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

11-6
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
distribution was fit to (11-8) from which a "mean excess path loss, μ ," and "standard
deviation, σ ," was derived. The model equations of Hess for PS = 90% valid in the
range of PL from 50% to 90% are given by
where
A ( PL
) = μ + k(
PL
) σ , (11-9)
μ = + a ENV + a HEAD + a FREQ + a SIDE + a ELEV , (11-10)
a0 1
2
3
4
5
σ = + b ENV + b HEAD + b FREQ + b SIDE + b ELEV . (11-11)
b0 1
2
3
4
5
In (11-9), k is the number of standard deviations for various values of PL and are given by
⎧ 0
⎪
1.
28
k = ⎨
⎪1.
65
⎪⎩
2.
33
P
P
P
P
L
L
L
L
=
=
=
=
50%
90%
95%
99%
. (11-12)
The model parameters ENV, HEAD, FREQ, SIDE, and ELEV are defined in Table 11-1.
We note that the model contains the following elements: (1) the local environment (ENV)
such as urban, semi-urban (commercial) and suburban, (2) the vehicle heading (HEAD)
with respect to the satellite azimuth, (3) the frequency (FREQ); UHF or L-Band, (4) the
side (SIDE) of the road driven (satellite located across opposing lane or not) and (5) the
elevation angle (ELEV) to the satellite. The downtown area of a city, with many tall
buildings and a rectangular street grid would be characterized as urban. Streets lined by
shopping centers as well as by businesses with off-street parking lots are classified as
commercial, and areas with small one- or two-story houses along moderately tree-lined
roads define the suburban environment. Data acquired in rural surroundings are included
in the suburban category. The coefficients for the mean fade μ and slope σ , given in
(11-10) and (11-11), respectively, are summarized in Table 11-2 along with their standard
errors.
The overall standard errors of μ and σ are
S. E.(
μ ) = 3.
65 dB , (11-13)
S. E.(
σ ) = 2.
5 dB . (11-14)
In order to extend the small-scale coverage from the modeled value of PS = 90% as given
by (11-9) to (11-11) and Table 11-2 to other values of PS, we use the following
formulation: