Mark:
Pros and cons of MMDS versus LMDS:
MMDS allows bigger cells, but the bandwidth available
(100MHz) is much smaller: TGNT has 400MHZ at 24GHz,
LMDS blocks A and B add up to 1.3GHz at in the 28 to 30
Ghz range, and WCII has blocks in the range of 700MHz at
38Ghz (depends of the markets). The FCC will soon
auction 16 licenses of 100Mhz each at 39Ghz. More
bandwidth means more information capacity. This is
partly offset by the fact that higher orders of
QAM modulation can be employed in the MMDS band. The
first LMDS systems used QPSK (carries less than
2 bits per Hz), but higher order of modulations are
now being introduced. Still, MMDS has a higher information
carrying capacity per Hz, but it has much less BW
to work with. Another problem of MMDS versus LMDS
is that it requires bigger and unsightly antennas.
Probably fine for rural areas, but questionable in
urban or suburban areas with strict zoning rules.
Also, the frequency reuse factor is much less
than for LMDS which has essentially a factor of 1
(all frequencies can be reused entirely in each cell).
LMDS frequencies allow also a much finer
sectorization.
On balance, LMDS is preferable, but the infrastructure
costs are much higher. So the tradeoff is really
technical benefits (LMDS) versus lower costs (MMDS).
My view is that MMDS will be useful to offer connectivity
rates of 1 to 3 times ISDN rates, but for true
broadband connectivity (T1 to T3 rates and up)
LMDS is unavoidable.
Incidentally, transmission on the BBFW thread is the
undisputed MMDS expert on SI.
Best regards,
Bernard Levy |
