Page 124 - Integrated Wireless Propagation Models

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

L = (the knife-edge diffraction loss) - (the maximum effective antenna height gain)

= L0 -20 log (�U � 0 (under a shadow condition) (3.1.2.5)

The effective antenna height h; is measured the height at the base station from the
intersected point of a line that is drawn from the tip of the hill along the slope of the
hillside to the base station. The description of h; is shown in Sec. 3.1.2.4.
a = the signal adjustment factor in dB, such as additional gains if the actual antenna
gains g; and g,; and antenna heights h; and h; at two terminals are different
from the standard conditions

= (g� - gb) + (g"' -g:,) + 20 log(� ) + 10 log(�: )

= !lgb + !lg"' + !lg,,j + !lg,2 (3.1.2.6)
The signal strength value given by the Lee single breakpoint model is composed of four
components:
1 . The area-to-area path loss, used as a baseline for the model, is derived from
a propagation slope (y) and 1-mile (or extrapolate to 1 km if not measured at
1 km) intercept value (P, ). P , may be obtained from the measured data.
i
o"
Because P , and y vary fr m c ty to city due to human-made structures and
,
only measured data can give the answer, the effect due to human-made
structures is accounted in the model. The area-to-area component includes
a frequency-offset adjustment (A1), which is used to adjust the actual center
frequency of your system to the model's reference frequency of 850 MHz
(see Table . 1 .2.1.2).
3
2. The effective antenna height gain G,ffi , is determined by the terrain contour
between the base station and the mobile where a specular reflection point is
located. This component is significant for the case of a nonobstructed direct
signal path, including LOS and NLOS paths. It accounts the terrain-contour
effect into the model.
3. Diffraction loss L is predicted using Fresnel-Kirchoff diffraction theory. For
multiple knife edges, Lee uses both a modified Epstein-Petersen method3 and
a separated knife-edge check to evaluate diffraction loss. This component is
significant for the condition of an obstructed direct signal path or called
diffraction path. It is also the effect due to the terrain contour and is also
accounted for in the model.
4. An adjustment factor compensates for the difference between a set of default
conditions for base station transmit with mobile parameters (which are used as
assumptions for calculating the area-to-area path loss component) and the
actual values for these parameters in each sector to be predicted.
Once received signal strength values have been predicted for each point along the sig­
nal path (radial), the Lee model can use a signal-smoothing process to produce the final
prediction.
A point-to-point model constantly calculates along the signal path for path loss and
checks for signal obstructions. There are three conditions for the direct path. When the