通信专业英语7.ppt

1、通信专业英语,Unit Seven Satellite communication,Part One In telecommunication, the use of artificial satellites provides communication links between various points on Earth. Communications satellites relay voice, video, and data signals between widely separated fixed locations (e.g., between the switching

2、 offices of two different national telephone networks), between a fixed location and numerous small fixed or mobile receivers in a designated area (e.g., direct satellite broadcasting of television programming), and between individual mobile users (e.g., aircraft, ships, motor vehicles, and personal

3、 handheld units). The technique involves transmitting signals from an Earth station to a satellite. Equipment onboard the satellite receives the signals, amplifies them, and retransmits them to a region of Earth. Receiving stations within this region pick up the signals, thus completing the link. He

4、nce the satellite must have a receiver and a receive antenna, a transmitter and a transmit antenna, some method for connecting the uplink to the downlink for retransmission, and prime electrical power to run all of the electronics. The exact nature of these components will differ, depending on the o

5、rbit and the system architecture, but every communications satell,A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits

6、, Molniya orbits, other elliptical orbits and low (polar and non-polar) Earth orbits. A typical satellite communication system consists of a number of repeaters (transponders), each of which provides a large-capacity communication channel. Each transponder has a receiver tuned to a frequency range t

7、hat has been allocated for uplink communication signals from Earth to the satellite. Following the receiver, each transponder consists of a frequency shifter to lower the received signals to a downlink frequency, a filter tuned to the frequency of the transponder and a power amplifier to transmit si

8、gnals back to Earth.,Satellites have significant advantages over other modes of transmission such as cable and land-line microwave. The cost of transmission is independent of geographical terrain or distance, as long as both sender and receiver are within line of sight of the satellite (about one-th

9、ird of the Earths surface). The communication capacity of a satellite is determined by the number of transponder channels and the volume of communication that can be transmitted on each channel. Although this varies from one type of satellite to another, the most commonly used satellite in 1995 had

10、24 transponders. Each can carry a color TV signal (or 6 digitally compressed TV signals) or at least 1200 telephone voice signals in one direction. Each new generation of satellites tends to have increased communication capability. Satellites are less costly for transmission over extremely long dist

11、ances - especially for relatively small volumes of communication. A communication signal can be sent to any number of reception points simultaneously, making satellites ideal for television and other forms of point-to-multipoint communication. Satellites are also extremely flexible because the sendi

12、ng and receiving points can be changed on short notice to meet changes in demand.,The transmitting and receiving stations on Earth (earth stations) range in size from sophisticated, expensive stations that send and receive all types of communication signals to relatively simple and less costly stati

13、ons (dish-shaped TV antennas) used only to receive television signals. The size and cost of Earth stations depend upon the power built into the satellite, as well as the frequencies used. The stronger the signal from the satellite, the smaller and less costly the receiving station. Direct Broadcast

14、Satellites are designed specifically to minimize size and cost.,New Words and Expressions,geostationaryadj. (人造卫星)与地球旋转同步的 Molniyan. 闪电，是前苏联制造的通信卫星 ellipticadj.椭圆的 transpondersn. 发射机应答器，脉冲转发器 geographic adj. 地理学的，地理的 terrainn. 地形，地势 volumen. 量，额；体积，容积 sophisticated adj.复杂的,精密的,高度发展的,Reading Material

15、,Part Two,This section addresses technologies or concepts that could be major departures or advances beyond todays satellite technology. Todays conventional definition of a communications satellite is a three-axis body-stabilized satellite that is positioned in GEO orbit and has a number of antenna

16、beams designed to concentrate RF power and to re-use available frequencies. That definition is expanding to cover LEO satellites in global constellations, LEO store-and-forward satellites, higher powered DBS and mobile satellites, and satellites with ISLs. Increasingly, communications satellites are

17、 moving to higher and higher frequencies despite advances in frequency re-use. These are essentially evolutionary developments driven as much by new applications as new technology. Possible break-through technologies or concepts have been discussed in popular, trade, and scientific journals around t

18、he world in the last few years. These ideas can be categorized as follows:,Advanced satellite technology in future,Use of high tensile strength, very long tethers to suspend satellites in lower orbits or to whip them into higher orbits. Use of aerostats to establish laser satellite connections above

19、 the earths primary atmosphere. Use of robotic drone rockets to stabilize space communications platforms in low earth orbits that are still geostationary. Use of ground-based power transmitters to help stabilize extremely low mass (i.e., 20 to 25 kg) space communications platforms in LEOs. These hig

20、h capacity, low mass satellites would be artificially maintained in low-earth geostationary orbit. Creation of massive global constellations of LEO satellites (configuration of up to 1,000 spacecraft) to create systems that are able to provide wideband fixed and mobile satellite services. Satellites

21、 that utilize mm wave frequencies in the EHF range. Other advanced concepts or architectures that involve radical departures from the past - such as extremely large space platforms or satellite clusters with many spacecraft configured to operate as a single unit in GEO.,All of these concepts - which

22、 imply major departures from todays basic paradigm of what a satellite is, how it operates, and how much it costs to provide services - could well be critical to the longer term viability of satellite communications and the mix of telecommunications services they provide. The advent of new terrestri

23、al wireless technologies and fiber optic cable could indeed require a totally new approach for the 21st century.,axis n. 轴，坐标轴 constellations n. 星座;星座区域 tensile adj.张力的，可伸展的 tether n. 拴绳，限度 aerostat n.轻航空器，浮空器 atmosphere n. 大气层，空气，气氛 paradigm n.范例，示例 viability n.生存力 terrestrial adj.地球（上）的，陆（地）的,Rele

24、vant Words,Talking Face to Face,Part Three,A: Good morning, Mr. Zhang! Our country launched a new communications satellite yesterday. It turned out to be successful. B: So excited! The news said the new communications satellite would be used for live television broadcast and put into use before the

25、Beijing Olympic Games in August. A: How many satellite antennas will be used to transmit the TV programs? B: Maybe 15. We will be able to watch live broadcasts of Olympic events via the satellite, even people in remote regions of China. A: Which Olympic Games became the fist program to be transmitte

26、d via satellite? B: In 1964, the Olympic Games in Tokyo. With the improvement of satellite communications and global telecasts of the events, the Olympics are consistently gaining supporters. A:I am looking forward to the Beijing Olympic Games. B: So am I. I believe it will be the best Olympic Games

27、 in history.,Grammar: Tense and Voice 倒装句和情态动词,Part Four,主语和谓语是句子的核心，它们之间有两种语序： 一是主语在谓语之前称为自然语序（Natural Order）； 二是主语在谓语之后则称为倒装语序（Inverted Order）。英语的最基本结构是主、谓结构，倒装将这种比较固定的结构加以颠倒，它是一种语法手段，用以表示一定句子结构的需要和强调某一句子成分的需要。 倒装有两种：将主语和谓语完全颠倒过来，叫做完全倒装(Complete Inversion)。如： 例1：In came a man with a white beard. 此

28、结构通常只用与一般现在时和一般过去时。 只将助动词(包括情态动词)移至主语之前，叫做部分倒装(Partial Inversion)。如： 例2：As the Internet becomes more and more commercialized, it is in the interest of business to universalize access - after all, the more people online, the more potential customers there are. 译文：随着国际互联网越来越商业化，普及上网会对商家有利，因为上网的人越多，潜在的顾客数量就越多。,倒装句,破折号后面的部分是用来解释句子主句的，在结构上是部分倒装句，属“（从句）the比较级，（主句）the 比较级”句型，这样的句子一般主谓不倒装。翻译