EGNOS TRAN: Broadcasting EGNOS messages over the Eurofix Datalink

ILA 32 – 4-7 November 2003 1 Gerard Offermans - reelektronika

EGNOS TRAN: Broadcasting EGNOS messages over the

Eurofix Datalink

Gerard Offermans, Arthur Helwig & Durk van Willigen

Reelektronika, the Netherlands


What is EGNOS?

• EGNOS = European WAAS

• Differential Corrections and Integrity for GPS

• Ground network of RIMS measure satellite range errors

• Range errors are spit into ionospheric component and satellite specific errors

• Broadcast of Wide-Area data via Geostationary Satellites

• All based on RTCA DO-229B documentation


Why EGNOS TRAN?

From: The GLORIA Project by M. Maurer, ILA-29, Washington, DC.

EGNOS GEO visibility in München

EGNOS Visible

EGNOS NOT Visible


EGNOS TRAN solution

• Eurofix datachannel capacity appr. 30 bps

• EGNOS bandwidth 250 bps

EGNOS TRAN solution

• EGNOS TRAN does not back-up GEO datalink

• EGNOS TRAN backs-up EGNOS functionality


EGNOS TRAN Local Area solution

• EGNOS receiver outputs RTCM SC104 LAAS correction data for all satellites in view of Loran Transmitter

• Eurofix Station converts this message to a standard Eurofix message

• User gets Local Area correction – Input into standard GPS receivers– Suffers from Spatial Decorrelation


EGNOS-Eurofix Local Area

EGNOS Rx calculates RTCM corrections based on reference position and EGNOS dataEGNOS/Eurofix PC unpacks RTCM messages and reformats to standard Eurofix messagesUser receives standard Eurofix messages and applies as LAAS correction

Thales EGNOS RX

EGNOS PC

250 kW Loran-C TX

RTCM

DGPS RX Eurofix RX

Eurofix data

Loran-C pulses

Loran-C TX

DGPS user position

H-field Loran-C Antenna

GPS Antenna

RTCM

RTCM to Eurofix data conversion & Eurofix transmission control

Including Eurofix to RTCM data conversion

EGNOS satellite


EGNOS TRAN Wide Area solution

• EGNOS receiver provides “raw” EGNOS data• Eurofix Station extracts information and reduces

dataset• Eurofix Station reformats information into E-

TRAN Eurofix message• User calculates ionospheric delay and satellite

clock errors for all satellites based on estimated User position– Pure Wide Area solution– No spatial decorrelation– Requires position feedback to the Eurofix receiver

(GPS or Loran-C)


EGNOS-Eurofix Wide Area

Thales Rx passes DO-229 EGNOS data on to EGNOS PCEGNOS PC unpacks EGNOS data and reformats into EGNOS Eurofix messagesUser receiver receives Eurofix messages and stores EGNOS dataUser receiver calculates optimal correction data based on user position (true wide area)

Thales EGNOS RX

EGNOS PC

250 kW Loran-C TX

EGNOS format

DGPS RX Eurofix RX

Eurofix data

Loran-C pulses

Loran-C TX

DGPS user position

H-field Loran-C Antenna

GPS Antenna

RTCM

EGNOS to Eurofix data conversion & Eurofix transmission control

Including EGNOS Eurofix to RTCM data

conversion

NMEA (position)

EGNOS satellite


ETRAN Message Types

E-TRAN Type

ContentEGNOS Source

0 Do not use ! 0

1 Fast corrections, 2 satellites/message 2-5

2 Fast & slow correction, 1 satellite/message 2-5 + 25

3 Slow correction, 1 satellite/message 25

4 Ionospheric grid 18

5Ionospheric Grid delay model parameters, 3 IGPs/message

26


Wide Area EGNOS TRAN message types

Field Bits # bits Units Range

Eurofix Type (8) 1-4 4 16

ETRAN Type (0) 5-7 3 8

Body (all zeroes) 8-56 49

CRC 57-70 14

Source: EGNOS message 0! (WAAS compatibility mode)

ETRAN type 0 – Do not use data






Satellite ID 8-15 8 256

Fast correction 16-27 12 0.125 m -256 – 255.875 m

UDREI 28-31 4 0-16



UDREI 52-55 4 0-16

Spare 56 1

CRC 57-70 14

ETRAN type 1 – Fast correction (2 satellites/message)

Source: EGNOS message 2,3,4,5 (satellite fast corrections) EGNOS message 0! (WAAS compatibility mode)



ETRAN type 2 – Fast & Slow correction (1 sattellite/message)






UDREI 28-31 4 0-16

IOD 32-39 8 256

δaf0 40-50 11 2-31 s 2-21 s

Spare 51-56 6

CRC 57-70 14

Source: EGNOS message 2,3,4,5,0 (satellite fast corrections) EGNOS message 25 (satellite slow corrections)



ETRAN type 3 – Slow correction (1 satellite/message)





IOD 16-23 8 256

δaf0 24-32 9 2-31 s 2-23 s

δx 33-40 8 0.250 m -32 – 32

δy 41-48 8 0.250 m -32 – 32

δz 49-56 8 0.250 m -32 – 32

CRC 57-70 14

Source: EGNOS message 25 (satellite slow corrections)



