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SUPPORT TO IWG25

SUPPORT TO IWG25. 12 th June 2013. 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.)

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SUPPORT TO IWG25

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  1. SUPPORT TO IWG25 12th June 2013

  2. 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 PROSBAS

  3. Analysis of clock prediction models • Tocharacterisetheaccurracy of clockpredictionmodels • Twodifferentclockcorrectionpropagationmodels • UDRE_ICD (ICD_1): RRC method (inheritedfrom L1 MOPS) • DFRE_ICD (ICD_2): Linear clockmodel • Twodifferentclockestimatesused as inputs fortheanalysis • Equivalenttocurrent EGNOS design (EGNOS V2) • Potentialevolution of EGNOS design: Precise Orbit and Clockestimationalgorithms (State of the art ODTS foreseenfor EGNOS V3) • Same set of SV’s(fromdifferent blocks) and daysusedforthecomparison PROSBAS

  4. Analysis of clock prediction models Definitionof Study Cases. ICDs UDRE ICD DFRE ICD RCC 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

  5. Analysis of clock prediction models • Resultscomparison • Conclusion : twoways of improvement of clockcorrectionspropagation (validforany ICD) • Use Precise Orbit and Clockestimationalgorithms in SBAS • Use a more accurateclockcorrectionpropagationmethod: Linear clockmodelbetterthan RRC PROSBAS

  6. Analysis of clock prediction models • OBAD analysis • Analysisto define a degradationmodel (OBAD or MT7/10 data) • Accelerationmodel (aiparameter): fromSBAS L1 MOPS • Polynomialmodel (Ccorr, Rcorr, Acorr): fromDFRE proposal • Accelerationmodel (current L1 MOPS): to be discarded. • Polynomialmodel OK • Recommendation: to tune scalefactorsforPolynomialmodel PROSBAS

  7. Analysis of clock prediction models • Conclusions • 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

  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) PROSBAS

  9. SBAS L1/L5 ICD models: Refinement of Definition & performances • 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) DFRE & DFRE Alternative ICD (ICD2 & ICD2 alternative) • MT2 update intervals are much smaller than those considered in DFRE ICDs PROSBAS 17 September, 2014

  10. SBAS L1/L5 ICD models: Preliminary Performances Summary Full System Protection Results (considering Integrity Message time-out for ICD2) • 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 PROSBAS 17 September, 2014

  11. SBAS L1/L5 ICD models: Preliminary Performances Summary Full System Protection Results (considering Integrity Message time-out for ICD2) 35 m 15 m 15 m 10 m 10 m • 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 PROSBAS 17 September, 2014

  12. ICD comparison • 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 FCivalues (provided by optimisedODTS 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) PROSBAS 17 September, 2014

  13. ICD comparison • 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 17 September, 2014

  14. Recommended way forward until end 2013 and for 2014 • 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 PROSBAS 17 September, 2014

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