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

Optical Methods for Assessing Fade Margins 10-17
Figure 10-14 shows an analogous set of diversity gains for Singapore. Although the
average elevation angle (38°) to the highest satellite is approximately the same as in
Tokyo (40°), the corresponding diversity gains are only about half of those achieved in
the more northern latitudes. This occurs because of the reduced choice of potentially
visible satellites at the equator.
Diversity Gain (dB)
10
9
8
7
6
5
4
3
2
1
0
50
40
Diversity Type
Dashed: Combining
Solid: Hand-off
30
3 Best Satellites
20 10
Probability (%)
2 Best Satellites
5
Best Satellite
Figure 10-14: Path diversity gains at 1.5 GHz derived from distributions for the
simulated Globalstar constellation with “combining” and “handoff” diversity for
Singapore.
10.9 Summary Comments and Recommendations
A method by Akturan and Vogel [1994, 1995, 1995a, 1995b, 1997], Vogel [1997] has
been described in this chapter to assess fade margins for outdoor mobile satellite systems.
This photogrammetric method involves taking fisheye lens images at potential user
locations and analyzing the images for the presence of clear sky, tree shadowing, or
blockage by solid obstacles. This method works for the following reasons: (1)
Propagation effects for Satellite-Personal-Communications Systems (SPCS) are imposed
by the physical environment within a short range from a mobile user’s terminal. (2)
Analysis of the propagation conditions is straightforward since the earth-satellite path is
elevated and the path-state is related to the ambient structure environment (as opposed to
terrestrial scenarios where propagation occurs via multipath from hidden multipath
structures). (3) The statistical properties of the received signal levels can be described by
a few physically reasonable distributions that are a function of the fade-state. (4) Suitable
parameters for the distributions have already been evaluated for a limited number of
cases (as described in this chapter).
A model known as the Urban Three-State Fade Model (UTSFM) is described here.
This model may be used for urban environments similar to that of Tokyo. The model
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1