Path Loss & Fading - IEEE Xplore

UNIVERSITY of SOUTH CAROLINA Department of Electrical Engineering

Antenna and Frequency Diversity in the Unmanned Aircraft Systems Bands for the Over-Sea Setting David W. Matolak, Ruoyu Sun DASC 2014

University of South Carolina

Outline Ȉ Introduction & Motivation Ȉ Channel Measurements Ȉ Over-sea path loss & dispersion Ȉ Correlations & small-scale fading – Stationarity distance – Ricean K-factor

Ȉ Channel modeling Ȉ Conclusion University of South Carolina

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Introduction & Motivation Ȉ Unmanned Aircraft System (UAS) use GROWING! – News items in popular press daily – Recent DoT report estimates # UAS in USA “will increase from few 100 in 2015 to > 230,000 in 2035”

Ȉ FAA charge: ensure UAS safety – ITU granted spectrum in 2 bands: L-band (960-977 MHz), & C-band (5030-5091 MHz) University of South Carolina

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Introduction & Motivation (2) Ȉ NASA supporting R&D for FAA Ȉ NASA project UAS in the National Airspace System (NAS) – Exploring/validating technologies for reliable CNPC – U. South Carolina working w/NASA on PHY/MAC ȈAir-ground (AG) channel ȈRadio mod/demod ȈNetworking


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Introduction & Motivation (3)) Ȉ There exist NO comprehensive, validated, wideband models for time-varying AG channel

• Existing measurements

- Sparse, & for different frequency bands in widely different environments - Not parameterized as function of - Elevation - GS antenna height - GS local environment

- Do not include airframe shadowing University of South Carolina

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Measurements: Channel Sounder Aircraft

GS Transmitter L-band Tx

C-band Tx

to Transmit Antennas Band L C

DS-SS Signal Bandwidth (MHz) 5 50

Receiver 1 L-band Rx

Receiver 2

C-band Rx

L-band Rx

from Receive Antennas Frequency Span (MHz) 960-977 5000-5100

Ȉ PTx~10 W (40 dBm) Ȉ C-band: HPA G~7 dB, LNAs G~30 dB Ȉ Rrep,max~ 3 kHz University of South Carolina

C-band Rx

from Receive Antennas Band L L C C

DS-SS Sequence Length N 511 1023 511 1023

WMAX (Ps) 102.2 204.6 10.2 20.4

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Measurement Equipment Ȉ Transportable ground site (GS), S-3B aircraft

1.29 m 1.32 m

20 m extendable tower

Four receiver (Rx) antennas: 2 in C-band, 2 in L-band


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Measurement Environment Ȉ Over-sea, GS near Oxnard, CA – – – –

June 2013 GC=6 dB, GL=5 dB hGS = 20 m El/Az beamwidths Ȉ40q/70 q for C Ȉ85q/60 q for L

– Aircraft antennas omni monopoles (“blades”) – Both straight & oval-shaped flight tracks (FTs) University of South Carolina

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Over Sea Measurement Site Ȉ Oxnard, CA, 11 June 2013 GS Antenna

• Over 26 GB data (>67 million PDPs) gathered University of South Carolina

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Oxnard,CA***06/11/2013***C-band Rx1***Track1

783 782

Curved Earth Flat Earth ENU

Elevation Angle (degree)

30

781 780 779 778 777 776

Oxnard,CA***06/11/2013***C-band Rx1***Track1

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25 20 15 10 5

0.5

1

1.5

0

2

Link Distance (m)

Altitude vs. link distance, straight FT1

x 10

0.5

4

1

1.5

2

Link Distance (m)

Elevation angle vs. link distance, straight FT1

400 350

Azimuth Angle (degree)

Relative height between Tx and Rx (m)

Example Flight Parameters

x 10

4

300 250 200 150

Azimuth angle vs. link distance, straight FT1

100 50 0

0.5

1

1.5

2

2.5

3

3.5

Tx-Rx Distance (m)

4

4.5


5 x 10

4

10

Over-sea Channel Characteristics 140 135 130 125 120

OxnardCA***06-11-2013***Track1***L-band Rx1&2 Measured L-band Rx1 Measured L-band Rx2 Free Space PL 2-Ray Curved Earth 2-Ray Flat Earth

Ȉ 2-ray behavior @ L-band • L2ray=20log[(4Sd/O)] - 20log{|1 + *v,cexp(-j2S'R/O)|} with *v,c=curved-earth vertical pol. reflection coef.

