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

Maritime-Mobile Satellite Propagation Effects 9-5
The measurements of Karasawa and Shiokawa were sufficiently scattered such that they
fell within the bounds of both (9-13) and (9-14).
The level of the maximum coherent component PCO of the reflected wave may be
determined by varying the antenna height on board the ship during calm sea conditions.
By determining the level difference between the minimum and maximum signals (for a
calm sea), the intensity of the coherent component of the scattered wave relative to the
direct wave component can be evaluated. The intensity of the incoherent component of
the scattered wave may be obtained through the assumption that the incoherent signal
follows a Nakagami-Rice distribution. Figure 9-1 shows the relation between the fading
depth and the mean total multipath power relative to the direct signal power assuming
this distribution. Karasawa and Shiokawa [1984] define the “fading depth” as the dB
difference between the signal level of the direct incident wave and a threshold level that
the resultant signal level exceeds with a probability of P percent of the time. The
individual curves denote the indicated probability of exceeding the ordinate fading depth.
Shipborne experiments carried out by Karasawa and Shiokawa [1988] have corroborated
use of this distribution for values of u ≥ 2. As an illustration of the dependence of u on
wave-height, Figure 9-2 is a plot of u given by (9-5) versus the RMS wave height h
(upper abscissa) and significant wave height H (lower abscissa). We note that at θ o = 5°,
u ≥ 2 implies H > 1.5 m and h > 0.4 m.
Fading Depthl (dB)
6
4
2
0
-2
-4
-6
-8
-10
-12
1%
10%
50%
90%
99%
-20 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5
Relative Multipath Power Level (dB)
Figure 9-1: Fading depth versus total multipath power relative to the direct signal level
for different exceedance probabilities (of the incoherent level) based on the Nakagami-
Rice distribution.