[毕业设计精品]第三代CDMA系统的仿真 外文文献及翻译

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1、Simulation of Third Generation CDMA SystemsByFakhrul AlamABSTRACTThe goal for the next generation of mobile communications system is to seamlessly integrate a wide variety of communication services such as high speed data, video and multimedia traffic as well as voice signals. The technology needed

2、to tackle the challenges to make these services available is popularly known as the Third Generation (3G) Cellular Systems. One of the most promising approaches to 3G is to combine a Wideband Code Division Multiple Access (WCDMA) air interface with the fixed network of Global System for Mobile commu

3、nications (GSM). In this thesis a signal simulator was implemented according to the physical layer specification of the IMT-2000 WCDMA system. The data is transmitted in a frame by frame basis through a time varying channel. The transmitted signal is corrupted by multiple access interference which i

4、s generated in a structured way rather than treating it as Additive White Gaussian Noise (AWGN). The signal is further corrupted by AWGN at the front end of the receiver. Simple rake diversity combining is employed at the receiver. We investigate the bit error rate at both uplink and downlink for di

5、fferent channel conditions. Performance improvement due to error correction coding scheme is shown. The simulator developed can be an invaluable tool for investigating the design and implementation of WCDMA systems.Chapter 1IntroductionThe goal for the next generation of mobile communications system

6、 is to seamlessly provide a wide variety of communication services to anybody, anywhere, anytime. The intended service for next generation mobile phone users include services like transmitting high speed data, video and multimedia traffic as well as voice signals. The technology needed to tackle the

7、 challenges to make these services available is popularly known as the Third Generation (3G) Cellular Systems. The first generation systems are represented by the analog mobile systems designed to carry the voice application traffic. Their subsequent digital counterparts are known as second generati

8、on cellular systems. Third generation systems mark a significant leap, both in applications and capacity, from the current second generation standards. Whereas the current digital mobile phone systems are optimized for voice communications, 3G communicators are oriented towards multimedia message ca

9、pability.1.1 First Generation Cellular SystemsThe first generation cellular systems generally employ analog Frequency Modulation(FM) techniques. The Advanced Mobile Phone System (AMPS) is the most notable of the first generation systems. AMPS was developed by the Bell Telephone System. It uses FM te

10、chnology for voice transmission and digital signaling for control information. Other first generation systems include: Narrowband AMPS (NAMPS) Total Access Cellular System (TACS) Nordic Mobile Telephone System (NMT-900)All the first generation cellular systems employ Frequency Division Multiple Acce

11、ss(FDMA) with each channel assigned to a unique frequency band within a cluster of cells.1.2 Second Generation Cellular SystemsThe rapid growth in the number of subscribers and the proliferation of many incompatible first generation systems were the main reason behind the evolution towards second ge

12、neration cellular systems. Second generation systems take the advantage of compression and coding techniques associated with digital technology. All the second generation systems employ digital modulation schemes. Multiple access techniques like Time Division Multiple Access (TDMA) and Code Division

13、 Multiple Access (CDMA) are used along with FDMA in the second generation systems. Second generation cellular systems include: United States Digital Cellular (USDC) standards IS-54 and IS-136 Global System for Mobile communications (GSM) Pacific Digital Cellular (PDC) cdmaOne1.3 Third Generation Cel

14、lular SystemsThird generation cellular systems are being designed to support wideband services like high speed Internet access, video and high quality image transmission with the same quality as the fixed networks. The primary requirements of the next generation cellular systems are: Voice quality c

15、omparable to Public Switched Telephone Network (PSTN). Support of high data rate. The following table shows the data rate requirement ofthe 3G systemsTable 1.1: 3G Data Rate RequirementsMobility NeedsMinimum Data RateVehicular144 kbpsOutdoor to indoor and pedestrian384 kbpsIndoor Office2 Mbps Suppor

16、t of both packet-switched and circuit-switched data services. More efficient usage of the available radio spectrum Support of a wide variety of mobile equipment Backward Compatibility with pre-existing networks and flexible introduction ofnew services and technology An adaptive radio interface suite

17、d to the highly asymmetric nature of mostInternet communications: a much greater bandwidth for the downlink than the uplink.Research efforts have been underway for more than a decade to introduce multimediacapabilities into mobile communications. Different standard agencies and governing bodies are

18、trying to integrate a wide variety of proposals for third generation cellular systems. The following figure, adopted from 1, shows the evolution of third generation cellular systems:Figure 1.1: Evolution of 3GReferences 2 and 3 provide further discussion on the evolution of third generation cellular

19、 Systems.1.4. WCDMA: Air Interface for 3GOne of the most promising approaches to 3G is to combine a Wideband CDMA(WCDMA) air interface with the fixed network of GSM. Several proposal supportingWCDMA were submitted to the International Telecommunication Union (ITU) and itsInternational Mobile Telecom

20、munications for the year 2000 (IMT2000) initiative for 3G.Among several organizations trying to merge their various WCDMA proposals are Japans Association of Radio Industry and Business (ARIB) Alliance for Telecommunications Industry Solutions (ATIS) T1P1 European Telecommunications Standards Instit

21、ute (ETSI) through its SpecialMobile Group (SMG)All these schemes try to take advantage of the WCDMA radio techniques without ignoring the numerous advantages of the already existing GSM networks. The standard that has emerged is based on ETSIs Universal Mobile Telecommunication System (UMTS) and is

22、 commonly known as UMTS Terrestrial Radio Access (UTRA) 1. The access scheme for UTRA is Direct Sequence Code Division Multiple Access (DS-CDMA). The information is spread over a band of approximately 5 MHz. This wide bandwidth has given rise to the name Wideband CDMA or WCDMA. There are two differe

23、nt modes namely Frequency Division Duplex (FDD) Time Division Duplex (TDD)Since different regions have different frequency allocation schemes, the capability to operate in either FDD or TDD mode allows for efficient utilization of the available spectrum. A brief definition of FDD and TDD modes is gi

24、ven next.FDD: The uplink and downlink transmissions employ two separated frequency bandsfor this duplex method. A pair of frequency bands with specified separation is assigned for a connection.TDD: In this duplex method, uplink and downlink transmissions are carried over thesame frequency band by us

25、ing synchronized time intervals Thus time slots in a physical channel are divided into transmission and reception part.We developed the simulator for a WCDMA system operating in the FDD mode. So allthe system description provided in chapter 2 holds for the FDD mode only.1.4.1 WCDMA Key FeaturesThe k

26、ey operational features of the WCDMA radio interface are listed below 3, 4: Support of high data rate transmission: 384 kbps with wide area coverage, 2Mbps with local coverage. High service flexibility: support of multiple parallel variable rate services oneach connection. Both Frequency Division Du

27、plex (FDD) and Time Division Duplex (TDD). Built in support for future capacity and coverage enhancing technologies likeadaptive antennas, advanced receiver structures and transmitter diversity. Support of inter frequency hand over and hand over to other systems,including hand over to GSM. Efficient

28、 packet access.1.4.2 WCDMA Key Technical CharacteristicsThe following table shows the key technical features of the WCDMA radio interface:Table 1.2: WCDMA Key Technical CharacteristicsMultiple Access SchemeDS-CDMADuplex SchemeFDD/TDDPacket AccessDual mode (Combined and dedicated channel)Multirate/Va

29、riable rate schemeVariable spreading factor and multi-codeChip Rate3.84 McpsCarrier Spacing4.4-5.2 MHz (200 kHz carrier raster)Frame Length10 msInter Base Station synchronizationFDD: No accurate synchronization neededTDD: Synchronization requiredChannel Coding SchemeConvolutional Code (rate 1/2 and

30、1/3)Turbo codeThe chip rate may be extended to two or three times the standard 3.84 Mcps toaccommodate for data rates higher than 2 Mbps. The 200 kHz carrier raster has been chosen to facilitate coexistence and interoperability with GSM.Chapter 5Conclusion and Future WorkWe implemented a signal simu

31、lator according to the physical layer specification of the IMT-2000 WCDMA system. The data is transmitted in a frame by frame basis through a time varying channel. The transmitted signal is corrupted by multiple access interference. The signal is further corrupted by AWGN at the front end of the rec

32、eiver. Simple rake diversity combining is employed at the receiver.We investigated the bit error rate at both uplink and downlink for two different timevarying channels. As expected the system is interference limited for higher number of users.We observed that without any channel coding schemes and

33、antenna diversity techniques, the BER approaches to 10% as the system load goes beyond 50%. This is not an acceptable performance. However the BER can be pushed back to an acceptable limit with channel coding and antenna diversity techniques.The developed simulator can be an invaluable tool to inves

34、tigate the performance of a WCDMA under various conditions. As for example the simulator can be used to investigate antenna diversity schemes at the receiver. The simulator is very flexibleand one can very easily make the necessary modification to incorporate complex statistical channel model based

35、on measurement and investigate the WCDMA performance under practical mobile channel condition. We have shown that it is very simple to employ the simulator to observe the performance of error correction coding. We implemented a convolutional coding scheme for an uplink voice application of 9.6 kbps.