115 110 105

80

100 95

OxnardCA***06-11-2013***Track1***C-band Rx1 Measured Moving Averaged

70

90 10

4

Link Distance (m)

Ȉ Dispersion

60

RMS-DS (ns)

Path Loss Recorded by Sounder (dB)

Ȉ Path Loss

50 40 30 20

– RMS-delay spread

10 0

0.5

1

1.5

Link Distance (m) University of South Carolina

2 x 10

4

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Correlations & Small-Scale Fading Ȉ Curved-earth two-ray (CE2R) deterministic Ȉ Communications engineers also use statistical models for channel effects Ȉ Channel is time-varying, so need to estimate distance (time) over which statistics remain constant—the stationarity distance (SD) LOS D01

Surface Reflection

D11

W

LOS

d=d1

W

Surface Reflection

D02 D01 D D 12 11

d=d2>d1

WW W


Ȉ 2-ray behavior as distance n, straight FT 12

Stationarity Distance Ȉ Compute power delay profile (PDP) correlation coefficient c('t, ti) Ȉ Channel stationary: 't such that c('t, ti) >0.9 ܿ ο‫ݐ‬, ‫ݐ‬௜ =

‫ܲ ׬‬௔௩௚,ே (߬, ‫ݐ‬௜ )ܲ௔௩௚,ே (߬, ‫ݐ‬௜ + ο‫߬݀)ݐ‬ ଶ

ଶ

݉ܽ‫ܲ ׬ ݔ‬௔௩௚,ே (߬, ‫ݐ‬௜ ) ݀߬ , ‫ܲ ׬‬௔௩௚,ே (߬, ‫ݐ‬௜ + ο‫߬݀ )ݐ‬ ௅೔

Ȉ PDP at time ti

ଶ

ܲ ߬, ‫ݐ‬௜ = ෍ ߙ௞,௜ ߜ(߬ െ ߬௞,௜ ) ௞ୀଵ ௜ାேିଵ

Ȉ Avg. PDP, ti to ti+NTs ܲ௔௩௚,ே

1 ߬, ‫ݐ‬௜ = ෍ ܲ(߬, ‫ݐ‬௜ ) ܰ ௜


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Stationarity Distance (2) Ȉ Collect SD statistics for all FTs Ȉ Use median SD Ȉ 'x=v't OxnardCA***06-11-2013***FT1

1

0.8

Contour of C-band PDP corr. coef. vs. link distance & ρǡ segment of FT1

CDF

0.6

0.4

0.2

0

C-band Rx1 C-band Rx2 10

20

30

40

'x (m)

50

60

70

SD CDFs of straight flight track (FT1)

Ȉ Median SD ~ 250 OC, or ~ 15 m


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Correlations Ȉ Inter-antenna correlation ɏ୅భ ,୅మ

E Aଵ െ Ɋ୅భ Aଶ െ Ɋ୅మ = ɐ୅భ ɐ୅మ

Ȉ A’s = amp vectors =(Aଵ,ଵ , Aଵ,ଶ , … , Aଵ,୧ , … , Aଵ,୬ ), μ=mean, V Vtd dev Intra-band Correlations C-band L-band Mean 0.72 0.04 Median 0.88 0.03 Max 0.98 0.84 Min -0.83 -0.63 Standard 0.38 0.21 deviation

Ȉ Inter-band UNcorrelated


Small-Scale Fading • After removal of path loss, small-scale envelope fading modeled as Ricean 40

OxnardCA***06-11-2013***FT1***C-band Rx1 22 20

30 25 KML

20

C-band

KMB 15 10

KML Linear Fit [n=0.17 ,V =1.7] KMB Linear Fit [n=0.17 ,V =1.7] 5

10

15

Link Distance (km)

Rician K Factor (dB)

Rician K Factor (dB)

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OxnardCA***06-11-2013***FT1***L-band Rx1 KML KMB

L-band

KML Linear Fit [n=0.07 ,V =1.0] 18

KMB Linear Fit [n=0.08 ,V =1.0]

16 14 12 10

20

5

10

15

Link Distance (km)

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Rician K factors vs. link distance University of South Carolina

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(Wideband) Channel Modeling Ȉ Tapped-delay line model

CE2R

Intermittent multipath components (MPCs)

Ȉ Sparse multipath channel Ȉ Statistics for intermittent MPCs being compiled University of South Carolina

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Conclusion • Reported channel measurements for AG channel, in over-sea environment – Propagation path loss ~well modeled by curvedearth two-ray model – RMS-DS moderate (10-50 ns, rare ~ 200 ns)

• Stationarity distance ~ 15 m for computing statistics – Ricean K-factors ~25 dB (C-band), ~12 dB (L-band) – Inter-band correlations generally large, intra-band correlations ~0 University of South Carolina

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Questions?

Thank You


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