Page 88 - Integrated Wireless Propagation Models

66 C h a p t e r T w o

I
2.9 CC R Model

2 . 9 . 1 Description of the Model
The CCIR (Comite Consultatif International des Radio-Communication, now ITU-R)
model takes topography into account using only statistical parameters, in contrast to
most other methods. These parameters are the effective antenna height of the transmit­
1
ter and a value t;.h (as shown in Fig. 2.9. . 1) defining the degree of terrain irregularity.
This model predicts the field strength for a given terrain over an extrapolated fre­
quency range of 100 to 3000 MHz, and its prediction method was conceived for land
mobile radio service with vertical polarization. A basic median attenuation is intro­
duced to quasi-smooth terrain in urban areas. Some correction factors are applied for
different transmitter and receiver antenna heights and for different terrain and envi­
ronmental clutter. The correction factors correspond to different effective antenna
heights and terrain irregularities as well as to isolated mountains, sloped terrain, and
open, quasi-open, or suburban areas and to different receiving antenna heights.
CCIR curves give field strengths at 900-MHz frequencies for 50 percent of locations
and 50 percent of the time in urban areas for mobile antenna heights of 1.5 m and base
1
antenna heights between 30 and 1000 m, as shown in Fig. 2.9.1.2. 5
To adjust for mobile antenna heights of 3 m instead of 1.5 m, a height-gain factor of
3 dB is suggested. Standard deviations are given as a function of distance and terrain
irregularity, assuming that propagation variations with location and time are character­
ized in decibels by the Gaussian distribution. Treatment of the median transmission loss
1
for frequencies near 900 MHz is based on the work of Okumura et al. 4 stated in Sec. 2.12.

Definition of he11

0 3 km 15 km
Okumura, CCIR

Definition of Ml
T T

10%
90%

Okumura CCIR
FIGURE 2.9.1.1 Defin i tion of the effective transmitter antenna height h•" and the parameter of
a
the terr i n irregularity !lh according to CCIR and Okumura et al.14