1. FAA GNSS Evolutionary Architecture Study
PNT Advisory Board
Leo Eldredge, FAA GNSS Group
March 27, 2008

2. FAA Satellite Navigation Vision

3. WAAS Architecture 38 Reference Stations 3 Master Stations 4 Ground
Earth Stations
2 Geostationary
Satellite Links
2 Operational
Control Centers

4. WAAS LPV Coverage - Current 2008 -

5. WAAS RNP Coverage - Current -

6. WAAS Enterprise Schedule
FLP Segment (Phase II)
LPV-200 Segment (Phase III)
Dual Frequency (Phase IV)
GEO #2 - Inmarsat
GEO #3 – Intelsat
GEO #4 – TeleSat
GEO #5 – TBD
GEO #6 – TBD
Approach Development 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 FY
Development
Operational
FOC
Technical Refresh
Operational
JRC
Technical Refresh
Operational
JRC
Lease Extension
9/06
Launch
10/05
Operational
Operational
Launch
9/05
Operational
Launch
7/12
Operational
Launch
7/15
~6,000
WAAS Procedure Development

7. Future Considerations
GNSS Modernization
GPS Dual Frequency (L1/L5) Service Provides Foundation
Potential for Larger GNSS or Use of Multiple GNSS Constellations
User Equipment Standards Development for New Signals
WAAS Dual Frequency Upgrade
Determine Appropriate Level of Dual Frequency Integration Required to Maximize Benefit With Minimum Impact
Established GNSS Evolutionary Architecture Study (GEAS) to Investigate Long Range Planning for Dual Frequency GPS
Develop Architectural Alternatives to Provide Worldwide LPV-200 Service in the ~ Timeframe
Leverage Lessons Learned on WAAS/LAAS to Identify the Best Architecture Alternative to Meet Aviation Integrity Requirements
Participation With The GPS Wing, DoD National Security Space Office (NSSO), DOT Research & Innovative Technology Administration (RITA), and the Joint Planning & Development Office (JPDO) for NextGen

8. GEAS Panel Deane Bunce (Co-Chair) FAA ATO-W Per Enge (Co-Chair)
Stanford University
Leo Eldredge
Deborah Lawrence
Calvin Miles
Kevin Bridges
FAA AVS
Hamza Abduselam
Tom McHugh
FAA ATO-P
Bill Wanner
David Schoonenberg
NSSO
Mike David
Karen Van Dyke
RITA/Volpe
Ed Sigler
GPS TAC
Tim Murphy
Boeing Aircraft
Geoff Harris
G-Wing/Aerospace
Karl Shallberg
GREI
Boris Pervan
IIT
John Dobyne
G-WIng/ARINC
Karl Kovach
Eric Atschuler
Sequoia Research
Chris Hegarty
MITRE
Young Lee
JP Fernow
Frank Van Graas
Ohio University
Juan Blanch
Stanford University
Todd Walter
Pat Reddan
Zeta Associates
AJ Van Dierendonck

9. Determination of Integrity
Aircraft Based
Integrity is determined on board the aircraft using redundant ranging sources or sensors
e .g. RAIM, AIME, …
Ground Based
Integrity determined external to User
e.g. SBAS, GBAS, GRAS, GNSS Monitoring, …
Satellite Based
Determination of integrity is made on board the satellite using redundant components
e.g. Clock Monitoring (TKS), Signal Deformation Monitoring (SDM)

10. Layered Approach
Ultimate integrity architecture will combine threat detection at all elements
Satellite
Best time to alarm (TTA) for rapid clock & digital errors
Ground
Necessary for absolute accuracy
Aircraft offers
Direct integrity monitoring by user
Mitigating ionosphere delays and local errors
Alternatives trade the degree of aircraft based augmentation (ABAS), constellation geometric robustness, user range accuracy, and augmentation
Need to find best trade for cost, TTA, integrity performance and constellation dependency

