EGNOS ICD presentation 22-06
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Transcript EGNOS ICD presentation 22-06
SUPPORT TO IWG25
12th June 2013
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Contents
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Reminder IWG#24
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2 families of candidate ICD’s
UDRE ICD (ICD1 - limitation 51SV no further studied) and its alternative (up to
90 active SV)
DFRE ICD (ICD2) and its alternative (use of spare CI bits to refresh DFRE when
less than 4 const.)
At IWG#25
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•
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8 April, 2015
Analysis of clock prediction models (incl. OBAD)
ICD1 alternative / ICD2 Performance comparison
Conclusion - Comparison with IWG partners results
(Stanford) and Recommended way forward
PROSBAS
2
Analysis of clock prediction models
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To characterise the accurracy of clock prediction models
Two different clock correction propagation models
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Two different clock estimates used as inputs for the analysis
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UDRE_ICD (ICD_1): RRC method (inherited from L1 MOPS)
DFRE_ICD (ICD_2): Linear clock model
Equivalent to current EGNOS design (EGNOS V2)
Potential evolution of EGNOS design: Precise Orbit and Clock
estimation algorithms (State of the art ODTS foreseen for EGNOS V3)
Same set of SV’s (from different blocks) and days used for the
comparison
8 April, 2015
PROSBAS
3
Analysis of clock prediction models
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Definition of Study Cases. ICDs
Clock estimation
UDRE ICD
DFRE ICD
magicSBAS_ODTS_UDRE_ICD
magicSBAS_ODTS_DFRE_ICD
magicSBAS_UDRE_ICD
magicSBAS_DFRE_ICD
(Input)
magicSBAS ODTS
Fast Corrections
magicSBAS Fast
Corrections
UDRE ICD
RCC method: Linear extrapolation
of two previous clock estimations
to current epoch
8 April, 2015
DFRE ICD
Linear Clock model: offset and drift clock computation
from previous clock estimation data and propagation to
current epoch
PROSBAS
4
Analysis of clock prediction models
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Results comparison
Conclusion : two ways of improvement of clock corrections
propagation (valid for any ICD)
•
•
8 April, 2015
Use Precise Orbit and Clock estimation algorithms in SBAS
Use a more accurate clock correction propagation method: Linear clock
model better than RRC
PROSBAS
5
Analysis of clock prediction models
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OBAD analysis
Analysis to define a degradation model (OBAD or MT7/10 data)
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Acceleration model (ai parameter): from SBAS L1 MOPS
Polynomial model (Ccorr, Rcorr, Acorr): from DFRE proposal
Acceleration model (current L1 MOPS): to
be discarded.
Polynomial model OK
Recommendation: to tune scale factors for
Polynomial model
8 April, 2015
PROSBAS
6
Analysis of clock prediction models
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Conclusions
Two ways of improving the extrapolation of clock corrections
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•
Precise orbit and clock estimation algorithms in SBAS
Using a more accurate method for propagating the clock
corrections to the current epoch (linear clock model instead of RRC)
OBAD analysis
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•
•
8 April, 2015
