外文翻譯---寬帶CDMA無線接入網(wǎng)的基本概念

1、.附錄3：英文資料Basic Concepts of WCDMA Radio Access Network 1. BackgroundThere has been a tremendous growth in wireless communication technology over the past decade. The significant increase in subscribers and traffic, new bandwidth consuming applications such as gaming, music down loading and video stre

2、aming will place new demands on capacity. 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 for real time multimedia services that en

3、sured international roaming. With the support of ITU (International Telecommunication Union) a specific spectrum was allocated - 20Hz for 3G telecom systems. The work was later taken over by the 3GPP (3rd Generation Partnership Project), which is now the WCDMA specification body with delegates from

4、all over the world.2. WCDMA a development from GSM and CDMANaturally there are a lot of differences between WCDMA and GSM systems, hut there are many similarities as well.The GSM Base Station Subsystem (BSS) and the WCDMA Radio Access Network (RAN) are both connected to the GSM core network for prov

5、iding a radio connection to the handset. Hence, the technologies can share the same 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

6、 GSM Radio Base Station (RBS) corresponds to the WCDMA RES, and the A -interface of GSM was the basis of the development of the Iu-interface of WCDMA, which mainly differs in the inclusion of the new services offered by WCDMA. The significant differences, apart from the lack of interface between the

7、 GSM BSCs and GSM Abis-interface to provide multi-vendor operability, are more of a systemic matter. The GSM system uses TDMA (Time Division Multiple Access) technology with a lot of radio functionality based on managing the timeslots. The WCDMA system on the other hand uses CDMA, which means that b

8、oth the hardware and the control functions are different. Examples of WCDMA-specific functions are fast power control and soft handover.Code Division Multiple Access and WCDMACode Division Multiple Access (CDMA) is a multiple access technology where the users are separated by unique codes, which mea

9、ns 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 technology for wireless communication, also referred to as WCDMA and CDMA2000.In CDMA One and CDMA2000, a 1.25MHz wide radio signal is mu

10、ltiplied by a spreading signal (which is a pseudo-noise code 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 extracted. Using unique

11、 codes means that the same frequency is repeated in all cells. which is commonly referred to as a frequency re-use of 1.WCDMA is a step further in the CDMA technology. It uses a 5MHz wide radio signal and a chip rate of 3.84Mcps, which is about three times higher than the chip rate of CDMA2000. The

12、main benefits of a wideband carrier with a higher chip rate are: Support for higher bit rates Higher spectrum efficiency thanks to improved trunking efficiency (i.e. a better statistical averaging) Higher QoS Further, experience from second-generation systems like GSM and CDMA One has enabled improv

13、ements to be incorporated in WCDMA. Focus has also been put on ensuring that as much as possible of WCDMA operators' investments in GSM 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

14、handover, the' subscribers need dual mode handsets.3. Radio Network FunctionalityFor optimal operation of a complete wireless system i.e. from handset to radio access network (RAN) several functions are needed to control the radio network and the many handsets using it. All functions described i

15、n this section, except' for Handover to GSM,' are essential and therefore necessary for a WCDMA system.3.1 Power controlThe 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 powe

16、r regulation thus provides 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 station shall receive the same power level from all handset

17、s in the cell regardless of distance from the base station. If the power level from one handset is higher than needed, the quality will be excessive, taking a disproportionate share of the resources and generating unnecessary interference with the other subscribers in the network. On the other hand,

18、 if power levels are too low this will result in poor quality. In order to keep the received power at a suitable level, WCDMA has a fast power control that updates power levels 1500 times every second. By doing that the rapid change in the radio channel is handled. To ensure good performance, power

19、control is implemented in both the up-link and the down-link, which means that both the output powers of the hanpset and the base station are frequently updated.Power control also gives rise to a phenomenon called "cell breathing". This is the trade-off between coverage and capacity, which

20、 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 base station. On the other hand, when the number of users in the cell is high, the large number of subscr

21、ibers generates a high interference level and subscribers have to get closer to the base station to achieve good quality.3.2 Soft and softer handoverWith soft and softer handover functionality the handset can communicate simultaneously with two or more cells in two or more base stations. This flexib

22、ility in keeping the connection open to more than one base station results in fewer lost calls, which is very important to the operator.To achieve good system performance with a frequency re-use of 1 and power control, soft and softer handover is required. Soft and softer handover enables the handse

23、t to maintain the continuity and quality of the connection while moving from. one cell to another. During soft handover, the handset will 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 differenc

24、e between soft and softer handover is that during soft 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 it requires additional hard