11. GNSS integrity Channel (GIC)
Key Feature:
Integrity Determination External to the User
Key Enabler
Rapid Messaging Rate
TTA of 6.2 Sec
Key Benefit
Redundant Ranging Signals Not Required
Key Challenge
Meeting TTA
User Avionics
No RAIM/FDE Required – WAAS/SBAS extension
Dual Frequency (L1/L5) – Ionosphere Delay Estimation
Ground Segment Monitor Network
Externally Monitor and Detect All SV Faults That Affect the User
Requires Monitoring Network Capable of Continuous Monitoring of All GNSS Satellites From At Least Two Locations
Network Latency to Support Time to Alarm of 6 Seconds
Signal-In-Space
Corrections & Integrity Messages
Data Rate Comparable to SBAS Broadcast of 250 bps
Broadcast Via GEOs Or Other Suitable Means
Space Segment
Nominal 24 SV Commitment is Included in the SPS PS

12. Time-To-Alert (TTA)
A significant challenge with a worldwide system (i.e., Galileo or GPS-IIIC integrity) is meeting the 6.2 second TTA requirement
WAAS is just able to meet TTA with its North American network
A different approach is required for worldwide system
Allocate the TTA requirement to the aircraft or satellite fault detection

13. Relative RAIM: Range Rate Residuals
Key Feature:
Real-Time Integrity Determination By User Using Carrier Phase Approach
Key Enabler
External Monitoring
Redundant Geometry
Key Benefit
TTA Latency Relaxed to Minutes
Propagate the most recent monitored position with carrier phase only
DHPL
DVPL
Most recent monitored position with corresponding horizontal protection level (HPL) and vertical protection level (VPL)
User Avionics
Integrity/Correction Messages Provide Starting Point
Dual Frequency (L1/L5) – Ionosphere Delay Estimation
RRAIM Algorithms Check Residuals Between Carrier Phase Measurements and Estimated Change in Position
Ground Segment Monitor Network
Requires Monitoring Network Capable of Continuous Monitoring of All GPS Satellites From At Least Two Locations
Time to Alarm of Up to 10 Minutes is Tolerable
Signal-In-Space Broadcast
RRAIM Coasting Enables Slow Integrity/Correction Messages
Suitable for SBAS GEOs, Possibly GNSS Messages or Other Low Data Rate Alternatives
Space Segment
Viable for Constellation of 27 or More (note 24 SV Commitment is Included in the SPS PS)
Growth in HPL and VPL due to RAIM on the carrier phase-based delta position updates
From Prof. van Graas, Ohio University

14. Absolute RAIM Key Feature: Key Enabler: Key Benefit
Real-Time Integrity Determination by the User (ABAS)
Key Enabler:
Redundant Ranging Sources
30 or More SVs
Key Benefit
Latency Relaxed to Hours
Similar to today’s RAIM, both use smoothed pseudoranges, absolute position fixes, and geometric redundancy
However, ARAIM requires tighter confidences, improved algorithms, and stronger constellations to provide horizontal and vertical guidance
Constellation requirement much more strict than today’s RAIM
Avionics
Receiver Autonomous Integrity Monitoring as the Primary Integrity Solution
Dual Frequency (L1/L5) – Ionosphere Delay Estimation
Ground Segment Monitor Network
Continuous Monitoring of All GPS Satellites From At Least Two Locations
Update error variance and mean for each Satellite
Time to alarm of 1 or more hours is tolerable
Signal-In-Space
Reliability Estimates (a Priori Probability) for Each SV
Broadcast Via GNSS or GEO Messages
Space Segment
Requires 30 or More GNSS SVs (note 24 SV Commitment is Included in the SPS PS)

15. Preliminary Results Constellation Architecture 24 minus 1 2427
30 minus 1 30
GIC
86.6%
100%
97.8%
RRAIM with
30 s coasting
81.2%
99.4%
96.8%
60 s coasting
74.4%
98.5%
92.8%
RRAIM with 300 s coasting
28.0%
76.1%
52.3%
99.6%
93.9%
ARAIM
7.80%
44.7%
30.6%
94.1%
90.5%
Note: Predictions Valid for WAAS-Like Integrity Assured URA’s of 1 Meter or Less

16. GEAS Next Steps Phase 1 Report – Completed Future Work Plan
Ready for Distribution
Future Work Plan
WAAS RRAIM Architecture
Detailed Analysis and Design Leading to Implementation of the RRAIM Architecture as the Dual Frequency Architecture for WAAS
Support to GPS-III/OCX Integrity & Continuity Assurance Activities
Provide Assistance to GPS Wing Program Office Team

17. Questions http://gps.faa.gov