Aviation Considerations for Multi-Constellation GNSS

1. Aviation Considerations for Multi-Constellation GNSS Leo Eldredge, GNSS Group Federal Aviation Administration (FAA) December 2008 Federal Aviation Administration

2. Introduction • GPS is an important component of today’s aviation guidance infrastructure • Its role will continue to increase over the coming years • Future GNSS constellations will also become important to contributors • However, their incorporation must be done with great care as the integrity requirements for aircraft guidance are very stringent • Less than 10-7 probability of misleading information • International standards define different types of augmentation to achieve this level of integrity

3. Integrity Monitoring • Space-based and ground-based augmentation systems provide independent monitoring of the GPS signals through calibrated ground monitors • Requires ground monitoring network and communication channel to aircraft • Receiver Autonomous Integrity Monitoring (RAIM) compares redundant satellite measurements against each other to determine identify and eliminate large faults • Requires a larger number of ranging measurements

4. GPS Supplemental Use - 1995 • Key Feature: • Integrity Determination by the User with RAIM • Key Enabler • Requires Redundant Ranging Sources • Key Benefit • Provides horizontal guidance for aircraft • Key Challenge • Accuracy & Availability

5. Key GPS Performance Parametersthat Support Horizontal Guidance • Good accuracy • Vertical and horizontal accuracies better than 10 m 95% • Nominal ranging accuracy better than 2 m 95% • Reliable signals • Low rates of failure - 10-5/hour/satellite and better • Good coverage • Good distribution of satellites in the sky • Good signal availability • Rarely more than one primary satellite out at a time

6. Two Civil Frequencies • The ionosphere creates the largest source of uncertainty affecting today’s use of GPS for aviation • When GPS L5 becomes widely available it will become possible to to directly remove the ionospheric influence • May allow RAIM to support vertical navigation • Unfortunately, the two frequency combination increases the effects of other noise sources • It is desirable to reduce these noise terms and/or add more satellites to offset this increase

7. Horizontal and Vertical Navigation • GNSS vertical accuracy is worse than horizontal • Satellites below the aircraft are blocked by Earth • Aviation requirements are more strict in the vertical • Vertical maneuvers bring the aircraft closer to the ground • Therefore, it is much harder for GNSS to meet aviation vertical guidance requirements • But, absolute vertical guidance from GNSS offers a strong safety benefit • Avoids manual calibration • Enables smooth, continuous approach paths • Want to provide vertical and horizontal guidance

8. New Constellations Provide New Opportunity • RAIM requires a sufficient number of satellites to assure redundancy and accuracy • Availability of horizontal guidance through RAIM not always 100% with today’s GPS constellation • If new GNSS constellations provided similar signals and performance to GPS, there would be an opportunity to combine information to expand seamless global navigation • Better horizontal performance and availability • If these signals are available on multiple civil frequencies there is the strong potential for vertical guidance using RAIM • Much greater utility than available today

9. Interoperability of Integrity • Interoperability should be a goal not just for GNSS signals, but for integrity provision as well • Augmentation systems already internationally coordinated • Open service signals should target performance comparable to or better than GPS L1 signals today • Different providers may make different design choices and different assurances • However, it is important to establish a common understanding of how RAIM depends on GNSS performance and how signals from different services could be combined to improve RAIM • Augmentation systems also benefit from new constellations • Cooperation and transparency are essential

10. Benefits of Multi-Constellation RAIM • Combining signals from multiple constellations can provide significantly greater availability and higher performance levels than be achieved individually • Provides a safety of life service without requiring GNSS provider to certify each system to 10-7 integrity levels • Creates a truly international solution • All service providers contribute • Not necessarily dependent on any single entity • Coverage is global and seamless

11. Requirements on New Signals and Constellations • Assure good nominal signal accuracy • Of order 1 m ranging accuracy • Perform a fault modes and effects analysis • Understand and make transparent potential faults and their effects • Assure low fault rates • Of order 10-5/SV/Hour • Assure good continuity of signals • Less than 10-5/hour probability of unexpected outages • Assure good availability of signals

12. Recommendation • Agree that GNSS constellations should seek to provide open service signals of sufficient quality to support the use of multi-constellation RAIM to allow vertical guidance of aircraft • Such signals could be incorporated into the augmentation systems as well

13. Summary • RAIM allows for worldwide aviation navigation without requiring additional ground infrastructure • Additional GNSS constellations can significantly improve performance and availability • New GNSS constellations should assure that their open service signals support RAIM • International cooperation and coordination will be essential to achieving this goal

14. Back up Slides

15. Initial Test FOC GPS L5 Production GPS-III FOC Integrity on 14 SVs Initial Test GPS-III (A, B, C) Production GPS-III+?? FOC Integrity GPS-III (+?) Production +16 SVs User Transition Time L5 Design L5 Implementation Cutover WAAS Operational Phase III Phase IV Life-Cycle Extension WAAS Avionics Development User Transition Period Standards Long Term Schedule FY 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 - - - 40 Solar Maximum Solar Maximum Solar Maximum L2 Semi-Codeless Transition TBD/Unfunded

16. Galileo (EU) GLONASS GPS Other? Future Considerations

17. Pathway for Aviation Use of GNSS 2003 • Single Frequency User (L1) • ABAS: RAIM (Supplemental) • SBAS: North America, Japan, Europe, India • GBAS: Operational Approval in 2009 2018 • Dual Frequency SBAS & GBAS • L1 & L5 for Iono & RFI • 24 SVs Minimum • 10-4 Failure Rate • Improved Failure Descriptions • GBAS for Category-III • Dual Frequency ABAS • L1 & L5 for Iono & RFI • 30+ Interoperable SVs (Multiple-GNSS?) • 10-4 Failure Rate • Improved Failure Descriptions • Open Service Safety of Life (SoL) 2030 • GNSS-Integrated Integrity • GPS III with Integrity (24+ SVs) or Other GNSS SoL • L1 & L5 User for Iono & RFI • 10-7 Failure Rate (Clock, Ephemeris, SDM ) • Improved Failure Descriptions • GBAS for Category-III

18. Summary • RAIM Currently Limited to Supplemental Use • GPS With Augmentation Providing Precision Approach • GPS Modernization Unlikely to Replace SBAS Before 2040 • Multi-Constellation GNSS Interoperability Key Enabler for ARAIM • Interoperability of GNSS SoL Services Needs to be Coordinated