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

9-20
Mean Fade Duration, T D (sec)
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Lower Bound f -10
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
Upper Bound f -10
P = 90%
5 6 7 8 9 10 11 12 13 14 15
Elevation Angle (deg)
Figure 9-17: Bounds of mean fade duration TD (P)
for multipath fade exceedance
percentage P = 90% at L-Band.
9.5 Multipath from Rough Seas and Frequency Dependence on Multipath
Fading
9.5.1 Rough Sea Model
Karasawa et al. [1990] executed an analysis in which multipath fading from very rough
seas (with significant wave heights H greater than 3 m) is examined. They developed a
model that takes account of the effect of smaller-scale waves superimposed onto the
dominant wave. They make use of the fact that the spectrum of ocean waves caused by
wind may be approximated by the Pierson-Moskowitz spectrum [1964] and that ocean
waves have the characteristics of gravity waves. The RMS slope of the sea surface is
calculated and applied to a theoretical model for estimating fade depths. A series of
curves is presented of the 99 th percentile of fading depth versus significant wave height H
for the following combinations of antenna gain and elevation angle (15 dBi, 5°), (21 dBi,
5°), and (15 dBi, 10°). The analytically derived multipath fading for “wind-wave” and
“swell” conditions are compared with results derived from the experiments of Karasawa
et al. [1986]; Matsudo et al., [1987], and Ohmori et al. [1985]. They show that the fading
depth tends to reach a peak for H between 1 and 2 m. The multipath fading peaks are
approximately 8 dB, 5 dB, and 4 dB for the above combinations of antenna gain and
elevation angle, respectively, consistent with their wind-wave model. For larger H, the
multipath fading decreases slightly for wind-waves conditions and remains relatively