通信專(zhuān)業(yè)畢業(yè)設(shè)計(jì)外文翻譯 (2)

1、<p><b>　　外文翻譯</b></p><p>　　Communication System</p><p>　　A generalized communication system has the following components:</p><p>　　(a) Information Source. This prod

2、uces a message which may be written or spoken words, or some form of data.</p><p>　　(b) Transmitter. The transmitter converts the message into a signal, the form of which is suitable for transmission over th

3、e communication channel.</p><p>　　(c) Communication Channel. The communication channel is the medium used transmit the signal, from the transmitter to the receiver. The channel may be a radio link or a direc

4、t wire connection.</p><p>　　(d) Receiver. The receiver can be thought of as the inverse of the transmitter. It changes the received signal back into a message and passes the message on to its destination whi

5、ch may be a loudspeaker, teleprinter or computer data bank.</p><p>　　An unfortunate characteristic of all communication channels is that noise is added to the signal. This unwanted noise may cause distorions

6、 of sound in a telephone, or errors in a telegraph message or data.</p><p>　　Frequency Diversion Multiplexing</p><p>　　Frequency Diversion Multiplexing(FDM) is a one of analog technologies. A sp

7、eech signal is 0~3 kHz, single sideband amplitude (SSB) modulation can be used to transfer speech signal to new frequency bands, four similar signals, for example, moved by SSB modulation to share the band from 5 to 20 k

8、Hz. The gaps between channels are known as guard spaces and these allow for errors in frequency, inadequate filtering, etc in the engineered system.</p><p>　　Once this new baseband signal, a “group” of 4 cha

9、nnels, has been formed it is moved around the trunk network as a single unit. A hierarchy can be set up with several channels forming a “group”, several groups a “supergroup” and several “supergroup” either a “mastergrou

10、p” or “hypergroup”.</p><p>　　Groups or supergroups 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

11、handle a supergroup provided 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 oscillator

12、s are required for every channel rather than for each group. However the failure of one module will lo</p><p>　　Time Diversion Multiplexing</p><p>　　It is possible, with pulse modulation systems

13、, to use the between samples to transmit signals from other circuits. The technique is known as time diversion multiplexing (TDM). To do this, it is necessary to employ synchronized switches at each end of the communicat

14、ion links to enable samples to be 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 an

15、alog signals be</p><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

16、stream of pulse, representing 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 commo

17、nly used.</p><p>　　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 modulation. It is not

18、 very useful in practice but 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,

19、 this being known as a binary system. In PCM the height of each sample is converted into a b</p><p>　　Optical Fiber Communications</p><p>　　Communication may be broadly defined as the transfer o

20、f information from one point 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

21、by superimposing or modulating 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

22、 and t</p><p>　　In this case the information source provides an electrical signal to a transmitter comprising an electrical stage which drives an optical source to give modulation of the light-wave carrier.

23、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 fiber cable and the receiver consists

24、of an optical detector which drives a further electrical stage and hence provides demodul</p><p>　　The optical carrier may be modulated by using either an analog or digital information signal. Analog modulat

25、ion involves the variation of the light emitted from the optical source in a continuous manner. With digital modulation, however, discrete changes in the light intensity are obtained (i.e. on-off pulses). Although often

26、simpler to implement, analog modulation with an optical fiber communication system is less efficient, requiring a far higher signal to noise ratio at the receiver than digi</p><p>　　Initially, the input digi

27、tal signal from the information source is suitably encoded for optical transmission. The laser drive circuit directly modulates the intensity of the semiconductor laser with the encoded digital signal. Hence a digital op

28、tical signal is launched into the optical fiber cable. The avalanche photodiode detector (APD) is followed by a fronted-end amplifier and equalizer or filter to provide gain as well as linear signal processing and noise

29、bandwidth reduction. Finally, the s</p><p>　　Mobile Communication</p><p>　　Cordless Telephone Systems</p><p>　　Cordless telephone system are full duplex communication systems that u

30、se 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 public switched telephone network (PSTN) .In first generat

31、ion cordless telephone systems (manufactured in the 1980’s), the portable unit communications only to the dedicated base unit and only over distances of a few tens of meters.</p><p>　　Early cordless telephon

32、es 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 generation cordless telephones have recently been intr

33、oduced 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 combined with paging receivers so that a subscribe

34、r 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 usually not possible to maintain a call if the user t&

35、lt;/p><p>　　Cellular Telephone System</p><p>　　A cellular telephone system provides a wireless connection to the PSTN for any user location within the radio range of the system. Cellular systems ac

36、commodate a large number of users over a large geographic area, within a limited frequency spectrum. Cellular radio systems provide high quality service that is often comparable to that of the landline telephone systems.

