Page 230 - Integrated Wireless Propagation Models

208 C h a p t e r F o u r

4.2.4.2 Shadow Region
We have already considered the signal received over the elevated terrain along the LOS
where there are effective antenna height gains or losses due to terrain variation. Now a
more complex case of having a mobile under a hidden condition or the mobile being
blocked by a knife-edge case is considered in this section.
The basic algorithm of detecting hidden conditions, where the direct path from the
mobile is obstructed by a hill, has been described in Sec. 3.3.2. The mobile signal has
occurred in an obstructed condition by terrain, as shown in Fig. 4.2.4.2.1.
The received signal P, takes a generalized form as the typical output in the predic­
tion analysis tool:

( 4.2.4.2.1)

where effective antenna gains G,11" can be calculated based on the terrain contour (see
Sec. 3.1.2.3). Loss L8 is due to building blocks (see Sec. 4.2.1.2), and diffraction loss L0
due to terrain (see Sec. 3.1.2.4).
Now we have to demonstrate how to use Eq. (4.2.4.2.1) to deal with the real mea­
surement conducted in various cities, as shown in Fig. 4.2.4.2.2. The current situation is
such that the mobile is far away from the base station transmitter in an elevated terrain
situation and 10 buildings are blocking the radio path propagation.
As shown in Fig. 4.2.4.2.3, considering only the loss due to building blockage on a flat
terrain, the sum of the 10 buildings' thickness is computed, and the building blockage
loss is L8• It is worth mentioning at this stage that the height of the building will not make
a significant difference because the incident angle e of the direct wave is very small.

Knife
edge
/
Antenna

a
FIGURE 4.2.4.2.1 Mobile blocked by terr i n .

230 ft
1 8 4 ft
1 3 8 ft
82 ft
46 ft
0 ft
0 0.2 0.4 0.6 0.8 1 . 0 1 . 2
Miles from site
FIGURE 4.2.4.2.2 The true transmitter and mobile situation.