Handbook of Propagation Effects for Vehicular and ... - Courses

11-24
11.5.1 Single Object Models
11.5.1.1 Point Scatterer Multipath
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
Frequently, signal variations observed in satellite land-mobile propagation experiments
can be correlated with the receiving vehicle passing in the vicinity of a generator of
multipath scattering, such as a utility pole or roadside sign. To increase understanding of
these multipath reflections observed from a moving platform, a physical model based on
the geometry of a single point scatterer has been developed [Vogel and Hong, 1988].
While the model does not address the major limitation of LMSS, shadowing, it provides a
tool to study the dependence of signal variations observed under clear line-of-sight
conditions on parameters such as antenna pattern, path azimuth and elevation angles,
distance of multipath sources, and bandwidth.
Z
From
Transmitter
ΘS
Y
Θ T ΦS
ΦT
From
Transmitter
Scattered
Wave
R(t)
X
Scatterer
(xS, yS, zS)
Figure 11-4: Propagation geometry for single object scattering in which a vehicle
traveling at a speed v carries an antenna with a given pattern along the x-axis.
A sketch of the propagation scenario considered is shown in Figure 11-4, in which a
vehicle carries an antenna with a given pattern along the x-axis with speed v. A plane
wave transmitted from a satellite propagates into the direction (ΘΤ, ΦΤ). In addition to
the line-of-sight wave, the vehicle also receives one multipath component scattered by an
object at (xS, yS, zS). The vector sum of the two waves constitutes the received signal. In
order to achieve simplicity in the numerical evaluation of the model, the following
assumptions were made: (1) there is only one scatterer, (2) it scatters isotropically, and
(3) the receiving antenna's gain is azimuthally omni-directional. The formula developed
by Vogel and Hong [1988] for the received electric field strength Er is