Horizontal Advanced RAIM: Operational Benefits and Future Challenges

Horizontal Advanced RAIM: Operational Benefits and Future Challenges International Technical Symposium on Navigation and Timing 2015 Session Air Navigation November 2015 Toulouse/France 1

ICAO ABAS augmentation ICAO has defined three types of augmentation systems: > ABAS > SBAS > GBAS ABAS systems were the first one implemented on-board aircraft based on > Airborne Autonomous Integrity Monitoring implementation > Receiver Autonomous Integrity Monitoring implementation RAIM technics > Provides an autonomous integrity monitoring capability based on satellite failure assumption for safety critical applications down to Non-Precision Approach or Lateral NAVigation > Uses the redundancy of satellites measurement to detect, exclude and overbound the navigation position. 2

RAIM assumptions and operational limitation Traditional RAIM algorithms were design to detect single failure > Not accounting for potential multiple failure cases Traditional RAIM algorithms allocate the same probability fault for each satellite The fault free state in RAIM algorithm is based on zero mean Gaussian distribution with know variance Some operational limitations have been observed for Non-Precision Approach service [1] > All GPS+RAIM implementation don t lead to 100% of NPA or LNAV operation over the globe 3

GNSS evolution GNSS elements are under development/modernization > GPS is broadcasting on L1 and (some SV) L5 frequencies > Galileo is being deployed and is broadcasting on E1 and E5a > GLONASS and Beidou are also looking at evolution plan to broadcast on L1/L5 equivalent band. GNSS will be dual-frequency and multi-constellation (DFMC) > ICAO supports the development of next-generation GNSS to further improve current services and benefit from increased performance > ABAS based on RAIM will be dramatically improved through the availability of new dual-frequency measurements 4

ARAIM Concept New integrity monitoring technique has been proposed by US GEAS program [2] : Advanced RAIM (ARAIM) > Taking credits for DFMC evolution context > Designing a measurement error model based on Gaussian distributions and nominal bias supported by a new kind of airborne integrity monitoring algorithm [3] > Targeting precision approach including global vertical guidance APV I / LPV 200 capability > Introducing a light ground infrastructure referred as Integrity Support Message (ISM) > Correcting current RAIM assumptions that no longer hold true The ARAIM concept has been further developed by EU-US WG-C ARAIM Technical Sub-Group which has detailed in its report ARAIM system architecture [4] : > ARAIM off line architecture sustaining horizontal then vertical guidance > ARAIM on line architecture providing additional information such as ephemeris overlay 5

Offline ARAIM Architecture 6

Aviation Standardisation Context RTCA SC 159 plans to develop new dual-frequency/multiconstellation equipment in 2020+ > Based on SBAS L1/L5 augmentation system > Based on DFMC RAIM in non SBAS area as current SBAS standard There is an interest to evaluate ARAIM performance for horizontal operation (H-ARAIM) because > Horizontal guidance requirements are less demanding than vertical guidance > Horizontal operations are less safety critical which can simplify the implementation of ARAIM feature in certified avionics > Horizontal operations needs may be less stringent on the ISM dissemination scheme to sustain acceptable operation performance - With less complexity on the GNSS core constellation or receiver design 7

A B C H-ARAIM benefits analysis Future challenges Conclusion 8

A B C H-ARAIM benefits analysis Future challenges Conclusion 9

Benefits Assessment Methodology Definition of the targeted operation > Identification of the associated requirements Definition of the tools and means to assess the benefits Definition of operational scenarios > Characterisation of H-ARAIM robustness based on nominal of degraded mode of operation > Characterisation of sensitive parameters to H-ARAIM performance Results analysis 10

