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.
- 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.
- 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.
- 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
- 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 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.