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SUPPORT TO IWG25
12th June 2013
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Contents
Reminder IWG#24• 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• Analysis of clock prediction models (incl. OBAD)• ICD1 alternative / ICD2 Performance comparison• Conclusion - Comparison with IWG partners results
(Stanford) and Recommended way forward
21 April 2023 PROSBAS
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To characterise the accurracy of clock prediction models
Two different clock correction propagation models• UDRE_ICD (ICD_1): RRC method (inherited from L1 MOPS)
• DFRE_ICD (ICD_2): Linear clock model
Two different clock estimates used as inputs for the analysis• 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
21 April 2023 3PROSBAS
Analysis of clock prediction models
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Definition of Study Cases. ICDs
21 April 2023 4
Clock estimation
(I nput)
UDRE I CD DFRE I CD
magicSBAS ODTS Fast Corrections
magicSBAS_ODTS_UDRE_ ICD magicSBAS_ODTS_DFRE_ ICD
magicSBAS Fast Corrections
magicSBAS_UDRE_ ICD magicSBAS_DFRE_ ICD
UDRE ICD DFRE ICDRCC method: Linear extrapolation of two previous clock estimations
to current epoch
Linear Clock model: offset and drift clock computation from previous clock estimation data and propagation
to current epoch
PROSBAS
Analysis of clock prediction models
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21 April 2023 5
Conclusion : two ways of improvement of clock corrections propagation (valid for any ICD)• Use Precise Orbit and Clock estimation algorithms in SBAS
• Use a more accurate clock correction propagation method: Linear clock model better than RRC
PROSBAS
Results comparison
Analysis of clock prediction models
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21 April 2023 6
Analysis to define a degradation model (OBAD or MT7/10 data)• Acceleration model (ai parameter): from SBAS L1 MOPS
• Polynomial model (Ccorr, Rcorr, Acorr): from DFRE proposal
PROSBAS
• Acceleration model (current L1 MOPS): to be discarded.
• Polynomial model OK• Recommendation: to tune scale factors for
Polynomial model
OBAD analysis
Analysis of clock prediction models
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21 April 2023 7
Two ways of improving the extrapolation of clock corrections• 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• 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
Conclusions
Analysis of clock prediction models
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21 April 2023 PROSBAS 8
SBAS L1/L5 ICD models:Refinement of Definition & performances
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)
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21 April 2023 9
• Bandwidth tuned for 75% margins FCs update intervals (DeltaT_FC values) used to estimate the Delta_FC parameters (key parameter to estimate performance) updated
SBAS L1/L5 ICD models:Refinement of Definition & performances
SATS in MASK
SATS monit MT1
MT2 Update Int MT2 # Mss
MT2_New
MT6-1 # Mss MT6-1
MT6-2 # Mss MT6-2
MT7+10 MT9 MT12 MT17
MT25 # Mss MT25
MT28 # Mss MT28 MT18 MT 26
MT30 # Mss MT 30
Num Messages per MT 1 1 1 1 3 0 0MT Update interval 120 6 6 120 60 300 300 240 240 300 300 300
TOTAL BW
