Page 405 - Integrated Wireless Propagation Models

T h e l e e C o m p r e h e n s i v e M o d e l - I n t e g r a t i o n o f t h e T h r e e l e e M o d e l s 383

a mature system while all the different cell size-specific models have been used in the
system. From this overall-view map provided by this model, the interference, area of
interface, Handoff (HO), and further growth among them can be solved.

6. 7 Propagation Prediction on Different Transmission M e dia
In this section, must call to the reader's attention that there are four different transmis­
sion media-satellite communication, underwater communication, bullet-train com­
munication, and aeronautical communication-in which that their transmitted signals
are predicted are different from those of predicting terrestrial mobile propagation. We
may highlight just the differences, so the interested reader will early understand the
differences and search for the right sources.

7
6. . 1 Prediction of Satellite Communication Signals
In satellite communications, space propagation phenomena affect the earth space link,
mainly propagation through two sky layers-troposphere and ionosphere. Most of the
propagation effect on the operational frequency in the ionosphere occurs below 1 GHz,
and most of the propagation effect on the troposphere occurs above 1 GHz.
The ionosphere involves interactions between the layers of charged particles around
the earth, the earth's magnetic field, and the radio waves. Ionospheric effects are Fara­
day rotation, group delay, dispersion, and ionospheric scintillation.
The tropospheric ozone layer involves interactions between the waves and the
lower layer of the earth's atmosphere, including the effects of the gases composing the
air and hydrometeors such as rain. Tropospheric effects are path loss, rain attenuation,
gaseous absorption, tropospheric refraction, tropospheric scintillation, depolarization,
and sky noise.
Also, the satellite communication signal is affected by local environment in the
vicinity of the earth station, such as terrain, trees, and buildings. These effects may be a
significant impairment and need to provide some site shielding of fixed earth stations
from terrestrial interferers. However, in mobile satellite systems, the direct path may
frequently be wholly or partially obscured from the surroundings. Local effects have
been treated in previous chapters.
6.7. 1 . 1 Path-Loss Models, Channel Models, and Overall Path-Loss Model
Here we are introducing the path-loss models (long-tern fading) and the channel
models (short-tern fading) of satellite communications.3 0

6.7. 1 . 1 . 1 Path-Loss Models for f > 1 GHz-Based on Atmosphere Conditions Usually, the
operational frequency of the satellite communication is around 10 GHz, and then the
tropospheric effects are a big concern. The path-loss models are applied to the frequency
above 3 GHz.
Two different modeling approaches have been considered. The first approach con­
siders all attenuation effects as being correlated; That is, the total path loss is given by

(6.7 1 .1)
.
where A0, AH, o, A ' A , A ML and A5 are the attenuation effects due to oxygen, water
R
C
vapor, cloud, rain, melting layer, and scintillation, respectively.