Availability of the EGNOS service for land mobile user Pavel Kovář, Libor Seidl, František...
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Transcript of Availability of the EGNOS service for land mobile user Pavel Kovář, Libor Seidl, František...
Availability of theEGNOS service
for land mobile user
Pavel Kovář, Libor Seidl, František Vejražka
Czech Technical University in PragueFaculty of Electrical Engineering
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
2
Agenda
• Introduction - EGNOS• EGNOS channel• Mathematical model• Results of experiments
− experimental GNSS receiver− signal availability− message availability− service availability
• Conclusions
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
3
EGNOS• European augmentation system of the
GPS and the GLONASS• Services
− Open (OS) - available this summer− Safety of Life (SoL) - available summer 2007
• Designed for navigation− aviation enroute− precision approach − maritime
• Planned for land mobile navigation
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
4
EGNOS
• Ranging signal• Data
− WAD corrections− Integrity information− Maintain EGNOS data up-to-date in
user receiver
Age of messages cannot exceed defined thresholds
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
5
EGNOS
Land mobile reception problem:Out-of-date messages due to satellite shadowing
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
6
Study objectives
• Mathematical modeling of shadowing process• Experiments with signal reception
model parameters• Signal availability• Message availability
Investigation of the EGNOS availability for a land mobile user:
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
7
EGNOS channel model
Two states: • Blocked LOS
− Rayleigh fading
• Unblocked LOS− Rice fading
Log-normalfading
,
ComplexGauss process
Spectrumshaping
RayleighfadingRice
fading
BlockUnblock
Block/Unblockprocess
Channel input Channel output
P(f)
c1/
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
8
Mathematical modelBlock/unblock process
− two-state Markov process − dependent on run distance− transition intensity matrix
− partial intensity of LOS unblocking− partial intensity of LOS blocking
Model parameters
− determined experimentally for various environments
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
9
Mathematical model - results
Statistics of
− message reception
− reception of at least one message from N
messages
− antenna diversity reception
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
11
Aim of experiments• EGNOS signal availability in various
environments− Assessment of model parameters− Estimates of EGNOS message statistics by
simulated run trough the shadowing environment
• EGNOS message availability• Estimation of EGNOS service availability
Requirement:Maximum possible elimination of the receiver acquisition delay
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
12
Experimental GNSS receiver
RF unit
RF unit
RF unit
RF unit
ADC FPGA
Software defined architecture
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
13
Experimental GNSS receiverSignal processing• Massive parallel correlation – 4.000 equivalent correlators• Cross-correlation function for all delay bins simultaneously• Fast signal detection (response on EGNOS < 4ms)• Fast acquisition for signal reception• EGNOS message demodulation immediately after signal
appeared
I&QDemodulator
IF ParallelCorrelator
NoncoherentIntegrator
PeakDetection
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
15
Signal availability - example
Country
Town
Unblocked
Blocked
Distance [km]
1 4 8
Unblocked
Blocked
Distance [km]
1 4 8
PRN 120 IOR, Prague, Czech Republic, elevation 15
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
17
Signal availability model parameters obtained by measurement
PRN 120 IOR, Prague, Czech Republic, elevation 15
Environment
[m-1]
[m-1]Visibility (0)
[%]Town
sparsely built-up0.06 - 0.1 0.02 - 0.04 60 - 80
Townnarrow streets
0.02 0.02 50
Country 0.002 - 0.006 0.01 - 0.02 90 - 95
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
18
Conformity of model and measurement
Comparison of • experimental (measured) and • modeled distribution
of unblocked and blocked distance
Distance [m]
0 250 500
PD
F
0.01
0.02
0.03
Unblocked Blocked
Distance [m]
0 250 500
PD
F0.01
0.02
0.03MeasurementModel
MeasurementModel
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
19
Conformity of model and measurement
510
1520
2530
2
4
6
8
100.4
0.5
0.6
0.7
0.8
0.9
1
510
1520
2530
2
4
6
8
100.4
0.5
0.6
0.7
0.8
0.9
1
Probability of reception of at least one message from N ones
Speed [m/s]Speed [m/s]
Re
cep
tion
pro
ba
bili
ty
Re
cep
tion
pro
ba
bili
ty
Model Simulated run
N N
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
20
Antenna diversity reception
Excellent technique for improvement of reception of signals in time variable channel
Problem with implementation due to the strong correlation of the EGNOS land mobile channels for practical separation of antennas
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
22
EGNOS message availability
0 Time [s] 800
0 800
Cor
rela
tor
outp
ut
Error
Dec
oded
mes
sage
No
60
30
0
Town – sparsely built-up area
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
23
EGNOS message availability
0 Time [s] 600
0 600
Cor
rela
tor
outp
ut
Error
Dec
oded
mes
sage
No
60
30
0
Undulating country
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
24
EGNOS message availability
0Time [s] 300
0300
Cor
rela
tor
outp
ut
Error
Dec
oded
mes
sage
No
60
30
0
Flat country
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
26
EGNOS service availability- requirements on message age
Msg. No. 2 18
ContentFast correction &
IntegrityIonosphere grid data
Tx period < 6 s < 300 s
Max. age
RTCA DO 229B
18 s*
12 s**1200 s
* Aircraft enroute nav. ** Aircraft precision approach nav.