37、 High capacity is achieved by limiting the coverage of each base station transmitter to a small geographic area called a cell so t</p><p>　　A basic cellular system consists of mobile station, base stations a

38、nd a mobile switching center (MSC). The Mobile Switching Center is sometimes called a mobile telephone switching office (MTSO), since it is responsible for connecting all mobiles to the PSTN in a cellular system. Each mo

39、bile communicates via radio with one of the base stations and may be handed-off to any number of base stations throughout the duration of a call. The mobile station contains a transceiver, an antenna, and control </p&

40、gt;<p>　　Broadband Communication</p><p>　　As can be inferred from the examples of video phone and HDTV, the evolution of future communications will be via broadband communication centered around video

41、 signals. The associated services make up a diverse set of high-speed and broadband services ranging from video services such as video phone, video conferencing, video surveillance, cable television (CATV) distribution,

42、and HDTV distribution to the high-speed data services such as high-resolution image transmission, high-speed data transmis</p><p>　　For realization of the B-ISDN, the role of several broadband communication

43、technologies is crucial. Fortunately, the remarkable advances in the field of electronics and fiber optics have led to the maturation of broadband communication technologies. As the B-ISDN becomes possible on the optical

44、 communication foundation, the relevant manufacturing technologies for light-source and passive devices and for optical fiber have advanced to considerable levels. Advances in high-speed device and integra</p><

45、;p>　　On the other, standardization activities associated with broadband communication have been progressing. The Synchronous Optical Network (SONET) standardization centered around the T1 committee eventually bore fru

46、it 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 based on optical co

47、mmunication. The standardization activities of the integrated servic</p><p>　　Various factors such as these have made broadband communication realizable. Therefore, the 1990’s is the decade in which matured

48、broadband communication technologies will be used in conjunction with broadband standards to realize broadband communication networks. In the broadband communication network, the fiber optic network will represent the ph

49、ysical medium for implementing broadband communication, while synchronous transmission will make possible the transmission of broadband service signals</p><p>　　Image Acquisition</p><p>　　A TV c

50、amera is usually used to take instantaneous images and transform them into electrical signals, which will be further translated into binary numbers for the computer to handle. The TV camera scans one line at a time. Each

51、 line is further divided into hundreds of pixels. The whole frame is divided into hundreds (for example, 625) of lines. The brightness of a pixel can be represented by a binary number with certain bits, for example, 8 bi

52、ts. The value of the binary number varies from 0 to 25</p><p>　　Image Processing</p><p>　　Image processing is for improving the quality of the images obtained. First, it is necessary to improve

53、the signal-to-noise ratio. Here noise refers to any interference flaw or aberation that obscure the objects on the image. Second, it is possible to improve contrast, enhance sharpness of edges between images through vari

54、ous computational means.</p><p>　　Image Analysis</p><p>　　It is for outlining all possible objects that are included in the scene. A computer program checks through the binary visual information

55、 in store for it and identifies specific feature and characteristics of those objects. Edges or boundaries are identifiable because of the different brightness levels on either side of them. Using certain algorithms, the

56、 computer program can outline all possible boundaries of the objects in the scene. Image analysis also looks for textures and shadings between l</p><p>　　Image Comprehension </p><p>　　Image Comp

57、rehension means understanding what is in a scene. Matching the prestored binary visual information with certain templates which represent specific objects in a binary form is technique borrowed from artificial intelligen

58、ce, commonly referred to as “template matching”. One by one, the templates are checked against the binary information representing the scene. Once a match occurs, an object is identified. The template matching process co

