電子信息類專業(yè)英語(西電第二版)Unit24Others課件

1、Unit 24 Others Passage A Satellite Fundamentals Passage B Microwave Radio System Passage C Introduction of Color Image Segmentation Passage A Satellite FundamentalsSatellite communication has become a part of everyday life in the late 1980s. An international telephone call is made as easily as local

2、 call to a friend who lives down the block. We also see international events, such as an election in England and a tennis match in France, with the same regularity as local political and sporting events. In this case, a television news program brings the signals and sounds of the world into our home

3、s each night.This capability to exchange information on a global basis, be it a telephone call or a news story, is made possible through a powerful communications tool-the satellite. For those of us who grew up at a time when the space age was not a part everyday life, satellite-based communication

4、is the culmination of a dream that stretches back to an era when the term satellite was only an idea conceived by a few inspired individuals. These pioneers included authors such as Arthur C. Clarke, who fostered the idea of a worldwide satellite system in 1945.This idea has subsequently blossomed i

5、nto a sophisticated satellite network that spans the globe.The first generation of satellites was fairly primitive when compared with contemporary spacecraft. These early satellites embodied active and passive designs.A passive satellite, such as the Echospacecraft launched in 1960, was not equipped

6、 with a two-way transmission system. Rather, Echo was a huge aluminized myriad balloon that functioned as a reflector. After the satellite was placed in a low earth orbit, signals relayed to Echo reflected or bounced off its surface and returned to different locations on the earth.In contrast with t

7、he Echo series, the Telstaractive communications satellite launched in 1962 carried receiving and transmitting equipment. It was an active participant in the reception-transmission process. As the satellite received a signal from a ground or earth station, a communications complex that transmitted a

8、nd/or received satellite signals, it relayed its own signal to earth.1 Telstar also paved the way for todays communications spacecraft since it created the worlds first international satellite television link.During the span of years that separates Telstarfrom today satellites, there have been a num

9、ber of improvements. For example, spacecraft such as Telstar and Echo were placed in low earth orbits. In this type of orbital position, a satellite traveled at such a great rate of speed that it was visible, and hence usable, to an individual ground station for only a limited period of time each da

10、y. The satellite appeared from below the horizon, raced across the sky, and then disappeared below the opposite horizon.Since the ground station was cut off from the now invisible satellite, a station situated below the horizon had to be activated to maintain the communication link. In a different s

11、cenario, it would have been necessary to launch a series of satellites to create a continuous satellite-based relay for any given earth station. As one satellite disappeared, it would have been replaced by the next satellite in the series. The latter type of satellite system would have entailed the

12、development of a very complex and cumbersome earth and space-based network. Fortunately though, this problem was eliminated in 1963 and 1964 through the launching of the Syncom satellites. Rather than circling the earth at a rapid rate of speed, the spacecraft appeared to be stationary or fixed in t

13、he sky. Todays communications satellites, for the most part, have followed suit and are new placed in what are called geo-stationary orbital positions or “slots”2.Simply stated a satellite in a geo-stationary orbital position appears to be fixed over one portion of the earth. An altitude of 22, 300

14、miles above the earths equator, a satellite travels at the same speed at which the earth rotates, and its motion is synchronized with the earth rotation. Even though the satellite is moving at an enormous rate of speed, it is stationary in the sky in relation to an observer on the earth.The primary

15、value of a satellite in a geo-stationary orbit is its ability to communicate with ground stations in its coverage area 24 hours a day. This orbital slot also simplifies the establishment of the communications link between a station and the satellite. Once the stations antenna is properly aligned, on

16、ly minor adjustments may have to be made in the antennas position over a period of time. The antenna is repositioned to a significant degree only when the station establishes contact with a satellite in a different slot. Prior to this era, a ground stations antenna had to physically track a satellit

17、e as it moved across the sky. Based on these principles, three satellites placed in equidistant positions around the earth can create a world-wide communications system in that almost every point on the earth can be reached by satellite. This concept was the basis of Arthur Clarkes original vision o

