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Propagation for Space Applications by

Bertram Arbesser-Rastburg Chairman ITU-R SG3

Invited talk at LAPC 2014 , Loughborough, UKbertram@arbesser.org

Abstract:The presentation covers the key propagation impairments for fixed and mobile satellite communications as well as for satellite navigation. This includes rain attenuation, cloud attenuation, shadowing and multipath. Specifically for satellite navigation systems the group delay introduced by the troposphere and by the ionosphere is also addressed. For the propagation prediction methods presented a reference is made to the models recommended by ITU-R.

Keywords: Slant path propagation, attenuation, depolarization, group delay, scintillations, troposphere, ionosphere.

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 2 of 18

Outline

Propagation issues for Fixed SatCom Services

– Clear Air attenuation, Rain attenuation, Cloud attenuation

– Depolarization by rain and ice

Propagation issues for Mobile Satellite Services

– Shadowing, blockage, multipath

Propagation issues for Satellite Navigation Services

– Ionospheric delay, Tropospheric delay, Ionospheric scintillations

– Shadowing, blockage, multipath

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 3 of 18

Propagation Effects

Environment

•Shadowing

•Blockage

•Multipath

Ionosphere

•Scintillations

•Faraday Rotation

•Delay

Troposphere

•Rain attenuation

•Cloud attenuation

•Scintillations

•XPD reduction

•Delay

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 4 of 18

Fixed SatCom Systems

The first satellite communications were using 6 / 4 GHz

WHY?

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 5 of 18

Fixed SatCom Systems – main propagation effects

For fixed Earth-space links at f > 5 GHz,

the main propagation impairments are:

Rain attenuation

Depolarization due to rain and ice

Cloud attenuation

Gaseous absorption

Frozen Precipitation

Rain

Melting layer

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 6 of 18

Gaseous Attenuation

The plot shows the atmospheric

absorption lines

Water vapour

Oxygen

Communication systems use the

frequencies below and between

the lines; the lines themselves

are used for remote sensing of

the atmosphere.

Line-by-line models are good but

computationally intensive

ITU-R Rec. P.676-10

H2O

H2O

O2 O2 H2O

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 7 of 18

Slant Path Propagation Measurements – what is needed?

Beacon receiver (copolar and crosspolar reception) good dynamic range, hydrophobic antenna, may need blowing device

for feed window, may need emergency power supply, may require

tracking

Radiometer Precision calibration, good retrieval algorithm

Meteorological Equipment rain gauge, distrometer, anemometer, radiosonde, WV-GPS Rx)

HIGH UPTIME !

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 8 of 18

Cumulative Distribution of Attenuation

Total AttenuationGreen: 30 GHzBlue: 20 GHzRed: 12 GHz

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 9 of 18

Cloud Attenuation

ITU-R Rec

P. 840-5 *

sin

lcloud

LKA [dB]

Where: L is the total columnar Liquid Water

Content [kg/m2] (reduced to 0 ˚C)

Kl is the specific attenuation

coefficient (function of frequency &

temperature) is the elevation angle

* Kl in Rec P. 840-6 (in force) is slightly different

Frequency (GHz)

Spec

ific

att

enu

atio

n c

oef

fici

ent,

((dB

/km

) / (g

/m³)

)K

l

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

10

5 10 20 50 100 200

0° C

20° C

10° C

– 8° C

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 10 of 18

Cloud Map

Annual Mean Cloud Cover ( 0 – 1)

Source: ECMWF ERA 15 Database

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 11 of 18

Mobile SatCom Systems

For Mobile Earth-space links the main

propagation impairments are:

Blockage (buildings, underpasses)

Shadowing (trees etc.)

Multipath (reflections)

Semi-Markov Model

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 12 of 18

Roadside Shadowing Model

0681-01

0

4

6

8

10

12

14

16

18

20

22

24

26

28

30

2

10 15 20 25 30 35 40 45 50 55 60

1%

2%

5%

10%

20%

30%

50%

Fading at 1.5 GHz due to roadside shadowing versus

elevation angle

Fad

e ex

ceed

ed (

dB

)

Path elevation angle (degrees)

Fade distribution at 1.5 GHz, valid

for percentages of distance traveled

of 20% p 1%, at the desired path

elevation angle, 60° 20°:

ITU-R Rec P. 681-7

where:

M() = 3.44 + 0.0975 – 0.002 2

N() = – 0.443 + 34.76

AL( p,) = – M() ln ( p) + N() [dB]

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 13 of 18

Channel characterization

• A channel sounder is used to characterize the

multipath environment for land mobile and

aeronautical mobile environments. For proper

modelling, azimuth and elevation of the

incoming components need to be measured

Channel Sounder:

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 14 of 18

Channel characterization

Delay spread in a multipath-rich environment.

The peak on the left (0 delay) is the Line-of-sight signal, showing shadowing and

blockage. The delayed components are multipath contributions.

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 15 of 18

Aeronautical Multipath Model

Model used in ITU-R Rec

P. 682-3 was established

using a flying channel

sounder

1: Line of Sight (LoS): del = 0, P = 0, Doppler BW = 0 Hz

2: Flat fading of LoS: del = 0, P = -14.2 dB, Doppler BW = <0.10 Hz

3: Fuselage multipath: del = 1.5 ns, P = -14.2 dB, Doppler BW = <0.1 Hz

4: Ground reflections: del = 900 – 10 ns, P = -15 to -25 dB, Dopp BW <20 Hz

→

IONOSPHERIC PROPAGATION EFFECTS

ON SATNAV SYSTEMS

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 17 of 18

Ionospheric Electron Density and Group Delay

For calculating ionospheric effects, the Electron Density along the

propagation path has to be integrated (Total Electron Content)

1 TECU = 10 16 el / m2

s = 40.3 TEC / f 2 [m] At 1.575 GHz 1 TECu causes 16 cm of group delay

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 18 of 18

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 19 of 18

Trans-Ionospheric propagation

Effects:

• Refractive index Group delay & Ray bending

• Irregularities Scintillations

• Magnetic field and electron density Faraday rotation

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 20 of 18

Ionospheric Scintillations

20

One of the most severe disruptions along a trans-ionospheric propagation path

for signals below 3 GHz is caused by ionospheric scintillation. Small-scale

irregular structures in the ionization density cause scintillation phenomena in

which the signal is fluctuating in amplitude and phase.

Measurement requires special

ionospheric scintillation

receivers:

Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 21 of 18

• There is a wide range of microwave systems in

space, spanning across all space applications and

a wide frequency spectrum.

• Space applications are demanding not only in

terms of mass, power consumption, reliability and

radiation hardness but also in the handling of time

varying propagation conditions.

• Propagation Experiments are needed to validate

the propagation prediction methods.

Conclusion

→

Thank you !

Bertram Arbesser-Rastburg

bertram@arbesser.org