ETRAN type 4 – Ionospheric Grid




Grid Sub ID 8-9 2 4

Total Subs 10-11 2 4

IODI 12-13 2 0-3

IGP mask bits 14-53 40

Spare 54-56 3

CRC 57-70 14

Source: EGNOS message 18 (ionospheric grid mask)Eurofix station coverage area & Gridpoints ‘in view’



ETRAN type 5 – Ionospheric Grid delay model parameters (3 IGPs/message)




IODI 8-9 2 0-3

First Grid point 10-17 8 160

IGP vertical delay estimate 18-26 9 0.125 m 0-63.875 m

Grid IVEI 27-30 4 0-15


Grid IVEI 40-43 4 0-15


Grid IVEI 53-56 4 0-15

CRC 57-70 14

Source: EGNOS message 26


Wide Area EGNOS message distribution

Fast and slow corrections are interleaved (2 to 1)

2 type-1 Fast corrections (2 SVs)

1 type-2 Fast & slow correctionor type-3 Slow correction

Satellite and Ionospheric corrections are interleaved: 2 Satellite Corrections to 1 Ionospheric Correction

Grid and IGP data messages are interleaved (1 to 7)

1 type-4 Ionospheric grid

7 type-5 IGP data (3 IGPs)

In total 113 IGP points for Sylt area, so a whole transmission sequence is:

3 type-4 messages (grid) + 38 type-5 messages (IGP data) interleaved 2 to 1

Approximately 123 (=3 times 41) messages before all (IGP) data is acquired

Sylt update rate is one message every 2 seconds (single rate)

EGNOS TRAN Cold start acquisition time 246 seconds (4 minutes)


Installation at Loran-C station Sylt

200-m Antenna mast

250-kW Solid State transmitter @ 100 kHz


Installation at Loran-C station SyltEGNOS TRAN equipment

← Thales EGNOS Rx

← Modem & power supply

← EGNOS TRAN PC

Existing Eurofix installation

← Eurofix Rx & power supply

← 2x GPS Rx & Modem

← CPU switch

← Integrity Monitor PC

← Reference Station PC

← UPS

Equipment RackAntenna mounts

ThalesEGNOS

GPSAntenna

EurofixIntegrityMonitor

GPSAntenna

EurofixReference

StationGPS

Antenna

EurofixDatalinkMonitorLoran-CAntenna


LORADD EGNOS TRAN Receiver

• ‘All-in-view’ Loran-C/Eurofix receiver, tracks all stations• Improved Loran tracking and Eurofix datalink performance through

advanced DSP algorithms

**

Get your EGNOS TRAN receiver upgrade today!!!

• Modified to perform User Differential Correction calculations based on received EGNOS TRAN messages

• Used in trials with EGNOS TRAN on 6731Z and Eurofix on 7499M (Sylt)


Measurements

• Performed by Teleconsult Austria

Country Mode– The Netherlands E-TRAN LAAS– Germany E-TRAN LAAS– France E-TRAN LAAS– Sweden E-TRAN RAAS


Measurement results - Göteburg


Measurement results - Göteburg

ETRAN 100% availabilityEGNOS GEO: 100% availability


Measurement results

• EGNOS TRAN Datalink performed well, even in areas where GEO is unavailable

• Generally, where GEO and EGNOS TRAN via Eurofix are available, the DGPS performance is similar

• E-TRAN Local Area mode is less accurate than E-TRAN Wide Area mode (spatial decorrelation)

• Proven EGNOS functionality back-up using “low bit-rate” data channel


Potential European

Eurofix coverage

…which is about the

footprint of EGNOS


Polar Routes

• Restricted Russian polar routes: Polar 1 to 4

• Preferred random routing in Canada

• 2005: 9000+ commercial polar flights estimated

• Savings:– Flying time: 2+ hrs– Costs: US$ 16

k/flight– Time slots Atlantic

• ‘Polar Routes Feasibility Study’, Nav Canada and FAAR, October 2000

4970M+5960Z 1,200 kW

4970X+5960Y 250 kW

5960X 1,200 kW

7001Y 250 kW

7270X+5930Z 800 kW

7960M 560 kW

9990Y+7960Z 1,000 kW

7001X+9007W 250 kW

9990Y+7960Z 1,000 kW


Conclusions

• ETRAN exceeds SBAS availability in cities, forests and mountainous environment

• Loran-C navigation function very dissimilar backup for GPS outages

• Loran-C TX modification low-cost, especially if station has access to WAAS or EGNOS data networks

• Can be implemented on Eurofix in Europe as well as on Loran-Comm in the US

• E-TRAN Data update can easily be improved by using dual-rate and multiple stations


More information

• http://galileo.cs.telespazio.it/egnostran/

• http://galileo.cs.telespazio.it/egnostran/home/files/etran4gis.pdf

• [email protected]

EGNOS TRAN: Broadcasting EGNOS messages over the Eurofix Datalink

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