18、f a globe-spanning communications network.Notes1 As the satellite received a signal from a ground or earth station, a communications complex that transmitted and/or received satellite signals, it relayed its own signal to earth.當(dāng)衛(wèi)星接收了從地面或地球站發(fā)來的信號(hào)后， 衛(wèi)星上的通信設(shè)備將要發(fā)送的和（或）已接收的衛(wèi)星信號(hào)復(fù)合起來后再發(fā)往地球。2 Today communi

19、cations satellites, for the most part, have followed suit and are placed in what are called geo-stationary orbital positions or “slots”.對(duì)于當(dāng)今的通信衛(wèi)星, 絕大部分都遵循此道, 放置在被稱之為相對(duì)地面靜止軌道的位置上。 Exercises1. Fill in the blanks.(1) This capacity to exchange information on a global basis, be it a telephone call or a n

20、ews story, is made possible through a powerful communications tool .(2) For those of us who grew up at a time when the space age was not a part of everyday life, satellite-based communication is a of a dream that stretches back to an era when the term satellite was only an idea conceived by a few in

21、dividuals.(3) Rather, Echo was a huge myriad balloon functioned as a .(4) In a different scenario, it would have been necessary to launch a series of satellites to create a continuous satellite-based relay for any given .(5) Todays communication satellites, for the most part, have followed suit and

22、are now placed in what are called orbital position or “ ”.(6) In order to create communications link, the satellite uses , the satellite equipment that conducts the two-way relays.(7) In line with this capability, a satellite may be able to support trans- mission.(8) With two-degree spacing standard

23、, an earth station must be equipped with an accurate antenna that can receive a satellites signal without created by a neighboring spacecraft.(9) Fortunately though, the FCC implemented a flexible timetable to the impact of their decisions.2. True/False.(1) Spacecraft such as Telstar and Echo were p

24、laced in low earth orbits.( )(2) The antenna is repositioned to a minor degree when the station establishes contact with a satellite in a different slot.( ) (3) The uplink for our purposes will refer to the transmission from the earth station to the satellite, while the downlink is the transmission

25、from the satellite to the earth station.( )(4) In the case of the United States, the transmission can be concentrated in one part of the country, and the East Coast could receive a stronger signal than the Midwest.( )(5) If an earth station pointed its receiving dish toward a specific satellite, it

26、could not intercept a different satellites signal.( )(6) The FCCs decision has had serious repercussions for organizations that use satellites.( )(7) A nation can launch and place a satellite in any slot it chooses since the slots are assigned on an international basis through the auspices of the In

27、ternational Communications Union.( )3. Fill the blanks with the best choice.(1) The early satellites embodied designs. a. active b. passive c. both a and b d. none of them(2) communications satellite launched in 1962 carried receiving and transmitting equipment. a. Echo b. Telstarc. Intelsat d. Inte

28、lsat (3) Based on these principles, satellites placed in equidistant positions around the earth can create a world-wide communications system in that almost every point on the earth can be reached by satellite. a. one b. two c. three d. four(4) The Intelsat satellites carried transponders that provi

29、ded the satellite with a total average transmission capacity of voice circuits. a. 12; 4000 b. 27; 4000 c. 2; 240 d. 48; 100, 000(5) A would fall on a narrowly defined geographical zone. a. footprint b. spot beam c. both a and b d. none of them(6) A dish could receive this spot beam transmission wit

30、hin the confines of the reception area. a. smaller b. less expensive c. a or b d. a and bPassage B Microwave Radio SystemForty years have passed since the research and development of microwave technology were launched in the United States, the United Kingdom, Germany, France and other countries. At

31、the beginning, research was mainly directed towards the development of radar technique. The results were first applied for military purposes. The development of the microwave radio-relay system was based on radar technique, and it now plays an important role as the transmission medium for multiplex

32、telephone and television signals.1Radio communication operating at medium or high frequencies was first applied to the fields, such as broadcasting, maritime mobile and intercontinental communication, where its superiority was evident. It was only after the advent of microwave communication technolo