59、ntinues until all possible objects in the scene ha</p><p><b>　　通信系統(tǒng)</b></p><p>　　一般的通信系統(tǒng)由下列部分組成：</p><p>　　（a）信源。它產(chǎn)生信息，可以是寫(xiě)成的或口頭的文字，或是某種形式的數(shù)據(jù)。</p><p>　?。╞）發(fā)信

60、機(jī)。發(fā)信機(jī)把信息轉(zhuǎn)換為信號(hào)，信號(hào)形式要適合在通信信道中傳輸。</p><p>　　（c）通信信道。通信信道用于從發(fā)信機(jī)傳送信號(hào)到接收機(jī)的媒質(zhì)。信道可以是無(wú)線(xiàn)電鏈路或者直接的有線(xiàn)連接。</p><p>　?。╠）接收機(jī)。接收機(jī)可以看作與發(fā)信機(jī)相反的東西。它把接收到的信號(hào)變回成信息，并把信息傳給終端，這個(gè)終端可以是一臺(tái)揚(yáng)聲器、電傳打字機(jī)、或一個(gè)計(jì)算機(jī)數(shù)據(jù)庫(kù)。</p><p&

61、gt;　　所有通信信道的一個(gè)不好的特征是信號(hào)上都疊加了噪聲。這種人們不希望存在的噪聲會(huì)引起電話(huà)中聲音失真，或者在電報(bào)報(bào)文或數(shù)據(jù)中出現(xiàn)的差錯(cuò)。</p><p><b>　　頻分復(fù)用</b></p><p>　　頻分復(fù)用是一種模擬技術(shù)，一個(gè)話(huà)音信號(hào)的頻段在0~3千赫，用單邊帶振幅調(diào)制（SSB）可以把話(huà)音信號(hào)搬移到新的頻段。例如，采用這種調(diào)制，搬移4路相類(lèi)似的信號(hào)，使之均分

62、5~20千赫頻段。各路之間的間隙成為保護(hù)間隔，這些間隔使得在實(shí)際系統(tǒng)中允許有點(diǎn)頻率誤差及濾波不足等缺陷。</p><p>　　一旦這個(gè)新的基帶信號(hào)（由4路組成的“群”）形成后，它就作為一個(gè)單一的單元在主干網(wǎng)中傳送。可以構(gòu)成一個(gè)分級(jí)的體系，即以若干路組成一個(gè)“群”，若干“群”組成一個(gè)“超群”，再以若干“超群”組成一個(gè)“主群”或“極群”。</p><p>　　通信設(shè)備把群或超群作為一些單一的單

63、元來(lái)傳送。對(duì)于無(wú)線(xiàn)電設(shè)備來(lái)說(shuō)，并不需知道含有多少路。只要有足夠的帶寬，無(wú)線(xiàn)電可以處理一個(gè)超群。群的大小采取折中考慮確定：因?yàn)樘幚砻恳宦范夹枰?dú)立的濾波器、調(diào)制器及振蕩器，這比每個(gè)群所需的這些設(shè)備要多得多，但是若有一個(gè)部件失效，則將失去與這個(gè)群相關(guān)的全部話(huà)路。</p><p><b>　　時(shí)分復(fù)用</b></p><p>　　采用脈沖編碼調(diào)制時(shí)，有可能利用抽樣值之間的時(shí)

64、間來(lái)傳送來(lái)自其它電路的信號(hào)，這種技術(shù)稱(chēng)為時(shí)分復(fù)用（TDM）。要做到這一點(diǎn)，必須在通信鏈路的兩端采用同步開(kāi)關(guān)，使對(duì)來(lái)自各路的抽樣值能一次輪流傳送，于是好幾個(gè)用戶(hù)看起來(lái)都像在同時(shí)使用這條鏈路，雖然每個(gè)用戶(hù)只有一些周期性的短時(shí)隙，抽樣值之間的原來(lái)的模擬信號(hào)卻可在接收機(jī)中重新構(gòu)成。</p><p><b>　　脈沖編碼調(diào)制</b></p><p>　　在模擬調(diào)制中，用信號(hào)來(lái)直

