# Presentation: 486123

## FAA GNSS Evolutionary Architecture Study

**PNT Advisory Board**
**Leo Eldredge, FAA GNSS Group**
**March 27, 2008**

## FAA Satellite Navigation Vision

## WAAS Architecture

- 38 Reference
- Stations

- 3 Master
- Stations

- 4 Ground
- Earth Stations

- 2 Geostationary
- Satellite Links

- 2 Operational
- Control Centers

## WAAS LPV Coverage- Current 2008 - 

**WAAS LPV Coverage****- Current 2008 - **

## WAAS RNP Coverage- Current -

## 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**

- Operational

- Launch
- 7/12

- Operational

- Launch
- 7/15

- ~6,000

- WAAS Procedure Development

- FOC

## 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 ~2020-2030 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

## GEAS Panel

| Geoff Harris | G-Wing/Aerospace |
| --- | --- |
| Karl Shallberg | GREI |
| Boris Pervan | IIT |
| John Dobyne | G-WIng/ARINC |
| Karl Kovach | G-Wing/Aerospace |
| Eric Atschuler | Sequoia Research |
| Chris Hegarty | MITRE |
| Young Lee | MITRE |
| JP Fernow | MITRE |
| Frank Van Graas | Ohio University |
| Juan Blanch | Stanford University |
| Todd Walter | Stanford University |
| Pat Reddan | Zeta Associates |
| AJ Van Dierendonck | Zeta Associates |

| Deane Bunce (Co-Chair) | FAA ATO-W |
| --- | --- |
| Per Enge (Co-Chair) | Stanford University |
| Leo Eldredge | FAA ATO-W |
| Deborah Lawrence | FAA ATO-W |
| Calvin Miles | FAA ATO-W |
| Kevin Bridges | FAA AVS |
| Hamza Abduselam | FAA AVS |
| Tom McHugh | FAA ATO-P |
| Bill Wanner | FAA ATO-P |
| David Schoonenberg | NSSO |
| Mike David | NSSO |
| Karen Van Dyke | RITA/Volpe |
| Ed Sigler | GPS TAC |
| Tim Murphy | Boeing Aircraft |

## 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)

## 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**

## GNSS integrity Channel (GIC)

**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

**Notes:**
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

## 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**

## Relative RAIM: Range Rate Residuals

**Most recent monitored position with****corresponding horizontal protection level (HPL) and vertical protection level (VPL)**

**Propagate the most recent monitored position**** with carrier phase only**

**Growth in HPL and VPL due to****RAIM on the carrier phase-based****delta position updates**

- VPL

- HPL

*From Prof. van Graas, Ohio University*

**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

**Notes:**
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)

## Absolute RAIM

**Key Feature:**
- Real-Time Integrity Determination by the User (ABAS)
**Key Enabler:**
- Redundant Ranging Sources
- 30 or More SVs
**Key Benefit**
- Latency Relaxed to Hours

**Notes:**
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)

## Preliminary Results

|  | Constellation |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- |
| Architecture | 24 minus 1 | 24 | 27 minus 1 | 27 | 30 minus 1 | 30 |
| GIC | 86.6% | 100% | 97.8% | 100% | 100% | 100% |
| RRAIM with 
30 s coasting | 81.2% | 99.4% | 96.8% | 100% | 100% | 100% |
| RRAIM with 
60 s coasting | 74.4% | 98.5% | 92.8% | 100% | 100% | 100% |
| RRAIM with 300 s coasting | 28.0% | 76.1% | 52.3% | 99.6% | 93.9% | 100% |
| ARAIM | 7.80% | 44.7% | 30.6% | 94.1% | 90.5% | 100% |

**Note:  Predictions Valid for WAAS-Like Integrity Assured URA’s of 1 Meter or Less**

## GEAS Next Steps

**Phase 1 Report – Completed**
- 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

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