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

Polarization, Antenna Gain and Diversity Considerations 6-7
Table 6-2: Coefficients of the fade reduction formulation at f = 870 MHz.
El. Angle (°) a0 a1 a2 a3 dB Range
30 -5.020 x 10 -3
0.3354 -2.439 x 10 -2
45 -0.8193 0.8430 -5.758 x 10 -2
60 -0.2305 0.2288 6.773 x 10 -2
Table 6-3: Coefficients of the fade reduction formulation at f = 1.5 GHz.
7.764 x 10 -4
1.222 x 10 -3
-3.608 x 10 -3
El. Angle (°) a0 a1 a2 a3 dB Range
30 0.3181 0.26153 -1.573x 10 -2
45 -1.073 0.8816 -4.651 x 10 -2
60 -8.127 x 10 -2
0.2044 5.781 x 10 -2
3.734 x 10 -4
7.942 x 10 -4
-2.235 x 10 -3
It is interesting to note that larger fade reductions occur at the greater elevation angles.
This arises because at the larger angles, a change of lanes may radically alter the earthsatellite
path from a shadowed to a non-shadowed state. At the lower elevation angles,
this change of state becomes less likely. It is noted from Figure 6-5 that the L-Band fade
is reduced from 10 dB to approximately 8 dB, 6 dB, and 4.5 dB at 30°, 45°, and 60°,
respectively. At UHF (Figure 6-4), the 10 dB fade is reduced to 8 dB, 7 dB, and 5 dB at
30°, 45°, and 60°, respectively.
6.5 Antenna Separation Diversity Gain
A space diversity simulation has been carried out employing the database corresponding
to 400 km of roadside tree shadowing measurements taken during the Australian
campaign [Vogel et al., 1992]. Space diversity operation for LMSS configurations may
be envisaged by the scenario of two spaced antennas mounted atop a vehicle where each
antenna is fed to a separate receiver system. Because the signal levels at the two
antennas are expected to be different at any instant of time, rapid switching between the
two receiver outputs followed by subsequent processing should enable the larger signal to
be accessed. Such a system should therefore require smaller fade margins for the same
“signal access distance” than single terminal systems. The “signal access distance”
represents that distance over which the received signal level operates within the designed
fade margin.
Questions addressed here are: (1) what is the increase in “signal access distance” as
a function of antenna spacing along the driving direction, and (2) what is the
improvement in terms of reduced fading (enhanced signal) for a given “signal access
distance” as a function of antenna spacing? The first question is addressed employing the
concept of “diversity improvement factor, DIF” and the second “diversity gain, DG”,
both of which are characterized in the following paragraphs.
2-20
2-12
2-11
3-25
3-17
3-15