IRNSS - Indian Regional Navigation Satellite System

IRNSS Overview, Credit: The Hindu

Very soon India will join the list of very few countries which have developed their own navigational satellite system, thanks to ISRO's prestigious Indian Regional Navigational Satellite System (IRNSS) project. This will be India's answer to USA's GPS (Global Positioning System) and Russia's GLONASS.
The salient feature of the IRNSS is to provide position accuracy less than 20 meters (possibly at 15m accuracy matching that of the GPS) covering a distance of 1500km 24*7 during all weather conditions. Touted to be useful for navigation and for military purposes.

IRNSS will have 3 segments:
1) Space Segment
2) Ground Segment
3) User Segment

Space Segment:

Courtesy:WikiPedia

As shown in the above illustrative picture, IRNSS will have a constellation of 7 satellites. 3 out of which will be fixed over the equator in a Geostationary orbit (GEO) over the equator. They seem to remain at fixed position when they are seen from the ground since their revolution period will match that of the Earth (24 hours).
The remaining 4 satellites are placed in inclined Geosynchronous orbits (GSO) in pairs, they appear to travel in figures of '8' when seen from the ground.

How Do They Work?
The satellites broadcast the navigation signals. These signals travel at the speed of the light and reach the receiving device.  The time delay between the transmission and the reception at the receiving device allows the device to compute its distance from the satellite involved.The signals from the satellites are usually sent in 2 different frequencies:
                                                                                    i) L5 (1176.45 MHz)
                                                                                   ii) S-band (2492.08 MHz)
Since the position is calculated using time delays, it is important to have clocks with maximum accuracy. Hence the navigational satellites are equipped with 3 Rubidium Atomic Frequency Standard (RAFS) which will have 3 Rubidium atomic clocks.

Ground Segment:
The ground segment will have 2 basic function to provide:
1) Health monitoring and maintenance of IRNSS constellation
2) Facilitating computing and generating position, navigation and timing data by the satellite.

IRNSS Ground Segment Architecture

these functions are performed by the recently opened ISRO Navigation Centre at Byalalu, Bangalore and MCF, Hassan.

User Segment:
The user segment may have 2 frequency receivers: Single frequency and Dual frequency. Dual frequency mode will be more accurate and the receivers will receive information with position, velocity and time information.

Applications:
IRNSS will find its applications in:

• Tranportation through air, water and land
• Geographic data collection for mapping, surveying and scientific atmospheric studies
• Assessing Tectonic plate movements
• Deformations
• Precision agriculture
• Town planning
• Search and rescue operations
• Fleet movements
• And in business through offering of location based services by banking, tourism etc.,

This is going to be launched along with PSLV-C22 on July 1, 2013.

Sources: 
WikiPedia
The Hindu Science & Tech