毕业设计论文英文原文.docx

1、毕业设计论文英文原文 毕业设计(论文)英文翻译原文院 （系）： 信息与通信学院 专 业： 电子信息工程 学生姓名： 张 晨 学 号： 030220606 指导教师： 田克纯 职 称： 高级工程师 2007年 6 月 6 日UMTS For effective, efficient communications, standardization is critical, and nowhere is this more evident than in the areas of mobile computing and cellular telephony. If you need data ac

2、cess or e-mail through your cell phone, youre likely to be using one of two different technologies: Code Division Multiple Access (CDMA) or Global Service of Mobile Communication (GSM). Both CDMA and GSM are second-generation (2G) technologies, and they have co-existed for several years. Each techno

3、logy has its supporters. CDMA phones are engineered specifically for an individual carrier, whereas GSM phones make use of a removable memory card called the Subscriber Identity Module (SIM). A SIM card contains all the key information required to activate a phone, including the users telephone numb

4、er, personal identification number, address book and encoded network identification details. A user can easily move a SIM from one phone to another. Though GSM phones are interoperable with one another, different countries use different parts of the frequency spectrum, so “world phones” typically mu

5、st be capable of using several frequencies. Today, the fastest-growing use of cellular networks is for the transmission of all kinds of data and rich media, including Web sites, video, music, images, and maps and driving directions. The older 2G networks simply couldnt handle that volume of traffic,

6、 and they couldnt offer the speed needed for transmitting large files. The answer was to make the services faster and build out the networks to deal with more traffic. Here, too, the CDMA and GSM paths continued their separate but parallel development. CDMA brought us CDMA2000 and 1xRTT networks. Th

7、e most recent developments are 1x Evolution Data Optimized, or EV-DO, and 1x Evolution Data/Voice, or EV-DV. Similarly, GSM begat General Packet Radio Service, or GPRS, which begat enhanced data rates for GSM evolution, or EDGE. EDGE was developed to enable the transmission of large amounts of data

8、at a high speed, 384Kbit/sec. The latest generation is called Wideband Code Division Multiple Access (WCDMA). And this finally brings us to Universal Mobile Telecommunications System. The International Telecommunication Union (ITU), a specialized agency of the United Nations, has attempted to coordi

9、nate these competing technologies to improve throughput and increase interoperability. The International Mobile Telecommunications 2000 standard is a third-generation digital communications specification from the ITU. And the European (i.e., GSM-based) implementation of IMT-2000 is UMTS, which is ba

10、sed on WCDMA. Previous cellular telephone data systems were mostly circuit-switched, requiring a dedicated connection. WCDMA is packet-switched, using the Internet Protocol. The first commercial WCDMA network was launched in Japan in 2001. UMTS has been specified as an integrated application for mob

11、ile voice and data systems with wide-area coverage. aUsing globally harmonized spectrum in paired and unpaired bands, early implementations of UMTS offer theoretical bit rates of up to 384Kbit/sec. in situations where the mobile device is actually moving. The current goal is to achieve 2Mbit/sec. wh

12、en both ends of the connection are (at least temporarily) stationary. UMTS operates on radio frequencies identified by the ITU IMT-2000 specification document and licensed to operators, using a 5-MHz-wide channel that simplifies deployment for network providers that have been granted large, contiguo

13、us blocks of spectrum. Most UMTS systems use frequencies between 1,885 and 2,025 MHz. UMTS assigns separate carrier frequencies to incoming and outbound signals, a process called frequency division duplexing (FDD). For symmetric traffic, such as two-way videophones, FDD is highly efficient, allowing

14、 uplink and download data rates to be equal, in contrast to technologies such as Asymmetric Digital Subscriber Line service, which typically offers upload rates that are much slower than its download rates. FDD reduces interference and wastes no bandwidth in switching from transmitting to receiving.

