System Composition of Global Navigation Satellite System
(1) U.S. GPS satellite navigation system
美国GPS
GPS global positioning system consists of three parts: the space part —— GPS constellation; ground control part —— ground monitoring system; user equipment part —— GPS signal receiver.
Space Part
The space part of GPS is composed of 24 working satellites, which are located 20 200km above the earth's surface, uniformly distributed on 6 orbital surfaces (4 per orbital surface), with an orbital inclination of 55°. In addition, there are 4 active backup satellites in orbit. The distribution of satellites makes it possible to observe more than 4 satellites anywhere on the globe, at any time, and to maintain geometric images with good positional resolution accuracy. This provides a continuous global navigation capability in time.GPS satellites produce two sets of codes, one set is called C/A code, one set is called P code (Procise Code 10123MHz), P code because of the higher frequency, not easy to be interfered with, high positioning accuracy, and therefore subject to the control of the U.S. military, and has a password, the general civilian population can not be interpreted, mainly for the U.S. military services.C/A code artificial C/A code is mainly open for civilian use after taking measures to deliberately reduce the accuracy.
Ground Section
The ground control section consists of a master control station, five global monitoring stations and three ground control stations. The stations are equipped with precision cesium clocks and receivers capable of continuously measuring all visible satellites. The stations transmit satellite observation data, including ionospheric and meteorological data, to the main control station after preliminary processing. The master control station collects tracking data from each monitoring station, calculates the satellite's orbit and clock parameters, and then sends the results to three ground control stations. The ground control stations inject this navigation data and the master station's commands into the satellites as each satellite orbits overhead. This injection occurs once a day for each GPS satellite and is finalized before the satellite leaves the injection station's range of action. If a ground station fails, the navigation information pre-stored in the satellite will be available for some time, but the navigation accuracy will gradually decrease.
Equipment component
European “Galileo” positioning system
User equipment part of the GPS signal receiver, its main function is to be able to capture a certain satellite cut-off angle selected by the satellite to be measured, and track the operation of these satellites. When the receiver captures the tracked satellite signal, it can measure the pseudo-distance from the receiving antenna to the satellite and the rate of change of the distance, and demodulate the satellite orbit parameters and other data. According to these data, the microprocessor computer in the receiver can carry out the positioning calculation according to the positioning solution method, and calculate the latitude, longitude, altitude, speed, time and other information of the user's geographic location. Receiver hardware and software and GPS data post-processing software package constitutes a complete GPS user equipment. the structure of the GPS receiver is divided into antenna unit and receiver unit two parts. Generally, the receiver adopts two kinds of DC power supply: internal and external. The purpose of setting the internal power supply is to replace the external power supply without interrupting the continuous observation. The internal battery is automatically charged when the external power supply is used. When the receiver is turned off, the internal battery supplies power to the RAM memory to prevent data loss. Various types of receivers are becoming smaller and lighter, making them easier to use for field observation.
GPS positioning technology has the advantages of high precision, high efficiency and low cost, so that it has been more widely used in various types of geodetic control network to strengthen the transformation and establishment, as well as in highway engineering measurement and deformation measurement of large structures.
(2) European “Galileo” satellite navigation system
Russian GLONASS satellite positioning system
The Russian GLONASS satellite positioning system consists of 30 medium-altitude circular orbit satellites, of which 27 are working satellites and 3 are alternates; the orbital altitude is 24,126 kilometers, and it is located in three orbital planes with an inclination angle of 56 degrees, with a maximum accuracy of less than 1 meter, and it is mainly used for civilian purposes. In December 28, 2005, the first experimental satellite was successfully launched in 2008 before the opening of positioning services.
(3) Russia's GLONASS satellite navigation system number: 24 satellites composed of; precision: about 10 meters; Use: dual-use military and civilian; Progress: 17 satellites have been in orbit in 2007, plans to deploy all in place in 2008.
(4) China & ldquo; Beidou & rdquo; satellite navigation system Quantity: 3 satellites, 2 for the work of the satellite, 1 for the backup satellite; use for dual-use. The first two satellites were successfully launched in 2000 and 2003 respectively. on December 27, 2012, the Beidou satellite navigation system officially operated.
China “s Beidou satellite navigation system
