外文翻譯--移動通信

1、<p><b>　　中文6190字</b></p><p><b>　　英文資料及中文翻譯</b></p><p>　　Mobile Communication</p><p>　　Cellular Telephone Systems</p><p>　　A cellular teleph

2、one system provides a wireless connection to the PSTN for any user location within the radio range of the system. Cellular systems accommodate a large number of users over a large geographic area, within a limited freque

3、ncy spectrum .Cellular radio systems provide high quality service that is often comparable to that of the landline telephone systems .High capacity is achieved by limiting the coverage of each base station transmitter to

4、 a small geographic area called a cell so t</p><p>　　A basic cellular system consists of mobile stations, base stations and a mobile switching center (MSC). The Mobile Switching Center is sometimes called a

5、mobile telephone switching office (MTSO),since it is responsible for connecting all mobiles to the PSTN in a cellular system. Each mobile communicates via radio with one of the base stations and may beheaded-off to any n

6、umber of base stations throughout the duration of a call .The mobile station contains a transceiver, an antenna, and control c</p><p>　　Cordless Telephone Systems</p><p>　　Cordless telephone sys

7、tems are full duplex communication systems that use radio to connect a portable handset to a dedicated base station ,which is then connected to a dedicated telephone line with a specific telephone number on the pubic swi

8、tched telephone network (PSTN).In first generation cordless telephone systems (manufactured in the 1980’ s ), the portable unit communicates only to the dedicated base unit and only over distances of a few tens of meters

9、.</p><p>　　Early cordless telephones operate solely as extension telephones to a transceiver connected to a subscriber line on the PSTN and are primarily for in-home use.</p><p>　　Second generat

10、ions cordless telephones have recently been introduced which allow subscribers to use their handsets at many outdoor locations within urban centers such as London or Hong Kong. Modern cordless telephones are sometimes co

11、mbined with paging receivers so that a subscriber may first be paged and then respond to the page using the cordless telephone. Cordless telephone systems provide the user with limited range and mobility, as it is usuall

12、y not possible to maintain a call if the user </p><p>　　Basic Knowledge of Communication </p><p>　　Communication System</p><p>　　A generalized communication system has the following

13、 components :</p><p>　　In formation Source .This produces a message which may be written or spoken words, or some form of data.</p><p>　　Transmitter .The transmitter converts the message into a

14、signal ,the form of which is suitable for transmission over the communication channel.</p><p>　　Communication Channel .The communication channel is the medium used transmit the signal, from the transmitter t

15、o the receiver. The channel may be a radio link or a direct wire connection.</p><p>　　Receiver. The receiver can be thought of as the inverse of the transmitter .It changes the received signal back into a me

16、ssage and passes the message on to its destination which may be a loudspeaker, teleprompters or computer data bank.</p><p>　　Once this new baseboard signal ,a “group” of 4 channels , has been formed it is mo

17、ved around the trunk network as a single unit .A hierarchy can be set up with several channels forming a “group”, several groups a “super group” and several “super group” either a “mastergroup”or “hyper group”.</p>

18、<p>　　Groups or super groups are moved around as single units by the communications equipment and it is not necessary for the radios to know how many channels are involved .A radio can handle a super group provide

19、d sufficient bandwidth is available .The size of the groups is a compromise as treating each channel individually involves far more equipment because separate filters , modulators and oscillators are required for every c

20、hannel rather than for each group .However the failure of one module will</p><p>　　Time Division Multiplexing </p><p>　　It is possible, with pulse modulation systems, to use the between samples

21、to transmit signals from other circuits .The technique is known as time division multiplexing (TDM).To do this it is necessary to employ synchronized switches at each end of the communication link to enable samples to be

22、 transmitted in turn ,from each of several circuits .Thus several subscribers appear to use the link simultaneously . Although each user only has periodic short time slots, the original analog signals betwe</p>&l

23、t;p>　　Pulse Code Modulation </p><p>　　In analog modulation, the signal was used to modulate the amplitude or frequency of a carrier , directly .However in digital modulation a stream of pulses ,representi

