通信工程專業(yè)外文翻譯--全球定位系統(tǒng)的介紹GPS

1、.畢 業(yè) 設(shè) 計(jì)（論 文）外 文 參 考 資 料 及 譯 文 譯文題目：Introduction to the Global Positioning System 全球定位系統(tǒng)的介紹 學(xué)生姓名： 學(xué) 號(hào)： 專業(yè)： 通信工程 所在學(xué)院： 指導(dǎo)教師： 職稱： Introduction to the Global Positioning System -From “Corvallis Microtechnology, Inc. 1996”Chapter One: What is GPS?The Global Positioning System (GPS) is a location system

2、based on a constellation of about 24 satellites orbiting the earth at altitudes of approximately 11,000 miles. GPS was developed by the United States Department of Defense (DOD), for its tremendous application as a military locating utility. The DOD's investment in GPS is immense. Billions and b

3、illions of dollars have been invested in creating this technology for military uses. However, over the past several years, GPS has proven to be a useful tool in non-military mapping applications as well.GPS satellites are orbited high enough to avoid the problems associated with land based systems,

4、yet can provide accurate positioning 24 hours a day, anywhere in the world. Uncorrected positions determined from GPS satellite signals produce accuracies in the range of 50 to 100 meters. When using a technique called differential correction, users can get positions accurate to within 5 meters or l

5、ess.Today, many industries are leveraging off the DOD's massive undertaking. As GPS units are becoming smaller and less expensive, there are an expanding number of applications for GPS. In transportation applications, GPS assists pilots and drivers in pinpointing their locations and avoiding col

6、lisions. Farmers can use GPS to guide equipment and control accurate distribution of fertilizers and other chemicals. Also，GPS is used for providing accurate locations and as a navigation tool for hikers, hunters and boaters.Many would argue that GPS has found its greatest utility in the field of Ge

7、ographic Information Systems (GIS). With some consideration for error, GPS can provide any point on earth with a unique address (its precise location). A GIS is basically a descriptive database of the earth (or a specific part of the earth). GPS tells you that you are at point X,Y,Z while GIS tells

8、you that X,Y,Z is an oak tree, or a spot in a stream with a pH level of 5.4. GPS tells us the "where". GIS tells us the "what". GPS/GIS is reshaping the way we locate, organize, analyze and map our resources.Chapter Two: Trilateration - How GPS Determines a LocationIn a nutshell,

9、 GPS is based on satellite ranging - calculating the distances between the receiver and the position of 3 or more satellites (4 or more if elevation is desired) and then applying some good old mathematics. Assuming the positions of the satellites are known, the location of the receiver can be calcul

10、ated by determining the distance from each of the satellites to the receiver. GPS takes these 3 or more known references and measured distances and "triangulates" an additional position.As an example, assume that I have asked you to find me at a stationary position based upon a few clues w

11、hich I am willing to give you. First, I tell you that I am exactly 10 miles away from your house. You would know I am somewhere on the perimeter of a sphere that has an origin as your house and a radius of 10 miles. With this information alone, you would have a difficult time to find me since there

12、are an infinite number of locations on the perimeter of that sphere.Second, I tell you that I am also exactly 12 miles away from the ABC Grocery Store. Now you can define a second sphere with its origin at the store and a radius of 12 miles. You know that I am located somewhere in the space where th

13、e perimeters of these two spheres intersect - but there are still many possibilities to define my location.Adding additional spheres will further reduce the number of possible locations. In fact, a third origin and distance (I tell you am 8 miles away from the City Clock) narrows my position down to

14、 just 2 points. By adding one more sphere, you can pinpoint my exact location. Actually, the 4th sphere may not be necessary. One of the possibilities may not make sense, and therefore can be eliminated.For example, if you know I am above sea level, you can reject a point that has negative elevation

15、. Mathematics and computers allow us to determine the correct point with only 3 satellites.Based on this example, you can see that you need to know the following information in order to compute your position:A) What is the precise location of three or more known points (GPS satellites)?B) What is th

16、e distance between the known points and the position of the GPS receiver?Chapter Three: How the Current Locations of GPS Satellites are DeterminedGPS satellites are orbiting the Earth at an altitude of 11,000 miles. The DOD can predict the paths of the satellites vs. time with great accuracy. Furthe

17、rmore, the satellites can be periodically adjusted by huge land-based radar systems. Therefore, the orbits, and thus the locations of the satellites, are known in advance. Today's GPS receivers store this orbit information for all of the GPS satellites in what is known as an almanac. Think of th

