外文翻譯--全球衛(wèi)星定位系統(tǒng)

1、<p><b>　　本科畢業(yè)論文</b></p><p><b>　　外文文獻(xiàn)及譯文</b></p><p>　　文獻(xiàn)、資料題目：Global Positioning System</p><p><b>　　文獻(xiàn)、資料來源：</b></p><p>　　http:/

2、/en.wikipedia.org/wiki/Global_Positioning_System</p><p>　　文獻(xiàn)、資料發(fā)表（出版）日期：2009.01.03</p><p>　　院 （部）： 土木工程學(xué)院</p><p>　　專 業(yè)： 土木工程</p><p><b>　　班 級： </b><

3、/p><p><b>　　姓 名： </b></p><p><b>　　學(xué) 號： </b></p><p><b>　　指導(dǎo)教師： </b></p><p><b>　　翻譯日期： </b></p><p><b&g

4、t;　　外文文獻(xiàn)：</b></p><p>　　Global Positioning System</p><p>　　The Global Positioning System (GPS) is a global navigation satellite system (GNSS) developed by the United States Department of De

5、fense and managed by the United States Air Force 50th Space Wing. It is the only fully functional GNSS in the world, can be used freely, and is often used by civilians for navigation purposes. The Global Positioning Syst

6、em (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was ori</p><p>　　History </p&g

7、t;<p>　　The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. Using a constellation of five satellites, it could provide a navigational fix approxim

8、ately once per hour. In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology that GPS relies upon. In the 1970s, the ground-based Omega Navigation

9、System, based on signal phase comparison, became the first worldwide radio </p><p>　　The design of GPS is based partly on similar ground-based radio navigation systems, such as LORAN and the Decca Navigator

10、developed in the early 1940s, and used during World War II. Additional inspiration for the GPS came when the Soviet Union launched the first man-made satellite, Sputnik in 1957. A team of U.S. scientists led by Dr. Richa

11、rd B. Kershner were monitoring Sputnik's radio transmissions. They discovered that, because of the Doppler effect, the frequency of the signal being transmitt</p><p>　　After Korean Air Lines Flight 007 w

12、as shot down in 1983 after straying into the USSR's prohibited airspace,[3] President Ronald Reagan issued a directive making GPS freely available for civilian use as a common good.[4] The satellites were launched be

13、tween 1989 and 1993.</p><p>　　Initially the highest quality signal was reserved for military use, while the signal available for civilian use was intentionally degraded ("Selective Availability", S

14、A). Selective Availability was ended in 2000, improving the precision of civilian GPS from about 100m to about 20m.</p><p>　　Of crucial importance for the function of GPS is the placement of atomic clocks in

15、 the satellites, first proposed by Friedwardt Winterberg in 1955.[5] Only then can the required position accuracy be reached.</p><p>　　Timeline </p><p>　　In 1972, the US Ai

16、r Force Central Inertial Guidance Test Facility (Holloman AFB) conducted developmental flight tests of two prototype GPS receivers over White Sands Missile Range, using ground-based pseudo-satellites.

17、 </p><p>　　In 1978 the first experimental Block-I GPS satellite was launched. </p><p>　　In 1983, after Soviet interceptor aircraft shot down the civilian airliner KAL

18、007 that strayed into prohibited airspace due to navigational errors, killing all 269 people on board, U.S. President Ronald Reagan announced that the GPS would be made available for civilian uses once it was completed.[

19、9][10] </p><p>　　By 1985, ten more experimental Block-I satellites had been launched to validate the concept. </p><p>　　On February 14, 1989, the first modern Block-II satellite was launched. &l

20、t;/p><p>　　In 1992, the 2nd Space Wing, which originally managed the system, was de-activated and replaced by the 50th Space Wing. </p><p>　　By December 1993 the GPS achieved initial operational ca

21、pability.[11] </p><p>　　By January 17, 1994 a complete constellation of 24 satellites was in orbit. </p><p>　　Full Operational Capability was declared by NAVSTAR in April 1995. </p><p

22、>　　In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President Bill Clinton issued a policy directive[12] declaring GPS to be a dual-use system and establishing an Interagenc

23、y GPS Executive Board to manage it as a national asset. </p><p>　　In 1998, U.S. Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability,

24、 particularly with respect to aviation safety. </p><p>　　On May 2, 2000 "Selective Availability" was discontinued as a result of the 1996 executive order, allowing users to receive a non-degraded s

