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Introduction to GAGAN &

GAGAN Enabled ReceiverBy

Vineet GeraAirports Authority of India

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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 ConstellationsGlobal Positioning System (GPS)Global Navigation Satellite System (GLONASS)Future Galileo & COMPASS Navigation Satellite System

GNSS ReceiverAugmentation Systems

GNSS Elements

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GNSS Signal-in-Space Requirements1. 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

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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.

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Augmentation Options

• Space Based Augmentations (SBAS)– WAAS, EGNOS, MSAS, GAGAN

• Ground Based Augmentations(GBAS)– LAAS, GRAS

• Aircraft Based Augmentations (ABAS)– RAIM, Inertials, Baro Altimeter

Error Component GBAS SBAS

Satellite Clock

Common Mode Differencing

Estimation and Removal

Ephemeris

Ionosphere Estimation and Removal

Troposphere Fixed Model

Multipath and Receiver

Noise Carrier Smoothing by User

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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.

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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.

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INRES # 1 - 15

DATA Communication Network - 1

Data Communication Network - 2

PRN 128 PRN 127

INLUS-1

1SG 1RF

INLUS-2

1SG 1RF

INLUS-3

1SG 1RF

INMCC - 1 INMCC - 2

Bangalore BangaloreGAGAN Configuration

GEO In-orbit SpareGPS Const.

Backup to INLUS 1/2

DelhiBangalore

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 coverageo 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 segmento 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

APV (Approach with Vertical Guidance)

RNP 0.1 (Required Navigation Performance)

Horizontal Accuracy (95%)

7.6 m 72 m

Vertical Accuracy (95%) 7.6 m NAIntegrity 1 x 10-7 /150 sec. 1 x 10-7 /hrTime to Alert 6.2 sec. 10 sec.Continuity (over 15 seconds)

1-8 x 10-6 1 x 10-4

Availability 99% 99%Horizontal Alert Limit 40 m 0.1 NM

(185.2 m)Vertical Alert Limit 50 m NACoverage 76% of Indian

LandmassIndian FIR

GAGAN Performance

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GAGAN GEO Footprint

GSAT-8

GSAT-10

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GAGAN Performance : Ahmedabad (accuracy)

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GAGAN Performance : Bangalore

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.

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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

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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.

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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)

Antenna

Position

Integrity(HPL, VPL)

Navigation Computer

Database

Controls

PilotDisplays

Autopilot

Deviations from desired path,

Alerts

Deviations,Steering

WAASClassBeta

(Sensor)

Reference : FAA TSO C-145

Class Gama Configuration ( Navigator )

Antenna

Navigation Computer

Database

Controls

PilotDisplays

Autopilot

Deviations from desired path,

Alerts

Deviations,Steering

PositionSensor

WAAS Class Gamma

Reference : FAA TSO C-146

Class Delta ConfigurationNavigation Computer

Database

Controls

PilotDisplays

Autopilot

Deviations from desired path,

AlertsPosition Sensor

Deviations,Steering

WAAS Class Delta

Antenna

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.

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SBAS Receiver Familiarization

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Typical Airborne SBAS Receiver

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Typical SBAS Receiver Performance Characteristics

Characteristics Specification

Conformity DO-229D / 301 / 228 / 178 B / 254 / 160TSO – 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 0.1 m/s

SensitivityGPS Acquisition / tracking - 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 5 W

Weight Approx. 500 gms.

Real Time Position Display with 5Mtrs Grid

SpeedDirection

GAGAN HPLGAGAN VPL

GAGAN GEOsPRN 127 &128

Thank You

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Backup Slides

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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)

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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.

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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

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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

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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 calculatedposition based on theWAAS corrections isthe center of the cylinder.

The aircraft’strue position

VPL

HPL

VAL

HAL

Protection level cylinder:VPL and HPL arecomputed by the user’sreceiver from errorbounds calculated byWAAS (UDRE andGIVE).