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1、The Effectiveness of Global Positioning System Electronic Navigation Michael Wright, Dion Stallings and Dr. Derrek PU Electronics and Computer Technology North Carolina Agricultural and Technical State University 2 11 Price Hall Greensboro, N.C 2741 1 The United States of America dbdunnncat.edu Abst
2、ract: Global Positioning System (GPS) is a worldwide radio-navigation system that consists of a constellation of twenty-four satellites located in six orbits, and their ground control stations. A unique device called the GPS receiver is responsible for the actual interface between the civil user and
3、 the Global Positioning System Network. Global Position System provides specially coded satellite signals that can be processed using a GPS receiver, enabling the receiver to compute position, velocity and time. Four GPS satellite signals are used to compute position in three dimensions (X, Y, and Z
4、) and the time offset in the receiver clock. The position in the X, Y, and Z dimensions along with time are converted in the receiver to calculate geodetic latitude, longitude and height above the ellipsoid. Our research utilizes the Earthmate High-performance GPS Receiver, Ashtech G8 GPS Receiver a
5、nd a Sigtech Subaltto MC 500 GPS Receiver. Our purpose is to test and evaluate the performance of the receivers to determine which gives more accurate position. In addition to position, we will determine the accuracy of the measurements computed by the receiver in comparison to those of a local area
6、 road map. This research will focus toward implementing GPS into an indoor environment. With this research, we can determine which receiver(s) would ISBN 0-7803-7856-3/03/$17.00 0 2003 IEEE. i_ be more effective for positioning, tracking, and navigation in a closed structure. 1. Introduction system
7、that is design to show your exact position on the Earth at anytime, anywhere, and in any weather. GPS satellites. 24 in Global Positioning System (GPS) is a all, orbit above the Earth at 1 1,000 nautical miles from the surface. Ground stations located worldwide continuously monitor them. The satelli
8、tes transmit signals that can be detected by anyone with a GPS receiver. There are many applications for the unique navigational system. This system can be used for aircraft and automobile navigation, missile guidance, and geographical mapping. Our main focus is to implement the Global Positioning S
9、ystem Network in an effective way that allows navigating, positioning, and tracking in an indoor environment. 2. Basic Elements GPS has three basic elements: the space segment, the user segment, and the control segment. The space segment Proceedings IEEE Southeastcon 2003 62 consist of 24 satellites
10、, also known as space vehicle, each in it own orbit 1 1,000 nautical miles above the Earth. The user segment consists of receiver that you can hold in your hand or mount in your vehicle (car, boat, plane, etc). The control segment consists of ground stations (five of them located around the world) t
11、hat make sure the satellites are working properly. orbit the Earth. Each satellite is equipped with an accurate clock to let it transmit signals coupled with a precise time message. The ground unit receives the satellite signal, which travels at the speed of light (3.0*108). Even at the speed of lig
12、ht, the signal takes a considerable amount of time to reach the receiver. The difference between the time the signal leaves the satellite and the time it is received, multiplied by the speed of light, enables the receiver to calculate the distance to the satellite. To compute precise latitude, longi
13、tude, and altitude, the receiver measures the time it took for the signal from four separate satellites to get to the receiver. The GPS satellite each take 12 hours to 3 The Principles of GPS The main principle of the Global Positioning System Network deals with the measurement between the GPS recei
14、ver and the actual satellites. The principles behind the operation of Global Positioning Systems can be simply described in five steps. The first step deals with the concept of triangulation from the satellites 2. The second step pertains to the actual GPS receiver measuring distance using the trave
15、l time of the radio signals being transmitted to and from the satellites to the receiver. The third step deals with the GPS receiver measuring the travel time of the radio signals. In order to measure the travel time of the radio signals, GPS needs very accurate timing 2. The fourth step pertains to
16、 knowing exactly where the satellites are positioned in space. This is important for precise positioning location. The fifth and final step deals with correcting any delays that the signal experience as it travels through the atmosphere 2. These delays are picked up and corrected by the GPS tracking
