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

Summary of Recommendations 12-3
the attenuation exceeds given fade margins,” also referred to as the “cumulative fade
distribution.”
12.3.1 The Extended Empirical Roadside Shadowing Model
This model (presently an ITU-R Recommendation) estimates the cumulative fade
distribution for mobile-satellite scenarios with the following caveats. (1) The earthsatellite
path is approximately orthogonal to the line of roadside trees. (2) The
percentage of optical shadowing is in the range of 55% to 75%. (3) Exceedance
probabilities range between 1% and 80%. (4) Elevation angles range from 7° to 60°.
(5) The frequency interval of validity is 0.8 GHz to 20 GHz. (6) The fade uncertainty in
the distribution at any given probability is ± 5 dB for elevation angles exceeding 20°.
(7) Below 20° the uncertainty may be larger because of the likelihood of blockage from
terrain and other obstacles. This model has been adopted by the ITU-R and the steps for
implementation are as follows:
Step 1: Calculate the fade distribution at L-Band ( f L = 15 . GHz), valid for percentages of
distance traveled of 20% ≥ P ≥ 1% , at the desired path elevation angle, 60°≥ θ ≥ 20°
using:
where
A( P, θ, f ) = − M( θ)ln( P) + N(
θ)
, (12-4)
L
M( θ) = 344 . + 0. 0975 θ − 0. 002θ 2 , (12-5)
N( θ) = − 0. 443 θ + 34. 76 , (12-6)
and θ is the elevation angle in degrees.
Step 2: Convert the fade distribution (12-4) at f L = 15 . GHz, valid for 20% ≥ P ≥ 1% , to
the desired frequency f (GHz) where 0. 8 GHz ≤ f ≤ 20 GHz using:
A( P, θ, f ) = A( P, θ,
f L )exp . ⋅
f L f
⎛ ⎞
⎜ ⎟ −
⎝ ⎠
⎛
⎧
⎪ ⎡ 1 1 ⎞
⎨15
⎢ ⎜ ⎟
⎣⎢
⎝ ⎠
⎩⎪
⎤⎫
⎪
⎥⎬
⎦⎥
⎭⎪
0. 5 0. 5 (12-7)
Step 3: Extend the fade distribution to percentages of distance traveled in the range
80% ≥ P > 20% using:
⎛ 80⎞
ln⎜
⎟
⎝ P ⎠
A( P, θ, f ) = A( 20%, θ,
f )
ln( 4)
(12-8)
Step 4: For path elevation angles in the range 20° > θ ≥ 7°
, the fade distribution is
assumed to have the same value as at θ = 20 ° . That is,