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Technology Stocks : CellularVision (CVUS): 2-way LMDS wireless cable.
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To: Steven Bowen who wrote (798)12/31/1997 2:25:00 PM
From: Bernard Levy  Read Replies (1) of 2063
 
Here is a rough answer to your question. For line
of sight communication, the power attenuation between
the transmitter and receiver is proportional to
the square distance between the transmitter and receiver
and to the square of the transmission frequency.
Because TGNT operates at 24GHz and WCII at 38GHZ,
the attenuation is therefore (1.5)^2 greater for
the WCII channel. This means that for identical channels,
WCII would need to have cells with a radius 66% smaller
than TGNT. To compensate for the larger attenuation
at higher frequencies, the FCC has made the bandwidth
per license larger at 38Ghz (100MHZ) than at
24GHz (80 MHz). How the larger bandwidth is exploited
depends on the choice of modulation format, but for
wideband FM (the simplest case of all) the signal to
noise ratio gain at the receiver output (with respect to
the receiver input) is proportional to the square of the
channel bandwidth. In other words, the wider the bandwidth,
the easier it is to reject the noise. For FM, this would
give a (1.25)^2 gain advantage to the 100MHZ licenses of
WCII versus the 80MHz licenses of TGNT. However, this is a
very rough analysis. I suspect that TGNT and WCII must
be using a digital modulaton technique, such as QPSK.
Then the wider bandwidth can be exploited by applying some
form of forward error correction. The analysis becomes
compicated.

The bottom line is that the FCC is less incompetent than
it may appear. They have obviously equalized the licenses
to take into account the spectrum location.

Going back to CVUS, because its license is at 28GHz,
a 100MHZ channel for WCII must be equivalent to
a 85MHz channel for CVUS, so the 1.15GHz CVUS bandwidth
would give them approximately 13 channels (instead of
11.5 in the earlier estimate by Brian Coakley).
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