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Andrea Ghirardini Business Development Spazio ZeroUno An efficient and effective method of conveying Differential GPS data...
Agenda <ul><li>The study </li></ul><ul><li>GPS </li></ul><ul><li>GPS Error sources </li></ul><ul><li>correction systems </...
A feasibility study carried out by Spazio ZeroUno and LABEN for improving GPS accuracy in railways systems The “DGPS on GS...
GPS basics <ul><li>24 satellites orbiting earth in 12 hours </li></ul><ul><li>Constellation provides 5 to 8 visible satell...
GPS error sources Error source Error range Correlation Impact Ephemeris error 3 m Satellite Clock  These errors can be cor...
DGPS: an augmentation system Error reduction efficiency largely depends on  Receiver-Station  distance  and  transmission ...
Cell Broadcast can be an  additional bearer based on the GSM network infrastructure Traditional bearers <ul><li>RDS/FM </l...
Augmentation algorithms Static Survey Kinematic Survey Dynamic Carrier DGPS Wide Area Code Differential Local / Regional  ...
Augmentation algorithms performance 1mm  1cm  10cm  1m  10m  100m <  50 Km <  30.000 Km Global  (no DGPS)  S  S Position...
Accuracy 1 – 10 m Summary Accuracy 20 – 30 m Positioning without DGPS correction Positioning with DGPS correction
Is CB a suitable bearer for DGPS in Railways applications? <ul><li>DGPS payload: 480 bit per 6 satellites </li></ul><ul><l...
Terrestrial network GSM-R network Elements and architecture GPS Rx  DGRS  GSM Rx BTS   Known Position! Bearer
Prototype architecture Cell Broadcast Center Server GSM network simulator Content management (Cell Broadcast Entity) corre...
Validating the concept 1 2 TRAIN Correction range for DGPS station 1 1 R -DGPS R -DGPS     50 – 100 Km 0.5 – 5 m  accuracy
Project summary <ul><li>Feasibility study carried out by Spazio ZeroUno and LABEN </li></ul><ul><li>Project submitted for ...
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Andrea Ghirardini

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Andrea Ghirardini

  1. 1. Andrea Ghirardini Business Development Spazio ZeroUno An efficient and effective method of conveying Differential GPS data to on-board positioning devices for train control. Cell Broadcast (CB) as a bearer for GPS augmentation in GSM-Railway applications
  2. 2. Agenda <ul><li>The study </li></ul><ul><li>GPS </li></ul><ul><li>GPS Error sources </li></ul><ul><li>correction systems </li></ul><ul><li>CB in the game </li></ul><ul><li>The system </li></ul>
  3. 3. A feasibility study carried out by Spazio ZeroUno and LABEN for improving GPS accuracy in railways systems The “DGPS on GSM-R CB” project Project submitted for financing to the Italian Space Agency (ASI) Next step: prototype development with real and simulated elements for concept assessment
  4. 4. GPS basics <ul><li>24 satellites orbiting earth in 12 hours </li></ul><ul><li>Constellation provides 5 to 8 visible satellites from any point on the earth </li></ul><ul><li>4 satellites are required to compute the 3 dimensions of position and time stamp </li></ul><ul><li>Precision ranges from 10 m to 100 m depending mainly on Selective Availability and Ionospheric effects </li></ul>GPS positioning is affected by error sources Error importance is related to the application
  5. 5. GPS error sources Error source Error range Correlation Impact Ephemeris error 3 m Satellite Clock These errors can be corrected by “Augmentation Systems” Ionospheric delay High correlation in Time & Space 3 – 4 m (night) 20 – 30 m (day) Tropospheric delay High correlation in Time & Space 3 m
  6. 6. DGPS: an augmentation system Error reduction efficiency largely depends on Receiver-Station distance and transmission delays Error correction = f (  T ,  S )  GPS Receiver (mobile) 1 Known reference position DGPS Station  2 Calculates correction factors 3 Bearer system   4 Calculates position 5
  7. 7. Cell Broadcast can be an additional bearer based on the GSM network infrastructure Traditional bearers <ul><li>RDS/FM </li></ul><ul><li>Radiobeacons </li></ul><ul><li>Special LF-transmitters </li></ul><ul><li>EGNOS </li></ul>Current bearers No bearer system has been standardized
  8. 8. Augmentation algorithms Static Survey Kinematic Survey Dynamic Carrier DGPS Wide Area Code Differential Local / Regional Area Code Differential SPS
  9. 9. Augmentation algorithms performance 1mm 1cm 10cm 1m 10m 100m < 50 Km < 30.000 Km Global (no DGPS)  S  S Position accuracy Static Survey Kinematic Survey Dynamic Carrier DGPS Wide Area Code Differential Local / Regional Area Code Differential SPS < 200 Km CB bearer
  10. 10. Accuracy 1 – 10 m Summary Accuracy 20 – 30 m Positioning without DGPS correction Positioning with DGPS correction
  11. 11. Is CB a suitable bearer for DGPS in Railways applications? <ul><li>DGPS payload: 480 bit per 6 satellites </li></ul><ul><li>12 satellites at most are in visibility, hence 960 bit </li></ul><ul><li>1 CB message bears 82x8 bits, hence 656 bit (equivalent to 8,2 satellites) </li></ul><ul><li>CB air interface manages 1 message every 1,8 seconds </li></ul><ul><li>Expected network delays are estimated in the order of 10 seconds </li></ul>Error within 1 to 5 m REQUIREMENTS Payload Bandwidth  T < 30 sec  S < 100 Km
  12. 12. Terrestrial network GSM-R network Elements and architecture GPS Rx  DGRS  GSM Rx BTS   Known Position! Bearer
  13. 13. Prototype architecture Cell Broadcast Center Server GSM network simulator Content management (Cell Broadcast Entity) correction GSM network simulator & CB bearer GPS Simulator position Correction and position data generator (1) Configuration parameters Terminal (simulator) RX GPS RX GSM/CB RX DGPS correction (2) Correction log files for all DGPS stations
  14. 14. Validating the concept 1 2 TRAIN Correction range for DGPS station 1 1 R -DGPS R -DGPS  50 – 100 Km 0.5 – 5 m accuracy
  15. 15. Project summary <ul><li>Feasibility study carried out by Spazio ZeroUno and LABEN </li></ul><ul><li>Project submitted for financing to the Italian Space Agency (ASI) </li></ul><ul><li>Objectives: </li></ul><ul><ul><li>validate CB as a bearer for DGPS over GSM-R </li></ul></ul><ul><ul><li>identify performance in worst case conditions </li></ul></ul><ul><ul><li>identify performance ranges (accuracy depending on speed, distance, delay) </li></ul></ul><ul><ul><li>define optimal deployment of DGPS stations with respect to GSM-Railway BTSs </li></ul></ul><ul><ul><li>identify evolution path towards GALILEO positioning system </li></ul></ul><ul><ul><li>structure a commercial offer to the Railways industry </li></ul></ul>

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