Aerospace Vehicle Systems Institute WAIC Radio Altimeter Interference

Aerospace Vehicle Systems Institute WAIC Radio Altimeter Interference Susceptibility Testing Texas A&M Engineering Experiment Station Michael Franceschini ICAO FSMP WG 4, ICAO APAC March 29 - April 7 2017

Overview of Radio Altimeter Interference Susceptibility Testing • Purpose: Derive meaningful SARP guidelines – Determine incident interference power limits to fielded Rad. Alts that ensure their continued safe operation • The 5 RA models identified cover the installed ATR base • Identifying a single worst case limit yields a unified RA SARP, simplifies any WAIC coexistence analyses & constraints – Understand the behavior of unique RA algorithms in the presence of various forms of interference signal types • Provides guidance for preferred WAIC signal designs • Will help understand aggregation, multi-channel impacts • Initial assessment: RAs seem robust against anticipated WAIC interference levels – Should yield reasonable WAIC installation criteria 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 2

Laboratory & Flight Tests Status • Test Rack (for flight test) is Complete & Calibrated • Uses DO-155 External Loop Loss, 45 deg BW (G=20) to set desired return signal levels • Tests will span RA operational altitude limits – 500, 1500, 3000, 5000, 8000 feet (ARINC 429 max) – Practical operation limits around 5000 feet – Tested 3 RA types at 508 feet to date • Carrier frequencies of 4240, 4300, 4360 MHz. • Four waveform types planned (Rec m. 2067) – Single Channel types: 802. 15. 4 MSK, 802. 11 a/g OFDM – Multichannel effects: Dual MSK, Dual OFDM • Rationale: assess band occupancy scalability (duty cycle effect) 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 3

27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 4

Tabular Summary of Test Cases Radio Altimeter Model Height WAIC Waveforms Single Carrier Dual Carrier MSK Single Channel OFDM Dual Channel OFDM 4. 3 GHz 4. 24 4. 36 4. 3 GHz GHz 4. 24 4. 36 GHz 500 ft. 1500 ft. 3000 ft. 5000 ft. 8000 ft. Cells entries can be filled with: level of first perturbation, accuracy spec exceeded, NCD limit 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 5

Initial Lab Test Results • All RAs seem to perform well in the presence of single constant envelope interference signals – Operate at 508 feet with higher than practical WAIC signal levels (good for landing scenarios) • consider 45 d. B LOS path loss at 1 m & 17 d. Bm PTX max – Tests span full interference level ranges of concern • well above M. 2059 specified receiver compression point • Must consider transient interference responses as well as steady state (WAIC burst effects) – algorithmic differences, overload recovery times… • Each RA model has unique degradation modes 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 6

ALA 52 B Single Carrier MSK Test VSG Ratio WAIC Waveform Single MSK - 2 Mcps (802. 15. 4) Low Rate: 5 MHz bandwidth VSG Output Signal to Strength RA Signal d. Bm Min -8 -6 -4 -2 0 2 4 6 8 10 Max 4. 3 GHz ARINC 429 (Feet) Variance Mean Interference at Rad. Alt Standard Rcvr Deviation I/S Max % Err d. Bm d. B 508 Ft Altitude; xx d. B VSG-to-Rad. Alt 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 7

ALA 52 B Single Carrier MSK Test Note: Accuracy Spec is +/- 10 ft +10 d. Bm is NCD 508 Ft Altitude; 25 d. B VSG-to-Rad. Alt 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 8

LRA 900 Single Carrier MSK Test 520 -8 d. Bm VSG 515 Note: Accuracy Spec is +/- 10 ft Radio Altimeter signal: d. Bm VSG interference: d. Bm Mean height : Mean after 3 sec. : Standard Deviation: Height (Feet) 510 505 VSG On 500 VSG Off 495 490 00: 01. 0 508 Ft Altitude; xx d. B VSG-to-Rad. Alt 00: 05. 0 00: 09. 0 27 Mar - 7 Apr 2017 00: 13. 0 00: 18. 0 Time (Seconds) ICAO FSMP - WG/4 00: 22. 0 00: 26. 0 00: 31. 0 00: 35. 0 9

520 LRA 900 -6 d. Bm Single Carrier MSK Accuracy Spec is +/- 10 ft 515 Height (Feet) 510 505 VSG On 500 490 00: 22. 0 VSG Off 495 00: 26. 0 27 Mar - 7 Apr 2017 00: 31. 0 00: 35. 0 00: 39. 0 Time (Seconds) ICAO FSMP - WG/4 00: 44. 0 00: 48. 0 00: 52. 0 10

