walter_IWG26_L5ICD
Download
Report
Transcript walter_IWG26_L5ICD
L1/L5 WAAS Support
Todd Walter
Stanford University
http://waas.stanford.edu
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)
2
Protection Levels (J)
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
3
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
4
Clock parameters in MT-12 like
message as part of correction
Identification of service regions
Ephemeris content validation
Authentication of service
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
5
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
6
Recommended by RTCA + EUROCAE
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
7
Current offsets greater than dynamic
range of the corrections
Splits correction information across
different messages
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
8
Needs to be coordinated among SBASs
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
9
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
10
Needs to be loss tolerant
Key management is an issue
Next Steps
Document agreed upon ICD elements
similar to appendices A & J of MOPS
Exchange documents to ensure
common understanding
Comment on descriptions
11
Identify missing details
Discuss options to address identified
issues
Update documentation with new
agreements
12