电子与通信工程专业英语Unit 7GPS-修改

1、1 1电子与通信工程电子与通信工程专业英语专业英语Unit 7 Unit 7 GPSGPS2 21What is GPS?GPS, which stands for Global Positioning System, is the only system today able to show your exact position on the Earth anytime, in any weather, anywhere 1. GPS satellite, 24 in all, orbit 11,000 nautical miles above the Earth. They are co

2、ntinuously monitored by ground stations located worldwide. The satellites transmit signals that can be detected by anyone with a GPS receiver. Using the receiver, you can determine your location with great precision.3 34 45 56 67 78 89 93GPS elements GPS has 3 parts: the space segment, the user segm

3、ent, and the control segment. The space segment consists of 24 satellites, each in its own orbit 11,000 nautical miles above the Earth. The user segment consists of receivers, which you can hold in your hand or mount in your car. The control segment consists of ground stations (five of them, located

4、 around the world) that makes sure the satellites are working properly.10 10One trip around the Earth in space equals one orbit. The GPS satellites each take 12 hours to orbit the Earth. Each satellite is equipped with an accurate clock to let it broadcast signals coupled with a precise time message

5、. The ground unit receives the satellite signal, which travels at the speed of light. Even at this speed, the signal takes a measurable amount of time to reach the receiver.11 11 The difference between the time the signal is sent and the time it is received, multiplied by the speed of light, enables

6、 the receiver to calculate the distance to the satellite. To measure precise latitude, longitude, and altitude, the receiver measures the time it took for the signals from four separate satellites to get to the receiver4.The GPS system can tell your location anywhere on or above the Earth to within

7、about 300 feet. Even great accuracy, usually within less than three feet, can be obtained with corrections calculated by a GPS receiver at a known fixed location.12 124Satellites in spaceAs weve said, the complete GPS space system includes 24 satellites, 11,000 nautical miles above the Earth, which

8、take 12 hours to go around the Earth once (one orbit). They are positioned so that we can receive signals from six of them nearly 100 percent of the time at any point on Earth. You need that many signals to get the best position information.Satellites are equipped with very precise clocks that keep

9、accurate time to within three nanosecondsthats 0.000,000,003, or three billionths, of a second. 13 13This precision timing is important because the receiver must know exactly how long it takes for its signal to get to each satellite and return. By knowing the exact amount of time the signal has take

10、n to get back from each satellite, it can calculate its position5.The first GPS satellite was launched in 1978. The first 10 satellites were developmental satellites, called Block.From 1989 to 1993, 23 production satellites, called Block, were launched. The launch of the 24th satellite in 1994 compl

11、eted the system.14 145Ground control stationsThe GPS control, or ground，segment consists of unmanned monitor stations located around the world (Hawaii and Kwajalein in the Pacific Ocean, Diego Garcia in the Indian Ocean, Ascension Island in the Atlantic Ocean, and Colorado Springs, Colorado), a mast

12、er ground station at Falcon Air Force Base in Colorado Springs, Colorado, and four large ground antenna stations that broadcast signals to the satellites. The stations also track and monitor the GPS satellites.15 156ReceiversGPS receivers can be hand carried or installed on aircraft, ships, tanks, s

13、ubmarines, cars, and trucks. These receivers detect, decode, and process GPS satellite signals. More than 100 different receiver models are already in use. The typical handheld receiver is about the size of a cellular telephone, and the newer models are even smaller.16 167How GPS worksSo you can mor

14、e easily understand some of the scientific principles that make GPS work, lets discuss the basic features of the system. The principle behind GPS is the measurement of distance (or “range”) between the receiver and the satellites. The satellites also tell us exactly where they are in their orbits. I

15、t woks something like this: If we know our exact distance from a satellite in space, we know that we are somewhere on the surface of an imaginary sphere with radius equal to the distance to the satellite radius. 17 17If we know our exact distance from two satellites, we know that we are located some

