Integrity and Interoperability for LIABILITY-CRITICAL APPLICATIONS · 2010. 3. 12. · Both IBPL (ECA) and MHSS (MRA) performance depends on the number of satellites. Page 12 ©GMV,

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LIABILITY-CRITICAL APPLICATIONS

Integrity and Interoperability for

© GMV, 20102010/03/08 Page 2Interoperability for LCA

� Hence similar to safety critical in what integrity is the key enabler

� No risks for human life or health involved

� Economic implications may demand similar integrity levels

LIABILITY CRITICAL APPLICATIONS(OF GNSS POSITIONING)

Those in which large unnoticed navigation errors may have legal or economic implications

HighHigh AccuracyAccuracy butbut no no integrityintegrity

LowLow AccuracyAccuracy butbut integrityintegrity

HighHigh AccuracyAccuracy butbut no no integrityintegrityHighHigh AccuracyAccuracy butbut no no integrityintegrity

LowLow AccuracyAccuracy butbut integrityintegrity


� Road user charging (road tolling)

� Pay-As-You-Drive (PAYD) insurance

� On-street parking pricing

� Traffic law enforcement (e.g. speed fining)

� Surveillance of Parolees

� Fleet management (special vehicle classes)

� …

EXAMPLES OF LCA


LCA SCHEME

Generic scheme

Example: RUC

© GMV, 2010

� The system needs credibility, must be reliable:

Users won’t admit being charged “by mistake”

� Thus we must be really sure when we charge a user

� RUC example: make sure that the vehicle is using the toll road

2010/03/08 Page 5Interoperability for LCA

WHY INTEGRITY IS NEEDED IN LCA?

Protection levels alert when there is a chance that the vehicle is NOT using the toll road, but a nearby one


CHALLENGING LCA SCENARIOS

� Dirty compared with aeronautical (multi-path, interference…)

� Especially in urban and suburban areas

� Main challenges in urban scenarios are:

– Reduced satellite visibility

– Heavy multi-path (especially NLOS threat)

800 1000 1200 1400 1600 1800 2000 2200 2400-150

-100

-50

0

50

100

150

200

250

Time

Err

or

(me

tre

s)

0 20 40 60 80 100 120 140 160 180 2000.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

Measurement error (metres)

Accu

mu

late

d r

ela

tive

fre

qu

en

cy

Highway

Urban 1

Urban 2


TWO DIFFERENT APPROACHES

� Measurement Rejection Approach (MRA):

Throw away NLOS measurements, then compute protection levels.

– Advantage: (almost) only healthy measurements used => smaller PL’s

– Drawbacks:

• Needs a powerful FDE

• Few measurements in urban environments:

– High DOP

– Less epochs with enough satellites to navigate

� Error Characterisation Approach (ECA):

Protection levels account for NLOS measurement errors.

– Drawback: larger position errors caused by NLOS => larger PL’s

– Advantages:

• Needs no FDE

• Many satellites to navigate (especially with HS Rx):

– Lower DOP

– More epochs with enough satellites to navigate


MRA EXAMPLES (I)

� Traditional RAIM techniques (e.g. parity space):

– Version for multiple fault conditions (needed to handle urban NLOS)

– FDE needed to ensure an upper bound to the number of faults

– GIC can help characterising the remaining “fault-free” errors


MRA EXAMPLES (II)

� Multiple Hypothesis Solution Separation (MHSS):

– Prepared for multiple faults

– FDE needed to ensure a minimum amount of healthy measurements

– GIC can help characterising the remaining “fault-free” errors


ECA EXAMPLES

� Isotropy-Based Protection Level (IBPL):

– Use residuals to compute adaptive PL’s that account for all errors

– Residuals retain error statistics under some assumptions (error isotropy)

– NLOS seems to violate the isotropy assumption

– However this assumption can be relaxed


OBSERVATIONS

� MRA needs a powerful FDE. No such FDE is known (to the authors) so far !!

� Can GNSS infrastructure help user-level FDE? (e.g. polarisation)

� Only ECA has been implemented so far through IBPL

� Isotropy is apparently violated by NLOS, but this assumption can be relaxed

� Both IBPL (ECA) and MHSS (MRA) performance depends on the number of satellites

© GMV, 2010Page 12

MHSS PERFORMANCE RESULTS

� Different HPL size statistics for different FDE capabilities andconstellation sizes:

� Note the improvement achieved by passing from two to three constellations

Interoperability for LCA 2010/03/08

© GMV, 2010Page 13

IBPL PERFORMANCE RESULTS

� Different HPL curves correspond to different confidence levels. Only the leftmost two can be compared with previous slide

� Note also the improvement achieved by passing from two to three constellations


© GMV, 2010Page 14

MAIN CONCLUSIONS

� LCA needs integrity

� Integrity in road applications faces challenges that in civil aviation can be disregarded (local effects)

� Mission segment-provided integrity is not enough due to local effects

� Hence, mission segment support to LCA cannot be oriented to error monitoring

� Different strategies analysed (MRA, ECA)

� The benefits of multiple constellations became clear in both cases


© GMV, 2010 Property of GMV

All rights reserved

Thank you

Miguel Azaola

GNSS Business Unit

Email: [email protected]

www.gmv.com

The work reported in this paper has been supported under a contract of the European Space Agency in the frame of the European GNSS Evolutions Programme. The views presented in the paper represent solely the opinion of the authors or their organizations and should be considered

as R&D results not necessarily impacting the present EGNOS and Galileo system design.

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Integrity and Interoperability for LIABILITY-CRITICAL APPLICATIONS · 2010. 3. 12. · Both IBPL (ECA) and MHSS (MRA) performance depends on the number of satellites. Page 12 ©GMV,