Page 96 - Integrated Wireless Propagation Models

74 C h a p t e r T w o

2 . 1 1.2.1 Empirical Model
The following equation was produced as the best fit for the London data:

f 1 0
L 0(dB) = -20log(0.7hb)- 8 l ogh"' + fa + 2 6 l og fa - 8 6log( � � )
5
5
f 1 0
+[40+ 14.15log( � � )Jogd + 0.265L-0.37H + K 1 (2.11.2.1)
5

=
where K1 0.087U - 5.5 for the highly urbanized area and 0 otherwise. H i s the dif­
ference in average ground height between the transmitter and receiver, while the
distance is limited by 0 ::; d ::; 10 km on the OS (Ordnance Survey, UK mapping
authority) map.

2 . 1 1.2.2 Semiempirical Model
This model is based on the plane earth equation. The median path loss is expressed as
the sum of the theoretical plane earth loss and an excess clutter loss termed �· The val­
ues of � at 168, 455, and 900 MHz were obtained for each test square.
The model is given as

(2.11.2.2)

where

� = 2 0 + {0+0.18L-0.34H+ K 2

and

K2 = 0 0.094U- 5.9

K2 is applicable only in the highly urbanized city center; otherwise, K2 0.
=
The root-mean-square prediction errors produced by the two models are summa­
1
rized in Table 2.11.2. .
o
o
L
i
o
The estimation f values f parameters , U, and H f the test squares s under
consideration.
Parameter H can be easily extracted from a map.
L and U can sometimes be obtained from other stored information or through the
estimation.
Frequency (MHz)
168 455 900
Empirical model 2 . 1 3.2 4.19
Semi-empirical model 2 . 0 3.3 5.8

TABLE 2.11.2.1 Root-Mean-Square Prediction Errors n Decibels
i
Produced by the Two models