65、接調(diào)制載波的振幅或頻率。但在數(shù)字調(diào)制中則是產(chǎn)生一個(gè)脈沖流來(lái)代表原來(lái)的信號(hào)，然后用這個(gè)脈沖流來(lái)調(diào)制載波，或者直接在電纜中傳輸。脈沖編碼調(diào)制是常用的兩種數(shù)字調(diào)制技術(shù)之一。</p><p>　　所有的脈沖系統(tǒng)取決于按規(guī)定的時(shí)間間隔抽樣的模擬信號(hào)的波形。對(duì)模擬話(huà)音輸入取樣所產(chǎn)生的信號(hào)稱(chēng)為脈沖調(diào)制信號(hào)。在實(shí)際中它不是很有用，但可用作進(jìn)一步形成脈沖編碼調(diào)制信號(hào)的一個(gè)中間階段。數(shù)字調(diào)制的大多數(shù)優(yōu)點(diǎn)來(lái)自發(fā)送的脈沖只有兩個(gè)電平，這

66、種系統(tǒng)稱(chēng)為二進(jìn)制系統(tǒng)。在PCM中，把每個(gè)抽樣值的大小變換成一個(gè)二進(jìn)制數(shù)。脈沖編碼調(diào)制過(guò)程有三步：抽樣、量化和編碼。</p><p><b>　　光纖通信</b></p><p>　　廣義地說(shuō)，把信息從一點(diǎn)傳送到另一點(diǎn)就稱(chēng)為通信。當(dāng)信息跨越一段距離被傳送時(shí)，就需要一個(gè)通信系統(tǒng)。在通信系統(tǒng)中，信息傳送時(shí)通過(guò)把信息疊加在電磁波上或?qū)﹄姶挪ㄟM(jìn)行調(diào)制來(lái)實(shí)現(xiàn)，電磁波起著載送信號(hào)的

67、作用。這一經(jīng)過(guò)調(diào)制的載波隨后被傳送到要求到達(dá)的目的地，在那里被接收，并且通過(guò)解調(diào)還原成原始信息。在運(yùn)用電磁載波的領(lǐng)域，高新技術(shù)得到進(jìn)一步的發(fā)展，比如射頻、微波以及毫米波的頻率都被用來(lái)作為載波頻率。在通信中，也可選擇光波的頻率作為載波頻率。</p><p>　　信源提供電信號(hào)給發(fā)射機(jī)，發(fā)射機(jī)組成一個(gè)電子平臺(tái)來(lái)驅(qū)動(dòng)光源以完成對(duì)光載頻的調(diào)制。光源是由發(fā)光二極管或半導(dǎo)體激光管構(gòu)成的，它完成光—電轉(zhuǎn)換。傳輸媒介由光纖組成。

68、光接收機(jī)包括一個(gè)含光檢測(cè)器的電路驅(qū)動(dòng)平臺(tái)，用以完成對(duì)已調(diào)光載波的解調(diào)。用于檢測(cè)光信號(hào)和進(jìn)行光—電轉(zhuǎn)換的器件有：光電二極管（P-N，P-I-N，或雪崩二極管）、發(fā)光三極管以及光敏電阻等。因此，在光系統(tǒng)鏈路的兩端都要求有電接口，并且在現(xiàn)階段，信號(hào)處理通常是通過(guò)電路實(shí)現(xiàn)的。</p><p>　　模擬或數(shù)字的信號(hào)均可用來(lái)調(diào)制光載波。模擬調(diào)制是指從光源處發(fā)射的連續(xù)光強(qiáng)度的變化，而數(shù)字調(diào)制則不然，它是通過(guò)光強(qiáng)度離散的變化（比

69、如有無(wú)光脈沖）來(lái)實(shí)現(xiàn)的。模擬調(diào)制在光系統(tǒng)調(diào)制中調(diào)制效率較低，而且與數(shù)字調(diào)制相比，需要高得多的信噪比。模擬調(diào)制所必需的線(xiàn)性不總是來(lái)源于半導(dǎo)體光源，尤其是在高頻調(diào)制中?；谏鲜鲈颍c數(shù)字光系統(tǒng)相比，模擬通信鏈路常被限制使用在更短的通信距離和更窄的帶寬上。</p><p>　　首先，信源的數(shù)字信號(hào)被適當(dāng)?shù)鼐幋a以進(jìn)行光傳輸。激光器的驅(qū)動(dòng)電路通過(guò)這些已編碼的數(shù)字信號(hào)來(lái)直接調(diào)制激光器的發(fā)光強(qiáng)度，然后數(shù)字光信號(hào)被注入光纖。在