24、ng the original ,is created .This stream is then used to modulate a carrier or alternatively is transmitted directly over a cable .Pulse Code Modulation (PCM)is one of the two techniques commonly used.</p><p&g

25、t;　　All pulse systems depend on the analog waveform being sampled at regular intervals. The signal created by sampling our analog speech input is known as pulse amplitude modulations .It is not very useful in practice b

26、ut is used as an intermediate stage towards forming a PCM signal .It will be seen later that most of the advantages of digital modulation come from the transmitted pulses having two levels only ,this being known as a bin

27、ary system .In PCM the height of each sample is converted into a</p><p>　　Optical Fiber Communications </p><p>　　Communication may be broadly defined as the transfer of information from one poin

28、t to another .When the information is to be conveyed over any distance a communication system is usually required .Within a communication system the information transfer is frequently achieved by superimposing or modulat

29、ing the information on to an electromagnetic wave which acts as a carrier for the information signal .This modulated carrier is then transmitted to the required destination where it is received and t</p><p>

30、　　Typical optical fiber communications system is shown in Fig.1-3.In this case the information source provides an electrical signal to a transmitter comprising an electrical stage which drives an optical source to give m

31、odulation of the light wave carrier .The optical source which provides the electrical-optical conversion may be either a semiconductor laser or light emitting diode (LED).The transmission medium consists of an optical fi

32、ber cable and the receiver consists of an optical detector whi</p><p>　　The optical carrier may be modulated by using either an analog or digital information signal.. Analog modulation involves the variation

33、 of the light emitted from the optical source in a continuous manner. With digital modulation, however, discrete changes in the length intensity are obtained (i.e. on-off pulses). Although often simpler to implement, ana

34、log modulation with an optical fiber communication system is less efficient, requiring a far higher signal to noise ratio at the receiver than di</p><p>　　Initially, the input digital signal from the informa

35、tion source is suitably encoded for optical transmission .The laser drive circuit directly modulates the intensity of the semiconductor laste with the encoded digital signal. Hence a digital optical signal is launched in

36、to the optical fiber cable .The avalanche photodiode detector (APD) is followed by a front-end amplifier and equalizer or filter to provide gain as well as linear signal processing and noise bandwidth reduction. Finally

37、,the sig</p><p>　　Broadband Communication</p><p>　　As can be inferred from the examples of videophone and HDTV, the evolution of future communications will be via broadband communication centere

38、d around video signals. The associated services such as video phone, video conferencing, video surveillance, cable television (CATV) distribution, and HDTV distribution to the high-speed data services such as high-resolu

39、tion image transmission, high-speed data transmission, and color facsimile. The means of standardizing these various broadband communicat</p><p>　　For realization of the B-ISDN, the role of several broadband

40、 communication technologies is crucial .Fortunately ,the remarkable advances in the filed of electronics and fiber optics have led to the maturation of broadband communication technologies .As the B-ISDN becomes possibl

41、e on the optical communication technologies .As the B-ISDN becomes possible on the optical communication foundation . the relevant manufacturing technologies for light-source and passive devices and for optical fiber ha

42、</p><p>　　On the other, standardization activities associated with broadband communication have been progressing. The Synchronous Optical Network (SONET) standardization centered around the T1 committee even

43、tually bore fruit in the form of the Synchronous Digital Hierarchy (SDH) standards of the International Consultative Committee in Telegraphy and Telephony (CCITT), paving the way for synchronous digital transmission base

44、d on optical communication .The standardization activities of the integrated servic</p><p>　　Various factors such as these have made broadband communication realizable. Therefore, the 1990’is the decade in w

45、hich matured broadband communication technologies will be used in cibhybctuib with broadband standards to realize broadband communication networks. In the broadband communication network, the fiber optic network will rep

46、resent the physical medium for implementing broadband communication, while synchronous transmission will make possible the transmission of broadband service signals o</p><p>　　Asynchronous Transfer Mode (ATM

