Hi Steve:
With respect to symmetry/asymmetry of broadband wireless
service, you can set up the service to be symmetric or
asymmetric. For business service, I expect the service
will be symmetric. For residential service, as LMDS was
originally conceived, the service will be asymmetric.
It would be a terrible waste to allocate the same amount
of BW to the downlink and uplinks. Note also that to
use the uplink BW efficiently, the return link may need a
higher power antenna, which would allow a higher-order
modulation scheme than QPSK. This higher-power antenna
makes sense on top of an office building, but not in
a residence.
With respect to what to do in rain storms, keep in mind
that broadband wireless service will offer huge amounts of
BW. To deal with rain conditions, the first option would be
boost power, second to fall back on a less efficient modulation
scheme (say downshift from 16-QAM to QPSK). Finally, one
more option (I don't know if it is implemented now, but it
would be feasible) would consist in using longer error correction
codes, or possibly concatenated codes (similar to those used
for satellite communications). This would cut into the available
transmission rate, but would certainly leave plenty for essential
services (such as voice), while possibly slowing down less
critical services such as data transfers... In other words,
the engineering technology exists to make the degradation of
service very gradual (not very different from what you might
see on a LAN when it gets congested).
Best regards,
Bernard Levy |
