Atul Singh
Jul 5, 2018 · 3 min read

Few days back, while working on my project my sister asked me “What exactly is GPS and GNSS , how do they work and whats the difference between them ..?”

Well these questions are quiet common and anyone with a bit of technical knowledge will say that “Yeah !! GPS I know about it .. Its GLOBAL POSITIONING SYSTEM which helps us to know the position of anything in global coordinate system..” . I too could have said the same to my sister but the question is “Is this the answer expected from a person from a technical background ..? ”

“No.. ” Exactly.. In this blog I will tell you how i made her understand about it by answering three questions

What is GPS/GNSS ..??

How does GPS work ..?

What is the difference between GPS and GNSS ..?

What is GPS/GNSS .. ??

GNSS(Global Navigational Satellite System ) it is a generic term for satellite navigation system. Its a platform which provides the pin point location of a user on the earth . Like your cell phones position .

And within this platform we have four operational satellite system :

  1. GPS

These operational satellite system are run by different countries of the world .

So GPS(Global Positioning System) is an operational satelite system which work within the GNSS platform . which means GPS is not only meant to know about the global positioning of the object but It also helps in performing navigation. Each GPS satellite cover the orbit of earth twice a day and a minimum of 24 GPS satellite are required for its proper functioning but Hail to NASA currently we have 31 GPS satellites in earth orbit where the extra satellite act as a backup . So possibility of GPS signals going down is too low..

How does GPS work ?

Suppose i want to know my location in global coordinate system. For that Its important that i should have direct line of sight with at least four satellites to have my pinpoint location.

Each satellite sends signal to my phone receiver as phone contains GPS unit which act as a receiver . Each satellite broadcast its timestamps and position to the receiver. A satellite calculates its timestamps by a atomic clock that is boarded on to it.

Timestamps helps in determining the distance between the phone and the satellite . As the GPS receiver calculates the time difference between the signal send and received. Since the speed of the signal is equivalent to the speed of the light . Now with the help of speed and time receiver calculates the distance from the satellites. One the distance is calculated receiver estimates the hemisphere of each satellite .

Hemisphere of each satellite

By knowing the hemisphere of each satellites the receiver keeps on estimating the position and gets an accuracy by 5–10 meter. This method of estimating the position using hemispheres is known as Trilateration.

What is the difference between GPS and GNSS ..?

As said earlier GNSS is a platform that have global coverage and have access to all the operational satellites which mean it will have access to 89 different satellite while the GPS is one of the operational satellite system controlled by US and currently using 31 satellites.

Atul Singh

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