India Encyclopedia: How NavIC works. (India GPS)

NavIC, or the Indian Regional Navigation Satellite System (IRNSS), will workthrough a constellation of seven satellites. NavIC ('Navigation with Indian Constellation' whose English meaning is 'sailor' or 'navigator'),

RNSS will be an independent and autonomous regional navigation system aiming a service area of about 1500 kilometers around India. The system will be under complete Indian control, with the space segment, ground segment and user receivers all being built in India. It will have a range of applications including personal navigation.

IRNSS Architecture

IRNSS will provide two types of services:

1. Standard Positioning Service (SPS), which is provided to all the users.

1. 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

How does the GPS work?
GPS or IRNSS- Which will be accurate?

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 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.”