17、 stations. 3.1 The Triangulation Concept The most important concept of the Global Positioning System Network is triangulation. This concept uses the satellites that are located in space as reference points of various locations on the earth. To triangulate means to calculate the position from the dis
18、tance measurement or range, between the GPS receiver and the actual satellite. Therefore, by very accurately measuring our distance from three satellites, our position can be triangulated from anywhere on the earth 2. The concept of triangulation can be explained and understood more in detail with t
19、he following example. are using has access to three satellites, satellites A, B, and C. Each satellite has an imaginary sphere around it with radius X, where X equals the distance between the GPS receiver and the actual satellite. Suppose we are able to measure the distance between the receiver and
20、the satellite. The measured distance between the GPS receiver and satellite A is 14,000 miles. By k n o w i n g this distance we can narrow down all of the possible locations that we could be in the entire universe, to a location on the surface of the imaginary sphere with a radius of 14,000 miles t
21、hat surrounds satellite A. Lets say that the measured distance between the GPS receiver and the second satellite, satellite B, is 15,000 miles. This tells us that we are not only located on the first imaginary sphere, but we are also located on the imaginary sphere produced by Satellite B that has a
22、 radius of 15,000 miles. These two imaginary spheres intersect and produce an imaginary circle. This has Lets say that the GPS receiver that we Proceedings IEEE Southeastcon 2003 63 now narrowed our position down to anywhere on the imaginary circle. The measured distance between the GPS receiver and
23、 the third satellite, satellite C is 16,000 miles. This 16,000-mile radius imaginary sphere intersects with the two imaginary spheres produced by satellite A and satellite B. There are two points where the three imaginary spheres intersect each other. These two points indicate the coordinates of our
24、 possible positions. One of these coordinates is our actual position while the other is a ridiculous coordinate that is too far f?om earth. The GPS receiver has the ability to differentiate between the actual, or reasonable coordinates and the ridiculous coordinates. The receiver then rejects the ri
25、diculous coordinates, leaving the user with the actual coordinates of his or her position. 4 GPS Experimentation , Recall that the purpose of this research is to test and evaluate the performance of the receivers to determine which gives more accurate position. In addition to position, we will deter
26、mine the accuracy of the measurements computed by the receiver in comparison to those of a local area road map. 4.1 Drive Test Procedures The procedures and methods used for conducting this experiment were the same for all three GPS receivers. The first step was to choose a route within the city of
27、Greensboro, N.C. that starts at one location and ends at that initial location. Next, the user segment of the Global Positioning System is setup inside the automobile. This segment consists of each individual GPS receiver and a laptop computer containing the GPS software. The next step consists of d
28、riving the selected route four to five times allowing the GPS receiver to collect data (i.e. latitude, longitude, altitude, etc.). As the route is being driven, the GPS receiver software maps out the route according to the data being used. After the appropriate data has been collected, use the data
29、collected by the GPS software to compare and contrast to the measurements of the local area road map. By using the scale and measurements of the local area road map, we can determine the accuracy of the GPS receiver in reference to the local area road map. Fig. I Driving route displayed on the local
30、 area roadmap. Distances (Based on the road map): Point A to B = approx. .97 mi. Point B to C = approx .SO mi. Point C to D = approx .93 mi. Point D to A = approx. .64 mi. Total Distance Traveled =approx. 3.34 mi. Proceedings IEEE Southeastcon 2003 64 Fig. 2 Driving route displayed by the GPS receiv
31、er. Distances (Based on the GPS receiver: Point A to B = approx. 1.01 mi. Point B to C = approx .70 mi. Point C to D = approx. 1.10 mi. Point D to A = approx. .53 mi. Total Distance Traveled =approx. 3.34 mi. Average Elevation = 887.1 ft above sea level. Difference between the measurements of the GP
32、S receiver map and those of the local area road map: Point A to B =approx. .04 mi. Point B to C =approx. .IO mi. Point C to D = approx. .I7 mi. Point D to A = approx. .11 mi. Total Differcnce or Error = approx. .42 mi. 4.3 Experiment Conclusion map to the local area road map there is a slight error
