University of South Carolina Outline Introduction & Motivation - - PowerPoint PPT Presentation

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University of South Carolina Outline Introduction & Motivation - - PowerPoint PPT Presentation

Feb 19, 2024 301 likes •547 views

ROLINA UNI NIVERSI ERSITY o of SOUTH C CARO Department of Electrical Engineering INITIAL RESULTS FOR AIRFRAME SHADOWING IN L- AND C-BAND AIR- GROUND CHANNELS Ruoyu Sun (Ph.D. candidate) David W. Matolak (Ph.D., Professor) ICNS 21-23

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University of South Carolina

UNI NIVERSI ERSITY o

  • f SOUTH C

CARO ROLINA

Department of Electrical Engineering

INITIAL RESULTS FOR AIRFRAME SHADOWING IN L- AND C-BAND AIR- GROUND CHANNELS

Ruoyu Sun (Ph.D. candidate) David W. Matolak (Ph.D., Professor) ICNS 21-23 April 2015

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University of South Carolina

Outline

  • Introduction & Motivation
  • Measurements

– Measurement Equipment – Measurement Site

  • Airframe Shadowing Results

– Shadowing Event Conditions – Shadowing Depth and Duration – Aircraft Antenna Diversity Gain – Small Scale Fading – Spatial Correlation

  • Conclusion

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University of South Carolina

Introduction & Motivation

  • Unmanned Aircraft System (UAS) use is

growing & will continue to grow rapidly

  • UAS integration in the National Airspace

System (NAS) via a reliable & safe link: Control & Non-payload Communication (CNPC)

  • New spectrum allocated for CNPC at ITU

World Radiocommunications Conference (WRC-12) – 61 MHz in C-band (5030-5091 MHz) & – 17 MHz in L-band (960-977 MHz)

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University of South Carolina

  • NASA Glenn Research Center (GRC) project:

Unmanned Aircraft Systems (UAS) Integration in the National Airspace System (NAS)

  • University of South Carolina (USC) sub-

project: Air-Ground (AG) Channel Measurements & Modeling

Introduction & Motivation (2)

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University of South Carolina

Introduction & Motivation (3)

  • Previous studies on the AG channel

– Sparse – Difference frequency bands – Different environments

  • Existing models do NOT include

– Airframe shadowing – Shadowing by large obstacles (e.g., trees, buildings) for small UAS

GS

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University of South Carolina

Introduction & Motivation (4)

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Narrowband Channel Models

  • Large scale path loss models

– Friis free space – Log-distance – Two-ray

  • Airframe shadowing

– Duration of shadowing – Depth of shadowing

  • Fading: distribution of signal

envelope

– Ricean (K-factor) – Rayleigh – Nakagami (m-factor)

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University of South Carolina

Measurement Equipment

  • DS-SS Stepped Correlator
  • Dual-Band SIMO
  • ~ 3000 Power Delay Profiles (PDPs) per sec

Band Signal Bandwidth (MHz) Frequency Span (MHz) Maximum Delay Span (μs) Transmit Power (W) Tx Amplifier (dB) Rx LNA Gain (dB) Cable Loss (dB) L 5 960-977 204.6 10

  • 15.5

4 C 50 5000-5150 20.46 10 7 30 7.5

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University of South Carolina

Measurement Equipment (2)

Transportable GS with 20 m tower S-3B Viking aircraft with four antennas on bottom

Tx (GS) Rx (Aircraft)

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University of South Carolina

Measurement Site

  • Over Sea: Oxnard, CA
  • Over fresh water: Cleveland, OH
  • Mountainous: Telluride, CO
  • Urban: Cleveland, OH
  • Suburban: Cleveland, OH, Palmdale, CA

& Latrobe, PA

  • Hilly: Latrobe, PA & Palmdale, CA

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University of South Carolina

Measurement Site (2)

Oxnard, CA Over Sea (Pacific Ocean) 10 Telluride, CO Mountainous (Rocky Mountain) Cleveland, OH Over Fresh water (Lake Erie) Urban (downtown Cleveland) Latrobe, PA Suburban (Latrobe township) Hilly (Appalachian Mountain) Palmdale, CA Suburban (Palmdale township) Desert (Mojave Desert) Hilly (San Gabriel Mountain) In total 82 flight tracks ~316 million PDPs ~146 GB raw data! The most comprehensive AG channel characterization in history!