47、)</p><p>　　Demand for rich media services such as Internet access ,video on demand ,digital television and voice over IP grows more clamorous every day .So ,too ,does the need for high-per-formic distributio

48、n technology .</p><p>　　To meet this demand , service providers are turning to ATM technology – a flexible ,scalable way of moving high-speed video and data across networks .ATM’s sophisticated bandwidth u

49、tilization capabilities enable providers to efficiently transport large ,complex video packets without taxing a network .</p><p>　　The majority of traffic ported over the ATM infrastructure is voice and data

50、, Video will soon be as prominent and will drive the need for more high-capacity ATM networks .The basis of ATM technology is a high-efficiency ,low –latency switching and multiplexing mechanism ideally suited to an envi

51、ronment in which there are specific bandwidth limitations.</p><p>　　ATM allocates bandwidth on demand by construction virtual channels and virtual paths between source and destination points on the ATM netwo

52、rk boundaries. These channels are not dedicated physical connections, but are permanent virtual connections or switched virtual connections that are deconstructed when no longer needed.</p><p>　　The speed an

53、d reliability of ATM switched networks can’t be matched by other popular WAN technologies, which are ill-equipped to transport high-performance data. However, even in an ATM environment, the nuances and peculiarities of

54、digital video make it impractical to transport real-time video in its native uncompressed format over ATM. Using MPEG-2 sophisticated compression techniques, providers can alleviate technical roadblocks when managing and

55、 ensuring the integrity of large ,super –fast vi</p><p>　　Local MPEG-2 video streams are typically transported via an interface known as digital video broadcast asynchronous serial interface .ATM edge devise

56、 deconstruct either an MPEG-2multiple program transport stream (MPTS) or single program transport stream to the program level and ultimately to the packet-identifier (PID) level .At the PID level., streams can be reorder

57、ed and combined back into another MPTS. This process is referred to as remultiplexin. Each packet of MPEG-2 data is then tagged wit</p><p><b>　　WDN</b></p><p>　　Even visionaries such

58、 as Albert Einstein and lascar Newton ,who contributed significantly to our understanding of the properties of light and its fundamental importance ,would not likely imagine the communications networks of today .Highways

59、 of light span the globe ,transmitting massive amounts of information in the twinkling of an eye .The equivalent of millions of telephone calls are transmitted on a single fiber ,thinner than a human hair .Astounding as

60、these advances may seem, we are only at</p><p>　　The current explosion of traffic in the worldwide networks is ample evidence of the speed with which we are adopting new communications technologies. The grow

61、th of wireless systems and the Internet are well-documented phenomena. No matter what application it is that is generating traffic, most of this traffic will be carried by the unifying optical layer. For this reason ,the

62、 growth of various applications such as telephony (whether cellular or fixed ),Internet ,video transmission ,computer comm</p><p>　　The most striking recent advances in optical networking have taken place in

63、 the field Wavelengths Division Multiplexing (WDM). These advances have benefited both terrestrial and submarine systems, increased available capacities by several orders of magnitude and, correspondingly reduced costs.&

64、lt;/p><p>　　Until quite recently, it was possible to send only one wavelength, or color, of light along each fiber .A lot of effort has therefore been concentrated in maximizing the amount of information that c

65、an be transmitted using a single wavelength. Commercial systems will soon be able to carry 40Gbit/s on a single wavelength, while in the labs 320Gbit/systems have already been demonstrated.</p><p>　　WDM, on

66、the other hand, makes it possible to transmit a large number of wavelengths using the same fiber. Effectively sending a “rainbow” of color, where there was only one color before. Already today , commercially available sy

67、stems can transmit 400 Gbit/s of information on a single fiber .That is equivalent to transmitting approximately 200 feature-length films per second .Recently ,a team of researchers from Bell Labs demonstrated long-dist