33、of .42 miles. When scaled to an equal size, it was verified that the map crcated by the GPS receiver was more accurate when dealing with determining the distance from one point to the other. Before this experiment was conducted, this was hypothesized because of the known precision of the GPS receive
34、r. The slightest change in driving the route, such When we compared the GPS designed as lane change or the sharpness of a tum, was displayed in the GPS designed map. Despite the different measurements of distances from one point to the other, the approximate total distance traveled was the same. Bas
35、ed on the results provided by the experiment, we can say that the Global Positioning System can be used as an effective means of electronic navigation. 4.4 Static Test Procedures The procedures and techniques are the same for all three receivers. The first step involved determining a location of whe
36、re you can collect data over an hours time period. Next, we set up the receiver and the computer (which collect the log positioning and satellite data) and ran the program for approximately one hour. After collecting the data, we sorted the data on a Microsoft Excel format for easy viewing. In sorti
37、ng the data, we extracted data that involved the latitude and longitude positions and the Geometric Dilution of Precision (GDOP) data. The next step involved plotting the receiver position using time in UTC versus latitude positioning in degrees and decimal minutes. We did the same procedure for plo
38、t the receiver position for longitude positioning. We made a scatter line graph for the latitude error and longitude errors. We determine the latitude and longitude errors by subtracting the highest values of the latitude and longitude from the lowest value. We also look at the GDOP data, which can
39、be, categorized as position DOP, vertical DOP, horizontal DOP, and time DOP to determine the relationships between the receiver position and the positions of the satellites the receiver is using for navigation. The last step involved comparing the data from all three receivers and determining each r
40、eceiver precision and errors. Proceedings IEEE Southeastcon 2003 65 4.5 Data/ Data Analysis T.atitiida Ponitinn Longitude Position Longitude Position Error 4.6 Experiment Conclusion the Ashtech G8 GPS Sensor and the Sigtech Subaltto Receiver. Our data showed that there was some difference as the sat
41、ellite transmitted signal to the receiver. The average latitude and longitude for the Ashtech receiver was 3604.39919 and 7950.143 10, respectfully, in degree and decimal minutes (ddmm.mmmmmm), while for the Sigtec Subaltto, the latitude and longitude was 3604.395479 and 7950.138887, respectfully, i
42、n degree and decimal minutes (ddmm.mmmm). The receiver gave exceptional Geometric Dilution of Precision (GDOP) data, which can be categorized as position DOP, horizontal DOP, vertical DOP, and time DOP. The average value received for the PDOP, HDOP, VDOP, and TDOP over the one- hour period for the A
43、shtech receiver were 1.59, 1.5, 0.5, and 0.8, respectfully. The Sigtec Subaltto receiver only displayed Horizontal DOP, which was 0.933. Both receivers produced excellent measurements, but we acquired some GPS errors while testing the receivers, which came from a combination of noise, bias, and huma
44、n error. Our research showed expected data for Average Latitude Position: 3604.39919 Longitude Position: 7950.143 10 Average GDOP: Positioning DOP: 1.59 Horizontal DOP: 1.5 Vertical DOP: 0.5 Time DOP: 0.8 5 Research Conclusion The Global Positioning System is a worldwide navigation system that can b
45、e utilized in any application that requires the use of tracking, location or positioning, and navigation. This unique system consists of three segments, which are the space segment, control segment, and user segment. Each individual segment has great contribution in the overall operation or function
46、 of the Global Positioning System. based on the Global Positioning Systems Network, an overview of how this navigational system operates can be obtained. Based on the results of each By conducting various experiments Proceedings IEEE SoutheastCon 2003 66 individual experiment, it can be derived that
47、 the Global Positioning System is a very important and useful tool that can be used as an effective means of electronic positioning, tracking, and navigation. References SJ Online Document Dana, Peter H. Global Positioninp Svstenz Overview. The Geographers CraJt Project, The University of Colorado a
48、t Boulder. Rev. 5/01/200 first published in Sept. 1994). http:/www. colorado. edu/Feograuhv/acraft /notes/ms/rrvs. html 2 Online Document The Global Positioning System html (3) Bao-Yen Tisu, James. Fundamentals of Global Positioninp System Receivers: A Software Approach. Wiley-Interscience. 1 Ed. May 9,2000. Proceedings IEEE Southeastcon 2003 67