Page 64 - Integrated Wireless Propagation Models

42 C h a p t e r 0 n e

1.9.3 Scattering
Scattering occurs when photons or electromagnetic waves pass through a medium,
such as water or glass, and the direction of propagation changes. Scattering can be of
two kinds: elastic scattering and inelastic scattering. If the scattered photon or electro­
magnetic wave has the same frequency as the incident wave, it is elastic scattering since
the photon energy of the scattered photons is not changed. If the photon energy of the
scattered photons changes because its frequency changed, it is inelastic scattering.

1.9.3. 1 Elastic Scattering
There are two typical kinds of elastic scattering: Rayleigh scattering and Mie scattering.
Because Mie scattering deals with spherical particles and less with wavelength and
because Rayleigh scattering deals mainly with wavelength. We talk only about Rayleigh
scattering here.
When the wavelength of an incident wave is equal to or larger than 10 times the
radius of scattered photons, the shape of the scattered photon does not matter any­
more and can be assumed as a spheroid. The principles of Rayleigh scattering state that
if the incident and scattered waves have the same frequency, then the intensity of the
scattered wave is related to the angle of the incident wave and inversely proportional
the to biquadrate of the wavelength of the incident wave. The expression of the equa­
tion is given by

(1.9.3.1)

where a is molecular polarizability, I is the intensity of the scattered wave, while I is the
0
intensity of incident wave, /.., is the wavelength, N is the number of scatters, 8 is the
incident angle, and R is the distance from scatters.
From Eq. (1.9.3.1), we see that the intensity of the scattered wave is proportional to
the incident angle 8 and that the number of scatters is inversely proportional to the
wavelength A, squared and the distance R.

1.10 Applications of the Prediction Models

1 . 10.1 Classification of Prediction Models
There are three different kinds of prediction models: the area-to-area model, the point­
to-area model, and the point-to-point model. The descriptions are shown below.

1.10.1 . 1 Area-to-Area Model
This kind of prediction model can predict the received signal strength in only a general
area, and the locations of both the base station and the mobile unit are not specified.

1.10.1.2 Point-to-Area Model
This kind of prediction model can predict the received signal strength in a general area
with the location of the base station specified but not the location of the mobile unit.