GAGAN (GPS Aided Geo Augmented Navigation)

PRAKHAR ADITYAPCE/EC/11/001

Ms. Uma RajchandaniASST. PROF.DEPT. OF ECE

CONTENTS

OVERVIEW AND IMPLEMENTATION OF GAGANTECHNOLOGY DEMONSTRATION AND INTEGRATIONSBAS-SATELLITE BASED AUGMENTATION SYSTEMSBAS SEGMENTS AND OPERATIONSGAGAN TECHNOLOGY DEMONSTRATIONSYSTEM CONFIGURATION OF GAGANINRESINMCCINLUSPOSSIBLE RANGING ERRORSADVANTAGES OF THE TECHNOLOGYCONCLUSION

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OVERVIEW AND HISTORY

Navigation experts from all over the world have been discussing for many years about the

concept of one navigation system that is available everywhere in the globe with esteemed

accuracy.

Satellite Navigation and positioning system represent the most important technological

breakthrough in civil aviation navigation surveillance and air traffic management.

The GPS, developed by United States is currently approved for supplemental use in all

weather conditions but for the civil aviation community whose requirement is stringent,

failed to meet the requirements.

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TECHNOLOGY DEMONSTRATION & INTEGRATION

The GAGAN system consists of a network of 15 Indian Navigation Reference Earth Stations

(INRES) spread over the country that are precisely surveyed to compare the position determined from GPS

satellite signals against the location of the receiver.

The GAGAN signal is currently being broadcast through two Geostationary Earth Orbit (GEO) satellites -

GSAT8 and GSAT10 - covering whole Indian Flight Information Region (FIR) and beyond.

One essential component of the GAGAN project is the study of the ionospheric behavior over the Indian

region. This has been specially taken up in view of the rather uncertain nature of the behavior of the

ionosphere in the region. The study will lead to the optimization of the algorithms for the ionospheric

corrections in the region.

GAGAN after its final operational phase completion, will be compatible with other SBAS systems such as

the Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay

Service (EGNOS) and the Multi-functional Satellite Augmentation System (MSAS) and will provide

seamless air navigation service across regional boundaries.

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SATELLITE BASED AUGMENTATION SYSTEM (SBAS)

Satellite-based augmentation systems (SBAS), such as EGNOS, complement existing global navigation

satellite systems (GNSS). SBAS compensate for certain disadvantages of GNSS in terms of accuracy,

integrity, continuity and availability.

The SBAS concept is based on GNSS measurements by accurately-located reference stations deployed

across an entire continent.

The GNSS errors are then transferred to a computing center, which calculate differential corrections and

integrity messages which are then broadcasted over the continent using geostationary satellites as an

augmentation or overlay of the original GNSS message. SBAS messages are broadcast via geostationary

satellites able to cover vast areas.

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MAJOR SBAS SEGMENTS6

CURRENT SCENARIO ACROSS THE GLOBE7

HOW GAGAN WORKS

The GAGAN system consists of a network of 15 Indian Navigation Reference Earth Stations

(INRES) spread over the country that are precisely surveyed to compare the position determined from GPS

satellite signals against the location of the receiver.

The observed deltas are then be sent to 2 Indian Navigation Master Control Centers (INMCC) where

computer processing will extrapolate the data to generate correcting deltas for GPS signals anywhere

within the network.

These correcting deltas will be relayed via 3 Indian Navigation Land Uplink Stations (INLUS)

and geostationary satellites to civil aircraft so more precise fixes of their position can be derived from GPS

satellite signals.

INRES sites and INMCCs are connected using Optical Fiber Cable Data Communication Network as well

as VSAT link.

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SYSTEM CONFIGURATION 9

INRES-INDIAN REFERENCE STATION

The INRES collect measurement data and broadcast messages from all

GPS and GEO satellites in view and forward to Indian Mission Control

Centre (INMCC).

Altogether 8 INRES Stations are established in India.

INRES Station Bangalore

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INMCC-INDIAN MASTER CONTROL SYSTEM

An Indian Master Control Centre (INMCC) is established at Kundalahalli, Bangalore.

The measurement data collected every second from each of the INRES receiver chains are transmitted in

real time to the INMCC for correction and integrity processing and generation of SBAS messages with the

aid of the navigation software resident.

The INMCC comprises of various subsystems like Data Communication Subsystem (DCSS), Correction and

Verification Subsystem (C&VS), Operation and Maintenance Subsystem (OMSS) and Service Monitoring

Subsystem (SMS).

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INLUS-INDIAN NAVIGATION LAND EARTH UPLINK STATION

The INLUS receives correction messages from the INMCC, format those messages for GPS compatibility

and transmit them to the GEO satellites for broadcast to user platforms.

The INLUS is collocated with INMCC at Bangalore. The INLUS also provides GEO satellite ranging

information and corrections to the GEO satellite clocks.

Message formats and timing will be according to the functional and performance specifications, which are

derived from MOPS (Minimum Operation Performance Standard).

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Bangalore INRES Facility

INMCC CTF Building

VSAT Antenna (6.3m Dia)

INLUS 11m Antenna

Ephemeris errors result when the GPS message does not transmit the correct satellite location.

Ionospheric Errors because of free electrons in the ionosphere, GPS signals do not travel at the vacuum

speed of light as they transit this region

Tropospheric Errors as variations in temperature, pressure, and humidity all contribute to variations in the

speed of light and radio waves.

Multipath is the error caused by reflected signals entering the front end of the receiver and masking the real

correlation peak.

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ADVANTAGES OF THE TECHNOLOGY

GAGAN enhances reliability and reduces delays to aircraft

GAGAN reduced workload of flight crew and Air Traffic Controllers.

It enhanced meteorological information

It also reduced congestion

It enhanced safety, reduced delays and increased airport & airspace capacity

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REFERENCES

1. ICAO International Standards and Recommended Practices, Annex 10 to the Convention pm

International Civil Aviation, Volume I Radio Navigation Aids, Section 3.7.1: Definitions

2. Mishra Pratap & Enge Per, Global Positioning System, Signals, Measurements and Performance (Ganga-

Jamuna Press, Lincoln, Mass, USA), 2001, pp.-123-173

3. Parkinson Bradford W & Spilker James J, Global Positioning System: Theory and Applications, Volume I, by

(Jr. American Institute of Aeronautics and Astronautics Inc, USA), 1996, pp. 10-17, 478-483, 485-513.

4. Klobuchar J A, P H Doherty, M B El-Arini, Lejeune R, Dehel T, de Paula E R & Rodrigues F S, Ionospheric

Issues for a SBAS in the Equatorial Region, Ionospheric Effects Symposium, Alexandria, Virginia, 7-9 May

2002.

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