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

6-2
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
The RMS deviation between the “best-fit linear” relation (6-2) and the data points for the
corresponding runs was 0.4 dB. We note from the plot in Figure 6-1 that the isolation
severely degrades as a function of fade level. For example, an approximate 11 dB
isolation is observed at a 5 dB fade. This result suggests that the simultaneous
employment of co- and cross-polarized transmissions in a “frequency re-use” system is
implausible because of the poor isolation due to multipath scattering into the crosspolarized
channel. Although the instantaneous isolation is poor, polarization diversity
may nevertheless be helpful in reducing the statistical interference between two satellite
systems that manage to share the same frequency band by employing code-division
multiple access (CDMA). In that case, one system’s signals contribute to the other’s
noise. Cross-polarizing the alternate system would tend to reduce the noise at the victim
satellite reverse-link receiver while the alternate system’s mobile earth terminals are in a
clear line-of-sight condition. Estimating the net benefits of such a scheme is not
straightforward, however, because the impact of power control has to be factored in.
Cross Polarization Isolation, CPI (dB)
20
18
16
14
12
10
8
6
4
2
0
0 1 2 3 4 5 6 7 8 9 10 11 12
Fade Level (dB)
Figure 6-1: Cross polarization isolation (CPI) as a function of co-polarization fade at
equi-probability levels.
6.3 Distributions from Low- and High-Gain Receiving Antennas
During the Australian campaign by Vogel et al. [1992], a number of repeated runs were
executed in which high- and low-gain antennas were employed. The characteristics of
these antennas are given in Table 6-1. Figure 6-2 shows a plot of the high gain receiver