16、where on the line where the two spheres intersect. And, if we take a third measurement, there are only two possible points where we could be located. One of these is usually impossible, and the GPS receivers have mathematical methods of eliminating the impossible location. 18 188GPS uses in everyday

17、 lifeThe GPS system was developed to meet military needs of the Department of Defense, but new ways to use its capabilities are continually being found. As you have read, the system has been used in aircraft and ships, but there are many other ways to benefit from GPS. Well mention just a few. Durin

18、g construction of the tunnel under the English Channel, British and French crews started digging from opposite ends: one from Dover, England, one from Calais, France. 19 19They relied on GPS receivers outside the tunnel to check their positions along the way and to make sure they met exactly in the

19、middle. Otherwise, the tunnel might have been crooked.Remember the example of the car with a video display in the dashboard? Vehicle tracking is one of the fastest-growing GPS applications. GPS-equipped fleet vehicles, public transportation systems, delivery trucks, and courier services use receiver

20、s to monitor their locations at all times.2020GPS is also helping to save lives. Many police, fire, and emergency medical service units are using GPS receivers to determine the police car, fire truck, or ambulance nearest to an emergency, enabling the quickest possible response in life-or-death situ

21、ations.21 21NEW WORDS AND PHRASESnauticaladj.船舶的, 海上的orbitvt.绕轨道而行precision n. 精确，精密度，精度prehistoricadj.史前的，陈旧的twign. 嫩枝，小枝，末梢Phoeniciansn.腓尼基人sextantn.六分仪2222needlen.针latituden.纬度longitude n.经度timepiecen.时钟，座钟chronometern.记时计yardstick n.尺码，准绳nanosecondn.纳秒(十亿分之一秒)crewn.全体人员，(工作)队crookvt.使弯曲dashboard

22、n.汽车等的仪表板2323NOTES1 GPS, which stands for Global Positioning System, is the only system today able to show your exact position on the Earth anytime, in any weather, anywhere.本句可译为：GPS代表全球定位系统，它是能告诉任何时间、任何天气、任何地点你在地球上的精确位置的唯一现代系统。24242 One drawback of using radio waves generated on the ground is that

23、 you must choose between a system that is very accurate but doesnt cover a wide area, or one that covers a wide area but is not very accurate.本句的主语是“One drawback”，第一个is是其谓语，其后面的that是宾语从句。system后面的两个that.是后置定语从句。2525本句可译为：利用地面产生的无线电波的一个缺点是必须在系统中进行选择：是需要精确但不能覆盖大的区域或是需要覆盖大的区域但是不那么精确。高频无线电波(如UHF TV)能够提供

24、精确的位置信息，但是只能针对小的、局部的区域。3 A transmitter high above the Earth sending a high-frequency radio wave with a special coded signal can cover a large area and still overcome much of the “noise” encountered on the way to the ground.2626本句的主语是“A transmitter”，谓语是“cover”和“overcome”。“high above the Earth”是修饰“tra

25、nsmitter”的，“sending a high-frequency radio wave with a special coded signal”是动名词短语，修饰“transmitter”。本句可译为：地球之上的一个电波发射机使用特殊编码信号发送高频无线电波，不但能覆盖广阔的范围，且能够克服到达地面路径中的大部分噪声。27274 To measure precise latitude, longitude, and altitude, the receiver measures the time it took for the signals from four separate sa

26、tellites to get to the receiver.“it took for the signals from four separate satellites to get to the receiver.”是后置定语从句，修饰前面的“the time”。本句可译为：为了测量准确的经度、纬度和高度信息，接收器需要分别测量来自4颗卫星的信号到达接收器的时间。28285 By knowing the exact amount of time the signal has taken to get back from each satellite, it can calculate i

27、ts position.“the signal has taken to get back from each satellite”是“time”的后置定语从句，修饰“time”。这里“it”代表“the receiver”。本句可译为：知道了信号从每颗卫星返回花费的时间后，接收器才能计算出它的位置。2929EXERCISES. Translate the following words or phrases.GPS nautical mile with great precisionmark a trailozone layer exact distance 经度信息 纬度信息 a grou

