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

8 December 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 probability of misleading information –International standards define different types of augmentation to achieve this level of integrity

8 December 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

8 December GPS Supplemental Use 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

8 December Key GPS Performance Parameters that 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 /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

8 December 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

8 December 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 December 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

8 December 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

8 December 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 integrity levels Creates a truly international solution –All service providers contribute –Not necessarily dependent on any single entity –Coverage is global and seamless

8 December 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 /hour probability of unexpected outages Assure good availability of signals

8 December 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

8 December 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

8 December Back up Slides

FY Long Term Schedule TBD/Unfunded L2 Semi-Codeless Transition Solar Maximum GPS L5 FOCInitial Test Production GPS-III (A, B, C) GPS-III FOC Integrity on 14 SVs Initial Test Production Life-Cycle Extension WAAS Avionics User Transition PeriodDevelopment Standards WAAS Phase III L5 Implementation Operational Phase IV Cutover L5 Design User Transition Time GPS-III (+?) GPS-III+?? FOC Integrity Production +16 SVs Solar Maximum Solar Maximum

8 December Future Considerations GLONASS GPS Galileo (EU) Other?

Pathway for Aviation Use of GNSS Single Frequency User (L1) ABAS: RAIM (Supplemental) SBAS: North America, Japan, Europe, India GBAS: Operational Approval in 2009 Dual Frequency SBAS & GBAS L1 & L5 for Iono & RFI 24 SVs Minimum Failure Rate Improved Failure Descriptions GBAS for Category-III 2018 Dual Frequency ABAS L1 & L5 for Iono & RFI 30+ Interoperable SVs (Multiple-GNSS?) 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 Failure Rate (Clock, Ephemeris, SDM ) Improved Failure Descriptions GBAS for Category-III 2003

8 December 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