25、ware resources on the network side, as the handset has multiple connections. In a well-designed radio network, 30%-40% of the users will be in soft or softer handover. As an example of soft or softer handover.3.3 Handover to GSM (inter-system handover) When WCDMA was standardized a key aspect was to

26、 ensure that existing investments could be re-used as much 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, is initially expecte

27、d to be very important since operators are expected to deploy WCDMA gradually within their existing GSM network . When a subscriber moves out of the WCDMA coverage area, a handover to GSM has to be conducted in order to keep the connection.Handover between GSM and WCDMA can also have a positive effe

28、ct 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 subscribers to the WCDMA network can be performed.Another function that is related to inter-system handover is the compres

29、sed mode. When performing handover to GSM, measurements have to be made in order 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.3.4 Inter-frequency handover (intra-system han

30、dover)The need for inter-frequency handover occurs in high capacity areas where multiple 5MHz WCDMA carriers are deployed. Inter-frequency handover, which is handover between WCDMA carriers on different frequencies, has many similarities with GSM handover, for example the compressed mode functionali

31、ty.3.5 Channel type switchingIn WCDMA there are 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 used to move subscribers between t

32、he 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 a voice conversation or downloading a web page. It utilizes the radio resources efficiently as it supports both p

33、ower control and soft handover.3.6 Admission controlAs there is a very clear trade-off between coverage and capacity in WCDMA systems, the admission control functionality is used to avoid system overload and to provide the planned coverage. When a new subscriber seeks access to the network, admissio

34、n control estimates the network load and based on the new expected load, the subscriber 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 service/information the subscriber wants to use

35、. 3.7 Congestion control 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 can be taken. First, congestion control is activated and reduces the bit

36、rate of non real-time applications, to resolve the overload. Second, if the reduced bit rate activity is not sufficient, the congestion control triggers the inter- or intra-frequency handover, which moves some subscribers to less loaded frequencies. Third, handover of some subscribers to GSM and fou

37、rth action is to discontinue connections, and thus protect the quality of the remaining connections.3.8 Synchronization One of the basic requirements when WCDMA was standardized was to avoid dependence on external systems for accurate synchronization of base stations. This has been achieved by a mec

38、hanism, where the handset, when needed, measures the synchronization offset between the cells and reports this to 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 sync

39、hronous nodes are supported.4. Basic architecture concepts/ System overview4.1 Radio Access Network (RAN) Architecture The main purpose of the WCDMA Radio Access Network is to provide a connection between the handset and the core network and to isolate all the radio issues from the core network. The

40、 advantage is one core network supporting multiple access technologies.The WCDMA Radio Access Network consists of two types of nodes:Radio Base Station (Node B)The Radio Base Station handles the radio transmission and reception to/from the handset over the radio interface (Iu). It is controlled from

41、 the Radio Network Controller via the Iub interface. One Radio Base Station can handle one or more cells.Radio Network Controller (RNC)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 t

42、he Iu interface. There are two distinct roles for the RNC, 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 protocols in the contact be

43、tween the handset and the WCDMA Radio Access Network.The Controlling RNC has the overall control of a particular set of cells, and their associated base stations. When a handset must use resources in a cell not controlled by its Serving RNC, the Serving RNC must ask the Controlling RNC for those res

44、ources. This request is made via the Iur interface, which connects the RNCs with each other. In this case, the 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 soft handover throughout the network.Radio Acces

45、s Bearers (RAB)The main 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 (QoS) parameters, such as bit rate and delay, and are diffe

46、rent depending on what kind of service/information to be transported.The RAB carries the subscriber data between the handset and the core 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 networ

47、k. 3GPP has defined four different quality classes of Radio Access Bearers:Conversational (used for e.g. voice telephony) - low delay, strict ordering Streaming (used for e.g. watching a video) - moderate delay, strict ordering Interactive (used for e.g. web surfing) - moderate delay Background (use

48、d for e.g. me transfer) - no delay 4.2 Transport in WCDMA Radio Access Network 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 transport technology, meani

49、ng 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.附錄4：英文資料譯文寬帶CDMA無線接入網(wǎng)的基本概念一、背景過去十年，無線通信技術(shù)有了巨大發(fā)展，用戶量的顯著增加，使得諸如游戲、音樂下載和視頻流量有了新的容量需求。對容量需求的解決辦法是，提供新的頻譜和開發(fā)新的技術(shù)一一寬帶CDMA或下面所說的WCDMA。為創(chuàng)建一個能夠在全球范圍內(nèi)漫游的實時多媒體服務(wù)標(biāo)準(zhǔn)，人