18、e almanac as a "bus schedule" advising you of where each satellite will be at a particular time. Each GPS satellite continually broadcasts the almanac. Your GPS receiver will automatically collect this information and store it for future reference.The Department of Defense constantly monit

19、ors the orbit of the satellites looking for deviations from predicted values. Any deviations (caused by natural atmospheric phenomenon such as gravity), are known as ephemeris errors. When ephemeris errors are determined to exist for a satellite, the errors are sent back up to that satellite, which

20、in turn broadcasts the errors as part of the standard message, supplying this information to the GPS receivers.By using the information from the almanac in conjuction with the ephemeris error data, the position of a GPS satellite can be very precisely determined for a given time.Chapter Four: Comput

21、ing the Distance Between Your Position and the GPS SatellitesGPS determines distance between a GPS satellite and a GPS receiver by measuring the amount of time it takes a radio signal (the GPS signal) to travel from the satellite to the receiver. Radio waves travel at the speed of light, which is ab

22、out 186,000 miles per second. So, if the amount of time it takes for the signal to travel from the satellite to the receiver is known, the distance from the satellite to the receiver (distance = speed x time) can be determined. If the exact time when the signal was transmitted and the exact time whe

23、n it was received are known, the signal's travel time can be determined.In order to do this, the satellites and the receivers use very accurate clocks which are synchronized so that they generate the same code at exactly the same time. The code received from the satellite can be compared with th

24、e code generated by the receiver. By comparing the codes, the time difference between when the satellite generated the code and when the receiver generated the code can be determined. This interval is the travel time of the code. Multiplying this travel time, in seconds, by 186,000 miles per second

25、gives the distance from the receiver position to the satellite in miles.Chapter Five: Four (4) Satellites to give a 3D positionIn the previous example, you saw that it took only 3 measurements to "triangulate" a 3D position. However, GPS needs a 4th satellite to provide a 3D position. Why?

26、Three measurements can be used to locate a point, assuming the GPS receiver and satellite clocks are precisely and continually synchronized, thereby allowing the distance calculations to be accurately determined. Unfortunately, it is impossible to synchronize these two clocks, since the clocks in GP

27、S receivers are not as accurate as the very precise and expensive atomic clocks in the satellites. The GPS signals travel from the satellite to the receiver very fast, so if the two clocks are off by only a small fraction, the determined position data may be considerably distorted.The atomic clocks

28、aboard the satellites maintain their time to a very high degree of accuracy. However, there will always be a slight variation in clock rates from satellite to satellite. Close monitoring of the clock of each satellite from the ground permits the control station to insert a message in the signal of e

29、ach satellite which precisely describes the drift rate of that satellite's clock. The insertion of the drift rate effectively synchronizes all of the GPS satellite clocks.The same procedure cannot be applied to the clock in a GPS receiver. Therefore, a fourth variable (in addition to x, y and z)

30、, time, must be determined in order to calculate a precise location. Mathematically, to solve for four unknowns (x,y,z, and t), there must be four equations. In determining GPS positions, the four equations are represented by signals from four different satellites.Chapter Six: The GPS Error BudgetTh

31、e GPS system has been designed to be as nearly accurate as possible. However, there are still errors. Added together, these errors can cause a deviation of +/- 50 -100 meters from the actual GPS receiver position. There are several sources for these errors, the most significant of which are discusse

32、d below:Atmospheric ConditionsThe ionosphere and troposphere both refract the GPS signals. This causes the speed of the GPS signal in the ionosphere and troposphere to be different from the speed of the GPS signal in space. Therefore, the distance calculated from "Signal Speed x Time" will

33、 be different for the portion of the GPS signal path that passes through the ionosphere and troposphere and for the portion that passes through space.As mentioned earlier, GPS signals contain information about ephemeris (orbital position) errors, and about the rate of clock drift for the broadcastin

34、g satellite. The data concerning ephemeris errors may not exactly model the true satellite motion or the exact rate of clock drift. Distortion of the signal by measurement noise can further increase positional error. The disparity in ephemeris data can introduce 1-5 meters of positional error, clock

35、 drift disparity can introduce 0-1.5 meters of positional error and measurement noise can introduce 0-10 meters of positional error.Ephemeris errors should not be confused with Selective Availability (SA), which is the intentional alteration of the time and ephemeris signal by the Department of Defe

