Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Andrea Ghirardini Business...
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Transcript of Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002 Andrea Ghirardini Business...
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 source Error range Correlation Impact
Ionospheric delay High correlation in Time & Space
3 – 4 m (night)20 – 30 m (day)
Tropospheric delay
High correlation in Time & Space3 m
Ephemeris error3 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 referenc
eposition
DGPS Station
2
Calculates correction
factors
3
Bearer system
4Calculate
s 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
< 30.000 Km
Global (no DGPS)
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 mPositioning 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
PayloadPayload
BandwidtBandwidthh
T < 30 secS < 100 Km
Spazio ZeroUno Cell Broadcast Forum Plenary, Milan, May 28-29th 2002
Terrestrial network
GSM-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 Simulatorposition
Correction and position data generator
(1)
Configuration parameters
Prototype architecture
Cell Broadcast Center Server
GSM network simulator
Terminal (simulator)
RX GPS RX 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
11
22TRAIN
Correction range for DGPS
station 1
11
R-DGPSR-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