Page 137 - Integrated Wireless Propagation Models

M a c r o c e l l P r e d i c t i o n M o d e l s - P a r t 2 : P o i n t - t o - P o i n t M o d e l s 115

antenna gain and includes the -3dB mobile antenna height adjustment. The adjustment
factor a in Eq. (3.1.2.5.1) can be simplified as follows:

.
a = 10 log(�') + (-3 dB) + (g� - g ) (3 1 . 2.5.2)
b
An example calculation is given next.
3.1.2.5. 1 Example of Adjustment In this example, the unadjusted signal strength of
-61 dBm is predicted at a point in the field under the standard conditions. However, the
actual base station output power and antenna gain are as follows:

=
P ; = 3 0 W g� 5 dBd
The adjustment factor in Eq. (3.1.2.5.2) is calculated as follows:

a = 1 0 log(���) + (-3 dB)+ (6 dB- 5 dB)

a = 10 log (3)+ (-3 dB)+ (1 dB)
a = (4.8 dB)+ (-3 dB)+ (1 dB) = 2.8 dB

The 2.8-dB adjustment factor is applied to the unadjusted prediction, giving an
adjusted signal strength of -58.2 dBm at this point. This value is subject to signal
smoothing if necessary as it will be described Sec. 3.1.2.6.

3 . 1 .2.5.2 Determining Actual Base Station Antenna Gain The Lee model assumes a base
station antenna gain of 6 dBd as one of the standard conditions. However, in any given
model, the antenna may have a different standard gain. Also, the actual gain at any
point is a function of the radiation pattern observed from both vertical and horizontal
angles that in turn depend on the angle of mechanical or electrical downtilt. We will
describe this issue in Sec. 3.1.7 1 . 1 .
.
Besides adjusting the antenna gain difference from the standard antenna gain, the
Lee model calculates the actual different base station antenna gains from the observed
angle at the mobile after the antenna is either electrically or mechanically down tilted.
When the electrical downtilt of an antenna is applied, the actual antenna gain from
the observed angle at the mobile can be obtained from the free space antenna pattern
at the angle.
However, when the mechanical downtilt is applied, the antenna pattern is no
more the same as a free space pattern but is in a different shape. Therefore, the calcu­
lation of the antenna gain from the mechanical downtilted antenna is different, as
shown in Sec. 3.1.7.

3.1.2.6 Signal-Smoothing Process

3. 1.2.6. 1 From the Raw Predicted Values The Lee single breakpoint model predicts a
signal strength value for each local point on every signal path (radial). These points are
spaced evenly along the radial at an equal distance. Once raw signal strength values
have been predicted from the Lee model, a signal-smoothing process is used to deter­
mine the final predicted value (P,) for each point. This process enhances the model and