36、 It was observed that channel coding could significantly lower the required SNR for a particular BER.The simulator employs a simple rake receiver to exploit the gain arising from temporal diversity. Spatial property of the multipath environment can be another source of diversity.Adaptive antennas ar

37、e used at the receiver to take the advantage of this diversity gain. The simulator can be used to investigate the diversity gain of different adaptive algorithms.Space-Time rake receivers 21, 22 or 2-D rake receivers 23 have been proposed to combine the temporal and spatial diversity at the receiver

38、. Transmit diversity techniques13, 14 at the downlink are gaining rapid popularity since they do not incur additional hardware complexity at the mobile station. We are investigating various transmit diversity schemes and different 2- D rake receivers for the WCDMA system. The simulator was modified

39、so that a large number of frames are transmitted rather than transmitting one frame at a time.Turbo coding has been specified for applications that require very low bit error rate.Turbo coding schemes can be incorporated to the simulator in the same way we employed convolutional coding.The simulator

40、 can be further improved by using statistical channel models based onmeasured data. The improvement in system performance by using multi user detection and interference cancellation can also be investigated.第三代CDMA系统的仿真 -Fakhrul Alam摘要下一代移动通信系统的目标是进行无缝集成高速数据、视频和多媒体以及声音信号。需要解决的提供这些服务所面临的挑战的技术即为俗称的第三代

41、（3g） 蜂窝系统。3g 最有前途的途径之一就是结合宽带码分多址(WCDMA) 空中接口与固定网络的移动通信的全球系统通信 (GSM)。在这篇论文中信号模拟器实施根据物理层的 imt-2000 WCDMA 系统的技术规范。数据的传输是基于时变信道的帧基础。传输的信号的破坏是结构化的方式生成的多址干扰而不是把它当作加性高斯白噪声 (AWGN)。信号被进一步破坏在 AWGN接收器的前端。简单的分集信号的合并依靠接收器。我们调查不同信道条件下的上行和下行通道误码率。显示于改善错误修正编码方案性能。仿真器将发展成为进行WCDMA通信系统设计与实现的非常有用的工具。第 1 章简介下一代移动通信系统的目标

42、是提供一个无缝的通信服务给任意人、任意时间与任意地点。预期下一代移动电话用户服务包括像高速传输数据服务、 视频和多媒体通信以及声音信号。需要解决的提供这些服务所面临的挑战的技术俗称第三代（3g） 蜂窝系统。第一代系统是为了传输语音应用程序的模拟通信系统。随后的数字通信被称为第二代蜂窝系统。第三代系统与当前二代标准相比，在应用程序和能力方面，标志着重大的飞跃。而当前的数字移动电话系统是优化的声音通信，3g 传达者是面向多媒体消息的能力。1.1 第一代蜂窝系统第一代蜂窝系统通常采用模拟频率调制(FM) 技术。先进移动电话系统 （AMPS） 是最显著的第一代系统。AMPS是由贝尔电话系统开发的。它使

43、用调频语音传输和数字信号控制信息的技术。其他第一代生成的系统包括：窄带模拟移动电话业务（NAMPS）全接入通信系统 （TACS)北欧移动电话系统 (NMT-900)所有第一代的蜂窝系统采用频分多址(多址接入）在同一小区内分配给每个信道唯一频段。1.2 第二代蜂窝系统用户数量迅速增长和第一代系统的不兼容是走向第二代蜂窝系统的主要原因。第二代系统利用编码技术与数字技术相关联。所有第二代系统采用数字调制方式。采用多址技术如时分多址(TDMA) 、码分多址 (CDMA)与频分多址一起使用。第二代蜂窝系统包括：美国第一套蜂窝系统 （USDC） 标准是 IS-54 和 IS-136全球移动通信 (GSM)

44、 系统太平洋数字蜂窝 (PDC)cdmaOne1.3 第三代蜂窝系统第三代蜂窝系统被设计为支持宽带服务如高速互联网接入、 视频等具有相同的高质量图像传输作为固定网络的质量。下一代蜂窝系统的基本要求是：话音质量敌得过公共交换电话网络 (PSTN)。支持高数据速率。下表显示3g 系统数据速率的要求表 1.1： 3 G 数据速率要求移动要求最低的数据速率车载144 kbps室外384 kbps室内2 Mbps支持分组交换和电路交换数据服务。更有效地使用可用的无线电频谱支持各种移动设备与原有的网络和灵活引进的新的服务和技术兼容自适应的无线接口，适合于大多数的高度不对称性质互联网通讯: 下行比上行链路更

