Page 130 - Integrated Wireless Propagation Models

108 C h a p t e r T h r e e

3.1.2.3 Effective Antenna Height Gain
Effective antenna height gain is the third component of the model as shown in
1
Eq. (3. . 2 . 1 ) . It is due to the terrain-contour effect. When the direct path from the base
station to the mobile is not obstructed by terrain, the received signal consists of direct
and reflected waves. In this situation, the adjustment of received signal strength due
to a change in antenna height at the base station does not depend solely on the actual
antenna height above the local ground level. Rather, it depends on the effective
antenna height (h) as determined by the terrain contour between the base station
and the mobile.
Once the effective antenna height is found, we can use it with the standard condi­
tion antenna height (h1) to calculate the effective antenna height gain (Gefll,) from the Lee
single breakpoint model, shown in Eq. (3.1.2.3).

3.1.2. . 1 Determining Effective Antenna Height Effective antenna height is determined
3
by deriving from a specular reflection point, which can be found using the following
parameters:

• Base station antenna height, h1
• Mobile antenna height, h 2
• Distance from the base station to the mobile, d
• Terrain elevations between the base station and the mobile

Note that both the base station antenna height and mobile antenna heights are consid­
ered. Both antennas are vertically lined up with y-axis, not perpendicular to the ground
slope, as shown in the figure. This is because, for illustration, the scales of antenna
heights and the scale of the ground are not the same. If the scales of x-axis and y-axis are
the same, then both antennas are almost perpendicular to the ground.
Effective antenna height is determined using the following steps:
1. Find the specular reflection point.
a. Connect the negative image of the transmitter antenna to the positive image
of the mobile antenna; the intercept point at the ground level is considered a
reflection point (RJ
b. Connect the negative image of the mobile antenna to the positive image of
the transmitter antenna; the intercept point at the ground level is also
considered a reflection point (R).
The Lee model uses the reflection point found closest to the mobile as the spec­
ular reflection point.
2. Extend a ground plane-tangent to the average elevation along the terrain
contour at the specular reflection point-from the specular reflection point
back to the location of the base station (transmitter) antenna.
3. Measure the effective antenna height (h) from the intersection of the extended
ground plane and the y-axis on which the vertical mast of the base station
antenna is located.
Four different cases are considered for calculating effective antenna height gain.