Page 109 - 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 1 : A r e a - t o - A r e a M o d e l s 87

The loss will be just a little more than 54 dB if the link distance is less than 500 m. The dis­
tance factor k d in Eq. (2.15.6) for L,, d is given by

(2.15.9)

L,, d increases with distance at 18 dB per decade if the base antenna is above the rooftops
(t1hb > 0). But if the antenna is below the rooftops, the k d is higher than 18 db per decade.
The frequency factor � in the formula for the multiscreen diffraction loss is given by
Hz
l 0.7( / MHz - 1 ) medium-size city and suburban areas
k . = - 4 + 925 (2.15.10)
MH z
1 . 5 ({2' - 1 ) metropolitan (urban) areas

L 5 and L,1, together give an increase of 30 dB per decade of frequency. For a typical
F
cellular frequency of 850 MHz, the value of k hz is about -4 dB for either situation, as
M
shown in Eq. (2.15.10), so the total dependence on frequency for the 800-MHz cellular
band is about 26 dB per decade.
If data are unavailable, the following default values are recommended:
=
h 3 m x (number of floors) + roof height
{ 3 m for pitched roofs
Roof height, h8 =
0 m for flat roofs
Building separation b = 20 to 50 m
Width of the street w = b/2
Angle of incident wave <1> = 90°
The COST model is applicable to the following range of parameters:

J MHz 800 to 2000 MHz
=
h = 4 to 50 m
b
h = 1 to m 3
"'
dkm = 0.02 to 5 km
The Walfisch-Ikegami model matches measurements quite well when the base
station antenna is above rooftop height, producing mean errors of about 3 dB with stan­
dard deviations in the range 4 to 8 dB.

2.16 Flat-Edge Model
2 0
The flat-edge model was created by Saunders et. al. 9•3 assuming that all buildings are of
equal height and spacing. The geometry is shown in Fig. 2.16.1, illustrating the following
parameters:
r = distance from the base station to the first building in meters
1
a = elevation angle of the base station antenna from the top of the final building in
radiant when = 0, the base station