28、nd-based radio-navigation system a hand-held GPS receiver3030. Translate the following paragraphs into Chinese.(1) GPS, which stands for Global Positioning System, is the only system today able to show your exact position on the Earth anytime, in any weather, anywhere. GPS satellite, 24 in all, orbi

29、t 11,000 nautical miles above the Earth. They are continuously monitored by ground stations located worldwide. The satellites transmit signals that can be detected by anyone with a GPS receiver. Using the receiver, you can determine your location with great precision.31 31(2) Scientists, therefore,

30、decided that the only way to provide coverage for the entire world was to place high-frequency radio transmitters in space. A transmitter high above the Earth sending a high-frequency radio wave with a special coded signal can cover a large area and still overcome much of the “noise” encountered on

31、the way to the ground. This is one of the main principles behind the GPS system.3232(3) During construction of the tunnel under the English Channel, British and French crews started digging from opposite ends: one from Dover, England, one from Calais, France. They relied on GPS receivers outside the

32、 tunnel to check their positions along the way and to make sure they met exactly in the middle. Otherwise, the tunnel might have been crooked.3333参考译文第七单元 全球定位系统1什么是GPS？GPS代表全球定位系统，它是能告诉任何时间、任何天气、任何地点你在地球上的精确位置的唯一现代系统。GPS共有24颗卫星，在地球上方11000海里的轨道上绕地球运行。它们不间断地受到全球各地地面站的监测。拥有GPS接收器的任何人都能接收到卫星发射的信号。使用接收器

33、你可以很精确地确定你所在的位置。34342什么是导航？从史前时代，人们就试图推算出一种可靠方法，(这种方法)能告诉他们所在的位置以及指导他们到达他们想去的地点。穴居人可能使用石头和树枝来标记他们出去打猎时的踪迹。早期的水手们紧紧沿着海岸航行以避免迷路。当航海家们初次航行到开阔的海洋时，他们发现可以利用沿途的星星来画出他们的航行路线。古代腓尼基人使用北极星(导航)可以从埃及到达克里特岛。按照荷马的说法，女神Athena曾告诉Odysseus，当他从Calypso的岛上出来时要沿着大熊星左侧走(才能到达目的地)。不幸的是，星星只能在晚上而且是晴朗的晚上才能看得见。3535磁性罗盘和六分仪是在探索完

34、美导航方法的过程中的第二个重要发展(阶段)。罗盘的针始终指向北方，所以总是能知道要去的方向。六分仪使用可调节的镜子来测量星星、月亮和太阳在地平线上的精确角度。但是，早期使用六分仪只能确定六分仪观测处的纬度，水手们仍然不能确定他们的经度(在地球上东或西的位置)，这在17世纪是一个严重的问题。(为了解决这个问题)英国组织了一个由著名科学家们组成的特别经度委员会。这个委员会提供了20000英镑(相当于今天的1亿美元)来奖励能在30海里内确定船只经度的人。这笔慷慨的奖励得到了好的结果。36361761年，一个名叫John Harrison的家具师设计了一个称为记时计的舷侧时钟，这个时钟一天只误差一秒在

35、那个时代这种准确是不可思议的。接下来的两个世纪里，(人们)联合使用六分仪和记时计来得到经度和纬度信息。20世纪早期人们开发了几种无线电导航系统，这些导航系统在二战时得到了广泛应用。盟军和敌军的船只飞机都使用了技术先进的、基于地面的无线电导航系统。3737一些基于地面的无线电导航系统直到今天仍在使用。利用地面产生的无线电波的一个缺点是必须在系统中进行选择：是需要精确但不能覆盖大的区域或是需要覆盖大的区域但是不那么精确。高频无线电波(如UHF TV)能够提供精确的位置信息，但是只能针对小的、局部的区域。较低频率的无线电波(如AM无线电)能覆盖大的地域，但是不能提供一个精确的准绳来标示所在的位置。3

