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

3-18
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
3.4.7 Comparison with ESA K-Band Measurements
We compare here EERS model distributions at 18.7 GHz with measured distributions by
Murr et al. [1995] obtained in a series of campaigns supported by the European Space
Agency (ESA). The campaigns used a radiating source on board the geostationary
satellite Italsat F1 [Paraboni and Giannone, 1991] and a mobile van with a tracking
antenna [Joanneum Research, 1995]. The elevation angles were between 30° and 35° and
a number of runs in four European countries were executed for different driving
directions relative to the satellite position. In Figure 3-16 are shown two measured
distributions (solid curves) made along tree shadowed roads in Munich, Germany [Murr
et al., 1995]. Also shown is the corresponding EERS model distribution (dashed curve).
We note that the two measured distributions generally flank the EERS model between
percentage values of 5% to 30% with fade deviations in excess of 10 dB occurring at
percentages smaller than 5%. Murr et al. [1995], in these measurements, found that a 90°
relative satellite azimuth scenario did not always represent a worst case fading situation.
Some distributions showed larger fades at the 45° relative satellite azimuths. This was
explained as follows: For some 90° cases, the Earth-satellite path encountered clear
spaces between adjacent trees giving rise to minimal fade conditions during the
corresponding time intervals. On the other hand, at 45°, the tree canopies overlapped and
the incidence of optically non-shadowed Earth-satellite path scenarios was not as
prevalent as for the 90° case. Hence the 45° case sometimes gave rise to longer periods
with extended shadowing.
Percentage of Distance Fade > Abscissa
100
9
8
7
6
5
4
3
2
10
9
8
7
6
5
1
4
3
2
Distribution Type
ESA Measurements
EERS
0 5 10 15 20 25 30 35 40 45 50
Fade (dB)
Figure 3-16: Measured cumulative distributions for tree shadowed environments at 18.7
GHz and elevation angle of 32.5°, where the satellite azimuth was 90° relative to the
driving direction [Murr et al., 1995]. The dashed curved represents the EERS model.