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UAT-WP-6-11 31 July 2001

UAT-WP-6-11 31 July 2001. RTCA Special Committee 186, Working Group 5. ADS-B UAT MOPS Meeting #6. Performance of Enhanced UAT in Multi-Aircraft Scenarios. Presented by James Higbie, Johns Hopkins University/Applied Physics Laboratory SUMMARY

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UAT-WP-6-11 31 July 2001

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  1. UAT-WP-6-11 31 July 2001 RTCA Special Committee 186, Working Group 5 ADS-B UAT MOPS Meeting #6 Performance of Enhanced UAT in Multi-Aircraft Scenarios Presented by James Higbie, Johns Hopkins University/Applied Physics Laboratory SUMMARY A computer simulation of UAT reception was run to predict the performance of an “enhanced” receiver using RS(48,34) decoding and 1.26 MHz or 0.8 MHz filter bandwidth. Interference scenarios included other co-site transmissions and external UAT and Link 16 transmitters, and DME transponders. The simulation conditions are described and simulation results are presented.

  2. Larry Bachman 240-228-6339 larry.bachman@jhuapl.edu as told to James Higbie, Al Muaddi & Paul Vichot Performance of Enhanced UATin Multi-Aircraft ScenariosPresentation to UAT MOPS WG531 July 2001

  3. Outline • UAT Receiver Model • Simulation Details • Performance Results: • Baseline (no DME or Link 16) • Loaded (DME & Link 16) • Link 16 & DME Excursions • Altitude of Receiving Aircraft • Airspace Restrictions • Single Switched Receiver

  4. UAT Receiver Model (1 of 4) • A new UAT receiver model was needed to handle narrower receiver bandwidths • 1.2 MHz and 0.8 MHz nominal • Comparing results of new model to previous results uncovered a bug in previous UAT model • Goes back to earliest results (TLAT) • Performance is actually better than we thought • Difference is substantial • Other-UAT interference impact was ~ 9 dB too strong • All results presented here are for corrected model • All previous multi-aircraft UAT simulation results were conservative

  5. UAT Receiver Model (2 of 4) • Incorporates all empirical data available for receiver noise and other-UAT interference: • New UPS-AT measurements on narrower bandwidth receiver • 1.2 MHz and 0.8 MHz bandwidths • Reported in WP-4-13 and WP-5-08 • Old (TLAT) JHU/APL measurements & simulation results on prototype (3 MHz) UAT • Impact of mixed interference environments • Gaussian noise + single UAT interferer • Multiple UAT interferers • Bit-level model, documented in WP-6-06

  6. UAT Receiver Model (3 of 4) • Impact of Link 16 interference: • Assumed same as white Gaussian noise for the same power in the receiver bandwidth • TX power spectrum = MITRE model in WP-2-03 • Without -73 dB broadband noise component (<= -117 dBm/MHz, = ~8 dB or more below receiver noise floor) • RX response spectrum modeled as butterworth filter • 1.2 MHz nominal: • 9-pole • 3 dB bw = 1.27 MHz vice 1.26 MHz Sawtek (“typical”) spec • 40 dB bw = 2.11 MHz = Sawtek spec • 0.8 MHz nominal: • 7-pole • 3 dB bw = 0.89 MHz vice 0.82 MHz Sawtek spec • 40 dB bw = 1.71 MHz = Sawtek spec

  7. UAT Receiver Model (4 of 4) • Impact of (external) DME interference: • On-channel: Assumed equivalent to UAT interferer at same power (averaged over each bit) • Adjacent-channel: Reduced by • 20 dB for 1.2 MHz • 40 dB for 0.8 MHz

  8. Simulation Details (1 of 7) • Assumed characteristics of each equipage class: • A0: • TX power = 37 - 41 dBm (5 - 12.5 W) • 50% basic messages, 50% extended messages • Maximum altitude increased to 18,000 ft. • A1: • TX power = 37 - 41 dBm (5 - 12.5 W) • 50% basic messages, 50% extended messages • Maximum altitude increased to 40,000 ft. • A2: • TX power = 41 - 45 dBm (12.5 - 32 W) • All extended messages • Maximum altitude = 40,000 ft. • A3: • TX power = 50 - 54 dBm (100 - 250 W) • All extended messages • Maximum altitude = 40,000 ft. Basic Message: RS(30,18), TX lasts 273 usec Extended Message: RS(48,34), TX lasts 411 usec

