Page 91 - 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 1 : A r e a - t o - A r e a M o d e I s 69
I
where K is 115.1 dB for transmission between two half-wave dipoles and is 118.7 dB in
2
the case of isotropic antennas. It is shown that for most cases,
(2.10.5)
One way to perform the calculations is to solve the propagation problem first for a
smooth spherical earth and then correct the solution with factors that account for differ­
ent conditions of wave propagation phenomena.
The plane earth propagation loss (dB) L; from the Blomquist-Ladell model is

(2.10.6)
where F8 is shown in Eq. (2.10.12 .
)
The total loss 4 can e expressed as
b
2 1
2
4(dB) = L + [(L - L ) + Lo ) 12 + Lv + Lu + LA (2.10.7)
;
F
F
where Lv is the vegetation loss, Lu is the urban loss, and LA is the loss from atmosphere.
The square-root model is frequently used. Over highly obstructed paths, L0 >>
;
(L - L ), the total loss of Eq. (2.10.3) can be approximated by
F
(2.10.8)
For unobstructed paths, L0 approaches 0, and the total loss from Eq. (2.10.3) becomes
4 (dB) = L; (2.10.9)
Besides diffraction losses being equal to 0, this result is similar to the one of Edwards
and Durkin, and it would in fact be identical if the same formula were used to estimate
L (Edwards and Durkin) and L� (Blomquist and Ladell).
P
The essential part of the Blomquist-Ladell9 model is an empirically developed formula.
The total loss is a weighted sum of free space loss, plane earth loss, and multiple-knife­
edge loss as

1
L + ( P + U )2 F8 o :o;
F
D
B
1
T
0
>
L - - L + ( P - U ) 2 F8 0 , but :::;I L o l (2.10.10)
F
B
1
>
>
L - ( P - U ) 2 F8 0 , but I L o l
F
D
B
where
(dB) (2.10.11)
When an isotropic antennas is used, the propagation factor F8 is
(2.10.12)
y { -2.8X X < .53
= (2.10.13)
-
6.7 + 10log10 X 1 0.2X .53 :::; X < 2
(2.10.14)