Wave propagationmodels

Wave Propagation Models

Principles &
Scenarios
© 2012 by AWE Communications GmbH

www.awe-com.com

Contents

• Wave Propagation Model Principles
- Multipath propagation
- Reflection
- Diffraction
- Scattering
- Antenna pattern

© by AWE Communications GmbH 2


Multipath Propagation
• Multiple propagation paths Rx
between Tx and Rx
Tx
• Different delays and attenuations
• Destructive and
constructive interference

Superposition of multiple paths

No line of sight (Rayleigh fading) Line of sight (Rice fading)



Multipath Propagation
• Superposition of multiple paths leads to fading channel
• Fast fading due to random phase variations
• Slow fading due to principle changes in the propagation channel (add. obstacles)

Example of a
measurement
route
• Fast fading (green)
• Slow fading (red)



Propagation Model Types
• Empirical models (e.g. Hata-Okumura)
• Only consideration of effective antenna height (no topography between Tx and Rx)
• Considering additional losses due to clutter data

• Semi-Empirical models (e.g. Two-Ray plus Knife-Edge diffraction)
• Including terrain profile between Tx and Rx
• Considering additional losses due to diffraction
• Deterministic models (e.g. Ray Tracing) 2D Vertical plane
• Considering topography Tx 3D Paths

• Evaluating additional obstacles

Rx1

Rx2


Basic Principle – Reflection I
• Reflections are present in LOS regions and rather limited in NLOS regions

• Refection loss depending on:
- angle of incidence
- properties of reflecting material: permittivity, conductance, permeability
- polarisation of incident wave
- Fresnel coefficients for modelling the reflection

Ei
r
Ei i Er
Er
i r
Material 1
1 , 1 , 1
n

QR Material 2
 2 ,  2,  2
Et
t
Et t



Basic Principle – Reflection II
• Fresnel coefficients for modelling the reflection:

Polarisation parallel to Polarisation perpendicular to
plane of incidence plane of incidence



Basic Principle – Breakpoint
130
• Free space: Two path model
Free space model

received power ~ 1 / d2
120
 20 dB / decade

• No longer valid from 110

a certain distance on Path Loss [dB]

• After breakpoint:
100

received power ~ 1 / d4
 40 dB / decade
90

• Deduced from 80

two-path model, i.e.
superposition of direct 70

and ground-reflected rays:
0,1 0,3 1,0 3,16 10,0
BP = 4htxhrx/ Distance [km]

Loss for 900 MHz and Tx height of 30m (Rx height 1.5m)
breakpoint distance = 1.7 km



Basic Principle – Transmission I
• Transmissions are relevant for penetration of obstacles (as e.g. walls)

• Transmission loss depending on:
- angle of incidence
- properties of material: permittivity, conductance, permeability
- Fresnel coefficients for modelling the transmission

Ei
r
Ei i Er
Er
i r
Material 1
1 , 1 , 1
n

QR Material 2
 2 ,  2,  2
Et
t
Et t



Basic Principle – Transmission II
• Fresnel coefficients for modelling the transmission:

• Penetration loss includes two parts:
- Loss at border between materials
- Loss for penetration of plate



Basic Principle – Diffraction I
• Diffractions are relevant in shadowed areas and are therefore important

• Diffraction loss depending on:
- angle of incidence & angle of diffraction
- properties of material: epsilon, µ and sigma
- UTD coefficients with Luebbers extension for modelling the diffraction

k

QD

i



Basic Principle – Diffraction II
• UTD coefficients with Luebbers extension for modelling the diffraction

• Fresnel function F(x)

• Distance parameter L(r) depending on type of incident wave



Basic Principle – Diffraction III
• Uniform Geometrical Theory of Diffraction (3 zones: NLOS, LOS, LOS + Refl.)

Diffractions are relevant
in shadowed areas



Basic Principle – Knife-Edge Diffraction I
• According to Huygens-Fresnel principle the obstacle acts as secondary source

• Epstein-Petersen: Subsequent evaluation from Tx to Rx (first TQ2 then Q1R)

• Deygout: Main obstacle first, then remaining obstacles on both sides



Basic Principle – Knife-Edge Diffraction II
• Additional diffraction losses in shadowed areas are accumulated

• Determination of obstacles based on Fresnel parameter

• Similar procedure as for Deygout model (start with main obstacle)

• Example:
Height in m

Distance in 50m steps



Basic Principle – Scattering
• Scattering occurs on rough surfaces

• Subdivision of terrain profile into numerous scattering elements

• Consideration of the relevant part only to obtain acceptable computation effort
Low attenuation if incident angle
• Example: Ground properties equals scattered angle: Specular
reflection

Absorber

Ground
Measurement results: RCS with respect to incident Measurement setup
angle alpha and scattered angle beta (independent
of azimuth)


Consideration of Antenna Patterns
• Manufacturer provides 3D antenna pattern

• Manufacturer provides antenna
gains in horizontal and vertical plane

Kathrein K 742212

Z

G 


1
Bilinear interpolation of 3D antenna characteristic G G



  1
2
 12  
 G   2G1   G  2G1  1 2 2
2  1  2
2
 1  2  1   2 
1 2  X

G  ,   
 

   
G

1  2  1 2 2  1  2  1 2 2 -Y

1  2  1  2 


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