520 LRA 900 -4 d. Bm Single Carrier MSK 520 515 510 505 Height (Feet) 515 LRA 900 -2 d. Bm Single Carrier MSK VSG On 500 VSG Off 495 490 00: 44. 0 VSG On 500 VSG Off 495 00: 52. 0 01: 01. 0 Time (Seconds) 27 Mar - 7 Apr 2017 01: 10. 0 490 01: 04. 0 01: 08. 0 ICAO FSMP - WG/4 01: 12. 0 VSG Off 01: 17. 0 01: 21. 0 Time (Seconds) 01: 25. 0 01: 29. 0 01: 34. 0 11

Height (Feet) 520 LRA 900 0 d. Bm Single Carrier MSK 515 510 505 VSG On 500 495 490 01: 25. 0 500 VSG Off 01: 29. 0 VSG Off 01: 34. 0 LRA 900 2 d. Bm Single Carrier MSK 01: 38. 0 01: 42. 0 Time (Seconds) 27 Mar - 7 Apr 2017 495 01: 47. 0 01: 51. 0 490 01: 44. 0 ICAO FSMP - WG/4 VSG On VSG Off 01: 53. 0 VSG Off 02: 01. 0 Time (Seconds) 02: 10. 0 12

Height (Feet) 520 LRA 900 4 d. Bm Single Carrier MSK 520 515 510 505 500 495 490 02: 06. 0 VSG On VSG Off 02: 14. 0 VSG On 500 VSG Off 02: 10. 0 LRA 900 6 d. Bm Single Carrier MSK 02: 19. 0 02: 23. 0 Time (Seconds) 27 Mar - 7 Apr 2017 02: 27. 0 495 02: 32. 0 490 02: 26. 0 ICAO FSMP - WG/4 VSG Off 02: 30. 0 02: 34. 0 VSG Off 02: 39. 0 02: 43. 0 Time (Seconds) 02: 47. 0 02: 52. 0 13

Height (Feet) 520 LRA 900 8 d. Bm Single Carrier MSK 520 515 510 505 VSG On 500 495 490 02: 46. 0 02: 54. 0 VSG On 500 VSG Off 02: 50. 0 LRA 900 10 d. Bm Single Carrier MSK VSG Off 02: 58. 0 03: 03. 0 Time (Seconds) 27 Mar - 7 Apr 2017 03: 07. 0 495 03: 11. 0 490 03: 06. 0 ICAO FSMP - WG/4 VSG Off 03: 11. 0 03: 15. 0 VSG Off 03: 19. 0 03: 24. 0 Time (Seconds) 03: 28. 0 03: 32. 0 14

Initial Multi-Carrier Test Issues • All 3 cases revealed unexpected RA behaviors – Performance did not scale linearly with I bandwidth • Warrants further investigation, focused tests 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 15

Next Step Test Plans • Performance at higher Altitudes – RA return signal strength decreases, I/S increases – Accuracy limits increase (+/- 2% of altitude) – Should also be lower interference levels experienced • Repeat all tests at lower and upper band edges – 4240 MHz, 4360 MHz are near FMCW sweep limits – Some variations across band have been witnessed • Might assess expanded multi-channel cases – For higher duty-cycle occupancy impacts, if not deemed to be linearly scalable with # of channels – Variations in relative amplitudes on each channel 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 16

Potential Expanded Tests • Out-of-band interference susceptibility – – Rec M. 2059 only estimated bandpass filter rolloffs Meaningful frequencies need to be determined Standalone, multichannel out-of-band… Simultaneous with in-band interference from WAIC • Identify other critical altitude breakpoints in algorithms (unique to each RA model) • Pulsed altimeter susceptibility (bizjet, GA) • Effects of combined WAIC & multiple RA sources • Additional waveform types; mixed modes • Other suggestions ? 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 17

Summary Comments on RA Interference Susceptibility • Lab test is ongoing and initial results are promising for WAIC compatibility – Highly tolerant to constant envelope signals – Need to proceed to higher altitude performance • Must further evaluate multi-channel cases • Many more cases may need to be addressed • SARPs may only need single NTE constraint – Interference incident <“x”d. Bm, RA must tolerate “x”d. B – May still need to spec aggregation limits (TBD) • For example, # of signals at “x”, or sum total of all to ”y”…. . 27 Mar - 7 Apr 2017 ICAO FSMP - WG/4 18