70、接收端，信號(hào)通過(guò)雪崩發(fā)光二極管（APD）后進(jìn)入前置放大器和均衡器或?yàn)V波器，放大器用來(lái)提高增益，濾波器用來(lái)對(duì)信號(hào)進(jìn)行線(xiàn)性處理和減少噪聲帶寬，最后，信號(hào)通過(guò)解碼得到原始信號(hào)。</p><p><b>　　移動(dòng)通信</b></p><p><b>　　無(wú)繩電話(huà)系統(tǒng)</b></p><p>　　無(wú)繩電話(huà)系統(tǒng)是全雙工通信系統(tǒng)。它通過(guò)

71、無(wú)線(xiàn)電將手持機(jī)與一專(zhuān)用基站連接起來(lái)，而后再接到PSTN上的某條電話(huà)線(xiàn)上。在第一代無(wú)繩電話(huà)系統(tǒng)（制造于20世紀(jì)80年代）中，手持設(shè)備僅能與一個(gè)專(zhuān)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(wú)繩電話(huà)只能起到電環(huán)延遲的作用，即把無(wú)線(xiàn)電收發(fā)機(jī)與一個(gè)PSTN 用戶(hù)連接起來(lái)，且用于室內(nèi)。</p><p>　　最近產(chǎn)生的第二代無(wú)繩電話(huà)允許用戶(hù)在都市（如倫敦或香港）中心所在的許

72、多地方使用手持機(jī)?，F(xiàn)在的無(wú)繩電話(huà)可以與尋呼機(jī)相連，以便使某用戶(hù)先收到尋呼記錄，然后再用無(wú)繩電話(huà)對(duì)此作出響應(yīng)。當(dāng)用戶(hù)外出不在基站服務(wù)區(qū)域內(nèi)而無(wú)法接收呼叫時(shí)，無(wú)繩電話(huà)系統(tǒng)就可以為這些受距離和移動(dòng)限制的用戶(hù)提供服務(wù)。典型的第二代（無(wú)繩電話(huà)的）基站所能覆蓋的范圍已達(dá)到幾百米。</p><p><b>　　蜂窩電話(huà)系統(tǒng) </b></p><p>　　一個(gè)蜂窩電話(huà)系統(tǒng)可以為在該系

73、統(tǒng)無(wú)線(xiàn)電收發(fā)范圍內(nèi)的任何用戶(hù)提供一個(gè)到PSTN的無(wú)繩電話(huà)連接。在一定的頻譜內(nèi)，蜂窩系統(tǒng)可以在一個(gè)大區(qū)域中擁有相當(dāng)多的用戶(hù)。蜂窩無(wú)線(xiàn)電系統(tǒng)?？梢蕴峁┍扔芯€(xiàn)電話(huà)系統(tǒng)更高質(zhì)量的服務(wù)。通過(guò)限制從每一個(gè)基站發(fā)射機(jī)到一個(gè)叫做蜂窩小區(qū)的范圍來(lái)獲得高容量，同一條無(wú)線(xiàn)電通道可以被其它遠(yuǎn)距離基站再次利用。當(dāng)一個(gè)用戶(hù)從某個(gè)小區(qū)移到另一個(gè)小區(qū)時(shí)，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><p>　　一個(gè)基

74、本的蜂窩系統(tǒng)由移到站、基站和一個(gè)移動(dòng)交換中心（MSC）組成。由于這個(gè)移動(dòng)交換中心負(fù)責(zé)一個(gè)蜂窩系統(tǒng)所有移動(dòng)電話(huà)到PSTN的連接，因而有時(shí)又被稱(chēng)為移動(dòng)電話(huà)交換局（MTSO）。每一次通信都要借助某個(gè)基站的無(wú)線(xiàn)電波傳送信號(hào)，并且在整個(gè)呼叫過(guò)程中可以摘機(jī)，撥打其它任何基站的電話(huà)號(hào)碼。一個(gè)移動(dòng)站包括無(wú)線(xiàn)電收發(fā)機(jī)、天線(xiàn)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。基站包括幾臺(tái)發(fā)射機(jī)和接收機(jī)，能同時(shí)進(jìn)行全雙工通信，通常還有用以支持收、發(fā)無(wú)線(xiàn)電的無(wú)

