GNSS DevelopmentStatus and Future Work

Eric Chatre, EC/ESA Rapporteur Technical WG, GNSS Panel

Agenda Item 6

Outline

• GNSS Elements

• GNSS Performance Requirements– Definition of parameters

– Relationship betweens parameters

• Integrity Principles

• GNSS Standards

• Future Work

GNSS Elements

GPS GLONASS

Core Constellations

Augmentations

ABAS

SBAS

GBAS

IOR

Aircraft-Based Augmentation System (ABAS)

• Stand-alone technique implemented in user equipment/software

• No accuracy improvement, lateral guidance only

• Provides integrity based on consistency check• Needs redundant satellite measurements (5

or more satellites in view with good geometry)• Integrity only• Performance and availability limited to some

phases of flight

Satellite-Based Augmentation System (SBAS)

• Objectives –Improve accuracy of GPS or GLONASS by

providing corrections for • Satellite errors : clock and ephemeris • Ionospheric errors : model over a geographic area

–Provide integrity information–Lateral and vertical guidance–Improved availability,

Satellite-Based Augmentation System (SBAS) (cont.)

• Architecture– Network of stations covering a wide area (e.g.

continent)– Transmission of information to users through

geostationary satellites

• Coverage and Service areas– Coverage : Wherever the geostationary

signals are received– Service : Wherever operations have been

approved by States

SBAS Architecture

Reference Reference StationsStations

Master StationMaster Station

Uplink Uplink StationStation

GEOGEO

GPSGPS

SBASSBASMessageMessage

Ground-Based Augmentation System (GBAS)

• Objectives –Improve accuracy of GPS or GLONASS

by providing for each satellite a composite correction

• Satellite errors : clock, ephemeris correction valid locally

• Ionospheric errors : local correction• Tropospheric errors : local correction

–Provide integrity information

Ground-Based Augmentation System (GBAS)(cont.)

• Architecture– Ground Reference Station (typically 1 per

airport) – Transmission of information to users through

a VHF data link (108 to 118 MHz)

• Coverage – Approach area (ILS like coverage)– Terminal area (positioning service)

GBAS Architecture

GPS and/or GLONASS, GEOs

User

Reference station and VDB

VHF DATA LINK

Aviation Performance Requirements for GNSS (signal-in-space)

Phase of

Flight

Accuracy

(95%)

Integrity Risk Continuity Risk

Availability

En Route H: 3.7 Km

1x10-7/h 1x10-4/h to 1x10-8/h

0.99 to 0.99999

Terminal H: 0.74 Km

NPA H: 220 m

APV I H: 16 m

V: 20 m

2x10-7/App 8x10-6/ 15sAPV II H: 16 m

V: 8m

Cat I H: 16 m

V: 6 to 4 m

Cat II/III

Surface Ops

Under Development

Interpretation of parameters

Accuracy : Characterize typical behavior of the system in presence of nominal error components

Integrity : Limit risk of abnormal behaviour of the system due to errors resulting from system failures

-Integrity Risk-Alert Limit-Time to Alert

Continuity : Limit risk of losing the service unexpectedly

Availability : Accuracy + Integrity [+ Continuity]

Relationship between parameters

Integrity

Accuracy

Continuity

Availability

•Availabilty

-Vertical accuracy/integrity is usually the main driver

-Decreases as accuracy increases

-Decreases as alert limit gets smaller

•GNSS performance is variable :- in time- in space

-New approach to ensure integrity for all users

-Protection Level concept

Integrity principles

Alert Limit

Computed Position

User Computed Protection Level

Protection Level > Alert Limit Alert

Protection Level < Alert Limit No Alert

Probability 1-1.10-7

GNSS Standards, Procedures, Guidance Material

• Standards and Recommended Practices (ICAO Annex 10, Vol I)

• GNSS NOTAMS and Phraseology (ICAO Annex 15, PANS-ABC Doc 8400, PANS- ATM Doc 4444)

• Procedure Design Criteria (PANS-OPS, Doc 8168)• Geodetic Reference Datum and Data Base Requirements

(ICAO Annexes 4,11,14 &15, WGS-84 Manual Doc 9674) • Information and guidance on implementation (GNSS Manual)• Industry Standards (RTCA and EUROCAE MOPS/MASPS)

Industry Standards

• The main actors are :– RTCA in the US, Special Committee 159– EUROCAE in Europe, Working Group 28

• The Documents – Minimum Operational Performance Specifications (MOPS)– Minimum Aviation System Performance Standards (MASPS)

• Existing Standards– ABAS/Basic GNSS receiver : DO-208 / ED-72 / (J)TSO-C129A– SBAS receiver : DO-229 C / TSO-145A/146A– GBAS Cat I receiver : DO-253A– Multi-Mode Receiver including GBAS : ED-88A

Future Work

• Evolution of currently standardized GNSS elements• GPS modernization with additional civil signal on L5

frequency (1176.45 MHz)• GLONASS modernization (GLONASS K) with additional

civil signal in the 1164-1215 MHz band• Extention of SBAS standards to accomodate new

signals• Extention of GBAS standards to accomodate new

signals and cover Category II/III and surface operations

Future Work (cont.)

• New GNSS elements• GALILEO system with 3 civil signals and a

dedicated integrity service• Ground-Based Regional Augmentation System

(GRAS)