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

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 April 2015 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 2 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) University of South Carolina

Introduction & Motivation (2) • 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 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 University of South Carolina

Introduction & Motivation (4) • Large scale path loss models Narrowband Channel 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) University of South Carolina 6

Measurement Equipment • DS-SS Stepped Correlator • Dual-Band SIMO • ~ 3000 Power Delay Profiles (PDPs) per sec Frequency Rx LNA Cable Signal Maximum Delay Transmit Tx Amplifier Gain Loss Band Bandwidth Span Span ( μs ) Power (W) (dB) (dB) (dB) (MHz) (MHz) L 5 960-977 204.6 10 -- 15.5 4 C 50 5000-5150 20.46 10 7 30 7.5 University of South Carolina

Measurement Equipment (2) S-3B Viking aircraft with four Transportable GS antennas on bottom with 20 m tower Rx Tx (GS) (Aircraft) University of South Carolina

Measurement Site • Urban: Cleveland, OH • Over Sea: Oxnard, CA • Suburban: Cleveland, OH, Palmdale, CA • Over fresh water: Cleveland, OH & Latrobe, PA • Mountainous: Telluride, CO • Hilly: Latrobe, PA & Palmdale, CA University of South Carolina 9

Measurement Site (2) The most In total comprehensive 82 flight tracks AG channel ~316 million PDPs characterization ~146 GB raw data! in history! Oxnard, CA Telluride, CO Over Sea Mountainous (Pacific Ocean) (Rocky Mountain) Palmdale, CA Suburban (Palmdale township) Cleveland, OH Latrobe, PA Desert (Mojave Desert) Over Fresh water (Lake Erie) Suburban (Latrobe township) Hilly (San Gabriel Mountain) Urban (downtown Cleveland) University of South Carolina Hilly (Appalachian Mountain) 10

Measurement Site (3) • Over Lake Erie • h GS = 20 m, h Aircraft = 580 m • Start from Pink circle • Elevation ∠ 1.7 ° ~ 1.8 ° • End at Black square • d = 20.3 ~ 21.8 km • Red oval indicates where • V = 76.5 m/s airframe shadowing • ~ 2750 PDPs/s for each of 4 Rxs occurred University of South Carolina

Shadowing Event Conditions • Shadowing event occurred only if all 3 conditions were satisfied  Abs( ∠ Roll ) > 5°  Abs( ∠ Heading － ∠ Azimuth ) > 30 °  P r,free space － P r,measured > 5 dB • ∠ Roll up to - 29.7 ° University of South Carolina 12

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 University of South Carolina 13

Shadowing Depth (2) • C-band P r 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 University of South Carolina 14

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 C-band L-band Rx1 Rx2 Rx1 Rx2 Shadow Duration (s) 36.5 37.3 41.9 39.8 Max 30.4 27.5 25.5 34.4 Min 0 4.2 2.6 5.0 Mean 9.1 17.2 10.3 14.2 Shadow Loss Median 6.3 16.9 9.6 12.9 (dB) Standard 7.4 6.4 4.4 5.9 Deviation Max 21.8 21.8 21.8 21.8 Distance (km) Min 20.5 20.5 20.1 20.3 University of South Carolina 15

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) University of South Carolina 16

Small Scale Fading University of South Carolina 17

Spatial Correlation 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 0.72 0.59 0.77 0.76 deviation University of South Carolina 18

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° University of South Carolina 19

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 University of South Carolina 20

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 University of South Carolina

Questions? Thank You! University of South Carolina