Satellite navigation system is an integrated electronic and technical system consisting of a combination of ground and space equipment designed to determine the location (geographic coordinates and altitude) and exact time, as well as movement parameters (speed and direction, etc.) for land, water and air objects.
The main elements of satellite navigation system:
- An orbital constellation consisting of several (from 2 to 30) satellites emitting special radio signals;
- Ground control and monitoring system (ground segment), which includes units for measuring the current positions of the satellites and transmitting the information received to them in order to correct orbital information;
- Satellite navigation systems consumer equipment (“satellite navigators”) used to determine coordinates;
- Optionally: ground-based radio beacon system, which allows to significantly increase the accuracy of determining the coordinates;
- Optional: a radio information system for transmitting corrections to users to significantly improve positioning accuracy.
The principle of satellite navigation systems is based on measuring the distance from the antenna on an object (the coordinates of which are to be obtained) to satellites whose positions are known with great accuracy. The table of positions of all satellites is called an almanac, which must be available to any satellite receiver before measurements can be taken. Normally, the receiver stores the almanac since it was last turned off, and if it is not out of date, uses it instantly. Each satellite transmits its entire almanac in its signal. Thus, knowing the distances to several satellites of the system, using the usual geometric constructions, based on the almanac, you can calculate the position of an object in space.
The method of measuring the distance from the satellite to the receiver’s antenna is based on the certainty of the speed of propagation of radio waves. In order to implement the possibility of measuring the time of the propagating radio signal, each satellite of the navigation system emits signals of exact time, using exactly synchronized with the system time atomic clocks. During the operation of the satellite receiver its clock is synchronized with the system time and during the further reception of signals the delay between the time of emission contained in the signal itself and the time of signal reception is calculated. Having this information, the navigation receiver calculates the coordinates of the antenna. All other movement parameters (speed, course, distance travelled) are calculated on the basis of the measurement of the time spent by the object in moving between two or more points with certain coordinates.