75、線(xiàn)塔。基站就像建立在一個(gè)蜂窩小區(qū)內(nèi)所有用戶(hù)和那些通過(guò)電話(huà)線(xiàn)或微波鏈接到MSC的集群呼叫連接之間的一座橋梁。MSC負(fù)責(zé)負(fù)責(zé)統(tǒng)一所有基站的操作及整個(gè)蜂窩系統(tǒng)到PSTN的連接。一個(gè)典型的MSC一次可以處理100000個(gè)蜂窩通信用戶(hù)，同時(shí)進(jìn)行5000個(gè)通話(huà)，并且完成所有計(jì)費(fèi)和系統(tǒng)維護(hù)功能。在大城市中，一個(gè)獨(dú)立的載波可以服務(wù)于若干個(gè)MSC。</p><p><b>　　寬帶通信</b></p&g

76、t;<p>　　從可視電話(huà)及高清電視的出現(xiàn)可以推斷出未來(lái)通信的變革將是以視頻信號(hào)為核心的寬帶通信。這些相關(guān)的業(yè)務(wù)組成了多種的高速的寬帶服務(wù)，其范圍從視頻服務(wù)，例如可視電話(huà)、會(huì)議電視、視頻監(jiān)視、有線(xiàn)電視分配器和高清電視分配器到高速數(shù)據(jù)服務(wù)，例如高分辨率圖像傳輸、高速數(shù)據(jù)傳輸及彩色傳真。將這些不同的寬帶通信業(yè)務(wù)標(biāo)準(zhǔn)化的最好方法莫過(guò)于采用寬帶綜合業(yè)務(wù)數(shù)字網(wǎng)，這樣能夠使這些服務(wù)以集成的方式提供。簡(jiǎn)言之，未來(lái)的通信網(wǎng)可以比喻為基于寬

77、帶綜合業(yè)務(wù)數(shù)字網(wǎng)之上的寬帶通信系統(tǒng)。</p><p>　　對(duì)于寬帶綜合業(yè)務(wù)數(shù)字網(wǎng)的實(shí)現(xiàn)，幾項(xiàng)寬帶通信技術(shù)起著至關(guān)重要的作用。幸運(yùn)的是，電子及光纖領(lǐng)域的顯著進(jìn)展導(dǎo)致了寬帶通信技術(shù)的成熟。隨著寬帶綜合業(yè)務(wù)數(shù)字網(wǎng)在光纖通信的基礎(chǔ)上成為可能，光源、無(wú)源器件及光纖的相關(guān)制造技術(shù)已經(jīng)有了相當(dāng)水平的提高。針對(duì)寬帶通信的高速器件和集成電路技術(shù)也有了令人矚目的進(jìn)步。取得顯著進(jìn)步的還有軟件技術(shù)、信號(hào)處理技術(shù)和視頻設(shè)備技術(shù)等。因此，從

78、技術(shù)的角度看，寬帶綜合業(yè)務(wù)數(shù)字網(wǎng)已經(jīng)最終達(dá)到了可以實(shí)現(xiàn)的程度。</p><p>　　另一方面，與寬帶通信相關(guān)的標(biāo)準(zhǔn)化活動(dòng)正在不斷取得進(jìn)展。圍繞T1委員會(huì)的光同步網(wǎng)（SONET）標(biāo)準(zhǔn)逐步成為了CCITT的同步數(shù)字體系標(biāo)準(zhǔn)，為基于光通信的同步數(shù)字傳輸鋪平了道路。隨著綜合窄帶業(yè)務(wù)的開(kāi)展，開(kāi)始于20世紀(jì)80年代早期的綜合業(yè)務(wù)數(shù)字網(wǎng)的標(biāo)準(zhǔn)化活動(dòng)逐步擴(kuò)展到了寬帶業(yè)務(wù)的范圍，并于80年代末期實(shí)現(xiàn)了寬帶綜合業(yè)務(wù)數(shù)字網(wǎng)的標(biāo)準(zhǔn)化，同

