Satellite/Terrestrial/monitor/receiver GPS Positioning
GPS system consists of three parts: the space segment-GPS satellite constellation;
Ground control-ground monitoring system;
User equipment part of-GPS signal receiving unit.
GPS satellite constellation
GPS satellites and constellations with 21 satellites and 3 in-orbit spare satellites GPS satellite constellation, denoted (21+3) GPS constellation. 24 satellites evenly distributed in 6 orbital plane, orbital inclination of 55 degrees, 60 degrees between the orbital plane and the 60 degrees right ascension of ascending node of the orbit. Of the satellites in each orbit plane rising angle from 90 degrees, a satellite in the orbit plane than the West side adjacent orbital planes, the corresponding satellite ahead of 30 degrees.
At a height of 20,000 km of GPS satellites, for stars, when the earth rotates once a week, they run around the Earth for two weeks, that is a week for the 12 stars around the Earth. Thus, for observers on the ground, 4 minutes earlier every day to see the same GPS satellite. Number of satellites located above the horizon as time and varies between locations, visible to at least 4 stars, can be seen up to 11. When using the GPS signal navigation, in order to settle a three-dimensional station coordinates, you must observe 4 GPS satellite, known as positioning constellation.
Ground monitoring system
For navigation, and GPS satellite is a dynamic known points. Star positions are based on satellite ephemeris-describe motion and orbit parameters calculated. Each GPS satellite broadcast ephemeris, is provided by the ground control system. On the satellite equipment is working properly, and whether the satellite has been running along the orbit, all performed by ground monitoring and control equipment. Ground monitoring and control system a critical role is to keep the standard-GPS-time system satellites at the same time. This requires ground stations to monitor the satellite time clock error is obtained. Then inject from the ground station to the satellite, the satellite navigation message is sent to a user's device. GPS satellite ground control system consists of a primary control station, injected three and five monitoring stations.