H-ARAIM operation targets in Navigation Most stringent horizontal NAV application defined by ICAO PBN [5] : > RNP 0.1 NM - Required Total System Error at 0.1 NM for accuracy and 0.2 NM for integrity - Allocation between Navigation System Error (NSE), Path Definition Error (PDE) and Flight Technical Error (FTE) is manufacturer/avionics-specific - 0.1 NM has been retained as integrity alerting requirement for the NSE - Definition of the HPL to achieve 99.9% Availability metric to characterize the H-ARAIM NSE performance. Current operation realized with ABAS RAIM equipment > Lateral Navigation (LNAV) Accuracy (m) Alert Limit (m) Integrity Risk LNAV 220 556 10-7 /hour RNP 0,1 92 184 10-7 /hour 11

H-ARAIM operation targets in Surveillance Automatic Dependent Surveillance Broadcast (ADS-B) applications uses GNSS positioning in ADS-B report Two types of ADS-B mandates have been issued currently > ADS-B mandate targeting non-radar airspace with the objective to provide radar-like separation services (e.g. Australia, Canada, Singapore, Fiji, Vietnam, etc.). > ADS-B mandate targeting ADS-B use in addition to radar based on RTCA DO-260 [6] - ADS-B mandate considered in Europe and in the United States - EU and US mandates are more stringent in terms of positioning information to be reported by the aircraft Accuracy (m) Alert Limit (m) Integrity Risk Europe Mandate 185 1111 10-7 /hour US Mandate 92 370 10-7 /hour 12

ARAIM simulation platform Space Segment Number of constellation Number of satellite Frequency broadcasted A simulation platform has been built with respect to the ARAIM concept architecture User segment User Grid Time setting User error models User ARAIM algorithm ISM configuration URA Psat Pconst Bnom 13

Operational scenarios: Objectives Provide simulation framework to assess the performance of the ARAIM algorithm for horizontal based operations Characterize the robustness of H-ARAIM operations Identify the most sensitive parameters on H-ARAIM performance Provide initial recommendation on realistic service commitment targets 14

Operational scenarios: Overview Operational scenarios take into account: > Potential nominal and fall back mode of the future DFMC receiver - Recent information on the Galileo IOC and FOC configuration [7] - The 2014 Federal Radio Navigation Plan [8] indicating that the GPS L5 FOC will be postponed to 2024 > Main inputs related to the ARAIM algorithm processing or the information provided by the ISM Scenarios introduced in this presentation: > Constellation/Satellite failure impact scenario > Satellite clock and ephemeris sensitivity scenario > Constellation/Satellite geometry impact scenario including - Downgraded or partial Galileo constellation design scenarios - Downgraded or partial GPS constellation design scenarios - Non-nominal GPS constellation design scenarios 15

Operational scenarios: Assumptions and Model Assumption > 5 mask angle and all in view - No implementation of minimum standard requirement in terms of tracking channel > 10 days of simulation sampled at 5 min > 5 *5 user grid over latitudes [-90 ;90 ] Model > Measurement error model as described in RTCA DO 229D [9] 2 2 - σ UERE = σ URA + σ 2 2 2 RX + σ MP + σ tropo plus nominal bias considered > Troposphere model of RTCA DO 229D [9] > Multipath and receiver noise based on SESAR 9.27 recommendations Constellation > GPS + Galileo scenarios case > GPS constellation simulated as provided in GPS SPS [10] - 24 satellites in a nominal configuration > Galileo constellation simulated as provided in latest public document [7] - 24 satellites in a nominal configuration Algorithm: ARAIM user algorithm [3] 16

Operational scenarios: Assumptions and Model Simulation reference setting > The following table provides the reference settings of the H- ARAIM algorithm used in simulation. > Each scenario introduce the specific parameters that is modified having in mind that the other or set according the reference table Parameters Settings Constellations 24 + 24 Signals URA / URE 1 / 0.5 L1/E1 + L5/E5a SISA / SISE 1,5 / 0,75 Bnom 0,75 P satgal / P satgps 10-5 / 10-5 P constgal / P constgps 10-5 / 10-5 17

