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? EGNOS GEO visibility in München EGNOS NOT Visible EGNOS Visible From: The GLORIA Project by M. Maurer, ILA-29, Washington, DC.

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 satellite 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 to Eurofix data conversion & Eurofix transmission control Including Eurofix to RTCM data conversion EGNOS Rx calculates RTCM corrections based on reference position and EGNOS data EGNOS/Eurofix PC unpacks RTCM messages and reformats to standard Eurofix messages User receives standard Eurofix messages and applies as LAAS correction

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

ETRAN Message Types E-TRAN Type Content EGNOS Source Do not use ! 1 Do not use ! 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 5 Ionospheric Grid delay model parameters, 3 IGPs/message 26

Wide Area EGNOS TRAN message types ETRAN type 0 – Do not use data 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)

Wide Area EGNOS TRAN message types ETRAN type 1 – Fast correction (2 satellites/message) Field Bits # bits Units Range Eurofix Type (8) 1-4 4 16 ETRAN Type (1) 5-7 3 8 Satellite ID 8-15 256 Fast correction 16-27 12 0.125 m -256 – 255.875 m UDREI 28-31 0-16 32-39 40-51 52-55 Spare 56 1 CRC 57-70 14 Source: EGNOS message 2,3,4,5 (satellite fast corrections) EGNOS message 0! (WAAS compatibility mode)

Wide Area EGNOS TRAN message types ETRAN type 2 – Fast & Slow correction (1 sattellite/message) Field Bits # bits Units Range Eurofix Type (8) 1-4 4 16 ETRAN Type (2) 5-7 3 8 Satellite ID 8-15 256 Fast correction 16-27 12 0.125 m -256 – 255.875 m UDREI 28-31 0-16 IOD 32-39 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)

Wide Area EGNOS TRAN message types ETRAN type 3 – Slow correction (1 satellite/message) Field Bits # bits Units Range Eurofix Type (8) 1-4 4 16 ETRAN Type (3) 5-7 3 8 Satellite ID 8-15 256 IOD 16-23 δaf0 24-32 9 2-31 s 2-23 s δx 33-40 0.250 m -32 – 32 δy 41-48 δz 49-56 CRC 57-70 14 Source: EGNOS message 25 (satellite slow corrections)

Wide Area EGNOS TRAN message types ETRAN type 4 – Ionospheric Grid Field Bits # bits Units Range Eurofix Type (8) 1-4 4 16 ETRAN Type (4) 5-7 3 8 Grid Sub ID 8-9 2 Total Subs 10-11 IODI 12-13 0-3 IGP mask bits 14-53 40 Spare 54-56 CRC 57-70 14 Source: EGNOS message 18 (ionospheric grid mask) Eurofix station coverage area & Gridpoints ‘in view’

Wide Area EGNOS TRAN message types ETRAN type 5 – Ionospheric Grid delay model parameters (3 IGPs/message) Field Bits # bits Units Range Eurofix Type (8) 1-4 4 16 ETRAN Type (5) 5-7 3 8 IODI 8-9 2 0-3 First Grid point 10-17 160 IGP vertical delay estimate 18-26 9 0.125 m 0-63.875 m Grid IVEI 27-30 0-15 31-39 40-43 44-52 53-56 CRC 57-70 14 Source: EGNOS message 26

Wide Area EGNOS message distribution Satellite and Ionospheric corrections are interleaved: 2 Satellite Corrections to 1 Ionospheric Correction Fast and slow corrections are interleaved (2 to 1) 2 type-1 Fast corrections (2 SVs) 1 type-2 Fast & slow correction or type-3 Slow 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 250-kW Solid State transmitter @ 100 kHz 200-m Antenna mast

Installation at Loran-C station Sylt Antenna mounts Equipment Rack EGNOS 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 Thales EGNOS GPS Antenna Eurofix Integrity Monitor GPS Antenna Eurofix Datalink Monitor Loran-C Antenna Eurofix Reference Station GPS Antenna

LORADD EGNOS TRAN Receiver Get your EGNOS TRAN receiver upgrade today!!! ** ‘All-in-view’ Loran-C/Eurofix receiver, tracks all stations Improved Loran tracking and Eurofix datalink performance through advanced DSP algorithms 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% availability EGNOS 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 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 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

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 G.Offermans@reelektronika.nl