1. Todd Walter Stanford University http://waas.stanford.edu
L1/L5 WAAS Support
Todd Walter
Stanford University

2. Key DFMC MOPS Components
Operational goals (1.3)
Equipment classes (1.4)
Constellation assumptions (B)
Equipment & tracking requirements (2.1, 2.2, 2.3)
Environmental assumptions (2.4)
Interference environment (C )
Test requirements (2.5)
Antenna requirements (separate MOPS)
Signal specification (A)
L5 physical layer (A.2 & A.3)
Message structure and content (A.4)
Protection Levels (J)

3. Recently Agreed to L5 MOPS Changes
Expanded PRN mask
Removal of fast corrections
Single satellite correction message
Smaller quantization errors
Alert message with DFRECIs
When more than 51 SVs corrected
Full DFREs can be sent in 2 messages
Updatable DFRE table
Support for more SBAS orbit types

4. ICD Topics Still Under Discussion
L5 reversionary mode
Optional ionospheric messages
Extra clock states in the G matrix
Separate state for each constellation
Correlation of tropospheric error
Clock parameters in MT-12 like message as part of correction
Identification of service regions
Ephemeris content validation
Authentication of service

5. L5 Reversionary Mode
The FAA is not pursuing ionospheric corrections on L5
L5/E5-only RAIM should provide lateral guidance for terminal through en route
Other ANSPs may elect to define messages to permit vertical guidance in L1/E1-denied areas
These messages are not required to support dual frequency vertical guidance

6. Separate Constellation Clock States
SBAS corrections can align the time offsets between constellations
May require separate clock terms
Differences in signal structures and satellite filters can create receiver dependent biases
Adding a clock state per constellation addresses dynamic range and biases
Small increase in protection levels
Recommended by RTCA + EUROCAE

7. Inter-GNSS Clock Parameters
Clock offset states can be broadcast in MT-12 like message
MT-12 currently only used for timing
Not currently broadcast by WAAS
Could also be applied to corrections to align GNSS timescales
Current offsets greater than dynamic range of the corrections
Splits correction information across different messages

8. Identification of Service Regions
May want to assist user in finding SBAS with highest availability
Interest expressed in specifying which SBAS to use in certain areas
May want to broadcast information about other SBAS satellites
Currently supported in L1, but not used
Additional messages could be defined to meet these goals
Needs to be coordinated among SBASs

9. Ephemeris Content Verification
Addresses issue of ephemeris content change without IODE change
Instead of IODE, correction message would contain a hash of full contents
Needs a large number of bits to fully assure unique hash (>24)
Adjacent ephemerides must have different hashes
Requires more bits than easily available
Looking into alternate methods to achieve goal
Perhaps a low bit count hash with the IODE

10. Signal Authentication
FAA is interested in having ability to authenticate SBAS signal
Level of authentication to be studied
Signal only
Data contents
Bandwidth requirements TBD
May only require a message per minute
May use Q-channel
Needs to be loss tolerant
Key management is an issue

11. Next Steps
Document agreed upon ICD elements similar to appendices A & J of MOPS
Exchange documents to ensure common understanding
Comment on descriptions
Identify missing details
Discuss options to address identified issues
Update documentation with new agreements