Introduction to GAGAN
&
GAGAN Enabled Receiver
By
Vineet Gera
Airports Authority of India
GAGAN
1
GNSS
• A worldwide position and time determination system that includes one or more
satellite constellations, aircraft receivers and system integrity monitoring,
augmented as necessary to support the required navigation performance for the
intended operation.
Core Satellite Constellations
GNSS Elements
Global Positioning System (GPS)
Global Navigation Satellite System (GLONASS)
Future Galileo & COMPASS Navigation Satellite System
GNSS Receiver
Augmentation Systems
2
GNSS Signal-in-Space Requirements
1. Accuracy – The difference between the estimated and actual aircraft
position
2. Integrity – A measure of the trust which can be placed in the correctness
of the information supplied by the total system. Integrity includes the
ability of a system to provide timely and valid warnings to the user
(alerts).
3. Continuity – The capability of the system to perform its function without
unscheduled interruptions during the intended operation.
4. Availability – The portion of time during which the system is
simultaneously delivering the required accuracy, integrity and continuity
GAGAN
3
Augmentation ? and Why Needed
• Augmentation of a Global Navigation Satellite System (GNSS) is a method of
improving the navigation system's attributes, such as accuracy, reliability, and
availability, through the integration of external information into the calculation
process.
• Standalone GPS can not meet requirements of all phases of flight
• Integrity is not guaranteed
• All satellites are not monitored all the time
• Time to alert could be minutes to hours
• No indication of quality of service to the User.
• Accuracy is not sufficient even with SA off, the vertical accuracy for 95% of the
time is >10m.
• Continuity and availability requirement shall be met.
GAGAN
4
Augmentation Options
• Space Based Augmentations (SBAS)
– WAAS, EGNOS, MSAS, GAGAN
• Ground Based Augmentations(GBAS)
– LAAS, GRAS
• Aircraft Based Augmentations (ABAS)
Error
Component
GBAS
Satellite
Clock
Estimation
and Removal
Ephemeris
Ionosphere
Troposphere
SBAS
Common Mode
Differencing
Estimation
and Removal
Fixed Model
– RAIM, Inertials, Baro Altimeter
Multipath
and Receiver
Noise
GAGAN
Carrier Smoothing by User
5
Augmentation
• Fundamental concept behind AUGMENTATION is Differential GPS.
• A technique for reducing the error in GPS-derived positions by using
additional data from a reference GPS receiver at a known position.
• Two Forms
• Local Area Differential GPS
• User’s GPS Receiver receives Pseudorange corrections from a Reference receiver,
generally located within line of sight.
• Corrections are lumped. Assumption is that the errors are common to User and
Reference Receiver.
• Wide Area Differential GPS
• Corrections are determined based upon measurements from a network of Reference
stations, distributed over a large geographical area.
• Separate corrections for specific error sources.
GAGAN
6
Space Based Augmentation System
• SBAS is an overlay System, requires establishing of
• Ground Monitoring Stations
• Monitors all GPS/GEO satellites in view and collects measurement data.
• Master control station
• Processes data, received from monitoring stations
• Computes corrections & determines integrity.
• Controls and Monitors SBAS system
• Uplink station
• Uplinks corrections and integrity information to the geostationary satellite.
• Space segment
• Broadcasts correction and integrity information to user community.
• Additional ranging source.
• Robust Communication Network
• Stringent data transportation requirement with 99.999% availability.
GAGAN
7
GPS
Const.
PRN 128
GEO In-orbit Spare
PRN 127
Backup to
INLUS 1/2
Bangalore
INLUS-1
1SG
1RF
Delhi
INLUS-2
1SG
INLUS-3
1RF
1SG
1RF
DATA Communication Network - 1
Data Communication Network - 2
INMCC - 1
Bangalore
INRES # 1 - 15
GAGAN Configuration
INMCC - 2
Bangalore
8
How GAGAN Works
•
Ground
– 15 Indian Reference Stations (INRES)
– Two Indian Master Control Centre (INMCC)
– Three Indian Land Uplink Stations (INLUS)
•
Space
– Two operational GEOs
– One In-orbit-spare
•
User
– Civil Aviation Community
– Non-Civil Aviation Users
o Widely spread network of INRES
track all the GPS satellites and SBAS
GEO in view and forward all
measurement data to Master control
centre for further processing.
o Master control centre uses the
measurement data from the reference
stations
to
generate
differential
corrections and integrity messages for
the designated service volume.
o These messages are transmitted
through Indian Land Uplink stations to
GAGAN GEO satellites.
o GEOs have common coverage
o GSAT-8/ 550 E, assigned PRN 127,
Operational for Non-Safety-of-Life
applications since Dec. 2011.
o GSAT-10/ 830 E, assigned PRN
128, currently undergoing integration
with ground segment
o GSAT 15/93.5, Launch planned in
2015, will work as in-orbit-spare.
o User gets benefitted with improved
positional accuracy and Integrity
information
Interoperability
GAGAN has been designed to meet ICAO defined standards on
SBAS. GAGAN is compatible to other SBASs in the world and
promises to provide seamless navigation.
