When any new site has been planned then it should be such a way the effect of Reflection, Diffraction, Scattering and Multipath should be Balance.

Reflection

  • Occurs when a wave impinges upon a smooth surface.
  • Dimensions of the surface are large relative to l.
  • Reflections occur from the surface of the earth and from buildings and walls.

Diffraction (Shadowing)

  • Occurs when the path is blocked by an object with large dimensions relative to l and sharp irregularities (edges).
  • Secondary “wavelets” propagate into the shadowed region.
  • Diffraction gives rise to bending of waves around the obstacle.

Scattering

  • Occurs when a wave impinges upon an object with dimensions on the order of l or less, causing the reflected energy to spread out or“scatter” in many directions.
  • Small objects such as street lights, signs, & leaves cause scattering

MultiPath

  • Multiple Waves Create “Multipath”
  • Due to propagation mechanisms, multiple waves arrive at the receiver
  • Sometimes this includes a direct Line-of-Sight (LOS) signal

multipath

Multipath Propagation

  • Multipath propagation causes large and rapid fluctuations in a signal
  • These fluctuations are not the same as the propagation path loss.

Multipath causes three major things

  • Rapid changes in signal strength over a short distance or time.
  • Random frequency modulation due to Doppler Shifts on different multipath signals.
  • Time dispersion caused by multipath delays
  • These are called “fading effects
  • Multipath propagation results in small-scale fading.