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

7-26
Percentage of Distance Fade > Abscissa
100
9
8
7
6
5
4
3
2
10
9
8
7
6
5
1
4
3
2
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
Extended ERS
0 5 10 15 20 25 30 35 40 45 50 55
Fade (dB)
Figure 7-31: Cumulative fade distributions at 20 GHz for roads in vicinity of Fairbanks,
Alaska (elevation = 8°). Solid curve extending to 50 dB is EERS prediction.
7.9 Summary Comments and Recommendations
We emphasize here again that the extent of fading is dependent on frequency, elevation
angle, bearing to the satellite, the density of foliage cutting the earth-satellite path and the
offset of trees from the road. Also affecting the fading are scattering and blockage effects
from telephone poles, street signs, and underpasses. Table 7-1 demonstrates the wide
range of 1% and 10% attenuation levels. In Table 7-2 are culled the 54 measured
distribution entries in terms of frequency and elevation with the indicated fade ranges due
to the other causes mentioned above. The last column of this table represents the number
of entries obtained from Table 7-1 to arrive at the indicated quantities. The numbers in
parentheses correspond to the EERS values. Where angle and/or frequency ranges are
given, the EERS value is calculated at the lower elevation angle and larger frequency
(worst case). The system designer interested in selecting a design fade margin may use
the worst case fade or the mid-value depending upon the individual system constraints.
Alternate suggested fade margin levels may be obtained using the indicated EERS values
which are dominantly representative of roadside tree shadowing where the trees density
exceeds 55%.