Wave propagationmodels

Wave Propagation Models

Principles &

Scenarios

© 2012 by AWE Communications GmbH

www.awe-com.com

http://www.awe-com.com/

© by AWE Communications GmbH 2

Contents

• Wave Propagation Model Principles

- Multipath propagation

- Reflection

- Diffraction

- Scattering

- Antenna pattern



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)

• Considering topography

• Evaluating additional obstacles

2D Vertical plane

Tx 3D Paths

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

Ei i

r

Er

E i r

r

n

QR

Et t

Material 1

1 ,

1 ,

1

Material 2

2,

2,

2

Et t



Basic Principle – Reflection II

• Fresnel coefficients for modelling the reflection:

Polarisation parallel to

plane of incidence

Polarisation perpendicular to

plane of incidence


s:

Path

Loss

[d

B]


Basic Principle – Breakpoint

• Free space:

received power ~ 1 / d2

20 dB / decade

• No longer valid from

a certain distance on

130

120

110

Two path model Free space model

• After breakpoint:

received power ~ 1 / d4

40 dB / decade

• Deduced from

two-path model, i.e.

superposition of direct

and ground-reflected ray

BP = 4htxhrx/

100 90

80

70

0,1

0,3

1,0 3,16 10,0

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

Ei i

r

Er

E i r

r

n

QR

Et t

Material 1

1 ,

1 ,

1

Material 2

2,

2,

2

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


Heig

ht

in m


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:

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

• Example: Ground properties Low attenuation if incident angle equals scattered angle: Specular

reflection

Absorber

Measurement results: RCS with respect to incident angle alpha and scattered angle beta (independent

of azimuth)

Measurement setup

Ground



Consideration of Antenna Patterns

• Manufacturer provides 3D antenna pattern

• Manufacturer provides antenna

gains in horizontal and vertical plane

Kathrein K 742212

Z

G

Bilinear interpolation of 3D antenna characteristic G

1

G

G

G

12 G

G

1 2

1

2 2

1 2 2 1

2 1 2 2 1 2 X

G , 1 2 1 2

G

12

12 -Y

1 2

2

1 2

2

1 2 1 2

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