There are many
people who use GPS, on phones and in cars, to find their way around a path, or
possible paths to take, but what they may not have known is that the Global Positioning System ,
known as GPS, works thanks to to 24 satellites , which are in orbit at a
height of 20,200 kilometers, in order to cover the entire surface of the
planet.
Allows the system to
determine the position of an object, telephone, PCs and automobiles throughout
the planet, it was developed, used and installed by the United States
specifically by the State
Department . It is also applied for topography,
geodesy, sports navigation, especially in aerial sports, location of minors and
sick people, agricultural location, as a fleet management and security system.
How Does the
Global Positioning System Determine Position?
In telephones or
automobiles, for example, it is located automatically, since they contain
a signal receiver ,
at the moment that it is required to know the position, for that to happen at
least three satellites of the network work together, the implanted receiver
receives the signals where it indicates the time of the clock and the
identification of each of them.
Well, then based
on these signals, the receiver synchronizes the GPS clock to then calculate the
time it takes for the signals to reach the electronic device, using the inverse trilateration method
. This is a method of determining relative positions, by means of
the geometry of triangles ,
similar to triangulation . This
technique is based on calculating the distance of each of the satellites to the
measurement point.
Once the distances
of the satellites are known, the true relative position with respect to them
can be easily determined. The position and coordinates of each one of them
are also known, by the emission of their signals and finally it is possible to
obtain the real coordinates of the measured point or the absolute
position. Extreme
accuracy is also tended to be achieved on the Global Positioning System clock .
The former Soviet Union built a
similar system which was called GLONASS, today
it is managed by the Russian
Federation . Also the People's Republic of China is
establishing its own navigation system which they call Beidou , it is planned to
have 12 and 14 satellites between 2011 and 2015, it is suspected that by 2020
it should have a total of 30
satellites . , in fact by April 2011 they only had 8 in
orbit.
System History.
The TRANSIT system
is a navigation technology that used satellites of the US Navy. Such a
navigation system provided its fleets with accurate and up-to-date position
displays. It was operational from 1964 and until 1967, it was not only
used for military use but
also commercial .
At that time, the
position updates were free every 40 minutes while the observing personnel had
to remain almost static, all this in order to obtain the appropriate information . Later,
for the same time and with the help of atomic clocks , a constellation of
satellites was prepared, each of them carrying these clocks. Based on a
given time reference, all the satellite clocks were synchronized.
The program of the
United States Air Force, which consists of encrypted transmission techniques
that imparted exact data using a PRN
modulated signal , was combined, which became known
as the Navigation
Technology Program , later renamed NAVSTRA GPS, with the
Navy program.
11 experimental
NAVSTRA prototype satellites were developed and launched into orbit between
1978 and 1985, finally sending a new
generation of satellites , until completing those
currently in operation. The United States government in 2009 offered a
standardized service of the position to collaborate with the needs of the OASI , and of course it
accepted such an offer.
Positioning System
Emission Signal.
Each of the Global Positioning System Satellites
emit a navigation message at 50 bits per second, with a microwave frequency of approximately
1600 MHz. To make an assumption of this frequency, let's look at the radio,
which emits between 87.5 to 108 .0 MHz while Wi-Fi networks run roughly between
5000 MHz and 2400 MHZ. Exactly all satellites emit frequency at 1575.42
MHz, known as signal L1, and at 1227.6 called signal L2.
The signal also
provides the exact time of the week, according to the atomic clock on the
satellite, the week number, and a status report to the satellite, so that it
can be deduced if it is faulty or not. Each and every transmission lasts
30 seconds and carries 1500 bits of encrypted data. This small amount of
data is encoded with a PRN sequence, pseudo random , the sequence is high speed
and different for each satellite. The GPS receivers know the PRN codes of
each satellite, so they can decode
the signal and distinguish
between the different satellites .
The transmitters
are timed to start exactly on the minute and second, as commanded by the satellites' atomic clock . A
first phase of the GPS signal shows the receiver the similarity between the
satellite clock and the GPS time. The second phase of data supplies the
receiver with information on the exact orbit of the satellite.
GPS Integrated to
the Mobile Phone.
In the mobile phone market today,
the trend is for manufacturers to integrate GPS technology ,
inserted into the devices. The use and widespread use of GPS is popularly
extended in Smartphone mobile phones, giving rise to a large software ecosystem for
a device like this.
Also new business
models in which the mobile terminal that provides traditional navigation is
used, such as Location Based Services or LBS. Among the uses of GPS within
mobile telephony are applications where it is possible to know the position
of close friends on a map .
Receiver
Operation.
The name of ephemeris is the
information that is useful to the receiver, to provide its position. In
such a way, each satellite emits its own ephemeris, which includes the position
in space, the health of the satellite, the dopper information, the atomic hour,
among others.
By means of trilateration the
position of the receiver is specified. Each of the satellites indicates
that the receiver is located at a certain point on the earth's surface , with radius
the total distance to the receiver and center on the satellite.
With the
information obtained from two satellites, a circumference is denoted, which
results when the two spheres intersect at some point where the receiver is located. The
additional information from a third satellite eliminates the inconvenience of
the lack of
synchronization between the satellite clocks and the clock
of the GPS receivers. Thus, the moment is reached when the receiver of the
global positioning system manages
to determine the exact position.
