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

Optical Methods for Assessing Fade Margins 10-7
Probability P (%)
95
90
70
50
30
10
5
Satellite Beacon Measurement
Karasawa Three-State Model
"Fitted" Three-State Model
Urban Three-State Model (UTSFM)
-5 0 5 10 15 20 25
Fade (dB) Exceeded at Probability P
Figure 10-4: The left set of curves denotes measured and modeled fade distributions in
Japan (urban regions) at 32° elevation and f = 1.5 GHz. The right-hand curves represent
the fade differences between the measured and modeled distributions at different
percentages.
-4 -2 0 2 4
Error (dB)
In Figure 10-4, the major qualitative difference between the measured and the modeled
CDF is that the modeled CDFs are much flatter than the measured one in the fade range
from 3 to 13 dB. The terraced shape of the CDF has been observed on open rural
freeways, where the unobstructed line-of-sight and strong multipath sources are both
blocked at the same time by overpasses for a certain fraction of the distance. In this case,
it is appropriate to use the Rayleigh distribution to describe the blocked state. On the
other hand, when the signal is blocked in the urban environment, specular reflections
from nearby illuminated building surfaces and diffracted rays are likely to also be
received. To account for these effects, the distribution in the urban blocked state was
changed from Rayleigh to Loo using the values given in the last column of Table 10-3.
This CDF (solid curve) is plotted in Figure 10-4 and gives a peak error smaller than 1.5
dB (Figure 10-4) and a corresponding RMS error of 0.5 dB. At the terrace part of the
curve, the maximum error is approximately 0.5 dB.