68、ance ,error-free transmission of 3.28 Gbit/s over a </p><p>　　The major advance that has led to the WDM revolution has been the invention of the Optical Amplifier (OA). Before the invention of the OA, after

69、having traveled down a fiber for some distance , each individual wavelength had to be concerted into electronic form ,then back into optical form and then retransmitted into the next span of fiber .This was relatively ex

70、pensive ,since the optical components involved are highly specialized devices .The OA ,however ,can boost the signal power of all wavel</p><p>　　The growing demand on optical network is a complex issue .On t

71、he one hand ,the growth in capacity demand is extraordinary ,and this in itself would be a big enough challenge to meet .However ,this in accompanied by an increasing variety of services and applications ,as well as much

72、 more exacting requirements for quality differentiation .For example ,there is quite a difference in the quality requirement for a signal being used to transmit an emergency telephone call or live video coverage of a m&l

73、t;/p><p>　　However, the same optical infrastructure is expected to support this wide variety of services. Internet Protocol (IP) traffic, in particular, is growing exponentially .In some parts of the world, it

74、is expected that IP will constitute the majority of traffic in the near future .Therefore ,existing networks will have to be progressively optimized to handle various types of traffic .WDM has a major advantage in this

75、regard ,which is that the different types of traffic can be assigned to different</p><p>　　Fortunately, we will soon be in a position to route individual wavelengths flexibly through an optical network. Feat

76、ures such as add/drop and cross-connection in the optical domain are being made possible by advance in potencies. I would like to draw attention to a few recent advances in this area, Firstly, the so–called digital wrapp

77、er is in the process of being standardized in the international bodies .A second significant development is the all-optical cross-connect. Bell Labs has recently un</p><p>　　A further aspect to consider is a

78、ccess to the optical network, Most users would like to have direct access to the optical network and the enormous capacity it provides .This will take place in stages .Multi –wave –length optical systems are rapidly spre

79、ading out from the core towards the end user .In regional and metropolitan areas ,the requirements are somewhat different from the long-distance area .The dream of Fiber To The Home (FTTH) or desktop is yet to materiali

80、ze ,mainly because of the c</p><p>　　We are at the beginning of a revolution in communications networks, where increasing capacity, variety of applications, and quality of service are placing enormous demand

81、s on the optical network.. The revolution of optical network is just beginning, and is advancing very swiftly towards a future online world in which bandwidth is essentially unlimited, reliable and low-cost.</p>&

82、lt;p>　　Circuit Switching and Packet Switching</p><p>　　There are tow basic types of switching techniques: circuit switching and message switching. In circuit switching, a total path of connected made, and

83、 the path remains allocated to the source-destination pair (whether used or not) until it is released by the communicating parties2. The switches, called circuit switches (or office exchange in telephone jargon), have no

84、 capability of storing or manipulating user’s data on their sage that finds its way through the network, seizing channels in the pa</p><p>　　In message switching, the transmission unit is a well-defined bloc

85、k of data called a message. In addition to the text to be transmitted5, a message comprises a header and a checksum. The header contains information regarding the source and destination addresses as well as other control

86、 information6; the checksum is used for error control purposes. The switching element is a computer referred to as a message processor7, with processing and storage capabilities. Messages travel independently and a</p

87、><p>　　A variation of message switching is packet switching. Here the message is 90broken up into several pieces of a given maximum length, called packets. As with message switching, each packet contains a head

88、er and a checksum. Packets are transmitted independently in a store-and-forward manner.</p><p>　　With circuit switching, there is always an initial connection cost incurred in setting up the circuit. It is c

89、ost-effective only in those situations where once the circuit is set up there is a guaranteed steady flow of information transfer to amortize the initial cost. This is certainly the case with voice communication in the t

90、raditional way, and indeed circuit switching is the technique used in the telephone system. Communication among computers, however, is characterized as bursty. Burstiness</p><p>　　Packet switching achieves t

91、he benefits discussed so far and offers added features .It provides the full advantage of the dynamic allocation of the bandwidth ,even when messages are long .Indeed, with packet switching ,many packets of the same mess

