A Complete GPS Global Positioning System
GPS system features:
1, world clock:
To provide users with continuous, real-time three dimensional position, velocity and precise time. Not affected by the weather.
2, high positioning accuracy:
Stand-alone position accuracies of better than 10 meters, differential positioning accuracy up to centimeters and millimeters.
3, many functions and application range:
The deepening along with the awareness of the GPS, GPS, not only in measurement, navigation, speed, time has been more widely used, and its areas of application have been extended.
The development of GPS:
Before the advent of satellite positioning systems, long-range radio navigation systems for navigation and location.
1, radio navigation system
Roland--C: at 100KHZ, made up of three ground navigation, navigating the work area 2000KM, 200-300M General accuracy.
Omega (Omega): work on shijiqian kHz. Made up of eight ground navigation, global coverage. Accuracy for several miles.
Doppler systems: using the Doppler shift principle and movement parameters are obtained by measuring the frequency shift (ground speed and drift angle), the calculated vehicle position, be owned dead reckoning system. Error with the range increases add up.
Cons: cover area small; radio wave propagation affected by atmospheric effects; high positioning precision
2, satellite positioning system
First satellite positioning system is the United States the meridian system (Transit), 1958-64 was officially put into use. Due to the number of satellites are smaller (5-6), running low (average 1000KM), observations from the ground station to the satellite for longer intervals (average 1.5h), thus it does not provide continuous real-time navigation and precision is low. To meet military and civilian sector urged in real-time and continuous navigation. 1973 United States Department of Defense develop GPS program.
3, GPS development
GPS implementation plan is divided into three phases:
First phase of the project and the preliminary design phase. From 1973 to 1979, a total of 4 satellite to be launched. Terrestrial receiver is developed and established ground tracking network. www.3s8.cn
Second stage is the stage of comprehensive development and testing. From 1979 to 1984, have been fired 7 test satellite, developed a variety of receivers. Experiments show that the design of GPS positioning accuracy far exceeds standards.
Third for utility network phase. February 4, 1989 the first GPS satellite was successfully launched shows that GPS system enter the construction phase of the project. End of 1993 practical GPS network (21+3) GPS constellation have been built, according to plans to replace a failed satellite in the future.
1, the composition of the GPS system
GPS consists of three independent parts:
The space segment: 21 operating satellites, 3 spare satellites.
Ground support system: 1 master control station, 3 injection, and 5 stations.
User equipment part: receive GPS satellite signals in order to obtain the necessary navigation and positioning information, data processing, navigation and positioning work done. GPS receiver hardware, antenna and power by the host.
2, GPS positioning
GPS positioning is based on the basic principle of high speed satellite moments as a known initial data, use of space distance intersection method, determine the location of the point to be tested. As shown in the figure, assuming that t are placing GPS receivers on the ground test point and determination of GPS signals can reach the receiver of the time t, plus the receiver receives and other satellite ephemeris data can identify the following four equations:
The four equations to be determined in the coordinates x, y, z and Vto for unknown parameters, di=c ti (i=1, 2, 3, 4).
Di (i=1, 2, 3, 4) respectively for satellite satellite 1, 2, 3, 4 to the distance between the receiver of satellite.
TI (i=1, 2, 3, 4) respectively for satellite satellite 1, 2, 3, 4 satellite signal reaches the receiver through time.
C for the GPS signal propagation speed (the speed of light).