  9. Simulation Details (2 of 7) • Two receiver bandwidths: • 1.2 MHz • 0.8 MHz • 3 traffic density scenarios from TLAT: • “Low-Density” • Core Europe 2015 • LA Basin 2020

  10. Simulation Details (3 of 7) • 2 types of interference scenarios: • “Unloaded” = UAT + co-site • “Loaded” = UAT + co-site + Link 16 + DME • Default scenarios: • UAT = Low-Density • JTIDS “heavy” scenario [b]: 50% at –50 dBm, +350% • 1 on-channel DME • 1 adjacent-channel DME • UAT = CE 2015 • JTIDS “light” scenario • 1 adjacent-channel DME • UAT = LA 2020 • JTIDS “baseline” scenario [a]: 50% at –50 dBm, +350% • 1 on-channel DME • 1 adjacent-channel DME • Excursions: • Other JTIDS / DME combinations to determine individual impacts

  11. Simulation Details (4 of 7) • JTIDS Received Levels • Includes receiver azimuthal antenna pattern • Random bearing recomputed every second • DME source modeling • On-channel DME-- Assumed received power levels: • -60 dBm at 40,000 ft. • -53 dBm at 18,000 ft. • -40 dBm on Ground • Adjacent-channel DME • Power reduced (20/40 dB) according to receiver bandwidth • 3600 pulse-pairs per second per DME • cos2 pulse shape designed to meet DME MOPS • 12 usec pulse-to-pulse spacing • Poisson + 60-usec pulse-pair separation statistics

  12. Simulation Details (5 of 7) • 3 receiving altitudes • 40,000 ft. (default) • “Standard” altitude used for earlier runs • Receiver = aircraft with largest number of interferers in view • 18,000 ft. (excursion) • Larger number of nearby interferers than 40,000 ft. • Receiver is closer to A0/A1 transmitters • Uses same horizontal location as aircraft at 40,000 ft. • Applies to reception by all equipage classes • On the ground (excursion) • Center of scenario • RX antenna pattern assumed same as DME ground antenna

  13. Simulation Details (6 of 7) • As an excursion, analysis was restricted to receptions from aircraft in close-in airspace (default = analyze transmissions from aircraft at all altitudes) • “Close-in airspace” defined as altitude difference no more than: • 3,000 ft. for range < 3 nm (vice 1,500 ft. discussed at last WG mtg.) • 10,000 ft. for range 3-10 nm (vice 6,000 ft.) • 20,000 ft. for range 10-20 nm (vice 15,000 ft.) • Restrictions were loosened because with the original restrictions there were very few data points for the A0/A1 class

  14. Simulation Details (7 of 7) • Single Switched Receiver (excursion) vice 2 independent Receivers (default) • Antenna switching once per second = T, B, T, B, T, … • Note: Only one instantiation of each scenario was run • Vice 4 instantiations for TLAT runs • Done to limit simulation run times • Results in greater statistical fluctuations

  15. Performance Results

  16. Core Europe 2015 Unloaded

  17. LA Basin 2020 Unloaded

  18. Unloaded Performance Results • Either 1.2 MHz or 0.8 MHz filter meets MASPS / Eurocontrol synch vector update criteria in absence of DME / Link 16 • Out to 150 nm (A3), and at close ranges • Criteria met for Core Europe 2015, LA Basin 2020, (and Low-Density) scenarios • 1.2 MHz slightly better than 0.8 MHz in these scenarios at ranges covered by MASPS

  19. Low Density Unloaded Vs. Loaded (JTIDS heavy [a] + on & adj DMEs)—A3

  20. Core Europe 2015 Loaded (JTIDS light + adj DME)

  21. LA Basin 2020 Loaded (JTIDS baseline [b] + on & adj DMEs)

  22. Loaded ScenarioPerformance Impact Results • MASPS are met in Low-Density and Core Europe Loaded Scenarios for 0.8 MHz bandwidth • For transmissions from all aircraft classes • MASPS are not met in Low-Density and Core Europe Loaded Scenarios for 1.2 MHz bandwidth • Transmissions from A3 exceed MASPS at ~120 to ~130 nm • MASPS are not met in LA Basin Loaded Scenario for either bandwidth • A0/A1 exceeds at ~15 nm • A2 exceeds at ~30 nm • A3 exceeds at ~70 nm (1.2 MHz) or ~90 nm (0.8 MHz)

  23. 1.2 MHz, Low Density Loaded Excursions(JTIDS heavy, light, or off; on-channel DME on or off)

  24. 0.8 MHz, Low Density Loaded Excursions(JTIDS heavy, light, or off; on-channel DME on or off)

