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

Earth-Satellite Propagation Effects Inside Buildings 8-9
Probability that Relative Signal Level < Abscissa (%)
95.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
5.0
2.0
1.0
0.5
0.1
1.75 GHz
1.25 GHz
f = 750 MHz
-18 -16 -14 -12 -10 -8 -6 -4 -2
Relative Signal Level (dB)
Figure 8-4: Example cumulative distributions of relative signal loss for Site 2 based on
model described by (8-1) through (8-3).
8.2.6 Space Diversity Considerations
Vogel and Torrence measured the position spacing between the minimum (troughs) and
maximum (crests) signal levels for all buildings and found the median value to be
between 35 cm and 45 cm and to be independent of frequency. An example of power
level versus spacing at a series of six frequencies spaced 5 MHz apart is given in Figure
8-5. It is noted that the relative power loss varies approximately between 0 dB and
-30 dB from crest to trough. Taking averages over frequency of the distances between
signal minima and maxima, this distance was found to be Gaussian distributed with a
mean near 41 cm with a standard deviation of 17 cm. No significant differences were
observed for movement along the vertical or horizontal directions. The above results
suggest optimal separation distances of antennas when space diversity concepts are
employed.