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

8-14
Relative Signal Level (dB)
0
-5
-10
-15
-20
-25
S-Band Co-Polarization
S-Band Cross-Polarization
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
L-Band Co-Polarization
L-Band Cross-Polarization
0 5 10 15 20 25 30 35 40 45 50
Relative Time (s)
Figure 8-7: Example of 50 s time series of relative signal level measured at the
Commons for both co-polarized and cross-polarized levels and fixed antenna positions.
8.3.3 Space Variability
Figure 8-8 illustrates the spatial variation of power levels received at 1618 and 2492 MHz
with co-polarized and cross-polarized antennas as a function of position inside the
Commons Building, and Figure 8-9 summarizes the statistics for the median, 5%, and
95% levels for all the site locations. Table 8-8 lists the median values for the L- and
S-Band frequencies as well as the overall average median at these wavelengths. Table 8-
9 and Table 8-10 also summarize the mean and standard deviation for the six site
locations for the co-polarized and cross-polarized cases, respectively. We note from
Table 8-8 and Table 8-9 that the overall average median and mean power levels show
1.0 dB and 0.5 dB larger fades at S-Band relative to L-Band. In fact, for some of the sites
the fading at L-Band is larger than at S-Band. We may conclude from these results that a
small difference in the fading exists at the two frequencies.
The relative attenuation at L- and S-Bands is complicated in that the fading into
buildings depends both on the absorption by building materials and the reflection and
scattering properties of the building skeleton and ambient obstacles. A steel mesh, for
example, may be less transmissive at the longer L-Band wavelength than at the shorter
S-Band wavelength, resulting in smaller attenuation for the latter. On average, the
overall mean powers (over all site locations) are -14.6 dB and -15.1 dB at L- and
S-Bands, respectively, with a standard deviation of 6.5 dB at both wavelengths. It is also
interesting to note that the power losses are for the most part uncorrelated, as the average
correlation coefficient is 0.28.