how gps works

how gps works? GPS (Global positioning System; The Global Positioning System or Global locator system) is a satellite network that sends regular encoded information, and it makes it possible to determine the exact location on Earth by measuring the distance between satellites.


This system consists of 24 satellites that are continuously orbiting the U.S. Department of Defense. These satellites emit very low-power radio signals. The GPS receiver on the earth gets the signals. Thus it is possible to determine location.

The first company goal of this system was purely for military purposes. GPS receivers are designed for use in military stickers and rocket firing. However, in the 1980s, the GPS system was opened for civilian use.

how gps works

* 1 Application areas

* 2 GPS system

O 2.1 Space Division

O 2.2 Control Department

O 2.3 User Section

* 3 bibliography


Application areas

Military: Used in GPS cruise missiles (cross-continent missiles) and precision-guided missiles. Ballistic missiles are also used to accurately calculate the launch position. It also includes GPS satellites nuclear explosion detectors as a major part of the American nuclear explosion monitoring system.



In parallel with the defence policy followed by the Turkish armed forces, it uses GPS applications in many areas. As an example, commando troops are taking advantage of GPs in many areas, such as the transfer, traverse, and terrain direction.

For non-missile use of civilian GPS receivers, the limit of 18 km height and 450km/h speed has been introduced.


Research: The most expensive GPS receivers are used by the cartographers for the location detection of borders, structures, map markings and road construction work.


For visually impaired: The projects titled "Mobic, Drishti, Brunel Navigation System for the Blind, Noppa, Braillenote GPs and Trekker" were conducted with the GPS, which entered into the late 1980s.

how gps works

Aviation: GPS is also used in addition to other navigation devices in aircraft. Some companies do not allow passengers to use handheld GPS receivers.


Reference time: Many synchronisation system uses GPS as a reference time source. The GPS system uses atomic clocks on its satellites, unlike UTC and GMT. They were reset on June 6, 1980, and they are now 14 seconds from UTC because the seconds are not correct. Therefore, periodically, the UTC time information is sent to GPS receivers.

GPS system

Generating GPS signals

Generating GPS signals


The Navstar system consists of the Space Division (satellites), control section (ground stations) and User section (GPS Receiver).


Space Division


The space division consists of at least 24 satellites (21 active satellites and 3 spares) and is the center of the system. Satellites are found in orbit over 20,200 km of Earth's surface, called "high orbit". Satellites with so much altitude have a wide range of visibility and are positioned in a way that a GPS receiver on earth can always see at least 4 satellites.


Satellites move at 7,000 miles an hour, and in 12 hours, they take a tour around the world. They work with solar energy and are designed to be used for at least 10 years. There are also small booster rockets for solar power outages (solar eclipse etc.), as well as replacement batteries and orbital corrections.


The GPS project started when the first satellite was fired in 1978. The 24-satellite network was completed in 1994. The budget for the continuity and development of the project belongs to the US Department of Defense.


Each of the satellites publishes two different frequencies and low-power radio signals. (L1, L2) Civilian GPS receivers are listening to the frequency of L1 (1575.42 MHz in the UHF band), the U.S. Department of Defense recipients L2 (1227.60 MHz). This signal advances line of sight in the "visibility". So it can pass through clouds, glass and plastic, but not through solid objects like walls and mountains.


Because the GPS signals are reflected from the buildings, the sensitivity of the city is reduced compared to the terrain. In the tunnels dug underground, the signal cannot be obtained. By differential GPS developed to be used in regions where faulty signals can be obtained or no signal is obtained, a more precise measurement may be made by minimizing these errors.


For a more comfortable understanding, if we want to compare the frequency of the radio station signals to the L1; FM radio stations are broadcast between 88 and 108 MHz, and L1 uses 1575.42 MHz. And GPS's satellite signals are very low-power. When the FM radio signals are 100,000 watts, the L1 signal is between 20-50 watts. Therefore, a clear field of sight is required to receive a clean signal from the GPS satellites.


The electromagnetic waves sent by the GPS satellites are bending through the atmosphere. Since the L1 and L2 bands have different wavelengths, it can be calculated differently by calculating the difference between the differences of atmospheric distortion and a much more precise location. With only the L1 tape (even with differential GPS), 98 m. Sensitivity can be achieved, while the joint use of L1 and L2 bands is possible to achieve sensitivity below 1 m.


Each satellite broadcasts two special pseudo-random code (encrypted random code) that allows the receiver to identify the signals. These are protected (protected P Code) code and Coarse/acquisition (C/A Code) code. By mixing the code of the P is prevented from unauthorized use of civilian, this event is called Anti-spoofing. Another name given to the code P is "p (y)" or just "Y".


The main purpose of these signals is that the receiver on the ground is able to measure the length of the signal's arrival time and calculate the distance to the satellite. The distance to the satellite is equal to the signal's arrival time and speed. The speed at which signals are accepted is the speed of light. This signal includes the satellite's orbital information and time information, general system Status info, and ionospheric latency. Satellite signals are scheduled using very reliable atomic clocks.


Control Section


As the name suggests, the control section provides accurate trajectory and time information by continuously monitoring GPS satellites. There are 5 control stations in the world. (Hawaii, Kwajalein, Colorado Spring (main centre), Ascension Islands and Diego Garcia) Four of them are unmanned, one manned main control center. The unmanned control centers send the information they collect to the main headquarters. This information is evaluated in the main center and the necessary corrections are reported to satellites.


User section


The user section is the recipients in the location. Any person who wants to locate using GPS for various purposes is included in the user section of the system. It is usually used by the commando units that are engaged.

Note: This page has been translated. Could be a word error. Please consult your specialist

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