79、時(shí)在其進(jìn)程中建立了異步傳輸模式（ATM）的概念。此外，視頻信號(hào)的標(biāo)準(zhǔn)通過(guò)幾個(gè)相關(guān)的組織機(jī)構(gòu)的合作，如國(guó)際電報(bào)電話(huà)咨詢(xún)委員會(huì)（CCITT）、國(guó)際無(wú)線(xiàn)電咨詢(xún)委員會(huì)（CCIR）和國(guó)際標(biāo)準(zhǔn)化組織（ISO）最終制定，高速分組通信的參考協(xié)議也通過(guò)國(guó)際標(biāo)準(zhǔn)化組織、國(guó)際電報(bào)電話(huà)咨詢(xún)委員會(huì)及電氣電子工程師協(xié)會(huì)（IEEE）實(shí)現(xiàn)了標(biāo)準(zhǔn)化。</p><p>　　種種這些努力使寬帶通信得以實(shí)現(xiàn)。所以，20世紀(jì)90年代是成熟的寬帶通信技術(shù)結(jié)

80、合寬帶標(biāo)準(zhǔn)被用于寬帶通信網(wǎng)的年代。在寬帶通信中，光纖網(wǎng)絡(luò)代表實(shí)現(xiàn)寬帶通信的物理媒介，與此同時(shí)，同步傳輸技術(shù)使得在光媒介上傳送寬帶信號(hào)成為可能。因此，建立在光媒介上和同步傳送技術(shù)上的寬帶通信網(wǎng)是實(shí)現(xiàn)寬帶通信的最基本的條件，異步傳輸模式這一通信方式則使其變成現(xiàn)實(shí)。寬帶綜合業(yè)務(wù)數(shù)字網(wǎng)所提供的最重要的寬帶業(yè)務(wù)就是高速數(shù)據(jù)通信業(yè)務(wù)和視頻通信業(yè)務(wù)。</p><p><b>　　圖像獲取</b></

81、p><p>　　攝像機(jī)被用來(lái)獲取實(shí)時(shí)圖像并將它們轉(zhuǎn)換成電信號(hào)。這些電信號(hào)又被進(jìn)一步轉(zhuǎn)換成計(jì)算機(jī)處理的二進(jìn)制數(shù)。攝像機(jī)在每一時(shí)刻進(jìn)行逐行掃描，每行被分解成幾百個(gè)像素，一幅圖像被分解成幾百行（如625行）。像素的亮度用一定比特的二進(jìn)制數(shù)表示，例如用8比特表示時(shí)，其二進(jìn)制數(shù)的范圍是0~255，其較大的范圍足以包容從實(shí)景中獲取圖像的可能的對(duì)比度。這些二進(jìn)制數(shù)被存儲(chǔ)在隨機(jī)存取存儲(chǔ)器（必須有很大的容量）中，以備計(jì)算機(jī)進(jìn)一步處理。

82、</p><p><b>　　圖像處理</b></p><p>　　圖像處理是用來(lái)改善所獲取的圖像的質(zhì)量。首先，需要提高信噪比。這里噪聲指使圖像模糊的任何干擾、缺陷或色差；第二，借助各種計(jì)算機(jī)手段可以提高對(duì)比度，增強(qiáng)圖像邊緣的銳度。</p><p><b>　　圖像分析</b></p><p>　　

83、圖像分析是為了獲取圖像中所有物體的輪廓。計(jì)算機(jī)通過(guò)檢查存儲(chǔ)在其中的二進(jìn)制圖像信息來(lái)識(shí)別這些物體的特征。其邊緣或邊界由于其亮度與周?chē)煌梢员蛔R(shí)別。采用一定的算法，計(jì)算機(jī)程序能將圖像中所有可能的邊緣輪廓提取出來(lái)。圖像分析也可以尋找線(xiàn)條間的結(jié)構(gòu)和陰影。</p><p><b>　　圖像識(shí)別</b></p><p>　　圖像識(shí)別即識(shí)別圖像是什么。方法是用先前存儲(chǔ)的二進(jìn)制視