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

9-14
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
where T ( 50%)
is the mean value of the fade occurrence interval at the fade
I
exceedance percentage of 50% and m(P) is given by (9-31). The mean value of the fade
duration at the fade exceedance P or T D (P)
may be calculated by
⎛ P ⎞
D ( P)
= T ( P)
⎜1
− ⎟ . (9-29)
⎝ 100 ⎠
T I
The mean fade occurrence interval at P = 50% may be calculated using
3
TI ( 50%)
= , (9-30)
f
−10
where f-10 is called the “-10 dB spectral bandwidth.” This corresponds to the bandwidth
over which the power density decays to –10 dB relative to the peak power density
(characterized in Figure 9-11). The parameter m(P) in (9-28) is evaluated using the
following equations.
2
m(
P)
= 2.
33 − 0.
847α
− 0.
144α
− 0.
0657α
α =
log( 100
− P)
for
70%
≤ P ≤
3
99.
9%
(9-31)
The bandwidth f-10 was derived from a theoretical fading model of Karasawa and
Shiokawa [1984b] and is plotted as a function of elevation angle in Figure 9-11 at
1.5 GHz for two maritime conditions. The upper bound (denoted by f-10U) corresponds to
a significant wave height of 5 m, ship velocity of 20 knots, with a roll of 30°. The lower
bound (f-10L) corresponds to a significant wave height of 1 m, ship velocity of 0 knots,
with 0° roll. Least square fits of the lower and upper curves in Figure 9-11 have the form
⎛θ
o ⎞
f−10
U , L = a + bexp⎜
⎟ . (9-32)
⎝ c ⎠
The values of a,b,c are tabulated in Table 9-3 for the upper bound f-10U and lower bound
f-10L.