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“The complete constellation of 7 satellites of IRNSS will be deployed by 2016”

Jul 2015 | No Comment

A S Ganeshan

Program Director, Satellite Navigation Program, ISRO Satellite Center, India

Congratulations for successful launch of 4th IRNSS satellite. What is timeline for the complete installation?

The successful launch of 4th IRNSS satellite is a proud moment for all of us. With IRNSS-1D on orbit, we have 4 operational IRNSS satellites meeting the minimum satellite requirement and Independent position solution using an Indian satellite-based navigation system is now a reality. The complete constellation of 7 satellites will be deployed by 2016.

What are ground stations preparations for the utilisation of IRNSS signals?

Ground Segment is responsible for the maintenance and operation of the IRNSS constellation. The IRNSS ground segment comprises spacecraft control facility, navigation centre, network timing centre, reference stations, two-way ranging stations, laser ranging stations and data communication network. Most of the ground stations are operational to support the satellites operations and navigation parameter generation required by the user for position estimation. The complete ground systems including the redundant systems will be functional by 2016.

Is it possible to achieve the positioning relying only on IRNSS signals?

Definitely Yes. With the 4th satellite broadcasting navigation signals, independent position determination with IRNSS is now possible. The receivers at ISRO and various academic institutes (like IIST, IIT Kanpur, IIT Gandhinagar, Jain University Bengaluru etc) are already receiving the signals and providing position solutions.

The analysis of results has shown accuracy better than 15 metres for 20 hrs in a day over India. It is to be noted that the position fix for duration of 20 hours in a day is possible because of uniqueness of the constellation design with the satellites located in the Geostationary Earth Orbit (GEO) and Geo Synchronous Orbit (GSO). This duration will improve as more satellites fill up the constellation.

Will using IRNSS signals have an edge vis-a-vis other contemporary systems especially over Indian subcontinent region?

For users in the Indian sub-continent IRNSS services shall be competitive with the performance of civilian services provided by other contemporary systems. The major advantage being the constellation designed for a regional system ensures 24 x 7 visibilities of all the spacecrafts over Indian subcontinent. The IRNSS signal and data structure has been uniquely designed to provide optimal performance to its users. IRNSS transmits unique Gridbased ionospheric parameters as part of its navigation message. The parameters provide a single frequency (L5) user with position accuracies comparable to that of a dual frequency user. The IRNSS signals are also transmitted in S-band which experience minimal ionospheric errors. IRNSS is designed to be interoperable with other GNSS services and thereby providing the users with improved accuracy for multi-GNSS receivers.

Are the existing receivers able to receive the IRNSS signals properly or will they need any technological modifi cation?

Conventional GNSS receivers operate in L1, L2 and L5 bands. The IRNSS signals for civilian users are available in L5 and S bands. For a single frequency user in L5, a firmware update may be required to the existing GNSS receivers to receive IRNSS signals. For a dual frequency or an S-band receiver RF frontend of the receiver needs to be suitably modified along with the firmware to utilize the IRNSS services in S-band.

What are your parameters to measure the success of IRNSS?

From the technological perspective, the independent positioning using IRNSS, after the launch of 4th satellite, demonstrated the proof of concept. This can be seen as a first step of success towards realizing an independent satellitebased navigation system in India. The next step is to achieve the primary objective of IRNSS, i.e providing an alltime, all-weather service to users over the primary service area (covering the Indian landmass and 1500km beyond its geo-political boundary), with a position accuracy better than 20m.

Also, various agencies within India (like National Atmospheric Research Laboratory (NARL) Gadanki, Trimble at Chennai etc) and outside the country (like Finnish Geodetic Institute at Finland, Javad at Moscow etc) have reported successful reception of IRNSS signals and have validated its performance.

At ISRO we consider IRNSS a success when the benefits of its positioning, navigation and timing services reach the common man of this country.

How are the industry and academia involved to assess the performance of IRNSS and encourage its uses?

