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

8-32
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
(fourth column), and the originating reference is listed in the last column. Similar type
results are given in Table 8-19 for the site location with the highest fading (again with the
exception of Site 6 as mentioned above). We may conclude that; (1) fade margins of at
least 30 dB (e.g., mean loss plus two standard deviations) are required to achieve
relatively reliable communications for most cases vis-à-vis the overall average fading,
and (2) 40 dB are required for the worst case sites.
Table 8-18: Summary of relative power losses in terms of overall average of worst case
fading (all site average with exception of Site 6 for the first row).
Mean (dB)
Standard
Dev. (dB)
Median
Loss (dB )
-10.2 5.8 -13.0
-15.1 6.5 -14.5
Tables
Table 8-3,
Table 8-4
Table 8-9,
Table 8-8
Freq. Interval
(GHz)
Reference
0.7-1.8 V&T [1993]
1.6, 2.5
V&T
[1995a,b]
-11.9 7.4 Table 8-14 0.5-3.0 V&T [1995c]
-9.1 3.0 Table 8-17 0.86-2.57 Wells [1977]
Table 8-19: Summary of relative power losses in terms of worst site location.
Site
Mean
(dB)
Standard
Deviation
(dB)
Median
Loss
(dB )
Frequency
Interval
(GHz)
Reference
Commons -15.4 8.4 -18.0 0.7-1.8 V. &T. [1993]
Commons -19.9 8.1 -18.6 1.6, 2.5 V. & T. [1995a,b]
House -19.5 11.6 0.5-3.0 V. & T. [1995c]
8.7.2 Fading Dependence on Frequency
8.7.2.1 Small and Large Bandwidths Effects
The relative signal level may dramatically vary as the frequency is swept over intervals of
100 MHz due to multipath variability. An example of this variability is depicted by the
fixed position frequency sweep in Figure 8-1, where the signal varies from -25 dB to
0 dB over the frequency interval 900 MHz to 1000 MHz, respectively. On the other
hand, the trend fading over larger bands between 0.5 GHz to 3.0 GHz is generally small
when the short frequency scale fluctuations are averaged. It may be deduced from Figure
8-19, that for five of the six sites the fade increased by only 3 dB and less over a 1 GHz
frequency span. This fade increase is considered small compared to the smaller scale
variability of fading over 100 MHz as shown in Figure 8-18. Wells [1977] also showed
from direct earth-satellite measurements that small increases of the average fading
occurred over the frequency interval between 0.86 and 2.57 GHz. From Table 8-17, the
overall average fade increase over this band is indicated to be less than 3 dB.