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

8-18
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
Table 8-11: Statistics associated with power differences between co-polarized S-Band
and L-Band for spatial scans at each of the site locations.
Probability that P diff < Abscissa (%)
Building Mean Difference (dB) STD (dB)
Commons 1.9 7.2
EERL -0.6 7.9
Farmhouse -0.5 7.9
House 1.0 7.2
Motel -0.30 8.2
Store -4.8 7.8
Average -0.55 7.7
99.87
97.73
84.13
50.00
15.87
2.27
Normal Probability Plot of Signal Level Difference in Commons
P diff = P(S) - P(L); AVG=1.88 dB, STD=7.2 dB
0.13
-3
-20 -15 -10 -5 0 5 10 15 20
Difference Power (dB)
Figure 8-10: Cumulative probability distribution of signal level difference of the
instantaneous S-Band minus the L-Band powers. The indicated straight line implies a
Gaussian distribution with a mean and standard deviation of 1.9 dB and 7.2 dB,
respectively.
8.3.4 Frequency Variability
Rapid changes of the power with frequency occur only when the average power level is
comparable to the diffusely scattered power. This concept is illustrated in the frequency
scan example in Figure 8-11 which shows the power levels relative to the center
frequencies of 1680 MHz and 2430 MHz obtained at the EERL Building. Four cases
were selected from all positions, namely frequency scans with mean relative received
power levels of -20, -15, -10, and -5 dB. It is noted that when the mean signal level is
-5 dB, the variability of the signal level over the 160 MHz band is relatively small (e.g.,
-3 dB maximum and -10 dB minimum for both L- and S-Bands). On the other hand, the
3
2
1
0
-1
-2
Normalized Variate (std)