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
27
EGNOS service availability- requirements on message age
positionmeassurement
maximumacceptable age
of message
FLAG
NO FLAG
position OK
message age
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
28
EGNOS service availabilityassessment
Estimation of probability that age of given EGNOS message exceeds given value
~
probability that among last N messages no one was successfully received
N= [(max. acceptable age)/(Tx period)]
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
29
EGNOS service availabilityExample: Msg. No. 2
0 50 100 1500
0.2
0.4
0.6
0.8
1
0 50 100 1500
0.2
0.4
0.6
0.8
1
Sparsely built-up town Undulating country Flat Country
0 50 100 1500
0.2
0.4
0.6
0.8
1
Age [s] Age [s] Age [s]
Pro
babi
lity
Pro
babi
lity
Pro
babi
lity
Probability that message age exceeds given threshold
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
30
EGNOS service availabilityExample: Msg. No. 2
0 50 100 1500
0.2
0.4
0.6
0.8
1
0 50 100 1500
0.2
0.4
0.6
0.8
1
Sparsely built-up town Undulating country Flat Country
0 50 100 1500
0.2
0.4
0.6
0.8
1
Age [s] Age [s] Age [s]
Pro
babi
lity
Pro
babi
lity
Pro
babi
lity
Probability that message age exceeds given threshold
threshold 18 s (for aircraft enroute navigation!)
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
31
EGNOS service availabilityExample: Msg. No. 18
0 100 200 300 400 5000
0.2
0.4
0.6
0.8
1
0 100 200 300 400 5000
0.2
0.4
0.6
0.8
1
0 100 200 300 400 5000
0.2
0.4
0.6
0.8
1
Sparsely built-up area Undulating country Flat Country
Age [s] Age [s] Age [s]
Pro
babi
lity
Pro
babi
lity
Pro
babi
lity
Probability that message age exceeds given threshold
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
32
EGNOS service availabilityExample: Msg. No. 18
0 100 200 300 400 5000
0.2
0.4
0.6
0.8
1
0 100 200 300 400 5000
0.2
0.4
0.6
0.8
1
0 100 200 300 400 5000
0.2
0.4
0.6
0.8
1
Sparsely built-up area Undulating country Flat Country
Age [s] Age [s] Age [s]
Pro
babi
lity
Pro
babi
lity
Pro
babi
lity
Probability that message age exceeds given threshold
threshold1200 s
threshold1200 s
threshold1200 s
Czech Technical Universityin Prague
IEEE/ION PLANS 2006San Diego, April 25-27, 2006
33
Conclusions• Level of EGNOS service to land mobile users is
limited due to shadowing.• The model of the EGNOS channel for a land
mobile users has been developed and validated.• EGNOS channel coding is inconvenient for burst
error channel. Convolutional code performance could be dramatically improved by implementation of the interleaving which would eliminate problem of messages ageing.
• Level of service strongly depends on environment.• Requirements on EGNOS service have been
defined for air navigation only by RTCA DO 229. Similar standard for land mobile users should be defined as soon as possible.
Thank you for your attention
Pavel KovářLibor Seidl
František VejražkaCzech Technical University in Prague,
Czech [email protected]