25、ignal globally. </p><p>　　In 2004, the United States Government signed an agreement with the European Community establishing cooperation related to GPS and Europe's planned Galileo system. </p>&l

26、t;p>　　In 2004, U.S. President George W. Bush updated the national policy and replaced the executive board with the National Space-Based Positioning, Navigation, and Timing Executive Committee. </p><p>　　N

27、ovember 2004, QUALCOMM announced successful tests of Assisted-GPS for mobile phones.[13] </p><p>　　In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2

28、C) for enhanced user performance. </p><p>　　On September 14, 2007, the aging mainframe-based Ground Segment Control System was transitioned to the new Architecture Evolution Plan.[14] </p><p>　　

29、The most recent launch was on March 15, 2008.[15] The oldest GPS satellite still in operation was launched on November 26, 1990, and became operational on December 10, 1990.[16] </p><p>　　Basic concept of GP

30、S</p><p>　　A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the Earth. Each satellite continually transmits messages containing the time the messag

31、e was sent, precise orbital information (the ephemeris), and the general system health and rough orbits of all GPS satellites (the almanac). The receiver measures the transit time of each message and computes the distanc

32、e to each satellite. Geometric trilateration is used to combine these distances with</p><p>　　It might seem three satellites are enough to solve for position, since space has three dimensions. However, even

33、a very small clock error multiplied by the very large speed of light[17]—the speed at which satellite signals propagate—results in a large positional error. Therefore receivers use four or more satellites to solve for x,

34、 y, z, and t, which is used to correct the receiver's clock. While most GPS applications use the computed location only and effectively hide the very accurately comput</p><p>　　Although four satellites a

35、re required for normal operation, fewer apply in special cases. If one variable is already known (for example, a ship or plane may have known elevation), a receiver can determine its position using only three satellites.

36、 Some GPS receivers may use additional clues or assumptions (such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer) to give a degraded position w

37、hen fewer than four satellites are</p><p>　　Position calculation introduction </p><p>　　To provide an introductory description of how a GPS receiver works, measurement errors will be ignored in

38、this section. Using messages received from a minimum of four visible satellites, a GPS receiver is able to determine the satellite positions and time sent. The x, y, and z components of position and the time sent are des

39、ignated as where the subscript i is the satellite number and has the value 1, 2, 3, or 4. Knowing the indicated time the message was received , the GPS receiver can compute t</p><p>　　Two sphere surfaces int

40、ersecting in a circle</p><p>　　The article, trilateration, shows mathematically that the surfaces of two spheres, intersecting in more than one point, intersect in a circle.</p><p>　　A circle an

41、d sphere surface in most cases of practical interest intersect at two points, although it is conceivable that they could intersect at zero points, one point, or in the very special case in which the centers of the three

42、spheres are colinear (i.e. all three on the same straight line) the sphere surface could intersect the entire circumference of the circle. Another figure, Surface of Sphere Intersecting a Circle (not disk) at Two Points,

43、 shows this intersection. The two intersections a</p><p>　　Correcting a GPS receiver's clock</p><p>　　The method of calculating position for the case of no errors has been explained. One of

44、the most significant error sources is the GPS receiver's clock. Because of the very large value of the speed of light, c, the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very se

45、nsitive to errors in the GPS receiver clock. This suggests that an extremely accurate and expensive clock is required for the GPS receiver to work. On the other hand, manufacturers prefer to build</p><p>　　I

46、t is likely that the surfaces of the three spheres intersect, since the circle of intersection of the first two spheres is normally quite large, and thus the third sphere surface is likely to intersect this large circle.

47、 It is very unlikely that the surface of the sphere corresponding to the fourth satellite will intersect either of the two points of intersection of the first three, since any clock error could cause it to miss intersect

48、ing a point. However, the distance from the valid estimate </p><p>　　(correct time) - (time indicated by the receiver's on-board clock), and the GPS receiver clock can be advanced if is positive or delay

49、ed if is negative. </p><p>　　System detail</p><p>　　Unlaunched GPS satellite on display at the San Diego Aerospace museum</p><p>　　System segmentation</p><p>　　The curr

50、ent GPS consists of three major segments. These are the space segment (SS), a control segment (CS), and a user segment (US).[21]</p><p>　　Space segment</p><p>　　See also: GPS satellite and

51、List of GPS satellite launches</p><p>　　A visual example of the GPS constellation in motion with the Earth rotating. Notice how the number of satellites in view from a given point on the Earth's surface,