50、們開發(fā)了WCDMA，ITU (國際電信聯(lián)盟)對此給予支持并為第三代（3G）電信系統(tǒng)分配了一個2GHz專用頻譜，隨后這項工作由3GPP (第三代伙伴項目)接管，現(xiàn)在它已經(jīng)是代表全球WCDMA的專業(yè)實體。二、基于GSM和CDMA發(fā)展起來的WCDMA WCDMA與GSM有很多差別，但同樣也有很多相同之處。GSM基站子系統(tǒng)(BSS)和WCDMA無線接入網(wǎng)(RAN)是兩個連接到GSM的核心網(wǎng)絡(luò)，用以提供對手持設(shè)備的無線連接。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線系統(tǒng)的。GSM基站控制器(BSC) 相對應(yīng)于WCDMA無線網(wǎng)絡(luò)控制器(RNC)。GSM

51、無線基站(RBS)對應(yīng)于WCDMA的無線基站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)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)采用基于時隙管理，具有多種無線功能的TDMA (時分多路接入)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。CDMA與WCDMA碼分多路接入(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刻使用同一頻率傳輸。

52、隨著信號處理的快速發(fā)展，這種技術(shù)對無線通信服務(wù)是可行的，即確定為WCDMA與CDMA2000。在CDMA One and CDMA 2000中，將帶寬為1.25 MHz的射頻信號與一個數(shù)據(jù)速率高于信息信號數(shù)據(jù)率的擴(kuò)頻信號(是一種偽噪聲編碼序列)相乘，其結(jié)果，信號表面上呈現(xiàn)隨機，但預(yù)定接收機卻有確知的編碼，通過相反的處理過程，使原始信號被提取。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。 WCDMA是CDMA技術(shù)的進(jìn)一步發(fā)展，它采用一個5MHz的寬帶無線信號和一個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

53、好處是:支持高比特速率。具有得益于改善中繼效能的高頻譜效能(即有較好的統(tǒng)計平均值)。具有較高的服務(wù)質(zhì)量。進(jìn)一步說，在第二代系統(tǒng)GSM和CDMA One取得的經(jīng)驗，改善了與WCDMA的融合， 重點放在了盡可能地使WCDMA運營商在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，全面共址和對GSM切換的支持是問題的焦點，為了使用GSM切換，用戶需要雙重模式的切換。三、無線網(wǎng)絡(luò)的功能性一個完備的無線系統(tǒng)優(yōu)化運行，從手持設(shè)備到無線接入網(wǎng)(RAN) ，需要一些功能來控制無線網(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WCDMA系統(tǒng)也是必要的。1.功

54、率控制功率控制用來調(diào)整終端和基站的發(fā)送功率，以獲得干擾小的結(jié)果，同時允許更多的用戶使用同一載頻。這樣通過對發(fā)送功率的調(diào)整，來提供更多的網(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。為每個用戶服務(wù)的目的是，無論手持設(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，通信質(zhì)量將會超過限值，將造成不按比例共享資源，并對網(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，這種情況將會導(dǎo)致質(zhì)量變壞，為了維持所接收到的功率電平為一個合適的數(shù)值，WCDMA具有每秒更新1500次的快速功率控制功能，由此對快速切

55、換無線信道進(jìn)行處理。為確保最佳運行，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。功率控制會引起一種被稱為是"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（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，就會產(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。 2.軟切換與次軟切換采用軟切換與次軟切換功能，手持設(shè)備可與兩個或兩個以上基站中的多個小區(qū)同時進(jìn)行通信，這種與一個以上基站保持開放連接的靈活性，

56、同時能獲得較低的呼叫損耗，對運營商非常重要。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)備從一個小區(qū)移動到另一個小區(qū)，維持連接不中斷并保持通信的質(zhì)量。在軟切換和次軟切換期間，手持設(shè)備將對需要最小發(fā)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小區(qū)。軟切換的缺點是，它需要在網(wǎng)絡(luò)側(cè)占用額外的硬件資源來實現(xiàn)手持設(shè)備的多連接。對于一個設(shè)計良好的無線網(wǎng)絡(luò)，有30%40%的用戶是處在軟切換和次軟切換的狀態(tài)。3.切換到GSM (系統(tǒng)內(nèi)部切換) WCDMA標(biāo)準(zhǔn)化的一個重要方面，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)需求來啟動。為覆蓋范圍，從WCDMA切換到GSM開始變得十分重要，因為運營商希望在現(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，為了維持連接，就需要進(jìn)行切換到GSM的操作。在GSM與WCDMA之間切換，同樣也會對載荷共享容量調(diào)整產(chǎn)生積極的效果