GAGAN
GAGAN Performance
Horizontal Accuracy (95%)
Vertical Accuracy (95%)
Integrity
Time to Alert
Continuity (over 15 seconds)
Availability
Horizontal Alert Limit
Vertical Alert Limit
Coverage
GAGAN
APV
(Approach
with Vertical
Guidance)
7.6 m
7.6 m
1 x 10-7 /150 sec.
6.2 sec.
1-8 x 10-6
99%
40 m
50 m
76% of Indian
Landmass
RNP 0.1
(Required Navigation
Performance)
72 m
NA
1 x 10-7 /hr
10 sec.
1 x 10-4
99%
0.1 NM
(185.2 m)
NA
Indian FIR
GAGAN GEO Footprint
GSAT-8
GSAT-10
GAGAN
12
GAGAN Performance : Ahmedabad (accuracy)
13
GAGAN Performance : Bangalore
14
GAGAN Services
Certified RNP 0.1 Service over
Indian FIR
APV 1 Service over Indian
Landmass, service expected to
be certified by end of 2014
 At Present GAGAN is certified for RNP 0.1
Operations over Indian FIR.
Real-time GAGAN Performance can be seen at
http://172.27.168.11/gagan
GAGAN Enabled Receiver
By
Vineet Gera
Airports Authority of India
GAGAN
Terminology in Vogue
• WAAS Capable
• Receiver can use SBAS services but the user must activate this function once
only, or each time it starts up.
• WAAS Enabled
• Receiver activates SBAS reception by default.
• Some manufactures clearly specify WAAS / EGNOS / MSAS / GAGAN
enabled, others just say WAAS Capable / WAAS Enabled.
• In general WAAS includes other SBAS systems too, but CAUTION
“Clarify” from the supplier.
GAGAN
Conformance to ….
• RTCA/DO-229D (Radio Technical Commission for Aeronautics)
• Minimum Operational Performance Standards for GPS/WAAS Airborne
Equipment
• RTCA/DO-160E
• Environmental Conditions and test Procedures for Airborne Equipment
• RTCA/DO-310
• Minimum Operational Performance Standards for GNSS Airborne Active
Antenna Equipment for the L1 Frequency Band.
• RTCA/DO-254
• Design Assurance Guidance for Airborne Electronic Hardware
GAGAN
Conformance to …
• RTCA/DO-178B
• Software Considerations in Airborne Systems and Equipment Certification
• RTCA Document DO-160 versions D, E, and F
• Environmental Conditions and Test Procedures for Airborne Equipment
• TSO-C145-b/c
• Minimum Performance standards for Airborne Navigation Sensors, using the
Global Positioning System (GPS) Augmented by the Wide Area Augmentation
System (WAAS)
• TSO-C146c
• Minimum performance standards for Class Gamma or Class Delta equipment,
using GPS augmented by WAAS.
GAGAN
SBAS Receiver : Functional Classes
• Beta
• Sensor Only. Does Not Have Navigation Function
• Generates Position, Velocity, Time, with Integrity
• Typically Provides PVT To An FMS Which Provides Navigation Function
• Gamma
• Typical Panel Mount Receiver
• Beta Sensor Plus Navigation Function With Procedure Database And User
Controls
• Delta
• Beta Sensor With Navigation Function That Provides Deviations to A Final
Approach Segment Only
• Functions Like ILS (e.g. Does Not Support En Route Navigation)
GAGAN
Class Beta Configuration ( Position Sensor)
Position
Antenna
WAAS
Class
Beta
(Sensor)
Integrity
(HPL, VPL)
Navigation
Computer
Deviations from
desired path,
Alerts
Pilot
Displays
Database
Controls
Deviations,
Steering
Autopilot
Reference :
FAA TSO C-145
Class Gama Configuration ( Navigator )
WAAS Class Gamma
Deviations from
desired path,
Alerts
Navigation
Computer
Antenna
Position
Sensor
Pilot
Displays
Database
Deviations,
Steering
Controls
Autopilot
Reference :
FAA TSO C-146
Class Delta Configuration
WAAS Class Delta
Antenna
Position
Sensor
Navigation
Computer
Deviations from
desired path,
Alerts
Pilot
Displays
Database
Autopilot
Controls
AAI Flight Calibration Aircraft
GAGAN In Operation
• What is available from GAGAN ?