52、 in this example at 45°N, changes with time.</p><p>　　The space segment (SS) comprises the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance. The GPS design originally called for 24 SVs, e

53、ight each in three circular orbital planes,[22] but this was modified to six planes with four satellites each.[23] The orbital planes are centered on the Earth, not rotating with respect to the distant stars.[24] The six

54、 planes have approximately 55° inclination (tilt relative to Earth's equator) and are separated by 60° right ascension of the ascend</p><p>　　Orbiting at an altitude of approximately 20,200 kil

55、ometers about 10 satellites are visible within line of sight (12,900 miles or 10,900 nautical miles; orbital radius of 26,600 km (16,500 mi or 14,400 NM)), each SV makes two complete orbits each sidereal day.[27] Th

56、e ground track of each satellite therefore repeats each (sidereal) day. This was very helpful during development, since even with just four satellites, correct alignment means all four are visible from one spot for a few

57、 hours each da</p><p>　　As of March 2008[update],[28] there are 31 actively broadcasting satellites in the GPS constellation, and two older, retired from active service satellites kept in the constellation a

58、s orbital spares. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. With the increased number of satellites, the constellation was changed to a nonuniform a

59、rrangement. Such an arrangement was shown to improve reliability and availability of the system, </p><p>　　Control segment </p><p>　　The flight paths of the satellites are

60、 tracked by US Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs, Colorado, along with monitor stations operated by the National Geospatial-Intelligence Agency (NGA)

61、.[30] The tracking information is sent to the Air Force Space Command's master control station at Schriever Air Force Base in Colorado Springs, which is operated by the 2nd Space Operations Squadron (2 SOPS) of the U

62、nited States Air Force (US</p><p>　　Satellite maneuvers are not precise by GPS standards. So to change the orbit of a satellite, the satellite must be marked 'unhealthy', so receivers will not use it

63、 in their calculation. Then the maneuver can be carried out, and the resulting orbit tracked from the ground. Then the new ephemeris is uploaded and the satellite marked healthy again.</p><p>　　User segment&

64、lt;/p><p>　　GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown here from manufacturers Trimble, Garmin and Leica (left t

65、o right).</p><p>　　The user's GPS receiver is the user segment (US) of the GPS. In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-proc

66、essors, and a highly-stable clock (often a crystal oscillator). They may also include a display for providing location and speed information to the user. A receiver is often described by its number of channels: this sign

67、ifies how many satellites it can monitor simultaneously. Originally limited to four or five, thi</p><p>　　A typical OEM GPS receiver module measuring 15×17 mm.</p><p>　　GPS receivers may in

68、clude an input for differential corrections, using the RTCM SC-104 format. This is typically in the form of a RS-232 port at 4,800 bit/s speed. Data is actually sent at a much lower rate, which limits the accuracy of the

69、 signal sent using RTCM. Receivers with internal DGPS receivers can outperform those using external RTCM data. As of 2006, even low-cost units commonly include Wide Area Augmentation System (WAAS) receivers.</p>&

70、lt;p>　　A typical GPS receiver with integrated antenna.</p><p>　　Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol, or the newer and less widely used NMEA 2000

71、.[33] Although these protocols are officially defined by the NMEA,[34] references to these protocols have been compiled from public records, allowing open source tools like gpsd to read the protocol without violating int

72、ellectual property laws. Other proprietary protocols exist as well, such as the SiRF and MTK protocols. Receivers can interface with other d</p><p>　　Navigation signals</p><p>　　GPS broadcast si

73、gnal</p><p>　　Each GPS satellite continuously broadcasts a Navigation Message at 50 bit/s giving the time-of-week, GPS week number and satellite health information (all transmitted in the first part of the m

74、essage), an ephemeris (transmitted in the second part of the message) and an almanac (later part of the message). The messages are sent in frames, each taking 30 seconds to transmit 1500 bits.</p><p>　　Trans

75、mission of each 30 second frame begins precisely on the minute and half minute as indicated by the satellite's atomic clock according to Satellite message format. Each frame contains 5 subframes of length 6 seconds a

76、nd with 300 bits. Each subframe contains 10 words of 30 bits with length 0.6 seconds each.</p><p>　　Words 1 and 2 of every subframe have the same type of data. The first word is the telemetry word which indi

77、cates the beginning of a subframe and is used by the receiver to synch with the navigation message. The second word is the HOW or handover word and it contains timing information which enables the receiver to identify th