33、gy that it became possible for radio technology to be applied in full scale in the field where cable transmission had been dominant. Thus, the microwave radio-relay system using analogue modulation grew into a very important transmission medium in the overall telecommunications networks in many coun

34、tries. Recently, a rapid advance in semiconductor and pulse circuit technologies gave impetus to the research and development of digital radio-relay systems.2 There is now a marked trend that the telecommunication network is moving gradually towards digital systems.Analogue radio-relay systemsThe fi

35、rst microwave radio-relay system was established in 1947 by Bell Telephone Laboratories (BTL) between New York and Boston (300 km).It carried 480 channels operating in the 4 GHz band, using frequency modulation and heterodyne repeater scheme. The fact that most of the present microwave systems use t

36、he same modulation and repeater method is a clear indication of the excellent foresight of BTL.3 In 1951, Bell System completed a transcontinental 4 GHz radio-relay system between New York and San Francisco. It carried 600 telephone channels or one television signal. After that, many countries in ev

37、ery region of the world undertook the development of microwave radio-relay systems. The present highest capacity microwave system in operation carries 2, 700 telephone channels. Recently, work has started for developing a system with a capacity of 3, 600 channels.Microwave systems are now playing a

38、very important role in the telecommunications networks of almost all countries. In vast countries, such as the United States and Canada, microwave systems carry the major portion of the long-distance traffic. On the other hand, in Europe, which consists of many small or medium countries, microwave s

39、ystems in the network seem to be slightly less important.In many developing countries, microwave radio-relay systems play the key role in the network. It is quite logical because the microwave system has the following features: the initial investment required for the construction of transmission rou

40、tes is low; the construction can be completed within a relatively short period; it is suitable for television transmission.Digital radio-relay systemsThe digital systems for which preliminary researches were conducted in the 1940s were unfortunately superseded by the rapidly developed frequency modu

41、lation (FM) systems, mainly because of the lack of high-speed pulse technique for multiplexing and the ineffectiveness in frequency spectrum utilization.4The study on microwave digital transmission systems was resumed in the early 1960s.According to various investigations on the microwave digital sy

42、stems, their features can be summed up as follows: the realization of low-cost high-speed PCM terminal equipment contributes a great deal to the reduction of the total system cost; the almost complete pulse regenerative repeating can be achieved provided the carrier-to-noise power ratio is above the

43、 threshold level, and the accumulation of noise due to multiple repeating is negligible. Therefore high-quality long-haul transmission is attainable; the flexibility in transmitting various kinds of signals, such as voice, data, and video, is available without mutual interactions among different sig

44、nals.The first full-scale commercial use of a digital radio-relay system with the above advantages commenced in 1969 by the introduction of a 2 GHz digital radio transmission system carrying 240 telephone channels, which was developed in Japan. 5 Since then, development has continued in various coun

45、tries all over the world, especially in the United States, Canada, Italy, United Kingdom, France and Japan. Frequency bands used for digital systems are mainly 2, 11 and 13 GHz at the present stage. The 2 GHz band is generally applied to small capacity systems about 10 Mbps and the 11 or 13 GHz band

46、 to medium capacity systems at 50 or 100 Mbps.6 These frequencies are generallyapplied to short-haul radio-relay systems. One example of a long haul digital system is the 6 GHz band system of 45 Mbps which has been operational for some years in the United States. There is a marked tendency that the

47、future telecommunications network in general will gradually evolve into the integrated digital network. For this reason, the digital technique applied to radio-relay systems is being actively studied all over the world. The target which is still to be pursued in the future development of the digital

48、 technique is the more efficient use of the frequency spectrum. In particular, efforts should be continued for a better use of the 110 GHz frequency band, which is the most valuable frequency resource.Notes1 The development of the microwave radio-relay system was based on radar technique, and it now

49、 plays an important role as the transmission medium for multiplex telephone and television signals.無線微波中繼的發(fā)展是以雷達(dá)技術(shù)為基礎(chǔ)的, 現(xiàn)在它在傳輸多路電話和電視信號(hào)方面起著重要作用。 這是一個(gè)由and連接的并列句。 句中的it即為the microwave radio-relay system。 for multiplex telephone and television signals是介詞短語, 作定語修飾transmission medium。 2 Recently, a rapid