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University of South Carolina

Measurement Site (3)

  • Over Lake Erie
  • Start from Pink circle
  • End at Black square
  • Red oval indicates where

airframe shadowing

  • ccurred
  • hGS = 20 m, hAircraft = 580 m
  • Elevation ∠ 1.7° ~ 1.8°
  • d = 20.3 ~ 21.8 km
  • V = 76.5 m/s
  • ~ 2750 PDPs/s for each of 4 Rxs
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University of South Carolina

Shadowing Event Conditions

  • Shadowing event occurred only if all 3 conditions

were satisfied

  • Abs(∠ Roll) > 5°
  • Abs(∠ Heading－ ∠ Azimuth) > 30 °
  • Pr,free space－ Pr,measured > 5 dB
  • ∠ Roll up to -29.7 °

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University of South Carolina

Shadowing Depth

  • Shadowing depth (max shadowing loss) in L-band

– L-band Rx1: 25.5 dB – L-band Rx2: 34.4 dB

  • Multiple aircraft antennas provide diversity gain

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University of South Carolina

Shadowing Depth (2)

  • C-band Pr sometimes < noise floor

– limits accuracy of shadowing depth

  • Shadowing depth in C-band

– C-band Rx1 > 30.4 dB – C-band Rx1 > 27.5 dB

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University of South Carolina

Shadowing Duration

  • Shadowing duration

– 36.5 ~ 41.9 seconds, can be a disaster for the CNPC link – Depends on antenna location, airplane outline, velocity & maneuver

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C-band L-band Rx1 Rx2 Rx1 Rx2 Shadow Duration (s) 36.5 37.3 41.9 39.8 Shadow Loss (dB) Max 30.4 27.5 25.5 34.4 Min 4.2 2.6 5.0 Mean 9.1 17.2 10.3 14.2 Median 6.3 16.9 9.6 12.9 Standard Deviation 7.4 6.4 4.4 5.9 Distance (km) Max 21.8 21.8 21.8 21.8 Min 20.5 20.5 20.1 20.3

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University of South Carolina

Spatial Diversity Gain

  • Multiple aircraft antennas diversity gain
  • Less than 5 dB outside shadowing area
  • 20.3 dB in L-band (968 MHz)
  • 15.7 dB in C-band (5060 MHz)

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University of South Carolina

Small Scale Fading

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University of South Carolina

Spatial Correlation

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Whole FT Shadowing Area C-band L-band C-band L-band Mean 0.42 0.59 0.23 0.26 Median 0.85 0.91 0.56 0.64 Max 1.00 1.00 1.00 1.00 Standard deviation 0.72 0.59 0.77 0.76

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University of South Carolina

Conclusion

  • Air-Ground channel measurements & models

– New spectrum (L-band, 960-977 MHz & C-band 5030-5091 MHz), aiming for CNPC link – Previous studies on airframe shadowing are sparse

  • Measured shadowing results

– Collected over the Lake Erie – Dual-band SIMO channel sounder

  • Airframe shadowing event

– Aircraft making a “U-turn” – Roll angle up to 30°

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University of South Carolina

Conclusion (2)

  • Airframe shadowing can severely downgrade the CNPC link
  • L-band (968 MHz) shadowing depth 34 dB
  • C-band (5060 MHz) shadowing depth > 30 dB
  • Airframe shadowing duration ~ 40 seconds
  • L-band Ricean K factor -20 dB in shadow (14 dB outside)
  • Multiple aircraft antennas mitigate the airframe shadowing

Outside Shadow Inside Shadow

  • Diversity gain < 5 dB 20.3 dB in L-band

15.7 dB in C-band

  • Spatial correlation 0.9 0.6

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University of South Carolina

Future Work

  • Develop airframe

shadowing models using more shadowing events

  • Evaluate airframe

shadowing by ray-tracing

  • Analyze other types of

shadowing in AG channel

– Mountain ridge shadowing – Building/tree shadowing for small UAS

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University of South Carolina

Questions?

Thank You!