Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 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

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Agenda The study GPS GPS Error sources correction systems CB in the game The system

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 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

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 GPS basics 24 satellites orbiting earth in 12 hours Constellation provides 5 to 8 visible satellites from any point on the earth 4 satellites are required to compute the 3 dimensions of position and time stamp Precision ranges from 10 m to 100 m depending mainly on Selective Availability and Ionospheric effects GPS positioning is affected by error sources Error importance is related to the application

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 GPS error sources Error sourceError rangeCorrelationImpact Ionospheric delay High correlation in Time & Space 3 – 4 m (night) 20 – 30 m (day) Tropospheric delay High correlation in Time & Space 3 m Ephemeris error 3 m Satellite Clock These errors can be corrected by “Augmentation Systems”

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Error reduction efficiency largely depends on Receiver-Station distance and transmission delays Error correction = f (  T,  S )  GPS Receiver (mobile) 1 DGPS: an augmentation system Known reference position DGPS Station  2 Calculates correction factors 3 Bearer system  4 Calculates position 5

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Cell Broadcast can be an additional bearer based on the GSM network infrastructure Traditional bearers RDS/FM Radiobeacons Special LF-transmitters EGNOS Current bearers No bearer system has been standardized

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Augmentation algorithms Static Survey Kinematic Survey Dynamic Carrier DGPS Wide Area Code Differential Local / Regional Area Code Differential SPS

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Augmentation algorithms performance 1mm 1cm 10cm 1m 10m 100m < 50 Km < Km Global (no DGPS) SS SS Position accuracy CB bearer Static Survey Kinematic Survey Dynamic Carrier DGPS Wide Area Code Differential Local / Regional Area Code Differential SPS < 200 Km

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Accuracy 1 – 10 m Summary Accuracy 20 – 30 m Positioning without DGPS correction Positioning with DGPS correction

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Is CB a suitable bearer for DGPS in Railways applications? DGPS payload: 480 bit per 6 satellites 12 satellites at most are in visibility, hence 960 bit 1 CB message bears 82x8 bits, hence 656 bit (equivalent to 8,2 satellites) CB air interface manages 1 message every 1,8 seconds Expected network delays are estimated in the order of 10 seconds Error within 1 to 5 m REQUIREMENTS Payload Bandwidth  T < 30 sec  S < 100 Km

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Terrestrial networkGSM-R network Elements and architecture GPS Rx  DGRS  GSM Rx BTS  Known Position! Bearer

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 GPS Simulator position Correction and position data generator (1) Configuration parameters Prototype architecture Cell Broadcast Center Server GSM network simulator Terminal (simulator) RX GPSRX GSM/CB Content management (Cell Broadcast Entity) correction GSM network simulator & CB bearer RX DGPS correction (2) Correction log files for all DGPS stations

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Validating the concept TRAIN Correction range for DGPS station R -DGPS R -DGPS  50 – 100 Km 0.5 – 5 m accuracy

Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Project summary  Feasibility study carried out by Spazio ZeroUno and LABEN  Project submitted for financing to the Italian Space Agency (ASI)  Objectives: validate CB as a bearer for DGPS over GSM-R identify performance in worst case conditions identify performance ranges (accuracy depending on speed, distance, delay) define optimal deployment of DGPS stations with respect to GSM- Railway BTSs identify evolution path towards GALILEO positioning system structure a commercial offer to the Railways industry