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

Maritime-Mobile Satellite Propagation Effects 9-13
Fading Depth (dB)
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
1%
10%
50%
90%
99%
Gain = 25 dBi
F = 1.5 GHz
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Path Elevation Angle to Satellite (deg)
Figure 9-9: Fading depth versus path elevation angle at different exceedance
probabilities assuming an antenna gain G0 = 25 dBi, 1.5 GHz, and circular polarization.
9.4 Model of Fade Durations Due to Sea Reflections
Karasawa and Shiokawa [1987] analyzed multipath fading due to sea surface reflections
at L-Band (1.54 GHz) and determined mean values of fade durations TD and fade
occurrence intervals TI from the fading power spectrum. The fade duration TD is defined
as the time interval between the instant the signal amplitude falls below a particular level
and the instant it reaches that level again (Figure 9-10). The fade occurrence interval TI
is defined as the interval of time between the instant the signal intensity drops below a
specified level Rp to the instant it falls below that same level again (Figure 9-10). The
signal level Rp in Figure 9-10 is assigned the exceedance percentage P.
Karasawa and Shiokawa [1987] arrived at a simple model for the mean values of TD and
TI which was also adopted by the ITU-R [1994, pp. 354-356]. The mean value of the
fade occurrence interval at the fade exceedance percentage P is denoted by TI (P)
and
is given by
2
⎛ m(
P)
⎞
I ( P)
= T ( 50%)
exp⎜
⎟ , (9-28)
⎝ 2 ⎠
T I