36、nse. A GPS signal bouncing off a reflective surface prior to reaching the GPS receiver antenna is referred to as multipath. Because it is difficult to completely correct multipath error, even in high precision GPS units, multipath error is a serious concern to the GPS user.Chapter Seven: Measuring G

37、PS AccuracyAs discussed above, there are several external sources which introduce errors into a GPS position. While the errors discussed above always affect accuracy, another major factor in determining positional accuracy is the alignment, or geometry, of the group of satellites (constellation) fro

38、m which signals are being received. The geometry of the constellation is evaluated for several factors, all of which fall into the category of Dilution Of Precision, or DOP.DOP is an indicator of the quality of the geometry of the satellite constellation. Your computed position can vary depending on

39、 which satellites you use for the measurement. Different satellite geometries can magnify or lessen the errors in the error budget described above. A greater angle between the satellites lowers the DOP, and provides a better measurement. A higher DOP indicates poor satellite geometry, and an inferio

40、r measurement configuration.Some GPS receivers can analyze the positions of the satellites available, based upon the almanac, and choose those satellites with the best geometry in order to make the DOP as low as possible. Another important GPS receiver feature is to be able to ignore or eliminate GP

41、S readings with DOP values that exceed user-defined limits. Other GPS receivers may have the ability to use all of the satellites in view, thus minimizing the DOP as much as possible.全球定位系統(tǒng)的介紹 -摘自Corvallis Microtechnology公司，1996第1章 ：什么是GPS？全球定位系統(tǒng)（）是一種基于顆高度大約英里的地球軌道衛(wèi)星的定位系統(tǒng)。是美國(guó)國(guó)防部（）因?yàn)槠湓谲娛露ㄎ谎b置方面巨大的應(yīng)用而開

42、發(fā)的。國(guó)防部對(duì)的投入是極大的。已經(jīng)有數(shù)十億美元的投資為了開發(fā)這種軍事應(yīng)用技術(shù)。然而，過去一段時(shí)間以來，已經(jīng)被證實(shí)是在測(cè)繪非軍事地圖應(yīng)用方面十分有用的工具。GPS衛(wèi)星的軌道足夠高以避免以土地為基礎(chǔ)的系統(tǒng)相關(guān)的問題，還可以在世界上任何地方提供每天24小時(shí)準(zhǔn)確的定位。在裸眼可視位置GPS衛(wèi)星信號(hào)產(chǎn)生的定位精度為到米。當(dāng)使用差分技術(shù)時(shí)，用戶可以得到精度為5米以下的定位。今天，許多行業(yè)都促使國(guó)防部改變。由于GPS單位正變得更小，更便宜，GPS的應(yīng)用正在不斷增加。在交通運(yùn)輸應(yīng)用方面，GPS協(xié)助飛行員和司機(jī)準(zhǔn)確定位它們的位置，避免碰撞。農(nóng)民可以使用GPS引導(dǎo)設(shè)備并且控制化肥和其他化學(xué)品的準(zhǔn)確分布。此外，GP

43、S用于提供準(zhǔn)確的位置，并作為徒步旅行者，獵人和船民的導(dǎo)航工具。很多人認(rèn)為，GPS已經(jīng)在地理信息系統(tǒng)（GIS）領(lǐng)域發(fā)揮最大的應(yīng)用。在考慮到一些誤差的情況下，GPS可以提供地球上任何一點(diǎn)的唯一一個(gè)地址（它的精確位置）。 GIS從根本上說是地球的一個(gè)描述的數(shù)據(jù)庫(kù)（或地球的特定部分）。 GPS會(huì)告訴你，你是在點(diǎn)X，Y，Z，而GIS告訴你，X，Y，Z點(diǎn)是一棵橡樹，或河流中的一個(gè)pH值5.4的點(diǎn)。 GPS告訴我們，“在哪里”， GIS告訴我們“是什么”。 GPS/ GIS正在重塑定位，管理，分析，并且映射我們的資源。第2章 ：三邊定位GPS是怎樣定位的簡(jiǎn)單地說，GPS是基于衛(wèi)星測(cè)距 -計(jì)算接收器和3顆或更