Feasibility confirmed through experimentation that OBAD model
included in “L1/L5 SBAS MOPS to Support Multiple Constellations”
paper is feasible
Linear or polynomial degradation (no more quadratic as in L1 MOPS)
Include this model in UDRE ICD MT7/10
Highly recommended: a tuning of scale factors and effective ranges of
the OBAD to allow a better fit to the degradation factors
PROSBAS
7
SBAS L1/L5 ICD models:
Refinement of Definition & performances
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Strategy followed in this analysis
Update the bandwidth considerations to refine key
parameters values (DeltaT_FC, DeltaT_IP) for each of the
candidate ICD’s
Re-evaluate preliminary performances achieved with the
SBAS L1/L5 ICDs under analysis (ICD1, ICD2 and
alternatives)
8 April, 2015
PROSBAS
8
SBAS L1/L5 ICD models:
Refinement of Definition & performances
•
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Bandwidth tuned for 75% margins FCs update intervals (DeltaT_FC values) used
to estimate the Delta_FC parameters (key parameter to estimate performance) updated
UDRE Alternative ICD (ICD1 alternative)
MT2
Update
MT2_Ne MT6-1 #
Int
MT2 # Mss w
Mss
SATS in SATS
MASK monit MT1
Num
Messages
per MT
MT
Update
interval
4C
3C
2C
1C
MT6-1
MT6-2 #
Mss
MT6-2
MT7+1
0
MT9
1
MT25 #
MT17 Mss MT25
MT12
1
1
1
3
120
0,0083
0,0083
0,0083
0,0083
60
0,0167
0,0167
0,0167
0,0167
300
0,0033
0,0033
0,0033
0,0033
300
0,0100
0,0100
0,0100
0,0100
MT28 #
Mss
MT30 #
MT 26 Mss
MT28 MT18
0
0
300
0,0000
0,0000
0,0000
0,0000
300
0,0000
0,0000
0,0000
0,0000
MT 30
TOTAL BW
91
82
58
31
91
68
45
24
120
0,0083
0,0083
0,0083
0,0083
54
24
11
5
4
3
4
2
0,0741
0,1250
0,3636
0,4000
1
1
0
0
6
0,1667
0,1667
0,0000
0,0000
1
1
1
1
6
0,1667
0,1667
0,1667
0,1667
23
17
12
6
240
0,09583
0,07083
0,05
0,025
46
34
23
12
240
0,1917
0,1417
0,0958
0,05
0
0
0
0
300
0,000
0,000
0,000
0,000
74,1574
71,7500
72,2803
68,8333
DFRE & DFRE Alternative ICD (ICD2 & ICD2 alternative)
SATS in SATS
MASK monit
MT_D
Upda MT_D
te Int No Mss MT_D
MT_B
MT_C
MT_F
MT_E
MT12
MT_G
MT18
MT30
No Mss
MT 26
MT 30
Num
Messages
per MT
MT
Update
interval
4C
91
91
120
0,0083
175
91
0,5200
6
0,1667
120
60
0,0083 0,0167
300
0,0033
120
0,0250
300
0,000
300
0,000
0
300
0,000
3C
68
68
0,0083
131
68
0,5191
0,1667
0,0083 0,0167
0,0033
0,0250
0,000
0,000
0
0,000
74,7417
2C
1C
45
24
45
24
0,0083
0,0083
87
47
45
24
0,5172
0,5106
0,1667
0,1667
0,0083 0,0167
0,0083 0,0167
0,0033
0,0033
0,0250
0,0250
0,000
0,000
0,000
0,000
0
0
0,000
0,000
74,5575
73,8972
1
1
1
1
1
3
0
0
TOTAL
BW
74,8333
MT2 update intervals are much smaller than those considered in DFRE ICDs
8 April, 2015
PROSBAS
9
SBAS L1/L5 ICD models:
Preliminary Performances Summary
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Full System Protection Results (considering Integrity Message time-out for ICD2)
VPL 95% Nominal Case. ECAC + AFI
VPL 95% Optimistic Case. ECAC + AFI
14
12
12
10
10
8
8
ICD_1
6
6
ICD_1 Alt magicSBAS
ICD_1 Alt magicSBAS ODTS
4
ICD_1 Alt magicSBAS
4
ICD_2
ICD_2 Alt magicSBAS
2
ICD_1
ICD_1 Alt magicSBAS ODTS
ICD_2
2
ICD_2 Alt magicSBAS
ICD_2 Alt magicSBAS ODTS
ICD_2 Alt magicSBAS ODTS
0
0
VPL 95% Pessimistic Case. ECAC + AFI
16
14
12
ICD1 alternative and ICD2 (with or w/o
alternative) provide quasi optimal
performance
10
ICD_1
8
ICD_1 Alt magicSBAS
6
ICD_1 Alt magicSBAS ODTS
4
ICD_2
ICD_2 Alt magicSBAS
2
ICD_2 Alt magicSBAS ODTS
0
8 April, 2015
NB:
- Pessimistic case slightly better for ICD1 alternative
than ICD2, yet felt due to (conservative) margins on
UDRE border effect in the model (effective
difference expected lower(tbc)).