• GAGAN Message, comprising of
• Correction for each GPS satellite (in view)
• Confidence Bounds (Integrity information),
• What SBAS receiver does with GAGAN Messages ?
• Corrects the computed position, using corrections
• Computes protection levels, using confidence bounds
• Protection level says that by how much the position in worst case could be Off ,
vertically and horizontally.
• XPE < XPL < XAL, safe navigation is assured with high level of confidence.
GAGAN
SBAS Receiver Familiarization
GAGAN
Typical Airborne SBAS Receiver
GAGAN
Typical SBAS Receiver Performance
Characteristics
Characteristics
Specification
Conformity
DO-229D / 301 / 228 / 178 B / 254
/ 160
TSO – C145-b/c Beta, C146 – c
Gama / Delta
General
1575.42 MHz, L1 C/A code
Receiver with SBAS Capability
Channels
10+ GPS, 2+ SBAS
Hor. Position Accuracy
3 m RMS
Diff. Position Accuracy
1 m RMS
Vertical Position Accuracy 5 m RMS
Velocity Accuracy
Sensitivity
GPS Acquisition / tracking
0.1 m/s
- 136 / -140 dBm
Characteristics
Specification
Approach Capability
LNAV, LNAV/VNAV, LPV
Altitude Aiding
Pressure, Baro-Aiding
TTFF (Cold / Warm Start ) 90 / 66 seconds
Integrity
RAIM, FD/FDE, ALERT, BIT
Interface
RS-232, RS -422
Input Power
10 – 32 V DC
Power Consumption
5W
Weight
Approx. 500 gms.
Real Time Position
Display with 5Mtrs
Grid
Speed
Direction
GAGAN HPL
GAGAN VPL
GAGAN GEOs
PRN 127 &128
Thank You
GAGAN
Backup Slides
GAGAN
SBAS Integrity Requirement
1/5
• SBAS integrity is defined as the ability of the system to provide a
timely warning to users when an individual correction or satellite
should not be used for navigation.
• Components of Integrity
• Alarm condition
• Time-To-Alert (TTA)
• Hazardously Misleading Information (HMI)
GAGAN
39
SBAS Integrity Requirement
2/5
• Alarm Condition exists when any of the following occur:
• An active UDRE becomes invalid
• The user-calculated protection level using active data does not bound the
actual position error from positions created from any set of satellites
• Data received from the satellite is insufficient to calculate corrections or
integrity and to ensure that active data bounds the position error.
GAGAN
40
SBAS Integrity Requirement
3/5
• Alarm is Used to Alert User that:
• Corrections for a particular Satellite Have Changed; or
• Corrections Can Not Be Used
• Time to Alarm: Defined as the time period starting when an alarm
condition occurs until the time the last bit of the first message in the
alarm sequence arrives at the user’s antenna
• 10 seconds for ER/NPA
• 6.2 seconds for LNAV/VNAV
GAGAN
41
SBAS Integrity Requirement
4/5
• Probability of HMI
• For PA 10-7 / Approach (if Either or Both Occurs):
• Computed VPL* < Actual Vertical Navigation System Error for Period of Time  Time To
Alarm
• Computed HPL* < Actual Radial Horizontal Navigation System Error for Period of Time 
Time To Alarm
• For ER/NPA: Computed HPL < Actual Radial Horizontal Navigation System
Error for Period of Time  Time To Alarm;
10-7/hour
GAGAN
42
SBAS Integrity Requirement
5/5
• SBAS User:
• Applies Fast Corrections, Long Term Corrections, and Ionospheric Corrections
• Calculates a Position Using GPS Range and Ephemeris Signals
• Uses UDRE and GIVE to Calculate a VPL and HPL, which define a “Protection Cylinder”
• Protection Cylinder Represents Uncertainty in the Calculated Position
Vertical and Horizontal Alert Limit cylinder are defined by the phase of flight
The aircraft’s calculated
position based on the
WAAS corrections is
the center of the
cylinder.
The aircraft’s
true position
VAL
VPL
HPL
HAL
Protection level cylinder:
VPL and HPL are
computed by the user’s
receiver from error
bounds calculated by
WAAS (UDRE and
GIVE).
43