Results: Constellation/Satellite Failure Scenario Operational 99.9 % HPL RNP 0.1 LNAV US ADS-B EU ADS-B Scenario (meters) Availability Availability Availability Availability Reference 20.26 100% 100% 100% 100% case Degraded 22.15 100% 100% 100% 100% Pconst effect Degraded 22.33 100% 100% 100% 100% Galileo case Realistic case 23.08 100% 100% 100% 100% NSE requirement below 30m is sufficient to provide generous FTE budget margin for RNP 0.1 applications in a 24+24 constellation case 100 % Availability reached in each scenario. > Limited impact observed on the 99.9% HPL > Not a key parameter in H-ARAIM compared to LPV 200 ARAIM analysis Parameters Settings Constellation 24 + 24 Signals L1/L5 and E1/E5a URA / URE 1 / 0.5 SISA / SISE 1,5 / 0,75 Bnom 0,75 Scenarios Reference case description P satgal / P satgps : 10-5 P constgal / P constgps : 10-5 Degraded Pconst effect P satgal / P satgps : 10-5 P constgal / P constgps : 10-4 Degraded Galileo case P constgps / P satgps : 10-5 P constgal / P satgal : 10-4 Realistic case P satgal / P satgps : 10-5 P constgal : 10-3 P constgps : 10-8 Demonstration of P const at 10-3 and P sat at 10-4 level from core constellation service provider (CSP) may be sufficient to sustain civil aviation needs for horizontal applications 18

Results: Reference Case Details 19

Results: Satellite Clock & Ephemeris Scenario Operational Scenario Optimistic GPS and Galileo Realistic GPS and Galileo Worst case Galileo 99.9 % HPL RNP 0.1 LNAV US ADS-B EU ADS-B (meters) Availability Availability Availability Availability 20.26 100% 100% 100% 100% 32.71 100% 100% 100% 100% 33.41 100% 100% 100% 100% Increased values for URA and SISA have a more significant impact on the results than low Psat/Pconst on the 99.9% HPL figure > but not on the availability results The worst case has been built upon the current GPS broadcasted URA value and the worst case SISA that could be encoded by Galileo > Leads to increase of 13 meters on the 99.9 % HPL which still provides a lot of margin compared to the requirements for all horizontal applications Parameters Settings Constellation 24 + 24 Signals L1/L5 and E1/E5a Bnom 0,75 P satgal / P satgps 10-5 / 10-5 P constgal / 10-5 / 10-5 P constgps Scenarios description Optimistic case URA = 1 m / URE = 0,5 m SISA = 1,5 m / SISE = 0,75 m Realistic case URA = 2,4 m / URE = 2 m SISA = 3 m / SISE = 1,5 m Worst Galileo case URA = 2,4 m / URE = 2 m SISA = 6 m / SISE = 3 m 20

Results: Constellation/Satellite Design Scenario Operational Scenario 24 GPS + 24 GAL 24 GPS + 18 GAL 27 GPS + 24 GAL 27 GPS + 18 GAL 23 GPS + 23 GAL with the DOP method 23 GPS + 23 GAL removing PRNs 2 99.9 % HPL RNP 0.1 LNAV US ADS-B EU ADS-B (meters) Availability Availability Availability Availability 20.26 100% 100% 100% 100% 1830 48.72% 57.50% 53.76% 60.76% 669.3 98.97% 98.96% 98.63% 100% 1830 48.72% 57.50% 53.76% 60.76% 1033 99.81% 99.85% 99.85% 99.96% 770.2 99.85% 99.89% 99.85% 100% Parameters Settings Signals L1/L5 and E1/E5a URA / URE 1 / 0.5 SISA / SISE 1,5 / 0,75 Bnom 0,75 P satgal / P satgps 10-5 / 10-5 P constgal / 10-5 / 10-5 P constgps H-ARAIM availability is above 99.8% in GPS/GAL 23 satellites downgraded constellation situation Sensitivity of ARAIM to the constellation design and number of satellites > An increased number of satellites don t necessarily bring additional performance benefits > Algorithm is very sensitive to partial / IOC constellations with the failure probability model used 21

