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

Theoretical Modeling Considerations 11-9
Large-Scale Probability P
L
That Fade > Abscissa
100
9
8
7
6
5
4
3
2
10
9
8
7
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1
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P s =
50% 70% 90%
Elevation
45°
30°
20°
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
FADE DEPTH (dB)
Figure 11-1: Probability distributions for LS-SS model for family of elevation angles and
indicated small-scale probabilities PS.
11.3.1.2 Discussion
The LS-SS model of Hess is derived from an extensive database of measurement results,
which is especially weighted for urban to suburban environments. It is simple to use and
has realistic parameterization for the most important environmental variables.
The model was derived from data taken with linearly polarized quarter wavelength
whip antennas. Such a system will not provide isolation from ground specular
reflections, as do low-gain LMSS type antennas previously described. While shadowing
loss measurements were not affected by the antenna choice, multipath and specular
effects were most likely enhanced. This may have caused overprediction of signal
variations especially in open rural areas where shadowing is statistically less significant
than multipath. It is also important to note that the experiment emphasized urban over
rural areas, making predictions from the database for rural areas less reliable.
11.3.2 Extended Empirical Roadside Shadowing Model
Since the empirical roadside shadowing (ERS) and extended empirical roadside
shadowing (EERS) models were addressed in Chapter 3, the model details will not be
described here. A short summary discussion is presented in the following paragraphs.