Interference Testing for Support of UAT Standards

1
Interference Testing for Support of UAT Standards
AMCP WGC3/WP17

• Presented by US Member
• Summary
• The FAA and RTCA are undertaking an extensive
  test and simulation program to support the
  introduction of UAT into the 960-1215 MHz band.
  The test portion of this effort employs actual
  equipment and established interference
  environments including DME, L16 and UAT self
  interference. This briefing presents the progress
  and results to date of the testing program.

2
Background

• UAT frequency assignment will be in band where
  compatibility with DME and the military L16
  system are issues.
• DME tolerance to UAT
• UAT tolerance to DME and L16 and self
  interference
• 978 MHz identified as the best frequency for
  UAT
• identified in Annex 10 as emergency use only
  for DME due to paired VHF nav conflict with FM
  broadcast
• used by DME ramp testers--very low power and
  close range
• no DME assignments in US minimal assignments (6)
  in Europe

3
Background (2)

• Extensive laboratory measurements have been made
  in support of UAT standards
• use actual equipment
• for validating models used for optimizing system
  parameters

4
UAT Interference on DME
5
UAT--gt DME Background

• UAT will reside in portion of band used by DME
  ground beacons only (reply channel). DME
  interrogation channel not a factor for UAT.
• Testing has been performed on 4 representative
  DME avionics units to determine their tolerance
  to UAT transmissions
• Bendix King KD-7000, circa 1978
• Narco DME-890, General Aviation
• Honeywell KDM-706A (Eurocontrol recommended)
• Rockwell/Collins DME 900 (Eurocontrol recommended)

6
Testing Approach

• Use Established Thresholds for DME performance
• ASOP is the test condition that renders the DME
  able to acquire
• BSOP is the test condition that causes the DME to
  break lock
• these thresholds were found to be nearly
  coincident
• Test conditions
• DME avionics test set provides desired DME reply
  signal at a variable reply efficiency--accounts
  for load on the ground station
• Variable DME desired signal level--relative to
  MOPS sensitivity level of -83 dBm
• Measurements taken
• establish SIR threshold when desired DME pulse
  pairs always overlapped with UAT message
• establish minimum reply efficiency threshold with
  no UAT interference

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Test-bed block diagram
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Relate Measurements to Future UAT Interference

• Establish distribution of UAT message amplitudes
  in time using high fidelity simulation of UAT in
  future environment
• accounts for distribution of UAT a/c in future
  environment
• accounts for UAT transmit protocol
• scale result by 0.7 to account for reply
  unavailability due to full load on DME ground
  beacon
• Relate resulting UAT interference environment to
  measured thresholds for minimum SIR and minimum
  reply efficiency to determine operating margin
  with UAT interference

9
Results (1)

• All units operated at reply efficiencies as low
  as 30--even at sensitivity
• SIR requirements with 100 overlap of DME pulse
  pair with UAT interference varied from 2 to 11
  dB for the four units
• Reply efficiency margins (_at_ -83 dBm MOPS
  sensitivity level) resulting from simulated UAT
  interference environment and measured SIR
  requirements varied in the range of 20-30 for
  the four units

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Results (2)
Minimum sensitivity required by DME MOPS
Reply efficiency margin
Minimum reply efficiency for acceptable DME
operation
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Summary/Conclusions

• UAT interference environment assessed is
  conservative
• it was Cochannel to DME
• it was at future LA2020 traffic level
• it assumed fully loaded DME ground beacon
• DME units tested represent large user population
• Measurements of the four DMEs are basically
  consistent with each other, i.e. no surprises.
• UAT operations should not adversely degrade DME
  operation--even when cochannel.

12
Interference to UAT
13
Background

• Tuning the UAT waveform to the expected
  interference environment has been a major
  activity of the UAT MOPS WG to date
• Waveform level changes have been made as a result
  of simulation models developed by JHUAPL and
  MITRE
• increases to Reed Solomon Forward Error Code
  rates
• narrowing the IF filter BW
• reduction in synchronization threshold
• A small number of Capstone UATs have been
  modified (Pre-MOPS units) to reflect these
  changes for purposes of
• validating analysis and simulations
• developing practical and effective MOPS tests for
  waveform compliance

14
Approach

• Two levels of testing will be performed against
  various conditions
• Message Error level--gtmeasures net effect on
  performance for a limited set of environments.
  Used for spot check of simulation models
• Bit Error level--gt for detailed model validation,
  requires more control of signal and interference
  environment and more sophisticated measurement
• Tests performed with DME, L16 and self
  interference, separately and in combination

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Status

• Pre MOPS units delivered 14 Sept
• MER testing with DME and L16 interference applied
  separately was begun 19 Sept--some data now
  available
• BER testing is in progress
• MER testing in full interference environment
  expected to be complete in early December

16
MER Testing

• Sensitivity with NO interference
• With L16 at 100 and 200 TSDF (extreme
  non-operational environments used to ensure some
  message failures)
• With one and two DMEs at 1 MHz displacement, 3600
  ppps, 12 usec
• All tests use Long ADS-B and Ground Uplink
  messages
• Results to date show good correlation with model
  predictions.

17
Comparing Measurement to Simulation
Not representative of operational environment
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Summary

• DME operation should not be adversely impacted by
  introduction of UAT--even when cochannel
• UAT has been designed to operate in L16 and DME
  environment.
• Bench measurements on Pre MOPS units made to date
  are basically consistent with the performance as
  modeled in the simulation tool (results reported
  separately)
• FAA/RTCA has undertaken a significant testing
  program to support introduction of UAT into the
  band. Substantial progress has been made