的發(fā)送和接收信號(hào)，由無(wú)線網(wǎng)絡(luò)控制器經(jīng)Iub接口對(duì)其進(jìn)行控制，一個(gè)無(wú)線基站可以處理一個(gè)或多個(gè)小區(qū)。</p><p>　　·無(wú)線網(wǎng)絡(luò)控制器(RNC)</p><p>　　無(wú)線網(wǎng)絡(luò)控制器是控制所有WCDMA無(wú)線接入網(wǎng)絡(luò)功能的節(jié)點(diǎn)，它將WCDMA無(wú)線接入網(wǎng)絡(luò)通過(guò)Iu接口連接到核心網(wǎng)絡(luò)。RNC有兩種獨(dú)特的作用，即服務(wù)和控制。

84、服務(wù)RNC對(duì)連接到WCDMA無(wú)線網(wǎng)絡(luò)的手持設(shè)備進(jìn)行全部控制，它控制手持設(shè)備在Iu接口上的連接，并終止在手持設(shè)備與WCDMA無(wú)線網(wǎng)絡(luò)之間的若干連接協(xié)議。</p><p>　　控制RNC對(duì)特殊小區(qū)群及其相關(guān)的基站進(jìn)行全面控制，當(dāng)一個(gè)手持設(shè)備必須使用一個(gè)小區(qū)的資源，而這個(gè)小區(qū)的資源沒(méi)有被服務(wù)RNC控制時(shí)，服務(wù)RNC必須向控制RNC請(qǐng)求使用這些資源，該請(qǐng)求經(jīng)過(guò)Iur接口產(chǎn)生并相互連接到RNCs。在這種情況下，對(duì)這個(gè)特殊手

85、持設(shè)備，控制RNC同樣會(huì)被認(rèn)為是一個(gè)浮動(dòng)的RNC，這種操作主要被用于通過(guò)網(wǎng)絡(luò)來(lái)提供軟切換。 </p><p>　　·無(wú)線接入承載器（RAB）</p><p>　　由WCDMA RAN提供得主要服務(wù)是無(wú)線接入承載器(RAB)。RAB用于在手持設(shè)備和基站之間建立一個(gè)呼叫連接，其特性由服務(wù)質(zhì)量（QoS)的參數(shù)決定，如比特速率和延遲，并隨所傳輸?shù)姆?wù)類型或信息類型不同而不同。 </

86、p><p>　　RAB承載手持設(shè)備與核心網(wǎng)之間的用戶數(shù)據(jù)，它由手持設(shè)備與服務(wù)RNC之間的一個(gè)或更多的無(wú)線接入承載器，以及一個(gè)位于服務(wù)RNC和核心網(wǎng)之間的Iu接口構(gòu)成。3GPP己定義了四個(gè)不同的無(wú)線接入承載器的質(zhì)量等級(jí): </p><p>　　●會(huì)話式的（如用于語(yǔ)音電話）——低延遲，有嚴(yán)格的順序；</p><p>　　●流動(dòng)式的(如用于看電視)——中等延遲，有嚴(yán)格的順序；

87、</p><p>　　●交互式的(如用于網(wǎng)絡(luò)沖浪)——中等延遲；</p><p>　　●后臺(tái)式的(如用于文件傳輸)——無(wú)延遲。</p><p>　　2. WCDMA無(wú)線接入網(wǎng)傳輸 </p><p>　　WCDMA無(wú)線接入網(wǎng)節(jié)點(diǎn)在傳輸網(wǎng)絡(luò)上相互通信，3GPP規(guī)范在無(wú)線相關(guān)功能與傳輸技術(shù)之間提供了一個(gè)非常明確的分離界限，這意味著對(duì)任何技術(shù)沒(méi)有特殊