15、 Ongoing work within the 3rd Generation Partnership Project promises increased throughput speeds over the WCDMA Radio Access Network. High-Speed Downlink Packet Access and High-Speed Uplink Packet Access technologies are already standardized, and commercial operators in Asia and North America are pu

16、tting them through network trials. With theoretical download speeds as high as 14.4Mbit/sec. and uplink speeds of up to 5.8Mbit/sec., these technologies will make it possible for UMTS to offer data transmission speeds comparable to those of hard-wired Ethernet-based networks. DATA COMMUNICATIONS A s

17、implified block diagram of a data communication link is shown in Fig. 14-1Although only one secondary is shown1，it represents a typical secondary in a multipoint systemOne of the functions of the host computer is to store the applications programs for the various secondariesThe end equipment which e

18、ither generates the digital information for transmission or uses the received digital data can be computers，printers，keyboards，CRTs，and so onThis equipment generally manipulates digital information internally in word units一all the bits that make up a word in a particular piece of equipment are trans

19、ferred in parallelDigital data，when transmitted，are in serial formParallel transmission of an 8-bit word would require eight pairs of transmission linesnot at all cost-effective3Data terminal equipment（DTE）is a general phrase encompassing all of the circuitry necessary to perform parallel-to-serial

20、and serial-to-parallel conversions for transmission and reception respectively and for data link managementThe DART（Universal Asynchronous Receiver/ Transmitter）and USART（Universal Synchronous/Asynchronous Receiver/ Transmitter）are the devices that perform the parallel-to-serial and serial-to-parall

21、el conversionsThe primary DTE includes a line control unit（LCU or LinCo）which controls the flow of information in a multipoint data link systemA station controller（STACO）is the corresponding unit at the secondariesIf there is software associated with the LCU，it is then called a front-end processor（F

22、EP）At one time，the DTE was the last piece of equipment that belonged to the subscriber in a data link systemBetween the DTEs，starting with the modems，was communications equipment owned and maintained by Telco4Recent judgments have removed modems from the realm of exclusive Telco propertyData communi

23、cations equipment（DCE）5accepts the serial data stream from the DTE and converts it to some form of analog signal suitable for transmission on voice-grade linesAt the receive end，the DCE performs the reverse function of converting the received analog signal to a serial digital data streamThe simplest

24、 form of DCE is a modem（modulator/ demodulator）or data setAt the transmit end，the modem can be considered a form of digital-to-analog converter，while at the receive end，it can be considered a form of analog-to-digital converterThe most common of modulation by modems are frequency shift keying（FSK），p

25、hase shift keying（PSK），and quadrature amplitude modulation（QAM）This is a typically data transmission mode using theanalog telephone lines，see the bottom line between the two DCEs in Fig. 14-1If you transmit data by digital channel（sometimes it is called“Digital T-carrier6”），a Pulse Code Modulation（P

26、CM）equipment must be used，see the middle part of Fig. 14-1A microwave transmission system can also be used for the data communicationFinally， you can use the satellite communication system for data transmission，non-shown in Fig. 14-1If the cables and signal levels used to interconnect the DTE and DC

27、E were left unregulated，the variations generated would probably be proportional to the number of manufacturersElectronics industries Association（EIA），an organization of manufacturers concerned with establishing industry standards，have agreed on the RS-232C as the standard interface between the DTE a

28、nd the modemThis is a 25-pin cable7 whose pins have designated functions and specified signal levelsThe RS-232C is anticipated to be replaced by an updated standardData Communication SystemsThere are five basic types of data communication system:Off-line data transmission is simply the use of a tele

29、phone or similar link to transmit data without involving a computer system.The equipment used at both ends of such a link is not part of a computer, or at least does not immediately make the data available for computer process, that is, the data when sent and/or received are off-line. This type of d

30、ata communication is relatively cheap and simple.Remote batch is the term used for the way in which data communication technology is used geographically to separate the input and /or output of data from the computer on which they are processed in batch mode.On-line data collection is the method of u

31、sing communications technology to provide input data to a computer as such input arises-the data are then stored in the computer（say on a magnetic disk）and processed either at predetermined intervals or as required.Enquiry-response systems provide, as the term suggests, the facility for a user to ex

32、tract information from a computer.The enquiry facility is passive, that is, does not modify the information stored.The interrogation may be simple, for example, RETRIEVE THE RECORD FOR EMPLOYEE NUMBER 1234 or complex.Such systems may use terminals producing hard copy and /or visual displays.Real-time systems are those in which information is made available to and processed by a computer system in a dynamic manner so that either the computer may cause action to be taken to influence events as they occur（for example as