- ICD1 performance suffers from DOP limitation when
more than 2 constellations
PROSBAS
10
SBAS L1/L5 ICD models:
Preliminary Performances Summary
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Full System Protection Results (considering Integrity Message time-out for ICD2)
Max VPL Optimistic Case. ECAC + AFI
Max VPL Nominal Case. ECAC + AFI
35
30
35 m
30
25
25
20
20
ICD_1
15
15
15 m
ICD_1 Alt magicSBAS ODTS
ICD_2
10 m
10
10
15 m
ICD_1 Alt magicSBAS ODTS
ICD_2
5
ICD_2 Alt magicSBAS
5
ICD_1
ICD_1 Alt magicSBAS
ICD_1 Alt magicSBAS
10 m
ICD_2 Alt magicSBAS
ICD_2 Alt magicSBAS ODTS
ICD_2 Alt magicSBAS ODTS
0
0
Max VPL Pessimistic Case. ECAC + AFI
40
35 m
35
30
25
ICD_1
20
ICD_1 Alt magicSBAS
15
ICD_1 Alt magicSBAS ODTS
10
ICD_2
15 m
10 m
ICD_2 Alt magicSBAS
5
ICD_2 Alt magicSBAS ODTS
0
8 April, 2015
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LPV-200: All cases below 35m
Cat I autoland (VAL 10m to 15m):
2 constellations cases always below 15m.
3 & 4 constellations and nom. & opt. cases
seem very promising especially with ICD1
alternative (and possibly also with ICD2,
since border effect is conservative in the
model), even for 10 m-threshold.
PROSBAS
11
ICD comparison
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ICD comparison Status at IWG#25
•
Availability: both ICD1 alternative and ICD2 (or its alternative)
achieve close to optimal performances: up to 4 constellation /
91SV’s, low DFREi/Delta FCi values (provided by optimised
ODTS and clock extrapolation), low VPL
•
ICD1 alternative (with up to 90 active SV)
Flexible as per current L1 MOPS :
Provides comfortable margins with respect to border effect
Offers capability to rapidly react (updating all DFREi’s) upon event
increasing (continuity) robustness
not constraining system design
Offers room for enhancement : removal of FC’s, replacement of user
RRC by system extrapolation parameter, optimised degradation model
and tuning of OBAD parameters
Bandwidth limitation to be further analysed (LTC/MT28 rate)
8 April, 2015
PROSBAS
12
ICD comparison
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ICD2
Basically tailored for simple scheduler
Yet ICD2 rigidity (e.g. wrt. events impacting many SV, UDRE border
effect) compared to current L1 MOPS. This is due to limitation in
DFREi update mechanism
ICD2 would deserve being enhanced with flexible/dynamic but simple
to implement mechanism (for instance by adding an on event pair of
MT6 like messages allowing to recover DFREi within 2s after a general
integrity alert message, or by another mechanism to be investigated)
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In the end, the enhanced ICD1 and enhanced ICD2 could
become very close to each other.
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Unification into a single/common (selected) DFMC ICD seems
now achievable target.
8 April, 2015
PROSBAS
13
Recommended way forward until end 2013 and for 2014
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Analyse the enhanced ICD1 and enhanced ICD2 (as defined in
previous slide) so that
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ICD1 is better optimised (incl. for BW) see slide #12
ICD2 is made capable of handling dynamic events without constraining
the system design
(Tentatively) Unify the above enhanced ICD’s in a unique and
common (pre-)selected ICD < end of 2013
Refine the mechanism to maintain integrity upon message loss
(handling of repetitions upon DFREi change, OBAD, DFREi
resolution table, etc.)
2014 would then be devoted to validate/refine the very details of
the selected ICD (e.g. using EC/ESA pro-SBAS simulator)
Objective : interim (validated) MOPS ICD < end 2014
8 April, 2015
PROSBAS
14