The industry and academia have gone hand-in-hand with ISRO in most of its projects and IRNSS is no different. Few industries have partnered with ISRO for the production of the initial set of IRNSS receivers. The receivers have been distributed among various ISRO centres and academic institutes to assess the initial performance of IRNSS. Also, ISRO is in touch with various receiver manufacturers to promote bulk production, miniaturization of IRNSS receivers, and development of various application softwares. The major challenge is the development and bulk production of ASIC based receivers by the time IRNSS becomes fully operational. Also, integrating IRNSS into today’s highly popular smartphone platform shall encourage maximum utilization of its services.

Is there any plan to engage the neighbouring countries to share the benefits of IRNSS?

The IRNSS civilian services are available free-to-air in the primary and secondary service areas which cover our neighbouring countries. Satellite Navigation has been one of the areas identified for mutual cooperation with some of our neighbouring countries, including all the SAARC nations. Bilateral discussions with various countries were held this year and areas of cooperation in satellite-based navigation have been identified.

What are the plans to encourage the uses of IRNSS and GAGAN?

ISRO has conducted a GNSS User Meet in 2013 and a conference on Space Based Navigation in 2014 at ISAC, to spread the awareness about IRNSS & GAGAN among the user community. A second GNSS User Meet with the theme “Towards self reliance in Satellite Navigation” is planned this year with expected participation from the GNSS community within and outside India. The meet shall mainly focus on applications using IRNSS and GAGAN.

Are users in India ready for IRNSS?

ISRO has released the ‘IRNSS Signalin- Space interface control document for Standard Positioning Service ver 1.0’, the document that comprehensively provides all the information required by a user to utilize service of IRNSS. The document is available at http://irnss.isro. gov.in. The ICD has been downloaded by leading GNSS receiver and chipset manufacturers, service providers and academia. Quite a few industries have expressed keen interest in developing IRNSS receivers and IRNSS-based applications. We are confident that once the IRNSS constellation is fully deployed the Indian user community will be ready for receiving IRNSS.

What are the plans to widen the usage of ISRO’s satellite navigation services on a bigger scale?

The utilization of Indian satellite navigation services can be maximized over the Indian region by integrating the mapping services of Bhuvan, and navigation services of IRNSS & GAGAN to provide location based services to users in the Indian subcontinent. BIG (Bhuvan-IRNSSGAGAN) is definitely good for various other applications too. It is essential to mandate usage of GAGAN and IRNSS for all applications including the emergency services by the Government and this certainly widen the usage of ISRO’s satellite based navigation services over India.

What is the current status of GAGAN?

Subsequent to the certification of GAGAN system by DGCA for Safety of Life APV1.0 level of service on 21st April 2015, the GAGAN system was commissioned for APV1.0 Precision Approach services over Indian landmass on 19th May 2015. GSAT-8 and GSAT-10 broadcast GAGAN signal with PRN 127 and 128 respectively for use by aviation and non-aviation users in Indian region.

How GAGAN is being used in India?

GAGAN being a high integrity system is primarily meant for Safety of Life (SoL) services in Civil Aviation Applications for En-route and Precision Approach operations. Airports Authority of India is in the process of developing GAGAN approach procedures and conducting flight test at various airports to use GAGAN signal within Indian airspace. Apart from Civil Aviation, GAGAN is being is used in surveying, road transportation, Railways, Urban development, forestry, timing applications etc.

Is there any effort to popularize GAGAN among GNSS users in India?

GAGAN is free to air service and most of the existing SBAS receivers available in the market are capable of receiving GAGAN signals. Efforts are underway to create awareness among the GPS user community about the benefits of GAGAN and its usage across India. ISRO and AAI conducted several user meets to highlight benefits of GAGAN and the Ministry of Civil Aviation had formed an Inter Ministerial Group(IMG) to explore the potential usage of GAGAN across various ministries and mandating them to use GAGAN services wherever possible. Also, the upcoming second Usermeet will give yet another opportunity to familiarise the benefits of GAGAN for position and timing applications.

How future development/ expansion of GAGAN is envisaged?

In the near future, another GEO Satellite, GSAT-15 with PRN139 will be added to existing space segment. Addition of more ground elements such as data communication network, up-link station, reference station etc., are planned to enhance/expand GAGAN services in the neighbouring regions. Expansions of GAGAN to the neighbouring countries have been taken up by AAI.

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