92、age may be in transmission simulsl over consecutive links of a path from source to destination.</p><p><b>　　移動通信</b></p><p><b>　　蜂窩電話系統(tǒng)</b></p><p>　　一個蜂窩電話系

93、統(tǒng)可以為在該系統(tǒng)無線電收發(fā)范圍內(nèi)的任何用戶提供一個到PSTN的無線電話連接。在一定的頻譜內(nèi)，蜂窩系統(tǒng)可以在一個大區(qū)域中擁有相當(dāng)多的用戶。蜂窩無線電系統(tǒng)常?？梢蕴峁┍扔芯€電話系統(tǒng)更高質(zhì)量的服務(wù)。通過限制從每一個基站發(fā)射機(jī)到一個叫做蜂窩小區(qū)的范圍來過得高容量，同一條無線電通道可以被其他遠(yuǎn)距離基站再次利用。當(dāng)一個用戶從某歌嘯傲去轉(zhuǎn)移到另一個小區(qū)時，采用一種復(fù)雜的交換技術(shù)就可以使摘機(jī)狀態(tài)的手機(jī)連續(xù)地進(jìn)行呼叫處理。</p><

94、p>　　一個基本的蜂窩系統(tǒng)由移動站、基站和一個移動交換中心（MSC）組成。由于這歌移動交換中心負(fù)責(zé)一個蜂窩系統(tǒng)所有移動電話到PSTN的連接，因而有時又被稱為移動電話交換局（MTSO）。每一次通信都要借助某個基站的無線電波傳送信號，并且在整個呼叫過程中可以摘機(jī)，撥打其他任何基站的電話號碼。一個移動包括無線電收發(fā)機(jī)、天線和控制電路，這種控制電路可以安裝在傳輸系統(tǒng)或手機(jī)里?；景◣着_發(fā)射機(jī)和接收機(jī)，能同時進(jìn)行全雙工通信，通常還有用以支

95、持收、發(fā)無線電的天線塔?；揪拖窠⒃谝粋€蜂窩小區(qū)內(nèi)所有用戶和那些通過電話線或I微波鏈接到MSC的集群呼叫連接之間的以一座橋梁。MSC負(fù)責(zé)統(tǒng)一所有基站的操作及整個蜂窩系統(tǒng)到PSTN的連接。一個典型的MSC一次可以處理100000個蜂窩通信用戶，同時進(jìn)行5000個通話，并且完成所有計費(fèi)和系統(tǒng)維護(hù)功能。在大城市中，一個獨(dú)立的載波可以服務(wù)于若干個MSC.</p><p><b>　　無繩電話系統(tǒng)</b&

96、gt;</p><p>　　無繩電話系統(tǒng)使全雙工通信系統(tǒng)。它通過無線電將手持機(jī)與一專用基站連接起來，而后再連接到PSTN上的某條電話線上。在第一代無繩電話系統(tǒng)（制造于20世紀(jì)80年代）中，手持設(shè)備僅能與一個專用的基本設(shè)備相連，而且工作距離也只有幾十米。</p><p>　　早期的無繩電話只能起到電話延伸的作用，即把無線電收發(fā)機(jī)與一個PSTN用戶連接起來，且主要用于室內(nèi)。</p>

97、<p>　　最近產(chǎn)生的第二代無繩電話允許用戶在都市（如倫敦或香港）中心所在的許多地方使用手持機(jī)?，F(xiàn)在的無繩電弧可以與尋呼機(jī)相連，以便使某用戶收到尋呼記錄，然后再用無繩電弧對此作出響應(yīng)。當(dāng)用戶外出不在基站服務(wù)區(qū)域內(nèi)而無法接收呼叫時，無繩電話系統(tǒng)可以為這些受距離和移動限制的用戶提供服務(wù)。典型的第二代（無繩電話的）基站所能覆蓋的范圍已達(dá)到幾百米。</p><p><b>　　通信基礎(chǔ)知識<