Wave propagationmodels

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Wave propagationmodels

  1. 1. Wave Propagation ModelsPrinciples &Scenarios© 2012 by AWE Communications GmbH www.awe-com.com
  2. 2. Contents • Wave Propagation Model Principles - Multipath propagation - Reflection - Diffraction - Scattering - Antenna pattern © by AWE Communications GmbH 2
  3. 3. Wave Propagation ModelsMultipath 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) © by AWE Communications GmbH 3
  4. 4. Wave Propagation ModelsMultipath 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) © by AWE Communications GmbH 4
  5. 5. Wave Propagation ModelsPropagation 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 © by AWE Communications GmbH 5
  6. 6. Wave Propagation ModelsBasic 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 © by AWE Communications GmbH 6
  7. 7. Wave Propagation ModelsBasic Principle – Reflection II • Fresnel coefficients for modelling the reflection: Polarisation parallel to Polarisation perpendicular to plane of incidence plane of incidence © by AWE Communications GmbH 7
  8. 8. Wave Propagation ModelsBasic Principle – Breakpoint 130 • Free space: Two path model Free space model received power ~ 1 / d2 120  20 dB / decade • No longer valid from 110 a certain distance on Path Loss [dB] • After breakpoint: 100 received power ~ 1 / d4  40 dB / decade 90 • Deduced from 80 two-path model, i.e.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 © by AWE Communications GmbH 8
  9. 9. Wave Propagation ModelsBasic 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 - polarisation of incident wave - 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 © by AWE Communications GmbH 9
  10. 10. Wave Propagation ModelsBasic Principle – Transmission II • Fresnel coefficients for modelling the transmission: • Penetration loss includes two parts: - Loss at border between materials - Loss for penetration of plate © by AWE Communications GmbH 10
  11. 11. Wave Propagation ModelsBasic 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 - polarisation of incident wave - UTD coefficients with Luebbers extension for modelling the diffraction k QD i © by AWE Communications GmbH 11
  12. 12. Wave Propagation ModelsBasic 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 © by AWE Communications GmbH 12
  13. 13. Wave Propagation ModelsBasic Principle – Diffraction III • Uniform Geometrical Theory of Diffraction (3 zones: NLOS, LOS, LOS + Refl.) Diffractions are relevant in shadowed areas © by AWE Communications GmbH 13
  14. 14. Wave Propagation ModelsBasic 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 © by AWE Communications GmbH 14
  15. 15. Wave Propagation ModelsBasic 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 © by AWE Communications GmbH 15
  16. 16. Wave Propagation ModelsBasic 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) © by AWE Communications GmbH 16
  17. 17. Wave Propagation Models 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  © by AWE Communications GmbH 17

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