GAGAN

Other SBAS
Title	GAGAN
Author(s)	GMV
Level	Basic
Year of Publication	2011

The GPS Aided Geo Augmented Navigation or GPS and Geo Augmented Navigation system (GAGAN) is the SBAS implementation by the Indian government.

GAGAN Introduction

In August 2001 the Airports Authority of India and the Indian Space Research Organization (ISRO) signed a memorandum of understanding for jointly establishing the GAGAN system. It is being implemented in three phases:

1. Technology Demonstration System (TDS).
2. Initial Experimental Phase (IEP).
3. Final Operational phase (FOP).

The TDS phase was completed in August 2007 using the INMARSAT 4F1 Navigation payload. The Initial Experimental Phase (IEP), planned to be finished by 2009, is still under implementation due to a series of delays. The first GAGAN navigation payload was integrated into the GSAT-4 geostationary satellite. GSAT-4 was launched on 15 April 2010, however it failed to reach orbit.

GAGAN Architecture

• 

  GAGAN overview.

The main components of the GAGAN Architecture are:

• Space segment: two operational GEO satellites, GSAT-8 & GSAT-9 satellites

• Ground segment: On the ground, the GPS Data is received and processed in the 8 Indian Reference Stations (INRES), located at Delhi, Ahmedabad, Bangalore, Thiruvananthapuram, Kolkata, Guwahati, Port Blair and Jammu. The Indian Master Control Center (INMCC), located at Bangalore, processes the data from the multiple INRESs to determine the differential corrections. Information from the INMCC is sent to the Indian Land Uplink Station (INLUS) and uplinked along with the GEO navigation message to the GAGAN GEO satellite.

• User segment: GAGAN-enabled GPS Receivers, with the same technology as WAAS Receivers, capable to use the GAGAN Signal-in-Space (SIS). User equipment for civil aviation shall be certified against several standards (see article SBAS Standards).

Raytheon company was awarded in 2009 of the contract to build the complete GAGAN system.

GAGAN Signals and Performances

The GAGAN GEO satellite will downlink navigation data via L1 and L5 WAAS signals, with Global Positioning System (GPS) type modulation. L1 and L5 WAAS signals were obtained from the United States Air Force and U.S Department of Defense on November 2001 and March 2005.

GAGAN augments the GPS system with integrity and corrections to make the GPS system a trusted navigational aid. It will be built to support the integrity required for APV I phases of flight, and to meet the performance requirements of international civil aviation regulatory bodies.

Ionospheric issues

One of the main concerns about an SBAS implementation in India is the ionospheric behavior at these latitudes. The ionosphere near the geomagnetic equator has physical process and features that rarely, if ever, affect mid-latitudes. These include the Appleton geomagnetic anomaly, plasma bubbles, and scintillation. India is in fact iunder the geomagnetic equator.

Current SBAS in the mid magnetic latitudes provide a precision guidance for the single frequency users [11]. The ionospheric phenomena mentioned above and typically found at the equatorial latitudes would significantly challenge SBAS approaches currently used in these mid magnetic latitudes for precision guidance. The peak large scale features could cause positioning inaccuracies to standard SBAS that may exceed the precision approach alert limits. Even when such extreme features are not present, the possibility of unobserved small scale features makes it difficult for an SBAS system to ensure integrity compatible with the precision approach alert limits.

GAGAN Development

GAGAN is primarily meant for civil aviation. The goal is to provide navigation system to safety-to-life operations over the Indian airspace and in the adjoining area. Once GAGAN is operational, it should improve air safety over India and aircraft will be able to make precision approaches within the coverage area. There are 449 airports and airstrips in the country, but only 34 have instrument landing systems (ILSs) installed.

The Indian government states that it will use the experience of building the GAGAN system in the creation of an autonomous regional navigation system called the Indian Regional Navigational Satellite System (IRNSS).

For the FOC Phase, new INRESs in Indore, Bhuj, Amritsar, Chennai, Nagpur, Lucknow and Visakhapatnam will be built, also a redundant Indian Master Control Centre (INMCC), an additional Indian Navigation Land Uplink Station (INLUS) and additional Communication links will be available. GAGAN is planned to be certified for civil aviation by the year 2014, and it will be compatible and interoperable with other SBAS systems such as WAAS, MSAS and EGNOS.