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

Theoretical Modeling Considerations 11-29
Figure 11-7: Calculated Doppler spectrum due to single multipath reflector averaged
over one second, while the vehicle is driving past the scatterer.
Similar cases to the one above, except for an outer radius of 500 m and the much higher
average area per scatterer of 625 m 2 , were examined with inner clearance radii from 30 to
400 m. The result demonstrates that multipath phenomena for LMSS scenarios are
significant only if the scatterers are located close to the vehicle. The standard deviation
of the logarithmic amplitude decreases monotonically with increasing inner clearance
from 0.22 dB to 0.07 dB.
As an outgrowth of geometric modeling, it has been ascertained that when higher
gain antennas are employed, the side of the road on which the scatterer is located
influences the multipath fading [Vishakantaiah and Vogel, 1989]. For example,
assuming an antenna with 80° half-power beamwidth in both the azimuth and elevation
planes, the multipath fading was 10 dB when a simulated scatterer (e.g., a utility pole)
was placed between the vehicle and the satellite. Only 1 dB multipath fading occurred
when the vehicle was between the scatterer and the satellite. Filtering of the signal by the
antenna pattern diminished fading for the latter case. On the other hand, when an
azimuthally omni-directional antenna was used, no change in the multipath fading (e.g.,
10 dB) was observed for the two cases. In an environment with many scatterers at
random heights and cross sections, the reduction of the fade fluctuations arising from
lower versus higher gain antennas is not as extreme, but still significant. For the case of
500 scatterers (having random heights and cross-sections) located at distances between