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17 August 2019

How Does GPS Work?

We hear a lot about GPS. Phrases like GPS satellite, GPS tracker, etc. have integrated into our daily lives. The question here is, ‘what is GPS?’. The follow-up question is, ‘how does GPS work?’ There can be many other questions like these. In this write-up, we are going to answer such questions. Are you ready to learn? We know you are ready to learn because you are awesome! Let us begin!

What is GPS?

GPS is an abbreviation. It stands for Global Positioning System. It is one mouthful of a name, but it is quite simple in concept. Unfortunately, it is nearly rocket science when it comes to implementation. The good news here is that we do not have to worry about its implementation. We are the end users.

GPS is responsible for giving us a navigation system based on satellites. It gives information on time and provides a location. GPS works in all-weather conditions. Why? It is because the satellite is in space outside the atmosphere of our Earth.

GPS satellites can send location and time information anywhere near Earth or on Earth. There is a condition to fulfill for the information transaction to succeed.

“The location with which the information transaction will take places must be in direct line of sight of not one but at least four satellites.”

GPS is a critical tool for military, but it also finds some critical usage in both civilian and commercial fields.

How GPS Works?

Heads up! This segment that deals with the ‘how’ is going to be technical, but stay with us. We are going to make it as simple as possible.

Several steps need to work in tandem for the GPS to work correctly. Those steps are:

Number and position of satellites

24 satellites make up a Global Positioning System. Of these 24 satellites, 21 are known as GPS satellites while the remaining three are called spare satellites. These satellites are 2,000 kilometers above the surface of Earth. The satellites continuously orbit our planet.

The distance of the satellites

These 24 satellites maintain a certain distance from each other. The calculation of the distance between two satellites is such that from any point on our blue orb, four satellites will stay right above the horizon.

Instruments of the satellites

Each of the GPS satellites contains of the following instruments:

  • One radio
  • One atomic clock
  • One computer

Each satellite is intelligent enough to understand the atomic clock as well as its changing position.

Broadcasting and correction

In space, there is something called time dilation. What it means is that time runs slow in space compared to time on Earth. It is because of this time dilation that atomic clocks are present in satellites that give them the ability to calculate time precisely.

Each satellite is intelligent enough to understand its very own orbit as well as the time as per the atomic clock it holds. Based on this understanding, each satellite continuously broadcasts the change in its position and time.

Each satellite has special programming that allows it to perform a comparative check of its time as well as its position with the data from a station on the ground. The comparative check allows the satellite to make minor adjustments to its clock and position, if necessary.

Ground receiver and trilateration

Back on Earth, there is a GPS receiver. The receiver has a computer to carry out complex geometric calculations known as trilateration. Trilateration is a concept in Geometry in which we determine the relative or absolute position or location of a point (or multiple points) by measuring distances using triangles, spheres, and circles.

The computer of the GPS receiver on Earth is responsible for trilateration of its location by calculating its distance from three satellites out of four. The computer then shows the results to us in the form of a geographical location or position (that is, latitude and longitude).

The ground receiver can do two more things provided all necessary conditions are in place. Those two things are:

  • If the receiver receives the fourth satellite as well, it can also calculate the altitude along with the distance.
  • If the receiver has a display screen capable of displaying maps attached to it, it can show the exact location on the map.

In addition to these, the computer of the ground receiver can also calculate the direction in which you are traveling along with the speed at which you are traveling. With all these data in hand, the receiver can quickly give you an estimate of the time at which you will reach a defined destination.

GPS Errors

Global Positioning Systems are not free of errors. They are prone to numerous errors. For instance, when a GPS satellite transmits a signal, it travels at high speed through space but, the very moment it enters and passes through ionosphere and troposphere of Earth’s atmosphere, the signal speed takes hit because of refraction. This refraction-led speed distortion can often lead to inaccurate data.

On the other hand, the receiver on the ground is prone to errors arising out of the noise and electrical interference. Again, the satellites move at high speed. So, when the receiver receives the signals, the satellites already change position. Also, we cannot ignore the time variations. One nanosecond variation in the atomic clock on a satellite can lead to an error of 0.3 meters back on Earth.

GPS and Mobile Tracking

Today’s smartphones have built-in GPS receivers. These receivers work in the same way as described above. However, to get the exact data, the target phone needs to have some software that can provide the exact location. Google Map’s location service is one such app that uses GPS tracking.

However, for more accurate data, specialized GPS tracker software provide far more accurate data than Google Maps. Installing such applications on someone else’s phone can be against the law because it is a direct violation of a user’s privacy. The target phone user should give express written permission to install such apps on his/her phone.


Everything in this write-up is a mere summary of a very complex system. GPS tracking requires immense technical know-how. Luckily we have readymade devices and apps that allow us to use these services without any a headache.

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