Page 90 - Integrated Wireless Propagation Models

68 C h a p t e r T w o

CCIR curves are based on a single parameter !;:,h, which is inadequate to define the
required correction factor with sufficient accuracy. Furthermore, terrain variations in
the immediate vicinity of the mobile are not explicitly taken into account. A more accu­
rate method is therefore required, as shown in the following section.

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d
2.10 Blomquist-La e l l and Edwards D u r kin Models
1
The Blomquist-Ladell 6 model is used for calculating transmission loss in the VHF and
UHF regions. It is a deterministic model giving the long-term median of the basic trans­
mission loss. The model considers the same type of losses as the JRC method (see Sec. 2.6)
but combines them in a different way in an attempt to provide a smooth transition
between points where the prediction is based on free space loss L and plane earth prop­
F
agation loss L . The ground dielectric constant and the terrain profile, including vegeta­
r
tion, are properly accountable.
The Blomquist-Ladell model considers two limiting propagation cases: the spheri­
cal earth can be regarded as smooth, and it can be represented by a number of knife
edges. Blomquist and Ladell introduce two empirical propagation models. The first
model calculates the propagation factor as
F loss = min (F F (dB) (2.10.1)
B' diffracti on)
where F is a total loss which is taking smaller number among two factors:
1oss
F8(dB) is the propagation factor based on the smooth, spherical earth field.
F (dB) is the propagation factor based on the obstacle diffraction field.
diffraction
The other model is the square root of the sum of the squares of F8 and F diffraction ' that is,
.
F;oss = F + F (dB) (2 1 0.2)
J £ �ffraction
Blomquist and Ladell consider the same types of losses as the Edwards-Durkin
model9 but combine them differently. The total propagation loss is given by an expression
of the following type:

(2.10.3)

where F8= L; - L (F8is given in Eq. [2.10.12])
F
L = free space propagation loss (dB)
F
L0 = diffraction losses due to irregular terrain (dB) (multiple-knife-edge loss
after Epstein and Petersons [Sec. 1 . 9.2.2.2])
L8 = propagation losses caused by buildings (dB)
4 = total propagation loss (dB)
L or L; = plane earth propagation loss (dB) the former is from the Edwards-Durkin
P
model and the latter from the Blomquist-Ladell model
=
F8 a correction term for the earth curvature effect of the troposphere and for
any factor other than diffraction over irregular terrain
Hb and H"' = effective antenna heights (m) of base and mobile stations, respectively
R = distance between base and mobile station (km)
Edwards and Durkin use an empirical L from Bullington:
P
L = K2 - 20 log (Hb) 2 0 log (H",) + 40 log(R) (dB) (2.10.4)
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