78、e subframe and provides the time the next subframe was sent.</p><p>　　Words 3 through 10 of subframe 1 contain data describing the satellite clock and its relationship to GPS time. Words 3 through 10 of subf

79、rames 2 and 3, contain the ephemeris data, giving the satellite's own precise orbit. The ephemeris is updated every 2 hours and is generally valid for 4 hours, with provisions for updates every 6 hours or longer in n

80、on-nominal conditions. The time needed to acquire the ephemeris is becoming a significant element of the delay to first position fix, because, as t</p><p>　　Advances in hardware have made the acquisition pro

81、cess much faster, so not having an almanac is no longer an issue. The second purpose is for relating time derived from the GPS (called GPS time) to the international time standard of UTC. Finally, the almanac allows a si

82、ngle-frequency receiver to correct for ionospheric error by using a global ionospheric model. The corrections are not as accurate as augmentation systems like WAAS or dual-frequency receivers. However, it is often better

83、 than no c</p><p>　　Satellite frequencies</p><p>　　L1 (1575.42 MHz): Mix of Navigation Message, coarse-acquisition (C/A) code and encrypted precision P(Y) code, plus the new L1C on future satell

84、ites. </p><p>　　L2 (1227.60 MHz): P(Y) code, plus the new L2C code on the Block IIR-M and newer satellites.</p><p>　　L3 (1381.05 MHz): Used by the Nuclear Detonation (NUDET) Detection System Pay

85、load (NDS) to signal detection of nuclear detonations and other high-energy infrared events. Used to enforce nuclear test ban treaties. </p><p>　　L4 (1379.913 MHz): Being studied for additional ionospheric c

86、orrection.</p><p>　　L5 (1176.45 MHz): Proposed for use as a civilian safety-of-life (SoL) signal (see GPS modernization). This frequency falls into an internationally protected range for aeronautical navigat

87、ion,</p><p>　　promising little or no interference under all circumstances. The first Block IIF satellite that would provide this signal is set to be launched in 2009.[37] </p><p>　　Demodulating

88、and Decoding GPS Satellite Signals using the Coarse/Acquisition Gold code.</p><p>　　Since all of the satellite signals are modulated onto the same L1 carrier frequency, there is a need to separate the signal

89、s after demodulation. This is done by assigning each satellite a unique pseudorandom sequence known as a Gold code, and the signals are decoded, after demodulation, using modulo 2 addition of the Gold codes corresponding

90、 to satellites n1 through nk, where k is the number of channels in the GPS receiver and n1 through nk are the pseudorandom numbers associated with the satell</p><p>　　If the almanac information has previousl

91、y been acquired, the receiver picks which satellites to listen for by their PRNs. If the almanac information is not in memory, the receiver enters a search mode and cycles through the PRN numbers until a lock is obtained

92、 on one of the satellites. To obtain a lock, it is necessary that there be an unobstructed line of sight from the receiver to the satellite. The receiver can then acquire the almanac and determine the satellites it shoul

93、d listen for. As it </p><p><b>　　P(Y) code</b></p><p><b>　　P(Y)碼</b></p><p>　　Calculating a position with the P(Y) signal is generally similar in concept, as

94、suming one can decrypt it. The encryption is essentially a safety mechanism: if a signal can be successfully decrypted, it is reasonable to assume it is a real signal being sent by a GPS satellite.[citation needed] In co

95、mparison, civil receivers are highly vulnerable to spoofing since correctly formatted C/A signals can be generated using readily available signal generators. RAIM features do not protect against spoofi</p><p&g

96、t;　　Error sources and analysis</p><p>　　Sources of User Equivalent Range Errors (UERE)</p><p>　　User equivalent range errors (UERE) are shown in the table. There is also a numerical error with a

97、n estimated value, , of about 1 meter. The standard deviations, , for the coarse/acquisition and precise codes are also shown in the table. These standard deviations are computed by taking the square root of the sum of t

98、he squares of the individual components (i.e. RSS for root sum squares). To get the standard deviation of receiver position estimate, these range errors must be multiplied by the app</p><p>　　Error Diagram S

99、howing Relation of Indicated Receiver Position, Intersection of Sphere Surfaces, and True Receiver Position in Terms of Pseudorange Errors, PDOP, and Numerical Errors</p><p>　　The term user equivalent range

100、error (UERE) refers to the standard deviation of a component of the error in the distance from receiver to a satellite. The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Positio