4C 91 91 0,0083 54 4 0,0741 1 0,1667 1 0,1667 0,0083 0,0167 0,0033 0,0100 23 0,09583 46 0,1917 0,0000 0,0000 0 0,000 74,15743C 82 68 0,0083 24 3 0,1250 1 0,1667 1 0,1667 0,0083 0,0167 0,0033 0,0100 17 0,07083 34 0,1417 0,0000 0,0000 0 0,000 71,75002C 58 45 0,0083 11 4 0,3636 0 0,0000 1 0,1667 0,0083 0,0167 0,0033 0,0100 12 0,05 23 0,0958 0,0000 0,0000 0 0,000 72,28031C 31 24 0,0083 5 2 0,4000 0 0,0000 1 0,1667 0,0083 0,0167 0,0033 0,0100 6 0,025 12 0,05 0,0000 0,0000 0 0,000 68,8333
MT2 update intervals are much smaller than those considered in DFRE ICDs
21 April 2023 PROSBAS
SATS in MASK
SATS monit MT_B
MT_D Update Int
MT_D No Mss MT_D MT_C MT_F MT_E MT12 MT_G MT18 MT 26
MT30 No Mss MT 30
Num Messages per MT 1 1 1 1 1 3 0 0MT Update interval 120 6 120 60 300 120 300 300 300
TOTAL BW
4C 91 91 0,0083 175 91 0,5200 0,1667 0,0083 0,0167 0,0033 0,0250 0,000 0,000 0 0,000 74,8333
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 45 45 0,0083 87 45 0,5172 0,1667 0,0083 0,0167 0,0033 0,0250 0,000 0,000 0 0,000 74,55751C 24 24 0,0083 47 24 0,5106 0,1667 0,0083 0,0167 0,0033 0,0250 0,000 0,000 0 0,000 73,8972
DFRE & DFRE Alternative ICD (ICD2 & ICD2 alternative)
UDRE Alternative ICD (ICD1 alternative)
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21 April 2023 10
SBAS L1/L5 ICD models:Preliminary Performances Summary
ICD1 alternative and ICD2 (with or w/o alternative) provide quasi optimal performance
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
21 April 2023 PROSBAS
Full System Protection Results (considering Integrity Message time-out for ICD2)
0
2
4
6
8
10
12
14
VPL 95% Nominal Case. ECAC + AFI
ICD_1
ICD_1 Alt magicSBAS
ICD_1 Alt magicSBAS ODTS
ICD_2
ICD_2 Alt magicSBAS
ICD_2 Alt magicSBAS ODTS
0
2
4
6
8
10
12
VPL 95% Optimistic Case. ECAC + AFI
ICD_1
ICD_1 Alt magicSBAS
ICD_1 Alt magicSBAS ODTS
ICD_2
ICD_2 Alt magicSBAS
ICD_2 Alt magicSBAS ODTS
0
2
4
6
8
10
12
14
16
VPL 95% Pessimistic Case. ECAC + AFI
ICD_1
ICD_1 Alt magicSBAS
ICD_1 Alt magicSBAS ODTS
ICD_2
ICD_2 Alt magicSBAS
ICD_2 Alt magicSBAS ODTS
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21 April 2023 11
SBAS L1/L5 ICD models:Preliminary Performances Summary
21 April 2023 PROSBAS
Full System Protection Results (considering Integrity Message time-out for ICD2)
0
5
10
15
20
25
30
35
Max VPL Nominal Case. ECAC + AFI
ICD_1
ICD_1 Alt magicSBAS
ICD_1 Alt magicSBAS ODTS
ICD_2
ICD_2 Alt magicSBAS
ICD_2 Alt magicSBAS ODTS
0
5
10
15
20
25
30
Max VPL Optimistic Case. ECAC + AFI
ICD_1
ICD_1 Alt magicSBAS
ICD_1 Alt magicSBAS ODTS
ICD_2
ICD_2 Alt magicSBAS
ICD_2 Alt magicSBAS ODTS
0
5
10
15
20
25
30
35
40
Max VPL Pessimistic Case. ECAC + AFI
ICD_1
ICD_1 Alt magicSBAS
ICD_1 Alt magicSBAS ODTS
ICD_2
ICD_2 Alt magicSBAS
ICD_2 Alt magicSBAS ODTS
• 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. .
35 m
15 m
10 m
35 m
15 m10 m
15 m
10 m
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21 April 2023 12
ICD comparison
21 April 2023 PROSBAS
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)
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21 April 2023 13
ICD comparison
21 April 2023
• 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)
• In the end, the enhanced ICD1 and enhanced ICD2 could become very close to each other.
• Unification into a single/common (selected) DFMC ICD seems now achievable target.
PROSBAS
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21 April 2023 14
Recommended way forward until end 2013 and for 2014
21 April 2023 PROSBAS
Analyse the enhanced ICD1 and enhanced ICD2 (as defined in previous slide) so that
• 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