  25. 1.2 MHz, Core Europe 2015 Loaded Excursions(JTIDS light or heavy; 1 or 2 adj-channel DMEs)

  26. 0.8 MHz, Core Europe 2015 Loaded Excursions(JTIDS light or heavy; 1 or 2 adj-channel DMEs)

  27. 1.2 MHz, LA Basin 2020 Loaded Excursions(JTIDS on or off; on-channel DME on or off)

  28. 0.8 MHz, LA Basin 2020 Loaded Excursions(JTIDS on or off; on-channel DME on or off)

  29. Link 16 & DME Excursion Results • Little difference in impact is observed between light and heavy JTIDS scenarios • Evaluations may only need to use “baseline” JTIDS • An on-channel DME causes more degradation than JTIDS • Removing JTIDS or the on-channel DME from the Low-Density loaded scenario allows the 1.2 MHz bandwidth to pass MASPS • A3 only considered • Removing the on-channel DME from the LA Basin loaded scenario allows the 0.8 MHz bandwidth to pass MASPS • 1.2 MHz exceeds MASPS at ~130 nm

  30. Core Europe 2015 Loaded, 1.2 MHzA0/A1/A2 at 3 Reception Altitudes

  31. Core Europe 2015 Loaded, 1.2 MHzA3 at 3 Reception Altitudes

  32. Core Europe 2015 Loaded, 0.8 MHzA0/A1/A2 at 3 Reception Altitudes

  33. Core Europe 2015 Loaded, 0.8 MHzA3 at 3 Reception Altitudes

  34. LA Basin 2020 Loaded, 1.2 MHzA0/A1/A2 at 3 Reception Altitudes

  35. LA Basin 2020 Loaded, 1.2 MHzA3 at 3 Reception Altitudes

  36. LA Basin 2020 Loaded, 0.8 MHzA0/A1/A2 at 3 Reception Altitudes

  37. LA Basin 2020 Loaded, 0.8 MHzA3 at 3 Reception Altitudes

  38. Reception AltitudePerformance Impact Results • Performance at 18,000 ft. receive altitude is comparable to performance at 40,000 ft. • A0/A1 reception slightly better (as expected) • For the loaded scenarios evaluated, an aircraft on the ground meets 12-sec SV update time out to: • A0/A1: ~20 nm for CE2015, ~40 nm for LA2020 • 0.8 MHz slightly better than 1.2 MHz bandwidth • A2: ~45 nm for 1.2 MHz bandwidth, ~60 nm for 0.8 MHz • Loaded LA2020 somewhat more severe than Loaded CE2015 • A3: >150 nm for CE2015, ~135 for LA2020 • 0.8 MHz slightly better than 1.2 MHz bandwidth

  39. LA Basin 2020 Loaded, 18K altitude, 1.2 MHzImpact of Airspace Restriction

  40. LA Basin 2020 Loaded, 18K altitude, 0.8 MHzImpact of Airspace Restriction

  41. Airspace Restriction Performance Impact Results • Airspace Restriction, at least the loose ones evaluated, do not affect SV Update Times • The restrictions on receptions from nearby altitudes were not observed to have any impact on 95% SV Update Time in the Core Europe 2015 Loaded Scenario at 18K altitude • The restrictions were observed to have negligible impact in the LA Basin 2020 Loaded Scenario at 18K altitude, and only on the A3 aircraft • Both receiver bandwidths were looked at • Tighter restrictions may require very long simulation runs to evaluate

  42. MSR Performance:Core Europe 2015 Loaded, 1.2 MHz, 40,000 ft.Impact of Single Switched Receiver

  43. State Vector Update Performance:Core Europe 2015 Loaded, 1.2 MHz, 40,000 ft.Impact of Single Switched Receiver

  44. Core Europe 2015 Loaded, 0.8 MHz, 40,000 ft.Impact of Single Switched Receiver

  45. Core Europe 2015 Loaded, 1.2 MHz, 18,000 ft.Impact of Single Switched Receiver

  46. LA Basin 2020 Loaded, 0.8 MHz, 18,000 ft.Impact of Single Switched Receiver

  47. Single Switched ReceiverPerformance Impact Results • A Top/Bottom Diversity Receiver performs considerable better than a Single Switched Receiver • 25% to 50% more messages received under most conditions evaluated • As far as meeting MASPS is concerned: • A3 [Diversity Receiver] is roughly the same as A0/A1/A2 [Switched Receiver] • For the scenarios evaluated • For the A0/A1/A2/A3 TX powers assumed

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