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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) - PowerPoint PPT Presentation
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L1/L5 WAAS Support
Todd Walter
Stanford University
http://waas.stanford.edu
Todd Walter
Stanford University
http://waas.stanford.edu
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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)
Recently Agreed to L5 MOPS Changes
Expanded PRN maskRemoval of fast correctionsSingle satellite correction message
Smaller quantization errors
Alert message with DFRECIsWhen more than 51 SVs correctedFull DFREs can be sent in 2 messages
Updatable DFRE tableSupport for more SBAS orbit types
3
ICD Topics Still Under Discussion
L5 reversionary modeOptional ionospheric messages
Extra clock states in the G matrixSeparate state for each constellationCorrelation of tropospheric error
Clock parameters in MT-12 like message as part of correction
Identification of service regionsEphemeris content validationAuthentication of service
4
L5 Reversionary Mode
The FAA is not pursuing ionospheric corrections on L5L5/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 areasThese messages are not required to
support dual frequency vertical guidance5
Separate Constellation Clock States
SBAS corrections can align the time offsets between constellationsMay 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 biasesSmall increase in protection levels
Recommended by RTCA + EUROCAE6
Inter-GNSS Clock Parameters
Clock offset states can be broadcast in MT-12 like message
MT-12 currently only used for timingNot currently broadcast by WAAS
Could also be applied to corrections to align GNSS timescalesCurrent offsets greater than dynamic range
of the correctionsSplits correction information across different
messages
7
Identification of Service Regions
May want to assist user in finding SBAS with highest availabilityInterest expressed in specifying which
SBAS to use in certain areas
May want to broadcast information about other SBAS satellitesCurrently supported in L1, but not used
Additional messages could be defined to meet these goalsNeeds to be coordinated among SBASs
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Ephemeris Content Verification
Addresses issue of ephemeris content change without IODE change
Instead of IODE, correction message would contain a hash of full contentsNeeds a large number of bits to fully assure
unique hash (>24)Adjacent ephemerides must have different hashes
Requires more bits than easily availableLooking into alternate methods to achieve goalPerhaps a low bit count hash with the IODE
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Signal Authentication
FAA is interested in having ability to authenticate SBAS signalLevel of authentication to be studied
Signal onlyData contents
Bandwidth requirements TBDMay only require a message per minuteMay use Q-channel
Needs to be loss tolerantKey management is an issue
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Next StepsDocument agreed upon ICD elements
similar to appendices A & J of MOPSExchange documents to ensure common
understandingComment on descriptions
Identify missing detailsDiscuss options to address identified
issuesUpdate documentation with new
agreements11
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