Interference Testing for Support of UAT Standards

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

7. Test-bed block diagram

8. 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 (@ -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

10. Results (2) Minimum sensitivity required by DME MOPS Reply efficiency margin Minimum reply efficiency for acceptable DME operation

11. 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-->measures net effect on performance for a limited set of environments. Used for “spot check” of simulation models • Bit Error level--> 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

15. 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

18. 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