Explain the direct wave path, line of sight path, out of sight path, and obstructive path?

7. Explain the direct wave path, line of sight path, out of sight path, and obstructive path?

A direct wave path is a path clear from the terrain contour. The line-of-sight path is a path clear from buildings. In the mobile radio environment, we do not always have a line-of-sight condition. When a lineof-sight condition occurs, the average received signal at the mobile unit at a 1-mi intercept is higher, although the 40 dB/dec path-loss slope remains the same. In this case the short-term fading is observed to be a rician fading. It results from a strong line-of-sight path and a ground-reflected wave combined, plus many weak building-reflected waves.

When an out-of-sight condition is reached, the 40-dB/dec path-loss slope still remains. However, all reflected waves, including ground reflected waves and building-reflected waves, become dominant. The short-term received signal at the mobile unit observes a Rayleigh fading. The Rayleigh fading is the most severe fading. When the terrain contour blocks the direct wave path, we call it the obstructive path. In this situation, the shadow loss from the signal reception can be found by using the knife-edge diffraction curves.