Page 127 - Integrated Wireless Propagation Models

M a c r o c e I P r e d i c t i o n M o d e I s - P a r t 2 : P o i n t - t o - P o i n t M o d e I s 105
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The standard conditions assumed for the path loss prediction include the following
base station transmit power and mobile parameters:
P1 b ase station transmit power = 10 W
=
=
h1 b ase station antenna height = 100 ft ( -30.5 m)
h2 = mobile antenna height = 10 ft (3 m)
=
gb b ase station antenna gain = 6 dBd (dB over dipole)
g = mobile antenna gain = 0 dBd (dB over dipole)
"'
The Lee model uses the standard base station antenna height to determine effective
antenna height gain. The model also uses the actual base station antenna height to
determine the diffraction loss.
An adjustment factor is also applied to the signal strength prediction to fine-tune for the
difference between the standard condition values and the values of the actual parameters.

3. 1.2. 1 . 1 Significance of the 1-Mile Intercept The 1-mile intercept (P,0) used by the Lee
single breakpoint model is an initial parameter at which the signal received, under stan­
dard conditions, at a distance of 1 mile (1.609 km) from the base station. There are four
main reasons the model uses a 1-mile intercept for predicting propagation for near-in
distances, as follows:
1. Within a radius of 1 mile, the antenna beam width is narrow in the vertical
plane; this is especially true of high gain omnidirectional antennas. Thus, the
signal reception is reduced at a mobile less than 1 mile away because of the
large elevation angle. This angle causes the mobile to be in the shadow region
outside the main beam. The larger the elevation angle, the weaker the reception
level due to the antenna's vertical pattern.
2. There are fewer roads within a radius of 1 mile around the base station, and the
data are insufficient to create a statistical curve. Also, the road orientation­
both in-line and perpendicular-close to the base station can cause a significant
difference (from 10 to 20 dB) in signal reception levels on those roads.
3. The nearby surroundings of the base station can bias the reception level-either
up or down-when the mobile is within the 1-mile radius. When the mobile is
more than 1 mile away from the base station, the effect due to the nearby
surroundings of the base station becomes negligible.
4. For a land-to-mobile propagation, the antenna height at the base station strongly
affects mobile reception in the near field; therefore, the mobile reception at 1 mile
away has to refer to a given base station antenna height.

For distances of less than 1 mile, the Lee macrocell model projects the path loss
curve predicted by the single breakpoint model extending backward from 1 mile to the
base station.

3.1.2.1.2 Slope and Intercept Reference Values Slope and intercept values for a specific
city can be obtained from the mean value of measured data. There are slopes and
intercept values for the major cities in a list. For future predictions in similar areas or
cities as in the list, we may copy the slopes and intercept values without further mea­
surement data. The available values from Table 3.1.2.1.1 shown below can be used.