Hi Steve:
The conterpoint to the higher attenuation at higher
freqencies is that antennas of the same size have a
larger gain as the frequencies go up-- because the wavelength
is smaller, the antenna looks larger, and has a bigger gain.
If the attenuation increases by x, the transmitter
and receiver antenna gains also increase by x each.
Of course the increased receiver gain will affect
not only the signal to be recovered, but background
noise as well. So, the increased attenuation at higher
frequencies is more than compensated by increased antenna gains
(unless you scale down the size of the antennas in
the same proportion as the shrinking of the wavelengths).
Another factor is of course that higher frequencies have
more rain fading. The fading factor is usually selected
to accommodate the worst weather conditions at a specific
location. So this factor tends to be larger in places like
Florida than in dry areas of the Southwest. The smaller
cell size used at higher frequencies is primarily due
to conservative rain fade considerations. However, in
dense urban areas there are other factors in the selection
of cell sizes: line of sight availability, and user density.
In high user density areas, it is better to have more
cells, to ensure enough BW is available per user.
When I did my analysis for the TGNT BW transfer, I had
concluded that 100MHz at 18GHz was worth about 125MHz at
24GHz. Roughly, I would say TGNT's 400MHz are probably worth
550MHz at 38Ghz-- less in dry areas, more in wet areas.
Best regards,
Bernard Levy |