36、838因此，科学家们认为能为整个全球提供导航覆盖的唯一方法是在高空放置一个高频无线电波发射机。地球之上的一个电波发射机使用特殊编码信号发送高频无线电波，不但能覆盖广阔的范围，且能够克服到达地面路径中的大部分噪声。这是GPS系统的一个主要原理。39393GPS的要素GPS由三个部分组成：空间部分、用户部分和控制部分。空间部分包含24颗卫星，每颗卫星都围绕地球在11000海里高的轨道上运行。用户部分包括持于手中或装于汽车上的接收器。控制部分包括5个确保卫星正常运行的地面站(位于世界各地)。卫星绕地球运行的路线就是轨道，每个GPS卫星绕地球一周需要12个小时。每颗卫星上都安装了准确的时钟，(这样)可

37、使它广播与准确时间信息一致的信号。地面单元接收以光速传播的卫星信号。即使是光速传播，信号到达接收器仍然需要一定的时间。4040信号发送时间和接收时间之间的差值乘以光速就可以计算出接收器到卫星之间的距离。为了测量准确的经度、纬度和高度信息，接收器需要分别测量来自4颗卫星的信号到达接收器的时间。GPS系统能分辨地球上无论何处或地球之上300英尺以内的你的位置。甚至，在已知固定地点还有更高的准确度，通常GPS的修正误差不超过3英尺。41 414空间段就像前面所说的，整个GPS空间系统包括24颗位于地球上空11000海里的卫星，围绕地球一周需要12个小时时间(每个轨道)。它们排列的位置使得我们可以在地

38、球任何地点在100%时间里接收到24颗中的6颗卫星的信号。人们需要许多信号获得最优的位置信息。 这些卫星上安装了非常精确的时钟，这些时钟的偏差在3纳秒之内，即0.000000003秒。这种精确计时非常重要，因为接收器必须准确地知道它的信号到达卫星和返回的时间长度。知道了信号从每颗卫星返回花费的时间后，接收器才能计算出它的位置。4242第一颗GPS卫星是1978年发射的。前10颗卫星是试验卫星，称为BLOCK。1989年到1993年，发射了23颗成品卫星，称为BLOCK。1994年，发射了第24颗卫星，(标志着)整个GPS系统的建成。43435地面控制站GPS控制或地面部分包括分布在世界各地的无

39、人监控站(太平洋上的夏威夷岛和考贾林环礁、印度洋上的迪亚戈加西亚及大西洋的阿森松岛和科罗拉多的科罗拉多泉)、科罗拉多的科罗拉多泉Falcon空军基地的地面主站和4个用来向卫星广播信号的大型地面天线站。地面站也跟踪和监视GPS卫星。44446GPS接收器GPS接收器可以手持或安装在飞机、轮船、坦克、潜艇、汽车和卡车上。这些接收器探测、解码和处理GPS卫星信号。正在使用的接收器有一百多种。典型的手持式接收器在尺寸上和移动电话差不多，新型的接收器体积更小。45457GPS是如何工作的GPS工作的科学原理很容易理解，所以这里讨论系统的基本特征。GPS的原理是测量卫星和接收器之间的距离。卫星也会告诉我们

40、它们在轨道上的具体位置。它是这样工作的：如果知道了我们距离卫星的精确空间距离，就知道了我们处于一个半径等于到达卫星界限的一个虚拟球体的某点处。如果知道了我们距离两颗卫星的准确距离，就知道了我们处于两个球体的相交线的某处。如果我们得到了第三个测量值，我们就仅仅处于两个可能的点上。其中的一个点通常是不可能的，GPS接收器使用数学方法来排除不可能的位置。46468在日常生活中使用GPS开发GPS系统是为了满足国防部部队的需求，但是人们却在不断地发现它的新用途。就像你了解的那样，该系统已经运用在了飞机和轮船上，不仅如此，其他的一些方面也能从GPS获益。我们将介绍的仅仅是一部分。 在英吉利海底隧道建设的