Results: Partial Galileo Constellation Details Additional analysis is conducted to further characterise this limitiation in terms of performance using > Recent information on 10-8 P const for GPS [11] > Downgrading satellite scenario for GPS 23

Results: Partial Galileo Constellation Scenario Operational Scenario 99.9 % HPL (meters) RNP 0.1 Availability LNAV Availability US ADS-B Availability EU ADS-B Availability Optimistic P satgal = 10-5 26.87 100% 100% 100% 100% Medium P satgal = 10-4 27.44 100% 100% 100% 100% Worst P satgal = 10-3 27.48 100% 100% 100% 100% Parameters Settings Constellations 24 GPS + 18 GAL Signals L1/L5 and E1/E5a URA / URE 1 / 0.5 SISA / SISE 1,5 / 0,75 Bnom 0,75 P satgps 10-5 P constgal / 10-3 / 10-8 P constgps The targeted applications are available at 100% A nominal high performing constellation mixed with a constellation with a limited service record could bring operational benefits > Overcoming current ABAS/RAIM limitations of operations based GPS L1 signals only. 24

Results: Partial GPS Constellation Scenario Operational Scenario 99.9 % HPL (meters) RNP 0.1 Availability LNAV Availability US ADS-B Availability EU ADS-B Availability Optimistic P satgal = 10-5 Infinite 47.39% 56.65% 53.35% 63.42% Medium P satgal = 10-4 Infinite 47.35% 56.57% 52.83% 63% Worst P satgal = 10-3 Infinite 47.27% 56.49% 52.79% 62.86% Parameters Settings Constellations 18 GPS + 24 GAL Signals L1/L5 and E1/E5a URA / URE 1 / 0.5 SISA / SISE 1,5 / 0,75 Bnom 0,75 P satgps 10-5 P constgal / 10-3 / 10-8 P constgps A very low level of availability is obtained > Due to the fact that not enough satellites where available in some areas when the Galileo constellation and one GPS satellite are out. > Same number of satellites is simulated compared to the previous results The constellation with the better failure probability needs to be well populated to sustain a user availability of anything near 99%. > Additional simulations have indicated that a 99% availability target can be achieved with 21 GPS satellites. 25

Non-nominal GPS constellation Operational Scenario 99.9 % HPL (meters) RNP 0.1 Availability LNAV Availability US ADS-B Availability EU ADS-B Availability Reference case 20.26 100% 100% 100% 100% Modified 24 GPS constellation 78.07 100% 100% 100% 100% Parameters Settings Constellations 24 GPS + 24 GAL Signals L1/L5 and E1/E5a URA / URE 1 / 0.5 SISA / SISE 1,5 / 0,75 Bnom 0,75 P satgal / P satgps 10-5 / 10-5 P constgal / 10-5 / 10-5 P constgps The availability of the targeted operations has not been harmed because of the high level of horizontal alert limit Increase of 280% of the 99.9 % HPL 26

A B C H-ARAIM benefits analysis Future challenges Conclusion 27

Main challenges for H-ARAIM Core constellations commitments ISM dissemination and implementation in the receiver ARAIM algorithm complexity ARAIM concept of operation and standardisation 28

Core constellation commitments The Integrity Support Message (ISM) information will not change the performance of H-ARAIM except if the P const goes below 10-7. > Such performance will provide a 100% availability even with a low number of satellites from the second constellation. > Drop of performance observed with an incomplete Galileo constellation is fully mitigated by a strong commitment on failure probabilities for GPS. > Some values of P sat and P const have a significant impact on the final user performance but not all combinations. There is a reduced need to qualify a new CSP with a very low P const for H-ARAIM as long as a robust constellation with low P const is used in addition The number of satellites and their slot alignment within the orbit shall be carefully monitored > Especially for the established constellation GPS 29

