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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  • Also error correction depends on the fact that the DGPS Station and the GPS Receiver see the same satellites. We’ll be considering railways applications in those aspects that will characterise the bearer system, that is imposing requirments on DS and TS in order to get the desired precision performances
  • In addition ETSI suggests the use of channels xxx-yyy to deliver DGPS signal. To validate CB as a bearer for DGPS correction we have to take a look at the algorithms implementing DGPS to understand what features they present.
  • 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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