44、多顆衛(wèi)星（4個(gè)或更多，如果需要高程）之間的距離，然后用一些以前的正確數(shù)字進(jìn)行計(jì)算。假設(shè)衛(wèi)星的位置是已知的，通過確定每個(gè)衛(wèi)星到接收機(jī)的距離，可以計(jì)算出接收機(jī)的位置。 GPS用這3個(gè)或更多的已知的參考和測(cè)量距離然后“三角測(cè)量”出額外的位置。作為一個(gè)例子，假設(shè)我要你根據(jù)我給你提供的很少的一些線索讓你在一個(gè)固定的位置找到我。首先，我告訴你，我離你的房子正好是10英里遠(yuǎn)。你會(huì)知道我在一個(gè)以你的房子為圓心，半徑10英里的球形邊界的地方。只有這些信息，你很難找到我，因?yàn)樵谶@球形的邊界上有無數(shù)的位置點(diǎn)。第二，我告訴你，我也正好離ABC雜貨店12英里遠(yuǎn)?，F(xiàn)在，你可以畫出一個(gè)以雜貨店為圓心，半徑12英里的球形。你

45、知道，我所在的地方，在兩個(gè)球形空間的周長(zhǎng)交叉的地方 - 但我的位置還是有很多的可能性。添加更多的范圍將進(jìn)一步減少可能的地點(diǎn)。事實(shí)上，第三個(gè)圓心和距離（我告訴你是8英里遠(yuǎn)的城市時(shí)鐘）使我的位置縮小到只有2點(diǎn)。再增加一個(gè)范圍，你可以找出我的確切位置。其實(shí)，第四球體可能不是必需的。其中一個(gè)可能是沒有意義的，并因此可以被消除。例如，如果你知道我是海平面上，你可以拒絕一個(gè)海拔為負(fù)的點(diǎn)。數(shù)學(xué)和計(jì)算機(jī)讓我們能夠只用3顆衛(wèi)星確定正確的點(diǎn)?；谶@個(gè)例子，你可以明白，你需要知道以下信息，以便計(jì)算你的位置：A）3個(gè)或更多的已知點(diǎn)（GPS衛(wèi)星）的精確位置是什么？B）已知點(diǎn)的位置和GPS接收器之間是多少距離？第3章 ：

46、如何確定GPS衛(wèi)星當(dāng)前位置GPS衛(wèi)星在高度為11000公里的軌道繞地球飛行。國(guó)防部可以非常準(zhǔn)確地預(yù)測(cè)衛(wèi)星的路徑與時(shí)間的關(guān)系。此外，衛(wèi)星還可以定期通過巨大的陸基雷達(dá)系統(tǒng)進(jìn)行調(diào)整。因此，軌道，衛(wèi)星的位置，都是預(yù)先已知的。今天的GPS接收器存儲(chǔ)所有的GPS衛(wèi)星的軌道信息，被稱為星歷。你的星歷像“巴士時(shí)刻表”，提醒你每顆衛(wèi)星在一個(gè)特定的時(shí)間點(diǎn)在什么地方。每個(gè)GPS衛(wèi)星不斷廣播星歷。你的GPS接收器會(huì)自動(dòng)收集這些信息，并將其存儲(chǔ)以供將來參考。國(guó)防部不斷地監(jiān)視衛(wèi)星的軌道預(yù)測(cè)值的偏差。任何偏差（由于自然的大氣現(xiàn)象，如重力），被稱為星歷誤差。當(dāng)被確定為存在衛(wèi)星星歷誤差，誤差被發(fā)送備份到該衛(wèi)星，依次將錯(cuò)誤作為標(biāo)準(zhǔn)的消息的一部分廣播，提供這種信息給GPS接收機(jī)。通過使用星歷表的信息誤差數(shù)據(jù)，可以很精確地在一個(gè)給定的時(shí)間確定GPS衛(wèi)星的位置。第4章 ：計(jì)算你的位置和GPS衛(wèi)星之間的距離GPS通過測(cè)量衛(wèi)星和接收機(jī)之間無線電信號(hào)（GPS信號(hào)）傳輸所花費(fèi)的時(shí)間來確定衛(wèi)星和接收機(jī)的距離。無線電波以光速傳播，這是大約每秒186,000英里的速度。因此，如果信號(hào)從衛(wèi)星到接收機(jī)的時(shí)間量是已知的，衛(wèi)星到接收機(jī)的距離（距離=速度×時(shí)間）可以被確定。如果信號(hào)發(fā)送和收到的時(shí)間確定，信號(hào)的傳輸時(shí)間才能確定。為了做到這一點(diǎn)，衛(wèi)