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What is GPS (Global Positioning System)?

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GPS stands for Global Positioning System.

It is the satellite-based radio navigation system owned by the US government and operated by the US Department of Defense.

On September 1, 1983, a Korean Airlines flight 007, carrying 269 passengers, was heading from New York City to Seoul via Anchorage.

During its journey, because of the lack of GPS inside it,  it deviated from its original planned route and flew through Soviet prohibited airspace, it was shot down by a Soviet Union Su-15 interceptor.

After this incident, Ronald Reagan, the president of the US decided to make the GPS open for public use.

Therefore, worldwide coverage, 24 satellites were required.

The first satellite was launched on 14 February 1989, and the 24th in 1994.

In 1995, it was opened for civilian use; however, with less quality and accuracy.

In 2000, after a lot of modifications by the US government, the GPS coverage with accuracy was available worldwide.

From 1978 till present, the US launched better satellites for the GPS; however, the launching of two among these was unsuccessful.

At present, out of 70 satellites, 33 satellites are 20,180 km above the earth’s surface out of which 31 satellites are fully activated.

At 2000 km above the earth’s surface, 24 satellites are enough to cover the earth, and the rest of these fills the gap between these 24 satellites. 


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What Does Gps Stand For?

GPS stands for Global Positioning System, originally NAVSTAR GPS (Navigation Satellite Timing and Ranging System GPS).


Component of GPS

The GPS is formed from a constellation of earth-orbiting satellites and their ground stations.

It uses reference points to calculate positions with accuracy up to centimeters.

So finding the exact position of an object, here are three segments, those are


  1. Space Segment

A segment that contains all the constellations of the satellite.

This segment is known as satellite or the space vehicle which is also called beep.

24 to 31 satellites that orbit the earth in a specific order and this is called a constellation.


  1. Control Segment

There are three different types of control segments, these are:

  1. Master Control

It can control all the satellites; they schedule and steer the satellites that are up in space.

  1. Monitoring Station

This is the place where all signal tracking and atmospheric data are collected.


  1. Ground Antenna

This is where all the directed related information of the space vehicles that they send to command the transmission and navigate messages are uploaded.


What is the Use of GPS?

It can be used by anyone to locate the position information anywhere in the world free of cost.

It provides geographic and the time information to a GPS receiver anywhere on or near the Earth where there is a clear line of sight to four or more GPS satellites.

It continuously sends data down to us on earth, which in turn is received by devices like our phones or navigational units in our cars, allowing us to see where we are on this planet.


Working of GPS

In our systems, there is a GPS receiver that receives the signals sent by the satellites in a fixed period. In that signal, the location and time of the satellite are always fixed.

For this purpose, the satellites have a synchronized atomic clock with high accuracy.

The GPS receiver reads the signals it receives. So it subtracts the time at which the signals were sent from the time it received to determine the distance and location of the satellite from which it received those signals.

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Suppose you are standing somewhere with your mobile phone, and its GPS receiver is receiving a signal from one satellite.

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Through one satellite, it becomes confusing to determine your exact location as you might be at any place in the coverage of this satellite.

Now, in place of one, your phone receives signals from three satellites, just like this:

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In Figure, the red part is you carrying your mobile phone.

According to satellite A, you’re in its coverage, similarly, for B and C, you’re in their coverage, respectively.

At the red mark, the coverage of satellites A, B, and C coincide. This is your exact location. 

Through three satellites, the GPS uses three parameters, East, North, and altitude, to determine your location, which is not enough, so there is a fourth parameter named time.

According to Einstein's general theory of relativity, time grows faster for an object that keeps on going away from gravity.

Similarly, the satellite is 2000 km away from the Earth; the atomic clock inside it is 38 microseconds faster than the Earth’s clock every day.

So, the fourth satellite is used to determine the exact time.

The orbit of the GPS satellite is made in a way that almost all the places on the Earth must be under the coverage of four or more satellites.

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FAQ (Frequently Asked Questions)

1. What is the Use of GPS on Mobile?

The smartphone takes a few seconds to track a location because mobile phones have an embedded Assisted GPS. When it requests for a location, the GPS receiver of our phone contacts the assistant server.

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This server has already stored information of its area. It transmits the signals to the receiver of our phone; this receiver reads the signals and determines the location.

2. What is Trilateration?

The process of determining your absolute or relative locations of points by measuring distances from satellites, using the geometry of circles, spheres of triangles is called trilateration.

3. Does GPS Work without the Internet?

Yes. It is possible to use the GPS on both iOS and Android phones in which mapping apps can track your location without requiring any data services. 

While smartphones have an A-GPS or Assistant-GPS embedded in it. So, they require connectivity to track your location, while the GPS radio can track the location of anything directly from the satellites if it needs to.

4. What are the Advantages of GPS?

There are some advantages of GPS, that are: 

  1. One of the benefits offered by the US government is providing GPS services on our smartphones for free. 

  2. It works as our guide while traveling to unknown places.