Definition
Of Gps
GPS Is A Satellite Navigation System
The GPS is a worldwide radio
navigation system formed from a constellation of 24 satellites and their ground
stations. GPS uses these “manmade stars” as reference points to calculate the
positions accurate to a matter of meters. In fact, with advanced forms of GPS
you can make measurements to better than a centimeter! In a sense it is like
giving every square meter on the planet a unique address, the system was
designed for and is operated by the U. S. military. GPS is funded by and
controlled by the U. S. Department of Defense (DOD). While there are many
thousands of civil users of GPS world wide. GPS has mainly 3 parts the space
segment, the user segment and the control segment. They are collectively called
as GPS Elements.
GPS
Elements
GPS has mainly three elements they are
the space segment the user segment and
the control segment .The space segment consists of the nominal GPS satellite
network that consists of a constellation of 24 satellites that orbit the earth
in 12 hrs. These space vehicles (SVs) send radio signals from space. The
Control Segment consists of a system of tracking stations located around the
world that make sure the satellites are working properly. The GPS User Segment
consists of the GPS receivers and the user community. GPS receivers convert SV
signals into position, velocity, and time estimates. Four satellites are
required to compute the four dimensions of X, Y, Z (position) and Time. GPS
receivers are used for navigation, positioning, time dissemination, and other
research. Now we can discuss about these GPS elements in detail.
Measuring
Distance
Here we can discuss how the receiver
and satellite work together to make this measurement .GPS receiver calculates
the distance to GPS satellites by timing a signal’s journey from satellite to
receiver, as it turns this is a fairly elaborate process.
At a particular time, the satellite
begins transmitting a long, digital pattern called a pseudo-random code. The
receiver begins running the same digital pattern also exactly at that time.
When the satellite’s signal reaches the receiver, its transmission lag a bit
behind the receiver’s playing of the pattern. The length of the delay is the
signal’s travel time. The receiver multiplies this time with the speed of the
signal to determine how far the signal traveled.
In order to make this measurement the
receiver and satellite both need clocks that can be synchronized down to the
nanoseconds. Thus every satellite is equipped with an expensive atomic clocks
and the receiver itself uses an ordinary quartz clock, which it constantly
resets.
In order for the distance information
to be of any use, the receiver also has to know where the satellites actually
are. The GPS receiver simply stores an almanac data that tells it where every
satellite should be at any given time. Things like pull of the moon and the sun
do change their orbits very slightly the
Department Of Defense constantly monitors their positions exactly and transmits
any adjustments to all GPS receivers as part of the satellite’s signals.
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