45、大的带宽。引入多媒体到移动通信的能力研究工作已进行超过十年。不同的标准机构和理事机构正试图集成多种第三代蜂窝系统的建议。下图中，通过从 1，显示的第三代蜂窝系统：图 1.1： 演化的 3g引用演变 2 和 3 提供进一步讨论的第三代蜂窝演变系统。1.4.WCDMA： 3g的空中接口3G 最有前途的途径之一就是结合宽带码分多址(WCDMA) 空中接口与固定的 GSM 网络。几个提案支持WCDMA 被提交到国际电信联盟 (ITU) 和其国际移动电信在2000年 （IMT2000) 的3G倡议。他们 WCDMA 的各项建议是试图合并几个组织之间：日本协会的无线电行业和业务 （ARIB）电信行业解决方

46、案 (ATIS) 联盟T1P1欧洲电信标准协会 (ETSI） 通过其特殊移动集团 (SMG)所有这些计划的尝试不忽视 WCDMA 无线电技术利用现有的 GSM 网络的众多优势。有的标准出现是基于对 ETSI 的通用移动通信系统 (UMTS)俗称为 UMTS 陆地电台访问 (UTRA) 。UTRAD的访问计划是直接序列码分多址 （DS-CDMA）。信息遍布大约 5 MHz 频带。这种宽的带宽引出名称宽带码分多址或 WCDMA。即有两种不同的模式频分双工 (FDD) 时分双工 (TDD)由于不同地区有不同的频率分配计划，进行操作的功能软驱或 TDD 模式允许有效运用现有的频谱。简介FDD，TDD

47、模式的定义是考虑下一步。FDD： 对于这种双工的方法上行及下行传输采用两个不同的频段。一双频段与指定的用户连接。TDD： 在这双工的方法中，上行和下行传输的转接通过同步的时间间隔，因此时段在同一频段通道分为传输和接收的一部分。我们制定了在 FDD 模式下运行的 WCDMA 系统仿真。因此，所有第 2 章中提供的系统描述仅适用于FDD 模式。1.4.1 WCDMA 关键技术WCDMA 无线接口的操作要点如下 3 4：支持高数据速率传输： 384 kbps 的广域覆盖，2Mbps本地覆盖。高服务灵活性： 每个连接支持多个并行的变率的服务。共同支持频分双工 (FDD) 和时分双工 (TDD)。建于对

48、未来的容量和覆盖加强技术支持如自适应天线，先进的接收机结构和变送器的多样性。支持频率与其他系统的兼容，包括兼容GSM 系统。有效数据包的访问。1.4.2 WCDMA 关键技术特征芯片的速度可能会延长至两倍或三倍到标准的 3.84 Mcps到容纳数据率高于 2 Mbps。选择了 200khz 载波间隔为方便共存和 GSM 系统的互操作性。第 5 章结论及未来工作我们实施了一种信号物理层规范仿真的 IMT-2000 WCDMA 系统。不同信道数据的传输是基于帧基础。多址干扰的情况下，传输的信号是已损坏。信号被进一步破坏是在信道前端的接收器。简单的Rake分集接收是利用接收器。我们在不同的时间不同的

49、信道调查上行和下行信道的误码率。按预期系统干扰受限于更多的用户。我们注意到，没有任何的信道编码方案和天线分集技术，误码率接近 10%作为系统负载超出 50%。这不是一种可接受性能。但是 BER 可以推回到通道可接受的限度编码和天线分集技术。发达国家的仿真器可以是宝贵的工具，以调查WCDMA 在不同条件下的性能。例如可以仿真用于天线分集接收机在调查。仿真是基于测量和研究 WCDMA 性能非常灵活和一个可以很轻松地把所需的复杂统计修改信道模型实用的移动通信信道条件。我们已经证实它可以很简单的仿真观察性能的纠错编码。我们实施9.6 kbps 的上行语音应用程序中的的卷积编码方案。有人说信道编码可以大

50、大降低特定信噪比下的误码率。该仿真采用简单的 rake 接收机，利用时间所产生的增益多样性。多径环境的空间属性可以是多样性的另一个来源。自适应天线接收器用于利用此分集增益。仿真可以用于研究不同的自适应算法的增益多样性。时空rake接收机或已拟二维RAKE接收机结合时间和空间的多样性。分集技术在下行日趋快速普及因为他们不会导致更多硬件移动基站的复杂性。我们正在研究各种发射分集计划和 WCDMA系统不同的二维 rake 接收机。该仿真器是动态的以便一大批帧传输而不是一次发射一个帧。Turbo 编码已指定需要很低的误码率的应用程序。以相同的方式，我们引用到仿真器可以纳入 Turbo 编码方案的卷积编码。该仿真可以通过使用基于统计信道模型测量的数据进一步改善。此外可以研究通过使用多用户检测系统性能的改善抵消干扰。