ISM issues The ISM and the means to disseminate the information is a key driver in performance/cost/complexity/readiness analysis > Different ISM architectures based on an on-line scheme or an off-line scheme have been introduced [4] > An ICD has been recently proposed describing the ISM message content [12] Results indicate that a dynamic ISM may not be required > H-ARAIM can operate under severe failure conditions > H-ARAIM can operate with degraded performance with respect to clocks and ephemeris error and downgraded satellites conditions An ARAIM receiver with fixed and conservative assumption with regards to ISM parameter may be capable to sustain operational needs > Accommodate receiver manufacturer concerns on complexity, cost and certification burdens expressed in EUROCAE and RTCA An updatable on-board ISM provides benefits in the long term as it can take credit of core constellations service changes without impacting airborne equipment certification A trade off has to be found on H-ARAIM to set a receiver architecture that can: > Accommodate change in the CSP performance > Minimize standardization/certification cost 30

ARAIM algorithm complexity Iteration loops are implemented for the computation of the HPL and VPL in the ARAIM algorithm The flexibility of ISM parameters may lead to different number of subsets to be evaluated > Non fix architecture > The computation power require may change pending on the P sat /P const information used These are limitations for the standardisation of the current ARAIM algorithm into certified avionics receiver 31

H-ARAIM ConOps and Standardisation There is an opportunity to embed H-ARAIM in the next generation of avionics receiver as a fall back integrity monitoring scheme to SBAS and GBAS. Standardisation bodies will require that a concept of operation is further developed to consider standardisation related activity. > For the definition of system SARPS > For the definition of user equipment MOPS It should include at least : > Complete description of the H-ARAIM architecture > Definition of message and retained solution for the provision of the ISM content > Description of the interaction between ARAIM actors, operation and system components > Allocation of responsibility over the different actors - CSP role and responsibility - ANSP role and responsibility - ISM provider role and responsibility - Receiver and aircraft role and responsibility 32

A B C H-ARAIM benefits analysis Future challenges Conclusion 33

A promising concept H-ARAIM is an interesting concept > Overcoming current operation limitation with GPS L1 + RAIM > Providing robustness navigation and surveillance service performance > Aligning its design with constellation failure and multiple satellite failures conditions > Taking credits of multiple constellations and dual frequency measurement There is a need to further develop an ABAS DFMC concept to back up ground based augmentation system solution in future DFMC receiver > H-ARAIM could be this new concept 34

with still challenges to be tackled Lot of uncertainties in the concept and architecture make the H-ARAIM concept not as mature as current SBAS DFMC concept. > ISM definition > User algorithm structure > Role and responsibility of ARAIM actors Commitments will be needed on core constellation failure probabilities to further developed > ICAO standard > User receiver standard 35

Thank you for the attention Thanks to Egis Partners on ARAIM: Questions? European Navigation Conference 2015 09 / 04 / 2015 36

Acronyms Acronym Description Acronym Description AAIM Airborne Autonomous Integrity Monitoring ISM Integrity Support Message ABAS Airborne Based Augmentation System LNAV Lateral Navigation APV Approach with Vertical Guidance LPV Localizer Performance with Vertical Guidance ARAIM Advanced RAIM NPA Non Precision Approach CSP Constellation Service Provider PBN Performance Based Navigation DFMC Dual Frequency Multi Constellation RAIM Receiver Autonomous Integrity Monitoring FOC Final Operational Capability RNP Required Navigation Performance GBAS Ground Based Augmentation System SARPS Standard and Recommendation Practices GNSS Global Navigation Satellite System SBAS Satellite Based Augmentation System HPL Horizontal Protection Level SISA Signal In Space Accuracy ICAO International Civil Aviation Organisation SV Satellite Vehicle ICD Interface Control Document URA User Range Accuracy IOC Initial Operational Capability VPL Vertical Protection Level European Navigation Conference 2015 09 / 04 / 2015 37

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