50、 advance in semiconductor and pulse circuit technologies gave impetus to the research and development of digital radio-relay systems.近來, 半導(dǎo)體和脈沖電路技術(shù)的迅速發(fā)展, 推動(dòng)了數(shù)字無線中繼系統(tǒng)的研究和發(fā)展。 本句的主語為advance, 而in semiconductor and pulse circuit technologies是介詞短語, 修飾advance。 3 The fact that most of the present microwave

51、systems use the same modulation and repeater method is a clear indication of the excellent foresight of BTL.目前, 多數(shù)微波系統(tǒng)均采用同樣的調(diào)制和中繼方法, 這一事實(shí)清楚地表明BTL很有先見之明。 本句中that most of the present microwave systems use the same modulation and repeater method是定語從句, 修飾主語中的主語that fact。 4 The digital systems for which

52、preliminary researches were conducted in the 1940s were unfortunately superseded by the rapidly developed frequency modulation (FM) systems, mainly because of the lack of high-speed pulse technique for multiplexing and the ineffectiveness in frequency spectrum utilization.在20世紀(jì)40年代, 由于缺乏高速脈沖復(fù)用技術(shù)以及數(shù)字

53、系統(tǒng)的頻譜利用率不高, 初期進(jìn)行的數(shù)字系統(tǒng)研究不幸由快速發(fā)展的頻率調(diào)制系統(tǒng)代替。 for which preliminary researches were conducted in the 1940s是一個(gè)定語從句, 修飾the digital systems。 because of之后應(yīng)接短語, 它有兩個(gè)并列的短語, 即the lack of .和the ineffectiveness in .。 5 The first full-scale commercial use of a digital radio-relay system with the above advantages c

54、ommenced in 1969 by the introduction of a 2 GHz digital radio transmission system carrying 240 telephone channels, which was developed in Japan.1969年, 日本開發(fā)了具有240條話音信道的2GHz數(shù)字無線傳輸系統(tǒng), 從而使具有上述優(yōu)點(diǎn)數(shù)字無線中繼系統(tǒng)全面投入商用。 carrying 240 telephone channels是分詞短語作定語, 修飾system。 6 The 2 GHz band is generally applied to sm

55、all capacity systems about 10 Mbps, and the 11 or 13 GHz band to medium capacity systems at 50 or 100 Mbps.2 GHz頻帶通常應(yīng)用于小容量系統(tǒng), 其速率約為10 Mbps; 11或13 GHz頻帶用于中等容量系統(tǒng), 其速率約為50或100 Mbps。 在and the 11 or 13 GHz band to medium capacity systems at 50 or 100 Mbps句中, band后面省略了applied, 這種省略使文章較為簡(jiǎn)潔。 Exercises1. Fil

56、l in the blanks.(1) This capacity to exchange information on a global basis, be it a telephone call or a news story, is made possible through a powerful communications tool .(2) For those of us who grew up at a time when the space age was not a part of everyday life, satellite-based communication is

57、 a of a dream that stretches back to an era when the term satellite was only an idea conceived by a few individuals.(3) Rather, Echo was a huge myriad balloon functioned as a .(4) In a different scenario, it would have been necessary to launch a series of satellites to create a continuous satellite-

58、based relay for any given .(5) Todays communication satellites, for the most part, have followed suit and are now placed in what are called orbital position or “ ”.2. True/False.(1) Spacecraft such as Telstar and Echo were placed in low earth orbits.( )(2) The uplink for our purposes will refer to t

59、he transmission from the earth station to the satellite, while the downlink is the transmission from the satellite to the earth station.( )(3) The early satellites embodied active and passive designs. ( )(4) Telstarcommunications satellite launched in 1962 carried receiving and transmitting equipmen

60、t.( )(5) Based on these principles, three satellites placed in equidistant positions around the earth can create a world-wide communications system in that almost every point on the earth can be reached by satellite.( )Passage C Introduction of Color Image SegmentationImage segmentation refers to pa