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



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

František Vejražka

Jsou tu opravdu dvě n????



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



5

EGNOS

Land mobile reception problem:Out-of-date messages due to satellite shadowing



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:

vejrazka

tady by snad mělo být jiné pořadí, aby odpovídalo tomu, co je dál. Možná by se to mělo jinak jmenovat - třeba experimental measurement



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/


Co je u vstupu do Riceovského kanálu???



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

vejrazka

Tyto dva modely spolu nesouhlasí. Předchozí je typicky rádiotechnický, tento sleduje jen statistiku přerušení kanálu. To je celke pochopitelné... Ale mělo by se to na konci mpředchozího slajdu říct.


tj. přepínač na předschozím slajdu



9

Mathematical model - results

Statistics of

− message reception

− reception of at least one message from N

messages

− antenna diversity reception

RESULTSOF

EXPERIMENTSAND

MODELING



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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



12

Experimental GNSS receiver

RF unit

RF unit

RF unit

RF unit

ADC FPGA

Software defined architecture



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

Signal availability



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


vybrat sní,mek, ev upraviot



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


Co to je ION???? To má být asi IOR ne?



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



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


Text nějak jinak a patří to sem, nebo až za zprávy???



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


Někam dozadu

Message availability



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


změnil jsem



23


0 Time [s] 600

0 600

Cor

rela

tor

outp

ut

Error

Dec

oded

mes

sage

No

60

30

0

Undulating country



24


0Time [s] 300

0300

Cor

rela

tor

outp

ut

Error

Dec

oded

mes

sage

No

60

30

0

Flat country

Service availability



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.



27

EGNOS service availability- requirements on message age

positionmeassurement

maximumacceptable age

of message

FLAG

NO FLAG

position OK

message age



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)]



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



30


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


Pro

babi

lity

Pro

babi

lity

Pro

babi

lity


threshold 18 s (for aircraft enroute navigation!)



31


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


Pro

babi

lity

Pro

babi

lity

Pro

babi

lity




32


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


Pro

babi

lity

Pro

babi

lity

Pro

babi

lity


threshold1200 s

threshold1200 s

threshold1200 s



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.

vejrazka

To není závěr studie??? - vynechat

vejrazka

body by se měly logicky zpřeházet

vejrazka

víme určitě, že není?


doplnit diversitulepší modulaci...

Thank you for your attention

Pavel KovářLibor Seidl

František VejražkaCzech Technical University in Prague,

Czech [email protected]

Availability of the EGNOS service for land mobile user Pavel Kovář, Libor Seidl, František...

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