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Northeast Today

IRNSS vs GPS: Battle of Accuracy

IRNSS vs GPS: Battle of Accuracy
June 15
15:51 2017

As India gets closer to the mission of creating its own version of the American GPS, there is an on-going debate whether ‘Desi GPS’ will be as accurate as American GPS. Many believe that it will be much more accurate than the GPS. We tried to dig deeper and found out more about the Indian Regional Navigation Satellite System (IRNSS).

Need for indigenous positioning system?

During the Kargil war in 1999, when Pakistani troops took the position in high mountains, one of the first things Indian military was trying to get their hands on was GPS data of the region. GPS could’ve provided vital information, but the United States denied access to India. The experience at Kargil made the nation realize the importance of indigenous navigation system and hence the idea of IRNSS began to take shape. With the help of Indian Regional Navigation Satellite System (IRNSS), India will become self-reliant to keep a close watch on its boundaries and much more.

What is Desi GPS

IRNSS (NavIC, named so by Indian Prime Minister Narendra Modi) is an independent regional navigation satellite system developed in the country. It is designed to provide accurate positioning information service to users in India as well as the region extending up to 1500 km from its boundary. It will give India its very own indigenous navigation system, which would provide information on location and time in all weather conditions.

IRNSS will provide two types of services:

Standard Positioning Service (SPS), which is provided to all the users.
Restricted Service (RS), which is an encrypted service provided only to the authorized users.

Some applications of IRNSS are:

Terrestrial, Aerial and Marine Navigation
Disaster Management
Vehicle tracking and fleet management
Integration with mobile phones
Precise Timing
Mapping and Geodetic data capture
Terrestrial navigation aid for hikers and travelers
Visual and voice navigation for drivers

What is GPS?

The Global Positioning System, commonly known as GPS, is a network of about 31 satellites orbiting the Earth at an altitude of 20,000 km. The system was originally developed by the US government for military navigation but now anyone with a GPS device can receive the signals and use it. Each satellite of the GPS constellation circles the Earth twice a day. It depends on only 24 satellites to provide the accurate location, rest of the satellites are spare ones.

How does the GPS work?

Wherever you are on the planet, at least four GPS satellites are ‘visible’ at any time. It requires only three satellites to provide the location. The other satellites add to the accuracy. The more satellites there are in the sky, the more accurately GPS can tell you about your location. Each one transmits information about its position and the current time at regular intervals. These signals, traveling at the speed of light, are intercepted by your GPS receiver. GPS receivers then calculate the distance of each satellite based on how long it took for the messages to arrive.

If you are positioned somewhere on Earth with three satellites in the sky and if you know how far away you are from satellite A, then you know you must be located somewhere on the red circle. If you do the same for satellites B and C, you can work out your location by seeing where the three circles intersect.

GPS or IRNSS- Which will be accurate?

GPS has 31 satellites, while IRNSS has only 7 satellites. So, how will we get an accurate location from IRNSS? I had the opportunity to ask this question to ISRO Chairman A.S Kiran Kumar and he said, “24 functional satellites of GPS is for the entire globe, while 7 satellites of IRNSS is covering only India and its neighboring countries. All these 7 satellites will be visible to the ground receiver all the time.”

Though GPS has 24 satellites, the number of satellites visible to the ground receiver is limited. The 24 satellites are in Medium Earth Orbit. At any time, at any given location at least four satellites must be within the view of the receiver. In the case of IRNSS, the seven satellites are in geosynchronous orbits hence always visible to a receiver in a region 1500Km around India. Another point is that the satellites are nearly vertical over India and therefore visibility in ‘urban canyons’ is much better than in the case of the GPS.

When we speak of accuracy today, we have GAGAN, which uses GPS signals and with additional information provided about the position of the satellites, it tells you which GPS satellites are giving you a more accurate position. It corrects the errors in GPS signals with the help of 28 receiving stations spread across the country. With all the ionospheric corrections that are required for instant computation, the information is provided in GAGAN. That’s how GAGAN enables you to get better accuracy than GPS. It is certified by the Civil Aviation Ministry for ‘safety of life and integrity is guaranteed’. It means that if you get a position in the GAGAN enabled receiver then you can depend on it for the safety of any life activity. Let me remind you again that GAGAN is using GPS signals. Imagine a situation when 7 dedicated satellites, which are visible to the ground receiving station 24/7, will provide you signals.

Tapan Misra, Director of Satellite Application Center [SAC], believes that NavIC is going to be better than GPS. Speaking to Geospatial Media’s Editor Arup Dasgupta, comments, “While GPS is using only L-Band signals, NavIC is using both L AND S Band. Since our signals are coming vertically from stationary reference, our NavIC is going to work better than GPS in crowded places. If you use both L and S bands, our accuracy is more than 5 meters. This has a better potential than a 20-meter accuracy GPS, which is actually supplemented by the GPRS information. But our NavIC can give you the accuracy that GPRS and GPS give combined and that accuracy is not only for cities but every rural part of the country.”

Game Changer

Navigation system is mainly used by security personnel, Air travel, important installations, and Navigation by common citizens. Paid L and S band signals of NavIC receivers are available to cater the Security and Air Travel industries. According to SAC Director, by the end of this year we will see NavIC enabled chips in the market, which can be used in handheld devices such as smart phones. In fact, SAC is developing its own chip and have already built a chip with 32 channel IRNSS receiver. This chip is now being tested, and by the end of this year a blueprint of the chip will be ready. Market penetration will start slowly and once people start seeing benefits, it will explode.

Source: geospatialworld.net


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