GPS is short for Global Positioning System. Basically is a radio navigation system based on satellites developed and controlled by the US Department of Defense that allows any user to know their location, speed and altitude, 24 hours a day, in any weather conditions and at any point on the globe.
After the Second World War, the US Department of Defense was determined to find a solution to the problem of accurate, absolute positioning. It was several projects and experiences over the next 25 years, including Loran, Transit and many other research. All possible to determine the position but were limited in accuracy or functionality. In the beginning of the 70s, a new project was proposed, called GPS.
The GPS has three components: space components, control and user.
The space component consists of a constellation of 24 satellites orbiting the Earth at an altitude of approximately 12000 milles, distributed in 6 orbital planes. These planes are spaced apart by about 60° in length and have inclinations close to 55° relative to the Earth’s equatorial plane. It was designed so that there are at least four satellites visible above the horizon at any point on the surface and at any height.
The control component consists of five tracking stations distributed throughout the globe and a master control station (MCS Master Control Station). This component tracks the satellites, updates their orbital positions and calibrates and sync up their watches. Another important function is to determine the orbits of each satellite and predict its path for the next 24 hours. This information is sent to each satellite and then is retransmitted, informing the local receiver where it is possible to find the satellite.
The user component includes all those who use a GPS receiver to receive GPS signal and convert the position, speed and time. It also includes all the necessary elements in this process, such as antennas and processing software
How GPS works?
The basics of GPS are based on determining the distance between a point, the receiver, to another reference points, in this case the satellites. Knowing the distance that separates us from 3 points is possible to determine our position on those same 3 points through the intersection of three circles whose radii are the distances measured between the receiver and satellites.
In reality, they needed at least 4 satellites to determine our position correctly, but let’s leave that for later.
Each satellite transmits a signal which is received by the receiver, this in turn measures the time it takes signals to reach it. Multiplying the measured time by the signal speed, we obtain the distance between receiver and satellite (Distance = Speed x Time).
However the satellite positioning is not that simple. Get precise measurement of the distance is not an easy task.
The distance can be determined through wave modulated codes sent by the satellite (C/A and P codes), or by analysis of the carrier wave. These codes are complicated.
The receptor was prepared so that only decodes this type of code, no other. By this way, the satellite is immune to interference from natural or intentional sources. This is one reason for the complexity of the code.
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