41、过程中，英国和法国工作人员从两端开始挖掘：一端从英国的多佛港，另一端从法国的加来。他们依靠隧道外的GPS 接收机来检验他们在隧道中的位置，确保他们能准确地在中间碰面。否则，隧道(挖掘)可能会走弯路。4747还记得汽车仪表盘的视频显示器的例子吗？车辆跟踪就是其中发展最快的一个GPS应用。安装了GPS的车队、公共交通系统、物流卡车、信件快递服务可以利用接收器全天时监视他们的位置。GPS也可以帮助救助生命。许多警察、消防和急救医疗部门使用GPS接收机来确定距离紧急情况最近的警车、消防车和救护车，这样可以在生死攸关的情况下尽快地进行救助。4848EXTENSIVE TEXTIntroduction t

42、o 3GThe mobile communications industry has evolved in three stages: AnalogDigitalMultimedia. Three generations of mobile phones have emerged so far, each successive generation more reliable and flexible than the last:Analog: You could only easily use analogue cellular to make voice calls, and typica

43、lly only in any one country. Digital mobile phone systems added fax, data and messaging capabilities as well as voice telephone service in many countries. Multimedia services add high speed data transfer to mobile devices,4949 allowing new video, audio and other applications through mobile phonesall

44、owing music and television and the Internet to be accessed through a mobile terminal.With each new generation of technology, the services which can be deployed on them becomes more and more wide ranging and truly limited only by imagination. We are reaching that stage with 3G.During the first and se

45、cond generations different regions of the world pursued different mobile phone standards, but are converging to a common standard for mobile multimedia called Third Generation (3G) that is based on CDMA technology. 3G will bring these incompatible standards together.5050The Third Generation of mobil

46、e communications systems will soon be implemented. Following on the heals of analog and digital technology, the Third Generation will be digital mobile multimedia offering broadband mobile communications with voice, video, graphics, audio and other information. This transition is shown below:Generat

47、ion Type Time Description.51 51First Analog 1980s Voice centric, multiple standards (NMT, TACS etc.).Second Digital 1990s Voice centric, multiple standards (GSM, CDMA, TDMA).2.5G Higher Rate Data Late 1990s Introduction of new higher speed data services to bridge the gap between the Second and Third

48、 Generation, including services such as General Packet Radio Service (GPRS) and Enhanced Data Rates for Global Evolution (EDGE).Third Digital Multimedia 2010s Voice and data centric, single standard with multiple modes.525213G Features3G has the following features:1) Packet EverywhereWith Third Gene

49、ration (3G), the information is split into separate but related packets before being transmitted and reassembled at the receiving end. Packet switching is similar to a jigsaw puzzlethe image that the puzzle represents is divided into pieces at the manufacturing factory and put into a plastic bag. Du

50、ring transportation of the now boxed jigsaw from the factory to the end user, 5353the pieces get jumbled up. When the recipient empties the bag with all the pieced, they are reassembled to form the original image. All the pieces are all related and fit together, but the way they are transported and

51、assembled varies.Packet switched data formats are much more common than their circuit switched counterparts. Other examples of pack-based data standard include TCP/IP, X.25, Frame Relay and Asynchronous Transfer Mode (ATM). In the mobile world, CDPD (Cellular Digital Packet Data), PDCP (Personal Dig

52、ital Cellular Packet), 5454General Packet Radio Service (GPRS) and wireless X.25 technologies have been in operation for several years. X.25 is the international public access packet radio data network standard.2) Internet EverywhereThe World Wide Web is becoming the primary communications interface

53、people access the Internet for entertainment and information collection, the intranet for accessing company information and connecting with colleagues and the extranet for accessing customers and supplier. These are all derivatives of the World Wide Web aimed at connecting different communities of i

54、nterest.5555 There is a trend away from storing information locally in specific software packages on PCs to remotely on the Internet. Web browsing is a very important application for packet data.3) High SpeedSpeeds of up to 2 Megabits per second (Mbps) are achievable with Third Generation (3G). The data transmission rates will depend upon the environment the c